optimization guidance manual - water technology...

Optimization Guidance Manual

for

Drinking Water Systems

2014

Ministry of the Environment

ISBN 978-1-4606-3734-0

Optimization Guidance Manual

for

Drinking Water Systems

2014

Ministry of the Environment

PIBS 9649e

DISCLAIMER i

Optimization Guidance Manual for Drinking Water Systems 2014

DISLAIMER

This optimization Guidance manual for drinking water systems (“Optimization Manual”) was

prepared by XCG Consultants Ltd. in collaboration with Her Majesty the Queen in right of

Ontario as represented by the Minister of the Environment (“Ministry”) and is intended to be a

representative compilation and assessment of the current state of knowledge on optimization

measures for drinking water systems in Ontario. The views and ideas expressed in this

Optimization Manual are solely those of the XCG Consultants Ltd.

The contents of the Optimization Manual were prepared in accordance with generally recognized

engineering principles and practices existing at the time of its preparation and are for general

information purposes only. In preparing the Optimization Manual, third party data and

information has been provided and relied upon which has not been independently verified and

which due to the nature or source of the data, is assumed to be accurate, complete, timely, non-

infringing and fit for the intended purpose. The Optimization Manual is a technical document and

is not a legal representation or interpretation of any environmental laws, rules, regulations, or

policies of the Ministry or any governmental agencies. All findings stated in the Optimization

Manual are based on facts and circumstances as they existed during the time period that the

Optimization Manual was prepared. Any changes in fact or circumstances which may have

occurred subsequent to the time of preparation of the Optimization Manual may change the

findings in the Optimization Manual.

XCG Consultants Ltd. and the Ministry make no representation or warranty of any kind

whatsoever with respect to the completeness or accuracy of the information contained in the

Optimization Manual. Readers are advised to obtain competent advice prior to relying on or using

any information contained in the Optimization Manual with respect to its suitability for general or

specific application.

XCG Consultants Ltd. and the Ministry and their respective officers, employees, servants or

agents expressly disclaim all liability for damages of any kind (including without limitation,

damages for loss of profits, business interruption, loss of information, or direct, indirect,

incidental, special, consequential or punitive damages) arising out of the use of, reference to, or

reliance on the information contained herein whether under contract, in tort or under any other

basis of liability.

Cette publication hautement spécialisée n’est disponible qu’en anglais en vertu du

règlement 441/97, qui en exempte l’application de la Loi sur les services en français.

Pour obtenir de l’aide en français, veuillez communiquer avec le ministère de

l’Environnement au (416) 327- 6949

ACKNOWLEDGEMENTS ii


ACKNOWLEDGEMENTS

The Optimization Guidance Manual for Drinking Water Systems was prepared by XCG

Consultants Ltd. under the guidance of the Technical Working Group identified below. This

document underwent review by various branches of the Ontario Ministry of the Environment

(MOE) and the following stakeholders and reviewers.

Technical Working Group

Robert Dumancic, M.A.Sc., P.Eng., Standards Development Branch, MOE

George Lai, M.Eng., P.Eng., Standards Development Branch, MOE

Xibo Liu, Ph.D., P.Eng., Safe Drinking Water Branch, MOE

Ranee Mahalingam, M.Eng., P.Eng., Safe Drinking Water Branch, MOE

Mirek Tybinkowski, M.Eng., P.Eng., Land and Water Policy Branch, MOE

The following stakeholders and reviewers reviewed and provided valuable input to the

Optimization Manual.

Stakeholders and Reviewers

Dr. William B. Anderson, Ph.D., Academia (University of Waterloo)

Dr. Susan Andrews, Ph.D., P.Eng., Academia (University of Toronto)

Jane Bonsteel, Ontario Water Works Association (Peel Region)

Steve Burns, P.Eng., Engineering Practitioner ( B.M. Ross and Associates Ltd.)

Ian Douglas, P.Eng., Drinking Water Quality Professionals (City of Ottawa)

Andrew Farr, P.Eng., Ontario Water Works Association (Peel Region)

Martin Gravel, P.Eng., Ontario Water Works Association (Genivar Ontario Inc.)

Patrick Halevy, M. Sc., Drinking Water Quality Professionals (City of Brantford)

Dr. William Hargrave, Ph.D., P.Eng., Engineering Practitioner (W.J. Hargrave &

Company Inc.)

Andrew J. Henry, P.Eng., Ontario Municipal Water Association (Lake Huron & Elgin

Area Primary Water Supply System)

Brian Jobb, Walkerton Clean Water Centre

Asim Massaud, P.Eng., Ontario Clean Water Agency

Judith Patrick, Standards Development Branch, MOE

Thom Sloley, P.Eng., Municipal Engineers Association (Durham Region)

Alex Vukosavljevic, B.A., Water Treatment Operators (City of Toronto)

Tim Walton, Ontario Water Works Association (Waterloo Region)

PREAMBLE iii


PREAMBLE

This Ministry of the Environment (MOE) Optimization Guidance Manual for Drinking Water

Systems is developed in response to the increasing need to improve performance, increase

capacity and/or reduce the operating costs associated with existing Ontario drinking water

systems. The selection and design of specific unit processes is beyond the scope of this manual.

Optimization is an important aspect in the protection of public health. Many outbreaks of

waterborne illnesses have occurred because the operation of unit processes or system components

were not optimized (e.g. North Battleford, Saskatchewan and Milwaukee, Wisconsin).

Drinking water treatment plants (WTPs) represent a significant capital investment for most

municipalities and their efficient operation and maintenance is critical to ensuring a safe and

adequate supply of drinking water. The combination of population growth and increasingly

stringent drinking water quality standards has prompted the need for increased treatment capacity

via upgrades and/or expansion, as well as addressing water quality issues for existing facilities. In

many cases, optimization of the treatment processes may meet the increased production demands,

improve performance and treated water quality, and can reduce the costs of upgrades and/or

expansion if additional treatment units are required. Optimization techniques are important for the

delivery of high quality water in the most efficient manner.

The intended users of this Manual are operating authorities, consultants, regulatory personnel and

others with the responsibility of achieving compliance or more consistent and efficient

performance from existing water treatment plants and distribution systems.

The users of this Manual should determine which statutes and regulations apply to a proposed

drinking water system optimization program and ensure that the users are familiar with treatment

requirements and approval/permits needed to carry out the optimization work. The

municipality/owner should contact the Safe Drinking Water Branch for information regarding

applicability of statutes/regulations and applications for approvals/permits.

TABLE OF CONTENTS iv


TABLE OF CONTENTS

DISLAIMER ........................................................................................................................ i

ACKNOWLEDGEMENTS ................................................................................................ ii

PREAMBLE ...................................................................................................................... iii

TABLE OF CONTENTS ................................................................................................... iv

ACRONYMS & ABBREVIATIONS............................................................................... vii

CHAPTER 1 INTRODUCTION ..................................................................................... 1-1

1.1 Purpose and Objectives of the Manual ................................................................... 1-1

1.2 Using the Manual ................................................................................................... 1-1

1.3 Regulatory Requirements ....................................................................................... 1-2

1.4 What is Optimization? ............................................................................................ 1-2

1.5 When Should an Owner/Operator Optimize?......................................................... 1-6

1.6 What are the Benefits of Optimization? ................................................................. 1-7

1.7 What Does Optimization Cost and How Long Does it Take?................................ 1-9

1.8 Who Should Conduct the Optimization? .............................................................. 1-10

1.9 What are the General Approaches to Optimization? ............................................ 1-10

1.10 References ............................................................................................................ 1-12

CHAPTER 2 QUALITY MANAGEMENT SYSTEMS ................................................. 2-1

2.1 Introduction ............................................................................................................ 2-1

2.2 Quality Management Systems ................................................................................ 2-1

2.3 Operational Plans and Operations Manuals ........................................................... 2-3

2.4 Role of Water Operations Staff in Water System Optimization ............................ 2-4

2.5 Training of Operations Staff ................................................................................... 2-4

2.6 References .............................................................................................................. 2-5

CHAPTER 3 COMPOSITE CORRECTION PROGRAM ............................................. 3-1

3.1 Introduction ............................................................................................................ 3-1

3.2 CPE Methodology .................................................................................................. 3-1

3.3 Carrying Out a CPE .............................................................................................. 3-13

3.4 CTA Methodology................................................................................................ 3-25

3.5 How to Conduct a CTA ........................................................................................ 3-35

3.6 Required Personnel Capabilities for Conducting a CTA ..................................... 3-39

3.7 References ............................................................................................................ 3-40

CHAPTER 4 GENERAL OPTIMIZATION TECHNIQUES ......................................... 4-1

4.1 Introduction ............................................................................................................ 4-1

4.2 Field Evaluations .................................................................................................... 4-1

4.3 Modelling and Simulation ...................................................................................... 4-7

4.4 Case Histories ....................................................................................................... 4-11

4.5 References ............................................................................................................ 4-15

CHAPTER 5 INTAKE STRUCTURES AND SCREENING ......................................... 5-1

5.1 Introduction ............................................................................................................ 5-1

5.2 Sources of Supply ................................................................................................... 5-1

5.3 Intake Structures ..................................................................................................... 5-6

5.4 Screens .................................................................................................................... 5-9

5.5 Low-Lift (Raw Water) Pumping .......................................................................... 5-11

TABLE OF CONTENTS v


5.6 Pre-Chlorination/Oxidation and Zebra Mussel Control ....................................... 5-15

5.7 Case Histories ....................................................................................................... 5-16

5.8 References ............................................................................................................ 5-19

CHAPTER 6 COAGULATION AND FLOCCULATION ............................................. 6-1

6.1 Introduction ............................................................................................................ 6-1

6.2 Coagulation and Flocculation ................................................................................. 6-1

6.3 Optimization Techniques........................................................................................ 6-7

6.4 Case Histories ....................................................................................................... 6-12

6.5 References ............................................................................................................ 6-19

CHAPTER 7 CLARIFICATION ..................................................................................... 7-1

7.1 Introduction ............................................................................................................ 7-1

7.2 Clarification ............................................................................................................ 7-1

7.3 Optimization Techniques........................................................................................ 7-6

7.4 Case Histories ......................................................................................................... 7-8

7.5 References ............................................................................................................ 7-11

CHAPTER 8 FILTRATION ............................................................................................ 8-1

8.1 Introduction ............................................................................................................ 8-1

8.2 Granular Media Depth Filters ................................................................................. 8-1

8.3 Slow Sand Filters .................................................................................................. 8-13

8.4 Membrane Filters.................................................................................................. 8-17

8.5 Case Histories ....................................................................................................... 8-24

8.6 References ............................................................................................................ 8-27

CHAPTER 9 DISINFECTION ........................................................................................ 9-1

9.1 Introduction ............................................................................................................ 9-1

9.2 Chemical Inactivation ............................................................................................. 9-1

9.3 Ultraviolet (UV) Irradiation ................................................................................. 9-15

9.4 Case Histories ....................................................................................................... 9-21

9.5 References ............................................................................................................ 9-25

CHAPTER 10 OTHER TREATMENT PROCESSES .................................................. 10-1

10.1 Introduction .......................................................................................................... 10-1

10.2 Aeration and Air Stripping ................................................................................... 10-1

10.3 Ion Exchange ........................................................................................................ 10-4

10.4 Biologically Active Filtration ............................................................................... 10-5

10.5 Iron and Manganese Control ................................................................................ 10-6

10.6 Taste and Odour Control .................................................................................... 10-11

10.7 Natural Organic Matter Removal ....................................................................... 10-16

10.8 Internal Corrosion Control ................................................................................. 10-20

10.9 Case Histories ..................................................................................................... 10-25

10.10 References .......................................................................................................... 10-27

CHAPTER 11 DISTRIBUTION SYSTEMS ................................................................ 11-1

11.1 Introduction .......................................................................................................... 11-1

11.2 Treated Water Pumping Stations .......................................................................... 11-1

11.3 Treated Water Storage .......................................................................................... 11-4

11.4 Distribution System Piping and Appurtenances ................................................... 11-8

11.5 Case Histories ..................................................................................................... 11-20

11.6 References .......................................................................................................... 11-22

TABLE OF CONTENTS vi


CHAPTER 12 RESIDUALS AND RECYCLE STREAMS ......................................... 12-1

12.1 Introduction .......................................................................................................... 12-1

12.2 Water Treatment Process Residuals ..................................................................... 12-1

12.3 Residuals Treatment Processes............................................................................. 12-3

12.4 Case Histories ..................................................................................................... 12-11

12.5 References .......................................................................................................... 12-14

CHAPTER 13 REPORTING RESULTS....................................................................... 13-1

13.1 Introduction .......................................................................................................... 13-1

13.2 Interim Reports – Technical Memoranda ............................................................. 13-1

13.3 Workshops ............................................................................................................ 13-2

13.4 Final Report .......................................................................................................... 13-3

13.5 Implementation of Recommendations and Follow-up ......................................... 13-5

APPENDICES

APPENDIX A: Classification System, Factor Checklist and Definitions ...................... A-1

APPENDIX B: Data Collection Forms........................................................................... B-1

APPENDIX C: Example CPE Report............................................................................. C-1

APPENDIX D: Example CPE Scheduling Letter and Letter to MOE Regarding

Project Approval ................................................................................... D-1

APPENDIX E: Example Special Study ........................................................................... E-1

APPENDIX F: Example CTA Summary Report ............................................................. F-1

APPENDIX G: Equations and Calculations ................................................................... G-1

A. Coagulation and Flocculation Calculations

B. Disinfection Calculations

ACRONYMS AND ABBREVIATIONS vii


ACRONYMS & ABBREVIATIONS

Abbreviation Definition

1-D one-dimensional

2-D two-dimensional

3-D three-dimensional

AOA Ammonia oxidizing archaea

AOB Ammonia oxidizing bacteria

AOC Assimilable organic carbon

AOP Advanced oxidation process

AWWA American Water Works Association

AwwaRF American Water Works Association Research Foundation

(now known as the Water Research Foundation or WaterRF)

BDOC Biodegradable organic carbon

CCP Composite Correction Program

CFD Computational fluid dynamics

C of A Certificate of Approval

CPE Comprehensive Performance Evaluation

CSMR Chloride to sulphate mass ratio

CT Disinfectant concentration (C) x contact time (T)

CTA Comprehensive Technical Assistance

CWA Clean Water Act, 2006

DAF Dissolved air flotation

DBP Disinfection by-product

DO Dissolved oxygen

DOC Dissolved organic carbon

DWQMS Drinking Water Quality Management Standard

ACRONYMS AND ABBREVIATIONS viii



DWS Drinking water system

DWSP Drinking Water Surveillance Program

DWWP Drinking Water Works Permit

EAA Environmental Assessment Act

EBCT Empty bed contact time

EBR Environmental Bill of Rights

EMS Environmental management system

EPA Environmental Protection Act

G Velocity gradient

GAC Granular activated carbon

GBT Gravity belt thickener

GCDWQ Guidelines for Canadian Drinking Water Quality

Gt Mixing intensity x detention time

GUDI Groundwater under the direct influence of surface water

HAA Haloacetic acid

HACCP Hazard Analysis and Critical Control Points

HDT Hydraulic detention time

HPC Heterotrophic plate count

HVAC Heating, ventilating and air conditioning

IDDF Integrated Disinfection Design Framework

IPZ Intake protection zone

ISO International Organization for Standardization

LPHO Low pressure high output

MAC Maximum acceptable concentration

MDWL Municipal Drinking Water License

ACRONYMS AND ABBREVIATIONS ix



MF Microfiltration

MIB Methylisoborneol

MOE Ministry of the Environment

MP Medium pressure

MSDS Material safety data sheet

NF Nanofiltration

NMA Nutrient Management Act, 2002

NOM Natural organic matter

NP Number of particles

NTU Nephelometric turbidity unit

O & M Operations and Maintenance

OWRA Ontario Water Resources Act

PAC Powdered activated carbon

PACl Polyaluminum chloride

PASS Polyaluminum silicate sulphate

PLC Programmable logic controller

Q Flow rate

QMS Quality management system

RDT Rotating drum thickener

RO Reverse osmosis

rpm Rotations per minute

RTD Residence time distribution

SCADA Supervisory control and data acquisition

SCD or SCM Streaming current detector or monitor

SDWA Safe Drinking Water Act, 2002

ACRONYMS AND ABBREVIATIONS x



SDWB Safe Drinking Water Branch

SOP Standard operating procedure

SOR Surface overflow rate

STP Sewage treatment plant

SVI Sludge volume index

TCU True colour units

THM Trihalomethane

THMFP Trihalomethane formation potential

TM Technical memorandum

TMP Transmembrane pressure

TOC Total organic carbon

TON Threshold odour number

TOT Time of travel

TS Total solids

TSS Total suspended solids

UF Ultrafiltration

UFRV Unit Filter Run Volume

USEPA United States Environmental Protection Agency

UV Ultraviolet

UVT Ultraviolet transmittance

VE Value Engineering

VFD Variable frequency drive

VOC Volatile organic compound

WHPA Wellhead protection area

WQA Water Quality Analyst

ACRONYMS AND ABBREVIATIONS xi



WTP Water treatment plant

WTR Water treatment residuals

zp Zeta potential


CHAPTER 1 INTRODUCTION

INTRODUCTION

1.1 Purpose and Objectives of the Manual ................................................................... 1-1

1.2 Using the Manual ................................................................................................... 1-1

1.3 Regulatory Requirements ....................................................................................... 1-2

1.3.1 Applicable Legislation Administered by the Ministry ............................ 1-2

1.3.2 Drinking Water Regulations and Support Documents ............................ 1-2

1.4 What is Optimization? ............................................................................................ 1-2

1.4.1 Overview of Optimization ....................................................................... 1-2

1.4.2 Total System Optimization including Unit Process Optimization ........... 1-5

1.4.3 Value Engineering and Optimization ...................................................... 1-6

1.5 When Should an Owner/Operator Optimize? ........................................................ 1-6

1.6 What are the Benefits of Optimization? ................................................................. 1-7

1.6.1 Reduce the Capital Cost of Expansion or Upgrading .............................. 1-7

1.6.2 Achieve Stricter Standards ....................................................................... 1-8

1.6.3 Improve Performance .............................................................................. 1-8

1.6.4 Reduce Operating Cost ............................................................................ 1-9

1.7 What Does Optimization Cost and How Long Does it Take? ............................... 1-9

1.8 Who Should Conduct the Optimization? .............................................................. 1-10

1.9 What are the General Approaches to Optimization? ............................................ 1-10

1.9.1 Operator Training .................................................................................. 1-11

1.9.2 Composite Correction Program (CCP) .................................................. 1-11

1.9.3 Modelling and Simulation ..................................................................... 1-11

1.10 References ............................................................................................................ 1-12

CHAPTER 1. Introduction 1-1


CHAPTER 1

INTRODUCTION

1.1 PURPOSE AND OBJECTIVES OF THE MANUAL

The previous ministry optimization manual titled “Guidance Manual for the Optimization of

Ontario Water Treatment Plants using the Composite Correction Program (CCP) Approach”

(MOE, 1998) was aimed at improving the performance of conventional or direct-filtration

surface WTPs and was based on the United States Environmental Protection Agency

(USEPA) Handbook entitled “Optimizing Water Treatment Plant Performance Using the

Composite Correction Program” (USEPA, 1998).

Although the CCP approach is applicable to all sizes of systems, the MOE experience is that

smaller systems are those most in need of optimization. The previous MOE Manual mainly

addressed activities directed at achieving improved particulate removal and disinfection to

meet regulations. This Manual has been expanded to consolidate optimization methodologies,

techniques and practices, as applicable to Ontario, which had not been covered in the

previous manual, including optimization of: pumping; slow sand filtration; membrane

filtration and manganese greensand filtration; optimization to reduce disinfection by-product

(DBP) formation; and optimization of distribution systems to meet drinking water quality

standards.

The purpose of this revised MOE Manual is to present procedures for identifying factors that

cause poor performance in both surface water and groundwater treatment plants, and outlines

techniques used to address these factors and improve performance. The methodology

presented in this Manual is based on the CCP’s two-step approach of combining

Comprehensive Performance Evaluation (CPE) and Comprehensive Technical Assistance

(CTA). The approach has been adapted to identify performance limiting factors on an

individual unit process or component basis, and evaluate the system components. In addition,

this Manual targets a variety of monitoring or regulated parameters rather than focusing

solely on particulate removal and disinfection.

1.2 USING THE MANUAL

The CCP approach described in this Manual emphasizes modifying existing facilities to meet

desired performance at existing water demands. Even though these procedures may identify

design shortcomings, this MOE Manual is not a detailed process audit document to be used

for studying facility expansion. If existing facilities are inadequate, the reader should refer to

the MOE Design Guidelines for Drinking Water Systems (MOE, 2008) to assess the need for

increased capacity as well as improved performance.

This Manual provides an overview of some of the general approaches to drinking water

system optimization, including the use of modelling and simulation, Quality Management

Systems (Chapter 2) and the CCP approach (Chapter 3).

In subsequent chapters (Chapters 4 to 12), optimization approaches that could be applied to

individual unit processes or components are discussed and described. Generally, each chapter

describes the purpose and expected performance of the unit process or component, provides a

summary of some of the typical design or operational problems that may be encountered, and



describes techniques that could be used to diagnose the cause of poor performance, improve

performance, increase capacity or reduce costs.

Each of the chapters can be used independently or with other chapters depending on the

scope of the drinking water system optimization program. If the objective is to troubleshoot

or optimize a specific unit process or component within the drinking water system, then

reference should be made to the contents of the chapter dealing with that unit process or

component. If a system-wide optimization program is undertaken, reference should be made

to the overview chapters and to unit process chapters that are relevant to the drinking water

system being optimized. In all cases, the references included in each chapter should be

reviewed to provide additional information.

1.3 REGULATORY REQUIREMENTS

1.3.1 Applicable Legislation Administered by the Ministry

The Environmental Assessment Act (EAA), the Safe Drinking Water Act, 2002 (SDWA), the

Ontario Water Resources Act (OWRA), the Clean Water Act, 2006 (CWA), the

Environmental Protection Act (EPA) and the Environmental Bill of Rights (EBR) are statutes

administered by the MOE that have application to drinking water systems. All can be

accessed from the Ontario e-Laws website http://www.e-laws.gov.on.ca or the ministry

website http://www.ene.gov.on.ca.

1.3.2 Drinking Water Regulations and Support Documents

The Drinking Water Systems regulation (O. Reg. 170/03) under the SDWA outlines

minimum requirements for treatment, sampling and monitoring, and other matters which

must be considered during the optimization of drinking water systems. The designer should

refer to O. Reg. 170/03 and to the latest edition of the Procedure for Disinfection of Drinking

Water in Ontario (Disinfection Procedure; MOE, 2006a), which is adopted by reference by

O. Reg. 170/03 under the SDWA, for more information.

For drinking water systems that are not governed by O. Reg. 170/03, refer to O. Reg. 319/08

and other applicable regulation(s).

Treated water must meet the Ontario Drinking Water Quality Standards regulation (O. Reg.

169/03) under the SDWA and should meet the aesthetic objectives and operational goals

described in the latest edition of Technical Support Document for Ontario Drinking Water

Standards, Objectives and Guidelines (Technical Support Document; MOE, 2006b).

1.4 WHAT IS OPTIMIZATION?

1.4.1 Overview of Optimization

In the 1980s and 1990s, designers, owners and operators of drinking water systems

recognized that there were opportunities to optimize water treatment facilities in order to

reduce capital cost of expansions, improve water quality, and reduce the cost of energy,

chemicals and other operational requirements. Over the past 20 years, the concept of WTP

optimization has evolved from a single study undertaken prior to an expansion of the system

to a process of continuous improvement or an operational philosophy that is championed by

the operating authority at all levels.

http://www.e-laws.gov.on.ca/

http://www.ene.gov.on.ca/



Optimization of WTPs is an iterative process that includes the following four major steps as

illustrated in Figure 1-1:

Step 1: Clearly define the objectives of the optimization program;

Step 2: Evaluate specific components of the drinking water system to establish the

baseline conditions and the processes or factors that limit the capacity or the

performance of the existing system;

Step 3: Develop and implement a study program aimed at mitigating the capacity or

performance limiting factors; and

Step 4: Conduct follow-up monitoring after upgrades or process changes have been

implemented to assess and document the results.

Figure 1-1 – Interactive Approach to Optimization of Drinking Water Systems

Adapted from National Guide to Sustainable Municipal Infrastructure (2003)

The specific details of the study program will depend on the optimization objectives.

Objectives can be broadly-based, covering all aspects of the design and operation of the

drinking water system, or can be focused on mitigating a specific problem. Optimization

objectives might include the following, among others:

Improving treated water quality to reduce the potential for adverse public health

effects;

Increasing the capacity of the system to service growth in the community;

Upgrading the performance of the water treatment plant to meet more stringent

regulatory requirements;

Improving the reliability, flexibility and robustness of the system;

Reducing the operating cost associated with energy, chemicals and labour;

Reducing water treatment process waste residuals production and management cost;

and/or

Improving water treatment plant performance to minimize problems associated with

aesthetic parameters.

Document Benefits

Establish Objectives

Identify Limiting Factors

Identify and Implement Changes



Often optimization of a drinking water system to achieve one goal can result in

improvements in other areas. For example, optimization to achieve lower chemical use and

lower chemical cost for particulate removal (e.g. coagulation/flocculation) will also result in

lower waste residuals (sludge) production and lower sludge management costs. Similarly,

improving the reliability and flexibility of the system can also result in improvements in

treated water quality.

Depending on the objectives of the optimization program, different approaches may be

applicable. Table 1-1 (Nutt and Ross, 1995) presents some of the investigations that might be

undertaken as part of an optimization project to address specific optimization objectives.

Table 1-1 – Activity and Objectives Matrix

ACTIVITY

OBJECTIVE

Performance

Improvement

Operating

Cost Savings

Increased

Capacity

Capital Cost

Savings

Hydraulic Analysis

Individual Process

Capacity Evaluation

Process Design

Modifications

Process Control

Modifications

Energy Audit

Operator Training

Activities

Optimization methods will vary from system to system depending on program objectives and

facility design; however, some steps are common. The following is a brief discussion of the

optimization methodology described in this Manual. Detailed guidance is provided in

Chapter 3.

After the optimization objectives have been defined, the next step is to establish the baseline

condition of the existing system or those components of the system that are of interest based

on the objectives. This usually involves a desk-top analysis of historic data for a period of

time that is representative of the design and operation of the existing system; usually a

minimum of three to five years will be considered.

A site visit is conducted in the accompaniment of operational and management staff. The key

objectives of the site inspection are:

To familiarize the optimization team with the physical facilities, including the water

treatment plant and distribution system layout; identify the locations of significant



sampling and monitoring stations; make a preliminary assessment of operational

flexibility of the existing processes or components;

To obtain input from plant operations staff regarding equipment, hydraulic or process

limitations in the plant based on their operating experience; and

To discuss standard operating procedures for major unit processes or system

components.

The design of the existing system is compared to standard design practices and guidelines

from references such as Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008),

“Ten State Standards” (Recommended Standards for Water Works, Great Lakes-Upper

Mississippi River Board of State Public Health and Environmental Managers, 2007), Water

Treatment Principles and Design (MWH, 2005), and Water Quality and Treatment (AWWA,

1999).

A process capacity chart should be developed that identifies the capacity and capability of

each unit process or the unit processes under investigation. This establishes the unit process,

or processes, that limit the capacity or performance of the overall system. It will also serve to

identify unit processes that would benefit from optimization and the field investigations that

may be warranted.

Field investigations can then be undertaken to confirm the findings of the desk-top analysis

and to identify the preferred method of optimizing the component of the drinking water

system that is of interest. The specific field investigations undertaken will vary depending on

the size of the facilities, the design of the system and the specific objectives of the

optimization program.

The design or operational improvements are implemented and follow-up monitoring is

undertaken to confirm the benefits.

A more detailed discussion of the historic data analysis and desk-top investigation is provided

in Section 3.2 of this Manual. Specific field investigations that might be undertaken to

confirm the findings of the desk-top study or to identify preferred optimization approaches

are described in subsequent chapters of the Manual.

1.4.2 Total System Optimization including Unit Process Optimization

This Manual provides a description of optimization approaches that could be applied to all

components of a drinking water system from source to tap, including treatment unit processes

and distribution systems.

In this regard, this Manual recognizes that all parts of the system should be optimized before

the performance, capacity and capability of the drinking water system can be considered to be

fully optimized. It is also important to recognize that optimization of one component of the

treatment system may adversely or beneficially impact the performance of other components.

Therefore the possible implications of optimization steps applied to part of the drinking water

system on other unit processes should be considered.



1.4.3 Value Engineering and Optimization

Value engineering (VE) is a systematic approach used to evaluate an engineering project with

the objective of improving its value. Normally, VEs are undertaken at various stages of a

design project to determine if the value of the project can be improved by using alternative

design approaches. VEs will typically involve a team of experts with expertise in a variety of

relevant engineering disciplines, construction and costing in a multi-day workshop

environment. VEs have been shown to successfully reduce project construction costs while

ensuring that the basic objectives of the project are preserved.

VEs can add value to optimization projects either at the planning stage or during the project

execution by serving as a forum for peer review of the work plan, the results and the

recommendations. The workshops described in Chapter 13 of this Manual could be

conducted using the principles of value engineering and involving a VE facilitator and a team

of experts knowledgeable in drinking water system design, operation and optimization.

1.5 WHEN SHOULD AN OWNER/OPERATOR OPTIMIZE?

In the United States, optimization of sewage treatment plants (STPs) became a priority when

the USEPA recognized that many new or expanded facilities that had been constructed in the

1970s with federal funding assistance were not performing as intended (USEPA, 1979;

USEPA, 1980). To address this issue, the U.S. supported the development of the CCP as a

means of evaluating STPs to determine the underlying cause(s) of poor performance

(USEPA, 1984; USEPA, 1985).

The success of the CCP in improving performance of STP led to the development of a similar

approach for surface water treatment facilities. The experience gained from a number of

optimization studies conducted in the U.S. and Ontario formed the basis for the development

of the previous MOE optimization manual.

Over time, optimization of drinking water systems (and other municipal infrastructure) has

become more common and, in some instances, has been adopted by municipalities with

multiple facilities, both water and sewage works, as a routine part of their operation (Wilson,

2009; Wheeler, 2009). Optimization as a tool to achieve continuous improvement is now

widely accepted; however, the following activities may warrant a more detailed optimization

study of a specific component or process:

Implementation of more stringent regulatory requirements (e.g. reduction of

trihalomethane levels in the distribution system);

Recurring non-compliance or poor performance, particularly when corrective action

is required by a Provincial Officer’s Order (e.g. filtration process not meeting

monthly performance criteria);

A need to increase rated capacity due to growth in the service area;

A requirement or desire to achieve a higher level of performance in terms of treated

water quality; or

A need to reduce operating cost due to escalating cost for energy, chemicals or other

operational requirements.



Case histories presented elsewhere in the Manual document performance improvements as

well as operating and capital cost savings that have been realized by the successful

optimization of drinking water systems (note: costs presented in case histories are as per the

date of publication). Realizing some of these benefits is ample reason to implement an on-

going program of drinking water system optimization.

1.6 WHAT ARE THE BENEFITS OF OPTIMIZATION?

Optimization of drinking water systems in Ontario, across Canada and internationally has

been shown to deliver benefits to the owner/operator, ranging from capital cost savings

during plant expansions, improvements in performance and reliability, and/or operating and

maintenance cost reductions. Numerous example case histories are presented in this Manual.

Some select examples are summarized briefly below.

It is important to recognize that when a drinking water process or system is optimized to

increase capacity or meet more stringent regulatory requirements than the system was

originally designed to achieve, the optimization should ensure that the overall robustness and

reliability of the system is maintained. This may include enhancement of the multiple

barriers, such as additional monitoring and/or implementation of control technologies, as well

as specific training for operational staff. Vigilance with respect to the operating conditions is

required to ensure that the optimized system continues to consistently achieve the new

requirements.

1.6.1 Reduce the Capital Cost of Expansion or Upgrading

Design guidelines for drinking water systems are, by necessity, conservative as they are

intended to ensure that the components or processes are capable of achieving an appropriate

level of performance on a consistent basis by providing a margin of safety in the design,

particularly when adequate historic data are lacking.

Some of the tools described in the Manual, such as Stress Tests, can be effectively used to

document that a unit process can achieve the required performance level at hydraulic loading

higher than typically stated in design guidelines. If such is the case, significant capital cost

savings can be realized when the facility is expanded or if an expansion could be deferred. In

some cases, the facility could be re-rated to a higher rated capacity with no or minimal

construction of new facilities.

The Regional Municipality of Wood Buffalo, Alberta, undertook a number of studies

to define potential options and costs for upgrading the water treatment plant in the

City of Fort McMurray. A combination of optimization measures and minor capital

improvements was used to expand the plant capacity from 40 to 50 ML/d while

ensuring compliance with water quality standards. The optimization of the existing

system allowed the municipality to defer additional plant expansions and conversion

to membrane filtration (Suthaker, 2007).

A filter re-rating study was conducted by the Southern Nevada Water Authority

(SNWA) to determine if filters could be operated safely at increased loading rates

while maintaining filter effluent water quality requirements. One year of full-scale

filter stress testing was conducted to determine if the hydraulic loading rate on the

filters could be increased from a rated capacity of 6 gpm/ft2 (15 m/h) to 7.5 gpm/ft

2

(18 m/h). The success of the trials allowed both of SNWA’s treatment facilities to



gain the operational flexibility to run at full production with several filters offline,

and one WTP gained an additional 100 mgd (380 ML/d) of capacity. SNWA

estimates the filter re-rating saved the utility more than $10 million in construction

costs alone for the additional capacity gained (Lew et. al., 2010).

1.6.2 Achieve Stricter Standards

Optimization approaches have been used to demonstrate that new or more stringent

regulatory requirements can be achieved at some facilities without costly capital works.

CPEs were conducted at four surface water treatment plants following revisions to

the Disinfection Procedure (MOE, 2006a), changing the performance criterion for

filter effluent turbidity from ≤ 0.5 NTU to ≤ 0.3 NTU in 95% of measurements each

month. The study results indicated that three of the four WTPs were able to produce

filtered water meeting the MOE’s turbidity criterion at the current average daily

flows (XCG, 2006a, b; MacViro, 2006; MMM, 2006).

Optimization studies were conducted at three Ontario drinking water treatment plants

with the goal of minimizing the formation of trihalomethanes (THMs) and haloacetic

acids (HAAs) to below 80 µg/L without major capital investment. Bench- and full-

scale trials were conducted to evaluate DBP formation strategies. Based on the

results of the study, enhanced coagulation was observed to reduce THM and HAA

formation in both the treated water leaving the plant and in the distribution system

(AH&A and RVA, 2009).

1.6.3 Improve Performance

Improvements in performance through operational improvements or improved process control

can often bring a drinking water system into compliance with its regulatory requirements or

improve the reliability of the system. The USEPA’s CCP approach was developed specifically to

address sewage plants that were unable to achieve their regulatory requirements (USEPA, 1984)

and this same approach has been widely used in Ontario (Wheeler et. al., 1994). There are many

successful examples of the usefulness of this approach in WTPs where the design of the system

was shown to be appropriate, but performance requirements were not consistently being met.

A Comprehensive Performance Evaluation was conducted at a small GUDI treatment

plant to identify operational procedures that were contributing to non-compliance

problems with respect to turbidity. The results of the CPE indicated that backwashing

and other maintenance procedures were the main cause of the non-compliance issues.

Changes to Standard Operating Practices (SOPs) and increased operator training

were implemented to improve plant performance (Wetzel, 2007).

The Ministry of Environment and Energy completed the Water Plant Optimization

Study in the early 1990s to document and review conditions at 44 drinking water

systems in Ontario to determine an optimum treatment strategy with emphasis on

disinfection and particulate removal processes. Several of the treatment facilities

included in the study had demonstrated problems with treated water turbidity levels

and residual aluminum concentrations. The study findings were used to provide

short- and long-term recommendations for physical improvements and operational

changes leading to improved performance (MOE, 1995).



1.6.4 Reduce Operating Cost

Optimization can identify opportunities to reduce chemical cost and/or improve energy use

efficiency.

The City of Ottawa conducted numerous bench- and pilot-scale studies to determine

the optimum alum dosage and pH conditions for the removal of organic matter,

colour and turbidity. Implementation of the optimum chemical combinations and

dosages at full-scale resulted in a $150,000 savings per year and reduced the

production of residual aluminum sludge (Douglas et. al., 2008).

The Region of Niagara conducted a pilot program applying OPIR® software to

optimize water treatment plant production and balance storage in the Grimsby

drinking water system. By pumping at average day rates rather than peak production

rates, water treatment plant performance was improved and an energy cost savings of

10 to 15 percent was expected (Tracy, 2009).

1.7 WHAT DOES OPTIMIZATION COST AND HOW LONG DOES IT

TAKE?

The cost and duration of a drinking water system optimization program depends on a number

of variables, including:

The project scope and objectives;

Plant location, size, complexity and configuration;

Maintenance and construction activities underway at the facility that affect the

availability of unit processes or equipment for testing;

Type and duration of field investigations;

Level of support provided by the owner/operator;

Equipment required to execute the field program;

Sampling and analytical cost;

Approval requirements; and

Reporting requirements.

It should be recognized in considering the time required to complete an optimization program

that optimization is an iterative and on-going process that involves continuous review of the

performance, cost, capacity and capability of the drinking water system. When a specific

optimization project is completed, further opportunities for optimization of the system may

be identified.

In 2010 dollars, the cost of an optimization program can range from about $20,000 to conduct

the CPE phase of the CCP at a small to medium-sized WTP, to about $50,000 to $100,000

for a full CCP including the CTA phase. Stress testing and other field testing activities to re-



rate a small or medium-sized WTP, including multi-season testing, can range in cost from

about $80,000 to $120,000. A comprehensive performance evaluation of all treatment

processes, including clarifier or filter stress testing, tracer testing, hydraulic modelling,

evaluation of flow instrumentation, and other activities at a large WTP can cost up to

$500,000, inclusive of analytical cost.

These cost ranges are a guide to the cost to undertake an optimization program, but should

not be used for detailed budgetary purposes. A detailed Terms of Reference should be

developed with specific tasks and activities identified and used as the basis for estimating the

cost of a proposed optimization program.

As shown by the case histories presented in this Manual, the cost for optimization are often

recovered in the form of reduced capital cost for plant expansions and/or reduced operating cost.

Also, there are often non-monetary benefits, such as improved operation, improved performance

and enhanced plant reliability.

1.8 WHO SHOULD CONDUCT THE OPTIMIZATION?

Optimization of a drinking water system should involve active participation of the owner and

the operating authority, if different from the owner. The owner should establish the objectives

of the optimization program and maintain an involvement throughout the process. Operating

staff play a critical role in identifying performance limitations or capacity restrictions in the

facility based on their hands-on experience in operating the system. They also can assist with

conducting specific testing or sampling during the field test program. This can result in an

enhanced level of process and system knowledge and a better understanding of process and

system control options and outcomes, with a resulting benefit in ongoing optimization

through a continuous improvement program. As described in Chapter 3, operating staff

should be involved in the development and implementation of Standard Operating Practices

(SOPs) related to the system that they operate.

Some elements of system optimization are best undertaken by an engineering professional

experienced in the specific area. Some of the test methods described in this Manual utilize

specialized equipment and training. In addition, the interpretation of the resulting information

often is best accomplished by an experienced drinking water process engineer.

It is often prudent to include representatives from the regulator, which in Ontario is the MOE.

This might include representatives of the Safe Drinking Water Branch (SDWB) and

Standards Development Branch (SDB). Any approvals necessary to undertake the

optimization program should be discussed with SDWB and the MOE Drinking Water

Inspector for that drinking water system, and appropriate contingency plans should be in

place in the event that there are any unexpected short term impacts on treated water quality

during field testing. Pre-consultation with MOE will ensure that the optimization program

planning is sufficient to support any future approval applications.

1.9 WHAT ARE THE GENERAL APPROACHES TO OPTIMIZATION?

This section of the Manual provides a brief introduction to some of the more common

approaches used for drinking water system optimization. These approaches are not mutually

exclusive but rather are complementary and are often used concurrently depending on the

program objectives.



More detailed discussions are provided in subsequent chapters as referenced herein.

1.9.1 Operator Training

It is recognized that a well-trained operating staff with process control skills and an

understanding of drinking water treatment processes and distribution system can produce

high quality finished water from a marginal facility and deliver it safely to the consumer.

When supported by a management team that encourages optimization and ensures that

adequate resources are available to operating staff, an optimized drinking water system will

be realized. The development of an empowered operating staff is the focus of the CTA phase

of the CCP, which is discussed in detail in Chapter 3.

1.9.2 Composite Correction Program (CCP)

As noted previously, the CCP was originally developed by the USEPA to identify factors that

limit the performance of sewage works. The CCP has been demonstrated in Ontario to be an

effective tool for assessing and optimizing WTPs and versions of the procedure have been

developed for use in both water and sewage treatment plants in Ontario (XCG Consultants

Ltd., 1992; Wastewater Technology Centre and Process Applications Inc., 1994).

The CCP is a two-step process. The first step, the CPE, evaluates the operation, design,

maintenance and administration of the water treatment plant and distribution system to

determine which factors are affecting system performance and their relative importance. If

the CPE determines that the design of the drinking water system should be adequate to allow

the performance requirements to be met consistently, then the next step in the CCP process,

the CTA, is initiated.

In the CTA, the performance limiting factors identified in the CPE are addressed with the

goal of achieving the desired performance. The emphasis of the CTA is on providing operator

assistance with process control to ensure that the performance achieved when the CTA is

complete can be maintained by a well-trained operating staff.

More detailed discussion of the role of the CCP in optimization of drinking water systems is

provided in Chapter 3 of the Manual.

The reader is also referred to the AWWA Partnership for Safe Drinking Water program,

which has adopted a similar methodology to the CCP, for additional information.

1.9.3 Modelling and Simulation

Numerical models can be used as tools to support the assessment of plant performance and

capacity as well as a means of predicting the impact of design or process changes on

performance and capacity. There are several areas where modelling and simulation can be

used to support drinking water system optimization.

Hydraulic models of the water treatment plant and/or distribution system can be used

to identify hydraulic bottlenecks in the drinking water system that may limit the

ability to treat peak flows.

Clarifier models can be used to estimate the effects of baffling or other clarifier

modifications on clarifier performance or capacity.



Mixing models, such as Computational Fluid Dynamics (CFD) models, can be used

to assess the degree of short-circuiting or dead-space in chlorine contact tanks, or the

effectiveness of mixing devices at various flow rates.

Water treatment models can be used to simulate operating conditions and predict

treated water quality based on raw water characteristics and/or automatically adjust

chemical dosages to ensure satisfactory or optimal performance (e.g. chlorine

dosages to ensure compliance with CT requirements).

More detailed discussion of the role of modelling and simulation in optimization of drinking

water systems is provided in the Chapter 4.

1.10 REFERENCES

American Water Works Association (1999). Water Quality and Treatment: A Handbook of

Community Water Supplies, 5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.

Andrews, Hofmann & Associates Inc. and R.V. Anderson Associates Ltd (2009).

Optimization Study to Control the Formation of THMs and HAAs, report for the Ontario

Ministry of the Environment.

Douglas, I., A. Campbell and J. Van Den Oever (2008). 25 Things You Probably Didn’t

Know About Drinking Water Treatment: Findings From 15 Years of Research and

Optimization, presented at the OWWA/OMWA Joint Annual Conference, London, Ontario.

Graef, S.P., C.S. Zickefoose, P.T. Karney, M.C. Mulbarger and T.M. Regan (1985). EPA

Handbook for Improving POTW Performance, Water Pollution Control Federation, ISBN 0-

9432244-76-5.

Great Lakes-Upper Mississippi River Board of State Public Health and Environmental

Managers (2007). Recommended Standards for Water Works, (known as the “Ten State

Standards”).

Lew, J., T. Pickle, D. Johnson and E. Wert (2010). Filter Rerating Increases Production.

American Water Works Association. Opflow Volume 36, No. 3, March 2010.

MacViro Consultants Inc. (2006). Optimization of Drinking Water Systems Utilizing

Chemically Assisted Filtration to Meet Lower Turbidity Levels – Draft Optimization Report,

report for the Ontario Ministry of the Environment.

Marshall Macklin Monaghan Ltd (2006). Longlac Water Treatment Facility Comprehensive

Performance Evaluation – Final Optimization Report, report for the Ontario Ministry of

Environment.

MOEE (1995). Water Plant Optimization Study: Plant Study Summary Report. ISBN 0-7778-

3906-7.

MOE (2006a). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.

MOE (2006b). Technical Support Document for Ontario Drinking Water Standards,

Objectives and Guidelines. PIBS 4449e01.



MOE (2008). Design Guidelines for Drinking Water Systems. ISBN 978-1-4249-8517-3.

MWH (2005). Water Treatment: Principles and Design, 2nd

Ed. John Wiley & Sons, Inc.

ISBN 0-471-11018-3.

National Guide to Sustainable Municipal Infrastructure (2003). Wastewater Treatment Plant

Optimization, Federation of Canadian Municipalities and National Research Council.

Nutt, S.G. and D. Ross (1995). “What is Optimization and Why Optimize,” presented at the

24th Annual Water Environment Association of Ontario Conference, Toronto, Ontario.

Suthaker, S. and G.E. Drachenberg (2007). “Modified Deep Bed Filtration: Low-cost Option

for Increasing Capacity and Improving Quality Within Existing Filter Cells”, presented at the

American Water Works Association Annual Conference & Exposition, Toronto, Ontario.

Tracy, H. (2009). “Water System Optimization & Energy Savings Using Predictive Control”,

presented at the OWWA/OMWA Joint Annual Conference, Toronto, Ontario.

USEPA (1979). Evaluation of Operation and Maintenance Factors Limiting Biological

Wastewater Treatment Plant Performance, EPA-600/2-79-078.

USEPA (1980). Evaluation of Operation and Maintenance Factors Limiting Municipal

Wastewater Treatment Plant Performance, Phase II, EPA-600/2-80-129.

USEPA (1984). Handbook: Improving POTW Performance Using the Composite Correction

Program, EPA/625/6-84-008.

USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the

Composite Correction Program, EPA/625/6-91-027.

Wastewater Technology Centre and Process Applications Inc. (1994). The Ontario

Composite Correction Program Manual for Optimization of Sewage Treatment Plants

(draft), Ontario Ministry of Environment and Energy, Environment Canada and Municipal

Engineers Association.

Wetzel, M. (2007). “Improving Water System Operations Using Comprehensive Performance

Evaluation Methodology”, presented at the American Water Works Association Annual

Conference & Exposition, Toronto, Ontario.

Wheeler, G. (1994). Assessment of the Comprehensive Performance Evaluation Technique

for Ontario Sewage Treatment Plants, prepared for the Ontario Ministry of Environment and

Energy.

Wheeler, G.W. (2009). City of Guelph, Personal Communication.

Wilson, P. (2009). Haldimand County, Personal Communication.

XCG Consultants Ltd. (1992). Assessment of Factors Affecting the Performance of Ontario

Sewage Treatment Facilities, report for the Ontario Ministry of Environment and Energy,

Environment Canada and the Municipal Engineers Association.



XCG Consultants Ltd. (2006a). Performance Evaluation Report – Alexandria Water

Treatment Plant, report for the Ontario Ministry of Environment.

XCG Consultants Ltd. (2006b). Performance Evaluation Report – Dunnville Water


Optimization Guidance Manual of Drinking Water Systems 2014

CHAPTER 2QUALITY MANAGEMENT SYSTEMS

QUALITY MANAGEMENT SYSTEMS

2.1 Introduction ............................................................................................................ 2-1

2.2 Quality Management Systems ................................................................................ 2-1

2.2.1 What is a Quality Management System? ................................................. 2-1

2.2.2 What is the Drinking Water Quality Management Standard? ................. 2-2

2.3 Operational Plans and Operations Manuals ........................................................... 2-3

2.4 Role of Water Operations Staff in Water System Optimization ............................ 2-4

2.5 Training of Operations Staff ................................................................................... 2-4

2.6 References .............................................................................................................. 2-5

CHAPTER 2. Quality Management Systems 2-1


CHAPTER 2

QUALITY MANAGEMENT SYSTEMS

2.1 INTRODUCTION

Part Two of the Report of the Walkerton Inquiry (O’Connor, 2002), recommended the

adoption of a quality management system (QMS) for drinking water systems. It was also

recommended that a quality management standard, specifically designed for drinking water

systems, be developed and implemented in Ontario. This resulted in the Drinking Water

Quality Management Standard (DWQMS).

Ontario has established a strong regulatory framework for drinking water systems. This

framework under the SDWA and related regulations focuses on compliance-based results that

are verified through the MOE’s compliance and inspection programs.

The DWQMS complements this legislative and regulatory framework by endorsing a

proactive and preventative approach to drinking water quality management. The Report of

the Walkerton Inquiry recommendations stated that:

“The purpose of the quality management approach in the context of drinking

water is to protect public health by achieving consistent good practice in

managing and operating a water system.

An important assumption of quality management is that, in evaluating or

improving a management system, one should look at the process by which

something is produced as well as the end product (O’Connor, 2002).”

This recommendation to adopt a QMS approach has been mandated by the provincial

government through the SDWA. As such, the requirement to implement the DWQMS is

applicable to the owners and operating authorities for all municipal residential drinking water

systems, including treatment, transmission and/or distribution systems.

Although the continuous improvement component of the DWQMS is directly related to the

improvement of the effectiveness of the QMS, the approach used to initiate corrective actions

and monitor improvement can be applied to optimization activities; for example, correcting

performance limiting factors as part of a CTA program.

2.2 QUALITY MANAGEMENT SYSTEMS

2.2.1 What is a Quality Management System?

A QMS is a system to: a) establish policy and objectives and achieve those objectives, and b)

direct and control an organization with regard to quality.

Quality management systems and management system standards are not new. They have

been around since the early 1950s. In 1987, the International Organization for

Standardization (ISO) released the first version of the ISO 9001 Quality Management System

Standard. Organizations can become certified to ISO 9001 to demonstrate their compliance to

the standard. The standard includes a requirement for continual improvement.



Similar to the ISO 9000 series, the ISO 14000 series of international standards is a set of

policies and procedures related specifically to Environmental Management Systems (EMS).

The aim of this standard is to reduce the environmental footprint of a business and to

decrease the amount of pollution or waste that the business generates. As with ISO 9001, a

business can become certified to demonstrate their compliance to the standard. In Ontario,

some water and sewage works owners and operators, such as the Lake Huron Primary Water

Supply System, the Region of York and the Region of Durham, have had their water and/or

sewage works certified to the ISO 14001 standard with the goal of improving performance

and compliance.

Most management system standards are generic. They can be applied to any type or size of

organization. They have been developed for the implementation of quality-based or

environmentally-based management systems in any type of organization.

Management system standards have also been developed for specific industries or product

sectors. For example, the Hazard Analysis and Critical Control Point (HACCP) standard is an

internationally recognized, science-based, food safety standard that was developed to help

ensure the manufacture of safe food products.

Quality management for Ontario’s municipal drinking water systems occurs through the

development and implementation of a QMS for each drinking water system based on

Ontario’s DWQMS.

The complexity of a QMS for a drinking water system will depend, to some degree, on the

size of the drinking water system and its processes. For a small drinking water system (e.g.

consisting of a well with chlorination), the QMS can be relatively simple. For a system with a

large number of staff, several connected surface water treatment plants, a complex

distribution system, and interconnections to other systems, the QMS will be larger and more

comprehensive.

2.2.2 What is the Drinking Water Quality Management Standard?

The DWQMS is a “Made-in-Ontario” management system standard required by the MOE’s

Municipal Drinking Water Licensing Program under O. Reg. 188/07 for municipal residential

drinking water systems. Its requirements are similar to ISO-based quality management

standards but not equivalent.

The DWQMS sets out a framework for the operating authority and the owner of a drinking

water system to develop a QMS that is relevant and appropriate for their specific system.

The DWQMS contains elements of both the ISO 9001 standard with respect to management

systems and the HACCP standard with respect to product safety. The DWQMS also

incorporates the HACCP approach to risk assessment and reflects the multi-barrier approach

for drinking water safety.

In general, the concepts outlined in the DWQMS reflect, for the most part, how owners and

operating authorities currently manage and operate their drinking water systems. The

DWQMS, however, requires that these concepts be formalized and documented in an

operational plan, and that there is a documented commitment throughout an organization to

continuously review and improve quality management practices.



The DWQMS approach emphasizes the importance of:

Proactive and preventative rather than strictly reactive management strategies to

identify and manage risks to public health;

The establishment and documentation of management procedures;

Meeting the management procedures; and

Continuous improvement of the management system.

The definition of QMS in the DWQMS refers to the establishment of policies and objectives.

The DWQMS has explicit requirements for policies but does not make specific reference to

objectives. Objectives are, however, embedded or implicit in most of the DWQMS elements.

The DWQMS is based on a “PLAN, DO, CHECK and IMPROVE” methodology that is

similar to that found in some international standards.

Additional information on the DWQMS is provided in the MOE guidance document entitled

Implementing Quality Management: A Guide for Ontario’s Drinking Water Systems (MOE,

2007).

2.3 OPERATIONAL PLANS AND OPERATIONS MANUALS

An operational plan is the documentation of a QMS. It is not an Operations and Maintenance

Manual. The PLAN requirements of the DWQMS identify the policies and procedures that

must be documented in the Operational Plan.

Additional information regarding the preparation and contents of operational plans is

provided in the MOE DWQMS Guidance Document (MOE, 2007).

An operations manual is generally supplied to the water works as an essential part of the

design and commissioning of a facility. The operations manual should include detailed

descriptions and explanations of the treatment process and operational strategies for meeting

the requirements of O. Reg. 170/03 and the Disinfection Procedure (MOE, 2006). All

standard operating procedures (SOPs) developed for the plant should be included in the

operations manual. The manual should cover the following topics:

A plant overview and process control philosophy statement;

Detailed unit operations and chemical dosing for normal operation and emergency

situations;

Simplified system schematics that take into account the spatial relationships

involved;

Storage and transmission descriptions and operational procedures;

Descriptions and operational procedures for facility utilities (HVAC, plant service

water, security, etc.);

General safety information, including Material Safety Data Sheets (MSDS);

Spill containment and emergency procedures;

Emergency power systems and electrical system operation;



Security of infrastructure, treated water, electronic files and/or programs and

response procedures to breaches or intrusions;

Applicable regulations;

Monitoring, reporting and documentation procedures;

Disinfection procedures for bringing equipment on-line after maintenance;

Reliability and redundancy analysis of system components;

Detailed routine maintenance procedures;

Alarm notifications and response procedures;

A list of emergency contacts and locations of contingency plans;

A list of major equipment suppliers with specifications, maintenance requirements

and spare parts lists for major equipment; and

A list of chemical suppliers (and alternates if possible) with emergency contact

names and phone numbers.

It is important to note that any changes to operating conditions or procedures that are the

result of optimization activities must be reflected in the documentation contained in the

Operations Manual and the Operational Plan, where applicable.

2.4 ROLE OF WATER OPERATIONS STAFF IN WATER SYSTEM

OPTIMIZATION

The quality of water leaving a water treatment plant and passing through the distribution

system has the potential to directly impact the health of its consumers. All staff associated

with the drinking water system, from the operator to the highest level administrator, have an

important role in protecting public health and a responsibility to provide drinking water that

minimizes the possibility of a disease outbreak.

Experience gained from implementing CCP optimization activities at plants has demonstrated

that, in most situations, once utility staff become aware of the importance of achieving

optimized performance goals, they have enthusiastically pursued these goals through a

variety of activities (USEPA, 1998). The subsequent chapters of this Manual present

comprehensive procedures for assessing and achieving optimum levels of performance.

2.5 TRAINING OF OPERATIONS STAFF

Optimization of a drinking water system should involve increasing the capabilities and

knowledge of the operations and management staff of the works and improving the

performance of the equipment and the treatment processes to be effective and sustainable.

Developing a capable and empowered operating staff with supportive management and

appropriate operating and maintenance procedures and practices is critical to achieving and

maintaining a high level of performance in the drinking water system. The success of the

CCP approach (Chapter 3) is, to a large extent, due to the transfer of skills and knowledge to

the operations and management staff during the CTA phase.

Training of operators and water quality analysts (WQA) as part of or as a result of a CCP or

optimization program should not be confused with operator/WQA certification or licensing,



which is regulated under O. Reg. 128/04 – Certification of Drinking Water System Operators and

Water Quality Analysts. The objective of the certification program is to ensure that drinking water

system operators and WQAs have the necessary education, training, knowledge and experience to

operate the works. Certification is based on passing certification exams and meeting the minimum

requirements for professional development or training per year.

CCPs undertaken in Ontario (XCG, 2006a, b; MacViro, 2006; MMM, 2006) and elsewhere

(USEPA, 1998) have shown that the lack of appropriate process control techniques and the

misapplication of process control concepts are among the most common performance

limiting factors in drinking water systems.

Providing operations staff with the knowledge, ability and tools needed to achieve a

consistent level of process control for the drinking water system should involve a

combination of classroom and hands-on training. The classroom training is aimed at

explaining the fundamental concepts of drinking water treatment, process control, and

distribution system management and operation. The hands-on training is intended to

demonstrate how the concepts apply to the specific works that are being operated.

There are numerous sources of classroom training available. Acquiring the requisite hands-on

training in monitoring and process control techniques is more difficult and expensive than

classroom training, particularly for smaller works that may not have in-house staff capable of

providing hands-on training. A regional approach to delivery of hands-on training can reduce

the high costs of this type of training for small facilities.

2.6 REFERENCES

MacViro Consultants Inc. (2006). Optimization of Drinking Water Systems Utilizing

Chemically Assisted Filtration to Meet Lower Turbidity Levels – Draft Optimization Report,

report for the Ontario Ministry of the Environment.

Marshall Macklin Monaghan Ltd (2006). Longlac Water Treatment Facility Comprehensive

Performance Evaluation – Final Optimization Report, report for the Ontario Ministry of

Environment.

MOE (2006). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.

MOE (2007). Implementing Quality Management: A Guide for Ontario’s Drinking Water

Systems. PIBS 6320e.

O’Connor, D. R. (2002). Part Two Report of the Walkerton Inquiry: A Strategy for Safe

Drinking Water. Toronto: Publications Ontario. ISBN: 0-7794-2621-5.


Composite Correction Program. United States Environmental Protection Agency. Office of

Ground Water and Drinking Water. Cincinnati, OH. EPA/625/6-91-027.

XCG Consultants Ltd. (2006a). Performance Evaluation Report – Alexandria Water


XCG Consultants Ltd. (2006b). Performance Evaluation Report – Dunnville Water


http://www.e-laws.gov.on.ca/html/regs/english/elaws_regs_040128_e.htm

http://www.e-laws.gov.on.ca/html/regs/english/elaws_regs_040128_e.htm


CHAPTER 3COMPOSITE CORRECTION PROGRAM

COMPOSITE CORRECTION PROGRAM

3.1 Introduction ............................................................................................................ 3-1

3.2 CPE Methodology .................................................................................................. 3-1

3.2.1 Evaluation of Major DWS Components .................................................. 3-1

3.2.2 Conducting Performance Assessment ..................................................... 3-5

3.2.3 Identification and Prioritization of Performance Limiting Factors ......... 3-6

3.2.4 Assessment of Applicability of a CTA .................................................. 3-12

3.2.5 CPE Report ............................................................................................ 3-13

3.3 Carrying Out a CPE .............................................................................................. 3-13

3.3.1 Personnel Capabilities ............................................................................ 3-14

3.3.2 Initial Activities ..................................................................................... 3-15

3.3.3 On-Site Activities .................................................................................. 3-16

3.3.4 CPE Report ............................................................................................ 3-24

3.4 CTA Methodology ............................................................................................... 3-25

3.4.1 CPE Results ........................................................................................... 3-25

3.4.2 Process Control Priority Setting ............................................................ 3-26

3.4.3 Long Term Involvement ........................................................................ 3-27

3.4.4 Facilitator Tools ..................................................................................... 3-27

3.4.5 Correcting Performance Limiting Factors ............................................. 3-31

3.5 How to Conduct a CTA ........................................................................................ 3-35

3.5.1 Initial Site Visit ...................................................................................... 3-35

3.5.2 Off-Site Activities .................................................................................. 3-37

3.5.3 CTA Results ........................................................................................... 3-37

3.5.4 CTA Summary Report ........................................................................... 3-38

3.6 Required Personnel Capabilities for Conducting a CTA ..................................... 3-39

3.7 References ............................................................................................................ 3-40

CHAPTER 3. Composite Correction Program 3-1


CHAPTER 3

COMPOSITE CORRECTION PROGRAM

3.1 INTRODUCTION

This chapter provides information on the two phases of the CCP approach used to improve

the performance of existing drinking water systems (DWS). The first evaluation phase of the

CCP, called the Comprehensive Performance Evaluation (CPE), is a thorough review and

analysis of a facility’s capabilities as designed and associated administrative, operational and

maintenance practices as they relate to the performance requirements for the water treatment

plant and/or distribution system. A primary objective is to determine if significant

improvements in performance can be achieved without major capital expenditures. The

objective of the second phase of the CCP, the Comprehensive Technical Assistance (CTA), is

to achieve a desired level of performance from an existing DWS without major

modifications.

In this chapter, the term “DWS component” will be used to refer to treatment unit processes,

such as sedimentation and filtration, as well as other major works included in the DWS, such

as: intake structures; distribution system piping; pumping stations; and storage facilities.

3.2 CPE METHODOLOGY

A CPE is a comprehensive evaluation of the administration, design, operation and

maintenance of a DWS. Although the evaluation focuses on the current condition of the

system (i.e. “a snapshot in time”), consideration is given to seasonal variations in raw water

quality and operating conditions. A CPE involves several activities:

Evaluation of the DWS components;

Assessment of DWS performance;

Identification and prioritization of performance limiting factors;

Assessment of applicability of follow-up CTA; and

Reporting results of the evaluation.

Although these are distinct activities, some are conducted concurrently. For example,

evaluation of DWS components and identification of performance-limiting factors are

generally conducted simultaneously. A more detailed discussion of these activities follows.

3.2.1 Evaluation of Major DWS Components

3.2.1.1 Overview

The evaluation of major DWS components is used to establish the potential of existing

components to achieve desired performance levels. If the CPE indicates that the major DWS

components are adequate, a major upgrade or expansion is probably not necessary, and a

properly conducted CTA should be implemented to optimize performance. If, on the other



hand, the CPE shows that major DWS components are inadequate, utilities should consider

modification of these components as the initial focus for achieving desired performance.

A rating system is used that allows the evaluator to rate each DWS component and the

overall system as either Type 1, 2 or 3. This evaluation approach is illustrated in Figure 3-1.

Type 1 systems are those where a CPE shows that current performance difficulties are not

caused by limitations in the size or capability of existing DWS components. In these cases,

problems are likely related to system operation, maintenance, aging infrastructure or

administration. Type 1 systems are projected to be most likely to achieve desired

performance through implementation of non-construction oriented follow-up assistance (e.g.,

a CTA as described later in this chapter).

Figure 3-1 – Major DWS Component Evaluation Approach

The Type 2 category is used to represent a situation where marginal capacity of DWS

components could potentially prohibit a DWS from achieving the desired performance level.

For Type 2 systems, it is expected that implementation of a CTA would lead to improved

Administrators or Regulators Recognize the Need to Evaluate or Improve System Performance

CPE Evaluation of Major DWS Components

TYPE 2 Major DWS Components

Are Marginal


Are Adequate


are Inadequate

Implement CTA to Optimize Existing

Facilities Before Initiating Any Facility Modifications

Implement CTA to Achieve Desired

Performance from Existing Facilities

Do Not Implement CTA Evaluate Options for Facility Modifications

Facility Modifications

Facility Modifications

Construct New

Facilities to Meet Demand

Desired Performance Achieved



performance, but might not achieve the required performance level without facility

modifications to the major DWS components.

Type 3 systems are those in which major DWS components are considered to be inadequate

to provide required capacity for existing water demands. For Type 3 systems, major

modifications are felt to be required to achieve the desired level of performance. Although

other performance-limiting factors may exist, such as the operators’ lack of process control

capability or the administration's unfamiliarity with DWS needs, consistent acceptable

performance cannot be expected to be achieved until any physical limitations of major DWS

components are eliminated. If severe public health problems exist with present system

performance, officials may conduct activities to improve system performance as much as

possible until major modifications can be completed. A Boil Water Advisory (which can only

be issued by the Medical Officer of Health) or water use restrictions may have to be

implemented until modifications are completed and performance is improved. The owners of

a Type 3 system could meet their performance requirements by pursuing modifications of

existing water treatment and/or distribution facilities. However, depending on future water

demands, more detailed study of feasible alternatives may be warranted. CPEs that identify

Type 3 systems are still of benefit to system administrators in that the need for construction is

clearly defined. Additionally, the CPE provides an understanding of the capabilities and

weaknesses of existing operation and maintenance practices, and administrative policies.

3.2.1.2 Approach

When using the CCP approach, major DWS components are generally evaluated based on

their capability to handle current peak instantaneous flow requirements. The evaluator should

use judgement in assessing the peak instantaneous flow rate, and anomalous operating

conditions should not be included in the data evaluation. When assessing DWS components

that have not been traditionally included in a CPE, such as distribution system piping or

storage facilities, the use of a different flow requirement (e.g. maximum day demand or fire

flow) may be more appropriate. It should be noted that for any DWS component, nominal

flow metering inaccuracies should be taken into account.

All major DWS components should be included in the evaluation; typically these are

flocculation, sedimentation, filtration and disinfection. These processes are selected for

evaluation based on the concept of determining if the "concrete" (e.g., basin size) is adequate.

The potential capacity of a major DWS component is not increased if "minor modifications",

such as providing chemical feeders or installing baffles, could be accomplished by the staff.

This approach is in line with the CPE intent of assessing adequacy of existing facilities to

determine the potential of non-construction alternatives and can be applied to other DWS

components, including distribution system components. Other components or plant

processes, such as rapid mix or pumping facilities, are not included in the major DWS

component evaluation but rather are evaluated separately as factors that may be limiting

performance. These components can most often be addressed through "minor modifications".

An approach using a "performance potential graph" has been developed to evaluate the major

DWS components. As an initial step in the performance potential graph approach, the CPE

evaluators are required to use their judgment to estimate the peak treatment or hydraulic

capacity for each of the major DWS components. It is important to note that the ratings are

based on achieving optimum performance from each of the major DWS components such

that each process maintains its integrity as a "barrier" to the passage of particulate matter,

microorganisms or other parameters targeted for optimization (e.g. colour, iron and



manganese, etc.). The projected capacity rating is then compared to the peak instantaneous

operating flow rate (or other flow rate, as determined by the evaluator) experienced by the

DWS during the most recent twelve months of operation. If the most recent twelve months is

not indicative of typical flow rates, the evaluator may choose to review a time period

considered to be more representative. The peak instantaneous operating flow is utilized for

the comparison because it is necessary that high quality finished water be produced and

delivered to consumers on a continuous basis.

The comparison of estimated DWS component capacity to peak instantaneous operating flow

rate is made using a performance potential graph, as shown in Figure 3-2. The components

evaluated are shown on the left of the graph and the flow rate units are shown on the "x"

scale across the top. Horizontal bars on the graph depict the estimated capacity for each DWS

component, and the vertical line represents the actual peak operating flow experienced at the

plant or in the distribution system. Footnotes are used to explain the conditions used to rate

the DWS components.

The approach to determine whether a DWS component is Type 1, Type 2 or Type 3 is based

on the relationship of the horizontal bars to the peak instantaneous operating flow rate. As

presented in Figure 3-2, a DWS component would be rated Type 1 if its projected capacity

exceeds the actual peak demand, Type 2 if its projected capacity was 90 to 100 percent of

actual peak demand, or Type 3 if its projected capacity is less than 90 percent of actual peak

demand.

Figure 3-2 – Example Performance Potential Graph

When rating the capability of a DWS component, it is important to consider several options

that are available for the operation of the DWS. For example, if a DWS components receives



a Type 3 rating, it may be able to achieve Type 2 or Type 1 status by reducing demand or by

extending the operating time and operating at a lower rate (e.g., if the peak instantaneous

operating flow rate of a plant is only occurring over a 12-hour period, the plant may be able

to be operated at half the flow rate for a 24-hour period). In addition, it may be possible for a

community to take steps to reduce demand by activities such as increasing water rates, water

rationing, or leak detection and repair. In these instances, the potential to decrease peak

instantaneous operating flow rate needs to be carefully assessed by the evaluator in order to

justify a change in the DWS component rating (see Section 3.2.1.3).

3.2.1.3 Rating Individual DWS Components

Typical assessment criteria to be used as a basis to rate individual DWS components are

presented in the individual DWS component chapters (Chapters 5 to 12). There is a wide

range in the criteria which can translate into large differences in estimated DWS component

capabilities. As such, using the performance potential graph approach requires a great deal of

judgment from an experienced water system evaluator to properly estimate the capacity of a

major DWS component.

These criteria are based on experience gained from CPEs and other sources including the

Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008). The evaluator should use

judgement in selecting evaluation criteria and should consider the original design of the

component, changes in raw water characteristics and operating conditions in the evaluation of

the component rating.

Major DWS component performance is assessed both with respect to the capability of

consistently contributing to overall treated water quality and with respect to providing

consistent individual DWS component performance. DWS component performance

capability is important to ensure that multiple barriers are maintained on a continuous basis.

3.2.2 Conducting Performance Assessment

The performance assessment step uses existing and on-site data evaluations to determine if

DWS component and total system performance have already been optimized. The

performance of each DWS component is assessed to ensure that multiple barriers are in place,

such that continuous optimum performance is achieved.

3.2.2.1 Data Analysis and Data Confidence

The evaluator should be confident in the accuracy and representativeness of the data to be

used in the component evaluation. Judgement is therefore required in analyzing and

potentially eliminating unusual or atypical data. This includes assessment of the presence of

short periodic breakdowns in the system caused, for example, by "bumping a filter" which

releases previously trapped particles. Such a practice could have a significant health effect if

the particles are Giardia or Cryptosporidium cysts and therefore represents a poorly

performing facility. Using these criteria, it is possible to identify poorly performing DWS

components and thus poorly performing systems even though these facilities may have

reported compliance with regulatory standards.

With the advancement of instrumentation and control in drinking water systems application,

data must be fully understood in terms of what it represents and how it has been acquired

from the field device or devices.



It is important to confirm that data generated by a field device is fully understood with

respect to how the measured parameter is analyzed, converted to a signal output, and

conveyed to devices such as programmable logic controllers (PLC) and supervisory control

and data acquisition (SCADA) systems. Such output signals may be conditioned by the

measuring device itself or set with variable dead-bands or scan rates that may impact the

understanding of the data. It should not be assumed that the instrument sends out an

instantaneous signal to the PLC and SCADA system; for example, some analyzers have built-

in calibration check cycles where the on-line measurement of a parameter is interrupted for a

period of time.

Confirmation that ranges, spans and signals from field devices correlate correctly for all

PLCs and SCADA systems acquiring such information is recommended. It is important that

data read at the device be identical to the data presented on charts, HMIs and databases

archiving such information. Analog to digital conversions from field devices to PLCs should

also be confirmed.

PLC scan rates should be set to the appropriate levels according to the criticality of the

measured parameter. Data archiving may or may not align with the defined device and PLC

scan rate setting. Retrieval of data from the SCADA historian or database on a granularity

lower than the scan rate must be understood to confirm such information is not modified by

arithmetic functions such as averaging, minimum or maximum functions. As an example, a

5-second turbidity scan rate provides 720 distinct parameter values into a database. Retrieval

of such information on an hourly granularity would likely result in a value that is the average

of 720 values. This must be known since other arithmetic functions could also be applied to

the data rolled up to an hourly value.

Once understood, data acquired from field devices can be used to safely develop conclusions

regarding process optimization initiatives.

3.2.3 Identification and Prioritization of Performance Limiting Factors

3.2.3.1 Identification of Performance Limiting Factors

A significant aspect of any CPE is the identification of factors that limit the existing system's

performance. This step is critical in defining the focus of follow-up efforts. To assist in factor

identification, a list of 65 different factors that could potentially limit DWS performance is

provided in Appendix A. These factors are divided into broad categories of administration,

maintenance, design and operation. Definitions of each factor are provided. This list and

definitions have been updated and modified based on the results of water treatment plant

CPEs that have been conducted in the U.S. and Ontario, and is provided for convenience and

reference. If alternate names or definitions provide a clearer understanding to those

conducting the CPE, they can be used. However, if different terms are used, each factor

should be defined and these definitions should be readily available to those conducting the

CPE and interpreting the results. It is desirable to adopt a consistent list to allow comparison

from system to system. Note that the list includes factors related to the capacity of major

DWS components. If the evaluation of major DWS component results in a Type 2 or 3

classification, these results can then be documented in the overall list of factors identified as

limiting an existing system’s performance.

A factor should only be identified if it impacts performance. As such, an observation that a

factor does not meet a particular "industry standard" (e.g., a documented preventive



maintenance program or good housekeeping practices) does not necessarily indicate a

performance limiting problem. An actual link between poor performance and the identified

factor must exist. Properly identifying a system's unique list of factors requires very careful

analysis because the actual problems in a system are often masked. This concept is illustrated

in the following example:

A review of plant records revealed that a conventional water treatment plant was

periodically producing finished water with turbidity greater than 0.5 NTU. The

utility, assuming that the plant was operating beyond its capability, was beginning to

make plans to expand both the sedimentation and filtration unit processes. Field

evaluations conducted as part of a CPE revealed that settled water and finished water

turbidities averaged about 5 NTU and 0.6 NTU respectively. Filtered water

turbidities peaked at 1.2 NTU for short periods following a filter backwash. Initial

observations could lead to the conclusion that the plant's sedimentation and filtration

facilities were inadequately sized. However, further investigation revealed the poor

performance was caused by the operator adding coagulants at dosages 200 percent higher

than required, leading to formation of a pinpoint floc that would not settle or filter, and

operating the plant at its peak capacity for only 8 hours each day, resulting in the washout

of solids from the sedimentation basins. It was determined that implementing proper

process control of the plant and operating the plant at a lower flow rate for 16 hours each

day would allow the plant to continuously achieve acceptable finished water quality. It was

further determined that the reason the plant was not operated for longer periods of time was

an administrative policy that limited plant staff to one person, which made both 16-hour

and weekend coverage difficult. Staffing with one operator would not allow continuous

successful operation of the plant because there would be periods of time when necessary

process control adjustments could not be made.

It was concluded that four factors contributed to the poor performance of the plant:

1. Operator Application of Concepts and Testing to Process Control – Inadequate

operator knowledge to determine proper coagulant doses and to set chemical feed

pumps to apply the correct chemical dose.

2. Administrative Policies – Restrictive administrative policy that prohibited hiring

an additional operator to allow reduced plant operating flow rate by increasing

operating time.

3. Process Control Testing – Inadequate test equipment and sampling program to

provide process control information.

4. Administrative Familiarity With Plant Needs – Poor administrative guidance that

resulted in a rate structure that would not support the needs of the plant.

Given the above observations, plant expansion was not required.

The above discussion illustrates that a comprehensive analysis of a performance problem is

essential to identify the actual performance limiting factors. If the initial conclusions regarding

sedimentation and filtration capacity had been pursued, improper corrective actions in the form of

unnecessary expenditures would probably have occurred. As well, the issues associated with

process control and administrative guidance would likely have been ongoing even with the

planned expansion giving continued poor performance. Instead, addressing the operational and



administrative factors identified would allow the plant to produce acceptable finished water on a

continuous basis without major expenditures for construction.

3.2.3.2 Prioritization of Performance Limiting Factors

After all performance limiting factors are identified, they are prioritized in order of their

adverse effect on allowing desired system performance to be achieved. This prioritization

establishes the sequence and/or emphasis of follow-up activities necessary to optimize system

performance. For example, if the highest ranking factors (i.e., those having the most negative

impact on performance) are related to physical limitations in DWS component capacity,

initial corrective actions are directed toward defining system modifications and obtaining

administrative funding for their implementation. If the highest ranking factors are process

control-oriented, initial emphasis of follow-up activities would be directed toward site-

specific operator training.

Prioritization of factors is accomplished by a two-step process. First, all factors that have

been identified are individually assessed with regard to adverse impact on system

performance and assigned an "A", "B" or "C" rating (Table 3-1). The checklist of factors in

Appendix A includes a column to enter this rating. The second step of prioritizing factors is

to list those receiving an "A" rating in order of severity, followed by listing those receiving

"B" rating in order of severity. "C" factors are not prioritized.

Table 3-1 – Classification System for Prioritizing Performance Limiting Factors

Rating

Impact On System Performance

A Major effect on long-term repetitive basis

B Minimum effect on routine basis or major effect on a periodic basis

C Minor effect

"A" factors are major sources of a performance deficiency and are the central focus of any

subsequent improvement program. An example "A" factor would be sedimentation facilities

that are inadequate to reduce the suspended solids loading to the filters at all times of the

year, such that desired finished water quality cannot be achieved.

Factors are assigned a "B" rating if they fall in one of two categories:

Those that routinely contribute to poor performance but are not the major problem.

An example would be insufficient plant process control testing where the primary

problem is that the staff does not have a good understanding of coagulation

chemistry, how to run or interpret jar tests, or the need for additional process control

testing.

Those that cause a major degradation of system performance, but only on a periodic

basis. A typical example is sedimentation basins that cause periodic serious problems

during spring run-off.



Factors receive a "C" rating if they contribute to a performance problem, but have minor

effect. For example, if raw water was being sampled from the rapid mix after chemical feed,

it could indirectly contribute to poor performance since raw water testing would not be

representative of actual conditions. The problem could be easily corrected and would not be a

major focus during follow-up correction activities.

As a comparison of the different ratings, the example of a factor with a rating of "A" above

(sedimentation) would receive a "B" rating if the basin was only inadequate periodically, for

example, during a run-off event. The factor would receive a "C" rating if the basin size and

volume were adequate, but minor baffling was required to improve its performance.

Typically, 5 to 15 factors are identified during a CPE. The remaining 50 to 60 factors that are

not identified as performance limiting represent a significant finding. For example, in the

example presented in Section 3.2.3.1, neither sedimentation nor filtration was identified as a

performance limiting factor. Since they were not identified, plant personnel need not focus on

the sedimentation basins or filters as a problem, which would preclude spending large

amounts of capital to upgrade these facilities. Factors that are not identified are also a source

for providing recognition to personnel for adequately addressing these potential sources of

problems.

Once each identified factor is assigned an "A", "B", or "C" rating, those receiving "A" or "B"

ratings are listed on a one page summary sheet (see Appendix A) in order of assessed severity

on system performance. The prioritized summary list of factors provides a valuable reference

for the next step of the CPE, assessing the ability to improve performance, and serves as the

foundation for implementing correction activities if they are deemed appropriate.

All factors limiting system performance typically may not be identified during the CPE

phase. It is often necessary to later modify the original corrective steps as new and additional

information becomes available during conduct of the performance improvement (CTA)

phase.

3.2.3.3 Evaluation of Performance Limiting Factors

Evaluation of administration, maintenance, design and operation factors occurs throughout

the conduct of a CPE. The following are some useful observations in identifying factors in

these areas.

Administration Factors

The evaluation of administrative performance limiting factors is a subjective effort, primarily

based on management and staff interviews. In small systems the entire staff, budgetary

personnel and administrators, including one or two elected officials, should be interviewed.

These interviews are more effective after the evaluator has been on a system tour and has

completed enough of the data development activities (including the major DWS component

and performance assessment evaluations) to become familiar with system capabilities and

past performance. With this information, the evaluator is better equipped to ask insightful

questions about the existing DWS. To accurately identify administrative factors requires

aggressive but non-threatening interview skills. The evaluator must always be aware of this

delicate balance when pursuing the identification of administrative factors.

Budgeting and financial planning are the mechanisms that system owners/administrators

generally use to implement their objectives. Therefore, evaluation of these aspects is an



integral part of efforts to identify the presence of administrative performance limiting factors.

Smaller utilities often have financial information combined with other utilities, such as

wastewater treatment, street repairs, and parks and recreation. Additionally, nearly every

utility's financial information is set up differently. Therefore, it is necessary to review

information with the assistance of operations and/or budgetary personnel to rearrange the line

items into categories understood by the evaluator. Forms for comprehensively collecting

DWS information, including financial information, have been developed and are presented in

Appendix B. These forms allow a consistency in development of financial information.

Reference should be made to the Financial Plans Regulation (O. Reg. 453/07) made under

the SDWA.

When reviewing financial information, it is important to determine whether the rate structure

creates sufficient revenue to adequately support the DWS. Water system revenues should

provide an adequate number of fairly paid staff and exceed expenditures sufficiently to allow

establishment of a reserve fund for future system modifications.

Typically, all administrators verbally support goals of low costs, safe working conditions,

good plant performance, and high employee morale. An important question that the evaluator

must ask is, "Where does treated water quality fit in?". An ideal situation is one in which the

administrators function with the awareness that they want to achieve high quality finished

water as the end product of their water treatment efforts. Administrators who are not

supportive of these objectives are typically identified as contributing to inadequate

performance during factor identification activities. The requirements of Section 19 of the

SDWA, Statutory Standard of Care, should be discussed with administrators to ensure they

are aware of their legal duties and responsibilities with regard to the protection and safety of

the users of municipal drinking water.

Technical problems identified by operating staff or the CPE evaluator, and the potential costs

associated with these problems, often serve as the basis for assessing administrative

performance limiting factors. For example, the water staff may have correctly identified

minor modifications needed for the facility and presented these needs to the utility manager,

but had their requests declined. The evaluator must solicit the other side of the story from the

administrators, to see if the administration is indeed non-supportive in correcting the

problem. There have been numerous instances in which operators or superintendents have

convinced administrators to spend money to "correct" problems that resulted in no

improvement in system performance.

Administrators can directly impact performance of a DWS by failing to provide adequate

staffing levels required for the efficient operation of a WTP. Inadequate staff coverage (e.g.

no one is on-site to adjust chemical dosages relative to raw water quality changes) often

results in poor performance. Another area in which administrators can indirectly affect

system performance is through personnel motivation. A positive influence exists if

administrators encourage personal and professional growth through support of training,

tangible awards for upgrading of certification levels, etc. If, however, administrators

eliminate or skimp on essential operator training, downgrade operator positions through

substandard salaries, require operators to perform too wide a range of duties not related to

water treatment or distribution, or otherwise provide a negative influence on operator morale,

administrators can have a significant detrimental effect on system performance.



Design Factors

Data gathered during a system tour, review of plant and distribution system drawings and

specifications, completion of design information forms in Appendix B, and the completed

evaluation of major DWS component capabilities, including the performance potential graph,

provide the basic information needed to assess design-related performance limiting factors.

Often, to complete the evaluation, the evaluator must make field investigations of the various

DWS components.

Field evaluations or special studies should be completed in cooperation with operations staff.

The evaluator must not make any changes in equipment operation unilaterally. Any field

testing desired should be discussed with the operator, whose cooperation should be obtained

in making any needed changes. This approach is essential since the evaluator may wish to

make changes that could improve system performance but could be detrimental to equipment.

The operator has worked with the equipment, repaired past failures, and read the

manufacturer's literature, and is in the best position to ascertain any adverse impact of

proposed changes. Field evaluations are discussed in more detail in Section 3.3.3.5.

Operational Factors

Operational factors are those that relate to the process control functions. Significant

performance limiting factors often exist in these areas (USEPA, 1998). The approach and

methods used in maintaining process control can significantly affect performance of DWS

that have adequate physical facilities.

A system tour provides an opportunity to initially assess process control efforts. For example,

the process control capability of an operator can be subjectively assessed during a plant tour

by noting if the operator recognizes the unit process functions and their relative influences on

plant performance. A good grasp of process control is indicated if this capability exists.

The heart of the operational factors assessment is the process control testing, data

interpretation, and process adjustment techniques utilized by operating staff. The primary

controls available to a water treatment plant operator are flow rate; chemical selection and

dosage; and filter backwash frequency. Other controls include flocculation energy input and

sedimentation sludge removal. Controls at the system level may include distribution system

pressure and storage tank levels. Process control testing is necessary to gain information to

make decisions regarding these available controls. It should be noted, however, that

instrument devices can have filtering and damping capabilities that condition the actual

parameter value. Data should be interpreted with a full understanding of the instrument

device output conditioning, if applicable. It is also important to fully understand how

parameter values are interpreted and presented in SCADA databases given that arithmetic

functions may be applied (e.g. average, minimum, maximum, etc.) to such raw parameter

values. Additional information on data confidence and analysis is provided in Section 3.2.2.1.

Information to assist in evaluating process control testing, data interpretation and process

adjustment efforts is presented in the individual component chapters.



Maintenance Factors

Maintenance performance limiting factors are evaluated throughout the CPE by data

collection, observations and questions concerning reliability and service requirements of

pieces of equipment critical to system performance. If units are out of service routinely or for

extended periods of time, maintenance practices may be a significant contributing cause to a

performance problem. However, equipment breakdowns are often used as excuses for

performance problems. For example, one operator blamed excessive turbidity levels from the

sedimentation basin on the periodic breakdown of the primary alum feeder. However, the

backup feeder, while of greater capacity, could have provided an acceptable alum dose. The

real cause of the poor sedimentation basin performance was a lack of understanding by the

operator of the importance of maintaining the chemical feed rate.

It is important that maintenance activities be evaluated with respect to their impact on system

performance and process criticality, and not on the basis of comparison to the availability of a

documented preventive maintenance program. As such, maintenance would not be identified

as a performance limiting factor of a system that is exhibiting a high degree of performance

but has no documented routine maintenance system.

3.2.4 Assessment of Applicability of a CTA

Proper interpretation of the CPE findings is necessary to provide the basis for a

recommendation to pursue the performance improvement phase (e.g., CTA described in

Section 3.4). It is at this assessment phase that the maximum application of the evaluator's

judgment and experience is required. The initial step in assessment of CTA applicability is to

determine if improved performance can be achieved by evaluating the capability of major

DWS components. A CTA is recommended if DWS components receive a Type 1 or Type 2

rating. However, if major DWS components are deficient in capacity, acceptable

performance from each "barrier" may not be achievable, and the focus of follow-up efforts

must include a more detailed evaluation of options for upgrades or expansion.

Although all performance limiting factors can theoretically be eliminated, the ultimate

decision to conduct a CTA may depend on the factors that are identified during the CPE. An

assessment of the list of prioritized factors helps assure that all factors can realistically be

addressed given the unique set of factors noted. There may be reasons why a factor cannot be

approached in a straightforward manner. Examples of issues that may not be feasible to

address directly are replacement of key personnel, increases in rate structures or training of

uncooperative administrators to support DWS needs. In the case of reluctant administrators

who do not take water quality seriously, regulatory pressure may be necessary before a

decision is made to implement a CTA.

For systems where a decision is made to implement a CTA, all performance limiting factors

must be considered as feasible to correct. These are typically corrected with adequate

"training" of the appropriate personnel. The training is addressed toward the operational staff

for improvements in process control and maintenance, toward the system administrators for

improvements in administrative policies and budget limitations, and toward operators and

administrators to achieve minor facility modifications. Training, as used in this context,

describes activities whereby information is provided to facilitate understanding and

implementation of corrective actions.



3.2.5 CPE Report

Results of a CPE are summarized in a brief written report to provide guidance for facility

administrators and operators and, if applicable, regulatory personnel. It is important that the

report be kept brief so that the maximum amount of resources is used for the evaluation

rather than preparing an all-inclusive report. The report should present enough information to

allow the decision-making official to initiate efforts toward achieving desired performance

from their system. It should not provide a list of specific recommendations for correcting

individual performance limiting factors. Making specific recommendations often leads to a

piecemeal approach to corrective actions, and the goal of improved performance is not

achieved. For Type 1 and Type 2 systems, the necessity of comprehensively addressing the

combination of factors identified by the CPE through a CTA should be stressed. For Type 3

systems, a recommendation for a more detailed study (e.g. process audit) may be warranted.

Appendix C includes a sample CPE report.

3.3 CARRYING OUT A CPE

A CPE involves conducting several activities within a structured framework to determine if

significant improvements in system performance can be achieved without major capital

improvements. A schematic of CPE activities is shown in Figure 3-3.

Initial activities are conducted prior to on-site efforts and involve notifying appropriate utility

personnel to ensure that they will be available. The kickoff meeting, conducted on-site,

allows the evaluators to describe on-site activities, to coordinate schedules, and to notify

personnel of the materials that will be required. Following the kickoff meeting, a system tour

is conducted by the superintendent or process control supervisor. During the tour, the

evaluators ask questions regarding the drinking water system and notice items that may

require additional attention during data collection activities. For example, an evaluator might

make a note to investigate more thoroughly the flow splitting arrangement prior to

flocculation basins.

Following the system tour, data collection activities begin. Depending on team size, the

evaluators split into groups to facilitate simultaneous collection of the administrative, design,

operations, maintenance and performance data. After data are collected, the major DWS

component evaluation and performance assessment are conducted. Completing these

activities prior to the interviews provides the evaluators with an understanding of DWS

component capability and current performance, which allows interview questions to be

focused on possible factors limiting system performance. Interviews and special studies are

then conducted which allow additional insight to be gained regarding actual system

performance and what factors are contributing to the level of performance observed.

After all information is collected, the evaluation team meets at a location away from the

utility personnel to review findings. At this meeting, factors limiting performance of the

system are identified and prioritized. The prioritized list of factors, performance data, and

major DWS component evaluation data are then compiled and copied for use as handouts

during the exit meeting. An exit meeting is held with appropriate operating and

administrative personnel where all evaluation findings are presented. Off-site activities

include assessing the applicability of a follow-up CTA and completing the written report. A

more detailed discussion of each of these activities follows.



Figure 3-3 – Schematic of CPE Activities

3.3.1 Personnel Capabilities

A CPE is typically conducted over a three to five day period by a team composed of a

minimum of two people. The team approach allows a system to be evaluated in a reasonable

time frame and for personnel to share impressions. Shared impressions are especially

important when identifying and prioritizing performance limiting factors and in assessing

major DWS component capability since these efforts require a significant amount of

Initial Activities

Kick-off Meeting

System Tour

Data Collection Activities

Administration Data

Design Data

Operations Data

Maintenance Data

Performance Data

Conduct Performance Assessment

Evaluate Major DWS

Components

Conduct Interviews

Conduct Special Studies

Identify and Prioritize Factors

Exit Meeting

Assess Applicability of a

CTA

CPE Report

Off-Site

Off-Site

On-Site



judgment. Persons responsible for conducting CPEs should have significant knowledge and

skills in the areas identified in Table 3-2.

Table 3-2 – Personnel Capabilities for Conducting a CPE

Technical Skills

Leadership Skills

Water treatment plant and distribution

system design

Communication (presenting, listening, interviewing)

Water treatment and distribution system

operation and process control

Organization (scheduling, prioritizing)

Regulatory requirements Motivation (involving people, recognizing staff abilities)

Maintenance Decisiveness (completing CPE within timeframe

allowed)

Utility management (rates, budgeting,

planning)

Interpretation (assessing multiple inputs, making

judgments)

Regulatory agency personnel with experience in evaluating drinking water systems and

consulting engineers who routinely work with system evaluation, process design and start-up

represent the types of personnel with adequate backgrounds to conduct CPEs.

Utilities/municipalities are encouraged to use the services of a consultant with specialized

expertise in drinking water treatment process and distribution system design and

troubleshooting, as opposed to a consultant whose focus is designing and building plants. It

may be beneficial to consult with the design engineer to discuss the original intent of the

design and how the facility was meant to be operated.

3.3.2 Initial Activities

To determine the magnitude of the field work required and to make the on-site activities most

productive, specific initial information should be gathered. This information includes basic

data on the system and sources for any additional information. If a person associated directly

with the system is the evaluator conducting the CPE, some of the steps may not be necessary.

The following is a list of items that the CPE team should bring during site visits. These items

will aid in the collection and handling of data and other information.

MOE Manual entitled Optimization Guidance Manual for Drinking Water Systems

(this document) and other reference materials (e.g. USEPA, 1998);

Bench-top or hand-held instruments/devices (e.g. turbidimeter, chlorine residual

analyzer, pH meter, filter media probe, etc.);

Lap-top computer with spread-sheet capability for analysis/presentation of data;

Tape measure; and

Camera.



3.3.2.1 Identify Key People

It is necessary to have key people available during the CPE. Therefore, these people should

be identified and their availability determined. The superintendent, manager or other person

in charge of the DWS must be available. If different persons are responsible for maintenance

and process control, their presence should also be required. These persons should be available

throughout the field activities. A person knowledgeable about details of the utility budget

must also be available. A one- to two-hour meeting with this person will typically be required

during the field work to assess the financial aspects of the utility. In many small

communities, this person is most often the Clerk. In larger communities, the Manager or

Superintendent can usually provide the best information.

Availability of key administrative personnel is required. In many small communities, an

operator or superintendent may report directly to the local Council or Chair of Council. In

larger communities, the key administrative person is often the Director of Public Works or

other non-elected administrator. In all cases the administrator(s) as well as representative

elected officials who have the authority to effect a change in policy or budget for the DWS

should be available.

If a consulting engineer is currently involved with the system, that individual should be

informed of the CPE and provided with a copy of the report. Normally, the consulting

engineer will not be directly involved in the conduct of the CPE. An exception may occur if

there is an area of the evaluation that could be supplemented by the expertise available

through the consultant.

3.3.2.2 Scheduling

When initiating a CPE, a letter should be sent to the utility describing the schedule of

activities that will take place and outlining the commitment required of operat ions and

administrative staff. An example letter is presented in Appendix D. Interviews of

personnel associated with the system are a key component of a CPE. As such, the major

criterion for scheduling the time for a CPE should be local personnel availabil ity. If the

CPE is conducted by personnel not associated with a regulatory agency, it may be

beneficial to inform regulatory personnel of the CPE schedule. Responsibility for this

task should be clearly identified by the evaluator and local personnel during the

scheduling of activities.

3.3.2.3 Pre-Meeting

It may be beneficial for the municipality/utility to hold a meeting with its operational staff at

some time prior to the CPE kickoff meeting. This will familiarize staff with the intent of the

CPE and allows them to be better prepared when the CPE begins. By including operators at

the earliest stages, they will be more likely to "buy-in" to the CPE process.

3.3.3 On-Site Activities

On-site CPE activities are largely devoted to collection and evaluation of data. As a

courtesy to the system owner and to promote efficient data collection, the field work is

initiated with a kickoff meeting. This activity is followed by a system tour (conducted by

senior operations staff) and a period of time where detailed data on the system are

gathered and analyzed.



3.3.3.1 Kickoff Meeting

A short (less than 30 minutes) meeting between key operations and administrative staff

and the evaluators should be held to initiate the field work. The major purposes of this

meeting are to present the objectives of the CPE effort, to coordinate and establish the

schedule, and to initiate the administrative evaluation activities. Each of the specific

activities that will be conducted during the on-site effort should be described. Meeting

times for interviews with non-operations and operations personnel should be scheduled.

A sign-up sheet (see Appendix B) may be used to record attendance and as a means of

assisting with recall of names.

Information and resource requirements should be established. Specific items that are required

and may not be readily available are: budget information to provide a complete overview of

costs associated with water treatment and distribution; a water rate schedule; historical

monitoring data for a period of at least one year; O & M Manuals, if available; and any

facility drawings and specifications or other engineering studies available for the existing

facilities.

Administrative factors that may affect system performance should be noted during this

meeting, such as the priority of high quality finished water, familiarity with system needs,

communication between administration and operations staff, and policies on funding. These

initial perceptions often prove valuable when formally evaluating administrative factors later

in the CPE effort.

3.3.3.2 System Tour

A system tour should follow the kickoff meeting. The objectives of the tour are to familiarize

the evaluator with the physical works of the water treatment plant and distribution system,

make a preliminary assessment of operational flexibility of the existing processes and

chemical feed systems, and provide an initial basis for discussions on performance, process

control and maintenance.

The evaluator should also consider other elements of the system, which may not be physical

work, that contribute to the delivery of safe drinking water. For example, the system tour may

include activities or discussions related to source control measures and/or programs targeted

directly at the end-users of water (e.g. backflow and cross-connection prevention).

For the water treatment facility, a walk-through tour following the flow from the raw water

source through the plant to the clearwell is suggested. It is then appropriate to tour backwash

and sludge treatment and disposal facilities, distribution system facilities, followed by the

support facilities, such as the laboratory and maintenance areas. The evaluator should note

the sampling points and chemical feed locations throughout the plant.

Pre-treatment

Pre-treatment facilities consist of raw water intake structures, screening equipment, raw water

pumps, pre-sedimentation basins and flow measurement equipment. Intake structures and

screening equipment can have a direct impact on plant performance. For example, if the

intake configuration is such that screens become clogged with plant growth or the intake

becomes clogged with silt, consistent supply of water may be a problem. While at the raw

water source, questions should be asked regarding variability of the raw water quality,



potential upstream pollutant sources, seasonal problems with taste and odours, raw water

quantity limitations and algae blooms.

Raw water pumping should be evaluated regarding the ability to provide a consistent water

supply and with respect to how many pumps are operated at a time. Frequent changing of

high volume constant speed pumps can cause significant hydraulic surges to downstream unit

processes, degrading plant performance. In addition, operational practices as they relate to

peak flow rates, peak daily water production, and plant operating hours should be discussed

to assist in defining the peak instantaneous operating flow rate.

Pre-sedimentation facilities are primarily found at water treatment plants where raw water

turbidities exceed several hundred NTUs. If plants are equipped with pre-sedimentation

capability, basin inlet and outlet configurations should be noted and the ability to feed

coagulant chemicals should be evaluated. Typically, most pre-sedimentation configurations

lower turbidities sufficiently to allow conventional water treatment plants to perform

adequately. If pre-sedimentation facilities do not exist, the evaluator must assess the

capability of existing water treatment unit processes to remove peak raw water turbidities.

Flow measurement facilities are important to accurately establish chemical feed rates,

backwash water rates and unit process loadings. The system tour should be used to observe

the location of flow measurement equipment and to ask questions regarding various plant

flows. Questions should be asked concerning maintenance and calibration of flow

measurement devices, the age of devices, ranges (device and PLC), telemetry, meter accuracy

ranges, data logging, etc.

Mixing/Flocculation/Sedimentation

Rapid mixing is utilized to provide a complete instantaneous mix of coagulant chemicals to

the water. The coagulants neutralize the negative charges on the colloidal particles allowing

them to agglomerate into larger particles during the gentle mixing of flocculation. These

heavier particles are then removed by settling in the quiescent area of the sedimentation

basin. These facilities, if properly designed and operated, provide the primary barrier to

pathogens, lowers the concentration of NOM and reduce the particulate load to the filters,

allowing them to "polish" the water. During the tour, observations should be made to

determine if the mixing, flocculation and sedimentation processes are designed and operated

to achieve this goal. The evaluator should also observe flow splitting facilities and determine

if parallel basins are receiving equal flow distribution.

Rapid mix facilities should be observed to determine if adequate mixing of chemicals is

occurring. The operator should be asked what coagulant chemicals are being added and what

process controls are employed to determine their dosage. Observations should be made as to

the types of chemicals that are being added together in the mixing process. For example, the

addition of alum and lime at the same location may be counter productive if no consideration

is given to maintaining the optimum pH for alum coagulation. If coagulant chemicals are

added without mixing, observations should be made as to possible alternate feed locations,

such as prior to valves, orifice plates or hydraulic jumps, where acceptable mixing might be

achieved.

When touring flocculation facilities, the evaluator should note inlet and outlet conditions,

number of stages and the availability of variable energy input. Flocculation facilities should

be baffled to provide even distribution of flow across the basin and to prevent velocity



currents from disrupting settling conditions in adjacent sedimentation basins. If multiple

stages are not available, the capability to baffle a basin to create additional staging should be

observed. The ability to feed flocculation aids to the gentle mixing portion of the basin

should be noted. The operator should be asked how often flocculation energy levels are

adjusted or if a special study was conducted to determine the existing levels. In the case of

hydraulic flocculation, the number of stages, the turbulence of the water, and the condition of

the floc should be noted to determine if the unit process appears to be producing an

acceptable floc.

Sedimentation basin characteristics that should be observed during the tour are visual

observations of performance and observations of physical characteristics such as

configuration and depth. Performance observations include clarity of settled water, size and

appearance of floc, occurrence of floc carryover, and presence of flow or density currents.

The general configuration, including shape, inlet conditions, outlet conditions, and

availability of a sludge removal mechanism should be observed. The operator should be

asked what process control measures are utilized to optimize sedimentation including sludge

removal.

Filtration

Filters are utilized to remove the particles that are too small to be removed in sedimentation

basins by gravity settling. The number and configuration of filters should be noted, including

the type of filter media. The filter rate control equipment should be observed and discussed to

ensure that it regulates filter flow in an even, consistent manner without rapid fluctuations.

The flow patterns onto each filter should be noted to see if there is an indication of uneven

flow to individual filters.

Backwash equipment including pumps, air compressors, and surface washers should be

noted. The availability of back-up backwash pumping is desirable to avoid interruptions in

treatment if a breakdown occurs. The operator should be asked how frequently filters are

backwashed and what process control procedures are used to determine when a filter should

be washed. Preferably turbidity, rather than head loss or filter run duration, should be the

parameter utilized since it relates to water quality. The operator's response to these inquiries

helps to demonstrate his understanding and priorities concerning water quality. The operators

should also be questioned concerning the backwash procedure and if all operators follow the

same technique.

Disinfection

The evaluator should tour disinfection facilities to become familiar with the equipment feed

points and type of contact facilities. Special attention should be given to the configuration

and baffling of clearwells and finished water reservoirs that provide contact time for final

disinfection. Observation of the in-line contact time availability should be made by noting the

proximity of the first consumer, which is often the water treatment plant.

The availability of back-up disinfection equipment should be observed to assess the

capability of providing an uninterrupted application of disinfectant. The addition of a

disinfectant prior to filtration, either as an oxidizing agent or disinfectant should also be

noted. The capability to automatically control the disinfection systems should be determined.



Water Treatment Process Residuals Handling and Disposal

During the tour, the evaluator should become familiar with the facilities available to handle

filter backwash water and sedimentation basin sludge. If backwash water and sludge are

discharged to the storm sewer system or a waterway, questions should be asked to determine

if the discharge is permitted and in compliance with Certificate of Approval (C of A) or

Drinking Water Works Permit (DWWP)/Municipal Drinking Water Licence (Licence)

requirements.

The location of any recycle streams should be identified during the tour. Recycle of

backwash water should be assessed relative to the feasibility of returning a potentially high

concentration of cysts to the plant raw water stream. Cysts are primarily removed by the

filters so that the recycle of backwash water in a plant where the raw water has a high

potential for substantial numbers of cysts may compound the health risk, depending on

washwater treatment.

Laboratory

The laboratory facilities should be included as part of the plant tour. Performance monitoring,

process control testing, instrumentation calibration and frequency, and quality control

procedures should be discussed with laboratory personnel. It is especially important to

determine if turbidity measurements represent actual plant performance. Available analytical

capability for other parameters (e.g. pH, chlorine residual) should also be noted.

Distribution System

For large distribution systems, the layout may be best ascertained by reviewing

distribution system drawings or schematics. Visits to major distribution system

components, such as major pumping stations or storage facilities, should be conducted.

The evaluator should note the location of sampling stations throughout the distribution

system as well as any interconnections with other drinking water systems (i.e.

neighbouring municipalities). The evaluator should review backflow and cross-

connection control programs or by-laws, and discuss their implementation and/or

enforcement.

Maintenance

Maintenance facilities should be included as part of the plant tour. Tools, spare parts

availability, storage, filing systems for equipment catalogs, general plant appearance and

condition of equipment should be observed. Questions on the preventive maintenance

program, including methods of initiating work (e.g., work orders), are appropriate.

During the conduct of a system tour the evaluator must be sensitive to the personnel

conducting the tour. Questions that challenge current operational practices or that put

operations personnel on the defensive should be avoided. The evaluator should maintain an

information gathering posture at all times. It is not appropriate to recommend changes in

facilities or operational practices during the tour although the evaluator will often be asked

for an opinion. A suggested response is to state that observations will be presented at the

conclusion of the on-site activities and after additional information is collected and analyzed.

Most of the questions asked on the tour will be asked again during formal data collection

activities. The staff should be informed that this repetitiveness will occur. The system tour



also provides an excellent opportunity for the evaluator to observe intangible items that may

contribute to the identification of factors limiting performance (i.e., operator knowledge of

the system operation and facilities, relationship of process control testing to process

adjustments, etc.). Suggestions to help the evaluator meet the objectives of the system tour

are provided in subsequent chapters.

3.3.3.3 Detailed Data Gathering

Following the system tour, formalized data collection procedures are initiated. Information is

collected through conducting interviews with operations and administrative staff; reviewing

operating records, drawings, specifications, process control data sheets, etc., and conducting

field evaluations.

3.3.3.4 Drinking Water System Records

A variety of drinking water system records including budgets, drawings and specifications,

MOE Drinking Water Surveillance Program (DWSP) reports, MOE Drinking Water System

Inspection Program reports, operational logs, O & M Manuals, and manufacturers' literature

are required for the formal data collection efforts. The forms in Appendix B have proven to

be valuable in compiling information from these multiple sources in a consistent manner.

Categories covered by these forms are listed below:

Kickoff Meeting

Administration Data

Design Data

Operations Data

Maintenance Data

Performance Data

Interview Data

Exit Meeting

When collecting information, the evaluator should be aware that the data are to be used to

evaluate the performance capability of the existing facilities. The evaluator should

continuously be asking "How does this information affect plant performance?". If the area of

inquiry is directly related to system performance, such as filter design or an indication of an

administrative policy to cut costs by reducing chemical addition, the evaluator should spend

sufficient time to fully develop the perceived effect of the information on system

performance.

3.3.3.5 Field Evaluations

Field evaluations are an important means of identifying performance problems. Typically,

field evaluations should be conducted to verify the accuracy of monitoring and flow records,

chemical dosages, drawings, and other operating conditions. Specific field evaluations that



could be conducted for major DWS components are discussed in the individual component

chapters.

Record drawings may have to be field verified by measuring basin dimensions with a tape

measure if there is doubt as to their accuracy. If no drawings are available, all basin

dimensions should be measured.

3.3.3.6 Evaluation of Major DWS Components

An evaluation of the system’s major DWS components is conducted to determine the

performance potential of existing facilities at peak instantaneous operating flow (or other

flow rate, as deemed applicable by the evaluator; see Section 3.2.1.2). This is accomplished

by developing a performance potential graph and rating the major DWS components as Type

1, 2, or 3, as discussed in Section 3.2.1. It is important that the major DWS component

evaluation be conducted early in the on-site activities since this assessment provides the

evaluator with the knowledge of the system's capability. If a poorly performing system’s

major components are determined to be Type 1 or 2, then typically factors in the areas of

administration, operation or maintenance are primarily contributing to the performance

problems. The completed major DWS component assessment allows the evaluator to focus

later interviews and data gathering to identify those performance limiting factors.

3.3.3.7 Performance Assessment

An assessment of the system's performance is made by evaluating existing recorded data and

by conducting on-site evaluations to determine if DWS component and total system

performance have been optimized. Typically, the previous twelve months of existing process

control data is evaluated and graphs are developed to assess performance of the system. Other

periods of process control data can be evaluated if they are more representative of system

operating conditions. Field evaluations are also conducted to determine if existing operating

records accurately reflect actual treated water quality. A detailed discussion of the methods

utilized in the performance assessment of individual DWS components is presented in

subsequent chapters.

3.3.3.8 Interviews

It is beneficial to complete the data collection forms and to complete the major DWS

component evaluation and performance assessment before initiating the formalized

interviews, since this background information allows the evaluator to better focus interview

questions. Interviews should be conducted with all of the operations staff, including the

superintendent and other key administrative personnel. Key administrators typically include a

Council or Board member (especially from a Water Committee), and the Utility

Director/Manager. The interviews should be conducted privately with each individual.

Approximately 30 minutes should be allowed for each interview.

Interviews are conducted to clarify information obtained from operating records and to

ascertain differences between real or perceived problems. Intangible items such as

communications, administrative support, morale, and work attitudes are also assessed during

the interview process. Administrative and operations staff are both interviewed to ensure that

a balanced opinion is obtained. The performance focus of the CPE process must be

maintained in the interviews. For example, an adamantly stated concern regarding



supervision or communication is only of significance if it can be directly related to system

performance.

3.3.3.9 Evaluation of Performance Limiting Factors

After all data have been gathered, the major DWS component evaluations have been

completed, system performance has been assessed, and formal interviews have been

completed, identification and prioritization of performance limiting factors should be

conducted. The identification of factors should be completed at a location that allows open

and objective discussions to occur (i.e. away from operations staff). Prior to the discussion, a

debriefing session should be held that allows the evaluators to discuss pertinent findings from

their respective efforts. This step is especially important if more than two evaluators are

involved in the CPE because, with larger evaluation teams, not all members can be exposed

to every aspect of the comprehensive evaluation. All data compiled during the evaluations

should be readily available to support the factor identification efforts.

The checklist of performance limiting factors presented in Appendix A, as well as the factor

definitions, provides the structure for an organized review of problems in the subject system.

The intent is to identify, as clearly as possible, the factors that most accurately describe the

causes of limited performance. Often a great deal of discussion is generated in this phase of

the CPE effort. Several hours should be allocated to complete this step and all opinions and

perceptions should be solicited. It is particularly important to maintain the performance focus

during the activity in order to avoid identifying factors that do not have this emphasis.

Each factor identified as limiting performance should be assigned an "A", "B", or "C" rating.

Further prioritization is accomplished by completing the Summary Sheet presented in

Appendix A. Only those factors receiving either an "A" or "B" rating are prioritized on this

sheet.

3.3.3.10 Exit Meeting

Once the evaluation team has completed the field work for the CPE, an exit meeting should

be held with the system administrators and staff. A presentation of preliminary CPE results

should include brief descriptions of the following:

System performance assessment;

Evaluation of major DWS components;

Prioritized performance limiting factors; and

System performance potential.

Handouts summarizing these topics can be utilized to assist in the exit meeting presentation.

Examples of handouts typically utilized to present performance assessment findings include

time versus turbidity plots (one year of data) and percentile plots for raw, settled and finished

water, and results of field evaluations such as turbidity profiles following a filter backwash.

The performance potential graph and factor summary sheet can be utilized to present

information regarding the major DWS component evaluation and performance limiting

factors, respectively.



If the CPE reveals that the system performance represents a significant health risk, this

should be carefully explained to the system owner and/or operating authority. System

administrators should be advised to be in contact with regulatory and public health officials.

If a utility is operating within applicable regulatory requirements, but not optimizing treated

water quality, a presentation can be made as to the potential health advantage of setting more

aggressive goals, such as a filtered water turbidity of less than 0.1 NTU. A brief presentation

on the function of each water treatment and distribution system component and the effort

required to produce and deliver acceptable finished water quality can also be made to

enhance understanding for the administrators.

It is important to present all findings at the exit meeting with local officials. This approach

eliminates surprises when the CPE report is received and lays the foundation for the approach

necessary for any follow-up activities. In situations where administrative or operating staff

shortcomings are difficult to present, the evaluator must be sensitive and use communication

skills to successfully present the results. Throughout the discussions, the evaluator must

remember that the purpose of the CPE is to identify and describe facts to be used to improve

the current situation, not to place blame for any past or current problems.

It is emphasized that findings, and not recommendations, be presented at the exit meeting.

The CPE, while comprehensive, is conducted over a short time and is not a detailed

engineering design study. Recommendations made without appropriate follow-up could

confuse operators and administrators, and lead to inappropriate or incorrect actions on the

part of the utility staff (e.g., improper technical guidance). For example, a recommendation to

set coagulant dosages at a specific level could be followed literally to the extent that the next

time the evaluator is at the plant, coagulant dosages may still be the same as that

recommended even though time has passed and raw water conditions have changed.

It should also be made clear at the exit meeting that other factors are likely to surface during

the conduct of any follow-up activities. These factors will also have to be addressed to

achieve the desired performance. This understanding of the short term CPE evaluation

capabilities is often missed by local and regulatory officials, and efforts may be developed to

address only the items prioritized during the CPE. The evaluator should stress that a

commitment must be made to achieve the desired improved performance, not to addressing a

"laundry list" of currently identified problems. An ideal conclusion for an exit meeting is that

the facility owners fully recognize their responsibility to provide a high quality finished water

and that, armed with the findings from the CPE, they are enthusiastic to achieve that goal.

3.3.4 CPE Report

At the conclusion of the field activities, a CPE report is prepared. The objective of a CPE

report is to summarize findings and conclusions (see Section 3.2.5). Eight to twelve typed

pages are generally sufficient for the text of the report. An example report is presented in

Appendix C. Typical contents are:

Introduction

System Information

Major DWS Component Evaluation

Performance Assessment



Performance Limiting Factors

Projected Impact of a CTA

As a minimum, the CPE report should be distributed to system administrators and all

operations personnel. Further distribution of the report (e.g., to the design engineer) depends

on the circumstances of the CPE, but should be done at the direction or with the awareness of

local administrators.

3.4 CTA METHODOLOGY

The methodology for conducting CTA is a combination of 1) utilizing CPE results as a basis

for follow-up, 2) implementing process control priority setting techniques and 3) maintaining

long term involvement to systematically train staff and administrators responsible for water

treatment and distribution.

If the results of a CPE indicate a Type 1 system (see Figure 3-1), then existing major DWS

components have been assessed to be adequate to meet current performance requirements.

For Type 1 facilities, major system modifications are not indicated and the CTA can focus on

systematically addressing identified performance limiting factors to achieve the desired

finished water quality.

For Type 2 facilities, existing major DWS components have been determined to be marginal.

Improved performance is likely through the use of CTA; however, the system may or may not

meet performance objectives without major facility modifications. For these systems, the CTA

focuses on obtaining optimum capability of existing facilities. If the CTA does not achieve the

desired finished water quality, DWS component deficiencies will be clearly identified and the

owner/operator can be confident in pursuing the indicated facility modifications.

For Type 3 systems, major DWS components have been assessed to be inadequate to meet

performance objectives. For these facilities, major construction is indicated and a

comprehensive study that focuses on alternatives to achieve these construction needs is

warranted. A study of this type should look at long term water needs, raw water source or

treatment alternatives, distribution or storage requirements, and financing mechanisms. Such

a study may be subject to the requirements of the Municipal Class Environmental Assessment

(MEA, 2007) process under the Environmental Assessment Act.

If existing system performance has the potential to cause a serious public health risk, officials

may want to address the most serious operating problems to reduce the risk until

modifications can be implemented.

3.4.1 CPE Results

Implementation of a CTA initially focuses on addressing the prioritized list of performance

limiting factors that was developed during the CPE. This list provides a system-specific

outline of those items that must be addressed if desired performance is to be achieved. A

combination of activities such as training, minor modifications, and process control

adjustments may all be used by the person implementing the CTA to address identified

factors. It is important to note that additional performance limiting factors, not identified in

the short duration of the CPE, often become apparent during the CTA. These factors must

also be addressed to achieve the desired level of performance.



3.4.2 Process Control Priority Setting

The areas in which performance limiting factors have been broadly grouped (administration,

maintenance, design and operation) are all important in that a factor in any one of these areas

can individually cause poor performance. However, when implementing the CTA the

relationship of these categories to achieving the goal of desired delivered water quality must

be understood. Administration, design and maintenance activities all lead to a DWS

physically capable of achieving desired performance. It is the operation, or more specifically

the process control activities, that enables a physically capable system to produce and deliver

drinking water of acceptable quality. This concept is illustrated graphically in Figure 3-4.

Figure 3-4 – Relationship of Performance Limiting Factors to Achieving a Performance

Goal

Focusing on process control efforts when implementing the CTA allows priorities to be

developed for making the required changes to achieve improved performance. In this way the

most direct approach to improve performance is implemented. For example, if filtered water

turbidities cannot be consistently maintained at required levels because operating staff are not

at the plant to make chemical feed adjustments in response to changing raw water quality,

then improved performance will require better staff coverage. In this case, identified

limitations in meeting process needs (e.g., limitations in making chemical feed adjustments)

establish the priority for improving staff coverage (e.g., an administrative policy) at the plant.

Additional staff would alleviate the identified deficiency (e.g., provide a capable system) and

allow process adjustments to be made, so that progress toward the performance goal can be

continued. Conversely, non-performance related improvements can be justifiably delayed

utilizing the same process control emphasis.



3.4.3 Long Term Involvement

To be effective, implementation of the CTA must constitute a long term effort, typically

involving several months, for several reasons:

Greater Effectiveness of Repetitive Training Techniques: Operator and administrator training

can be conducted under a variety of actual operating conditions (e.g., seasonal water quality

or demand changes). This approach allows development of observation, interpretation and

implementation skills necessary to maintain desired finished water quality during periods of

variable raw water quality.

Time Required to Make Minor Facility/System Modifications: For changes requiring

financial expenditures, both time and a multiple step approach are typically required to gain

administrative (e.g. Local Council) approval. First, the need for minor modifications must be

demonstrated through process control efforts. Then council/administrators must be shown the

need and ultimately convinced to approve the funds necessary for the modifications. These

activities normally take several months before the identified modification is implemented and

operational. In addition, depending on the nature of the modifications, an amendment to the

plant's C of A or DWWP/Licence may be required.

Time Required to Make Administrative Changes: Administrative factors can prolong CTA

efforts. For example, if the utility rate structure is inadequate to support system performance,

extensive time can be spent implementing required changes in the rate structure. Communication

barriers between administrative and operational staff may have to be addressed for improved

performance. If the staff is not capable, personnel changes may have to be made for the CTA to

be successful.

Time Required to Address Additional Performance Limiting Factors That May Be Found

During the CTA: During the conduct of a CTA, new problems are often encountered that

were not apparent during the CPE, or arise as a result of actions taken early in the CTA.

3.4.4 Facilitator Tools

Experience has shown that no single approach can address the unique combination of factors

at every DWS; therefore, actual details of implementation must be site specific and should be

left to the individual implementing the CTA. However, general techniques that have been

successfully used in implementing CTAs are presented.

The individual who implements a CTA is called a facilitator. This individual is typically an

"outsider" and accomplishes the objectives utilizing periods of on-site involvement (e.g. site

visits) interspersed with off-site limited involvement (e.g. phone calls). This approach is

graphically illustrated in Figure 3-5.

Site visits are used by the facilitator to verify or clarify system status, initiate major process

control changes, test completed facility/system modifications, provide on-site operator or

administrative training, and report progress to utility staff. Dates for site visits should be

scheduled as indicated by the system status and training requirements and not necessarily be

established at specific intervals. As shown in Figure 3-5, fewer site visits and telephone calls

will typically be necessary as the CTA progresses. This is in line with the transfer of

responsibility to the operations staff that occurs during the CTA. The number of site visits

required by a CTA facilitator is dependent on system size and on the specific performance



limiting factors. For example, some administrative (e.g., staffing and rate changes) and

design factors could significantly increase the number of site visits required to complete a

CTA. Typically two to four days are spent touring the DWS facilities during site visits. A

final site visit is conducted to present a report.

Figure 3-5 – Typical Scheduling of CTA Activities

Telephone calls are used to routinely monitor CTA progress. Routine phone contact is used to

train and encourage operations personnel concerning system observations, data interpretation,

and follow-up implementation activities. Telephone calls are limited in effectiveness in that

the CTA facilitator must completely rely on observations of the operations staff. To enhance

communication, the CTA facilitator should always summarize important points, describe

decisions that have been reached, and identify actions to be taken. Further, both the CTA

facilitator and operations personnel should maintain written phone logs. Typically, two to

four hours each week are spent on phone calls and data development and interpretation.

Specific tools have been used to increase the effectiveness of site visits and telephone calls,

and to enhance the transfer of capability for achieving and maintaining desired finished water

quality to plant administrators and staff. These are further described below.

Contingency plans should be prepared for the occasions where a CTA is initiated at a DWS

that is producing unacceptable finished water quality, or where a CTA is being conducted and

finished water quality deteriorates to an unacceptable level. The contingency plan should

include actions such as reducing plant flow rate to improve performance, shutting down the

plant, isolating portions of the distribution system, initiating public notification and/or

initiating a boil water advisory. If finished water exceeds a health-based objective, the

regulatory agency (Ministry of Health/Ministry of the Environment) must be immediately

informed and public notification procedures mandated by the SDWA followed. To minimize

the chance of producing unacceptable finished water while conducting a CTA, all

experimentation with treatment processes, such as chemical doses and different coagulant

products, should be done at bench scale (e.g. jar test) before implementing changes at full

scale.

Action-implementation plans should be developed and updated by the facilitator throughout

the CTA to ensure progressive implementation of performance improvement activities. The

"Action" plan lists items to be completed, including the name of the person that is assigned a

particular task and the projected due date. The plan is normally updated and distributed to



administrators and operations personnel after a site visit. Phone calls are used to encourage

and monitor progress on the assigned action items. An example format for an "Action" plan is

shown in Table 3-3.

Table 3-3 – Example Action/Implementation Plan

Item

Action Person

Responsible Due Date

1 Develop calibration curve for polymer feed

pump Phil 12/05/2011

2

Draft special study procedure to study impact

on performance of reducing plant flow to 300

m3/h

Phil 19/05/2011

3

Process control:

a) develop daily process data sheet

b) develop routine sampling plan

c) calibrate on-line instruments and

telemetry

Jane

Jane

Jane

12/05/2011

18/05/2011

31/05/2011

Special studies can be used to evaluate and optimize DWS components, to document past

performance, to modify process control activities, or to justify administrative or design

changes necessary to improve system performance. They are a structured, systematic

approach of evaluating operating conditions. The format, which is shown in Table 3-4,

consists of a one page write-up that defines the hypothesis, approach, duration of the study,

expected results, documentation/conclusions and implementation plan. The hypothesis should

be narrow in scope and should clearly define the study that is to be conducted. The approach

should provide a detailed procedure of how the study is to be conducted, including when and

where samples are to be collected, who is to collect the samples, what analyses are to be

conducted, and how the results are to be tabulated. This approach should be developed in

conjunction with the operations staff to obtain staff commitment and to eliminate "bugs" on

paper prior to beginning the study. It is important that the study results be documented using

tools such as graphs, figures or tables. This allows the findings to be presented to the

operations staff, administrators, regulatory officials, or other "observers" as a basis for a

change in operations, design, maintenance or administration leading to improved system

performance. An implementation plan in conjunction with documentation addresses the

procedural changes and support required to implement special study results. If all of the steps

are followed, the special study approach ensures involvement by the operations staff, serves

as a basis for ongoing training, and increases confidence in system capabilities. An example

special study is presented in Appendix E.



Table 3-4 – Example Special Study Format

Special Study Name:

Hypothesis: Narrow in scope. Try to show definite cause/effect relationship.

Approach: Detailed procedure of conducting study. Involve operations staff in

development.

Duration of Study: Important to define limits of the study since "extra work" is typically required.

Expected Results: Projections of results focus attention on interim measurements and define

success or limitations of effort.

Conclusions: Documented impact of study allows the effort to be used as a training tool for

all interested parties. Allows credit to be given for trying an approach.

Implementation: Changes or justifies current operating procedures. Formalizes the mechanisms

to improve system performance.

Operating procedures can be used to formalize activities that are essential to ensure

consistent system performance. Examples of procedures that can be developed include: jar

testing, chemical feed calculations, filter backwashing and distribution system flushing.

Procedures are most effective if they are developed by the operations staff. Through the

staff's participation, operator training is enhanced and operator familiarity with equipment

manuals and operating procedures is obtained. Also, when operators are able to prepare a

procedure, it indicates that they have gained a thorough understanding of the DWS

component that was discussed.

Process control data sheets are used to formalize the recording of results of process control

testing that is initiated. Typically, a daily sheet is used to record results of tests, flow data,

chemical use, etc. These data are transferred to a monthly sheet that allows observation and

trending of the data.

Graphs or trend charts can be used to enhance the interpretation of process control results.

The data developed can be plotted over long periods to show seasonal trends, changes in

water demand, etc., or over shorter periods to show instantaneous performance.

Letter reports are recommended to promote clarity and continuity. Since a CTA is an action-

oriented program, only concise status reports are recommended. Short (one-page) written

summaries should be prepared after each site visit and for each facility modification. Initially

reports should be prepared by the CTA facilitator, but the responsibility should ultimately be

transferred to the operations staff.

A final CTA report should be prepared to summarize activities. Since all major

recommendations should have been implemented during the CTA, current status of the

system performance should be the main focus of this report.



3.4.5 Correcting Performance Limiting Factors

The major emphasis of a CTA is addressing factors identified as limiting performance.

Correcting these factors provides a capable system and allows improved process control to

move the DWS to continuous compliance with desired water quality objectives. Activities

that can be conducted to address factors in the areas of design, administration, maintenance

and operation are discussed below.

3.4.5.1 Design Performance Limiting Factors

The performance of Type 2 and 3 systems may be limited by design factors that require

major modifications to correct. Major modifications require the development of engineered

drawings and specifications, and hiring a construction company to complete the

improvements. Examples include improvements such as adding a sedimentation basin or

filter. Major modifications can often be avoided, for example, by operating a WTP at a lower

flow rate for longer periods of time, thereby reducing the hydraulic loading rate to a range

that allows adequate performance to be achieved.

The performance of Type 1 and Type 2 systems can often be improved by making minor

modifications or additions to the DWS. A minor modification is defined as a modification

that can be completed by the operations staff without major construction. Minor

modifications include improvements such as adding a chemical feeder, developing additional

chemical feed points, or installing baffles in a sedimentation basin.

Ideally, the CTA facilitator and operations personnel should be able to justify each proposed

DWS design modification based on the resulting increased performance capability that the

modification will provide. A sound basis is to relate design modifications to the need to

provide a capable system such that process control objectives can be met (see Figure 3-4).

The degree of justification required usually varies with the associated costs and system-

specific circumstances. For example, little justification may be required to add a sampling tap

to a filter effluent line, whereas, justification for adding baffles to a flocculation basin would

require much more effort. Additionally, extensive justification may be required for a facility

where water rates are high and have recently been raised, yet there is no money available for

an identified modification.

The CTA facilitator should transfer to the operations staff the capability to formally

document the need for minor modifications. This documentation is valuable in terms of

presenting a request to supervisory personnel and in providing a basis for the operations staff

to continue such requests after the CTA has been completed. For many requests, the special

study format can be used as the approach for documenting the change (see Section 3.4.4). For

modifications with a larger cost the following items may have to be added to the special

study format:

Purpose of the proposed change (e.g., how does the change relate to the development

of a capable system so that process control can be used to improve performance?).

Detailed description of the change and an associated cost estimate.

Modifications to the DWS, other than repair and maintenance items, such as temporary

changes to operation for experimental purposes (e.g. alternate chemicals, alternate feed

points, changing flocculator speed, changing flow splits etc.) may require an amendment to



the C of A or DWWP/Licence. If there is any doubt as to whether an amendment for either a

temporary or permanent change is needed, the facilitator should recommend contacting the

local MOE District Office.

Once the proposed modification has been approved by system administrators and the MOE,

the CTA facilitator should serve as a technical and managerial reference throughout the

implementation of the modification. Following completion of a modification, the CTA

facilitator should ensure that a formal presentation of the improved system capability is given

to the administration. This feedback is necessary to build rapport with the system

administrators and to ensure support for future requests. The intent of the presentation should

be to identify the benefits in performance obtained from the resources expended.

3.4.5.2 Maintenance Performance Limiting Factors

Maintenance can be improved in nearly all DWSs, but it is a significant performance limiting

factor in only a small percentage of systems (Renner, 1989; Renner, 1990). The first step in

addressing maintenance factors is to document any undesirable results of the current

maintenance effort. If system performance is degraded as a result of maintenance-related

equipment breakdowns, the problem is easily documented. Likewise, if extensive emergency

maintenance events are experienced, a need for improved preventive maintenance is easily

recognized. Ideally, maintenance factors should have been previously identified and

prioritized during a CPE. However, most DWSs do not have such obvious evidence directly

correlating poor maintenance practices with poor performance; therefore, maintenance

factors often do not become apparent until the CTA is conducted.

Simply formalizing record keeping will generally improve maintenance practices to an

acceptable level in many DWSs, particularly smaller ones. A suggested four-step procedure

for developing a maintenance record keeping system is to:

List all equipment;

Gather manufacturers' literature on all equipment;

Complete equipment information summary sheets for all equipment; and

Develop time-based preventive maintenance schedules, advanced forms of predictive

maintenance, reliability centered maintenance, etc.

Equipment lists can be developed by touring the system and by reviewing available

equipment manuals. As new equipment is purchased, it can be added to the list. Existing

manufacturers' literature should be inventoried to identify missing but needed materials.

Maintenance literature can be obtained from the manufacturer or from local equipment

representatives. Once sheets are completed for each piece of equipment, a time-based

schedule can be developed. This schedule typically includes daily, weekly, monthly,

quarterly, semi-annual and annual check-off lists of required maintenance tasks.

The above method for developing a maintenance record keeping system has worked

successfully at numerous DWSs. However, there are many other good maintenance systems,

including computer-based systems. The important concept to remember is that adequate

maintenance is essential to achieve consistent delivered water quality.



3.4.5.3 Administrative Performance Limiting Factors

Changes to drinking water legislation and regulations in Ontario, as well as the

implementation of the DWQMS, has greatly enhanced the awareness that administrators have

with regards to the importance of the delivery of safe drinking water and the reliability of

drinking water systems. However, experience gained in CCP studies in the U.S. and Ontario

have shown that administrators who are unfamiliar with system needs, and thus implement

policies that conflict with system performance, are a commonly identified factor. For

example, such items as implementing minor modifications, purchasing testing equipment, or

expanding operator coverage may be recognized by operations personnel as needed

performance improvement steps, but changes cannot be pursued due to lack of support by

non-technical administrators.

Administrative support and understanding are essential to the successful implementation of a

CTA. The following techniques have proved useful in addressing identified administrative

factors limiting performance:

Build a rapport with administrators such that candid discussions concerning physical

and personnel resources can take place.

Involve administrators from the start. Initial visits should include time with key

administrators to explain the process and possibly include a joint DWS tour to

increase their understanding of processes and problems.

Focus administrators on their responsibility to deliver a "product" that not only meets

but exceeds regulatory requirements on a continuous basis. Section 19 of the SDWA,

Statutory Standard of Care, should be discussed with administrators. Often

administrators are reluctant to pursue actions aimed at improving performance

because of a lack of understanding of both the health implications associated with

operating a water treatment plant and/or distribution system and of their

responsibilities in producing safe drinking water. Administrators must be informed

that even momentary excursions in water quality must be avoided to prevent

pathogenic organisms from passing through the treatment plant and into the

distribution system. Such a breakdown in the system could result in sickness of

numerous consumers. Administrators must understand that to minimize the exposure

of consumers to pathogenic organisms in their drinking water that all DWS

components must be performing optimally on a continuous basis. This provides a

"multiple barrier" to prevent passage of pathogenic organisms through the DWS.

Establishment and continuous achievement of high quality treated water goals

minimizes the risk that pathogenic organisms will reach consumers. As such,

administrators should be convinced to establish goals for high quality treated water

that exceed current objectives, and to emphasize to the operating staff the importance

of achieving these goals.

Listen carefully to the concerns of administrators so that they can be addressed.

Some of their concerns or ideas may be technically unimportant, but are very

important "politically." Political influence as well as technical requirements must be

addressed and are considered to be an integral part of the activities of a CTA

facilitator.



Use technical data based on process needs to convince administrators to take

appropriate actions; do not rely on "authority". Alternatives should be presented,

when possible, and the administrators left with the decision.

Solicit support for involvement of operations staff in the budgeting process. Budget

involvement has been effective in encouraging more effective communication and in

motivating operations staff.

Encourage development of a "self-sustaining utility" attitude. This requires financial

planning for modification and replacement of equipment and structures, which

encourages communication between administrators and operations staff concerning

the need to accomplish both short- and long-term planning. It also requires

development of a fair and equitable rate structure that requires each water user

(domestic, commercial, and industrial) to pay their fair share. The revenues generated

should be sufficient to support long-term as well as short-term modification and

replacement costs plus provide for ongoing items such as proper staffing, training

and chemical supplies. Reference materials are available to assist the CTA facilitator

in guiding activities in this area (AWWA, 2000).

Encourage long-term planning for future water supplies and facility improvements

necessary to meet more stringent water quality requirements.

3.4.5.4 Operational Performance Limiting Factors

Improvement of system performance is ultimately achieved by providing process control

procedures tailored for the particular DWS that can be used to move a capable system to the

desired finished water quality goal. Initial efforts should be directed toward the training of the

key process control decision makers. In most small systems (e.g. flows less than 2,000 m3/d),

one person typically makes and implements all major process control decisions. In these

cases, on-the-job training is usually more effective than classroom training and is

recommended. If possible, in systems of this size, a qualified "back-up" person should also be

trained. As the number of operators to be trained increases with system size, the need for and

effectiveness of combining classroom training with on-the-job training also increases. Since

on-the-job training or site-specific training greatly enhances the operators' capability to apply

knowledge, this "hands-on" approach must be an integral part of the CTA.

Process Sampling and Testing

Successful process control of a DWS involves producing and delivering a consistent, high

quality treated water from an often highly variable raw water surface source and under a

variety of operating conditions. To accomplish this goal, it is necessary that the performance

of each DWS component be optimized. This is important because a breakdown in any one

DWS component places a greater burden on the remaining processes and increases the

chance of viable pathogenic organisms reaching the distribution system and consumers’ taps.

By optimizing each DWS component, the benefit of providing multiple barriers prior to

delivery to consumers is realized.

To optimize each DWS component, information must be routinely obtained and recorded on

raw water quality and on the performance of the various unit processes in the plant so that

appropriate controls can be exercised to maintain consistent treated water quality. The term

“routinely” is stressed because it is advantageous to have the plant staffed at all times it is in



operation to allow information to be gathered and for process control adjustments to be made

whenever water quality conditions dictate. The gathering of information in an organized and

structured format involves development of a process control sampling and testing schedule.

Recommendations for process-specific sampling and testing are provided in the subsequent

individual DWS component chapters.

The process control data should be recorded on daily sheets, and these data should be

transferred to monthly sheets to allow observation of water quality trends. The daily sheets

should include space for recording actual chemical feed rates and the conversion of these

values to a mg/L dosage so that dosage and water quality can be correlated. This database can

then be used by the operator to better predict chemical feed requirements when raw water

quality characteristics change suddenly. Graphs and trend charts greatly enhance these

correlation efforts.

3.5 HOW TO CONDUCT A CTA

3.5.1 Initial Site Visit

A good working relationship between the CTA facilitator and the operations staff and

administration should be established during the initial site visit. Such a relationship is based

on mutual respect and good communication. Understanding the objective of the CTA greatly

enhances the potential for success. During the initial site visit, CPE results are used to

prioritize follow-up activities. Ideally, activities for addressing all major performance

limiting factors (rated "A" or "B" in the CPE) should be initiated.

Before implementing any major changes, the facilitator must carefully consider the potential

adverse impact on system performance and public health. Contingency plans should be

prepared for the case where a CTA is initiated for a system that is producing unacceptable

finished water quality (see Section 3.4.4). Actions could include plant shutdown, lowering

plant flow rate, isolating areas of a distribution system or initiating an order to boil water. In

all cases, contact with appropriate health/regulatory officials to notify them of the problem

must be made. If process adjustments are grossly out of line, corrective actions should be

initiated to minimize the adverse effect of the treated water. Jar tests or other bench scale

testing should be done prior to initiating a process adjustment in order to avoid full-scale

experimentation that could actually result in a further deterioration in treated water quality.

After a contingency plan has been developed to ensure protection of public health, the CTA

facilitator can begin directing the implementation of process control adjustments to optimize

system performance. Changes in process control direction must be made with consideration

of the operators' morale and traditional approaches to chemical dosing (such as more

disinfectant is "safer"). All recommendations for process control changes should be

thoroughly explained prior to implementation. Even with this approach, a CTA facilitator

should not expect to obtain immediate enthusiastic support from operations personnel. A

response such as "well let’s try it and see" is often the best that can be expected. Some

changes may have to be made with only the degree of consensus expressed with the

statement, "I don't think it will work, but we can try it."

If operations factors are top ranking, the initial site visit should be used to introduce the staff

to proper process control activities, such as conducting jar tests and chemical feed

calculations (see Section 3.4.4). Existing chemicals and dosages should be utilized in initial



adjustments. Special studies can be initiated later in the CTA to determine the effectiveness

or necessity of alternative chemicals.

Understanding how to determine correct chemical dosages and how to set the chemical

feeders is extremely important in achieving optimum system performance. Procedures that

clearly describe these activities should be reviewed, or developed if they don't exist, during

the initial visit. The operations staff then has a written description that can be consistently

followed.

Existing process control testing should also be reviewed and modified so that all necessary

process control elements are adequately monitored. Sampling frequency and location,

collection procedures, and laboratory analyses should be reviewed and, if necessary,

standardized so that data collected can be used for evaluating progress. New or modified

sampling and analysis procedures should be demonstrated and documented.

The necessary process control equipment is not always available to operators. Any needed

sampling or testing equipment should be noted and the purchasing process should be

implemented as quickly as possible. Provisions may be made for loaner equipment for

essential items.

Data sheets, which summarize process control parameters and performance monitoring

results, should be developed. It is important that a common understanding of information on

the summary sheets be reached during the initial site visit since they will be used by

operations staff to provide data to the CTA facilitator throughout the CTA. The CTA

facilitator reviews the data, sets operating targets and makes process control decisions in

conjunction with the operations staff. Often, weekly summaries of data are used. However, if

computer capability is available, electronic transfer of data can be used to allow daily data

exchange.

System performance is often limited by the performance goals established by utility

personnel. For example, many plants only try to achieve a finished water quality as required

by the regulatory standard. This attitude negatively affects the attainment of optimum unit

process performance (multiple barriers) and continuous finished water quality that minimizes

public exposure to pathogenic organisms. It is essential that the facilitator work with

operations staff and administrators to establish aggressive treatment goals during the initial

site visit and to instil in the operators and administrators the tenacity to achieve those goals.

The change in attitude to support these goals often does not occur until it is demonstrated that

the DWS, given more intense process control, can consistently achieve a very high quality

delivered water. However, once this is experienced, the administrators and operators are

driven by pride to maintain consistent, high quality delivered water. With this pride comes

the willingness of administrators to provide adequate budgets and staffing to support

optimum delivered water quality.

Activities to implement any minor design changes identified as necessary during the CPE and

confirmed by the CTA facilitator should be initiated during the site visit. Some design

changes often require significant amounts of time for approvals, delivery of equipment or

construction. It is important to have the upgraded facilities in place with the desired capacity

when the CTA is undertaken.



Efforts to address administrative factors are also appropriate to be implemented during the

initial site visit. Administrative changes such as increasing rates, changing personnel, or long

range planning activities require significant time and diplomacy to address. The sensitivity of

these issues may require that significant background information be obtained before action is

taken.

3.5.2 Off-Site Activities

The CTA facilitator should provide a short letter summarizing activities during the first site

visit and include an implementation plan. Any procedures or process control sheets that were

developed in conjunction with the operations staff should also be formalized and returned to

the utility. Phone calls should be made at least weekly to obtain operating information and to

make certain that action items are being accomplished in a satisfactory manner. A return or

intermediate site visit should be made when operating conditions dictate or when process

control equipment (e.g., jar testing equipment, instrumentation, etc.) or minor design

modifications that were determined necessary for future CTA activity are implemented.

3.5.2.1 Follow-Up Site Visits

During intermediate site visits, follow-up training should be presented to the operations staff

on chemical feed calculations, jar testing and other procedures initiated during the initial site

visit. Repetitive training in this manner is effective in transferring capability to the operating

staff. Typically, the concept of special studies (Section 3.4.4) is also introduced at the first

follow-up site visit and a prioritized list of special studies is developed in conjunction with

the utility staff. During remaining site visits the facilitator should follow up on special study

activities and set additional direction as required.

The facilitator should present graphs depicting performance improvement achieved during

the CTA. This, coupled with additional discussion on the necessity of achieving continuous

high quality water and praise regarding improved performance obtained to date, provides the

operators with the incentive to continue striving to produce the highest quality water possible.

During site visits, discussions must also be held with administrators to inform them of

progress made and to convince them to continue supporting optimum performance through

adequate budgeting and staffing. During the final site visit, the results of the CTA should be

presented to administrators and operations staff.

3.5.3 CTA Results

The success of conducting CTA activities can be measured by a variety of parameters, such

as improved operator capability, cost savings, improved maintenance, etc. However, the true

success of a CTA should be documented improved performance to the degree that the DWS

has achieved the desired performance goals, which should consist of, as a minimum, meeting

or exceeding the Ontario Drinking Water Quality Standards and Objectives. Given this

objective, the results of a successful effort can be easily depicted in graphical form.

Results from an actual CTA conducted at a conventional filtration plant are presented in

Figure 3-6. As shown, plant performance was inconsistent as depicted by the variations in

finished water turbidity. After CTA activities had been implemented the treated water quality

remained consistent at about 0.3 NTU. It is recommended that CTA results be presented in

this format.



Figure 3-6 – Example Treated Water Quality Achieved During Conduct of a CTA

3.5.4 CTA Summary Report

A CTA summary report should be prepared and presented to utility personnel upon

completion of the CTA. The objective is to summarize the conclusions and document

achievement of improved system performance. The report should be brief and outline

activities that were implemented to address the factors limiting system performance. Graphs

documenting the improvement in system performance should also be presented. If other

benefits were achieved these should also be documented. Eight to twelve pages are typically

sufficient for the text of the report. An example CTA report is shown in Appendix F.

Typical contents are:

Introduction (reasons for the CTA);

CPE Results (briefly summarize information from the CPE report);

CTA Significant Events (chronological summary of activities conducted);

CTA Results (graph of system performance plus other CTA benefits); and

Conclusions (efforts required to maintain improved performance).

As a minimum, the CTA report should be distributed to administrators and key operating

personnel. Further distribution of the report, for example to the design engineer or regulatory

agency(ies), depends on the circumstances of the CTA, but should be done at the direction or

with the awareness of local administrators.



3.6 REQUIRED PERSONNEL CAPABILITIES FOR CONDUCTING A CTA

Persons responsible for conducting a CTA must have a comprehensive understanding of

water treatment and distribution principles and practices, extensive hands-on experience in

drinking water system operations, and strong capabilities in personnel motivation.

Comprehensive understanding of water treatment is necessary because current state-of-the-art

in water treatment leaves room for individual judgment in both design and process control.

The CTA facilitator must be familiar with all types of unit processes, raw water quality

characteristics and chemical products available for successful water treatment. In addition,

those responsible for implementing a CTA must have sufficient process experience to

determine appropriate application of a strategy to the personnel capabilities of the plant in

question.

Experience in distribution system operations and understanding of the factors that affect

water quality in distribution systems are also key assets. Leadership and motivational skills

are required to fill the multi-faceted "facilitator" role required of individuals responsible for

implementing a CTA.

Individuals who routinely work in the area of improving water treatment plant performance

and distribution system water quality likely will be best qualified to be CTA facilitators.

These people are typically engineers or operators who have focused their careers on drinking

water system troubleshooting and have gained experience in correcting deficiencies in

systems of various types. It is important that CTA facilitators have experience in a variety of

systems because the ability to recognize true causes of limited performance is a skill

primarily developed through experience. Similarly, the successful implementation of a cost-

effective CTA is greatly enhanced by experience.

By the very nature of the approach, the CTA facilitator must often address improved

operation, maintenance and minor design modifications with personnel already responsible

for these functions. A "worst case situation" is one in which the operations staff is trying to

prove that "the facilitator can't make it work either". The CTA facilitator must be able to deal

with this personnel issue in such a manner that allows all parties involved to focus on the

common goal of achieving system performance.

A CTA facilitator must be able to conduct training in both formal and on-the-job situations.

Training capabilities must also be developed so that they are effective with both operating as

well as administrative personnel. When addressing process control limitations, training must

be geared to the specific capabilities of the process control decision makers. Some may be

inexperienced; others may have considerable experience and credentials. "Administrative"

training is often a matter of clearly providing information to justify or support CTA activities.

Although many administrators are competent, some may not know what their facilities

require in terms of staffing, minor modifications or specific funding needs.

CTA facilitators include consultants, regulatory personnel or utility employees. However, the

desired "existing facility" focus of a facilitator must be maintained, since a substantial

construction cost can be incurred if an inexperienced facilitator is not able to bring a capable

DWS to the desired level of performance. For example, a consultant, involved primarily with

facility design, may not have the operational experience to utilize the capability of existing

DWS components to their fullest extent and may be biased toward designing and constructing

new facilities.



If utilities/municipalities decide to conduct a CTA with people closely associated with the

system, they should recognize that some inherent problems may exist. The individuals

implementing the CTA, for example, often find it difficult to provide an unbiased assessment

of the area in which they normally work. Operating personnel tend to look at design and

administration as problem areas while administrators typically feel that operating personnel

should be able to do better with what they have. In addition, the engineer who approved a

facility’s design is often reluctant to admit design limitations. These biases should be

considered before personnel closely associated with the facilities initiate a CTA.

3.7 REFERENCES

American Water Works Association (2000). AWWA Manual M1: Principles of Water Rates,

Fees, and Charges. 5th Ed. ISBN 1-58321-069-5.

Municipal Engineers Association (2007), Municipal Class Environmental Assessment.

October 2000, as amended 2007.


Renner, R.C., B.A. Hegg and D.L. Fraser (1989). “Demonstration of the Comprehensive

Performance Evaluation Technique to Assess Montana Surface Water Treatment Plants”,

presented at the 4th Annual ASDWA Conference, Tucson, Arizona.

Renner, R.C., B.A. Hegg and J.H. Bender (1990). EPA Summary Report: Optimizing Water

Treatment Plant Performance with the Composite Correction Program. U.S EPA Centre for

Environmental Research Information. EPA 625/8-90/017.




CHAPTER 4GENERAL OPTIMIZATION TECHNIQUES

GENERAL OPTIMIZATION TECHNIQUES

4.1 Introduction ............................................................................................................ 4-1

4.2 Field Evaluations .................................................................................................... 4-1

4.2.1 Performance Monitoring and Verification ............................................... 4-1

4.2.2 Controlling Plant Flow Rate .................................................................... 4-2

4.2.3 Control of Chemical Dosages .................................................................. 4-2

4.2.4 Filter Investigations ................................................................................. 4-3

4.2.5 Tracer Testing .......................................................................................... 4-3

4.2.6 Stress Testing ........................................................................................... 4-6

4.2.7 Pilot Plants ............................................................................................... 4-7

4.3 Modelling and Simulation ...................................................................................... 4-7

4.3.1 Applications of Modelling and Simulation .............................................. 4-8

4.3.2 Clarifier Modelling .................................................................................. 4-8

4.3.3 Modelling Reactor Flow Characteristics ................................................. 4-9

4.3.4 Mixing Modelling .................................................................................. 4-10

4.3.5 Distribution System Modelling .............................................................. 4-10

4.3.6 Limitations of Modelling and Simulation .............................................. 4-11

4.4 Case Histories ....................................................................................................... 4-11

4.4.1 Peterborough Utilities Commission – Distribution System Tracer

Study ...................................................................................................... 4-11

4.4.2 City of Toronto – CFD Modelling of Flocculation Mixing

Performance ........................................................................................... 4-14

4.5 References ............................................................................................................ 4-15

CHAPTER 4. General Optimization Techniques 4-1


CHAPTER 4

GENERAL OPTIMIZATION TECHNIQUES

4.1 INTRODUCTION

A number of general techniques are available to improve the operation and performance of a

drinking water system (DWS) that are not specific to a particular unit process. The objective

of this chapter is to present an overview of these techniques that can be applied as part of a

DWS optimization study, such as field investigation, modelling and simulation.

4.2 FIELD EVALUATIONS

Field evaluations are an important aspect of the on-site activities conducted as part of an

optimization study. Typically, field evaluations are conducted to verify the accuracy of

monitoring and flow records, chemical dosages, record drawings, filter integrity and

backwash capability. A discussion of various field activities is provided in the following

subsections.

4.2.1 Performance Monitoring and Verification

Performance monitoring records can be verified, for example, by utilizing a properly

calibrated continuous recording instrument to assess process performance over a 24-hour

period. It is important that the field evaluation team acquire or have made available to them

properly calibrated instruments to support field efforts. If recording on-line instruments are

not available, an instrument that allows individual analysis of grab samples can be used. If

the evaluation team does not have access to a specific instrument, the plant’s instruments can

be used providing they are calibrated prior to the sampling and testing activities.

Treated water quality obtained during the field evaluation can be compared with plant

recorded data to make a determination whether the performance monitoring records

accurately represent treated water quality. Differences in actual versus recorded finished

water quality can be caused by sampling location, sampling time, sampling procedures and

testing variations. The evaluation team’s instrument can also be used to assess the plant’s

instrument accuracy and calibration techniques.

The accuracy of flow records can be verified by assessing the calibration of flow

measurement equipment. It may also be helpful to assess upstream and downstream meter

flows in order to assess the overall flow consistency within meter effort ranges, where

applicable. This is often difficult because of the type of meter utilized (e.g. propeller, venturi,

magnetic). If these types of meters are utilized, it may be necessary to conduct a timed fill-

and-draw test to check the accuracy of the flow metering equipment.

If accuracy of metering equipment is difficult to field-verify, the frequency of calibration of

the equipment by the plant staff or outside instrumentation technicians can be evaluated;

however, it is important to recognize that calibration of flow metering equipment often

involves only the secondary element (the pressure differential measurement device, for

example) and does not include calibration of the primary measurement device. In such cases,

it is important to review the flow meter installation to ensure that it meets the manufacturer’s

specifications or follows good engineering principles. Ideally, a full station calibration



(primary and secondary elements) should be undertaken to confirm the accuracy of flow

metering equipment.

Throughout the document, recommendations are provided for monitoring DWS component

performance. These recommendations are in addition to required regulatory monitoring, and

should in no way compromise sampling or monitoring activities related to regulatory

compliance. It should be noted that the results of additional monitoring are required to be

reported under the applicable drinking water regulations. Additional information on sampling

parameters, frequency, etc., for performance monitoring is provided in Kirmeyer (1999);

AwwaRF (2002); Kirmeyer (2002); and AWWA (2010). Information on the collection and

handling of drinking water samples is provided in Practices for the Collection and Handling

of Drinking Water Samples (MOE, 2009).

4.2.2 Controlling Plant Flow Rate

Plant flow rate is a primary means for process control at many small plants that are operated

for less than 24 hours each day. At these plants, an excessive hydraulic loading rate on the

treatment processes can be avoided by operating at a lower flow rate for a longer period of

time. Eliminating or reducing the frequency of starts and stops of the treatment processes,

and high hydraulic loading rates on start-up, can also improve performance. This provides an

option to meet more rigorous performance requirements with existing units without major

capital improvements.

The capability to reduce plant flow rate to improve performance is offset by the need to staff

the plant for longer periods of time, or the provision of additional automated controls, which

adds to operating costs. Therefore, plant administrators, in conjunction with the CTA

facilitator, should evaluate both options. The ability to modify plant flow rate also depends

on the availability of storage at the plant or in the distribution system.

4.2.3 Control of Chemical Dosages

Dosages of key treatment chemicals, such as primary coagulants, should be verified. Feed

rates from dry feeders can be checked by collecting a sample for a specified time and

weighing the accumulated chemical. Similarly, liquid feeders can be checked by collecting a

sample in a graduated cylinder for a specified time. In both cases, the feed rate in mL/min or

mg/min of chemical should be converted to mg/L based on flow measurements made at the

point of chemical addition at the same time as the chemical addition rate is measured. The

calculated dosage should be compared with the reported dosage. Dosage checks for liquid

chemical feed systems should ideally be conducted by replicating actual pump suction and

discharge head conditions.

During this evaluation, the operating staff should be asked how they conduct chemical feed

calculations, prepare polymer dilutions and set chemical feeders. Additionally, staff should

be asked how they arrived at the reported dosage.

If jar testing is used, the evaluation team should discuss this procedure, including preparation

of stock solutions. Often, this discussion can be used to assess the operators’ understanding

of jar testing as a coagulation control technique.



4.2.4 Filter Investigations

Field evaluations should be conducted to assess the integrity of the filter media, support

gravel and underdrain system for a selected filter. This requires that the filter be drained and

that the evaluation team inspect the media.

The filter should be investigated for surface cracking, proper media depth, mounding,

mudballs and segregation of media in dual media filters. The media can be excavated to

determine the depth of the different media layers in multi or dual media filters. The media

should be placed back in the excavated filter in the reverse sequence that it was removed. The

filter should also be probed with a steel rod to check for displacement of the support gravel

and to verify the media depth within the filter, where appropriate. Variations of over 5 cm in

depth of media or support gravel from the design would signify a potential problem.

Deviations in media depth, uniformity coefficient and effective size relative to the design

specifications should be noted. Media loss should be quantified and assessed.

If possible, components downstream of the filters and the clearwell should be observed for

the presence of filter media. Often, operations staff can provide feedback on media in the

clearwell if access is limited. If support gravel or media loss is apparent, a more detailed

study of the filter should be undertaken.

Filter backwash capability often can be determined from the flow measurement device on the

backwash supply line. If this measurement is in question or if the meter is not available, the

backwash rate should be field-verified by assessing either the backwash rise rate or bed

expansion. Rise rate is determined by timing the rise of water for a specific period within the

filter box. For example, a filter having a surface area of 14 m2 would have a backwash rate of

approximately 49 m/h if the rise rate was 27 cm in 20 seconds (Backwash rate = (0.27 m ÷ 20

s) x 3600 s/h = 48.6 m/h). This technique is not suitable for filters where the peak backwash

rate is not reached until the washwater is passing over the troughs.

Bed expansion is determined by measuring the distance from the top of the unexpanded

media to a reference point (e.g. top of filter wall) and from the top of the expanded media to

the same reference point. The difference between these two measurements is the bed

expansion. A variety of techniques can be used to determine the top of the expanded bed. A

light-coloured can lid attached to the end of a pole is effective. The percent bed expansion is

determined by the bed expansion measurement divided by the total depth of expandable

media (i.e. media depth less gravel) multiplied by 100. A proper wash rate should expand the

filter a minimum of 25 percent (ASCE & AWWA, 2004). The backwash rate should be

variable, with the maximum rate designed to provide for 50 percent expansion of the filter

media bed at the highest water temperature (MOE, 2008).

4.2.5 Tracer Testing

Tracer test techniques evaluate the hydraulic characteristics of process tanks. Test results can

indicate short-circuiting, determine existing mixing regimes, locate dead zones within the

fluid volume, evaluate baffling arrangements and identify predominant flow patterns within

the process tank (MOE et. al., 1999). Tracer tests may be applied to coagulant mixing,

flocculation, sedimentation basins, chlorine contact tanks, distribution system storage

facilities or other unit processes for which it is necessary to evaluate or control residence time

characteristics. Information on the conduct of tracer studies is provided in USEPA (1990) and

Teefy (1996).



A tracer test is started by adding a conservative (i.e. non-reactive) chemical into a basin and

observing the change in concentration of this chemical over time in the basin effluent until a

steady state is reached. The shape of the resulting concentration versus time curve provides

insight as to the degree of short-circuiting within the basin and the actual residence time of

the water in the basin.

Commonly used tracer chemicals include fluoride, rhodamine WT, lithium, sodium, chloride

and calcium (Teefy, 1996). In selecting a tracer chemical, consideration must be given to

whether the tracer will react with other chemicals used in the water treatment process. In

addition, all chemicals used in the conduct of tracer tests should meet all applicable quality

standards for chemicals and other water contacting materials set by AWWA and the

consumer safety standards NSF/ANSI Standard 60: Drinking Water Treatment Chemicals -

Health Effects and NSF/ANSI Standard 61: Drinking Water System Components - Health

Effects.

Tracer tests most commonly used in water treatment plants are pulse (slug dose) and step

(continuous-feed) inputs.

A pulse input test involves adding the entire amount of tracer to be used at the beginning of the

test as a slug. The addition of the slug tracer must be as instantaneous as possible, and the

chemical must be completely mixed with the influent flow stream. One of the disadvantages of

the pulse input test is the risk of not adequately measuring the peak tracer concentration exiting

the unit process being evaluated. This means that when a pulse input test is conducted through a

basin that may have a significant amount of short-circuiting, care should be taken to collect

enough samples early in the test to define the output tracer curve properly.

A step input test involves continuously feeding the tracer into the process basin to be

tested at a constant rate. Step inputs can be conducted in either an increasing or

receding mode. For the increasing mode, the start of the test is triggered by the

beginning of the addition of the tracer at a constant feed rate to the basin influent. The

increase in tracer concentration over time is measured in the basin effluent. For the

receding mode, the test begins when the tracer feed is discontinued, and the decrease in

tracer concentration is measured over time in the basin effluent.

Example tracer response curves for both pulse and step input tests are presented in Figure 4-1.



Figure 4-1 – Example Tracer Response Curve

Adapted from USEPA (1990)

Table 4-1 summarizes the advantages and disadvantages of the pulse input and step input

tests.



Table 4-1 – Summary of Advantages and Disadvantages of Pulse and Step Input Tests

Adapted from Tracer Studies in Water Treatment Facilities: A Protocol and Case Studies

(Teefy, 1996)

Testing Mode Advantages Disadvantages

Pulse Input Less chemical is needed

Mean residence time can be

determined more readily

Chemical addition can be simple (e.g.

use existing chemical feed systems or

manually add a slug of chemical) in

most situations

Danger of missing the peak if

sampling frequency is not

sufficient

More mathematical manipulation

of results is needed to determine

effective contact time

Cannot repeat the test easily (no

receding curve available)

Difficult to determine the amount

of tracer that should be added for

the test

Step Input Sometimes can be done with existing

plant chemical feed equipment

Effective contact time can be

determined graphically from curve

Results can be verified by monitoring

the receding curve if an increasing

and receding curve is available

More tracer chemical is required

Cannot reliably calculate mean

residence time

May have to install chemical feed

equipment if not already present

4.2.6 Stress Testing

Stress testing involves increasing the hydraulic loading to the existing process in order to

identify the “failure point”. Stress testing is generally applied to clarification and/or filtration

processes, therefore the failure point can be defined either as an exceedance of the settled

water turbidity goal, or excessive head loss or turbidity breakthrough in the subsequent

filtration process.

Both continuous monitoring and grab sampling are required to evaluate process performance

during a stress test. For example, frequent grab sampling for testing the settled water turbidity

or continuous monitoring of filter effluent turbidity are needed to identify the “failure point”.

In addition, the sludge blanket depth should be measured regularly during a stress test of a

clarifier.

Criteria for evaluating performance of clarification and/or filtration processes are provided in

Chapters 7 and 8, respectively.

Consideration should be given to the potential impact on treated water quality if testing

involves stressing a unit process to the “failure point”. Contingency plans should be

developed in consultation with the local MOE District Office and the Drinking Water

Inspector for the drinking water system, to ensure that the water directed to consumers during

the test meets all applicable regulations.



4.2.7 Pilot Plants

Pilot plants are used to provide a physical simulation of a drinking water system. Pilot-scale

testing combines chemical responses with physical processes so that results are reasonably

reflective of full-scale plant conditions (Douglas et. al., 2008). Pilot-scale testing also

provides the advantage of being able to study non-optimal conditions without jeopardizing

the quality of the finished water. In general, pilot plants are designed with the same treatment

processes that are used in the full-scale system; however, they can also be designed to allow

for insertion (e.g. chemical addition) or removal (e.g. sedimentation to simulate direct

filtration) of unit processes to simulate various operating conditions.

Pilot plants are commonly used for the evaluation of:

Filter media changes;

Eliminating pre-chlorination;

Enhanced coagulation and flocculation;

Optimizing aluminum residuals; and

Taste and odour control.

The use of pilot-scale facilities can be advantageous, as the costs, time and resources needed

for pilot scale experiments are generally lower than those that would be required for full scale

testing. In addition, they can serve as a valuable training tool for operations staff.

While the design and construction of a pilot plant may not be practical or economically

feasible for smaller systems, the construction of pilot filters is relatively simple. Pilot filters

can be used to supplement jar testing results for the optimization of direct and conventional

filtration processes.

Information on the design of pilot plants and pilot-scale experiments is provided in Lang et.

al. (1993); Ndiongue et. al. (2006); Ford et. al. (2001); and Huck et. al. (2002).

4.3 MODELLING AND SIMULATION

A model is a set of mathematical relationships that are used to describe physical, chemical

and biochemical interactions. In some cases, the mathematical relationships that form a

model can be quite simplistic, as is the case when describing the concentration of a treatment

chemical in a completely mixed reactor. In other cases, the model can be quite complex and

involve multiple interacting relationships, such as models that describe nitrification reactions

in a distribution system. The model complexity required often depends on the modelling

objectives.

Models require calibration and validation to ensure that they provide meaningful results.

Calibration involves modifying model parameters so that the model output matches actual

field measurements. Validation involves running a series of model calculations using field

data independent from those used for calibration, and comparing the model output to actual

field results. If the output during validation matches the actual field results, the model can be

assumed to be properly calibrated.



Simulators are computer programs which use a model, or set of models, as a basis for

calculations. The user can configure the simulator to describe the physical layout of a

treatment plant or specific unit processes within the plant. The simulator can be used to

perform simulation runs at various operating conditions to identify impacts on process

performance. Some simulators allow both steady-state (static) and dynamic (time varying)

simulations.

4.3.1 Applications of Modelling and Simulation

4.3.1.1 Hydraulic Modelling

A hydraulic model is used to determine the hydraulic capacity of an existing drinking water

system by describing the characteristics of flow through pipes, channels, process tanks,

pumps, and flow control devices, such as weirs, gates and baffles. Hydraulic modelling can

be used to:

Determine a facility’s hydraulic capacity;

Identify hydraulic bottlenecks;

Identify locations of flow imbalances; and

Identify optimal locations for chemical addition to promote mixing.

The first step in developing a hydraulic model is to identify the hydraulic elements within the

facility. On-site measurements and surveying may be required to confirm the dimensions and

elevations of hydraulic elements, channels, piping and other structures shown on plant record

drawings.

Under ideal conditions, flow through a WTP changes very gradually. As a result, steady-state

hydraulic calculations can be used, greatly simplifying the complexity of the required

calculations.

There are very few commercially available hydraulic modelling software packages. In most

cases, a spreadsheet program or computer programming languages are used to develop

hydraulic models on a case-by-case basis.

Details regarding the calibration and validation of hydraulic profiles can be found in Nicklow

& Boulos (2005).

4.3.2 Clarifier Modelling

Clarifier hydrodynamic models describe the characteristics of flow and solids settling that

take place within a clarifier. Development of clarifier models is based on fluid dynamics,

solids flux theory, and the physical configuration of the clarifier(s). Clarifier hydrodynamic

modelling can be used to:

Determine a clarifier’s hydraulic capacity;

Predict the impact of operational changes on clarifier performance; and

Determine optimal baffling, inlet structure, and weir configurations to improve

clarifier performance.



Clarifier hydrodynamic models can be divided into three types, namely one-dimensional (1-

D), two-dimensional (2-D), and three-dimensional (3-D).

Generally, 1-D models are based on flux theory. Only the settling processes that occur in the

vertical direction are modelled, as it is assumed that the horizontal velocity and concentration

profiles are uniform. These models can be calibrated with actual plant data, and can provide a

good representation of the solids inventory within the system. However, the 1-D model cannot

take into account influences from tank geometry, sludge removal processes, density currents or

short circuiting. Due to its simplistic nature, a 1-D model may only be capable of identifying a

settling problem within a clarifier. More detailed 2-D or 3-D modelling may be required to

identify the nature and cause(s) of other operational problems.

2-D models take into account flux theory, entrance and exit effects, and sludge removal

processes. Only the settling and flow processes that occur in the vertical and horizontal (from

clarifier entrance to exit) directions are modelled, as it is assumed that the flow characteristics

within the clarifier are consistent across all cross sections perpendicular to the bulk flow. 2-D

models are reported to give reasonably good predictions of the behaviour of circular clarifiers

and some rectangular clarifiers, and can therefore be used to estimate the impact of baffle

installation or modification on clarifier performance. A 3-D model may be required for

circular clarifiers that are subject to asymmetric flow due to the configuration of the inlet port

or effluent weirs, or rectangular clarifiers with non-uniform lateral feed. Square clarifiers

often exhibit strong 3-D flow impacts and, as such, a 2-D model may not be capable of

providing sufficient information regarding the flow characteristics within these clarifiers.

3-D models take into account flux theory, entrance and exit effects, sludge removal

processes, and variations in flow patterns in all three dimensions. Although these models

provide detailed information regarding the characteristics of flow within the clarifier, they

require a great deal of input data and computing power.

4.3.3 Modelling Reactor Flow Characteristics

The two simplest models that can be used to describe flow through a reactor are the

“complete mix model” and the “plug flow model”. In a complete mix reactor, it is assumed

that the composition of the reactor contents is homogeneous throughout the reactor volume,

and that mixing of the influent occurs instantaneously. In a plug flow reactor, it is assumed

that all influent to the reactor has the same residence time, and that the flow moves as a

“plug” down the length of the reactor. Therefore, in a plug flow reactor, the composition of

the reactor contents varies in the direction of flow.

In practice, full scale reactors only approximate the behaviour of complete mix or plug flow

reactors due to non-ideal flow conditions, such as dead zones, short circuiting, and

longitudinal dispersion in plug flow reactors. Tracer testing can be used to identify and

quantify the effects of these non-ideal flow conditions. Information regarding tracer testing

methods and data analysis is presented in Section 4.2.5. Depending on the objectives of the

reactor modelling and/or the severity of non-ideal flow conditions, complete mix and plug

flow models can provide a good approximation of reactor flow characteristics.

Typical examples of reactors in drinking water systems that approximate complete mix

characteristics can include flocculators and storage facilities that are designed to be

completely mixed. Examples of reactors that approximate plug flow characteristics can

include ultraviolet (UV) reactors and chlorine contact tanks.



If more detailed information is required for complete mix reactors, mixing modelling can be

used to describe the reactor hydrodynamics. This is explained in more detail in Section 4.3.4.

The behaviour of plug flow reactors can be approximated by modelling several complete mix

reactors operating in series. The number of complete mix reactors to be used in the model

depends on the geometry of the plug flow reactor, the flow rate through the reactor, and any

known non-ideal flow conditions.

A 2-D or 3-D model would be required to identify the causes of non-ideal flow conditions,

and to evaluate alternative options to optimize the plug flow behaviour of the reactor, such as

baffle installation or modification of inlet and/or outlet structures.

4.3.4 Mixing Modelling

Hydrodynamic mixing models describe the characteristics of flow and suspended solids

mixing that take place within a mixed reactor, such as flocculation tank. The development of

mixing models is based on fluid dynamics, including the rheology of the reactor contents (i.e.

the manner in which the fluid flows), and the physical configuration of the subject reactor.

Hydrodynamic mixing modelling can be used to:

Identify potential dead-zones within a mixed reactor;

Identify potential short-circuiting within a mixed reactor;

Predict the impact of operational changes on mixing performance; and

Determine optimal baffling and mixer configurations to improve performance.

Mixing modelling is generally accomplished through the use of 3-D models. In general, a

simulator computer program utilizes computational fluid dynamics (CFD) theory to solve the

model’s system of equations, and to allow for the user to modify reactor configuration to

model the impact on mixing performance.

The presence of dead-zones and/or short-circuiting within a complete mix reactor reduces the

effective reactor volume available, thus reducing the effective treatment capacity. In such

cases, the mixing efficiency can be optimized by making adjustments, such as installation of

baffles, addition or modification of mechanical mixers, and/or inlet and outlet structure

modifications. Mixing modelling can be used to evaluate the impact of these changes on

process performance and to select the optimal upgrade approach.

4.3.5 Distribution System Modelling

A variety of mathematical models of water distribution systems have been developed and

used by water utilities to assess the movement of water and water quality parameters within

the distribution system. Such models may be divided into three general categories:

Hydraulic models, which simulate the flow quantity, flow direction and pressure in

the system;

Steady state water quality models and flow-tracing models, which determine the

movement of substances, including their flow paths and travel times, through the

network under steady state operational and demand conditions; and



Dynamic water quality models, which simulate the movement and transformation of

substances in the water under conditions that vary over time.

Optimization models incorporating water quality, that examine a wide range of operational

and/or design variables and select the best solution based on a stated objective function and

specified constraints, are also available. Each type of model serves a particular purpose in

assessing distribution system water quality and is essential in investigating water quality

issues in a distribution system.

Additional information on hydraulic and water quality models for distribution system

optimization can be found in Clark & Grayman (1998) and AWWA (2005).

4.3.6 Limitations of Modelling and Simulation

4.3.6.1 Safety Factors

Due to the nature of the mathematical relationships used, models may have a less inherent

safety margin than typical design guidelines. Dynamic modelling may give a more

representative prediction of system performance than steady-state modelling; however,

dynamic modelling may not always be feasible, due to a lack of suitable data available for

calibration, limitations of the model, and/or the type of system being modelled. As a result, a

separate safety factor should be applied to designs based on modelling results and/or field

testing should be completed to confirm the modelling results (Section 4.2).

4.3.6.2 Quality of Data

The accuracy of a model depends on the quality of the data used in its development,

calibration and validation. For this reason, all data should be screened to identify any outliers

or other inconsistencies, and to identify any data gaps that would require additional data

collection.

4.3.6.3 Improper Calibration

Improper calibration occurs when key model parameters are incorrectly adjusted to match

actual field data.

During model calibration, it is possible to adjust model parameters to make the simulator

output match actual field data; however, this alone does not ensure that the model is

accurately describing the actual behaviour within the system. If improperly calibrated, the

model would not be able to predict system behaviour for any conditions other than those used

for calibration.

4.4 CASE HISTORIES

4.4.1 Peterborough Utilities Commission – Distribution System Tracer Study

The following case study is based on information presented in Light (2003).

System Description



The expansive nature of the Peterborough distribution system, which includes approximately

380 km of buried pipe, 1,872 hydrants and 24,141 water services connections, had

historically led to issues with increasing water age. Water age is the amount of time it takes a

certain volume of water to travel from the water treatment plant to a point in the distribution

system. Excessive water age can contribute to water quality problems, including disinfection

by-product (DBP) formation, tastes and odours, microbial growth and sediment deposition

within distribution piping.

An assessment of water age in a distribution system can be used to indicate hydraulic

deficiencies in the system, such as long retention times in storage facilities, short-circuiting,

areas that may require redesign or operational changes, and other system problems (closed

valves, pipe roughness, oversized watermains, dead ends, etc).

Optimization Strategies

The Peterborough Utilities Commission (PUC) undertook a tracer study in the distribution

system to identify areas with excessive water age. For this study, fluoride was chosen as the

tracer chemical because it persists in the distribution system, was already being added as part

of the treatment process, could be analyzed easily by operations staff and was approved for

use in drinking water systems.

The concentration of fluoride in the source water, the Otanabee River, is approximately 0.12

mg/L. The dose applied at the WTP for fluoridation is usually between 0.50 and 0.60 mg/L,

for a total fluoride concentration of approximately 0.60 to 0.70 mg/L. Fluoridation at the

WTP was ceased for a period of two to three weeks prior to the study to eliminate fluoridated

water within the distribution system.

When fluoridation was resumed for the purposes of the study, the total fluoride concentration

leaving the WTP was maintained at 0.60 mg/L. Samples were collected from 19 locations

throughout the distribution system over a period of five days, starting the day the fluoride

feed was restarted.

Results of the distribution system sampling indicated that it took from 10 to more than 105

hours to attain a target fluoride concentration of 0.50 mg/L at the various locations

throughout the city. The tracer travel time for each location was plotted and then graded in

increments of 15 hours, with an “A” grade representing the shortest time to reach the target

concentration of 0.50 mg/L (0 to 15 hours) and an “F” grade representing the longest time

(more than 105 hours). Figure 4-2 shows a distribution system map of Peterborough with the

colour-coded grades (A to F) assigned for each of the 19 sample locations.

The longest tracer response times were noted in reservoirs and elevated tanks, even though

the storage facilities, in some cases, were located relatively close to the WTP. The graph

shown in Figure 4-2 indicates that in some cases, the fluoride concentrations never reached

the target concentration of 0.50 mg/L during the study (e.g. at the end of 105 hours). These

sample locations were under the direct influence of storage facilities that had a lower fluoride

concentration than the water in the distribution mains.



Figure 4-2 – Tracer Travel Time for Distribution System Sample Locations

From Light (2003)

Summary

In large volume reservoirs (22.7 ML total storage capacity), the study duration was not

sufficient to draw down the entire volume of water within the reservoir and the target fluoride

concentration of 0.50 mg/L was not achieved. It should also be noted that it is difficult to

turnover these reservoirs completely while still maintaining adequate volumes for fire

protection and consumer demand.

The results of the testing identified areas of the distribution system where increased sampling

and monitoring would be beneficial for improving control of chlorine residuals and DBPs.

The PUC also modified their operating strategies for reservoirs and elevated tanks to increase

the frequency of water turnover and reduce water age. The study also identified areas in need

of more frequent flushing to reduce water age, and in some cases, led to the installation of



“bleeder” lines to allow a controlled flow of water-to-waste, particularly in areas where

watermains are oversized.

4.4.2 City of Toronto – CFD Modelling of Flocculation Mixing Performance

The following case study is based on information presented in Zhang et. al. (2006).

System Description

The City of Toronto’s (the City) R.L. Clark WTP is a conventional treatment plant that treats

water from Lake Ontario and has a rated capacity of 615 ML/d. The treatment process

consists of coagulation, flocculation, sedimentation, filtration, fluoridation and chlorine

disinfection. This plant has three parallel coagulation/flocculation trains. After adding alum

prior to rapid mixers, water flows through over-and-under hydraulic mixing chambers in

series for coagulation, followed by flocculators. Each flocculation tank consists of a primary

cell and a secondary cell. At the time of this study, the primary flocculation tanks had been

retrofitted with impeller-type mixers and the old walking beam mixing equipment in the

secondary cells were also being replaced with impeller-type mixers.

The purpose of this study was to develop a three-dimensional CFD model and apply it to

provide indications of the mixing performance of a complex full-scale flocculator with a

vertical shaft impeller mixer to assist the upgrading of the secondary flocculation process at

the R.L. Clark WTP.


A three-dimensional model of the secondary flocculator was generated by inputting the

geometry of the flocculation tank and impellers using commercial software applications. The

flows in the flocculator were assumed to be isothermal. The influent flow rate used for the

modelling was 2.55 m3/s.

Simulations were conducted to evaluate the effects of impeller speed and the location of

baffle walls on the residence time distribution (RTD) and velocity gradient, G, within the

flocculator.

It was observed that the velocity of the incoming water could significantly influence the flow

field and lead to short-circuiting and dead zone problems, particularly at low impeller speeds

(5 rpm). At higher impeller speeds (20 and 30 rpm) the effects of the influent flow rate were

reduced; however, the mixing efficiency of the impellers may be reduced at higher speeds

because of the presence of local swirls. Longer residence times were also predicted at lower

impeller speeds.

G value distributions were predicted inside the flocculator for the different impeller speeds.

At 5 rpm, local G values at locations around the impellers were in the range of 100 to 1000 s-1

and significantly lower (less than 30 s-1

) at locations close to the walls. With impellers speeds

of 20 or 30 rpm, the local G values in most areas in the tank were higher than 100 s-1

, which

is higher than the desired range for this process (see Chapter 6).

To obtain a better G value distribution and reduce swirling in the flocculator, simulations

were conducted to evaluate the benefits of installing baffle walls in the tank where, (1) the

baffle was installed in the middle of the tank, and (2) the baffle was installed near the tank



inlet. For the first simulation, the velocity profiles indicated that the flow mixing regime in

the region downstream of the baffle had been improved; however, the region upstream of the

baffle was still poorly mixed. With the baffle installed 1.5 m downstream of the inlet, the G

value distribution was improved throughout the tank, with an average G value for the total

tank being approximately 44 s-1

.

Summary

This study demonstrated the potential of CFD as an efficient tool for understanding impeller

mixing performance and provided useful information for the design and operation of the

flocculation process. The initial CFD simulation results suggested that dead zones and short-

circuiting may exist in the secondary flocculation tank as a result of the installation of vertical

shaft turbine flocculation impellers at the R.L. Clark WTP, which may have an impact on

flocculation efficiency. CFD simulation showed that installing a single baffle at the inlet

would be a better choice than positioning a baffle in the middle of the tank. It was also

suggested that experimental studies, such as tracer testing to evaluate the actual detention

time in the tank, be conducted to validate the CFD modelling results.

4.5 REFERENCES

American Society of Civil Engineers and American Water Works Association (2004). Water

Treatment Plant Design, 4th Ed. McGraw-Hill. ISBN 0-07-141872-5.

AWWA (1999). Water Quality and Treatment: A Handbook of Community Water Supplies,

5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.

AWWA (2005). Water Quality in the Distribution System. First Edition. American Water

Works Association. Denver, CO. ISBN 1-58321-323-6.

AWWA (2010). Water Quality: Principles and Practices of Water Supply Operations. 4th

Ed. AWWA. Denver, CO. ISBN 1-58321-780-1.

AwwaRF (2002). Online Monitoring for Drinking Water Utilities. AWWA Research

Foundation and AWWA. Denver, CO. ISBN 1-58321-183-7.

Clark, R.M. & W.M Grayman (1998). Modeling Water Quality in Drinking Water

Distribution Systems. American Water Works Association. Denver, CO. ISBN 0-89867-972-

9.

Ford, R., M. Carlson and W.D. Bellamy (2001). Pilot Testing with the End in Mind. Journal

AWWA, Vol. 93, Issue 5, May 2001, p. 67-77.

Huck, P.M., B.M. Coffey, M.B. Emelko, D.D. Maurizio, R.M. Slawson, W.B. Anderson, J.

Van den Oever, I.P. Douglas and C.R. O'Melia (2002). Effects of Filter Operation on

Cryptosporidium Removal. Journal AWWA, Vol. 94, Issue 6, June 2002, p. 97-111.

Hudson, H.E., Jr. (1975). Residence Times in Pretreatment. Journal AWWA, Vol. 67, No. 1.

January 1975.

Kirmeyer, G.J. (1999). Maintaining Water Quality in Finished Water Storage Facilities.

AwwaRF and AWWA. Denver, CO. ISBN 0-89867-983-4.



Kirmeyer, G.J. (2002). Guidance Manual for Monitoring Distribution System Water Quality.

AwwaRF and AWWA. Denver, CO. ISBN 1-58321-186-1.

Lang, J.S., J.J. Giron, A.T. Hansen, R.R. Trussell, W.E. Hodges, (1993) Investigating Filter

Performance as a Function of the Ratio of Filter Size to Media Size. Journal AWWA, Vol.

85, Issue 10, October 1993, p. 122-130.

Light, Kevan M. (2003). Follow the Fluoride to Decrease Water Age. Opflow, Vol. 29, Issue

1. AWWA. January 2003.

MOE (2008). Design Guidelines for Drinking Water Systems, 2008. ISBN 978-1-4249-8517-

3.

MOE (2009). Practices for the Collection and Handling of Drinking Water Samples. Version

2.0. Queen's Printer for Ontario. PIBS 4464e01.

MOE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process Audits.

Ndiongue, S., W.B. Anderson, A. Tadwalkar, J. Rudnickas, M. Lin and P.M. Huck (2006).

Using Pilot-Scale Investigations to Estimate the Remaining Geosmin and MIB Removal

Capacity of Full-Scale GAC-Capped Drinking Water Filters. Water Quality Research Journal

of Canada. Volume 41, No. 3, p. 296–306.

Nicklow, J.W., Boulos, P.F. (2005). Comprehensive Water and Wastewater Treatment Plant

Hydraulics Handbook for Engineers and Operators, MWH Soft: Pasadena, California. ISBN

0-9745689-4-5.

Teefy, S.M. (1996). Tracer Studies in Water Treatment Facilities: A Protocol and Case

Studies. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-857-9.

USEPA (1990). Guidance Manual for Compliance with the Filtration and Disinfection

Requirements for Public Water Systems Using Surface Water Sources. Office of Drinking

Water, USEPA. Washington, DC.

Zhang, J., W.B. Anderson, P.M. Huck, G.D. Stubley and A. Tadwalkar (2006). Evaluation of

a Computational Fluid Dynamics Modelling Approach for Prediction of Flocculation Mixing

Performance at the City of Toronto’s R.L. Clark Water Treatment Plant, presented at the

2006 OWWA/OMWA Joint Annual Conference. Toronto, ON.


CHAPTER 5 INTAKE STRUCTURES AND SCREENING

WATER SOURCES, INTAKE STRUCTURES AND SCREENING

5.1 Introduction ............................................................................................................ 5-1

5.2 Sources of Supply ................................................................................................... 5-1

5.2.1 Source Water Quality and Treatment ...................................................... 5-1

5.2.2 Evaluating Performance ........................................................................... 5-2

5.2.3 Common Problems and Potential Impacts ............................................... 5-3

5.2.4 Optimization Techniques ......................................................................... 5-5

5.3 Intake Structures ..................................................................................................... 5-6

5.3.1 Purpose and Types of Surface Water Intake Structures .......................... 5-6

5.3.2 Purpose and Types of Well Components ................................................. 5-7




5.4 Screens .................................................................................................................... 5-9

5.4.1 Purpose and Types of Screens ................................................................. 5-9

5.4.2 Evaluating Performance ......................................................................... 5-10

5.4.3 Common Problems and Potential Impacts ............................................. 5-10

5.4.4 Optimization Techniques ....................................................................... 5-11

5.5 Low-Lift (Raw Water) Pumping .......................................................................... 5-11

5.5.1 Purpose of Low-Lift Pumping and Types of Stations ........................... 5-11



5.6 Pre-Chlorination/Oxidation and Zebra Mussel Control ....................................... 5-15

5.6.1 Purpose and Types of Pre-Oxidation Processes for Zebra Mussel

Control ................................................................................................... 5-15



5.7 Case Histories ....................................................................................................... 5-16

5.7.1 County of Oxford – Source Water Protection Program ......................... 5-16

5.7.2 City of Brandon – Source Water Blending Study .................................. 5-17

5.8 References ............................................................................................................ 5-19

CHAPTER 5. Water Sources, Intake Structures and Screening 5-1


CHAPTER 5

WATER SOURCES, INTAKE STRUCTURES AND SCREENING

5.1 INTRODUCTION

In the design of new DWSs, the selection of a water supply source, whether surface water,

groundwater or GUDI, involves a review of the alternative sources available and their

respective characteristics. Raw water quality affects the treatment processes selected as well

as the cost of water treatment.

When optimizing an existing facility, in general it will not be possible or cost effective to

select a new source of water for a DWS; however, measures can be taken to ensure the best

possible raw water quality from the existing source by a) implementing a source water

protection plan and b) optimizing the means by which raw water is conveyed to the treatment

process. Consideration should also be given to potential changes in water quality and quantity

as a result of climate change.

5.2 SOURCES OF SUPPLY

5.2.1 Source Water Quality and Treatment

The general categories of water supply sources are surface water, groundwater and GUDI.

Although water quality is variable from source to source, surface waters have many qualities

in common; likewise, groundwater supplies have many similar characteristics. However,

treatment requirements for surface water and groundwater supplies are different. Reference

should be made to applicable regulations under the SDWA, 2002, and the Procedure for

Disinfection of Drinking Water in Ontario (MOE, 2006b), for specific minimum treatment

requirements for drinking water systems.

Surface water and GUDI supplies are susceptible to seasonal (e.g. stratification, algal growth)

and sometimes event-driven (e.g. heavy rains, snow melt) changes. Consequently, treatment

processes should be designed and operated with consideration given to the occurrence of such

events. Water quality problems most often associated with surface water sources include high

particulate content (i.e. turbidity), colour, taste and odour, and microbiological content

(AWWA, 1999).

Groundwater is relatively constant in quality from season to season; however, groundwater

supplies may be highly variable in quality from one well location to another. Changes in

hydrogeological conditions can produce different water quality over a relatively short

distance. The most common water quality problems associated with groundwater supplies are

high concentrations of hardness, iron and manganese (AWWA, 1999).

The available capacity of the water source (as defined by the Permit to Take Water) should

be evaluated relative to the projected water demand for the design period.

Source water protection can be implemented to prevent, minimize or control potential sources

of pollution or enhance raw water quality. In addition to reducing public health risks,

effective watershed management minimizes operating costs by reducing the degree of

drinking water treatment required, the quantity of chemicals used during treatment and the



creation of treatment by-products (CCME, 2002). Additional information regarding source

water protection programs is provided in Section 5.2.4.1.

5.2.2 Evaluating Performance

5.2.2.1 Source Water Quality Evaluation

In a multiple barrier system for providing safe drinking water, the selection and protection of

a reliable, high quality drinking water source is the first barrier. The previous raw water

characterization used in the water treatment system design, as well as any subsequent

changes in source water quality and/or quantity, should be reviewed to determine if the

impact of those changes on the water treatment system are addressed adequately during the

optimization of a drinking water system.

5.2.2.2 Aquifer Performance

Aquifer performance can be evaluated using the following three methods:

Drawdown method;

Recovery method; and

Specific-capacity method.

In the drawdown method, the production well is pumped and water levels are periodically

observed in two or more observation wells. The data are plotted and analyzed by various

methods to relate drawdown in meters (or feet) to time measured in hours or days at a

specific pump rate.

The recovery method involves measuring the change in water level in an observation well

after pumping has stopped.

The specific-capacity method is the well yield per unit of drawdown. It does not indicate

aquifer performance as completely as the other methods, however, it is useful for evaluating

well production after a period of time and in making comparisons with data collected when

the well was new. A sudden drop in specific capacity indicates problems, such as screen

plugging or other operating issues.

The presence of other wells in the same aquifer can influence the well yield. Two wells

located close to each other and drawing from the same aquifer may experience interference,

which increases the drawdown in both wells. Well interference is possible in confined and

unconfined aquifers. For some wells, this additional drawdown may not affect well yield, but

will lead to higher pumping costs because the water must be lifted a greater distance. For

other wells, the additional drawdown may lower the water level in the well below the pump

intake causing the well to go “dry”. In this case, it may be necessary to lower the level of the

pump in the affected well.

New wells or increased pumping from existing wells can also lead to potential changes in

groundwater quality. The potential effects from nearby sources of contamination should be

considered, including naturally occurring poor water quality such as induced recharge from

adjacent formations.



5.2.3 Common Problems and Potential Impacts

5.2.3.1 Source Water Quality Changes

The quality of a water source can be impacted by both natural and human factors. The degree

of the impact of these factors will vary depending on the type and characteristics of the

source. The major factors that may influence source water quality are outlined in Table 5-1.

Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts

Adapted from Water Quality and Treatment, AWWA (1999)

Factor Potential Impact

Natural Factors:

Climate Too much or too little precipitation can affect water quality as

well as quantity (high or low flow rates, run off, temperature

changes, etc).

Watershed characteristics The natural characteristics of a watershed (i.e. flora and fauna)

can have a significant impact on water quality (e.g. organics,

microorganisms).

Geology Geology directly impacts the source water quality (e.g.

hardness, recharge rates).

Microbial growth (nutrients) Algal and cyanobacterial growth can affect treatment

processes, causing filter clogging and taste and odour

problems.

Fire The destruction of brush and forest increases the likelihood of

erosion and increased runoff rates.

May lead to higher sediment and organic loading in the water

supply.

Density (Thermal stratification) Changes in water quality can occur either due to higher water

temperatures in summer, or in winter if an ice cover develops.

Lake or reservoir turnover can result in increased nutrient and

solids concentrations.

Human Factors (Point-source):

Wastewater discharges Sewage treatment plant by-passes or sewer failures can lead to

increased bacterial loadings and higher levels of organic and

inorganic contaminants.

Septic tanks and leach fields Improperly sited and/or maintained septic systems can release

organic and inorganic compounds, as well as microbiological

contaminants.



Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts (cont’d)



Industrial discharges Industrial activities can affect water quality through the release

of contaminants by air, water or soil.

Hazardous waste facilities The operation of a hazardous waste facility within a water

supply watershed or aquifer requires extensive precautions to

prevent accidental or intentional release of hazardous

contamination to the potable water supply.

Mine drainage Mining operations can disturb subsurface topography leading

to erosion and re-suspension of sediments, turbidity, colour,

etc.

Drainage from mining activities may also cause a change in

acidity of the receiving water.

Spills and releases Spills and accidental or intentional releases can have a major

impact on water quality depending on the nature of the

contaminant.

Improperly abandoned wells and

exploration holes Abandoned wells provide a direct pathway for surface runoff

and/or other sources of contamination.

Human factors (non-point source):

Agricultural runoff Application and storage of manure, pesticides, herbicides and

fertilizers can affect both groundwater and surface water

quality.

Erosion cause by improper tilling techniques can lead to

increased sediment load, colour and turbidity.

Livestock The presence of livestock in watersheds and over aquifers has a

direct effect on bacterial and protozoan concentrations.

Urban runoff Runoff from highways, city streets and commercial areas can

direct a number of contaminants, such as petroleum products,

metals (e.g. cadmium, lead), salt and other de-icing

compounds, and sediment into water sources.

Land development Development may increase erosion and therefore sediment

loading.

Land development may also decrease percolation, which

reduces groundwater quantities.

Landfills Landfill leachate can lead to groundwater contamination.

Erosion Erosion of soil may cause increased turbidity, colour and

eutrophication.



Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts (cont’d)



Atmospheric deposition Airborne contamination, such as “acid rain” can adversely

affect surface water quality.

Recreational activities Swimming, boating and camping in water supply reservoirs

and watersheds can impact surface water quality.

Water quality in streams and rivers can be impacted by upstream users within the watershed.

Spills from barges, leaks from tank facilities, broken pipelines, accidental industrial spills and

other incidents can impact water quality. Some watercourses also have occasional periods

when water quality is especially poor as a result of natural causes, such as heavy spring

runoff.

Lakes and reservoirs are also vulnerable to natural and human contamination. Runoff from

agricultural areas may increase pathogen concentrations, nitrates and other nutrient

concentrations in the source water. Excessive growth of algae, cyanobacteria and aquatic

weeds in reservoirs is also quite common and can lead to taste and odour problems as well as

the development of toxic by-products; this is usually caused by high levels of nutrients in the

water.

5.2.4 Optimization Techniques

5.2.4.1 Source Water Protection

Under the CWA, 2006, communities are required to develop plans to protect both the quality

and quantity of their municipal drinking water sources. The CWA requires the identification

of vulnerable areas related to drinking water sources and the activities in those areas that are,

or could be, significant drinking water threats. The committees are also required to develop

source protection plans containing policies intended to eliminate or prevent significant

drinking water threats.

For surface water supplies, a Surface Water Vulnerability Analysis is conducted to identify

surface water areas that may be vulnerable to contamination. An intake protection zone (IPZ)

is designated around the drinking water intake. A vulnerability score is assigned for the IPZ,

which refers to the comparative likelihood of a contaminant of concern reaching an intake.

The scores depend on various factors, such as the depth of the intake from the water’s

surface, the length of the intake from the shoreline, the size of the water body where the

intake is located, and how water interacts within the zone (MOE, 2006a).

A Groundwater Vulnerability Analysis is conducted by first identifying the vulnerable areas

within the Source Protection Area, and second, by mapping the relative vulnerability of the

aquifers within each vulnerable area. The vulnerable areas considered in the assessment

include:



Wellhead Protection Areas around municipal drinking water supply wells;

Highly Vulnerable Aquifers;

Significant Groundwater Recharge Areas; and

Future Municipal Supply Areas.

The relative vulnerability within each of these areas will be characterized as high, medium or

low (MOE, 2006a).

5.2.4.2 Blending Source Waters

Source water blending can be used to increase the available quantity of raw water or to

improve raw water quality. For example, various blending ratios can be used to obtain a

target concentration for a specific parameter (e.g. blending surface water with a groundwater

supply to decrease total organic carbon concentrations) (XCG, 2009).

5.3 INTAKE STRUCTURES

5.3.1 Purpose and Types of Surface Water Intake Structures

Intake structures are used to draw water from lakes, reservoirs or rivers. In Ontario,

submerged single- or fixed-level intake systems are the most common type of intake

structure. The single-level intake is generally placed in the deepest location or area of the

river or reservoir to ensure that service can be provided if water levels are reduced in the

supply body (i.e. drought conditions) and to avoid water quality changes that may occur at or

near the water surface. Figure 5-1 shows a typical single level intake.

Figure 5-1 – Surface Water Intake Schematic From AWWA (1995)

The advantage of single-inlet intake structures is that they are usually much less complicated

and therefore much less costly to construct and operate than multi-level structures.

Major disadvantages of single-level intake facilities become apparent when they are used in

deeper, more complex lake environments. In some cases, water entering the inlet during

spring, summer and fall months may be of poorer quality due to lake stratification.



Multi-level intake structures have inlets to the system at depths ranging from near the surface

to the deeper zones. Variable depth intakes can allow different levels to be accessed as raw

water conditions change during the year. To obtain good water quality, it may be necessary to

draw water from different levels during different seasons.

The advantage of this type of intake structure is that water can be provided from the depth

where the best quality of water is located at a given time. The disadvantages are that they are

generally more complex and expensive to construct and operate than single-level intakes.

Although submerged intakes are generally more common in Ontario, there are some systems

using surface intakes or open channel intakes, which consist of a natural or artificial

waterway or conduit that is used to convey water from the source to the treatment plant.

These intakes can be simpler to construct and maintain; however, common problems

associated with these structures include the accumulation of silt and debris, ice formation, as

well as algae and bacterial growth.

5.3.2 Purpose and Types of Well Components

In general, the sub-surface components of a well include the well casing, seal, intake screen

and gravel packing. All of these components must be properly designed and installed to

prevent contamination of the well and to maximize the well yield.


The intake size and well yield should be sufficient for the projected water demand over an

extended design period.

Raw water sampling and testing programs should be in place to monitor water quality, for

both process control and for trending water quality changes over time.


5.3.4.1 Zebra Mussels

Zebra mussels have the potential to obstruct public water supply intakes and cause loss of

intake capacity, as well as contribute to taste and odour problems. A discussion of zebra

mussel control systems is provided in Section 5.6.

5.3.4.2 Icing

In cold weather conditions, frazil ice or anchor ice can occur. When water is almost at the

freezing point and is rapidly being cooled, small, disk-shaped frazil ice crystals will form and

be distributed throughout the water mass. When the frazil crystals are carried to the depth of a

water intake, they can adhere to the intake screen and quickly build up to a solid plug across

the opening. Anchor ice is slightly different in that it is composed of sheet-like crystals that

adhere to and grow on submerged objects.

Icing of an intake will cause loss or reduction of intake capacity, plug screens and/or may

cause damage to pumps. It is generally best to stop using the intake immediately when icing

is noticed, if possible, because the blockage will only get worse with continued pumping.



5.3.4.3 Siltation

Siltation occurs when sediment carried by a stream or river is deposited when water loses

velocity upstream from a dam or other impediment to flow. The rate of siltation is generally a

function of both the type of soil in the area and how well the land is protected from erosion

(AWWA, 1995).

5.3.4.4 Well Deterioration

Well deterioration can be caused by chemical, biological and physical problems. Chemical

and biological causes are mainly associated with corrosion and incrustation of the well

components. The physical causes of well deterioration include changes in hydrogeologic

conditions, subsidence due to a decline in water level, effects of variations in verticality and

alignment, mechanical blockage, sand pumping and erosion-corrosion (AwwaRF, 1993).


5.3.5.1 Maintenance of Surface Water Intake Structures

Proper design, maintenance and operation of intake structures are essential to prevent partial

or complete shut-down of the drinking water system. It is recommended that lake or river

intake piping and screens be inspected by divers to ensure no damage has occurred over the

winter. If necessary, cleaning of the intake should also be performed.

For small intakes, consideration should be given to backflushing the intake, if practical.

5.3.5.2 Minimizing Frazil Ice Formation

Potential solutions for water systems that frequently experience icing may include: providing

the intake with piping to backflush the line, or blowing the line with compressed air or steam.

If more than one intake is available, the use of each intake can be alternated to allow any

accumulated ice to melt and float away from the intake opening. Throttling the intake pumps

to decrease the flows into the plant is another possible remedy if immediate shut-down is not

possible.

Design considerations for new or modified intake structures to minimize ice formation are

provided in the Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008).

5.3.5.3 Well Maintenance and Restoration

Wells are subject to a natural aging process, which can be slowed or minimized with proper

prevention and remediation techniques. The design of groundwater wells must conform to the

requirements of the Wells Regulation (O. Reg. 903), made under the Ontario Water

Resources Act, 1990, and AWWA Standard A100: Water Wells.

Prevention and maintenance strategies for wells should focus on:

Preventing occurrence and limiting recurrence of corrosion;

Preventing occurrence and limiting recurrence of incrustation;

Preventing biofouling;



Preventing structural failure and sanding; and

Pump maintenance.

Well restoration, remediation or rehabilitation are the processes that may be necessary once

prevention and maintenance have failed to forestall a problem or when prevention and

maintenance are neglected. Well rehabilitation should be conducted by an experienced,

licensed well contractor with the technical assistance of a consultant. Additional information

regarding well maintenance activities is provided in AwwaRF (2003).

5.4 SCREENS

5.4.1 Purpose and Types of Screens

In surface water treatment plants screens are used to remove large debris from raw water,

such as logs or fish, or other unwanted material (e.g. algae). Screens can be designed to

remove coarse or fine matter. A discussion of various types of screens is provided below.

Bar Screens

Bar screens are used to screen out large debris (e.g. logs and fish). They vary in size from

fine (1.5 to 13 mm) to coarse (32 to 100 mm). Bar screens are cleaned either mechanically

(which is necessary if there are large amounts of debris) or manually. They are generally

installed at 60 to 80 degrees to horizontal.

Wire Mesh Screens

Wire-mesh screens are usually made of corrosion resistant material, such as stainless steel.

The size of the openings in the screens typically varies between 0.4 mm and 10 mm. One

type of wire-mesh screen is a “travelling screen” which consists of an endless belt made of

fine wire mesh mounted on a chain that moves the screen through the water. These screens

can be cleaned manually or automatically. When the screen rises above the water level, the

debris is collected and discharged into a trough, usually with the help of a water jet.

Travelling screens are usually located in the inflow channel to the pumps for easy access for

inspection and maintenance.

Microstrainers

Microstrainers are very fine screens used primarily to remove algae and other aquatic

organisms. They usually consist of a rotating drum with finely woven material

(approximately 250 openings per square millimetre). Water passes through the screen, into

the drum, while the unwanted material does not. High pressure water jets remove

accumulated material from the exterior of the drum. Due to the small size of the openings,

problems such as siltation, zebra mussel growth and frazil ice formation must be carefully

controlled.




Table 5-2 presents recommended monitoring, in terms of sampling locations and analyses, in

order to evaluate the performance of screens and strainers. Typically, screen performance is

evaluated based on the achieved removal of screenings.

Table 5-2 – Screening – Recommended Monitoring to Evaluate Performance

Location Types of Sample /

Measurement

Parameters /

Analyses Comments

Upstream and

Downstream of

Screens

Level Measurement Head loss across

screens

The maximum operating

head loss across a screen unit

is usually provided by the

supplier.

Upstream and

Downstream of

Screens

Flow Measurement Velocity across

screens

The maximum velocity of

water through the screen

should be 0.6 m/s regardless

of water level in the screen

well (MOE, 2008).

Screenings Bin Quantity Measurement Mass of screenings

Volume of

screenings

The quantity of screenings

depends on the water source,

screen type, and type of

washing system.

Figure 5-2 presents a process schematic of a typical screening process, along with the

identification of various sampling locations.

Screen

To Pumping or TreatmentRaw Water

ScreeningsScreenings Quantity

Measurement

Water Level

Measurement

Water Level

Measurement

Figure 5-2 – Screening – Process Schematic and Sampling Locations


Clogging and corrosion are the most common problems associated with screening.




5.4.4.1 Maintenance of Screening Equipment

As a screen traps coarse material and debris, the screen develops more resistance to the flow

of water through the openings. This increases water levels upstream of the screen and the

overall head loss experienced across the screen.

Screens are generally designed so that they can be removed for inspection, maintenance and

cleaning. Methods of cleaning screens at the treatment plant include the use of rakes, brooms,

bristle brushes, and water sprays.

Some screens have devices that measure the head loss between the water surface upstream

and downstream from the screen. When a specified head loss is exceeded, a cleaning cycle is

started. The cleaning cycle might consist of high-pressure water sprays which clean the

screen in place, or the screen might need to be lifted out of the water for cleaning.

5.5 LOW-LIFT (RAW WATER) PUMPING

5.5.1 Purpose of Low-Lift Pumping and Types of Stations

Low-lift pumps are used to lift surface water and convey it to a treatment plant. These pumps

move large volumes of water at relatively low discharge pressures.

Well pumps are used to draw water from shallow or deep wells and discharge it to a

treatment plant or into the distribution system. They can either be submerged or located at the

ground surface.

In either case (low-lift or well pumping), the pumping station can either be located within the

treatment plant facility or be remote from the facility (e.g. when the treatment plant is not

located near the raw water source).


Symptoms and causes of common problems encountered with low-lift and well pumping

stations are presented in Table 5-3.



Table 5-3 – Raw Water Pumping – Symptoms and Causes of Common Problems

Problem Common Symptoms and

Potential Impacts Common Causes

Lack of hydraulic

capacity at pump

station

Operating above rated capacity for

extended periods

Undersized pumps

Clogged pumps

Frequent cycling of

pump operation Inconsistent flows resulting in

alternating periods of flow and no-

flow (and loading) to treatment

processes

Settling of solids and debris in

channels, pipes or wet wells during

no-flow or low flow conditions

Oversized pumps

Pumps not equipped with variable

frequency drives (VFDs)

Insufficient storage and/or

mismatched supply and demand


5.5.3.1 Pump Selection and Sizing

The selection and sizing of pumps should be based on firm capacity, meaning that the raw

water pumping station should be able to supply the water treatment plant design capacity with

the largest unit out of service. Multiple pumps should be provided, and pumping stations should

be designed to handle the 20-year design flow, or for the ultimate service area requirement, if

practicable (MOE, 2008).

To optimize pump efficiency in pumping stations with a wide range of operating flows,

consideration should be given to the installation of multiple pumps of different sizes or

variable capacities to cover the expected range of flows (MOE, 2008). In small pumping

stations, a minimum of two units, each sized to meet the design flow, should be provided.

Oversized pumps can operate in an on-off mode during low flow conditions, causing uneven

flows or periods of no-flow to downstream unit processes. This can cause settling of

suspended solids in downstream processes and conduits, bumping of particles in filters and

other operational problems.

Problems with pump over-sizing are commonly encountered in new or newly expanded

facilities where the pumps were sized to be capable of handling the expected design flows at

build-out, without consideration of the demand at current conditions. The installation of

multiple, smaller capacity pumps, which operate according to a filtration rate set point or

treated water storage level can minimize the frequency of on-off cycling and provide

consistent flows to the WTP throughout the day. Pump efficiency and operational energy

savings should be considered during pump selection.

5.5.3.2 Variable Frequency Drives

Where the existing pumping station configuration does not allow for the installation of

multiple, lower capacity pumps in place of a single larger capacity pump, a variable

frequency drive (VFD) can be installed on the existing pump(s).



The purpose of a VFD is to allow a degree of control over the output of the pump by varying

the frequency of the power to the motor. By varying the power to the motor, the speed of the

motor and pump can be controlled. As opposed to throttling the output of the pump with

control valves, adjusting the operating speed of the motor and pump reduces the output of the

pump from the source and saves energy by optimizing the pump operation.

Installation of a VFD allows the pump to operate at different pump outputs to match varying

flow conditions and by providing flexibility to operate over a range of flows. This effectively

maintains the desired flow to downstream processes, minimizing process upsets and

optimizing pump operation.

VFDs can also allow for soft starts and stops of the pump motor, minimizing hydraulic and

mechanical stresses on system piping, channels and unit processes and equipment. Hydraulic

stresses, often referred to as water-hammer, are the result of sudden increases in pressure, sending

out shock waves and potentially damaging system components. Mechanical stresses refer to the

mechanical wear that motors and pumps undergo as a result of frequent starts and stops.

Installation of VFDs can optimize energy usage by reducing the power going to the motor at

lower flows, and reducing the frequency of energy intensive pump start cycles.

Most pumps with VFDs are operated between 50 and 100 percent of the rated capacity. This

is limited by the motor and equipment. Motors are typically cooled by a fan on the same

drive as the motor, and the fan operates at the same speed as the motor. At low speeds, the

fan does not rotate rapidly enough to provide sufficient airflow to cool the motor, resulting in

increased mechanical stress and rapid wear. Equipment manuals or suppliers should be

referred to in order to determine the optimum operating range for the existing pump and

motor assembly. It is also important to consider the larger switchgear footprint needed for

VFDs being incorporated into an existing facility.

Sequence control (i.e. controlling the number of operating pumps) is applicable to pump

groups consisting of constant-speed pumps and variable-speed pumps. Sequence control of

constant- and variable-speed pumps in combination results in more economical and precise

operational control at larger pumping stations.

When controlling a number of pumps with different capacities, an operating sequence and

combination that gives optimum control efficiency should be determined. This leads to

operation in the higher region of the pump efficiency curve, contributing to energy savings

(AwwaRF and Japan Water Works Association, 1993).

Control Strategies

Several control strategies can be employed at pumping stations:

Level setpoint control;

Level band control; and

Discharge flow rate control.

In level setpoint control, pump station operation is dictated by the water level in the treated

water storage reservoir (i.e. clearwell). Specific setpoints are established based on different



water levels within the reservoir, and pump start sequence and operation are based on the

setpoints. Maintaining control too tightly can reduce the effectiveness of treated water storage

levels in moderating flows to the plant. The drive speed of the pumps may also vary wildly in

an attempt to maintain the reservoir level with varying flows.

Level band control is a variation on level setpoint control where pump operation steps are

based on clearwell level ranges rather than setpoints based on distinct clearwell levels. By

setting the steps to operate across overlapping ranges, the discharge flow rate is smoothed.

This has the benefit of dampening peak flows to the treatment process.

For larger systems, level control may not be as important; in such cases, discharge flow

control (e.g. based on a set filtration rate) can be used. This control strategy can optimize the

flows to downstream processes, ensuring even, consistent flows to the WTP.

5.5.3.3 Impeller Modification

Where a pump is undersized or oversized, or where downstream hydraulic conditions have changed,

impeller replacement or modification can potentially eliminate the need for pump replacement.

Modifying or replacing the impeller in a centrifugal pump shifts the pump’s operating curve,

effectively changing the efficiency operating point of the pump. In addition to potentially

avoiding costs associated with pump replacement, impeller modification or replacement can

allow for more efficient operation of the pump, reducing operating costs.

Depending on the size of the pump volute and existing impeller, it may not always be

possible to replace the impeller with one of a larger or smaller size. In such cases, if a smaller

impeller is required for an oversized pump, the impeller can be trimmed to reduce its size.

Conversely, if a larger impeller is needed, total pump replacement may be required.

The selection or modification of a pump impeller is based on the size of the pump, the system

head curve, pump configuration, pump power and required capacity. Pump suppliers should

be consulted when considering modification or replacement of an impeller, to ensure that the

new or modified impeller will not negatively impact pump performance.

5.5.3.4 Clogged Pumps

One of the most common groundwater pumping problems is plugging of the well pump

screen. The causes can be mechanical, chemical or bacteriological in nature. Repairs to well

components should always be performed by a licensed pump installer.

Bacteriological samples should be collected periodically from each well. These samples should

be analyzed for total coliforms, heterotrophic plate count bacteria, iron bacteria and sulphate

reducing bacteria. If there are indications of contamination, regular disinfection of the well may

be necessary to prevent growth of nuisance bacteria that can lead to production problems.

As noted in Section 5.4, screens are commonly used in surface water systems for the removal

of coarse material and debris from raw water prior to pumping, minimizing pump downtime

for cleaning of clogged pumps. For details regarding the design and selection of screening

devices, reference should be made to the Design Guidelines for Drinking Water Systems,

2008 (MOE, 2008).



5.6 PRE-CHLORINATION/OXIDATION AND ZEBRA MUSSEL CONTROL

5.6.1 Purpose and Types of Pre-Oxidation Processes for Zebra Mussel Control

Chemical oxidants are often added before water enters the treatment plant, mainly to control

algae and other forms of biological growth (e.g. zebra mussels) that may occur at the intake or

in wet wells. Oxidants are also added in the first step of treatment either as first-stage

disinfectants or for other purposes such as control of biological growth in basins, colour

removal, control of taste and odours, reduction of specific organic pollutants, precipitation of

metals, and as coagulant aids (AWWA, 1999). These applications are discussed in Chapters 9

and 10.

The most accepted and currently recommended form of chemical treatment for zebra mussel

control in public water supplies is the use of oxidants such as chlorine, chlorine dioxide,

potassium permanganate and ozone (MOE, 2008). Chemical dosages are typically applied at

the intake through solution piping and a diffuser to prevent the formation of zebra mussel

colonies within the intake and piping. In addition, intake screens manufactured with special

alloys that prevent the growth of zebra mussels on the intake itself are available.


Table 5-4 presents a list of parameters that should be monitored to either measure the

effectiveness of zebra mussel control strategies or monitor for environmental conditions that

may favour zebra mussel reproduction.

Table 5-4 – Monitoring Parameters for Zebra Mussel Control Processes

Adapted from Mackie (2008)

Parameter Comment

Chlorine (or other oxidant) residual Assess effectiveness of applied dose relative to chlorine

demand

Calcium Dissolved calcium in water is an essential constituent of

shells for zebra mussels growth (Chang, 1996)

Alkalinity May be an indication of availability of calcium

pH May be an indication of availability of calcium

Hardness May be an indication of availability of calcium

Dissolved oxygen May indicate an area that is suitable for zebra mussel

infestation (Chang, 1996)

Nutrients (phosphorus, nitrogen) Indication of when reproduction and larval development will

occur

Temperature Indication of when reproduction and larval development will

occur (temperatures above 12 to 15°C)




Pre-chlorination has been the most common treatment for control of zebra mussels; however,

the main concern with the application of chlorine to raw water is the potential formation of

THMs and other disinfection by-products. In addition, concerns have been raised regarding

the release of oxidant chemicals, such as chlorine, into the natural environment. Several other

chemical and non-chemical alternatives have been evaluated with varying levels of success,

including: potassium permanganate, oxygen deprivation, thermal treatment, exposure and

desiccation, UV light irradiation, manual scraping, high-pressure jetting, mechanical

filtration, removable substrates, molluscicides, ozone, antifouling coatings, electric currents

and sonic vibration.

Experience has shown that low levels of chlorine can be applied to control settlement of

zebra mussel veligers (larval stage); higher dosages and contact times may be required to

control adult colonies once established (Van Benschoten, 2008).

Other studies have shown that it may be possible to optimize chemical addition for zebra

mussel control by monitoring environmental parameters that indicate seasonal sensitivity of

larvae and adults and the seasonal toxicity of molluscicides (Mackie, 2008).

5.7 CASE HISTORIES

5.7.1 County of Oxford – Source Water Protection Program

The following case study is based on information presented in Goudreau (2007).

System Description

The County of Oxford (the County) owns and operates the City of Woodstock (the City)

Water Supply System, which consists of 10 municipal groundwater wells. Approximately 80

percent of the City’s permitted water capacity is from the Thornton and Tabor well fields

located southwest of the City in a predominately agricultural area. Several of the wells within

the Thornton well field have elevated levels of nitrates. Nitrate levels in the aquifer began

increasing in the 1970s and have been attributed to historical farming practices on the

surrounding lands.

Groundwater Characterization and Protection Studies

Work to protect the Thornton Supply wells started in the mid-1990s from two different

perspectives. The former Woodstock Public Utilities Commission (PUC), which operated the

water system at the time, began looking at the well field to determine the source of the rising

nitrate levels. Around the same time, the County began to assess the vulnerability of its

municipal well supplies. In conjunction with the University of Waterloo, the County and the

PUC undertook a number of studies to characterize the extent and source of the nitrate plume,

as well as numerous County-wide groundwater protection studies addressing potential threats

to drinking water.

Mitigation Strategies

Based on the results of these studies, the County has begun implementing proactive measures

to reduce the nitrate loading to the Thornton aquifer. Specific measures include:



Groundwater Protection: Several groundwater studies were undertaken starting in the

mid-1990s, leading to the development of Wellhead Protection Areas (WHPAs) for

each municipal well. The WHPAs consisted of the 2, 5, 10 and 25 year time of travel

(TOT) zones for the well or well field.

Nutrient Management Strategies: A Nutrient Management Committee was formed,

which led the development of a County-wide Nutrient Management Strategy and

ultimately resulted in the implementation of bylaws that require farm operations over

a certain size to follow best practices for nutrient application, manure storage and

separation distances. These by-laws are being superseded by the provincial Nutrient

Management Act (NMA), 2002.

Nitrate Investigations: In conjunction with the University of Waterloo, the

Woodstock PUC undertook a number of studies to estimate the spatial distribution

and concentration of nitrates in the area. The studies showed that agricultural

activities were likely the main contributor to nitrate levels, and significant quantities

of nitrates were stored in unsaturated zones beneath the study area’s agricultural

lands. Research indicates that it may take several (e.g. 15 to 30) years to “flush”

excess nitrates from the aquifer system.

Land Use Management: Since 2003, the County has purchased approximately 300

acres of farmland within the 2-year TOT of the Thornton well field. Plots of land are

leased back to farmers for agricultural production. The farmers leasing the plots are

required to maintain “enhanced” Nutrient Management Plans that are more stringent

than provincial requirements under the NMA.

Well Pumping and Treatment: In order to reduce nitrate concentrations to well below

the Ontario Drinking Water Quality Standard of 10 mg/L, the County has

implemented a pumpage strategy that includes minimizing the use of high nitrate

wells and blending the water with water from low-nitrate wells.

Additional Servicing: The Village of Sweaburg (the Village) is located entirely

within the 2-year TOT of the Thornton WHPA. In 2003, residents were serviced by a

combination of municipal and private well systems. In order to remove the threat of

contamination from the preferential pathway to the aquifer, both the private and

municipal wells were recommended for abandonment. The Village was connected to

the new Thornton water treatment plant and the distribution system was extended to

service the properties that had used private wells. A sanitary servicing study is also

planned for Sweaburg to determine the best way to mitigate the approximately 300

septic systems that are located in the 2-year TOT of the Thornton well field.

Summary

Early results of the management strategies discussed above are positive and suggest that they

would be useful for protection of sensitive sources outside the Thornton well field. The

County is supporting continued research on the effects of the management strategies and new

research into in-situ remediation to reduce current nitrate levels.

5.7.2 City of Brandon – Source Water Blending Study

The following case study is based on information presented in XCG (2009).



System Description

The City of Brandon (the City) Water Treatment Plant (WTP) is a conventional lime-soda

ash softening plant, with filtration and disinfection using chlorine. The raw water source is

the Assiniboine River. The Assiniboine River flows from its headwaters in eastern

Saskatchewan into and across the western portion of Manitoba to its confluence with the Red

River within the City of Winnipeg. Raw water data collected by the City indicate that

concentrations of turbidity, total organic carbon (TOC), colour, alkalinity and hardness are

elevated and highly variable based on seasonal conditions.

Disinfection Study Methodology

A study was initiated to minimize the formation of DBPs in the City’s drinking water system.

The first phase of the study consisted of an evaluation of the existing treatment and

disinfection practices at the Brandon WTP and their effect on the DBP concentrations.

The recommended alternative for the reduction of DBPs in the drinking water system was

the implementation of chloramination for secondary disinfection. The second phase of the

Disinfection Study included bench-scale testing and additional sampling to evaluate the

benefits of chloramination for minimizing the formation of THM and HAA in the treated

water. The monthly chloramination jar testing program was carried out over a period of

one year; at that time, it was decided to investigate source water blending.

The City was interested in investigating blending of the Assiniboine River source with

the Curran Park (Turtle Crossing) and Canada Games (Westbran Park) wells as a

potential option for the reduction of TOC in the raw water. Bench-scale jar testing was

completed and a full-scale trial was conducted to confirm the results of the bench-scale

analysis.

Samples of the raw water from each well were analyzed for parameters contained in the

Guidelines for Canadian Drinking Water Quality (GCDWQ). The results of the well raw

water quality analyses indicated that the average TOC levels in the groundwater sources

approximately 2.2 mg/L, while those in samples collected from the Assiniboine River were

approximately 9.8 mg/L.

The rated capacities of the Brandon WTP and the two wells were evaluated and a ratio of 55

percent groundwater to 45 percent Assiniboine River water was selected for the bench-scale

study. The average TOC concentration in the raw water at this blending ratio was

approximately 7.5 mg/L (note: the average concentrations were based on a number of

monthly samples, which resulted in a variation in the average blended TOC).

Summary

The results of the jar testing indicated that THM concentrations measured after a 24-hour

chlorine contact time were found to be 91 µg/L and 80 µg/L, during the spring and summer

trials, respectively. Concurrently with the summer trial, during which the Brandon WTP was

supplied solely from the Assiniboine River, samples were collected at the furthest point in the

Brandon distribution system and the THM concentration was 149 µg/L. These results

indicated the potential for a 46 percent reduction in the total THM concentration by blending

the surface and groundwater sources at the above mentioned ratio.



Further reductions in the total THM concentration were achieved in jar testing runs using

chloramination for secondary disinfection.

Full-scale plant trials confirmed the results of the jar testing. In addition, the results of the

plant trial indicated that the higher the ratio of groundwater to surface water, the greater the

reduction in THMs.

5.8 REFERENCES

American Water Works Association (1995). Water Sources, 2nd

Ed. AWWA. ISBN 0-89867-

778-5.

American Water Works Association (1999). Water Quality and Treatment: A Handbook of

Community Water Supplies, 5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.

American Water Works Association Research Foundation (1993). Evaluation and

Restoration of Water Supply Wells. AwwaRF and AWWA. ISBN 0-89867-659-2

American Water Works Association Research Foundation and Japan Water Works

Association (1993). Instrumentation & Computer Integration of Water Utility Operations.

ISBN 0-89867-630-4.

Chang, T.J., M.A. Hoover, and T.A. Bartrand (1996). Optimization of a Vacuum Device for

Zebra Mussel Control.

CCME (2002). From Source To Tap: The Multi-Barrier Approach to Safe Drinking Water,

prepared by the Federal-Provincial-Territorial Committee on Drinking Water and the Water

Quality Task Group of the Canadian Council of Ministers of the Environment.

Goudreau, D. (2007). “Addressing and Mitigating Known Water Quality Issues: A Source

Protection Case Study”, presented at the 2007 OWWA-OMWA Joint Annual Conference,

Town of the Blue Mountains, ON.

Mackie, G. (2008). “Control and Disinfection II. Optimizing Chemical Disinfections”,

presented at the American Water Works Association Research Foundation (AwwaRF)

Workshop on Quagga/Zebra Mussel Control Strategies for Water Users in the Western

United States. AwwaRF Project #4200.

MOE (2006a). Assessment Report: Draft Guidance Modules. PIBS 5600e.

http://www.ene.gov.on.ca/envision/water/cwa-guidance.htm

MOE (2006b). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.


Van Benschoten, J. (2008). “Control of Dreissenid Mussels by Chemical Oxidants”,

presented at the American Water Works Association Research Foundation (AwwaRF)

Workshop on Quagga/Zebra Mussel Control Strategies for Water Users in the Western

United States. AwwaRF Project #4200.



XCG Consultants Ltd. (2009). “Evaluation of Disinfection Formation with Source Water

Blending”, report for the City of Brandon.


CHAPTER 6COAGULATION AND FLOCCULATION

COAGULATION AND FLOCCULATION

6.1 Introduction ............................................................................................................ 6-1

6.2 Coagulation and Flocculation ................................................................................. 6-1

6.2.1 Purpose of Coagulation and Types of Coagulation Chemicals ............... 6-1

6.2.2 Purpose of and Types of Flocculation ..................................................... 6-2



6.3 Optimization Techniques ....................................................................................... 6-7

6.3.1 Jar Testing ................................................................................................ 6-7

6.3.2 Zeta Potential ......................................................................................... 6-10

6.3.3 Streaming Current Detectors ................................................................. 6-10

6.3.4 Particle Counters .................................................................................... 6-10

6.3.5 Residual Aluminum Control .................................................................. 6-10

6.3.6 Optimizing Residence Time in Flocculators ......................................... 6-11

6.4 Case Histories ....................................................................................................... 6-12

6.4.1 Regional Municipality of Waterloo – Mannheim WTP ........................ 6-12

6.4.2 City of Owen Sound – R.H. Neath WTP ............................................... 6-16

6.5 References ............................................................................................................ 6-19

CHAPTER 6. Coagulation and Flocculation 6-1


CHAPTER 6

COAGULATION AND FLOCCULATION

6.1 INTRODUCTION

Surface water sources are likely to contain particulate impurities, such as bacteria and algae,

as well as suspended and dissolved organic and inorganic material. The objective of

coagulation and flocculation is to increase the size of the particulate matter present in the raw

water, especially the nonsettleable solids (e.g., colloidal particles, algae and colour) to

improve the removal of these impurities through the clarification and/or filtration processes.

The focus of this chapter is on coagulation and flocculation as a treatment strategy to remove

particulate matter. Optimization techniques related to coagulation for the removal of other

parameters, such as enhanced coagulation and flocculation for removal of natural organic

matter (NOM) to reduce DBP formation, are addressed in Chapters 9 and 10. The impact of

changes in coagulants and coagulant dosage on corrosion control in the distribution system

and premise plumbing are discussed in Chapter 11.

6.2 COAGULATION AND FLOCCULATION

6.2.1 Purpose of Coagulation and Types of Coagulation Chemicals

Coagulation involves the rapid dispersion of a chemical coagulant into water to destabilize

particles so they can agglomerate or come together and form larger particles or “floc”.

Coagulation of turbidity in water treatment occurs predominantly by two mechanisms

(AWWA, 1999):

1. Charge neutralization

– Most particles in water are negatively charged and repel each other. The

coagulant is positively charged and neutralizes particle charge to allow the

particles to agglomerate during the subsequent flocculation process.

2. Sweep-floc coagulation

– Sufficient coagulant is added to form a precipitate that settles and sweeps, or

enmeshes, suspended particles.

– Higher coagulant dosages are used for sweep coagulation than for charge

neutralization.

There are advantages and disadvantages to the use of either method. For example, with

charge neutralization, if too much coagulant has been added the particles will attain a positive

charge and re-stabilize, resulting in higher residual turbidity. For sweep-floc coagulation,

higher coagulant dosages are needed than for charge neutralization, resulting in higher

chemical costs, greater sludge production and potentially leading to higher iron or aluminum

residuals in the treated water. However, the use of sweep-floc coagulation may be

advantageous for systems where raw water turbidity and organic carbon concentrations are

elevated and/or variable. Additional information on the application of these coagulation



mechanisms, and guidance on process selection and design, is provided in AWWA (1999),

MWH (2005) and AWWA (2007).

The mixing of the coagulant chemical into the raw water is commonly referred to as flash

mixing. The purpose of the flash mix is to rapidly and thoroughly mix the coagulant chemical

throughout the water. The entire process occurs in a very short time (i.e. seconds) and results

in the formation of very small floc particles.

Mixing can be achieved with a number of different types of devices. Mechanical mixers

(paddles, turbines, propellers and jet mixers) are frequently used in coagulation facilities.

Hydraulic mixing with in-line static mixers, baffles or throttling valves works well in systems

that have sufficient water velocity to cause significant turbulence in the water being treated.

The chemicals most frequently used as primary coagulants include:

Aluminum sulphate or “alum” (Al2(SO4)314H2O)

Polyaluminum chloride (PACl)

Iron-based coagulants:

– Ferric chloride (FeCl36H2O)

– Ferric sulphate (Fe2(SO4)39H2O)

– Ferrous sulphate (FeSO47H2O)

Polymers (polyelectrolytes)

Poor control of the coagulation process (e.g. coagulation pH, dosage, mixing, etc.) may result

in elevated iron or aluminum residuals in the treated water. As such, monitoring of these

parameters in the treated water is needed to verify that their concentration is below the

aesthetic objective or operational guideline, as applicable.

Coagulant aids can be used in conjunction with a primary coagulant, such as alum or other

metallic salts, to provide bridging between floc particles and to create larger, heavier and/or

stronger floc. The three general types of coagulant aids are:

Activated silica (Na2SiO3)

Weighting agents (e.g. bentonite clay)

Polymers (polyelectrolytes)

6.2.2 Purpose of and Types of Flocculation

Flocculation is a process that involves the gentle agitation of water to promote contact

between particles to form particle clusters called “floc”. As particles collide, they become

larger through chemical joining and bridging. Larger particles are more easily settled and/or

filtered.



The purpose of flocculation is to create a floc of an optimum size, density and strength for

later removal in the clarification and filtration processes. Flocculation normally follows

coagulation, which is the first step necessary to destabilize particles with surface charges and

allow flocculation to occur.

Sufficient detention time, proper mixing intensity and a properly shaped basin for uniform

mixing are needed to allow efficient flocculation. While coagulant mixing is designed to

allow rapid and complete dispersion of the coagulant chemicals under very turbulent

conditions, flocculation is a much more gentle stirring process. Insufficient mixing may cause

poor floc formation, while excessive mixing may shear flocculated particles. Sheared

particles cannot re-agglomerate, which can result in higher settled and filtered water

turbidity.

Two common types of mechanical flocculators are horizontal paddle wheel types and vertical

flocculators (paddle, turbine or propeller). Hydraulic flocculators of various configurations

are also common in Ontario.


The selection of chemical coagulants and coagulant aids is a continuing process of trial and

evaluation. Table 6-1 presents monitoring recommended, in terms of sampling locations and

analyses, in order to evaluate the performance of the coagulation and flocculation processes.

The following can be indicators of inadequate coagulant mixing, inadequate flocculation

mixing, or incorrect chemical dosage:

Very small floc (called pinpoint floc), unless specifically desired for direct filtration.

High turbidity in settled or filtered water;

Too-frequent filter backwashing; and

Elevated aluminum or iron concentration in treated water (depending on the

coagulant used).

Table 6-1 – Coagulation/Flocculation – Recommended Monitoring to Evaluate

Performance

Location Types of Sample / Measurement Parameters / Analyses

Raw water Continuous monitoring Temperature

Continuous monitoring pH

Grab sample Alkalinity

Continuous monitoring Turbidity

Grab sample Colour



Table 6-1 – Coagulation/Flocculation – Recommended Monitoring to Evaluate

Performance (cont’d.)


Flocculation

chambers/basins Visual observation Size and distribution of floc

Filtered or treated

water

Grab sample or continuous

monitoring

pH



Particle counts

Grab sample Colour

Grab sample Aluminum or Iron residual (depending

on the coagulant used)

Figure 6-1 presents a process schematic of a typical coagulation and flocculation process,

along with the identification of various sampling locations.

Raw Water

Sample Location

Raw Water

To Clarification or

Filtration

Coagulant

Addition with

Rapid Mixing

Coagulant Aid Addition

(if applicable)

with Rapid Mixing

Flocculation Basins

with Mechanical Mixing

Figure 6-1 – Coagulation/Flocculation – Process Schematic and Sampling Locations

The rapid mix/coagulation step can be achieved either in a separate process tank or by the use

of an in-line mixer. The detention period in the mixing zone should be minimized and limited

to no more than 30 seconds. Typically, a rapid mixing with a mixing intensity velocity

gradient, G value, in the order of 1000 s-1

is effective (MOE, 2008). G values can be

calculated using the formula presented in Appendix G.

The projection of flocculation basin capacity is based primarily on available hydraulic

detention time (HDT). The detention time required for adequate flocculation is highly

variable depending water temperature and downstream processes. When sedimentation is



included in the treatment process, HDTs of 25-30 minutes are usually sufficient in summer.

However, when water temperatures are less than 5°C, floc formation can be delayed. In these

instances, longer (30-40 minute) detention times may be required.

In assessing the adequacy of flocculation HDT, seasonal variations in flow should be

considered. Plant flows are generally lower in winter, but not always. In northern Ontario,

flows are often highest during winter when consumers allow their taps to run continuously to

avoid frozen service lines.

For direct filtration plants, detention times as low as 15 minutes may be adequate. Even

shorter times may be adequate for coagulation/flocculation for membrane filtration processes

or for in-line flocculation processes with high quality raw water sources. Because of these

variables, judgement should be used when assessing the required HDT of flocculation basins.

Jar testing can be used to obtain additional information on the HDT needed for adequate

flocculation.

In general, G values of 10 to 70 s-1

are needed for successful flocculation. Tapered

flocculation (reducing G in each stage) is desirable and is typically designed as three or four

sequential process tanks. Lower velocity gradients are required for the more fragile organic

floc than for flocculated suspended material (turbidity). Higher G values are needed for direct

filtration to produce denser pinpoint floc (MOE, 2008).

To permit flexibility of operation and for maintenance purposes, two separate parallel

flocculation tanks should be provided as a minimum. It is desirable to have at least two stages

per tank to prevent short-circuiting.

Since variable mixing energy and staging can often be added as “minor” modifications, these

items are not considered as significant in the capacity rating. If adequate basin volume is

available as determined during a CPE (e.g. typically a Type 1 DWS Component), a one-stage

flocculation basin may result in a Type 2 capability rating, and follow-up CTA activities

would be required to establish if added baffling or flocculator drives could improve

performance.

Criteria used to evaluate flocculation processes as part of the major DWS component

evaluation are presented in Table 6-2.

Table 6-2 – Flocculation – Criteria for Major DWS Component Evaluation Using the

Performance Potential Graph Rating System

Characteristic Typical Assessment Criteria

Hydraulic Detention Time (minutes) 15 – 40

Velocity Gradient (G), sec-1

10 – 70

Stages 2 – 3




Symptoms and causes of common problems encountered with coagulation and flocculation

are shown in Table 6-3.

Table 6-3 – Coagulation/Flocculation – Symptoms and Causes of Common Problems

Adapted from Water Treatment Plant Operation: Volume I (1999), California State University

Problem Description

Mitigation

Source water quality

changes

(Turbidity, colour,

temperature, pH,

alkalinity)

Poor floc formation

Over- or under-dosing of

coagulant chemicals

Increase in settled water

turbidity

Early turbidity

breakthrough and/or

significant change in

particle counts in

individual filter effluent

Elevated aluminum or iron

residual in treated water

Increase frequency of raw water and process

monitoring

Perform jar tests, if needed

Adjust coagulant dosage, alkalinity or pH

Add coagulant or filter aid

Adjust flash mixing/flocculator mixing

intensity1

Low raw water

temperature Lower rate of floc settling

Decrease in floc strength

(higher turbidity

breakthrough in filters)

Optimize coagulation pH

Adjust coagulant dosage

Consider addition of weighting agent to

increase floc density and/or other coagulant

aid to increase floc strength

Consider use of an alternative coagulant

Insufficient raw

water alkalinity Slow floc formation Increase raw water alkalinity by adding

lime, soda ash or other alkali

Low raw water

turbidity Slow floc formation Artificially increase raw water turbidity by

recycling sludge from sedimentation basins

or by adding weighting agent (e.g. bentonite

clay)



Table 6-3 – Coagulation/Flocculation – Symptoms and Causes of Common Problems

(cont’d.)

Adapted from Water Treatment Plant Operation: Volume I (1999), California State University

Problem Description

Mitigation

Poor floc formation

(size, dispersion,

strength)

Floc carryover from

sedimentation basins to

filters

Cloudy or foggy

appearance of water in

flocculation basins

Excessive sludge

production

Elevated aluminum or iron

residual in treated water

Increase frequency of raw water and process

monitoring

Perform jar tests and adjust chemical

dosages, if needed

Verify process performance: (a) check

chemical feed rates and pumps and (b) flash

mixer operation

Adjust flocculation mixing, if possible

Assess flocculation time based on operating

flow rate

Notes:

1. Very few treatment plants have provisions for adjusting the flash mixer. However, many

plants have variable-speed drives on flocculators to allow for adjustment of mixing intensity.

6.3 OPTIMIZATION TECHNIQUES

6.3.1 Jar Testing

Jar testing is the most common coagulant control and optimization technique. Jar tests may

be used for the following (AWWA, 1999):

Coagulant selection;

Coagulant dosage selection;

Coagulant aid selection;

Coagulant aid dosage selection;

Determination of need for alkalinity adjustment;

Determination of optimum pH;

Determination of point of addition of pH adjustment chemicals and coagulant aids;

Optimization of mixing energy and time for rapid mixing and slow mixing; and

Determination of optimum dilution of coagulant.

Jar tests can be set up to represent plant operating conditions by determining actual plant

theoretical mixing, flocculation and sedimentation detention times, and by setting jar test



mixing energy inputs, mixing times and settling times to values similar to those in the plant.

The jar test procedure should then be adjusted as necessary to obtain results similar to actual

plant operation. For example, if the apparent optimal dose in the plant is much greater than

indicated by jar tests, then mixing and flocculation conditions should be checked and

adjusted. The use of square jars rather than round graduated cylinders is recommended

because experience has shown that square jars are more representative of the geometry of

the flocculation tanks than round beakers or graduated cylinders. A jar testing apparatus is

shown in Figure 6-2.

Chemicals should be added to duplicate plant conditions. For example, if alum is added to the

flash mix and polymer is added to a pipeline 30 seconds later downstream from the flash mix,

the same sequence should be used in the jar test. The use of syringes without needles to

measure and deliver the appropriate chemical dose to each jar simplifies chemical addition.

Another essential part in the successful use of a jar test for coagulant control is the

interpretation of the test results. For direct filtration plants, a small volume (about 50 mL)

should be removed from the jars and passed through filter paper. Typically, a 5 or 8 µm filter

paper can be used to approximate filter performance (MWH, 2005). The filtered samples

should be tested for turbidity, colour, aluminum residual and other parameters of concern.

The sample that provides the optimum results for the combination of these parameters

represents the optimum dose.

Figure 6-2 – Jar Testing Apparatus

For conventional plants, the jar contents should be allowed to settle for a period of time

relative to the surface overflow rate of the basins. The sampling time, which is based on

particle settling velocity, can be determined using the formula presented in Appendix G

(USEPA, 1998).



After the correct sampling time is determined, samples should be drawn from a sample tap

located 10 cm from the top of the jar, and the turbidity, colour and aluminum or iron residual

of the sample should be determined. If sample taps are not available on the jars, pipettes can

be used to draw-off samples from the jars. Supernatant can be filtered using 5 or 8 micron

filter paper to approximate filtration.

Excellent references are available to guide the facilitator in implementing jar testing to

determine optimum coagulant doses (AWWA, 2007; Hudson, 1981).

Once the correct chemical dose is determined, the staff should be able to adjust the chemical

feeders to deliver the desired dosage. This requires the ability to conduct chemical

calculations and to develop and utilize calibration curves for chemical feeders. For example,

a concentration dose in mg/L has to be converted to a feed rate (e.g. kg/day or mL/min) in

order to correctly adjust chemical feed equipment. Calibration curves, which indicate feed

rate setting versus feeder output, should be developed for all chemical feeders to ensure the

correct feeder setting for a desired chemical dosage.

Some chemicals, such as polymers, must often be prepared in dilute solutions prior to

introduction into the plant flow stream. Therefore, the capability to prepare chemical

dilutions should be transferred to the operators during a CTA.

The chemical dose should not only be carefully controlled, but the correct type of coagulants,

flocculants and filter aids should also be applied.

Typically, a metal salt (alum or iron based coagulants) and polymer should be added

in the coagulation zone prior to flocculation. The metal salt should always be added

to the rapid mix; however, the addition point of the polymer, which may be before,

after, or into the rapid mix, should be determined on a site-specific basis by

conducting a special study.

If alum is being utilized with a raw water pH exceeding 8.0 to 8.5, consideration

should be given to switching to iron salts or polyaluminum chloride, the use of pH

depressing chemicals, or acidified alum.

The use of a polymer to enhance floc formation and settling can also be investigated.

Investigation of filter aid polymers should be conducted since these aids may be

required if filtered water turbidities less than 0.1 NTU are to be achieved on a

continuous basis. These products should be introduced into the plant flow stream at a

point of gentle mixing since excessive turbulence will shear the polymer chains and

make the product ineffective.

For low alkalinity water (e.g. less than 20 mg/L), consideration should be given to

adding alkalinity (e.g. soda ash, lime).

Competing chemicals should not be added at the same location. For example, the addition of

lime and alum at the same point is counterproductive if the lime is raising the pH to the

extent that the optimum range for alum coagulation is exceeded.



6.3.2 Zeta Potential

Zeta potential (zp) is a measure of the excess number of electrons found on the surface of

particulate matter (AWWA, 2005). It can be measured by a zeta meter, and its value

determines the extent of the electrostatic forces of repulsion between charged particles. The

zp of particles in natural water are typically -20 to -40 mV (AWWA, 1999). Suspensions that

are well destabilized (likely to flocculate) by the charge neutralization mechanism following

coagulant addition have a zp close to zero. The zp is not a reliable predictor of optimum

sweep coagulation.

For plant optimization, the zp of coagulated particles after the rapid mixing or slow mixing

operation in jar tests are measured. For conventional treatment, the zp after the rapid mixing

is preferred. The optimum coagulant dosage is determined when the zp of the charge-

neutralized particles is close to zero.

6.3.3 Streaming Current Detectors

A streaming current monitor is an instrument that passes a continuous sample of coagulated

water past a streaming current detector (SCD). The detector produces a continuous readout of

the measurement of the net ionic and colloidal surface charge in the sample. Comparison

between zeta potential and SCD data indicate that a strong correlation exists between these

measurements and that either one is suitable for determination of charge neutralization

(AWWA, 1999).

The optimal SCD reading varies with source water pH; changes in pH therefore require

different SCD goal readings. The potential advantage of the SCD compared to zp is that it

provides continuous monitoring for coagulation control and may be used for automatic

control of coagulant dosage if the pH remains constant (AWWA, 1995).

6.3.4 Particle Counters

There is increasing interest in optimizing the coagulation/flocculation/filtration process to

ensure removal of Cryptosporidium and Giardia lamblia cysts. The only practical real-time

or on-line method to determine the presence of cysts in water at this time is to monitor the

size and concentration of minute particles in the finished water (AWWA, 1995). Turbidity

measurement is inadequate for this task because the concentration of cysts considered

undesirable is well below the normal range that can be indicated in turbidity tests; in addition,

turbidity tests give no indication of particle size.

In addition, for drinking water systems that are able to achieve filtered water turbidities of

less than 0.1 NTU, turbidity measurements may not be responsive to small changes in

coagulant dosage. In this instance, the number of particles larger than 2 µm per mL in filtered

water has proved sensitive to minor variations in coagulant dosage to optimize filter

operating conditions. As such, total cumulative particle counts (NP ≥ 2.0 µm/mL) portrayed

as percentile or probability plots can be used in optimization studies as an indicator of plant

performance (Hargesheimer et. al., 1998).

6.3.5 Residual Aluminum Control

One of the reasons for using zeta potential or SCD measurements is to avoid overdosing

alum-based coagulants and therefore minimize the residual aluminum in the finished water.



The most common strategy to reduce residual aluminum levels in treated water is the

adjustment of pH to 6.0, close to the minimum solubility of aluminum (AWWA, 1999).

Other effective strategies for reduction of total aluminum residuals are:

Use of alternative coagulants (such as polyaluminum chloride or iron-based

coagulants);

Reduction of alum dosage by alum-polymer combinations, keeping in mind that

either too high or too low an alum dosage can increase residual aluminum levels; and

Optimized removal of floc during filtration.

6.3.6 Optimizing Residence Time in Flocculators

As discussed in Section 6.2.3, residence time in flocculators has a direct impact on plant

performance. Too little and too much mixing can have a detrimental effect on sedimentation

performance (Hudson, 1975). Key residence time characteristics of flocculation basins

include plug flow, mixed flow and dead space. Other factors that contribute to performance

problems include back-mixing and process recirculation.

Means for evaluating and optimizing detention time and mixing, such as tracer testing, stress

testing and hydraulic modelling, are discussed in Chapter 4. Other strategies, such as

reducing plant flow rate, improving mixing and providing baffles, are discussed below.

6.3.6.1 Controlling Plant Flow Rate

Plant flow rate is a primary means for process control at many small plants that are operated

for less than 24 hours each day. At these plants, an excessive hydraulic loading rate on the

flocculation process can be avoided by operating at a lower flow rate for a longer period of

time. This provides an option to meet more rigorous performance requirements with existing

units without major capital improvements. The capability to improve plant performance by

reducing the plant flow rate is offset by the need to staff the plant for longer periods of time,

which adds to operating costs. Therefore, plant administrators, in conjunction with the CTA

facilitator, should evaluate both options.

Adequate time for chemical reaction is typically more important in water with temperatures

below 5°C, and this time can often be extended operationally by reducing plant flow.

6.3.6.2 Mixing Intensity, Patterns and Time

In general, experience has shown that improvements in flocculation performance can be

obtained by using compartmentalization (e.g. three or four cells in a flocculator) and tapering

the velocity gradients from a G value of 40 to 60 s-1

in the first cell down to 15 to 25 s-1

in the

last cell (AWWA, 1999). The higher G values are needed to produce high-density floc

quickly, while the lower G values are needed to prevent settling of floc in the flocculator.

In addition, the dimensionless parameter Gt (mixing intensity multiplied by retention time in

the floc tank) can be used to represent the degree of flocculation. In general, Gt values

ranging from 104 to 10

5 are recommended (AWWA, 1999).



Optimum G and Gt values are best determined by pilot studies and/or full scale trials. Jar

testing does not always involve back-mixing, which is typical for flocculation processes, and

is therefore a limited guide for optimization of flocculation mixing (MOE, 2008).

Flocculation energy input is often fixed at small plants, either by hydraulic flocculation

systems or by constant speed flocculation drives. However, flocculation energy, if low

enough to allow formation of settleable floc, is not considered an essential variable to achieve

desired performance of a small plant. More important are the plug flow characteristics of the

flocculation system. Plug flow characteristics, similar to those found in most hydraulic

flocculation systems, result in the formation of floc particles of uniform size, which greatly

aids settleability. As such, greater priority may be placed on installing baffling in flocculation

systems rather than trying to optimize mixing energies.

6.3.6.3 Baffling

For horizontal flow flocculators, mixing by hydraulic means can be possible by installing

vertical baffles arranged for over-and-under or around-the-end flow patterns. The baffles

cause hydraulic head loss or energy dissipation, which are associated with velocity gradients

in the liquid stream, and minimize the amount of mechanical equipment used for flocculation.

Typical designs use 0.25 to 0.40 m/s for the horizontal velocity of flow (AWWA, 1999).

6.4 CASE HISTORIES

6.4.1 Regional Municipality of Waterloo – Mannheim WTP

The following case study is based on information presented in DeWolfe et. al. (2003).

System Description

The Mannheim Water Treatment Plant (WTP), located in Kitchener, Ontario, treats

approximately 72 ML/d (19 mgd). There are two identical treatment trains, each able to treat

approximately 36 ML/d (9.5 mgd). Raw water is drawn from the Grand River into a pre-

sedimentation reservoir.

Treatment begins with flash mix in-line blenders, where the coagulation chemicals are added.

Coagulation is followed by two-stage flocculation, where the coagulant aid (polymer) is

added in the second stage, stirred by mechanical paddle wheels. Sedimentation takes place by

discrete settling in lamella plate settlers to achieve a settled water turbidity goal of less than 1

NTU. Ozonation then takes place for primary disinfection, taste and odour control, and

colour removal. There are four gravity filters, two granular activated carbon (GAC) and two

dual media (anthracite/sand), operated at a fixed flow rate to maintain the plant flow rate

during backwashing of a filter. Chlorination takes place to maintain chlorine residual in two

30 ML (8 Mgal) clearwells. A higher chlorine dose is required in the winter when high raw

water ammonia concentrations are experienced. Treated water is then pumped into a 5-cell

580 ML (153 Mgal) reservoir where the water is blended with groundwater, chloraminated at

the reservoir inlet, and finally pumped through the distribution system.

Coagulant Testing Facilities and Strategies

The Mannheim WTP was using alum for coagulation, but was having difficulties achieving

low settled water turbidity during cold water conditions, decreasing filter run times and



increasing the frequency of backwashing. The Region identified the chemical coagulant

vendors in their area and invited each of them to jar test their products at the plant. They

initially compared each candidate coagulant’s performance to the performance of alum in

terms of turbidity removal. Any coagulant that did not perform as well as alum was not

considered further. Additional jar testing was conducted to determine the optimum dose of

each product, then all products at their optimum doses were compared simultaneously

through jar testing. After one product was selected as the best alternative, a full scale plant

trial confirmed that this product would perform as desired.

Six candidate coagulants, in addition to alum, were evaluated through extensive jar testing at

the Mannheim WTP. Characteristics of these products are shown in Table 6-4.

Table 6-4 – Initial Coagulant Comparison – Mannheim WTP

Coagulant Strength

(%)

Estimated

Cost

($/dry ton)

Freezing

Point

(°C)

Dosage

(dry mg/L)

Water Treatment

Residual (WTR)

(kg/kg coagulant)

Alum 48.5 211 -15 40-45 0.44

PACl-11

33 1,242 -12 15-20 0.80

PACl-21 33 1,373 -12 15-20 0.83

PACl-31 43 2,212 -11 15-20 1.20

PASS2

34 868 < 0 18-21 0.66

Ferric chloride 27 458 -35 40-45 0.083

Ferric sulphate 44 513 -35 NA NA

Notes:

1. Polyaluminum chloride (PACl). Trade names are not identified. PACl from different vendors

are identified as 1, 2 and 3.

2. Polyaluminum silicate sulphate (PASS).

3. This data point appears to be inconsistent with the other values; however, it was reproduced

as per the original case study (DeWolfe et. al., 2003).

NA - not available.

The jar testing protocol that was used was as follows:

1. Measure raw water temperature, turbidity, true and apparent colour, dissolved

organic carbon (DOC) and pH.

2. Add raw water to 2-litre jars in water bath maintained at ambient temperature.

3. Add full strength coagulant at desired dosage to 2-litre jars.

4. Rapid mix at 300 revolutions per minute (rpm) for 1 minute.



5. Add 0.01% polymer at desired dose to 2-litre jars.

6. Mix for 1 minute at 100 rpm.

7. Continue mixing at 15 rpm for 15 minutes.

8. Record speed of floc formation, size, colour and density of floc.

9. Stop mixing, settle floc for 7 minutes, and record observations.

10. Take water samples at mid-point of beakers using a pipette.

11. Measure final turbidity, apparent colour, true colour and pH, in that order.

12. Filter samples for DOC measurement.

13. Record results.

It is noteworthy that flocculation and settling times used in jar testing were one half the full-

scale values at the WTP’s maximum flow rate.

From the initial screening, ferric sulphate did not perform better than alum, but it was

included in subsequent jar testing. The optimum doses of each of the coagulants and alum are

shown in Table 6-5. The typical alum dose used was 35 to 45 mg/L (dry weight as alum), and

all three PACl products were effective at dosages less than half (18 mg/L dry weight as alum)

that needed with alum. The performance of all three PACl products was comparable. There

was slightly better colour and DOC removal using PACl-3. Ferric chloride did not perform

well at the dose recommended by the vendor, but it did perform well at twice the originally

recommended dosage. PASS did not perform as well as any of the three PACl coagulants. A

higher PASS dose of 21 mg/L (dry weight) was necessary to achieve the desired settled

turbidity of less than 1 NTU.



Table 6-5 – Summary of Optimum Coagulant Doses and Jar Test Results –

Mannheim WTP

Parameter Alum PACl-1

PACl-2 PACl-3 PASS Ferric

chloride

Coagulant dose

(mg/L) 35-45 18 18 18 21 45

Polymer dose

(mg/L) 0.075 0.075 0.075 0.075 0.075 0.075

Final turbidity

(NTU) > 2 0.53 0.47 0.57 0.84 0.92

Final pH NA 7.96 7.93 7.97 8.05 7.42

Final true

colour NA 9 10 5 11 8

Final apparent

colour NA 16 14 11 17 24

Final DOC

(mg/L) NA 4.7 4.9 4.2 NA 3.4

Notes:

1. NA - not available.

Table 6-6 summarizes the coagulant comparison for the Mannheim WTP, including the

water treatment residual (WTR) generation rates (in kg per million litres of treated

water). The approximate amount of solids generated by each coagulant was an

important evaluation criterion.

PACl-1 and PACl-2 both generated about 20 percent less WTR than alum. PACl-3

generated 8 percent more WTR than alum. PASS generated the least amount of WTR.

Ferric chloride produced the greatest amount of WTR, due to the high dose required (45

mg/L). WTR generation was estimated from the dry weight of total solids, raw water

solids and polymer solids left in the jar, using the equation shown below:

TS – RWS – PS = CS

where:

TS = total solids in jar in mg (dry weight)

RWS = raw water solids in jar in mg (dry weight)

PS = polymer solids in jar in mg (dry weight)

CS = coagulant solids in jar in mg (dry weight)



For example, using an 18 mg/L dose of PACl-1 in a 2-litre jar test volume, TS was 17.5 mg,

RWS was 3.55 mg and PS was 0.075 mg. This produced an estimated quantity of CS of 13.88

mg (17.5 – 3.55 – 0.075 = 13.88).

Table 6-6 – Summary of Coagulant Comparison – Mannheim WTP

Coagulant Performance

Optimum

Dose

(mg/L)

Cost

($/ML)

Residuals

(kg/ML)

Alum High settled water

turbidity 42 0.62 1.29

PACl-1

Low settled water turbidity 18 1.56 1.00

PACl-2 Low settled water turbidity 18 1.72 1.04

PACl-3 Low settled water

turbidity; slightly better

DOC and colour removal

18 2.76 1.51

PASS Low settled water turbidity 21 1.27 0.97

Ferric chloride Low settled water

turbidity; slightly better

DOC and colour removal

45 1.44 2.51

Summary

From extensive jar testing, the Region was able to identify one coagulant from a number of

candidates as the one most suited to their unique water treatment characteristics. PACl-1

performed better than alum in cold water and provided treatment equal to or better than other

candidate coagulants. At an optimal dosage of 18 mg/L, PACl-1 produced less WTR than

alum and equal to or less than other candidates. Ferric chloride also yielded low turbidity

values, but the high doses required produced considerably more residuals than PACl-1. All

candidate coagulants did cost more than alum, but with the exception of the ferric sulphate,

their performance was far superior to alum in the cold water.

While the cost of the selected coagulant was greater than alum, the improved treatment

performance documented in the jar testing and plant scale trial, which leads to a more robust

treatment and therefore barrier, justify its use as the primary coagulant during cold water

conditions.

6.4.2 City of Owen Sound – R.H. Neath WTP

The following case study is based on information presented in XCG (1999).



System Description

The R.H. Neath WTP is a direct filtration plant with the following unit process components:

pre-chlorination for seasonal zebra mussel control, coagulant addition (polyaluminum

chloride) and flash mixing, flocculation, filtration, post-chlorination for disinfection and

fluoridation. The R.H. Neath WTP contains two water treatment trains. Each treatment train

is equipped with similar unit process components, but convey separate flow streams

according to equipment on line, demand and their individual rated capacities.

Coagulant Testing Facilities and Strategies

PACl is used year round at the R.H. Neath WTP for coagulation. The average PACl dosage

for period from 1993 to 1995 was 1.02 mg/L as Al (or 6.30 mg/L as PACl). Typically,

coagulant dosages range from 0.2 to 1.0 mg/L as Al for direct filtration facilities using alum.

Therefore, the average PACl dosage at the facility over the historic period was at the high end

of the typical range for direct filtration facilities.

The PACl is added to the raw water at the rapid mix tanks where turbine mixers evenly

distribute the coagulant throughout the flow. Theoretically determined mixing intensities, G

values, have indicated that the rapid mixer is providing between 335 to 387 s-1

in Plant 1 and

between 386 to 446 s-1

in Plant 2 over the temperature range from 5 to 15C. The typical

design value at the time (MOE, 1982) recommended a G value at around 1,000 s-1

.

To identify the optimum conditions for coagulation for the R.H. Neath WTP, a bench scale

investigation consisting of jar testing was developed. The objective was to identify the

optimum coagulant, coagulant aid, pH, and dosages to minimize the filtered water turbidity,

soluble aluminum residual and solids production.

Jar testing was conducted using alum, PACl and ferric chloride, with and without pH

adjustment. The optimum coagulant and dosage with pH adjustment was then tested to

determine if a coagulant aid polymer would provide any additional benefit. Jar testing should

normally be performed to mimic the mixing velocity gradients and retention times in the

rapid mix and flocculation mix tanks. However, the jar testing equipment at the plant could

not attain the impeller speeds required and therefore, 2 minutes of rapid mix at 100 rpm and

30 minutes of flocculation mix at 25 rpm were used.

The results of the jar testing indicated that:

Alum and PACl performed well on their own, with slightly higher than target

aluminum residuals;

pH adjustment to lower levels (7.0 and 6.5) resulted in a decrease in the aluminum

residuals for both alum and PACl;

Ferric chloride performed well with respect to filtered water turbidity at dosages

greater than 1 mg/L as Fe, but produced more solids than alum or PACl for

comparable turbidity results; and

No additional benefit was observed with addition of coagulant aid polymer.



Two full scale trials using acidified alum were conducted at the plant. The primary purpose

of these trials was to compare the performance of acidified alum and PACl on the finished

water aluminum residual concentration. The results of the trials indicated that the use of

acidified alum resulted in a lower average aluminum residual, but that the water treated with

PACl had an average filtered water turbidity lower than the water treated with acidified alum.

Bench Scale Evaluation of Rapid Mixing Intensity

The rapid mixing intensity applied at the facility was less than half that recommended by the

MOE Design Guidelines. Bench scale testing, while showing some small differences in

treated water turbidity, was inconclusive. It was recommended that, if the issue of uniform

coagulant dispersion arises in the future, pilot scale testing be conducted to evaluate the

impacts of increasing the rapid mixing intensity on the finished water quality.

Streaming Current Monitors for Process Control

Two streaming current monitors (SCM), installed in one flocculation tank of each plant train,

were not being used for operational control. To determine how the SCM could be applied to

operating practices, a desktop evaluation of the accumulated historical data was performed.

The data review indicated that the SCM output signal correlated to the raw water turbidity.

No other significant correlation to either raw water parameters or operating variables was

observed. It was recommended that a program be developed to familiarize facility staff with

adjusting the coagulant dose using the SCM and to incorporate the use of the SCM into

everyday operations; ultimately, the SCM could be used to automatically control coagulant

dosing.

Bench Scale Evaluation of Flocculation Mixing Intensity

The first phase of the study had looked at the mixing intensities, G values, being provided by

the mixing equipment in the flocculation tanks in each of the plant trains. The calculated G-

values ranged from 84 to 101 s-1

, which is typical of mixing intensities recommended for

direct filtration plants. The Gt values (mixing intensity multiplied by retention time in the

floc tank) were also determined for both the current average day flow of 10,260 m3/d and the

plant design flow of 60,480 m3/d. At the current average day flow, the Gt values were

extremely high, ranging from 884,394 to 1,020,875 in Plant 1 and from 510,104 to 588,823 in

Plant 2 depending on the water temperature. The recommended design value at the time for

Gt for flocculation was between 50,000 and 125,000 (MOE, 1982).

To determine if the flocculation mixing intensity was affecting the finished water quality, a

bench scale investigation consisting of a jar test was performed. The jar test performed

involved adding equal amounts of coagulant to two jars, providing equal rapid mix intensity

and time, followed by providing 20 minutes or 2 hours of flocculation time. The treated water

was then filtered and tested for turbidity and aluminum residual.

The results obtained showed a large increase in filtered soluble aluminum residual with the

increase in flocculation time. These retention times were sometimes experienced in the plant.

The long retention time may be breaking up the floc causing it to resolubilize.



Summary

In this case study, jar testing was successful for evaluating coagulant chemicals and dosages;

however, bench-scale testing of the rapid mix was inconclusive and experiments with

flocculation mixing could not be repeated at full-scale conditions. To further improve facility

performance, the construction of a pilot plant was recommended for optimizing coagulant

dosages on an on-going basis. A pilot plant could also be used to investigate the effects of

flocculation mixing intensity and duration on finished water quality, as well as investigate

treatment options for other operational problems identified during the study.

6.5 REFERENCES

American Water Works Association (1995). Water Treatment, 2nd

Ed. AWWA. ISBN 0-

89867-789-0.



AWWA (2007). M37: Operational Control of Coagulation and Filtration Processes. 2nd

Ed.

AWWA. ISBN 978-1-58321-055-0.

California State University (1999). Water Treatment Plant Operation: Volume I. 4th Ed.

DeWolfe, J., B. Dempsey, M. Taylor and J.W. Potter (2003). Guidance Manual for

Coagulant Changeover. AwwaRF & AWWA. Denver, CO. ISBN 1-58321-289-2.

Hargesheimer, E.E., N.E. McTigue, J.L. Mielke, P. Yee, and T. Elford (1998). Tracking

Filter Performance with Particle Counting. Journal AWWA, Vol. 90 No. 12. December

1998.


January 1975.

Hudson, H.E. Jr. (1981). Water Clarification Processes: Practical Design and Evaluation.

Van Nostrand Reinhold Co. ISBN 9780442244903.

MOE (1982). Guidelines for the Design of Water Treatment Works. Publications Ontario.

ISBN 0-7778-4878-3.


3.

MOEE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process

Audits.

MWH (2005). Water Treatment Principles and Design. 2nd


ISBN 0-471-11018-3.

Teefy, S.M. (1996). Tracer Studies in Water Treatment Facilities: A Protocol and Case

Studies. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-857-9.





XCG Consultants Ltd. (1999). Report for R. H. Neath WPP Optimization Practices

Study, prepared for Owen Sound Public Utilities Commission.


CHAPTER 7CLARIFICATION

CLARIFICATION

7.1 Introduction ............................................................................................................ 7-1

7.2 Clarification ............................................................................................................ 7-1

7.2.1 Purpose and Types of Clarification ......................................................... 7-1



7.3 Optimization Techniques ....................................................................................... 7-6

7.3.1 Optimizing Flow Arrangements .............................................................. 7-6

7.3.2 Controlling Plant Flow Rate .................................................................... 7-7

7.3.3 Optimizing Sludge Removal .................................................................... 7-7

7.3.4 Tracer Testing .......................................................................................... 7-7

7.3.5 Stress Testing ........................................................................................... 7-8

7.4 Case Histories ......................................................................................................... 7-8

7.4.1 Town of Slave Lake, Alberta – Optimization and Upgrading Study ....... 7-8

7.4.2 Newport News, Virginia – Sludge Control Study ................................... 7-9

7.5 References ............................................................................................................ 7-11

CHAPTER 7. Clarification 7-1


CHAPTER 7

CLARIFICATION

7.1 INTRODUCTION

Clarification is the process used to remove suspended solids following coagulation and

flocculation and reduce solids loading on subsequent filtration processes. This can be

achieved by gravity sedimentation or flotation. Clarification is also used to remove the

chemical precipitates formed during the lime-soda softening process.

This chapter describes different types of sedimentation basins or clarifiers. It also provides

information about methods that can be used to evaluate and improve process performance.

Optimization of the sedimentation process can involve modifying flow control structures

(such as effluent weirs or baffles within the clarifiers) and operational practices (such as

sludge removal frequency or coagulant chemical dosage) to improve performance with

respect to solids removal.

7.2 CLARIFICATION

7.2.1 Purpose and Types of Clarification

As noted above, the purpose of the clarification process is to reduce the solids loading onto

the filtration processes which follow. Clarification processes can be categorized into the

following general types.

Horizontal flow sedimentation basins are generally classified as either rectangular or

circular centre-feed types. They are typically large concrete or steel basins, designed to keep

the velocity and flow distribution as uniform as possible. A diagram of a typical

sedimentation tank is shown in Figure 7-1.

Figure 7-1 – Typical Horizontal Flow Sedimentation Basin



Upflow reactor and sludge blanket clarifiers include several types of solids contact units,

such as simple upflow sludge blanket clarifiers, pulsed upflow sludge blanket clarifiers, and

reactor clarifiers. These units combine coagulation, flocculation and clarification in a single

unit. They generally allow the controlled removal of solids and are usually proprietary

designs. The advantages of the solids-contact clarifier include a good turbidity removal in a

compact and economical design. The disadvantages are that they are sensitive to changes in

flow and temperature, and time is required to build up the necessary sludge blanket. They

also have relatively high maintenance costs and require greater operator skill than for simple

sedimentation basins.

Adsorption clarifiers combine coagulation, flocculation and clarification processes in a

single upflow clarifier. Coagulant is added to the raw water, which enters at the bottom of the

unit and passes through a bed of plastic media that floats on the surface of the water. The

solids adhere to the media, which results in relatively high removal rates (AWWA, 1995).

The media must be cleaned when the solids accumulation results in excessive head loss, or

when effluent quality becomes unacceptable.

Dissolved air flotation (DAF) is a process in which dissolved gases under pressure are

released as micro-bubbles and attach to solid particles causing them to rise to the surface

rather than settle. The sludge that accumulates on the surface is called “float”, and must be

removed either by flooding the basin to overflow the float or by mechanical scraping.

Sand-ballasted flocculation-sedimentation or high-rate microsand sedimentation involves

the addition of ballast (usually microsand) that attaches to the floc and increases the settling

velocity of the floc by increasing its density. These are proprietary systems that have surface

loading rates that are several times greater than those used for conventional sedimentation

basins.

Inclined plates or tube settlers can be used with rectangular and circular sedimentation

basins and are designed to increase settling efficiency. These types of equipment provide a

high ratio of effective settling surface area per unit volume of water and reduce the distance

that floc have to fall. Settled particles collect on the inside surfaces of the tubes or plates, and

slide down the surface to settle at the bottom of the tank.

Additional information regarding the design of clarification processes is provided elsewhere

(MOE, 2008; MWH, 2005; AWWA, 1995).


In conventional surface water treatment plants, clarification is one of the multiple barriers

normally provided to reduce the potential of turbidity and microorganisms to pass through the

treatment process and into the distribution system. The performance of the clarification

process is assessed based on achieving a settled water turbidity of less than 1 NTU 95 percent

of the time when the average raw water turbidity is less than or equal to 10 NTU, and less

than 2 NTU 95 percent of the time when the average raw water turbidity exceeds 10 NTU

(USEPA, 1998).

Criteria to be used to evaluate clarification processes as part of the major DWS component

evaluation are shown in Table 7-1. The projection of sedimentation basin capacity is

primarily based on surface overflow rate (SOR), with consideration given for depth and

sludge removal characteristics. Greater depths generally result in more quiescent conditions



and allow higher SORs to be used. Sludge removal mechanisms should also be considered

when establishing an SOR for projecting sedimentation capability. If sludge is manually

removed from the sedimentation basin(s), additional depth is required to allow volume for

sludge storage and the selected SOR should therefore be lowered.

In cases where flocculated colour (i.e. a lightweight floc) and/or low water temperatures are

encountered, the projected capacity should be based on the lower SORs in Table 7-1. Criteria

are shown for rectangular and upflow solids contact units with or without tube settlers.

Table 7-1 – Clarification – Criteria for Major DWS Component Evaluation Using the

Performance Potential Graph Rating System

Conventional (circular and rectangular) and Solids Contact Units (Cold Water < 5°C)

Conventional

Depth (m)

Solids

Contact

Depth (m)

Operating Mode

Turbidity Removal

SOR (m/h)

Softening

SOR (m/h)

Colour Removal

SOR (m/h)

3.0 3.7 – 4.3 1.2 1.2 0.7

3.7 – 4.3 4.3 – 4.9 1.5 1.8 1.0

> 4.3 > 4.9 1.7 2.4 1.2

Conventional (circular and rectangular) and Solids Contact Units with Vertical (> 45°)

Tube Settlers

Depth (m)

Operating Mode

Turbidity Removal

SOR (m/h)

Softening

SOR (m/h)

Colour Removal

SOR (m/h)

3.0 2.4 3.7 1.2

3.7 – 4.3 3.7 4.9 1.8

Higher SORs than those shown in Table 7-1 can be used to project capacity in cases where

plant data demonstrate that a sedimentation basin achieves the desired settled water turbidity

performance goals at the higher loading rates.

Loading rates for projecting performance potential of other settling processes are discussed

briefly below (MOE, 2008).

Dissolved Air Flotation – The retention time and loading rates for DAF units largely

depends on the water being treated, the nature of the contaminant being removed, the

coagulants used and the design of the DAF process. Traditional loading rates have been in the

10 to 12 m/h range; however, higher loading rates, up to 29 m/h, can be used if confirmed

through appropriate pilot testing.



Ballasted Flocculation and Clarification – Typical surface loading rates are 35 to 73 m/h.

A specific combination of chemicals may be needed for effective treatment depending on raw

water characteristics.

Adsorption Clarifiers – These systems are proprietary; SORs are in the range of 19.5 to 25.5

m/h.

Table 7-2 presents monitoring recommended, in terms of sampling locations and analyses, in

order to evaluate the performance of the clarification process.

Table 7-2 – Clarification – Recommended Monitoring to Evaluate Performance


Raw water Continuous monitoring Temperature

Turbidity

Influent to

Clarification

Continuous monitoring Flow rate

Grab sample Turbidity

Alkalinity

Effluent from

Clarification

Continuous monitoring or Grab sample Turbidity

Process waste

stream (settled

sludge)

Continuous monitoring or Grab sample Flow or volume

Total suspended solids

Chlorine residual (if applicable)

Additional monitoring may be required for proprietary systems; the evaluator should review

manufacturer’s literature for recommended process monitoring parameters.

Figure 7-2 presents a process schematic of a typical clarification process, along with the

identification of various sampling locations.

From Coagulation /

FlocculationClarifier Effluent

Clarifier Blowdown

(settled sludge)

Clarifier Influent

Sample Location

Clarification Effluent

Sample Location

Sludge Sample Location

Clarifier

Figure 7-2 – Clarification – Process Schematic and Sampling Locations



In addition to the recommended sample locations and analyses presented in Table 7-2,

consideration should also be given to the performance of coagulation and flocculation (see

Chapter 6) when evaluating the performance of clarification processes.


A summary of symptoms and causes of common problems encountered with clarification

processes is presented in Table 7-3.

Table 7-3 – Clarification – Symptoms and Causes of Common Problems


Potential Impacts

Common Causes

Uneven flow

distribution between

clarifiers

Some clarifiers are overloaded,

potentially resulting in poor

effluent quality due to limited

settling.

Other clarifiers are underloaded,

potentially resulting in stagnant,

septic conditions, reducing effluent

quality due to resuspension of

sludge and/or causing tastes and

odours.

Uneven rate of effluent flow

between clarifiers visible in

effluent launders.

Uneven clarifier weir levels.

Different clarifier weir lengths.

Poor hydraulics of upstream flow

control devices.

Hydraulic short-

circuiting within

clarifiers

Increased clarifier effluent

turbidity.

Regions of high flow and poor

settling within clarifier.

Erratic clarifier performance.

Poor design of inlet structures and

in-clarifier baffling (Section 7.3.1).

Density currents due to temperature

gradients, and/or wind-driven

circulation cells (Section 7.3.1).

Long sludge

retention time Deep sludge blanket, resulting in

increased effluent turbidity due to

floc carryover, especially during

periods of increased demand (high

flow).

Development of septic sludge,

reducing effluent quality and

potentially causing taste and odour

problems.

Poor control of sludge pumping

(Section 7.3.3).



Table 7-3 – Clarification – Symptoms and Causes of Common Problems (cont’d.)


Potential Impacts

Common Causes

Short sludge

retention time Low sludge solids concentration,

resulting in increased hydraulic

loading on residuals handling

processes.

Little to no sludge blanket.

Poor solids removal performance.

Poor control of sludge pumping

(Section 7.3.3).

Poor clarification

performance not

attributable to

problems identified

above

Removal efficiencies below typical

removal rates, resulting in poor

effluent quality.

Changes to raw water quality (e.g.

cold water temperatures leading to

reduced settling rates).

Floc carryover due to poor

coagulation/flocculation

performance (Chapter 6).

Clarification process hydraulically

overloaded as a result of operating

at flows exceeding design values.

7.3 OPTIMIZATION TECHNIQUES

7.3.1 Optimizing Flow Arrangements

Short-circuiting occurs when water bypasses the normal flow path through the basin and

reaches the outlet in less than the design detention time.

Inlets and outlets should be designed to ensure that water is distributed evenly across the

clarifier/settling tank at uniform velocities to minimize short-circuiting.

In horizontal-flow basins where problems with flow distribution have been identified, baffles

may be installed at the inlet and outlet to improve flow conditions. In evaluating different

inlet baffling methods, consideration should be given to:

The number of ports provided;

The distribution of the ports (e.g. uniform distribution of flow across the baffle wall)

Head loss through the ports; and

The potential for floc breakage across the baffle wall.

Density currents caused by changes in water temperature, wind effects, and solids

concentrations should also be minimized to prevent short-circuiting. The provision of a cover

or structure over the sedimentation basin can reduce the impact of the sun and wind on

settling efficiency. Installation of baffles or diffuser walls can promote mixing of the density



current with the ambient water, improving the flow distribution in the tank and the efficiency

of hydraulic performance (MWH, 2005).

Hydraulic modelling packages (e.g. computational fluid dynamics) can be used to evaluate

existing in-tank hydraulics (see Chapter 4). Calibrated models can then be used to project the

impact of inlet and outlet structure upgrades or modifications on sedimentation performance.

Tracer testing can be used to support hydraulic modelling to evaluate hydraulic conditions.

After modifications are implemented, tracer testing can also be used to verify the impact of

these changes on hydraulic performance (see Chapter 4).

7.3.2 Controlling Plant Flow Rate

In many small plants that are operated less than 24 hours each day, plant flow rate is the

primary means for process control. At these plants, an excessive hydraulic loading rate on the

sedimentation process can be avoided by operating at a lower flow rate for a longer period of

time. Continuous flow through the sedimentation units is generally a preferable operating

mode, especially for upflow units where start-up can disrupt the sludge blanket as well as

take time to stabilize operation.

Controlling plant flow rates provides an option to meet more rigorous performance

requirements with existing units without major capital improvements. The capability to

reduce plant flow rate to improve performance is offset by the need to staff the plant for

longer periods of time, which adds to operating costs. Therefore, both options should be

considered.

7.3.3 Optimizing Sludge Removal

Sludge needs to be removed from conventional sedimentation basins frequently enough to

prevent solids carryover to the filters. To optimize sludge removal, the amount of sludge

accumulated in a basin can be determined by using a sludge depth measuring device such as a

sludge judge.

For basins with mechanical and/or automatic sludge removal systems, the duration of sludge

pumping can be determined by collecting samples during draw-off (e.g. every 30 seconds)

and determining when the sludge begins to thin. A centrifuge, graduated cylinder or Imhoff

cone can be used to observe the density changes (USEPA, 1998).

Sludge control is very important in the operation of reactor type upflow sedimentation basins

that operate using a sludge blanket. The reactor section of the basin must be monitored daily

and the appropriate amount of sludge removed from the basin to maintain the optimum

reactor concentration and sludge blanket depth. Inadequate monitoring of the basin can lead

to a loss of the sludge blanket over the weirs, which significantly impacts basin and,

ultimately, filter performance.

7.3.4 Tracer Testing

As discussed in Chapter 4, tracer test techniques are used to evaluate the hydraulic

characteristics of unit process tanks. For sedimentation basins, tracer testing can be used to

identify hydraulic short-circuiting and locate dead-zones, identify density currents and sludge

blanket carryover problems, and evaluate baffling arrangements (MOE et. al., 1999).



Additional information regarding the conduct of tracer tests is provided in Chapter 4.

7.3.5 Stress Testing

Stress testing involves increasing the hydraulic loading to the existing process in order to

identify the “failure point”. For clarification processes, the failure point can be defined either

as an exceedance of the settled water turbidity goal, or excessive head loss or turbidity

breakthrough in the subsequent filtration process.

Both continuous monitoring and grab sampling are required to evaluate sedimentation

process performance during a stress test. For example, frequent grab sampling for testing the

settled water turbidity or continuous monitoring of filter effluent turbidity are needed to

identify the “failure point”. In addition, the sludge blanket depth should be measured

regularly during the stress test.

Criteria for evaluating performance of clarification processes in terms of settled water

turbidity are provided in Section 7.2.2. More detailed information regarding typical stress

testing protocols can be found in Chapter 4.

7.4 CASE HISTORIES

7.4.1 Town of Slave Lake, Alberta – Optimization and Upgrading Study

The following case study is based on information presented in Drachenberg et. al. (2007).

System Description

The Town of Slave Lake (the Town) is located in the north-central area of the province of

Alberta and receives its water supply from Lesser Slave Lake. The existing conventional

WTP has a rated capacity of 7 ML/d and consists of coagulation, flocculation, clarification

and dual media filtration, followed by pH adjustment, fluoridation and disinfection.

The source water posed many treatment challenges. Periodic high winds caused turbidity

increases from 6 NTU to 100 NTU within a period of hours. Heavy rains also caused

significant increases in colour and turbidity. During periods of elevated raw water colour and

turbidity, reducing plant production was the only means for ensuring adequate settling and

filter performance.

Several operating problems associated with the original design of the WTP had been

identified and a conversion to membrane filtration was being considered to meet anticipated

changes to provincial regulations and guidelines. As such, a series of studies and reports were

commissioned to evaluate the plant’s ability to meet new treated water requirements and to

identify improvements needed to enhance treatment effectiveness.


The objective of the WTP study was to improve plant performance to meet a filtered water

turbidity objective of less than 0.05 NTU and particle counts of less than 20 particles larger

than 2µm/mL with a minimum of upgrades.



An assessment of available plant operating data, water quality data and hydraulic data was

undertaken. The results of the data review led to the development of bench-scale and full-

scale studies to define the most appropriate upgrade path for the Town.

As part of the bench-scale studies, jar testing was conducted to determine optimum coagulant

chemical dosages and verify the effectiveness of the existing mixing equipment. The results

of the jar testing in conjunction with various pilot-scale studies led to the adoption of an

enhanced coagulation approach consistent with the strategy presented in the Enhanced

Coagulation and Enhanced Precipitative Softening Guidance Manual (USEPA, 1999).

A tracer study was conducted for the flocculation and sedimentation tanks to establish the

effective residence times. Short-circuiting of water in the sedimentation tank was confirmed.

The existing sedimentation tanks were not equipped with mechanical sludge removal systems

and had to be cleaned manually twice per year.

As part of the upgrading plan, modifications to the existing sedimentation tanks were

proposed, including upgrades to improve inlet flow distribution, re-alignment of the

collection troughs, installation of tube settlers and automatic sludge collection equipment.

Summary

As a result of the improvements completed as part of the upgrade plan as well as the

implementation of enhanced coagulation, the WTP achieved all of its treatment goals. The

upgrades also allowed the Town to extend the service life of the treatment facility beyond its

original design period, which could postpone future upgrades, including the installation of

membrane filtration, by several years.

7.4.2 Newport News, Virginia – Sludge Control Study

The following case study is based on information presented in Hoehn et. al. (1987).

System Description

The City of Newport News (the City) owns and operates two WTPs. Both the Lee Hall WTP

and the Harwood’s Mill WTP are conventional plants that draw raw water from the

Chickahominy River. The raw water source is generally high in organic content, moderately

coloured, and has low alkalinity.

In 1982, the City discontinued pre-chlorination at the WTPs to reduce THM formation. Since

then, problems associated with the deterioration of alum sludge in sedimentation basins had

been observed, as well as occasional declines in settled water quality. Laboratory and field

studies showed that anaerobic conditions had developed in manually cleaned sedimentation

basins (but not in those that were mechanically cleaned), allowing manganese to be released

from the sludge into the overlying water.

As such, a study was designed with the following three objectives:

To contrast rates of development of anaerobic conditions in manually cleaned and

mechanically cleaned sedimentation basins;



To determine the extent to which anaerobic conditions in the sedimentation basins

altered settled water quality, filter performance and sludge dewatering characteristics;

and

To evaluate the benefits of pre-oxidation of the raw water with an oxidant that would

not contribute to THM formation (chlorine dioxide).


Laboratory studies were conducted to evaluate changes in sludge dewatering characteristics

and in the quality of the supernatant. Field studies were conducted which measured dissolved

oxygen (DO) concentration profiles across the depth of the sedimentation basins, as well as

iron, manganese and TOC in the clarifier effluent. Sludge dewatering characteristics were

also evaluated during the field studies by the specific resistance test.

The laboratory study indicated that seasonal changes in raw water quality had a significant

effect on sludge and supernatant quality. Concentrations of TOC, iron and manganese in the

supernatant were much higher in samples collected in summer (June) compared to those

collected in spring (March). It was concluded that the strongly reducing environment that

developed in June were likely created by biological activity that was stimulated either by a

greater concentration of organic matter within the sludge or by an increase in the

biodegradability of the organic matter.

The results of the field studies indicated that the frequency of basin cleaning had a significant

impact on sludge conditions and supernatant quality. Testing was conducted at the Lee Hall

WTP, where one of the basins was manually cleaned approximately every six weeks, whereas

the other was mechanically cleaned for four hours each morning. The manually cleaned basin

had been drained and cleaned only four days before the first DO measurements were made,

yet significant reductions in DO concentrations were observed at depths below 3 m. In

contrast, DO persisted to the bottom of the mechanically cleaned basin (up to 5 m). The data

indicated that the accumulation of sludge, even for a period as brief as a few days, could

create anaerobic conditions in the sludge blanket.

In the third phase of the study, pre-oxidation using chlorine dioxide was initiated at the

Harwood’s Mill WTP. Improvements in performance were noted, including better manganese

removal, faster sludge dewatering rates and longer filter runs.

Summary

The results of the study confirmed the effectiveness of chlorine dioxide pre-oxidation as an

alternative to no pre-oxidation. Although the study notes that the results are likely site-

specific, the benefits to WTP performance were noted through the following improvements:

Manganese release from settled sludge to the overlying water was suppressed;

Alum sludge dewatering was improved, due to increased particle size in the settled

sludge when chlorine dioxide was applied; and

The length of the filter runs was doubled, from approximately 30 hours to more than

60 hours.



7.5 REFERENCES

American Water Works Association (1995). Water Treatment – Principles and Practices of

Water Supply Operations. 2nd


Drachenberg, G.E., S. Suthaker and H.C. Suan (2007). “Getting membrane Performance Out

of a Conventional Filtration Plant in a Small Community”, presented at the 2007 American

Water Works Association Annual Conference and Exposition, Toronto, ON.

Hoehn, R.C., J.T. Novak and W.E Cumbie (1987). Effects of Storage and Preoxidation on

Sludge and Water Quality. Journal AWWA, Vol. 79, No. 6. June 1987.


January 1975.


MOEE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process

Audits.



ISBN 0-471-11018-3.


Composite Correction Program. EPA/625/6-91-027.

USEPA (1999). Enhanced Coagulation and Enhanced Precipitative Softening Guidance

Manual. U.S. EPA, Office of Water. EPA 815-R-99-012.


CHAPTER 8 FILTRATION

FILTRATION

8.1 Introduction ............................................................................................................ 8-1

8.2 Granular Media Depth Filters ................................................................................. 8-1

8.2.1 Purpose and Types of Granular Media Depth Filters .............................. 8-1




8.3 Slow Sand Filters .................................................................................................. 8-13

8.3.1 Purpose of Slow Sand Filters ................................................................. 8-13




8.4 Membrane Filters ................................................................................................. 8-17

8.4.1 Purpose and Types of Membrane Filters ............................................... 8-17




8.5 Case Histories ....................................................................................................... 8-24

8.5.1 Racine, Wisconsin – Optimizing Membrane Maintenance ................... 8-24

8.5.2 Fort McMurray, Alberta – Filter Media Optimization and Upgrading

Study ...................................................................................................... 8-26

8.6 References ............................................................................................................ 8-27

CHAPTER 8. Filtration 8-1


CHAPTER 8

FILTRATION

8.1 INTRODUCTION

The purpose of filtration is to remove suspended particulate matter from water. Filtration is a

key component of the multi-barrier approach. All regulated drinking water systems that

obtain water from a surface water source or GUDI source must provide a minimum level of

treatment consisting of chemically-assisted filtration and disinfection or other treatment

capable of producing water of equal or better quality (MOE, 2006).

Filtration processes discussed in this chapter include granular media filtration, slow sand

filtration and membrane filtration. Filtration processes designed for other purposes (e.g.

greensand, granular activated carbon, biologically active filters) are discussed in Chapter 10.

8.2 GRANULAR MEDIA DEPTH FILTERS

8.2.1 Purpose and Types of Granular Media Depth Filters

Granular media filtration is the most widely used filtration process in drinking water

treatment (LeChevallier, 2004). In granular filtration, water passes through a filter consisting

of a packed bed of granular materials. The removal of particles occurs throughout the

granular medium (depth filtration) rather than on the top layer only (cake filtration).

Granular filters can be constructed as monomedium (e.g. silica sand), dual media (e.g.

anthracite coal and sand) and trimedia (e.g. coal, sand and garnet). Granular activated carbon

(GAC) is often used when both the removal of particles and adsorption of organic

compounds, such as taste and odour producing compounds, are desired. The use of GAC for

this purpose is discussed in Chapter 10.

Depending on raw water quality, granular filters can be operated within three different

treatment processes:

Conventional treatment, which includes addition of coagulants, flocculation,

sedimentation and filtration;

Direct filtration, in which the sedimentation step is omitted; or

In-line filtration, in which coagulation and flocculation occur within the influent

piping to a filter.

Conventional treatment is appropriate for most surface water sources, whereas direct and in-

line filtration may be used for raw waters with consistently low levels of turbidity and colour.

Guidance on selecting an appropriate treatment strategy is provided in the Design Guidelines

for Drinking Water Systems, 2008 (MOE, 2008) and Ten State Standards (Recommended

Standards for Water Works, Great Lakes-Upper Mississippi River Board of State Public

Health and Environmental Managers, 2007).



There are two basic modes of filtration control:

Constant rate filtration; and

Declining rate filtration.

In constant rate filtration, the flow to each filter is maintained at as constant a rate as possible,

with clearwell storage absorbing fluctuations in demand and in total filter output (i.e. when a

filter is taken out of service for backwashing). This is typically accomplished by a flow meter

and a flow modulation valve on each filter effluent pipe, or by constant level filtration with

equal flow splitting inlet weirs, a water level sensor, and a flow modulating valve.

In declining rate filtration, the filtration rate is not kept constant. Rather, the rate for a

particular filter gradually decreases as the filter captures particles and the head loss increases.

Using this method, all filters receive water from a common influent channel without any

devices to measure or control the flow to individual filters. Each filter accepts the proportion

of total flow based on its bed condition (e.g. accumulated solids and head loss). As a filter

gets “dirty”, the flow through it decreases. Flow is then redistributed to cleaner filters and

total plant capacity does not decrease. To prevent excessive flow rates from occurring in

clean filters, a flow restricting orifice plate may be placed in the effluent line of each filter.

Regardless of the control strategy used, the system should control the flow to each individual

filter, divide the total flow among the individual filters equally, and accommodate rising head

loss through each individual filter run. Flows to individual filters should remain constant.

Backwashing and changes in demand and should be met as much as possible with clearwell

storage at the plant.

Filters must be backwashed periodically to remove accumulated solids. The need for

backwashing is generally determined based on one of the following criteria: terminal head

loss, a fixed time interval, or a breakthrough of solids (measured as turbidity or particle

counts).


8.2.2.1 Major DWS Component Evaluation

Filter performance should be assessed based on the capability to achieve effluent turbidity of

less than 0.1 NTU continuously to ensure the integrity of filtration as a viable barrier in the

treatment scheme. Operation of filters to produce filtered water quality of less than 0.1 NTU

is attainable by many plants, and provides greater confidence that pathogens, such as

Cryptosporidium oocysts and Giardia cysts, are being removed prior to disinfection, the final

treatment barrier. If particle counters are available, the maximum filtered water measurement

should be less than 10 particles (in the 3 to 18 µm range) per mL (USEPA, 1998).

Projection of filtration capacity is based primarily on hydraulic loading rates, with

consideration given to media type. For example, a monomedium sand filter would be

assessed at a maximum rate of 7 m3/m

2·h (or m/h) because of the susceptibility of this filter

to surface blinding by removing particles at the top of the filter media; whereas a dual or

mixed media filter would be assessed at a higher rate because of the ability to utilize the

solids storage capacity within the anthracite layer.



Limitations caused by air binding can also impact the selected loading rate for projecting a

filter’s performance potential and could bias the selected loading rate toward more

conservative values within each range.

Inadequate backwash or surface wash facilities, rate control systems, media depth and

underdrain integrity are areas that can often be addressed through minor modifications. These

would be assessed during a CPE as performance limiting factors, but are typically not

considered in evaluating the filter loading rate.

Criteria to be used to evaluate filtration processes as part of the major DWS component

evaluation are shown in Table 8-1. Direct and in-line filtration processes should be assessed

based on the same criteria as conventional filtration processes.

Table 8-1 – Granular Media Depth Filtration – Criteria for Major DWS Component

Evaluation Using the Performance Potential Graph Rating System

Characteristic Typical Assessment Criteria

Filtration Rate (m/h)

Monomedium

Dual/mixed media

2 – 7

7 – 18

Backwash Rate (m/h) 37 – 50

Bed Expansion During Backwash (%) 25 – 50

Backwash Duration (minutes) 10 – 15

The rate of filtration should be determined through consideration of such factors as raw water

quality, degree of pre-treatment provided, filter media type(s) and depth, and the competency

of operating personnel. For traditional conventional dual media filter designs with a

maximum filtration rate of 12 m/h, this rate may not be achievable with floc formed from

highly coloured water (MOE, 2008). Higher filtration rates, up to 20 m/h or higher, may be

achievable while still maintaining filtered water quality. The maximum filtration rate to be

used as part of the DWS component evaluation should be assessed based on stress testing.

Continuous effluent turbidity measuring and recording devices should be provided for each

filter (MOE, 2008). Particle counters should be used if it is necessary to analyze the number

and size of particles in the filter effluent at levels below the detectable range of a turbidimeter

(AWWA, 1995). Table 8-2 presents monitoring recommended, in terms of sampling

locations and analyses, in order to evaluate the performance of the filtration process.



Table 8-2 – Granular Media Depth Filtration – Recommended Monitoring to

Evaluate Performance

Location Types of Sample/

Measurement

Parameters/ Analyses

Filter influent Continuous monitoring or


Individual filter Continuous monitoring Loss of head

Flow rate

Filter run time

Individual filter effluent Continuous monitoring Turbidity

Particle counts

Filtered water Grab sample Colour

pH

Alkalinity

Aluminum or iron residual

Microbiological parameters, zooplankton,

etc.

Backwash Continuous monitoring Backwash duration

Washwater flow

Duration and rate of air application (air

scour systems)

Process waste stream

(backwash water)

Continuous monitoring or

Grab sample Flow or volume

Turbidity or total suspended solids


Figure 8-1 presents a process schematic of a typical granular media filtration process, along

with the identification of various sampling locations.



Filter Influent (from clarification or

coagulation/flocculation)

Filter Effluent

Filter Effluent

Sample Location

Filter Influent

Sample Location

Anthracite

Sand

Support Gravel

Underdrain

Figure 8-1 – Granular Media Depth Filtration – Process Schematic and Sampling Locations

8.2.2.2 Field Evaluations

Field evaluations should be conducted to assess the integrity of the filter media, support

gravels and underdrain system for a selected filter. This requires that the filter be drained and

that the evaluation team inspect the media. Additional information on conducting filter

investigations is provided in Section 4.2.4.


Most filtration problems occur in the following major areas:

Chemical treatment before the filter;

Control of filter flow rate; and

Backwashing the filter.

If these three procedures are not performed effectively, the quality of the filtered water, filter

run times, and production will suffer, and additional maintenance problems may occur.

The following are common indicators that proper filter control is not practiced.

Individual filter performance is not monitored;

Rapid increases in overall plant flow rate (poor ramping of filter flow changes) are

made without consideration of filtered water quality;

Filter performance after backwash is not monitored;

Filters are removed from service without reducing plant flow rate, resulting in the

total plant flow being directed to the remaining filters;

Operators backwash filters without regard for filter effluent turbidity; or

Operators backwash at a low rate for a longer period of time, or stop the backwash

when the filter is still dirty to "conserve" water;



Filters have significantly less media than specified, there is damage to underdrains or

support gravel, and/or there is a significant accumulation of mudballs and these

conditions are unknown to the operating staff because there is no routine examination

of the filters;

The purpose and function of the rate control device cannot be described.

Design issues that may contribute to poor performance and that can be addressed through

minor modifications include:

Insufficient freeboard above the filter (particularly in cold water conditions); and

Improper media selection, including media type, depth, effective size, uniformity co-

efficient, or a combination of these factors.

Symptoms and causes of other common problems encountered with granular media filtration


Table 8-3 – Granular Media Depth Filtration – Symptoms and Causes of Common

Problems

Problem Description

Mitigation

Rapid head loss Large floc accumulating on

surface Optimize coagulation/flocculation

(Chapter 6)

Monitor head loss across various

points within the media depth

Mudball formation Floc/media sticking together Improve backwashing (Section

8.2.4.3)

Optimize coagulation/flocculation

(Chapter 6)

Excessive head loss

remaining after filter

backwash

Filter media not clean Check if underdrain system clogged

Check for mudballs

Improve backwashing (Section

8.2.4.3)

Faulty head loss measurement

equipment

Decreased turbidity

removal efficiency with

no increase in influent

water turbidity

Filter cannot hold solids Perform backwash


(Chapter 6)

Filter bed sand boil Backwash rate(s) too high Control backwash rate, surface wash

rate or duration, and time sequence or

duration of backwash (Section 8.2.4.3)



Table 8-3 – Granular Media Depth Filtration – Symptoms and Causes of Common

Problems (cont’d.)

Problem Description

Mitigation

Media loss Media is being lost during

backwash Control backwash rate, surface wash



Decreased turbidity

removal efficiency with

increase in influent water

turbidity

Filter cannot hold solids Optimize coagulation/flocculation to

reduce solids loading (Chapter 6)

Shortened filter runs Decrease in the pre-

treatment performance

resulting in floc carryover

Filtration rates too high

Excessive mudball

formation

Clogging of the filter

underdrain system

Air binding


(Chapter 6)

Reduce filter rates, if possible

Check for clogged or broken

underdrains

See air binding (below)

Air binding (Gas bubbles

accumulate in the filter

between backwashes)

Dissolved air in the water

Increased head loss

Shortened filter runs

Violent agitation during

backwashing, causing loss

of media

Terminate the filter run before the total

head loss is greater than the depth of

the water above the unexpanded media

Allow time for the air to dissipate

before beginning a backwash

Filter bed cracking Filter has reached terminal

head loss resulting in

negative pressures

Terminate the filter run before the total

head loss is greater than the depth of

the water above the unexpanded media

Control backwash rate, surface wash



Check underdrains, or for foreign

objects in the filter which may be

blocking the underdrains

Gravel mounding Backwash rate too high

Underdrain broken

Optimize filter backwash rate

Check underdrains




As noted in the previous section, most operational problems associated with filtration

processes are related to pre-treatment, filter flow control and backwashing. Optimization

techniques to address each of these issues are discussed below.

Extensive information regarding the optimization of filtration processes is available in other

references (AWWA, 2007; Nix and Taylor, 2003; Beverly, 2005; Cleasby et. al., 1992;

Amirtharajah et. al., 1991; Hess et. al., 2002; Patania et. al., 1995).

8.2.4.1 Optimizing Chemical Pre-Treatment

Proper chemical pre-treatment of the water prior to filtration, as previously discussed, is the

key to acceptable filter performance. For waters that are properly chemically conditioned,

acceptable performance can be achieved even at higher filtration rates.

Floc should be strong enough not to shear apart when subjected to the hydraulic forces occurring

within the filter bed, and the settled water turbidity applied to the filter should be low enough to

provide reasonable filter runs between backwashes. If weak floc is a problem, even after

seemingly good pre-treatment, it may be beneficial to use a filter aid polymer to strengthen the

floc. Testing of a filter aid polymer can be accomplished either through jar testing, pilot studies or

full scale trials.

A number of chemical pre-treatment optimization strategies were presented in Chapter 6,

including the use of jar testing, zeta potential, particle counters, streaming current monitors,

etc. In addition to these tests, the filterability of water to which coagulant has been added can

be measured to determine how efficiently the coagulated water can be filtered.

The filterability test measures the amount of water filtered in a given time when flocculated plant

flow (i.e. before sedimentation) is passed through a small diameter tube known as a “pilot filter”.

The pilot filter usually contains the same type of filter media used in the plant filters and is

equipped with a recording turbidimeter to continuously monitor the filtered water effluent. The

amount of water passing through the filter before turbidity breakthrough occurs can be correlated

to how well the plant filters will operate under the same coagulant dosage.

The water used in the pilot filter is usually the actual coagulated/flocculated water from the plant;

however, the test can also be applied to settled water supernatant from jar testing trials. Because

the test takes much less time than it would for the coagulated and flocculated water to pass

through the full-scale plant (e.g. several hours retention time in sedimentation basins and filters),

changes in coagulant dosages can be applied as raw water quality changes, preventing

deterioration of plant effluent quality. This test is particularly useful for direct filtration plants,

where it is essential to properly control the chemical dosage in the short time span between

application of the chemicals and the point where the water reaches the filters.

8.2.4.2 Improving Filter Control

The most important aspect of flow rate control related to filter performance is minimizing the

magnitude of a change in flow rate and the speed at which the change occurs (Renner et. al.,

1990; Cleasby et. al., 1963). Rapid, high magnitude flow rate increases cause a large number

of particles to be pushed through the filter as evidenced by significant increases in turbidity.

This breakdown in filter performance, which allows previously contained/removed particles



to pass into the distribution system, disrupts the continuous performance that is required in

water treatment. Since filtration is the most effective barrier within the treatment system to

cysts such as Cryptosporidium, even short-term performance problems can potentially expose

consumers to significant concentrations of cysts. These performance failures can occur even

when the finished water turbidity objectives are being met.

Filtration rate changes most often occur when:

A filter is removed from service for backwashing;

High volume constant speed raw water pumps are cycled on and off;

A filter is started when it is dirty; or

A filter rate controller is malfunctioning.

Removing a filter from service for washing and directing the entire plant flow to the

remaining filter(s) causes an instantaneous flow increase on the remaining filters, causing

attached particles to be swept out of the filter. This can be prevented by lowering the plant

flow rate prior to removing the filter from service, thereby controlling the hydraulic loading

on the filters remaining in service.

Starting dirty filters results in a rapid increase in flow rate and subsequent poor filtered water

quality. Backwashing of filters prior to returning them to service is essential to maintaining

the integrity of the filtration process.

Rapid changes in plant influent flow by starting and stopping constant speed raw water

pumps also hydraulically pushes particles through filters. This may be prevented by using a

control valve (automatic or manual) to slowly adjust plant influent flow rate or by

installing/modifying pumps with variable frequency drives.

Filter control valves should not leak. Malfunctioning filter rate control valves can result in

rapid changes in filter flow rate. Proper installation and an on-going preventive maintenance

program are necessary to keep the valves in good working order and avoid this source of poor

filter performance. If the hydraulic loading rate that the filters are expected to handle is too

high, reduction of flow rate to the plant should be considered.

The use of a low dose of filter aid polymer can improve filtered water quality in dual or

mixed media filters; however, these products, while effective, are very “sticky” and can

quickly cause surface blinding of a filter when used inappropriately. They should therefore be

used at optimum doses (generally less than 0.1 mg/L) to avoid excessively short filter runs.

Polymer-based coagulants, such as polyaluminum chloride, can be used as a filter aid

provided the dose does not exceed 5 percent of the initial coagulant dose. The optimum

dosages can be determined using jar testing (see Chapter 4). These products are subject to

shearing because of their long polymer chains and should be fed at points of low turbulence,

such as flocculation basins or sedimentation basin effluent pipes or channels. Filter

backwashing also needs to be operated optimally to ensure removal of these products.



8.2.4.3 Optimizing Backwash Processes

Filters must be backwashed periodically to prevent accumulated particles from washing

through the filter, to prevent the filter from reaching terminal head loss, to prevent

compaction of the media or to prevent excessive biological growth in the media. Filters

should be backwashed based on effluent turbidity if breakthrough occurs before terminal

head loss to prevent poor filtered water quality. For example, particles that are initially

removed by the filter are often "shed" when velocities and shear forces increase within the

filter as head loss accumulates (e.g. filter becomes "dirty").

Operators should reduce or limit the duration of the filtration cycle prior to bed exhaustion or

maximum head loss. One approach that can be used as a starting point when assessing the

proper duration for a filter run is to determine the unit filter run volume (UFRV). UFRV

varies according to site-specific conditions, but a UFRV of approximately 200 m3 per m

2 of

filter area per cycle can be used as an initial assessment. This corresponds to filter runs of 20

to 40 hours at filtration rates of 10 m/h and 5 m/h, respectively. Net water production (UFRV

less the amount used for backwashing) should also be considered. Very long filter runs (e.g.

in excess of 90 hours) should be avoided because they can make filters difficult to clean

during backwash due to compaction of the media and can also allow an increase in biological

growth on the filter (Logsdon et. al., 2002).

Inadequate washing, both in terms of rate and duration, can also result in a residual

accumulation of particles in the filter, resulting in poor filtered water quality when filtering is

resumed.

The filter backwash duration and intensity should be great enough to clean the filter, but not

so great as to damage the support gravels/underdrain system or to blow media out of the

filter. The length of wash should be long enough to produce clean spent backwash water,

because inadequate washing can result in a degradation of filter performance and the possible

formation of mudballs. The accumulation of mudballs takes up effective filter surface area

and raises the filtration rate through those areas of the filter where water can still pass. The

filter can also reach a point where minimal additional particles can be removed because

available storage sites within the media already have an accumulation of filtered particles. It

should be noted that excessively long backwashes may lead to increased residuals

management volumes and handling costs.

In some cases, changing the rate at which backwash water is throttled back can optimize

mixing at the interface between different layers of filter media and improve filter

performance.

Figure 8-2 shows a profile of turbidity in spent backwash water as a function of time. This

type of graph can be developed as part of a special study or field investigation and may assist

in the determination of optimum backwash duration. As shown in the graph, turbidity in

spent backwash water may peak at levels greater than 300 NTU depending on the pre-

treatment processes used and raw water conditions, but generally decrease to below 10 NTU

within 6 to 8 minutes of backwashing (Wolfe, 2003).



0

50

100

150

200

250

300

350

400

450

0 1 2 3 4 5 6 7 8 9 10Time (min.)

Tu

rbid

ity

(N

TU

)

Figure 8-2 – Filter Backwash Turbidity Versus Time

Adapted from Filtration Fundamentals (Wolfe, 2003)

Other special studies that could also be conducted to evaluate the effectiveness of

backwashing include a time versus turbidity profile conducted on filters before and after

backwashing. Acceptable performance is judged to be an increase in filtered water turbidity

of less than 0.2 to 0.3 NTU for less than 10 minutes following a backwash. An example of

unacceptable filter performance is depicted in the turbidity versus time graph presented in

Figure 8-3.

As shown, a significant breakthrough of turbidity occurred after the backwash (e.g., turbidity

increased to 24 NTU). Samples taken from the clearwell at the same time showed turbidity

values of 6.3 NTU, far in excess of regulatory criteria for finished water turbidity.

At some plants where high quality filtered water cannot be achieved (after the filter is placed

into service), modifications allowing filter to waste capability, or an equivalent procedure,

during filter ripening should be implemented. This allows directing the initial filtered water

to a drain until quality improves to the extent that the water can be redirected to the clearwell.

Another parameter that should be monitored after backwashing is the initial filtering head

loss which can give an indication of the “cleanliness” of the filter.



Figure 8-3 – Filter Effluent Turbidity Versus Time

The investigation should determine whether inadequate washing is caused by a design or an

operational limitation. The filter should be probed periodically (semi-annually or annually) to

inspect for support gravel problems and to check media depths. Other field evaluations, such

as bed expansion and rise rate, that can be conducted to determine the capability of backwash

facilities were discussed in Section 8.2.2.2.

Operating procedures should be developed to describe consistent methods of backwashing

filters. The procedure should include measures to prevent rapid flow rate increases to the

remaining filter(s), to ensure the filter is properly cleaned, and to prevent damage to the filter

by operating valves too quickly. The method of returning a filter to service should also be

described because this is another time when degraded filter performance can occur. This can

be minimized by optimizing coagulation chemicals and filter aid dosages and by increasing

the filtration rate gradually when returning a recently washed filter to service. Additional

information is provided in Logsdon et. al. (2002).

8.2.4.4 Optimizing Filter Configuration

The type and size of media affects filter throughput, performance and head loss.

Characteristics such as media size, shape, composition, density, hardness and depth can be

considered during optimization, although some of these parameters are difficult to change as

part of an optimization program. If an issue is identified, it can be considered as part of

longer term planning for filter upgrades.

The most common types of media in granular filters are anthracite and sand. Problems may

arise with the filter due to improper media selection. If the media grain size is too small, head

loss during the filter run will increase. If the media grain size is too large, smaller particulate



matter in the filter influent may not be removed effectively. Additional information regarding

the selection and design of media in granular filters is provided in MOE Design Guidelines

(MOE, 2008).

8.2.4.5 Stress Testing

As discussed in Chapter 4, stress testing can be used to quantify the capacity and

performance of the filter under high flow or solids loading conditions. Temporary changes to

operation for experimental purposes should be discussed with the Ministry of the

Environment (local MOE District Office) before testing is undertaken. During the test, the

flow rate to each filter should be incrementally increased. Effluent quality parameters (e.g.

turbidity and/or particle counts) are monitored and compared to the required effluent quality.

The capacity of the filter is assessed based on the ability of the filter to meet effluent limits

for turbidity at increasing flow rates.

Incremental solids loading impacts can be used to assess the filter response to higher solids

loading rates due to challenging conditions (i.e. increased sedimentation effluent turbidity

levels due to upsets).

8.3 SLOW SAND FILTERS

8.3.1 Purpose of Slow Sand Filters

Slow sand filtration involves passing water through a sand filter by gravity at a very low filtration

rate (e.g. less than 0.4 m/h), generally without the use of coagulation pre-treatment. The filter

typically consists of a layer of sand supported on a layer of graded gravel. The use of a slow sand

filtration process is limited by the quality of raw water sources (or influent water after pre-

treatment) having turbidity of less than 10 NTU and colour less than 15 TCU (MOE, 2006).

Design criteria for slow sand filters are provided in the Design Guidelines for Drinking Water

Systems, 2008 (MOE, 2008). Slow sand filtration systems can be difficult to optimize after they

are designed. Proprietary enhanced slow sand filtration technologies are available that can be used

for a wider range of applications than conventional slow sand filter designs.

Removal of particles by slow sand filtration occurs predominantly in a thin layer on top of

the sand bed. This biologically active layer is termed schmutzdecke. As operation progresses,

deposited materials and biological growth on the sand medium increase the head loss across

the filter. When the head loss reaches the operational limit (normally 1 to 2 m), the filter is

removed from service. It is then usually cleaned by scraping away some of the accumulated

material and sand from the top layer of the sand bed, before being returned to service. A

typical filter run could be from one to six months, depending on raw water quality and

filtration rate (LeChevallier, 2004).


As noted in Section 8.2.2, the projection of filtration capacity is based mainly on hydraulic

loading rates and the ability to meet filter effluent turbidity objectives. The operational

guidelines for slow sand filters specified in the Disinfection Procedure (MOE, 2006) include

the following criteria:

Maintain an active biological layer;



Regularly carry out effective filter cleaning procedures;

Use filter-to-waste or an equivalent procedure during filter ripening periods;

Continuously monitor filtrate turbidity from each filter or take a daily grab sample;

and

Meet the performance criterion for filtered water turbidity of less than or equal to 1.0

NTU in 95 percent of the measurements each month.

Criteria to be used to evaluate slow sand filtration processes as part of the major DWS

component evaluation are shown in Table 8-4.

Table 8-4 – Slow Sand Filtration – Criteria for Major DWS Component Evaluation

Using the Performance Potential Graph Rating System

Characteristic Typical Assessment Criteria (MOE, 2008)

Filtration Rate (m/h) 0.04 – 0.4

Sand Media

Depth (m)

Effective Size (mm)

Uniformity coefficient

0.75 – 1.5

0.15 – 0.30

< 2.5

Higher filtration rates than those shown in Table 8-4 may be used in installations where pre-

treatment processes are provided and/or as demonstrated through pilot studies.

Because of the selective mechanisms of slow sand filtration processes, filter effluent turbidity

levels exceeding 1.0 NTU can occur as a result of passage of inorganic particles through the

filter without influencing the effective removal of harmful organisms. Therefore, turbidity

may not be a suitable surrogate for evaluating removal of pathogens by slow sand filtration.


order to evaluate the performance of the slow sand filtration process.



Table 8-5 – Slow Sand Filtration – Recommended Monitoring to Evaluate Performance


Measurement

Parameters/ Analyses

Raw water Continuous monitoring Turbidity

pH

Temperature


Grab sample Colour

Total and/or dissolved organic carbon

Dissolved oxygen

Pre-treatment effluent (if

applicable)




Dissolved oxygen (for systems using ozone

as pre-treatment)

Individual filter Continuous monitoring Loss of head

Flow rate

Water level above filter media

Individual filter effluent Continuous monitoring Turbidity

Filtered water Grab sample Colour

pH


Dissolved oxygen (to monitor biological

conditions in filter, i.e. aerobic vs.

anaerobic)

Figure 8-4 presents a process schematic of a typical slow sand filtration process, along with

the identification of various sampling locations.



Sand

Raw Water

Inlet SchmutzdeckeVent

Filter Effluent

Sand

Raw Water

Inlet SchmutzdeckeVent

Filter Effluent

Figure 8-4 – Slow Sand Filtration – Process Schematic and Sampling Locations


A properly designed and constructed slow sand filter should operate reliably with very little

operator intervention.

The primary maintenance activity associated with slow sand filters is cleaning, or scraping,

which is discussed in the following subsection.


8.3.4.1 Scraping and Resanding

Similar to rapid rate granular media filters, slow sand filters operate over a cycle of two

stages, consisting of a filtration cycle and a cleaning cycle. Slow sand filters, however, are

not backwashed. Head loss builds slowly during a filter run that may last up to weeks or

months. Filter runs are generally terminated when the head loss reaches between 1 to 2 m.

After the overlying water is drained below the surface of the sand media, the filter is cleaned

by removing the schmutzdecke along with a small amount of sand (1 to 2 cm). Scraping can

be accomplished either mechanically or manually.

The sand that is removed is usually cleaned hydraulically and stockpiled for later replacement

in the filter. The operation and scraping cycle can be repeated several times until the bed

depth has decreased to approximately 0.4 to 0.5 m, at which time the stockpiled sand or new

sand is added to the filter.

A filter with new media typically has a ripening period that can last several days, during

which the schmutzdecke forms and the effluent quality improves. The schmutzdecke is said

to be ‘mature’ when the microbial population becomes well established and the filter

produces acceptable filtered water quality. Frequent monitoring of the filter effluent is needed

to ensure that acceptable removal of microorganisms and turbidity is occurring. Additional

information is also provided in Logsdon (2008) and Eighmy et. al. (1993).

Filter-to-waste piping should be provided to allow for disposal of filtered water during the

ripening period. After several filter runs and scrapings, however, the microbial community



can become established deeper in the bed and the ripening period is reduced or eliminated.

The duration of filter-to-waste needed during the ripening period should be determined

through pilot- or full-scale testing.

The longer a filter is drained for the scraping operation, the longer the ripening period will be

during the subsequent run (Cullen and Letterman, 1985). Therefore, cleaning should be done

quickly, and the filter returned to service as soon as possible.

It may be possible to extend the time between scraping by raking the surface of the filter

between scrapings. In general, the run time gained with each raking diminishes, and when the

scraping is required, it may be necessary to remove up to 15 cm of sand (Cleasby et. al.,

1984).

8.3.4.2 Pre-treatment for Enhancement of Slow Sand Filtration

The operation of slow sand filters can be enhanced by the use of additional pre-treatment

processes prior to the slow sand filter to allow treatment of more challenging source waters.

Most of these processes are proprietary systems; optimization of these systems is beyond the

scope of this manual, and the manufacturer should therefore be consulted.

Where organic material in the raw water is not easily biodegradable, the application of ozone

(up to 1 mg/L) upstream of the slow sand filter can promote biological activity by making the

NOM in the water more amenable to biological removal. Ozone addition also increases

dissolved oxygen, which is beneficial to microbial activity. However, residual ozone needs to

be removed before water enters the slow sand filter.

8.4 MEMBRANE FILTERS

8.4.1 Purpose and Types of Membrane Filters

In the simplest membrane processes, water is forced through a porous membrane under

positive or negative pressure, while suspended solids, larger molecules or ions are held back

or rejected. The four general membrane processes used in drinking water systems include

microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).

Table 8-6 provides a summary of operating pressure, pore sizes, primary application and the

type of microorganism that can be removed with the various membrane types.



Table 8-6 – Overview of Membrane Filtration Processes Used in Drinking Water

Treatment

Adapted from AWWA (1996) and AWWA (1999)

Membrane

Type

Operating

Pressure

(kPa)

Pore Size

(µm) Primary Applications Microbes Removed

MF 30 – 50 0.1-0.2 Removal of particles and

turbidity

Algae, protozoa and

most bacteria

UF 30 – 50 0.01-0.05 Removal of dissolved non-

ionic solutes

Algae, protozoa, most

bacteria and viruses

NF 500 – 1000 0.001-0.0051

Removal of divalent ions

(softening) and dissolved

organic matter



RO 1000 – 5000 Non-porous1

Removal of monovalent

ions (desalination)



Notes:

1. For NF and RO membranes, the concept of discernable "pores" is inappropriate and the

ability of the membrane to remove a particular contaminant is described by the molecular

weight cutoff (MWCO) rather than pore size. The MWCO for NF membranes ranges from

200 to 1,000 Daltons, while for RO membranes, the typical range of MWCO levels is less

than 100 Daltons (USEPA, 2005).

MF and UF are the membrane systems most commonly used in Ontario. There are a few NF

systems in Ontario, and there are some installations across Canada used primarily for

organics removal. Reverse osmosis membrane systems are mainly used as point-of-entry or

point-of-use treatment systems in Ontario. Given the limited application of these systems in

the province to date, optimization measures for these processes are not presented in this

Manual.

Chemical coagulation is not usually needed before membrane treatment for the removal of

suspended solids and microorganisms. However, pre-treatment is sometimes employed to

reduce membrane fouling (caused by accumulation of chemicals, particles and biological

growth on membrane surfaces) and to avoid membrane degradation from chemical attack

(LeChevallier, 2004). Pre-treatment systems may include microstraining, pH adjustment and

addition of pre-oxidants. If the source water is of poor quality, advanced pre-treatment

systems (e.g. conventional coagulation, flocculation and sedimentation, or other membrane

processes) may be necessary.

The water passing through the membrane is called permeate, and water remaining on the feed

side is called retentate or reject water. As solids accumulate against the filter, the

transmembrane pressure (TMP) across the filter that is required to maintain constant

permeate production increases. To minimize fouling, TMP should be kept below 100 kPa

(MWH, 2005).

Membrane filters operate over a repeating filtration and backwashing cycle, similar to

granular filters. Although the backwash removes accumulated solids, a gradual but



continuous loss of performance occurs due to fouling of the membranes. Fouling is removed

with periodic chemical cleaning, which typically involves soaking the membranes for several

hours in one or more warm solutions containing surfactants, acids or bases. The cleaning

frequency may range from a few days to several months, depending on the membrane

material, operating conditions and raw water quality.

Membrane degradation is inevitable, although membrane manufacture as well as performance

have shown continual improvement since membranes came into more general use in the

drinking water industry. There are measures that can be taken to prolong membrane life;

however, experience with full scale applications in Ontario have generally shown that

membrane replacement is generally required every 7 to 10 years.


MF and UF membranes have chemically formed and uniformly sized pores that are 1 micron

(1 µm) or less in diameter (MOE, 2006). Membrane filtration removes pathogens, such as

Cryptosporidium and Giardia, mainly by size exclusion (i.e. microbes larger than the

membrane pores are removed). Virus removal capability will vary with the type and

manufacturer of a particular membrane.

As noted in Section 8.2.2, the projection of the capacity of a filtration process is based mainly

on hydraulic loading rates and the ability to meet filter effluent turbidity objectives. For

membrane systems, the filtration rate, or flux, is defined by the volume or mass of permeate

(water) passing through the membrane per unit area per unit time (MOE, 2008). The flux is

commonly expressed as m3/m

2/s or m/s.

The operational requirements for membrane filtration systems specified in the Disinfection

Procedure (MOE, 2006) include the following compliance criteria (or as required by the most

recent version of the Disinfection Procedure):

Maintain effective backwash procedures, including filter-to-waste or an equivalent

procedure, to ensure that the effluent turbidity requirements are met at all times;

Monitor integrity of the membrane by continuous particle counting or equivalently

effective means (e.g., intermittent pressure decay measurements);

Continuously monitor filtrate turbidity; and

Meet the performance criterion for filtered water turbidity of less than or equal to 0.1

NTU in 99 percent of the measurements each month.

Membrane filtration systems are proprietary and the manufacturer should be consulted for

specific design criteria. Consideration should also be given to water demand during the cold

season, as cold water will significantly reduce the flux in a membrane system.


order to evaluate the performance of membrane filtration processes.



Table 8-7 – Membrane Filtration – Recommended Monitoring to Evaluate Performance


Measurement Parameters/ Analyses


pH

Temperature

Flow rate into membrane system or

individual membrane trains


Grab sample Colour


Iron and manganese (if applicable)

Pre-treatment effluent

(if applicable)




Individual permeate line

(each membrane train)

Continuous monitoring Filtration rate and volume of permeate

Turbidity

Particle counts

Individual membrane

train

Continuous monitoring Transmembrane pressure (to measure

degree of fouling and initiate cleaning)

Backpulse pressure (prevent damage to

membranes)

Individual reject or

concentrate lines (each

membrane train)

Continuous monitoring Flow and volume of waste stream (to

calculate overall recovery rate)

Individual backwash

lines

Continuous monitoring Backwash flow rate and volume

Combined filter effluent Continuous monitoring or

Grab sample Flow rate

Colour

pH


Iron and manganese (if applicable)

Aluminum or iron residual (if applicable)



Table 8-7 – Membrane Filtration – Recommended Monitoring to Evaluate Performance

(cont’d.)


Measurement Parameters/ Analyses

Process waste stream

(membrane backwash

water)


Grab sample Flow or volume

Turbidity or total suspended solids


Individual membrane

Clean-in-place tank


Grab sample pH

Residual measurement (cleaning solution

concentration)

Other cleaning solution strength

measurement (as recommended by the

manufacturer)

Additional monitoring may be required for proprietary systems; the evaluator should review

manufacturer’s literature for recommended process monitoring parameters.

Figure 8-5 presents a process schematic of a typical membrane filtration process, along with

the identification of various sampling locations.

Filter Influent

Combined

Filter Effluent

Sample Location

Individual Train

Permeate Line

Sample Location

MF/UF Membrane

System

Filter Influent

Sample Location

Figure 8-5 – Membrane Filtration – Process Schematic and Sampling Locations


Symptoms and causes of common problems encountered with the membrane filtration

process are shown in Table 8-8.



Table 8-8 – Membrane Filters – Symptoms and Causes of Common Problems

Problem Description

Mitigation

Fouling Adsorption or clogging of material

on the membrane surface which

cannot be removed during the

backwash cycle.

Fouling reduces the recovery rate

achieved by the system.

Caused by raw water or feedwater

with iron or other metal oxides,

organics, colloids, bacteria and other

microorganisms.

The rate of membrane fouling can

be reduced but it cannot be

prevented from occurring over time.

Pre-treatment prior to membrane

filtration (such as upstream

clarification and/or fine screening).

Membrane backwashing with water

and/or membrane scouring with air.

Chemical cleaning of membranes.

Increase membrane surface scouring

or crossflow velocity.

Increase amount of membrane

surface area to reduce applied flux.

Optimization of upstream chemical

addition (coagulant and/or polymer).

Scaling Formation of scales or precipitates

on the membrane surface.

Scaling occurs in raw water or

feedwater with calcium sulphate,

calcium carbonate, metal oxides and

silica (AWWA, 1995).

Preventative cleaning (backwashing

or chemical cleaning).

Adjustment of operational variables,

recovery rate, pH, temperature.

Optimization of upstream chemical

(coagulant and/or polymer) addition.

Membrane

degradation Gradually with time, membrane

degradation is inevitable (MWH,

2005).

Over time, the flux gradually

decreases and less permeate is

produced by the membrane (MWH,

2005).

To prolong membrane life the

following substances should be

limited in the feedwater: acids, bases,

pH extremes, chlorine and other

oxidants, bacteria (AWWA, 1995).

Eventual replacement of membranes

required, generally after a period of 5

to 10 years (MWH, 2005).

Poor effluent

quality Increase in turbidity or particle

count may indicate damage to

membrane, process piping or

process seals.

Optimization of upstream processes.

Integrity testing should be performed

to identify possible damage to

membranes, process piping or

process seals.

Increase or

decrease in

transmembrane

pressure

Either a gradual increase or a sudden

drop in membrane pressure is

observed.

Membrane performance is strongly

affected by changes in temperature.

At low temperatures, water viscosity

increases and membrane

permeability decreases.

Gradual increase indicates that a

membrane cleaning sequence needs

to be initiated.

Sudden decrease is a sign of

membrane damage.

Temperature of the feed water should

be monitored.




8.4.4.1 Optimizing Pre-Treatment

Optimization of pre-treatment, such as upstream coagulation/flocculation and clarification,

and/or micro-screening, will increase the efficiency and life of the membranes. Pre-treatment

requirements will depend on the quality of the raw water, the type of membrane used and

filter effluent turbidity goals. Membrane fouling, backwashing and chemical cleaning

frequency can also be minimized through the optimization of pre-treatment processes. Jar

testing and/or pilot testing is recommended (see Chapter 4).

Additional information regarding optimization of screening, coagulation/flocculation and

clarification processes is presented in Chapters 5, 6 and 7 of this Manual, respectively.

8.4.4.2 Optimizing Membrane Cleaning

Operating membranes at elevated flux levels can increase fouling potential. Routine

monitoring of membrane flux is recommended to ensure that the membrane is operating

within the design value at which deterioration of system performance begins to occur. The

optimum membrane design flux is normally established during pilot testing and is based on

the fouling characteristics of the raw water or feedwater, the membrane material and the

membrane system configuration. Conversely, operating at a reduced flux can result in

inefficient use of installed membrane capacity. Membrane modules can be taken off-line or

put back on-line to allow operation at an optimum flux for performance and membrane life.

Optimization of backwash frequency will aid in maintaining low TMP during operation of a

membrane system. Consideration should be given during optimization to ensure that the

increased backwashing does not decrease the overall recovery of water. As with granular

filters, the production per filter run (e.g. m3 of filtrate per m

2 of filter area per cycle) should

be monitored.

Backwashing of membranes generally involves forcing permeate water through the fibre wall

in the reverse direction at a pressure higher than the normal filtration pressure (MWH, 2005).

Backwash can include air scour to loosen material on the membrane surface. The frequency

and duration of backwash can vary depending on the type of membrane used. The

manufacturer/supplier of the membranes should be consulted for appropriate cleaning

procedures. An enhanced chemical backwash, which involves using chlorinated backwash

water, can be used to control biological growth on the membranes in some systems.

Despite frequent backwashing, membrane filters gradually lose filtration capacity due to

fouling or adsorption of materials that cannot be effectively removed during the backwash

cycle. A chemical clean-in-place is a method of cleaning in which the membranes are

submerged in proprietary cleaning solutions that are often heated to 30 or 40°C (MWH,

2005).

Frequency of chemical cleaning is site specific and should be determined based on pilot study

data or as directed by the manufacturer (MOE, 2008). The frequency of cleaning will depend

on the fouling characteristics of the raw water, the applied flux, and use of chlorine upstream

of the membrane.



8.4.4.3 Integrity Testing

Integrity testing is used to routinely evaluate membrane and housing integrity and overall

filtration performance. There are two basic types of integrity testing: continuous indirect

integrity testing and periodic direct integrity testing.

Indirect integrity testing includes on-line particle counting or turbidity used as a continuous

indication of the membrane integrity. In general, sustained particle counts in the filtrate

should remain below 20 counts/mL. If filtrate particle counts exceed 20 counts/mL for an

extended period of time, this may be an indication that a membrane fibre has been breached

and the membrane module should be isolated and checked for integrity.

Direct integrity testing includes such measures as pressure decay, vacuum hold, bubble point

or sonic testing. The frequency of direct integrity testing will depend on the quality of the raw

water and the robustness of the membranes. The manufacturer should be consulted for

additional information.

Integrity testing, as noted above, is a requirement if the membrane process is to be used for

disinfection removal credits (refer to the Disinfection Procedure; MOE, 2006). The integrity

monitoring technique used should be able to confirm numerically that the required log

disinfection credit is being achieved and process train leaks are repaired to consistently

achieve this performance.

8.5 CASE HISTORIES

8.5.1 Racine, Wisconsin – Optimizing Membrane Maintenance

The following case study is based on information presented in Kosterman (2010).

System Description

The Racine Water Utility (RWU) owns and operates a conventional water treatment plant.

Following the Cryptosporidium outbreak in Milwaukee in 1993 and two boil-water notices in

the spring of 1994, the RWU began investigating advanced treatment technologies to

improve the protection of public health. In 2005, the RWU began operating a 190 ML/d

immersed membrane system that was installed downstream of the conventional plant to

provide an additional barrier against potential pathogens.

RWU’s UF membrane plant consists of 4,032 modules in 7 trains (each train with 6 cassettes

of 96 modules). Each module’s filtration surface area is approximately 46 m2 with between

20,000 and 30,000 individual fibres. Integrity testing of the membranes is conducted three

times per day, in accordance with federal and state regulations. The membranes are air

pressurized and the pressure decay is measured for 5 minutes and a log removal value is

calculated from the pressure decay.

With more than 120 million fibres in the membrane plant, even a small percentage of breaks

can lead to significant membrane repair. RWU’s membrane repair constitutes the single

largest investment of labour dedicated to the membrane plant.

Backwashing of the membrane includes air scour and is conducted once every 30 minutes.

Chemical clean-in-place is also conducted periodically to remove fouling.




Because of the consistently high level of performance of the membrane filtration process, the

installation of membrane filters at the plant has allowed a shift in operating strategy at the

RWU from optimizing water quality to optimizing water production. Optimization goals

therefore focus on reducing membrane fouling and train downtime.

Maintenance Clean: Original SOPs required a daily maintenance clean on each train. After a

lengthy full-scale trial study, permission was granted by the manufacturer to decrease

maintenance cleans to once per week. This change decreased maintenance cleans from 49 to

7 per week, increased available production time by 24.5 hours per week and significantly

lowered chemical use.

Minor Equipment Modifications: Additional membrane modules were installed to provide

additional filtration surface area, resulting in lower operating TMPs and extending the time

between chemical cleans. In addition, the membrane integrity testing air system regulator was

replaced with a higher capacity unit, allowing faster pressurization. Other modifications were

also completed resulting in more efficient priming of the membranes and piping after integrity

test completion. With these equipment changes, the duration of the integrity test was reduced

from approximately 45 minutes to 25 minutes. For RWU, this increased production time by 7

hours per day. By decreasing membrane downtime and increasing filtration surface area, it was

possible to operate the trains at a lower flux and TMP.

Membrane Fouling Reduction: RWU had traditionally used an iron-based coagulant as part

of the conventional treatment process. Over time, however, operations staff noticed

discolouration of the membrane fibres during membrane repairs. Staff members believed that

iron carryover from the conventional treatment process was causing a build-up on the

membrane surface and increased fouling. A series of total and dissolved iron tests were

conducted on the membrane feed and permeate waters, confirming that iron was depositing

on the fibres. After consulting with the manufacturer, the RWU switched to a PACl coagulant

and a plant trial was initiated. Almost immediately, a noticeable increase in permeability

occurred. The chemical pre-treatment change in the conventional plant decreased membrane

fouling, decreased citric acid cleans, and reduced TMPs (and permeate pump speeds), making

operations more efficient and reducing costs.

Cold-Water Operations Improvements: RWU had experienced increased transmembrane

pressures and fouling rates when water temperature fell below 10°C, requiring more frequent

chemical cleans. RWU, in consultation with the manufacturer, modified the control system to

allow more trains to be switched on to produce the same amount of water, resulting in lower

TMP and fouling rates and returning the system to normal chemical clean intervals.

Summary

The RWU has found that membrane filtration is a considerable capital and operational

investment. Optimizing membrane operations decreases costs as well as chemical and

mechanical stresses on membrane fibres. Even minor modifications can result in more

efficient operation and reduce costs.



8.5.2 Fort McMurray, Alberta – Filter Media Optimization and Upgrading Study

The following case study is based on information presented in Suthaker et. al. (2007).

System Description

The Fort McMurray WTP is owned and operated by the Regional Municipality of Wood

Buffalo (RMWB). The WTP draws raw water from the Athabasca River and the rated

hydraulic capacity of the plant is 40 ML/d. The treatment process consists of pre-disinfection,

coagulation, flocculation, clarification and filtration.

As a result of a robust economy and massive expansions to the oil sands operations in the

region, rapid population growth within the RMWB area occurred. Between 2000 and 2002,

the RMWB undertook a number of studies to define potential options and costs for upgrading

the Fort McMurray WTP. The two plant upgrading concepts consisted of expansion using

either conventional treatment or membrane filtration. In view of the population growth

uncertainty, the RMWB opted for a flexible, staged expansion strategy. Costs for upgrading

to a membrane filtration process to provide 60 ML/d of capacity were estimated at $11

million (2002 CDN dollars). During a Value Engineering session conducted in 2003, the

RMWB elected to proceed with a combination of optimization measures and minor capital

improvements to expand the plant capacity to 50 ML/d and to defer the membrane upgrades.


One of the key optimization goals was to improve the filtration process to meet new

regulatory requirements at the target expanded capacity. The filters had originally been

designed to treat 44 ML/d by operating at a filtration rate of 11.2 m/h; however, the process

could not meet filter effluent turbidity goals at these elevated filtration rates. The current

maximum filtration rate of 8 m/h (needed to maintain regulatory compliance) limited the

plant capacity to 30 ML/d. Given the challenges of turbidity and particle count compliance,

the existing filters needed to be upgraded to meet the expanded capacity of 50 ML/d. It was

decided to modify the existing filters to allow for deep bed filtration operating at much higher

filtration rates (up to 20 m/h). As such, pilot studies were initiated to evaluate media depth,

size and backwash considerations, as well as pre-treatment requirements.

Filtration objectives used to evaluate filter performance during the pilot studies were

established as follows:

Turbidity of less than 0.3 NTU;

Particle counts (> 2 µm) of less than 50/mL (according to Alberta Environment

Standards); and

Differential head loss increase of 1.5 m.

Filter runs would be terminated if any of the above criteria were exceeded.

Pilot testing indicated that an optimum combination of filtered water quality and filter run

length could be achieved using a dual media configuration (0.5 mm size crushed quartz and 1

mm anthracite) and total media depth between 1.6 and 1.9 m.



The pilot testing also confirmed that the existing backwash facilities were sufficient to

provide for adequate air scour, backwash rate and bed expansion for the upgraded filters.

At full scale, additional process optimization was conducted to minimize the solids loading

on the filters, including upgrading the clarifiers with tube settlers and increasing the

coagulant dosage (based on the results of the pilot testing). The physical improvements to the

sedimentation process resulted in longer filter runs and slightly improved particle counts in

the full-scale filters. Increasing the coagulant dose also had a dramatic effect on particle

counts and filter run length. Lower colour and turbidity levels were also recorded in the filter

effluent following the coagulation change.

Summary

Modifying existing filtration facilities for deep bed high-rate filtration offers an alternative to

expansion of conventional treatment plants and can improve finished water quality to meet

more stringent regulatory requirements. Filtration rates of over 18 m/h were achieved as a

result of the upgrades. Pilot studies are recommended to establish appropriate design

parameters specific to site conditions (raw water quality, pre-treatment requirements, etc.).

8.6 REFERENCES

American Society of Civil Engineers and American Water Works Association (2004). Water

Treatment Plant Design, 4th Ed. McGraw-Hill. ISBN 0-07-141872-5.

Amirtharajah, A., N. McNelly, G. Page and J. McLeod (1991). Optimum Backwash of Dual

Media Filters and GAC Filter-Adsorbers with Air Scour. AwwaRF and AWWA. Denver,

CO. ISBN 0-89867-576-6.

AWWA (1995). Water Treatment, 2nd


AWWA, Lyonnaise des Eaux and Water Research Commission of South Africa (1996).

Water Treatment Membrane Processes. McGraw-Hill Inc. New York.



AWWA (2007). M37: Operational Control of Coagulation and Filtration Processes. 2nd

Ed.

AWWA. ISBN 978-1-58321-055-0.

Beverly, R.P. (2005). Filter Troubleshooting and Design Handbook. AWWA. Denver, CO.

ISBN 978-1-58321-349-0.

Cleasby, J.L, M.M. Williamson and E.R. Baumann (1963). Effect of Filtration Rate on

Changes in on Quality. Journal AWWA, 55:869-878.

Cleasby, J.L., D.J. Hilmoe, C.J. Dimitracopoulos and L.M. Diaz-Bossio (1984). Effective

Filtration Methods for Small Water Supplies. Project Summary U.S. EPA Cooperative

Agreement CR808837-01-0. EPA 600/S2-84-088.



Cleasby, J.L.. G.L. Sindt, D.A. Watson and E.R. Baumann (1992). Design and Operation

Guidelines for Optimization of the High-Rate Filtration Process: Plant Demonstration

Studies. AwwaRF and AWWA. Denver, CO. ISBN 0-89867-604-5.

Cullen, T.R. and R.D. Letterman (1985). The Effect of Slow Sand Filter Maintenance on

Water Quality. Journal AWWA, Vol. 77, No. 12. December 1985.

Eighmy, T.T., J.P. Malley Jr. and M.R. Collins (1993). Biologically Enhanced Slow Sand

Filtration for Removal of Natural Organic Matter. AWWA. Denver, CO. ISBN 0-89867-

644-4.

Great Lakes-Upper Mississippi River Board of State Public Health and Environmental

Managers (2007). Recommended Standards for Water Works, (known as the “Ten State

Standards”).

Hess, A., M. Chipps and A. Rachwa (2002). Filter Maintenance and Operations Guidance

Manual. AwwaRF and AWWA. Denver, CO. ISBN 978-1-58321-234-9.

Kosterman, M. (2010). Decrease Operational Costs with Membrane Maintenance. AWWA

Opflow, Vol. 36, No. 4. April 2010.

LeChevallier, M.W. and K.-K. Au (2004). Water Treatment and Pathogen Control: Process

Efficiency in Achieving Safe Drinking Water. World Health Organization. ISBN 92-4-

156255-2.

Logsdon, G.S., A. Hess, M. Chipps and A. Rachwa (2002). Filter Maintenance and

Operations Guidance Manual. AwwaRF & AWWA. Denver, CO. ISBN 1-58321-234-5

Logsdon, G.S. (2008). Water Filtration Practices: Including Slow Sand Filters and Precoat

Filtration. AWWA, Denver, CO. ISBN 978-1-58321-595-1.



3.



ISBN 0-471-11018-3.

Nix, D.K and J.S. Taylor (2003). Filter Evaluation Procedures for Granular Media. AWWA.

Denver, CO. ISBN 978-1-58321-026-0.

Patania, N.L., J.G. Jacangelo, L. Cummings, A. Wilczak, K. Riley and J. Oppenheimer

(1995). Optimization of Filtration for Cyst Removal. AwwaRF and AWWA. Denver, CO.

ISBN 0-89867-825-0.

Renner, R.C., B.A. Hegg and J.H. Bender (1990). EPA Summary Report: Optimizing Water

Treatment Plant Performance with the Composite Correction Program. U.S. EPA Centre for

Environmental Research Information. Cincinnati, OH. EPA 625/8-90/017.



Suthaker, S.S., G.E. Drachenberg and M.H. Mack (2007). Modified Deep Bed Filtration:

Low-cost Option for Increasing Capacity and Improving Quality Within Existing Filter Cells,

presented at the 2007 American Water Works Association Annual Conference and

Exposition, Toronto, ON.

USEPA (2005). Membrane Filtration Guidance Manual. Office of Drinking Water.

Cincinnati, OH. EPA 815-R-06-009.

Wolfe, T. (2003). Filtration – Part I: Filtration Fundamentals, presented at the 2003 Annual

Kentucky Water and Wastewater Operators’ Conference, Fort Mitchell, Kentucky, March

2003.


CHAPTER 9DISINFECTION

DISINFECTION

9.1 Introduction ............................................................................................................ 9-1

9.2 Chemical Inactivation ............................................................................................. 9-1

9.2.1 Purpose and Chemicals Commonly Used ................................................ 9-1




9.3 Ultraviolet (UV) Irradiation ................................................................................. 9-15

9.3.1 Purpose and Mode of Disinfection ........................................................ 9-15




9.4 Case Histories ....................................................................................................... 9-21

9.4.1 Port Rowan WTP – pH Control for Optimizing Disinfection ............... 9-21

9.4.2 Ameliasburgh WTP – Optimization Study to Control the Formation of

DBPs ...................................................................................................... 9-22

9.5 References ............................................................................................................ 9-25

CHAPTER 9. Disinfection 9-1


CHAPTER 9

DISINFECTION

9.1 INTRODUCTION

The disinfection process is the most important barrier in the treatment process and is

responsible for inactivating pathogens that have not been removed by upstream unit

processes. For the purposes of this Manual, the assessment of disinfection capability is based

on the requirements of the Procedure for Disinfection of Drinking Water in Ontario

(Disinfection Procedure, MOE, 2006) adopted by reference by O. Reg. 170/03 under the

SDWA, 2002.

A clear distinction is made between primary disinfection and secondary disinfection, which

are often completely separate treatment processes and are designed with different objectives.

Primary disinfection is a process or a series of processes intended to inactivate human

pathogens, such as viruses, bacteria and protozoa, potentially present in raw water before the

water is delivered to the first consumer. The entire process of primary disinfection must be

completed within the water treatment component of the drinking water system, which may

include a dedicated part of the distribution system before reaching the first consumer.

Secondary disinfection is the maintenance of a disinfectant residual throughout the

distribution system to protect the drinking water from microbiological re-contamination,

reduce microbial re-growth, control biofilm formation and serve as an indicator of

distribution system integrity.

Five disinfection agents are commonly used in drinking water treatment: free chlorine,

combined chlorine, ozone, chlorine dioxide and UV light. The first four agents are chemical

oxidants, whereas UV light involves the use of electromagnetic radiation (MWH, 2005). A

discussion of advantages and disadvantages of various primary disinfectants, as well as

process selection and design guidance for these processes, can be found elsewhere (USEPA,

1999; White, 1999; USEPA, 2006).

This chapter covers the various disinfection processes used in primary disinfection of

drinking water to inactivate pathogenic microorganisms. Secondary disinfection is addressed

in Chapter 11.

9.2 CHEMICAL INACTIVATION

9.2.1 Purpose and Chemicals Commonly Used

The selection of an appropriate disinfection process depends upon site specific conditions and

raw water characteristics that are unique to each drinking water system. The choice of

disinfectant should consider and balance the need to inactivate pathogens with the need to

minimize the formation of DBPs. Chemical disinfectants accepted for use in primary

disinfection in Ontario include chlorine, chlorine dioxide and ozone.



9.2.1.1 Chlorine

Chlorine is the most commonly used disinfectant in water treatment in Ontario and

throughout the world. Chlorine is a strong oxidant that is highly effective for inactivating

bacteria and viruses. It has been found to affect reproduction and metabolism, cause

mutations, and ultimately cause death of microorganisms. Protozoan cysts are highly resistant

to chlorine and may require prolonged contact times at a high chlorine residual to achieve

adequate inactivation (LeChevallier, 2004).

The most common chlorine chemicals used for drinking water disinfection are chlorine gas

(Cl2), sodium hypochlorite (NaOCl) and calcium hypochlorite (Ca(ClO)2).

Free chlorine, in the form of hypochlorous acid (HOCl) and hypochlorite ion (OCl-), is

formed by the reaction between chlorination chemicals and water.

If ammonia is present in the water, HOCl will react readily with ammonia to form three

species of chloramines, which are generally referred to as “combined chlorine”.

Monochloramine, usually the predominant form of combined chlorine, is a weak disinfectant

and rarely suitable for use as a primary disinfectant, because it requires very long contact

times at typical concentrations to achieve adequate disinfection. Because of its persistence in

the distribution system, monochloramine is more commonly used as a secondary disinfectant

(see Chapter 11).

In situations where breakpoint chlorination is being practiced (to oxidize natural raw water

ammonia), the reaction should be effectively complete before the water leaves the

disinfection process; otherwise, the chlorine residual may be prematurely and rapidly lost

through continuing chemical reactions. Where ammonia and other nitrogenous substances are

present in the influent water, the application of chlorine should be such that the resulting free

chlorine residual comprises more than 80 percent of the total chlorine residual at the end of

the primary disinfection process.

9.2.1.2 Chlorine Dioxide

When chlorine dioxide (ClO2) is used as a disinfecting agent, it must be generated on-site

through the reaction of sodium chlorite with chlorine gas, hypochlorous acid or hydrochloric

acid (HCl), or through the use of an electrochemical process.

Chlorine dioxide is a more powerful disinfectant than chlorine, but less than ozone. Chlorine

dioxide is also more effective over a greater pH range (pH 5 to 10) than free chlorine

(LeChevallier, 2004). Chlorine dioxide is an effective disinfectant for control of cysts and

oocysts. Chlorine dioxide also has the capability of providing a lasting residual and has been

used as a secondary disinfectant.

Chlorine dioxide is capable of oxidizing iron and manganese, removing colour, and oxidation

of natural organic compounds without THM formation. It also oxidizes many organic and

sulphurous compounds that cause tastes and odours. The application of chlorine dioxide for

these purposes is discussed in Chapter 10.



9.2.1.3 Ozone

Ozone (O3) must be generated on-site by means of an electrical discharge in oxygen or dry

air. Although ozone is a highly effective disinfectant, it does not produce a lasting residual,

and is therefore not suitable for secondary disinfection.

Once dissolved in water, ozone begins a process of decay that results in the formation of

radicals, such as hydroxyl radicals (HO·). Ozone reacts with microorganisms and other

contaminants in two ways: (1) by direct oxidation and (2) through the action of hydroxyl

radicals generated during its decomposition.

The disinfection efficiency of ozone is not affected by pH, although ozone decomposition

occurs faster in solutions with higher pH; therefore, more ozone should be applied at high

pHs to maintain required ozone concentrations (USEPA, 1999).

In addition to its use as a primary disinfectant, ozone can be used for oxidation of iron

and manganese, taste and odour causing compounds and natural organic matter, as a

potential flocculant aid and for the destruction of algal toxins. The application of ozone

for purposes other than disinfection is discussed in Chapter 10.


9.2.2.1 CT Approach

In Ontario, the minimum level of treatment required for municipal and regulated non-

municipal residential drinking water systems is specified in the Disinfection Procedure

(MOE, 2006). The treatment requirements for these drinking water systems are as follows:

For groundwater systems, the treatment process must consist of disinfection and must

be credited with achieving an overall performance that provides, at a minimum, 2-log

(99%) removal or inactivation of viruses.

For surface water or groundwater under the direct influence of surface water (GUDI)

systems, the treatment process must consist of chemically assisted filtration and

disinfection (or other treatment capable of producing water of equal or better

quality), and achieve an overall performance that provides, at a minimum, 2-log

(99%) removal or inactivation of Cryptosporidium oocysts, 3-log (99.9%) removal or

inactivation of Giardia cysts, and 4-log (99.99%) removal or inactivation of viruses.

It should be noted that these are the minimum levels of removal or inactivation required for

human pathogens, and the disinfection requirements for a specific system may need to be

increased if the raw water source is subject to excessive contamination from cysts and/or

viruses. Cyst and virus removal credits for the different types of treatment processes (e.g.

conventional filtration, membrane filtration, etc.) are provided in the Disinfection Procedure

(MOE, 2006).

The Disinfection Procedure (MOE, 2006) ensures that the required levels of chemical

disinfection are achieved by using the CT concept. CT values are calculated using the

disinfectant residual concentration (C) multiplied by the actual time (T) that the finished

water is in contact with the disinfectant. In the Disinfection Procedure, CT values are



provided that can be used to determine the log inactivation for various disinfectants at

specific operating conditions (e.g. temperature, pH and disinfectant residual).

The calculated CT value should, at all times during plant operation, be equal to or greater

than the required CT value. Where pH and disinfectant residual levels change significantly in

different sections of the process, a more accurate estimate of the overall treatment is

obtainable by adding log inactivation values for each type of microbial threat in each section.

The Integrated Disinfection Design Framework (IDDF) (Bellamy, et. al., 1998) method for

accounting for disinfection decay and true process hydraulics can be used for determining the

CT values and associated logs of microbial inactivation as a means of optimizing pathogen

control while minimizing DBP formation.

The approach described below can be used to determine the capability of a plant to meet

the disinfection requirements based on the CT values presented in the Disinfection

Procedure. Procedures are presented for both pre- and post-disinfection, with pre-

disinfection defined as adding the disinfectant ahead of the filtration process and post -

disinfection defined as adding the disinfectant following filtration. Whether or not a

utility can use pre-disinfection depends on raw water quality. Concerns associated with

pre-disinfection include the potential formation of DBPs and the possible ineffectiveness

of disinfectants in untreated water.

Any volume required for providing storage for fire or equalization is not available for

contact time and should not be included in CT calculations.

Post-Disinfection

The following procedure is used to assess the plant’s disinfection capability when using only

post-disinfection:

Project the total log Giardia reduction and inactivation required by the water

treatment process based on the raw water quality or watershed characteristics.

Typically, Giardia inactivation requirements are more difficult to achieve than the

virus requirements; consequently, Giardia inactivation is the basis for this

assessment.

Project the log removal capability of the existing treatment plant. Expected removals

of Cryptosporidium, Giardia and viruses by various types of filtration processes are

presented in the Disinfection Procedure. A 2.5 log Giardia reduction may be

assigned for a conventional plant with adequate unit treatment process capability

(e.g. Type 1 units preceding disinfection as determined during the CPE). If the

existing plant does not meet the performance goals to be rated as a Type 1 facility, a

lower log removal capability may need to be assigned to the facility. For the purposes

of the projection of major DWS component capability, it should be assumed that the

plant will be operated to achieve optimum performance from existing units.

Select the required CT value from the tables in the Disinfection Procedure based on

the required log removal/inactivation, the log removal capability projected for the

plant, the maximum pH and minimum temperature of the water being treated, and the

projected maximum disinfectant residual. The maximum pH and minimum

temperature of the water being treated are selected to evaluate capability under worst



case conditions. When chlorine is used as the disinfectant, the maximum residual

utilized in the evaluation should not exceed 2.5 mg/L free residual, based on research

that indicates that contact time is more important than disinfectant concentration at

free chlorine residuals above 2.5 mg/L (Regli, 1990).

Using these parameters, calculate the required detention time, Treq, to meet the

required CT (equations are provided in Appendix G; sample calculations are included

in the example CPE provided in Appendix C).

Determine an effective volume of the existing clearwell and/or distribution piping to

the first user. Effective volume refers to the volume of a basin or piping that is

available to provide adequate contact time for the disinfectant. Effective volumes are

estimated by multiplying the nominal basin and/or piping volumes by a baffle factor.

The nominal basin and/or piping volumes are calculated based on worst case

operating conditions using the minimum operating depths, in the case of basins. This

is especially critical in plants where high lift pumps significantly change the

operating levels of the clearwell and for plants in which the backwash water is

supplied from the clearwell. Depending on the information available, there are two

ways to determine the effective volume.

Tracer studies or mathematical modelling (see Chapter 4) can be conducted to

determine the actual contact time of basins. Effective contact time is defined as T10,

which is the length of time during which not more than 10 percent of the influent

water would pass through that process. The use of T10 ensures that 90 percent of the

water will have a longer contact time. For plants where T10 has been determined

through tracer studies, the effective volume is the peak instantaneous operating flow

rate (m3/minute) multiplied by the T10 value (minute). It is important to note that the

tracer study results must also consider peak instantaneous operating flows as well as

minimum operating depths in order to determine an accurate CT.

For those plants where tracer studies have not been conducted, the effective volume

upon which contact time will be determined can be estimated by multiplying the

nominal clearwell and/or piping volumes by a baffle factor. The baffle factor is

defined as the ratio of T10/T, where T is the theoretical mean residence time and is

equal to the basin and/or piping volume divided by the bulk flow rate. A summary of

baffle conditions and baffle factors to be used in determining effective volume is

presented in the Disinfection Procedure.

Calculate a flow rate (Q) where the plant will achieve the required CT values for

post-disinfection based on the above determined effective volume. Equations are

provided in Appendix G. Use this flow rate to project the post-disinfection system

capability on the performance potential graph.

Pre-Disinfection

The following procedure is used to assess the plant’s disinfection capability when using pre-

disinfection along with post-disinfection. For purposes of the calculations, the approach

assumes that the disinfection requirements can be met independently by both pre- and post-

disinfection; therefore, these capabilities are additive when projecting plant disinfection unit

process capability. The procedure is used to determine the additional disinfection capability



provided by using pre-disinfection. If pre-disinfection is practised and the utility is concerned

about DBP formation, the performance potential graph should be developed with two bars for

disinfection: one including pre- and post-disinfection, and one including only post-

disinfection capability. This allows the evaluators and the utility to assess process capability

if pre-disinfection is excluded.

Project the total log Giardia reduction and inactivation required by water treatment

processes based on the raw water quality or watershed characteristics.

Project the log removal capability of the existing treatment plant and determine the

log inactivation required.

Select the required CT value for pre-disinfection from the tables in the Disinfection

Procedure. This value should be based on the required log reduction, the log removal

capability of the plant, the maximum pH and minimum temperature of the water

being treated and the projected maximum disinfectant residual. The required pre-

disinfection CT value may be different than the post-disinfection conditions if

different temperature, pH and residual conditions exist for the two processes (e.g.

addition of lime or soda ash to increase the pH of finished water would change the

required post-disinfection CT value relative to the pre-disinfection value).

Calculate Treq (i.e.. CT value required divided by the projected operating disinfectant

residual as presented in the post-disinfection procedure).

Select an effective volume available to provide adequate contact time for pre-

disinfection. Assess which basins, pipes and conduits will provide contact time.

These typically include the flocculation and sedimentation basins, but could

include raw water transmission lines if facilities exist to inject disinfectant at the

intake structure. Filters typically are not included because of the short detention

times typically provided by filtration and the reduction in chlorine residual that

often occurs through filters. The actual basin volumes should be converted to

effective volumes by applying baffle factors as described in the Disinfection

Procedure and discussed previously in the post-disinfection procedure. Add the

individual effective volumes together to obtain the total effective pre-disinfection

volume.

Calculate a flow rate where the plant will achieve the required CT values for both

pre- and post-disinfection using the formula shown in Appendix G. Use this flow rate

to project the pre- and post-disinfection system capability on the performance

potential graph.

9.2.2.2 Monitoring of Primary Disinfection

Routine monitoring of the relevant parameters associated with the performance of the

disinfection process must be carried out to ensure that the finished water has been properly

disinfected. Primary disinfection facilities, for all regulated drinking water systems, must

be equipped with continuous disinfection process monitoring and recording devices with

alarms unless otherwise specified in O. Reg. 170/03.

Where appropriate instrumentation is available, consideration should be given to using

continuous monitoring data to provide a real-time and recorded display of the relevant



CT data and microbial log removal/inactivation actually being achieved by the overall

treatment process for all targeted microbial threats.

Table 9-1 presents recommended monitoring, in terms of sampling locations and

analyses, in order to evaluate the performance of the disinfection process using free

chlorine, chlorine dioxide and ozone.

Table 9-1 – Primary Disinfection (Chemical Inactivation) – Recommended Monitoring

to Evaluate Performance


Measurement1 Parameters / Analyses Comments

Upstream of

the primary

disinfection

process

Continuous

monitoring Turbidity

pH

Temperature

Flow rate

Factors that may affect the

effectiveness of

disinfection and/or

influent disinfectant

demand

Individual

filter effluent

Continuous


Particle counts

To monitor the

effectiveness of the

filtration process for

particulate removal and

assess log removal

Chlorination

feed system

Continuous

monitoring Chlorine gas flow rate

(evaporators)

Chlorinator feed rate

(chlorinator)

Chlorine feed rate (liquid

chlorine systems)

To monitor disinfectant

dosage (note: can be

augmented with scale

weight loss over time)

Chlorine

dioxide2

generation

system

Continuous

monitoring Sodium chlorite flow rate

Chlorine gas (or HCl, or

HOCl) flow rate

Water flow rate

Chlorine dioxide

concentration


dosage

Ozone3

generation

process

Continuous

monitoring Gas flow rate

Water flow rate

Applied ozone dose and off-

gas concentration


dosage



Table 9-1 – Primary Disinfection (Chemical Inactivation) – Recommended Monitoring

to Evaluate Performance (cont’d.)


Measurement Parameters / Analyses Comments

Downstream of

primary

disinfection

process

Continuous

monitoring Disinfectant residual

concentration (either free

chlorine residual, chlorine

dioxide residual or ozone

concentration, as applicable)

Where primary disinfection

is accomplished through a

series of distinct

disinfection

processes/steps, a

continuous sample must be

taken at the downstream

end of each distinct

process/step

Grab sample THM

HAA

Chlorite and/or chlorate (if

applicable)

Bromate (if applicable)

Total coliform, E. coli and

heterotrophic plate count

Notes:

1. Although continuous monitoring is recommended for several parameters, for small systems or

groundwater systems where water quality is relatively consistent, grab sampling may be more

appropriate, except where continuous monitoring is required by regulation.

2. Chlorine dioxide generation systems are proprietary and the associated monitoring equipment

may vary by supplier.

3. Ozone generation systems are proprietary and the associated monitoring equipment may vary

by supplier. Many systems include residual monitoring at various points in the contactor to

maintain desired ozone residual and prevent energy-wasting overdosing. Some advanced

control strategies allow the ozone treatment process to continue using power and liquid

oxygen feed information in lieu of a temporarily malfunctioning ozone residual analyzer in

order to maintain disinfection continuity and water quality.


Table 9-2 presents the symptoms and causes of common problems encountered with primary

disinfection processes.



Table 9-2 – Chemical Disinfection – Symptoms and Causes of Common Problems



Loss of or Low

Disinfectant Residual

Concentration

Higher than typical disinfectant

dosages required to maintain

target disinfectant residual.

Potential for detection of

microbiological indicator

organisms in treated water.

Upstream process upsets.

Underdosing of disinfectant

chemical.

Poor performance of upstream

treatment processes (Section

9.2.4.1).

Changes in raw water quality

leading to increase disinfectant

demand.

Insufficient Initial

Mixing of

Chlorination

Chemical



target disinfectant residual.




Inadequate mixing energy

available at chemical addition

point (Section 9.2.4.2).

Insufficient Contact

Time



target CT.




Short-circuiting or dead zones in

contact chamber (Section 9.2.4.3).

Adequate plug flow conditions not

achieved in contact chamber

(Section 9.2.4.3).

Disinfection By-

Product Formation

Detection of elevated

concentrations of DBPs in

treated water.

Excessive disinfectant dose or

contact time (Section 9.2.4.5).

Insufficient removal of DBP

precursors (Section 9.2.4.5).

Tastes and Odours Customer complaints.

“Swimming pool” odour (for

systems using chlorine).

Over or underdosing of

disinfection chemical (9.2.4.4)

relative to the breakpoint curve.


9.2.4.1 Optimizing Pre-Treatment Processes

Treated water quality (or filter effluent quality) has a strong impact on disinfectant demand

and disinfection efficiency. Generally, the characteristics of the filter effluent affect the

efficiency of chemical disinfection in two ways:

1. Exerting an additional oxidant demand thereby requiring a higher disinfectant

dosage to achieve the same level of pathogen reduction; and

2. Interference with the disinfection process.

Water characteristics that have a significant impact on the efficiency of disinfection may

include:



NOM;

Turbidity;

Ammonia, nitrite and organic nitrogen;

Iron and manganese;

pH;

Low water temperature;

UVT; and

Higher than normal loading of microbial pathogens.

Generally, optimizing upstream processes will improve the efficiency of disinfection by

reducing the disinfectant demand and preventing the shielding of pathogens by suspended

solids.

In many cases, it may not be possible to change the characteristics of the raw water (i.e.

presence of cysts and viruses, water temperature, etc.); however, the following approaches

can be used to optimize disinfection:

Practice enhanced coagulation to reduce NOM concentrations in filtered water

(Section 9.2.4.5) resulting in lower DBP formation and reduced disinfectant demand.

Optimize filtration processes to reduce turbidity (Chapter 8).

Address causes of process upsets (e.g. floc carryover and/or poor coagulant chemical

dosage control) which may result in poor filter effluent quality and reduce the

effectiveness of disinfection.

Consider a change to ozonation with or without biofiltration, or consider eliminating

pre-chlorination to promote biological activity in filters (Chapter 10).

Seasonal variations in water quality (e.g. spring run-off, anaerobic conditions under

prolonged ice-cover) can affect the oxidant demand for disinfection. Variability in

water quality can cause difficulty in predicting the required chlorine dosages.

Incorporate measures such as increased monitoring of raw water and implementing

source water protection programs, if required.

9.2.4.2 Optimizing Initial Mixing

The disinfection effectiveness of chlorine is greatly enhanced by effective mixing of the

water and chlorine solution. Proper mixing optimizes the disinfection process in the

following ways:

Optimizes the amount of contact between the chlorine and the pathogens in the

water; and

Avoids the formation of chlorine concentration gradients resulting in inefficient

disinfection.



In general, the use of a diffuser is sufficient to provide adequate mixing of chlorine in the

water stream. However, when ammonia is present, it is important that the chlorine be rapidly

blended with the bulk flow. If this is not accomplished, disinfection is compromised and both

chlorine and ammonia are lost in localized breakpoint reactions (MWH, 2005). In this case,

rapid mixing is required.

Disinfection can be optimized by the installation of, or improvements to, chemical diffusers,

mixing baffles or mechanical mixers, or other mechanisms to create a highly turbulent

regime. In some instances, moving the chemical addition point to a more turbulent location

can result in improved initial mixing.

Tracer tests and/or mathematical modelling (i.e. CFD) can be used to assess the degree of

mixing available for chlorination (Chapter 4).

9.2.4.3 Optimizing Contact Time

To optimize the inactivation of pathogens, it is necessary to maintain contact between the

target microorganisms and a minimum disinfectant residual concentration for a specified

period of time. As noted previously, this is assessed on the basis of the CT concept. The CT

achieved should exceed the CT required at all times. It should be noted, however, that

excessive contact times can lead to increased formation of DBPs (see Section 9.2.4.5).

Chemical inactivation of pathogens normally occurs in a contact chamber, which is typically

designed as a serpentine chamber to create plug flow conditions. In some drinking water

systems, the discharge piping or a portion of the distribution system prior to the first

consumer is used to provide some or all of the contact time.

Tracer tests should be conducted to verify that the required contact time is provided and to

ensure that there is no short-circuiting in the contact chamber (Chapter 4).

The following modifications can be incorporated to optimize contact time and prevent short-

circuiting:

Modify contact chambers to create plug flow conditions. Baffles or walls can be

incorporated to create a serpentine flow configuration. Length to width ratios of at

least 40:1 should be provided;

Provide rounded corners to reduce dead zone areas and eddy currents; and

Outlet structures of contact chambers should be provided with either a diffuser baffle

or a launder-type weir (White, 1999).

Chlorine contact chambers should also be cleaned regularly to ensure efficient performance.

9.2.4.4 Optimizing Disinfectant Dose

As discussed previously, current disinfection requirements for drinking water systems subject

to O. Reg. 170/03 are based on the CT approach presented in the Disinfection Procedure. In

general, the calculations used to achieve a desired CT for a target log inactivation tend to be

conservative, as they factor in worst case conditions for pH, temperature, flow, etc. and may

not reflect actual operating conditions. For example, temperatures are typically lowest in

winter, while peak flows are typically experienced in summer. The two challenging



conditions may not coincide, and the actual CT achieved may be much higher than the CT

required.

Several optimization strategies, techniques and software tools are available that allow

operators to evaluate CT based on actual operating conditions. Examples include the IDDF

(Bellamy, et. al., 1998) and Disinfection Profiling and Benchmarking (USEPA, 2003). A

disinfection profile is a graphical representation of a system’s level of Giardia or virus

inactivation measured during the course of a year. A benchmark is the lowest monthly

average microbial inactivation achieved during the disinfection profile time period.

Proprietary spreadsheet or modelling tools can be used to support the implementation of

IDDF or disinfection profiling.

Monitoring of the actual CT achieved with regards to the CT required may allow a reduction

in the disinfectant dosage, resulting in reduced chemical usage and potentially reducing the

formation of DBPs.

9.2.4.5 Minimizing DBP Formation

The application of disinfectants and other oxidants to water may result in the formation of

disinfection by-products, some of which may be a public health concern.

Table 9-3 presents a summary of the most common DBPs formed as a result of the use of

chlorine, chloramines, chlorine dioxide and ozone during drinking water treatment.

Table 9-3 – Common Disinfection By-Products

Class By-Product

Chemical Agent

Trihalomethanes1 Chloroform Chlorine

Bromodichloromethane Chlorine

Dibromochloromethane Chlorine

Bromoform Chlorine, Ozone

Haloacetic acids2 Monochloroacetic acid Chlorine

Dichloroacetic acid Chlorine

Trichloroacetic acid Chlorine

Monobromoacetic acid Chlorine

Dibromoacetic acid Chlorine

Oxyhalides Chlorite Chlorine Dioxide

Chlorate Chlorine Dioxide

Bromate Ozone

Table 9-4 – Common Disinfection By-Products (cont’d.)



Class By-Product

Chemical Agent

Nitrosamines N-Nitrosodimethylamine Chlorine, Chloramines

Notes:

1. Several other THM compounds are known; however, only these four are included in the O.

Reg. 169/03 maximum acceptable concentration (MAC) for total THMs.

2. Four other HAA compounds are known; however, regulatory standards for HAAs are

generally based on the total of these five compounds (HAA5).

Chlorine By-Products

Optimization strategies to reduce the formation of THMs and HAAs include:

Elimination of pre-chlorination;

Improving precursor removal (enhanced coagulation, membrane filtration, GAC

filtration, ion exchange);

Optimizing pH during disinfection;

Optimizing chlorine dosage through disinfection profiling and benchmarking; and

Using alternative disinfectants.

Additional information is presented in Strategies for Minimizing the Disinfection By-

Products Trihalomethanes and Haloacetic Acids (MOE, 2009).

Technologies are also available for the removal of THMs and HAAs, such as GAC filtration

and aeration or air stripping; however, the application of these technologies at water

treatment plants is seldom practical compared to the other DBP reduction strategies discussed

above (MWH, 2005).

Other by-products, such as perchlorate, bromate, chlorate and chlorite, have also been found

as impurities in hypochlorite solutions. These contaminants may form during manufacturing,

or transport and storage. Dilution, temperature control, and less storage time are considered

to be the most practical approach for reducing by-products being added to finished water

from hypochlorite solutions (Stanford et. al., 2010).

Chlorine Dioxide By-Products

Chlorine dioxide does not form halogenated by-products like chlorine; however, it does

produce two inorganic by-products, chlorite and chlorate.

Chlorate may be naturally present in raw waters as a result of agricultural or industrial

activity and is also a degradation product of chlorine in liquid hypochlorite solutions (MWH,

2005).

Chlorite may be injected into the water stream as a result of inefficient chlorine dioxide

generation (sodium chlorite is one of the chemicals used to generate ClO2). The decay of

chlorine dioxide after it is applied to the water may also result in the formation of chlorite and

chlorate through one of two ways:



The oxidation of various water constituents, such as reduced iron, manganese or

NOM; or

Under high temperature and/or high pH conditions, chlorine dioxide disproportionate

to form chlorite and chlorate.

The formation of chlorite limits the chlorine dioxide dose that can be applied during drinking

water disinfection, unless chlorite removal technologies are implemented downstream.

Currently, the only available measure to reduce chlorite formation is to reduce the chlorine

dioxide dose, which is accomplished by reducing the chlorine dioxide demand (i.e. improving

NOM removal and/or improving iron and manganese precipitation using other oxidants, prior

to application of chlorine dioxide).

The most common chlorite destruction or removal technologies for full scale WTPs are:

Reduction of chlorite to chloride with ferrous iron;

Reduction or removal with activated carbon; and

Oxidation with ozone.

Ozone By-Products

When added to water, ozone reacts with NOM and bromide (if present) to form various by-

products, including bromate. Strategies that can be implemented to reduce ozone by-products

include reducing NOM and/or bromide concentrations before the application of ozone, or

using less ozone.

Reducing ozone dosage is generally not practical, because the ozone dose is determined by

other factors, such as disinfection requirements or taste and odour control. Options for the

removal of NOM are the same as those discussed for minimizing the formation of

chlorination by-products (enhanced coagulation, GAC filtration, etc).

The following two measures have also been used to reduce the formation of bromate:

pH depression: Lowering the pH of water during ozonation hinders the formation of

intermediate compounds that react with ozone to form bromate.

Ammonia addition: Ammonia further reduces the concentration of intermediate

compounds that react with ozone to form bromate. Combining pH depression and

ammonia addition to some waters can be used to reduce bromate formation by more than

90 percent (MWH, 2005).

Several technologies exist for the removal of bromate and organic by-products formed as a

result of ozonation, including ion exchange, membrane filtration and biological filtration.



9.2.4.6 Improving Process Control

Most municipal drinking water systems have some form of automated process control

system, particularly when alternative disinfectants (such as ozone, which require a greater

degree of operator attention) are employed. However, a chlorination system with manual

control can be optimized by employing an automated feed control strategy to regulate the

chlorination dosage. This approach will minimize chemical consumption and ensure that a

minimum chlorine residual is maintained at all times.

Control systems for chlorination dosage typically consist of:

1. Manual control: The operator adjusts dosages manually based on process conditions

and measured chlorine residual.

2. Flow proportional (or open-loop) control: The chlorine feed rate is paced to the flow

rate as measured by the filtered water meter (where post-disinfection is practiced).

Flow proportional control is sometimes referred to as “feed-forward” control.

3. Automatic residual (or closed-loop) control: The chlorine dosage is controlled by the

automatic measurement of the chlorine residual with an on-line chlorine analyzer.

Residual control is sometimes referred to as “feed-back” control.

4. Automatic compound-loop control: The chlorine dosage is controlled by both the

water flow rate and an automatic chlorine analyzer. The output from the water flow

meter and the residual analyzer is used by a programmable logic controller (PLC) to

control chlorine dosage and residual.

The chlorine residual analyzer is a key piece of instrumentation available to optimize the

chlorination disinfection process. Accurate measurement of chlorine residual is important to

ensure proper disinfection, while avoiding excessive chemical dosages and the potential

formation of DBPs.

The analytical method adopted to monitor chlorine residual at a water treatment plant must be

able to measure a range of concentrations with an appropriate level of accuracy and

reproducibility. In addition, proper maintenance and calibration, in accordance with

manufacturer’s instructions, must be conducted to ensure continued analyzer accuracy.

9.3 ULTRAVIOLET (UV) IRRADIATION

9.3.1 Purpose and Mode of Disinfection

The application of UV light is an acceptable primary disinfection process; however, since it

does not produce a residual, it is not suitable for secondary disinfection.

Specific requirements for the design and operation of UV systems are provided elsewhere

(MOE, 2006; MOE, 2008; USEPA, 2006).

UV systems are proprietary. Different UV technologies are available, including low pressure,

medium pressure (MP) and low pressure high output (LPHO) lamps.

The mechanism of disinfection by UV light differs considerably from the mechanisms

associated with chemical disinfectants such as chlorine and ozone. Chemical disinfectants

inactivate microorganisms by destroying or damaging cellular structures, interfering with



metabolism and growth. UV light inactivates microorganisms by damaging their nucleic acid,

thereby preventing them from replicating. A microorganism that cannot replicate cannot

infect a host.

It has been determined that the germicidal effect of UV light is most effective at wavelengths

between 250 and 265 nm (White, 1999). Low-pressure lamps emit light at a specific

wavelength, 254 nm (MWH, 2005). Newer lamp technologies exist, as mentioned above,

which provide UV radiation at wavelengths different than 254 nm; therefore, the dosage

provided by a specific UV reactor should always be expressed as a 254 nm-equivalent UV

dose.


Similar to the CT concept, the degree to which the destruction or inactivation of

microorganisms occurs by UV radiation is directly related to the UV dose. UV dose is

defined as the product of the UV light intensity (W/m2 or mW/cm

2) and the exposure time

(s). Units commonly used to express UV dose are mJ/cm2 or J/m

2.

The UV dosage, at a target design 254 nm-equivalent UV dose, required for water

disinfection for groundwater systems is set by the Disinfection Procedure as a pass-through

UV dose of 40 mJ/cm2. For surface water and GUDI systems, where other treatment barriers

ensure pathogens such as viruses and bacteria are removed, or inactivated by chemical

disinfection, or where UV is used only for a part of primary disinfection, lower UV doses

may be acceptable.

UV manufacturers commonly design their reactors to operate using either:

The UV Intensity Setpoint Approach; or

The Calculated Dose Approach.

The monitoring approach used for a particular system depends on the type of unit used. As

specified in the Disinfection Procedure, all UV disinfection facilities must continuously

monitor those parameters that allow the operator to determine that the target design 254 nm-

equivalent UV pass-through dose or higher is being delivered. All systems must annunciate

failure alarms when this design dose is not being delivered.

Table 9-4 presents monitoring recommendations, in terms of sampling locations and

analyses, in order to evaluate the performance of the UV disinfection process.



Table 9-5 – UV Disinfection – Recommended Monitoring to Evaluate Performance


Measurement1

Parameters /

Analyses Comments


pH

Temperature

Flow rate

Filter effluent or

other location

upstream of UV

disinfection

process (for

systems not using

filtration)


UV transmittance

(UVT)

Turbidity may shield

pathogens from UV light.

UVT has a direct impact on

UV dose delivery.

Grab sample pH

Alkalinity, Hardness

Calcium

Iron and manganese

Water quality parameters

that can affect the type and

amount of sleeve fouling

that occurs in UV reactors.

UV System Continuous monitoring UV dose To evaluate performance of

UV disinfection process

Downstream of

UV disinfection

process

Continuous monitoring Disinfectant residual

(if chemical

disinfectant is applied

downstream of the UV

process)

UV disinfection used in

combination with another

disinfectant may be more

effective than either

disinfectant acting alone.

Grab sample Total coliform, E. coli

and heterotrophic plate

count

Notes:

1. Although continuous monitoring is recommended for several parameters, for small systems or

groundwater systems where water quality is relatively consistent, grab sampling may be more

appropriate, except where continuous monitoring is required by regulation.


Table 9-5 presents the symptoms and causes of common problems encountered with UV

disinfection.



Table 9-6 – UV Disinfection – Symptoms and Causes of Common Problems



High Levels of

Turbidity in UV

Influent

Higher than typical

disinfectant dosages

required to maintain target

disinfectant residual.




Upstream process upsets.

Poor performance of upstream treatment

processes.

Low UVT in UV

Influent

Reduced ability of water to

transmit UV light.




Due to raw water characteristics, such as

organic compounds (e.g. natural organic

matter) and inorganic compounds (iron,

manganese).

Use of iron-based coagulants, as iron has

a high absorbency of UV light.

Fouling Reduces the intensity of the

UV light that reaches the

microorganisms.

Higher UV dosage required.




Lamp fouling occurs due to the

accumulation of inorganic, organic, and

biological solids on the quartz sleeves

that surround the lamp.

Biofilms and algae growth can be a

problem if these are not removed in

upstream processes.

Inadequate cleaning and maintenance of

UV lamps.

Poor System

Hydraulics

Reduces the average contact

time resulting in ineffective

disinfection.

Density currents causing flow to move

along the bottom or top of the lamps.

Entry and exit conditions that lead to the

formation of eddy currents, thereby

inducing uneven velocity profiles.

Dead spaces or zones within the reactor

reduce the effective reactor volume and

shorten the average hydraulic retention

time.

System is hydraulically overloaded.

Poor Disinfection

Performance not

Attributable to

Problems

Identified Above

Detection of


organisms in treated water

or increased demand in

subsequent chemical

disinfection processes.

Burned out UV lamps.

Operating at flows in excess of design

flow capacity.

Excessive turbidity, such that micro-

organisms are being shielded from the

UV rays. Particle size distribution testing

can be used to diagnose this problem.




9.3.4.1 Optimizing Pre-Treatment Processes

Poor raw water quality or poor filter effluent quality can reduce the effectiveness of UV

disinfection. Generally, the characteristics of the water to be treated affect the efficiency of

UV disinfection in three ways:

1. Absorbing and/or scattering UV light, thereby reducing the UV light that reaches the

microorganisms;

2. Shielding of microorganisms from exposure to UV light by suspended solids; and

3. Contributing to fouling of quartz sleeves that surround the lamp, reducing the

intensity of the UV light that reaches the microorganisms.

The UVT of the raw water or filter effluent can be variable. This can be attributed to diurnal

or seasonal variations in raw water quality as a result of climatic conditions (e.g. heavy rain

and runoff, prolonged ice cover leading to anaerobic conditions).

In many cases, it may not be possible to change the characteristics of the water to improve

the efficiency of UV disinfection. However, the following approaches to optimize UV

disinfection are available:

Implement on-line monitoring of UVT to measure and document any diurnal or

seasonal variations in UVT and apply UV dosage corrections;

Increase raw water monitoring and implementing source water protection programs,

if required;

Optimize upstream pre-treatment processes to reduce turbidity and improve UV

transmittance (Chapter 8); and

Address causes of process upsets (e.g. floc carryover or poor coagulant chemical

control) which may result in poor filter effluent quality, reducing the effectiveness of

UV disinfection.

9.3.4.2 Minimizing Fouling

Fouling of quartz sleeves that surround the UV lamp will reduce the intensity of the UV light

that reaches the microorganisms, thereby reducing the efficiency of UV disinfection. The

total hardness, manganese and iron concentrations of the water are indicators of the potential

for fouling of the UV lamps.

Lamp fouling can be caused by:

Accumulation of inorganic, organic, and biological materials on the quartz sleeves

that surround the lamp;

High iron concentrations due to the addition of iron-based coagulants;



High levels of calcium and magnesium due to elevated hardness;

Organic fouling; and

pH (which can affect the solubility of the scaling material).

To optimize performance, fouling can be controlled by mechanical, sonic or chemical

cleaning units. Lamps should be regularly cleaned and maintained according to the

manufacturer’s recommendations to sustain performance.

Pumping-to-waste on well start-up can be used to reduce sleeve fouling.

The presence of algae and/or biofilms in the water can also reduce the effectiveness of UV

disinfection by shielding bacteria and other microorganisms, or by growing on the lamps and

reducing the amount of light transmitted. It may be necessary to provide pre-treatment, such

as microscreening (see Chapter 5) and/or chlorination (see Section 9.2) to reduce algae or

control biofilm formation, upstream of the UV reactors.

Optimization techniques for coagulation processes to reduce iron residuals in the treated

water are presented in Chapter 6.

9.3.4.3 Optimizing Reactor Hydraulics

Reactor hydraulics are a key factor in the performance of UV disinfection. Plug-flow

conditions with radial mixing are required for efficient disinfection. Good radial mixing is

required to prevent microorganisms from passing through the UV reactor between lamps and

receiving a smaller UV dose than the average value. Radial turbulence is important because it

ensures adequate mixing, minimizing the effects of short-circuiting and particle shading.

These conditions are typically controlled by the reactor geometry, the lamp array geometry,

and the flow rate of water to the UV disinfection system.

Poor system hydraulics will reduce the efficiency of the UV disinfection process. Common

hydraulic problems that result in short-circuiting include:

Density currents causing influent flow to move along the bottom or top of the lamps;

Entry and exit conditions that lead to the formation of eddy currents inducing uneven

velocity profiles; and

Dead spaces or zones within the reactor, reducing the effective reactor volume and

shortening the average hydraulic retention time.

Although it may not be possible to change the reactor hydraulics of an existing system,

techniques such as offsetting the inlet and outlet and using perforated stilling plates, have

been used to accommodate the contradicting characteristics of plug flow and turbulence

(USEPA, 1996).

Additional information is presented in MOE (2008) and Bolton & Cotton (2008).



9.3.4.4 Collimated Beam Testing

Collimated beam tests can be used with raw water or filter effluent samples collected over a

representative range of operating conditions to produce a dose-response relationship. The

dose-response relationship established can be used to establish the required UV dose to meet

inactivation requirements.

Plant operators or owners should contact a UV system supplier to discuss collimated beam

testing.

9.3.4.5 Improving Process Control

Process control strategies, such as flow pacing and dose pacing, can be used to optimize the

performance of UV disinfection systems.

Flow pacing controls the lamp intensity and/or the number of lamps in operation based on the

flow rate through the UV disinfection system. This can reduce energy use during low flow

periods. On-line flow monitoring equipment is required to implement flow pacing.

Dose pacing involves adjusting the lamp intensity and/or the number of lamps in operation

based on not only the flow rate through the UV disinfection system, but also the UVT of the

stream being treated. This ensures that a constant UV dose is being applied. Online UVT

sensors and flow monitoring, or UV intensity sensors, are required to implement dose pacing.

Additional information regarding instrumentation and control strategies and requirements can

be found in USEPA (2006).

9.4 CASE HISTORIES

9.4.1 Port Rowan WTP – pH Control for Optimizing Disinfection

The following case study is based on information presented in Poisson and Wilson (2006).

System Description

The Port Rowan WTP draws raw water from Long Point Bay on Lake Erie and serves the

Town of Port Rowan and outlying areas. The rated capacity of the WTP is 3,040 m3/d. The

treatment process consist of coagulation, flocculation, sedimentation and filtration in two

Ecodyne Monoplants, disinfection by chlorine contact time in a clearwell and GAC

adsorption for taste and odour control.

Due to several regulatory changes in 2000 and 2001, a number of upgrades were required for

the disinfection system. The C of A issued to the Port Rowan WTP in 2001 required 3.0 log

removal/inactivation of Giardia and 4.0 log removal/inactivation of viruses. Given that the

existing chemically-assisted filtration process was operating well, the plant was credited with

2.5 log removal of Giardia and 2.0 log removal of viruses, meaning the remaining

disinfection credits of 0.5 log reduction of Giardia and 2.0 log removal of viruses were

required to be achieved through inactivation.



Based on an analysis of alternative disinfection methods, it was decided to install a UV

disinfection system to provide for Giardia inactivation and achieve the remaining 2.0 log

virus inactivation using free chlorine.

Due to increased algal growth in the summer months, the raw water pH at the Port Rowan

WTP usually exceeds 9.5. This relatively high pH increases the CT required to achieve a

target log inactivation. Using the existing chlorine contact facilities, an increase in CT

required an increase in chlorine dose, which likely contributed to higher treated water and

distribution system THM concentrations. Also, higher chlorine dosages were reducing the

useful life of downstream GAC filters. To address both the CT and THM issues, it was

decided to install a pH control system as part of the plant upgrades.


A number of studies were undertaken prior to the plant upgrades to evaluate the capability of

the existing system and to establish design criteria for the upgraded works.

A review of existing conditions was undertaken to establish historical data for raw water

temperature, pH, peak flow and chlorine residual. It was determined that the limitations on

the CT achieved at the existing plant were influenced by two factors:

Cold winter water temperatures (0.5°C); and

Requirement to maintain a low chlorine residual concentration (0.2 mg/L) leaving the

clearwell and entering the GAC filters.

This evaluation also showed that the 2 log inactivation of viruses could only be achieved

within the existing plant and dedicated section of watermain by maintaining higher chlorine

residuals, possibly affecting the GAC contactors and increasing the formation of THMs.

The study also showed that by decreasing the pH of the influent water to 8.0, the pre-

chlorination residual could be maintained at the operational objective of 0.2 mg/L and the

plant could meet the required 2 log inactivation of viruses for most water temperatures. It was

also determined that the GAC filters could be by-passed during the period of December to

April (when taste and odour causing compounds are generally not present) and water

temperatures are at their lowest, allowing higher chlorine dosages to achieve the required CT.

Summary

A carbon dioxide injection system was installed at the plant, resulting in a consistent pre-

treatment water pH of approximately 8 throughout the year. This improved the plant’s ability

to meet CT requirements for virus inactivation while maintaining chlorine residuals within

established operational guidelines. THM concentrations in the distribution system also

decreased significantly, particularly for samples collected in August and November, as a

result of the decrease in pH.

9.4.2 Ameliasburgh WTP – Optimization Study to Control the Formation of

DBPs

The following case study is based on information presented in Andrews, Hofmann &

Associates and R.V. Anderson Associates (2009).



System Description

The Ameliasburgh WTP draws water from Roblin Lake and has a rated capacity of 360 m3/d.

Raw water is screened and then pumped into a 7.3 m3 high lift well. Sodium hypochlorite is

added at the discharge pipe of the high lift well to target a free chlorine residual of

approximately 0.2 mg/L measured at the inlet to the downstream pressurized clarifier.

The high lift pumps supply water to two parallel 180 m3 Culligan Multi-Tech filtering trains,

each consisting of a clarifier and pressure filter. Coagulant is added just upstream of a static

mixer and the clarifiers/filters. Post-chlorination (following filtration) is performed through

injection of sodium hypochlorite into the discharge header, with a target free chlorine

residual of 2.4 mg/L at the inlet of the contact pipe (400 mm diameter, 112 m long).

Historical plant water quality data indicated that treated water THM concentrations ranged

between 18 and 137 µg/L, while distribution system THM concentrations ranged from 17 to

273 µg/L. Historical HAA data were not available for the Ameliasburgh WTP.

Bench scale treatability and full scale testing was undertaken to determine if changes in

coagulant dosage could be used to achieve a reduction in THM and HAA formation to below

80 µg/L.


Jar tests were performed with various coagulants and doses and were designed to simulate

plant conditions where possible. A number of raw water quality parameters were evaluated in

filtered samples, and testing was conducted for chlorine decay and Simulated Distribution

System (SDS) THM formation.

For the Ameliasburgh WTP, the optimum coagulant dose was selected based on the highest

TOC removal. Optimized samples resulted in 5 to 20 percent lower TOC levels than the

control sample (existing plant dosage). THM concentrations were approximately 30 to 50

percent lower in optimized samples than in the control samples, while HAA levels were

approximately 25 to 40 percent lower than the control sample.

Subsequent to the bench scale studies, full scale testing was conducted to evaluate the effect

of optimized coagulation (application of the optimal coagulant dose determined during jar

testing) on potential DBP reduction. The results of the full scale testing at Ameliasburgh

indicated that:

Implementation of enhanced coagulation resulted in minor improvements in TOC

removal;

Enhanced coagulation, when compared to historical (lower) coagulant doses, resulted

in reductions in THM and HAA formation; and

SDS tests appeared to provide a reasonable estimate of DBP formation levels in the

treated water and distribution system. This relationship may be useful when

considering future disinfection optimization, by allowing testing to be performed at

bench scale.



A modified disinfection benchmarking evaluation was also undertaken to determine if

reductions in chlorine dosage could further reduce DBP formation, while still maintaining

adequate CT. The Amerliasburgh CT values were recalculated to consider varying flow rates,

temperature and pH, and the corresponding Giardia and virus inactivation levels were

determined.

A spreadsheet was used to calculate the CT (mg·min/L) that was achieved at the WTP for

each day in 2005 and 2006. The results of the disinfection benchmarking are presented in

Figure 9-1. The required CT was not met 18 times in the 2005-2006 period. Most of these

occurrences were between January and March. Conversely, in the summer and fall of 2005-

2006, the CT values provided were much higher (approximately 20 to 200 mg·min/L higher)

than the required CT. This indicated that lower doses of chlorine could potentially have been

applied while still meeting CT requirements, providing that an adequate residual was

maintained throughout the distribution system. As a result, chlorine usage may have been

reduced and a reduction in THM and HAA formation could potentially have been achieved.

0

20

40

60

80

100

120

140

160

180

200

01/0

1/20

05

01/0

3/20

05

01/0

5/20

05

01/0

7/20

05

01/0

9/20

05

01/1

1/20

05

01/0

1/20

06

01/0

3/20

06

01/0

5/20

06

01/0

7/20

06

01/0

9/20

06

01/1

1/20

06

Date

CT

(m

g-m

in/L

)

CT Provided

CT Required

Figure 9-1 – CT Provided and Required for 1.0-log Giardia Inactivation (2005-2006) –

Ameliasburgh WTP

Summary

Based on the results of the bench and full scale testing, enhanced coagulation appeared to

provide a reduction in THM and HAA formation in both the treated water and in the

distribution system. As such, enhanced coagulation is an easily implemented strategy for

reducing TOC, and therefore DBP formation, without major capital investment.



9.5 REFERENCES

Andrews, Hofmann & Associates Inc. and R.V. Anderson Associates Ltd. (2009).

Optimization Study to Control the Formation of THMs and HAAs – Optimization Report,

prepared for the Ontario Ministry of the Environment.

Bellamy, W.D., G.R. Finch, C.N. Hass (1998). Integrated Disinfection Design Framework.

AWWA Research Foundation and AWWA. Denver, CO. ISBN0-89867-933-8.

Bolton, J.R. and C.A. Cotton (2008). The Ultraviolet Disinfection Handbook. AWWA.

Denver, CO. ISBN 978-1-58321-584-5.


MOE (2009). Strategies for Minimizing the Disinfection By-Products Trihalomethanes and

Haloacetic Acids. PIBS 7152e.



ISBN 0-471-11018-3.

Poisson, R. E. and D. Wilson (2006). “Using pH Control by Carbon Dioxide Injection to

Reduce Required CT and Distribution System THM Concentrations”, presented at the 2006

OWWA/OMWA Joint Annual Conference and Trade Show. Toronto, ON.

Regli, S. (1990). “How’s and Why’s of CTs”, presented at AWWA Annual Conference,

Cincinnati, OH.

Stanford, B.D., A.N. Pisarenko, S.A. Snyder and G. Gordon (2009). Minimize Perchlorate

Formation in Hypochlorite Solution. AWWA Opflow, Vol. 35, Iss. 10, October 2009.

USEPA (1996). Ultraviolet Light Disinfection Technology in Drinking Water Application -

An Overview. Office of Ground Water and Drinking Water. EPA 811-R-96-002.


Composite Correction Program. EPA/625/6-91-027.

USEPA (1999). Alternative Disinfectants and Oxidants Guidance Manual. Office of Water.

EPA 815-R-99-014.

USEPA (2003). LT1ESTWR Disinfection Profiling and Benchmarking Technical Guidance

Manual. Office of Water. EPA 816-R-03-004.

USEPA (2006). Ultraviolet Disinfection Guidance Manual For the Final Long Term 2

Surface Water Treatment Rule. Office of Water. EPA 815-R-06-007.

White, Geo. Clifford (1999). Handbook of Chlorination and Alternative Disinfectants. Fourth

Edition. John Wiley & Sons Inc. New York, NY. ISBN 0-471-29207-9.


CHAPTER 10 OTHER TREATMENT PROCESSES

OTHER TREATMENT PROCESSES

10.1 Introduction .......................................................................................................... 10-1

10.2 Aeration and Air Stripping ................................................................................... 10-1

10.2.1 Purpose and Types of Aeration and Air Stripping Systems .................. 10-1




10.3 Ion Exchange ........................................................................................................ 10-4

10.4 Biologically Active Filtration ............................................................................... 10-5

10.5 Iron and Manganese Control ................................................................................ 10-6

10.5.1 Purpose and Types of Iron and Manganese Control Processes ............. 10-6



10.5.4 Optimization Techniques ..................................................................... 10-10

10.6 Taste and Odour Control .................................................................................... 10-11

10.6.1 Purpose and Types of Taste and Odour Control Processes ................. 10-11

10.6.2 Evaluating Performance ....................................................................... 10-12

10.6.3 Common Problems and Potential Impacts ........................................... 10-13


10.7 Natural Organic Matter Removal ....................................................................... 10-16

10.7.1 Purpose and Types of NOM Removal Processes ................................ 10-16




10.8 Internal Corrosion Control ................................................................................. 10-20

10.8.1 Purpose and Types of Internal Corrosion Control Processes .............. 10-20




10.9 Case Histories ..................................................................................................... 10-25

10.9.1 Washington, D.C. – Optimization of Orthophosphate Addition ......... 10-25

10.9.2 Chicago, IL – Optimization of Taste and Odour Control with Pilot

Plant Testing ........................................................................................ 10-26

10.10 References .......................................................................................................... 10-27

CHAPTER 10. Other Treatment Processes 10-1


CHAPTER 10

OTHER TREATMENT PROCESSES

10.1 INTRODUCTION

The previous unit process chapters presented in this Optimization Manual focused primarily

on improving the performance of conventional unit treatment processes using the approach of

the USEPA Handbook entitled Optimizing Water Treatment Plant Performance Using the

Composite Correction Program (USEPA, 1998). The USEPA CCP approach is designed to

improve particulate removal and disinfection to meet regulatory requirements through the

optimization of coagulation, flocculation, sedimentation, filtration and disinfection.

In this chapter, the optimization of other unit processes that may or may not be included in a

conventional water treatment train are presented. Processes described include aeration and air

stripping, and processes used for control of iron and manganese, taste and odour, NOM and

corrosion.

10.2 AERATION AND AIR STRIPPING

10.2.1 Purpose and Types of Aeration and Air Stripping Systems

Aeration and air stripping are gas-liquid contact processes. The primary use of aeration in the

water treatment industry is for the removal of:

Carbon dioxide (CO2);

Hydrogen sulphide (H2S);

Methane;

Volatile organic chemicals (VOCs);

Radon;

Iron and manganese, which are oxidized and then removed by settling and/or

filtration; and

Tastes and odours.

Aeration can also be used to add dissolved oxygen (DO) to water.

Air stripping is the aeration process most commonly used in Ontario for the removal of

methane and/or H2S from groundwater.

Aeration and air stripping can be achieved by the use of multiple tray spray aerators or

towers, pressure aerators and packed towers, diffused air, cascades and mechanical aeration.


The performance of aeration and air stripping processes is assessed on the basis of removal of

the targeted compound.



Table 10-1 presents monitoring recommended, in terms of sampling locations and analyses,

in order to evaluate the performance of aeration processes.

Table 10-1 – Aeration – Recommended Process Monitoring to Evaluate Performance


Measurement

Parameters / Analyses Comments

Influent to

aeration process

Continuous monitoring

or grab sample1

Temperature

pH

Water temperature

affects the solubility of

oxygen in water

Grab sample Iron

Manganese

CO2

Tastes and odours

VOCs

To measure the

effectiveness of aeration

for the removal of the

parameter(s) of concern

Treatment process Continuous monitoring Air flow rate

Water flow rate

For process control

Aeration effluent Continuous monitoring

or grab sample1

pH

pH is an indicator of

CO2 removal

Controlling pH can help

to optimize removal of

other targeted

parameters (iron,

manganese, H2S)

Dissolved oxygen Monitoring DO

concentration can help

to optimize air addition

and minimize energy

costs

Grab sample Iron

Manganese

CO2

Tastes and odours

VOCs

To measure the

effectiveness of aeration

for the removal of the

parameter(s) of concern

Notes:

1. Test frequency depends on both the variability of raw water quality and the parameter

measured. For example, groundwater temperature tends to be relatively constant and less

frequent monitoring may be warranted.



In addition to the recommended sample locations and analyses presented in Table 10-1, it is

recommended that frequent visual inspections of the aeration equipment and downstream

processes be conducted to monitor for common problems associated with aeration equipment,

as described in the following subsection.


Symptoms and causes of common problems encountered with aeration processes are shown

in Table 10-2.

Table 10-2 – Aeration – Symptoms and Causes of Common Problems

Problem Description

Mitigation

Corrosion Excessive DO concentration can

accelerate the corrosion of metal

surfaces in downstream unit

processes or in the distribution

system.

Operate the aeration process to

provide an adequate but not

excessive level of DO (see Section

10.2.4).

Provide protective coatings on

exposed metal surfaces.

Floating Floc in

Clarifiers Excessive aeration can cause air

bubbles to come out of solution and

attached to floc particles in

clarification processes, causing the

particles to float rather than settle.

Increased solids loading on filters.

Optimize DO concentration.

Air Binding of

Filters Dissolved air in the water causes

gas bubbles to accumulate in the

filter between backwashes.

Increased head loss.

Shortened filter runs.

Violent agitation during

backwashing, causing loss of

media.

Optimize DO concentration.

Terminate the filter run before the

total head loss is greater than the

depth of the water above the

unexpanded media (see Chapter 8).

Allow time for the air to dissipate

before initiating a backwash.

If aeration process is included in

treatment train, relocate to

downstream of filters.

Slime Growth on

Aerator Surfaces Bacteria growing on surfaces of

trays, cascades and spray

equipment may result in tastes and

odours in the treated water, as well

as sloughing of bacteria.

Routinely inspect equipment

surfaces and maintain a chlorine

residual, if needed.



Table 10-2 – Aeration – Symptoms and Causes of Common Problems (cont’d.)

Problem Description

Mitigation

Increased Turbidity

During H2S Removal Undesirable reaction of oxygen and

ionized H2S to release elemental

sulphur, which results in fine

colloidal particles and gives water a

milky appearance.

Optimize pH of the water prior to

aeration to improve removal

efficiency (see Section 10.2.4).

Clogged Diffusers Clogging of diffusers as a result of

dust, oil, debris or chemical

deposits around diffuser opening.

Maintain clean air filters.

Avoid over-lubricating blowers.

Prevent backflow of water into

diffusers.


Optimization of aeration processes is achieved through proper control of the DO

concentration, pH and temperature of the water.

Knowing the DO concentration needed for a particular treatment objective and monitoring

the amount of DO present in the water will prevent over- or under-aeration. For example, on

a stoichiometric basis, 1 mg of oxygen can oxidize 7 mg of soluble iron and 3.4 mg of

soluble manganese (MWH, 2005). The actual amount of oxygen required will be site specific

and can vary seasonally as water quality changes. Monitoring of DO concentrations is

required to determine the correct amount. As a general rule, DO concentrations of 2 to 4

mg/L are sufficient (AWWA, 1995).

The pH of the water can be used to monitor CO2 removal, as pH decreases CO2 is removed.

pH will also affect the effectiveness of H2S, iron and manganese removal. The best pH range

for H2S scrubbing is 6 or less, while iron and manganese are best treated in a pH range of 8 to

9 (AWWA, 1995).

The saturation concentration of oxygen in water varies based on water temperature, with the

amount of dissolved oxygen decreasing as water temperature increases. Therefore, operators

should adjust the aeration process to maintain the correct level of DO as water temperature

changes.

10.3 ION EXCHANGE

Ion exchange is a process in which ions of like charge are exchanged between the water

phase and the solid resin phase. The ion exchange resin is regenerated periodically using a

suitable regenerant. Brine solutions are used to regenerate exhausted water softeners.

Water softening is one of the more common applications of ion exchange, and is achieved by

cation exchange. Water is passed through a bed of cationic resin, and the calcium ions and

magnesium ions in the water are absorbed on the cationic resin in replacement of the sodium

ions.



Anion exchange can be used to remove contaminants such as nitrate, which is exchanged for

chloride. Nitrate-specific resins are available for this purpose. Other contaminants that can be

removed through the use of ion exchange and inorganic adsorbents in full-scale operations

include barium, radium, fluoride, arsenate, perchlorate and uranium. In addition, the MIEX®

process, which operates in a completely mixed reactor, has been developed to remove

dissolved organic carbon (MWH, 2005).

An ion exchange plant normally consists of two or more resin beds contained in pressure

shells with appropriate pumps, pipework and ancillary equipment for regeneration. The

pressure shells are typically up to 4 m in diameter, containing 0.6 to 1.5 m depth of resin

(WHO, 2008). Ion exchange units may be of pressure or gravity type, with either an upflow

or downflow design (MOE, 2008).

The design of ion exchange processes will vary depending on the size of the installation and

the application (i.e. type of contaminant to be removed). As such, assessment criteria and

monitoring programs to be used for the evaluation of ion exchange processes should be

developed in consultation with the design engineer and/or the manufacturer.

Ion exchange processes have to date not been widely used in large-scale water treatment

plants in Ontario; therefore, limited optimization guidance is available. There are a number of

operational parameters that should be considered in the development of an optimization

program for ion exchange processes:

Characteristics and type of the ion exchange resin;

Raw water or feed water characteristics;

Rate of flow applied to the ion exchange unit(s);

Brine concentration; and

Brine contact time.

Additional information on the optimization of ion exchange processes is provided in Clifford

& Zhang (1994); Liu & Clifford (1998); Ghurye, Clifford & Tripp (1999); and Clifford,

Ghurye & Tripp (2003).

10.4 BIOLOGICALLY ACTIVE FILTRATION

In a biologically active filter, microbial growth developed in the filter medium can have

several beneficial aspects. Some specific compounds can be removed by biological oxidation

rather than by adsorption, such as dissolved organic carbon, DBP precursors, geosmin and

MIB, and many more (AWWA, 1999).

Intentional biologically active filtration often includes the use of ozone as a pre-oxidant to

break down natural organic materials into more easily biodegradable organic matter.

Granular activated carbon filter media is often used to support denser biofilms because it has

more surface area than other traditionally employed media. Design guidelines for

conventional and biological granular media filters are provided in the MOE Design

Guidelines for Drinking Water Systems, 2008 (MOE, 2008).



In general, the evaluation of a biologically active process will be based on the degree of

removal achieved for the target parameter(s). Assessment criteria and recommendations for

monitoring for conventional granular filters were presented in Chapter 8. Table 10-3 presents

a summary of typical process parameters for biologically active filters based on DOC

removal.

Table 10-3 – Biologically Active Filtration – Typical Assessment Criteria

Parameter Typical Assessment Criteria

Ozone dosage (if applicable) 0.5 to 1.0 g O3/g DOC

Biological degradation ~ 100 g DOC/(m3)(day)

O2 demand (for DOC oxidation) ~ 200 g O2/(m3)(day)

Empty bed contact time (EBCT) 15 to 30 min

Process control considerations that are needed to prevent undesirable effects in biologically

active filters include:

Aerobic conditions should be maintained at all times within the filters to support the

biomass; anaerobic conditions may develop (and cause odour problems) if oxygen

concentrations are depleted. This may occur if large concentrations of ammonia enter

the filter, if insufficient dissolved oxygen is in the water, or if the bed is allowed to

stand idle for a period of time (AWWA, 1999).

Biological activity may be limited during periods of the year when low water

temperatures (e.g. less than 5°C) occur.

EBCT, media type and depth will have an impact on the distribution of

microorganisms, with deeper beds generally having a lower number of organisms in

the filtrate.

Additional information on the optimization of biologically active filters is provided in Liu,

Huck & Slawson (2001); Smith & Emelko (1998); Elhadi, Huck & Slawson (2006); and

Huck et. al. (2000).

10.5 IRON AND MANGANESE CONTROL

10.5.1 Purpose and Types of Iron and Manganese Control Processes

Iron and manganese are frequently encountered nuisance parameters that can affect aesthetic

water quality. They can cause visible colour and turbidity in water, and cause brown and

black staining of plumbing fixtures and laundry. These effects can occur at specific locations

in a distribution system even when the concentration of either metal in the treated water

entering the distribution system is below the aesthetic objective stated in the Technical

Support Document for Ontario Drinking Water Standards, Objectives and Guidelines (MOE,

2006). This occurs as a result of precipitation and resolubilization processes, which can

produce local pockets of elevated iron and manganese concentrations.



Elevated iron and manganese concentrations occur most frequently with groundwater

sources. Surface water sources may also have elevated concentrations of these metals at

anoxic depths in lakes or seasonally under long-duration ice cover. Five control technologies

are commonly used in Ontario.

Removal of iron by oxidation (air or chlorine) and sedimentation is used in groundwater

treatment systems where iron levels are near the aesthetic objective. On exposure to active

chlorine or oxygen, dissolved iron is rapidly oxidized to an insoluble state and precipitates as

a brown solid. Oxygen and chlorine oxidize manganese at too slow a rate for effective

removal unless the manganese is present at very low levels relative to the iron concentration.

Sequestering with silicates or polyphosphates is an inexpensive and commonly adopted

palliative measure for iron control that slows, but does not stop, the formation of the typical

yellow/brown colour of iron precipitates. Sequestering temporarily traps the iron in a

complexed or colloidal form; at most, the effects last for only a few days. Oxidized iron will

then be slowly released into the water.

Ion exchange water softeners are often used by consumers in small groundwater systems to

reduce hardness. An added feature of ion exchange softening is that dissolved iron and

manganese are also removed in the same way as calcium and magnesium on the exchanger

resin beads. The resin must be regenerated periodically by treating it with a brine solution.

Oxidation and removal by greensand processes has historically depended on using

greensand, a manganese ore, as the filter medium downstream of the addition of a chemical

oxidizing agent. Proprietary media has replaced manganese ore particles in current

“greensand” processes. The media used are surface treated to physically adsorb and retain an

oxidized iron and/or manganese surface layer. The filters require periodic backwashing to

remove the deposited materials.

Pre-oxidation and chemically-assisted granular or membrane filtration may be used when iron

and manganese control is required in addition to pathogen removal. Oxidants commonly used in this

treatment process include potassium permanganate (KMnO4) or ozone (O3).

Biological processes can also be used for iron and manganese removal (see Section 10.4).


The performance of iron and manganese control processes is generally assessed based on the

degree of removal of either or both parameters and by monitoring iron and manganese

concentrations in the distribution system.

Sequestering does not remove iron and manganese from the water; therefore, the performance

of the process should be measured based on other parameters, such as turbidity and colour,

particularly at remote points in the distribution system.


in order to evaluate the performance of iron and manganese control processes.



Table 10-4 – Iron and Manganese Control – Recommended Process Monitoring to


Location Types of

Sample /

Measurement


Raw water Grab sample Temperature

pH

Total and dissolved iron

Total and dissolved

manganese

pH and temperature can affect the

rate of oxidation of iron and

manganese

Treatment

Process1

Continuous

monitoring Oxidant or sequestrant

dosage

Head loss and filtration rate

(if filtration is used)

Dissolved oxygen (if

aeration is used)

For process control

Treated

water

Continuous


Oxidant residual (oxygen,

chlorine, KMnO4 or ozone

concentration), if

applicable

pH

Iron and manganese should be

measured in the treated water to

evaluate effectiveness of removal

process

Increases in turbidity and/or

colour may indicate poor removal

and are caused by oxidation and

precipitation of iron and

manganese

pH can influence degree of

removal, particularly for

greensand processes

Grab sample Total iron

Total manganese

Colour

Sequestrant concentration

Distribution

system

Grab sample Total iron

Total manganese

Turbidity

Colour

Free chlorine residual

Deposition of iron and manganese

precipitates in the distribution

system may require more frequent

flushing

Maintenance of a minimum free

chlorine residual is required to

prevent growth of iron bacteria,

particularly when sequestering is

used as the control technique

Notes:

1. Reference should be made to Chapter 7 (Clarification) and Chapter 8 (Filtration) for

additional information on recommended process control monitoring for these types of

processes. See Section 10.2 for information on process control monitoring for aeration

systems.




Symptoms and causes of common problems encountered with iron and manganese control

processes are shown in Table 10-5.

Table 10-5 – Iron and Manganese Control – Symptoms and Causes of Common

Problems and Potential Optimization Strategies

Process Problem

Mitigation

Sequestering Stabilization reaction duration

shorter than expected; deposition of

iron and/or manganese in

distribution system, or increase in

colour or turbidity

Evaluate sequestrant chemical,

dosage and expected duration (i.e.

delay time to perceptible colour

development) through bench-scale

testing (see MOE Design

Guidelines, 2008)

Excessive growth of iron bacteria

in the distribution system

Increase free chlorine residual in

treated water to achieve at least 0.2

mg/L at all points in the

distribution system

Ion Exchange Decrease in iron and manganese

removal efficiency

Resin should be regenerated using

appropriate brine solution

Increased fouling and more

frequent regeneration of resin

needed to maintain process

efficiency

Examine raw water quality for

presence of oxidized iron or

manganese or dissolved oxygen

Ensure no oxidants are added

upstream of ion exchange process

Prolonged exposure may require

replacement of resin

Oxidation and

Sedimentation Lack of or poor formation of

precipitates, resulting in ineffective

removal

Evaluate optimum oxidant dose and

process pH through jar testing (see

Chapter 4)

Evaluate other oxidant chemicals

Slow oxidation reaction or poor

settling of precipitates leading to

deposition of iron and/or

manganese in distribution system

Optimize detention time by

conducting bench-scale settleability

tests

Optimize settling/contact basin

hydraulics to promote settling (see

Chapter 7)

Oxidation with

Potassium

Permanganate

Underdosing resulting in poor

removal of manganese

Overdosing resulting in a pink

colour in the water

Determine optimum dose through

bench-scale testing (see Chapter 4)



Table 10-5 – Iron and Manganese Control – Symptoms and Causes of Common

Problems and Potential Optimization Strategies (cont’d.)

Process Problem

Mitigation

Oxidation with

Conventional or

Membrane Filtration

Lack of or poor formation of

precipitates, resulting in ineffective

removal

Evaluate optimum oxidant dose and

process pH through jar testing (see

Chapter 4)


Slow oxidation reaction resulting in

dissolved iron and/or manganese

passing through filters, leading to

deposition of iron and/or

manganese in distribution system

Optimize detention time by

conducting bench-scale settleability

tests (see Chapter 4)

Optimize settling/contact basin

hydraulics to promote settling (see

Chapter 7)

Excessive head loss across filter Verify condition of filter media and

filter hydraulic loading rate (see

Chapter 8)

Improve backwashing procedures

(see Chapter 8)

Greensand Filtration Low iron concentration and high

manganese concentration in treated

water

Increase frequency of bed

regeneration

Verify oxidant chemical dosages

Elevated iron and manganese

concentrations in treated water

Determine optimum process pH

through jar testing (see Chapter 4)

Verify condition of filter media and


Chapter 8)

Consider coagulant addition prior

to filtration to improve solids

removal

Excessive head loss across filter Verify condition of filter media and


Chapter 8)

Improve backwashing procedures

(see Chapter 8)


The information presented in Table 10-5 above provides an overview of general optimization

techniques that may be used to optimize iron and manganese removal and control processes.

Additional information is provided in Sommerfeld (1999).



Depending on the type of iron and manganese control method used, reference should also be

made to other chapters of this Manual for optimization strategies for clarification (see

Chapter 7) and filtration (see Chapter 8) processes.

10.6 TASTE AND ODOUR CONTROL

10.6.1 Purpose and Types of Taste and Odour Control Processes

There are a number of possible causes of tastes and odours in drinking water. The presence of

specific metals or salts, H2S, synthetic organics or water treatment chemicals may cause

objectionable tastes and odours. Decaying vegetation and metabolites of microorganisms,

such as cyanobacteria and actinomycetes, can produce compounds such as geosmin and

methylisoborneol (MIB), which are probably the most common sources of taste and odour

problems in surface water supplies (AWWA, 1999). Specific information regarding the

identification and control of odorous algal metabolites is provided in Rashash et. al. (1996).

As discussed in Chapter 5, source water management to prevent the occurrence of taste and

odour problems is an important aspect of any taste and odour control strategy. Treatment

plant and distribution system maintenance activities, including removal of screening debris

and sludge, regular flushing and disinfection of equipment and piping, can also assist in

reducing taste and odour problems.

Where treatment is required to control taste and odour in a drinking water system, the type of

process used will depend on the specific taste and odour causing compound(s) present in the

source water. Two general approaches are used for control of taste and odour causing

compounds: removal and destruction. Removal may be accomplished by microscreening,

conventional treatment (i.e. coagulation, flocculation, clarification and filtration), activated

carbon adsorption or aeration. Destruction is typically accomplished through conventional or

advanced oxidation processes.

Microscreens or microstrainers are mechanical screens with very small openings capable

of removing suspended matter from the water by straining. They are used during periods

when raw water contains nuisance organisms, such as algae.

Improving coagulation, flocculation and sedimentation can be an effective means for

removing the taste and odour of water, depending on the type of taste and odour causing

compounds present in the raw water. This strategy may be particularly effective if taste and

odour quality has deteriorated during a period when sudden changes in raw water turbidity,

colour or pH have occurred (e.g. spring or fall turnover of lakes or reservoirs, high flows,

storm runoff, algal blooms, etc).

Activated carbon can be used to remove a wide range of water contaminants that cause

offensive tastes and odours. Activated carbon may be in powdered (PAC) or granular (GAC)

form.

Aeration is effective for taste and odour control only for the removal of gases and organic

compounds that are relatively volatile. Aeration may also change some compounds by

oxidation, such as producing insoluble inorganic compounds (e.g. iron or manganese).

Aeration typically does not provide a sufficiently strong oxidant to destroy organic taste and

odour causing compounds.



Oxidation can be used to control many taste and odour causing substances through chemical

oxidation to less odorous substances. Chemical oxidants used for taste and odour control

include chlorine, monochloramine, chlorine dioxide, potassium permanganate, hydrogen

peroxide and ozone.

Advanced oxidation processes (AOPs) are processes that provide powerful oxidizing

conditions to break down organic water contaminants. AOPs involve the use of any one of

several possible combinations of UV, hydrogen peroxide, ozone and titanium dioxide to

create hydroxyl radicals (HO·). Although AOPs have been demonstrated to be effective in

destroying geosmin and MIB, it is unlikely that AOPs would be used in a water treatment

plant only for taste and odour removal, because ozone alone is generally effective in

eliminating geosmin and MIB (MWH, 2005). The use of AOPs for this application is

therefore not discussed further in this chapter.


The performance of taste and odour control processes is assessed on the basis of removal of

the targeted compound, and the monitoring program will therefore differ depending on the

contaminant of concern and the control method used.

The threshold odour number (TON) is a subjective test that can be used to evaluate the odour

of a drinking water sample. The TON test involves diluting a sample with odour-free water

until the least definitely perceptible odour is achieved (American Public Health

Association/American Water Works Association/Water Environment Federation, 2005).

Similar subjective tests, such as flavour profiling (APHA/AWWA/WEF, 2005), can also be

used for the measurement of taste or flavour in water.

Table 10-6 presents potential monitoring, in terms of sampling locations and analyses, in

order to evaluate the performance of taste and odour control processes.

Table 10-6 – Taste and Odour Control – Recommended Process Monitoring to Evaluate

Performance


Measurement


Raw water Continuous monitoring

or grab sample Parameter of concern,

may include:

Geosmin

MIB

H2S

VOCs

Metals

Salts

The frequency of

sampling will be site

specific and will

depend on the nature of

the contaminant,

whether it is present

year-round, ability to

perform testing on-site,

etc.



Table 10-6 – Taste and Odour Control – Recommended Process Monitoring to Evaluate



Measurement



or grab sample Temperature

pH

Dissolved oxygen

Nutrients

These parameters may

be indicators that raw

water quality is

changing, and can

potentially be used to

predict the occurrence

or onset of a taste and

odour event (e.g. lake

turnover, anoxic

conditions, algal

growth, etc.).

Treatment

Process1

Continuous monitoring Oxidant dosage and

residual concentration.

Head loss (if screening

or filtration is used).

Will vary depending on

the type of treatment

process used. See

Section 10.6.4 and

Chapter 8 for

additional information.

Treated water Continuous monitoring

or grab sample Parameter of concern,

may include:

Geosmin

MIB

H2S

VOCs

Metals

Salts

To evaluate degree of

removal of parameter

of concern.

Notes:

1. Reference should be made to Chapter 5 (Screening), Chapter 7 (Clarification) and Chapter 8

(Filtration) for additional information on recommended process control monitoring for these

types of processes. See Section 10.2 for information on process control monitoring for

aeration systems.


Symptoms and causes of common problems encountered with taste and odour control

processes are shown in Table 10-7.



Table 10-7 – Taste and Odour Control – Symptoms and Causes of Common Problems

and Potential Optimization Strategies

Process Problem

Mitigation

Microscreens or

Microstrainers See Chapter 5 See Chapter 5

Coagulation,

Flocculation and

Sedimentation

See Chapter 6 and 7 See Chapter 6 and 7

Activated Carbon

Adsorption Poor removal of taste and odour

using PAC

Evaluate optimum PAC dose and

type, mixing intensity and contact

time through jar testing (Section

10.6.4.1)

Excessively high dosages of PAC

(greater than 50 mg/L) are required

for effective removal

Consider change to GAC contactor,

as high PAC dosages can make

process cost prohibitive

Caking of PAC on filter surfaces,

shortening filter runs and

increasing backwash frequency

Optimize upstream treatment to

improve removal of PAC in settling

processes (see Chapter 7)

Penetration of PAC through filters,

resulting in “dirty water”

complaints from consumers

Reduce carbon dose or filtration

rate, if possible

Consider addition of filter aid

Poor removal of tastes and odours

through GAC contactors

Frequent need for GAC media

regeneration or replacement

See Section 10.6.4.2

Aeration See Section 10.2.3 See Section 10.2.4

Chemical Oxidation Odours are not being removed

through oxidation, and in some

cases increase (particularly when

using chlorine as oxidant and/or if

phenols are present in raw water)

Evaluate optimum oxidant dose

through jar testing (see Chapter 4)

Increase contact time or optimize

hydraulics to improve effective

contact time


Very high doses of chlorine are

required to achieve sufficient

reduction in taste and/or odour

Consider implementation of

superchlorination followed by

dechlorination, if disinfection by-

products are not a concern



Table 10-7 – Taste and Odour Control – Symptoms and Causes of Common Problems

and Potential Optimization Strategies (cont’d.)

Process Problem

Mitigation

When using KMnO4, pink coloured

water is carrying over into

clearwells

Conduct jar testing to determine

maximum KMnO4 dosage that can

be applied and determine required

contact time (see Chapter 4);

additional information specific to

jar testing for KMnO4 addition is

available elsewhere (California

State University, 1999)


10.6.4.1 Optimizing PAC Addition for Taste and Odour Control

The appropriate dose of PAC for a particular drinking water issue will vary depending upon

the nature of the target contaminant, the concentration of the substance to be removed, the

mixing available, the contact time and the location of the application points. Jar tests should

be used to determine the necessary PAC doses required to treat the specific taste and odour

problem. If the concentration of the taste and odour compound varies significantly during a

taste and odour event, jar testing should be conducted frequently during the event to ensure

that the optimal dose is being applied.

Adsorption isotherms can be developed to evaluate the dosage and type of PAC used for a

specific application. The test is performed by exposing a known quantity of adsorbate (the

target compounds to be removed, for example, geosmin) in a fixed volume of liquid to

various dosages of adsorbent (PAC). Additional information on performing adsorption

isotherms is provided in MWH (2005), Najm et. al. (1991) and McGuire et. al. (1989).

Jar testing can be used to determine the most effective range of carbon dosage by simulating

actual mixing intensity and detention times achieved within the plant for a variety of

application points.

Analytical testing identified in Table 10-6 can be used to evaluate the effectiveness of

different carbon dosages used during jar testing. The TON method can also be used if only a

few tests are required. Accurate determination of the TON is difficult when several jar tests

are conducted concurrently because a person’s sense of smell becomes rapidly fatigued

following just two or three individual TON tests (California State University, 1999).

10.6.4.2 Optimizing GAC Filtration for Taste and Odour Control

The operation of GAC filters is similar to the procedures used for the operation of

conventional granular media filters (see Chapter 8).

Two specific considerations for GAC filters are the empty bed contact time (EBCT) and the

frequency of regeneration or replacement of the carbon. The EBCT required for taste and



odour control depends on the nature of the taste and odour compounds and typically varies

from 10 to 30 minutes (MOE, 2008).

Periodic regeneration or replacement of GAC is necessary as the capacity of the filter to

adsorb and retain organic compounds decreases with time. The time between regenerations or

replacement will vary with the type of compound being removed and the volume of water

treated.

Spent GAC can be regenerated on-site for larger installations; for smaller systems, it may be

more cost effective to have the GAC processed off-site.

Pilot testing (Chapter 4) should be conducted to evaluate the required EBCT and regeneration

or replacement frequency for a particular application.

10.7 NATURAL ORGANIC MATTER REMOVAL

10.7.1 Purpose and Types of NOM Removal Processes

NOM has traditionally been partly removed from drinking water for aesthetic reasons, as it

often imparts colour to the water. The low molecular weight fractions of NOM are mostly

responsible for chlorination by-product formation (see Chapter 9) and therefore, a reduction

of the NOM concentration is desirable. The presence of NOM may also affect other water

treatment processes, including:

Coagulation – change of coagulant dosage and optimum pH;

Membrane filtration – potential for increased fouling;

Disinfection – increase in disinfectant demand or decrease in UVT;

Activated carbon adsorption – Increased activated carbon usage rates; and

Distribution system water quality – potential for bacteriological regrowth and DBP

formation.

Enhanced coagulation can be used in some systems to achieve improved removal of DBP

precursors by optimizing conventional treatment processes and coagulant dosages

specifically for TOC removal. The effectiveness of enhanced coagulation is measured by

achieving a targeted percentage removal of TOC, a surrogate for NOM. Additional

information is provided in the USEPA’s Enhanced Coagulation and Enhanced Precipitative

Softening Guidance Manual (USEPA, 1999).

PAC addition and GAC filtration can be used for reducing NOM concentration, and may also

be operated in a biologically active mode for NOM reduction. The use of GAC to adsorb

NOM is generally not very effective or economically attractive as the GAC rapidly loses

adsorption capacity.

Nanofiltration can be used to remove a large fraction of the NOM. This process can be costly

as relatively high pressures are used and pre-treatment is needed to protect the membranes

from particulate accumulation. Nanofiltration has not yet found wide application in Ontario,



and specific optimization techniques for this process are therefore not presented in this

Manual.


The sampling locations and parameters to be analyzed for monitoring NOM removal

processes will depend on the type of treatment provided and on whether the NOM removal

processes occur as part of a conventional treatment process (e.g. enhanced coagulation) or as

a stand-alone unit process (e.g. GAC contactors).


in order to evaluate the performance of NOM removal processes.

Table 10-8 – NOM Removal – Recommended Process Monitoring to Evaluate

Performance


Measurement


Raw water Continuous monitoring pH

Grab sample TOC or DOC

Colour

UVT

UV254

Alkalinity

THM formation

potential and/or THM

simulated distribution

system

TOC, DOC, colour and

UVT can be used as

surrogates for NOM.

Higher alkalinity

waters are more

challenging to treat, as

it is more difficult to

achieve the optimum

pH for TOC removal

during coagulation.

Treatment

Process (for

conventional

treatment with

enhanced

coagulation)

Continuous monitoring Coagulation pH

Coagulant dosage

Mixing intensity

Flocculation detention

time

Filtration rate

Optimal pH and

coagulant dosage for

NOM removal

typically is different

than for turbidity

removal.

Typically, lower

mixing intensity,

longer flocculation

detention times and

lower filtration rates

are needed for NOM

removal (see Chapter 6

and Chapter 8).



Table 10-8 – NOM Removal – Recommended Process Monitoring to Evaluate



Measurement


Treatment

Process (GAC

contactors with or

without

conventional

treatment)

Continuous monitoring EBCT as function of

flow rate

To ensure optimum

EBCT is provided.

Grab sample Bacterial populations To evaluate bacterial

activity within the

filter.

Treated water Grab sample UVT

UV254

DBP formation potential

TOC or DOC

Colour

Surrogate parameters

used to measure the

effectiveness of NOM

removal.


Symptoms and causes of common problems encountered with NOM removal processes are

shown in Table 10-9.

Table 10-9 – NOM Removal – Symptoms and Causes of Common Problems and

Potential Optimization Strategies

Process Problem

Mitigation

Coagulation,

Flocculation and

Sedimentation

See Chapter 6 and 7 See Chapter 6 and 7, as well as

Section 10.7.4

Activated Carbon

Adsorption Poor removal of NOM using PAC Evaluate optimum PAC dose and

type, mixing intensity and contact

time through jar testing (Section

10.7.4)

Develop adsorption isotherm (see

references in Section 10.7.4 for

procedures)

Excessively high dosages of PAC

(greater than 50 mg/L) are required

for effective removal

Consider change to GAC contactor,

as high PAC dosages can make

process cost prohibitive



Table 10-9 – NOM Removal – Symptoms and Causes of Common Problems and

Potential Optimization Strategies (cont’d.)

Process Problem

Mitigation

Caking of PAC on filter surfaces,

shortening filter runs and

increasing backwash frequency

Optimize upstream treatment to

improve removal of PAC in settling

processes (see Chapter 7)

Penetration of PAC through filters,

resulting in “dirty water”

complaints from consumers

Reduce carbon dose or filtration

rate, if possible

Consider addition of filter aid

Poor removal of NOM through

GAC contactors

Frequent need for GAC media

regeneration or replacement

Develop adsorption isotherm (see

references in Section 10.7.4 for

procedures)

See Section 10.7.4


The removal of NOM in water treatment is often problematic and extensive research has been

conducted on the optimization of treatment processes for NOM removal.

For conventional treatment plants, the process can be optimized by enhanced coagulation,

which may include adjusting the pH and coagulant dose to improve NOM removal or by

using a different coagulant chemical. Jar testing can be used to evaluate the optimum

conditions for coagulation pH, chemical and dose. Information on enhanced coagulation

gained from studies conducted in Ontario is provided in Anderson et. al. (1995).

Optimization of flocculation and clarification processes, such as improving mixing and

providing adequate hydraulic detention times as discussed in Chapters 6 and 7, can also

improve NOM removal.

Jar testing can also be used to evaluate different types and dosages of PAC to improve NOM

removal. Adsorption isotherms can be performed to quantify the affinity of the target organic

compounds for a specific type of activated carbon.

Comprehensive information on the optimization of conventional and activated carbon

treatment for NOM removal is available, including:

Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual

(USEPA, 1999);

Characterization of Natural Organic Matter and Its Relationship to Treatability

(Owen et. al., 1993);

Control of Organic Compounds with Powdered Activated Carbon (Najm et. al.,

1991); and



Optimization and Economic Evaluation of Granular Activated Carbon for Organic

Removal (McGuire et. al., 1989).

10.8 INTERNAL CORROSION CONTROL

10.8.1 Purpose and Types of Internal Corrosion Control Processes

Corrosion of water distribution system materials can cause failure of the distribution

infrastructure resulting from leakage or reduced hydraulic capacity and/or the release of

corrosion by-products, such as lead, copper, iron and antimony. In Ontario, lead is used as an

indicator of corrosion and for the potential requirement for corrosion control under the

Drinking Water Systems Regulation (O. Reg. 170/03).

Many different types of corrosion exist, depending on the materials used and construction of

the system, the formation of scale and hydraulic conditions. In some cases, corrosion may be

relatively uniform, while in others pits or tubercules may form.

Corrosion can occur for a variety of reasons. For example, differences in potential may exist

due to differences or imperfections in the structure of the metal, or due to the concentrations

of oxidants and reductants in the water (AWWA, 1999). Galvanic corrosion occurs when two

different types of metals or alloys contact each other; one metal serves as the anode (and

deteriorates) while the other serves as the cathode. Additional information on the different

types of corrosion is presented in AwwaRF & TZW (1996).

The primary approaches to internal corrosion control in drinking water systems are to modify

the water chemistry to make it less corrosive and to encourage formation of less soluble

compounds (passivation). This is typically accomplished through pH and/or alkalinity

adjustment or through the addition of a corrosion inhibitor.

Although a corrosion control strategy may be developed specifically to reduce lead

concentrations in a distribution system, most treatment techniques will also be beneficial for

reducing corrosion of copper, iron, steel and galvanized pipe.

pH and/or alkalinity adjustment can be accomplished via chemical or non-chemical means.

Chemical methods include addition of:

Sodium hydroxide, NaOH (caustic soda);

Potassium hydroxide, KOH (caustic potash);

Calcium hydroxide, Ca(OH)2 (lime);

Sodium carbonate, Na2CO3 (soda ash);

Sodium bicarbonate, NaHCO3; or

Carbon dioxide (CO2).

Limestone contactors and aeration are two other commonly used pH and/or alkalinity

adjustment strategies.



Phosphate corrosion inhibitors are available in a variety of compositions: phosphoric acid,

orthophosphate, zinc orthophosphate, polyphosphates and blends of orthophosphate and

polyphosphate. They are generally proprietary compounds with varying percentages of

orthophosphate, the active agent in the formation of passivating films for lead control.

Guidance for corrosion control planning is provided in the Guidance Document for

Preparing Corrosion Control Plans for Drinking Water Systems (MOE, 2009) and the

Revised Guidance Manual for Selecting Lead and Copper Control Strategies (USEPA,

2003).


Assessing the effectiveness of corrosion control involves monitoring of:

Operating conditions for the corrosion control process;

Lead levels and other corrosion related parameters in the distribution system and

premise plumbing; and

Secondary water quality impacts that may occur.

Typically, a corrosion control monitoring program will include testing for regulated and

aesthetic parameters, as well as tracking of customer complaints (e.g. dirty water). Many

physical and chemical factors can affect corrosion or corrosion control; the inclusion of

specific parameters in a testing program will be site specific. Parameters to be considered

include: temperature, pH, alkalinity, dissolved inorganic carbonate (DIC), hardness,

dissolved oxygen, total dissolved solids, chlorine residual, chloride and sulphate, hydrogen

sulphide, ammonia, natural organic matter and metals (e.g. iron, zinc, manganese, copper,

etc.).


in order to evaluate the performance of corrosion control processes.



Table 10-10 – Corrosion Control – Recommended Process Monitoring to Evaluate

Performance


Measurement


Raw water Continuous monitoring pH


Treatment process

(post-adjustment)

Continuous monitoring pH

Inhibitor dosage (if

applicable)

Air/water flow rates (if

aeration is used)

For process control


Inhibitor concentration

(if applicable)

DO concentration (if

applicable)

Treated water Continuous monitoring

or Grab sample Lead

Alkalinity

pH

Temperature

Total dissolved solids

Specific conductance

Chloride:sulphate mass

ratio (CSMR)

To monitor the

consistency of treated

water quality and for

comparison with

distribution system water

quality

Note that this table is in addition to the required regulatory monitoring under the Drinking

Water Systems Regulation (O. Reg. 170/03).

MOE recommendations for distribution system sampling to evaluate the effectiveness of a

corrosion control plan are provided in Table 10-11.



Table 10-11 – Corrosion Control – Recommended Distribution System Monitoring to


Adapted From Guidance Document for Preparing Corrosion Control Plans for Drinking

Water Systems (MOE, 2009)

Parameters Distribution System

Residential and

Non-Residential

Taps

Distribution System

Dead Ends and Areas

of Low Chlorine

Residual

Lead X X X

Alkalinity, pH X X X

Orthophosphate

and/or silicate X X X

Temperature,

TDS, specific

conductance

X X X

Dissolved oxygen X

Iron, manganese X X

Chloride, sulphate X X

Turbidity, colour X X

Calcium, zinc,

aluminum X X

Microbiological

parameters

(coliform, HPC)

X X

Nitrate, nitrite,

free ammonia1

X X

Notes:

1. For systems that operate with chloramination for residual maintenance in the distribution

system.

Additional information on the frequency and number of samples to be collected is provided

in O. Reg. 170/03 and the Guidance Document for Preparing Corrosion Control Plans for

Drinking Water Systems (MOE, 2009).




Symptoms and causes of common problems encountered with corrosion control processes are

shown in Table 10-12.

Table 10-12 – Corrosion Control – Symptoms and Causes of Common Problems and

Potential Optimization Strategies

Process Problem

Mitigation

Calcium hydroxide

(slaked lime or

quicklime) addition

Oversaturation may cause calcium

deposits

pH control is difficult when applied

to poorly buffered water

Slurry feed can cause excess

turbidity

Careful monitoring of the finished

water is required to prevent

oversaturation

To prevent increase in turbidity,

lime can be dissolved in water and

clarified prior to being added to the

treated water

Sodium hydroxide

(caustic soda)

addition

pH control can be difficult when

applied to poorly buffered water

Solution tends to freeze in colder

temperatures

Consider process that also increases

alkalinity

Consider lower strength solution or

dilution to prevent freezing

Sodium bicarbonate

or sodium carbonate

(soda ash) addition

Dry solid must be mixed to form

solution feed; solid tends to form

cake in presence of moisture

Ensure large dissolving chambers

are provided to ensure adequate

detention time and mixing

Inhibitor addition May cause leaching of lead in

stagnant waters

May encourage growth of

microorganisms (by increasing

availability of nutrients)

May not be compatible with some

industrial processes or downstream

wastewater treatment processes

Conduct jar testing to determine

optimum treated water pH and

inhibitor concentration to prevent

destabilization of existing scales

Ensure adequate chlorine residuals

persist in all areas of distribution

system

Aeration See Section 10.2.3 See Section 10.2.4


Several techniques are available for the optimization of corrosion control processes. As

mentioned in previous subsections, comprehensive information is provided in the Guidance

Document for Preparing Corrosion Control Plans for Drinking Water Systems (MOE, 2009)

and USEPA’s Revised Guidance Manual for Selecting Lead and Copper Control Strategies

(USEPA, 2003).

Optimization studies for corrosion control processes should be conducted over a minimum of

6 to 9 months, as corrosion rates are commonly observed to take from 6 months to 1 year to

stabilize after changes have been made to water quality (MOE, 2008). A reliable testing



technique is to make changes to water composition in one area of a distribution system while

leaving the water composition unchanged in the remainder of the system. Test results from

the two areas should then be compared after a period of 6 months to a year.

10.9 CASE HISTORIES

10.9.1 Washington, D.C. – Optimization of Orthophosphate Addition

The following case study is based on information presented in Standard (2006).

System Description

The Washington (D.C.) Aqueduct operates and maintains the raw water supply facilities and

two treatment plants that supply water to the Washington, D.C., Water and Sewer Authority

(WASA) and parts of Northern Virginia (Arlington County and the City of Falls Church).

Combined, the two treatment facilities treat an average of 680 ML/d (180 mgd).

In November 2000, Washington Aqueduct switched its secondary disinfectant from chlorine

to chloramines in an effort to meet the new total THM maximum contaminant level (MCL)

requirement of the Stage 2 Disinfectants and Disinfection Byproducts Rule (USEPA, 2006).

WASA reported a significant increase in lead levels in its distribution system for the Lead

and Copper Rule monitoring period following the conversion to chloramines. Continued

sampling at homes served by lead service lines showed that lead levels exceeded the federal

action level for lead in drinking water.


Computer modelling by the Washington Aqueduct determined that raising the pH by

increasing the dosage of calcium hydroxide to improve corrosion control would result in

excessive levels of calcium carbonate precipitation in the distribution system. In a series of

separate experiments, it was determined that orthophosphate addition could decrease lead

leaching from service lines.

Orthophosphate was first added to water in a small, isolated section of the distribution

system. The purpose of this trial was to determine if any negative effects would occur as a

result of the orthophosphate addition. The trial was successful and full-scale orthophosphate

addition was implemented.

Automated orthophosphate feed systems were installed with continuous on-line phosphate

residual monitoring. The chemical feed system is designed to be controlled either manually

or automatically, with flow pacing being the preferred control method. The feed system is

controlled by the plants’ supervisory control and data acquisition (SCADA) system based on

an operator-entered dosage set point, the actual flow rate and actual orthophosphate feed rate.

Continuous on-line orthophosphate monitoring at both plants is supplemented by daily grab

samples that operators use to assess and verify the accuracy of the on-line analyzers.

The current orthophosphate dose at both plants is approximately 2.5 mg/L as PO4 entering the

distribution system. Pipe-loop studies are on-going to determine whether dosage levels can

ultimately be reduced. The calcium hydroxide system is also carefully controlled so that the

optimum pH for inhibitor addition (between 7.4 and 7.8) for lead control is maintained.



Summary

For the WASA reporting periods of January-June 2005 and July-December 2005, the 90th

percentile lead level had been significantly reduced, but was still at levels near the federal

action level of 15 µg/L. For the period of January-June 2006, the 90th percentile lead level

was found to be 10 µg/L.

The results of the study to date indicate that lead levels in Washington’s distribution system

will continue to decrease, provided that orthophosphate residuals in the distribution system

are maintained consistently and within the optimal pH range.

10.9.2 Chicago, IL – Optimization of Taste and Odour Control with Pilot Plant

Testing

The following case study is based on information presented in Putz et. al. (2007).

System Description

The City of Chicago Department of Water Management (DWM) owns and operates two large

water treatment plants, the Jardine Water Purification Plant (WPP) and the South WPP. Both

plants consist of a conventional treatment train, with chlorine, polymer and fluoride addition

followed by coagulation with alum, flocculation, sedimentation and rapid sand filtration.

Blended phosphate is applied to the treated water for distribution system corrosion control.

The source water, Lake Michigan, has raw water quality typical of the Great Lakes, with

turbidity being the parameter with the most variability. Raw water temperature also has a

large seasonal range that typically peaks in August. An increase in temperature often

correlates with an increase in the microbial production of taste and odour causing

compounds, such as MIB and geosmin. This taste and odour season lasts from June through

October.


The DWM had been unsuccessful in attempts to control these taste and odour events using

PAC. A pilot study was undertaken to evaluate the effectiveness of ozone for the oxidation of

taste and odour causing compounds.

Several trials were undertaken to determine the required ozone dosage, ozone demand and

ozone decay rates. MIB and geosmin were added to the raw water to simulate an extreme

taste and odour event. The raw water was treated at ozone dosages of 1.5 and 3.0 mg/L for

contact times ranging from less than 10 seconds up to 30 minutes.

The results indicated that geosmin and MIB removal occurred more rapidly at the higher

ozone dosage of 3.0 mg/L. Following 10 minutes of contact time, MIB and geosmin were

reduced by approximately 96 and 74 percent, respectively, to below 5 ng/L. It should be

noted, however, that at this ozone dosage, bromate concentrations were found to exceed the

MCL of 10 µg/L set under the Stage 2 Disinfectants and Disinfection Byproducts Rule

(USEPA, 2006) due to the oxidation of naturally-occurring bromide in the raw water.



Additional pilot plant trials were conducted to evaluate ozonation strategies that would

control taste and odour while minimizing the formation of bromate, including a reduction of

the ozone dosage, lowering the pH and ammonia addition.

The results of the testing indicated that bromate formation increased significantly with ozone

doses higher than 2.5 mg/L at a pH of 8.3; at this dosage, bromate levels were above the

MCL for all tested contact times. By decreasing the ozone dosage to 1.5 mg/L for a contact

time of less than 13 minutes, bromate concentrations were maintained below the MCL of 10

µg/L. Reducing the pH to 7.3 or lower (with an ozone dosage of 1.5 mg/L and a contact time

of 13 minutes) was also effective in reducing bromate formation to below the MCL.

Ammonia addition (doses ranging from 0.065 to 0.13 mg/L) was also effective in reducing

bromate formation.

Summary

The findings of the pilot study indicated that ozonation is a viable option for full-scale taste

and odour control. Additional full-scale trials are needed to evaluate the optimum treatment

conditions for effective taste and odour control while maintaining bromate levels below the

MCL of 10 µg/L.

10.10 REFERENCES

American Public Health Association/American Water Works Association/Water

Environment Federation (2005). Standard Methods for the Examination of Water &

Wastewater. 21st Edition. APHA/AWWA/WEF. ISBN 0-87553-047-8.

Anderson, W.B., I.P. Douglas, J. Van Den Oever, R.B. Hunsinger and P.M. Huck (1995).

Enhanced Coagulation With and Without Pre-Ozonation for Turbidity, NOPC and Colour

Control. Proceedings, AWWA Annual Conference, Water Quality Section, Anaheim, CA.

AWWA (1995). Water Treatment – Principles and Practices of Water Supply Operations. 2nd




AwwaRF & DVGW-Technologiezentrum Wasser (1996). Internal Corrosion of Water

Distribution Systems. 2nd Ed. AwwaRF and AWWA. Denver, CO. ISBN 0-89867-759-9.

California State University (2008). Water Treatment Plant Operation – Volume 1. 6th Ed.

California State University, Office of Water Programs. Sacramento, CA. ISBN 978-

1593710033.

Clifford, D.A., Z. Zhang (1994). Modifying Ion Exchange for Combined Removal of Uranium

and Radium. Journal AWWA, Vol. 86, Iss. 4, April 1994, p. 214-227.

Clifford, D.A., G.L. Ghurye, A.R. Tripp (2003). Arsenic Removal Using Ion Exchange with

Spent Brine Recycling. Journal AWWA, Vol. 95, Iss. 6, June 2003, p. 119-130.



Elhadi, S., P.M. Huck, R.M. Slawson (2006). Factors Affecting the Removal of Geosmin and

MIB in Drinking Water Biofilters. Journal AWWA, Vol. 98, Issue 8, August 2006, p. 108-

119.

Ghurye, G.L., D.A. Clifford, A.R. Tripp (1999). Combined Arsenic and Nitrate Removal by

Ion Exchange. Journal AWWA, Vol. 91, Iss. 10, October 1999, p. 85-96.

Huck, P.M., B.M. Coffey, A. Amirtharajah and E.J. Bouwer (2000). Optimizing Filtration in

Biological Filters. Submitted to American Water Works Association Research Foundation

and American Water Works Association, Report No. 90793. Denver, CO. ISBN 1-58321-

065-2.

Liu, X., D.A. Clifford (1998). Ion Exchange With Denitrified Brine Reuse. Journal AWWA,

Vol. 88, Iss. 11, November 1996, p. 88-99.

Liu, X., P.M. Huck, R.M. Slawson (2001). Factors Affecting Drinking Water Biofiltration.

Journal AWWA, Vol. 93, Issue 12, December 2001, p. 90-101.

McGuire, M.J., M.K. Davis, L. Liang, C.H. Tate, E.M. Aieta, I.E. Wallace, D.R. Wilkes, J.C.

Crittenden and K. Vaith (1989). Optimization and Economic Evaluation of Granular

Activated Carbon for Organic Removal. AwwaRF and AWWA. Denver, CO. ISBN0-89867-

469-7.

MOE (2006). Technical Support Document for Ontario Drinking Water Standards,

Objectives and Guidelines. PIBS 4449e01.


3.



ISBN 0-471-11018-3.

Najm, I.N., V.L. Snoeyink, T.L. Galvin and Y.R. Degrémont (1991). Control of Organic

Compounds with Powdered Activated Carbon. AwwaRF and AWWA. Denver, CO. ISBN 0-

89867-528-6.

Owen, D.M., G.L. Amy and Z.K. Chowdhury (1993). Characterization of Natural Organic

Matter and Its Relationship to Treatability. AwwaRF and AWWA. Denver, CO. ISBN 0-

89867-698-3.

Putz, A.R.H., A. Atassi, C. Feizoulof and J.F. Spatz Jr. (2007). “Optimizing Full-Scale

Operations Using Pilot Plant Studies”, presented at the 2007 AWWA Annual Conference &

Exposition. Toronto, ON.

Rashash, D.M.C., R.C. Hoehn, A.M. Dietrich, T.J. Grizzard and B.C. Parker (1996).

Identification and Control of Odorous Algal Metabolites. AwwaRF and AWWA. Denver,

CO. ISBN 0-89867-855-2.

Smith, E.F., M.B. Emelko (1998). Benefiting From Biological Growth in Filters. Opflow,

Vol. 24, Issue 11, November 1998, p. 1, 4-5.



Sommerfeld, E.O. (1999). Iron and Manganese Removal Handbook. AWWA. Denver, CO.

ISBN 1-58321-012-1.

Standard, D.S. (2006). On-line Orthophosphate Monitoring, Automated Dosing Optimize

Washington, D.C.’s Lead Reduction Program. Journal AWWA, Vol. 98, Issue 10, October

2006, p.p. 38-40.


Composite Correction Program, EPA-625-6-91-027.

USEPA (1999). Enhanced Coagulation and Enhanced Precipitative Softening Guidance

Manual. Office of Water. EPA-815-R-99-012.

USEPA (2003). Revised Guidance Manual for Selecting Lead and Copper Control

Strategies. Office of Water. Washington, DC. EPA-816-R-03-001.

USEPA (2006). National Primary Drinking Water Regulations: Stage 2 Disinfectants and

Disinfection Byproducts Rule; Final Rule. Federal Register, Vol. 71, No. 2. January 4, 2006.

World Health Organization (2008). Guidelines for Drinking Water Quality - Volume 1:

Recommendations. Third Edition. World Health Organization. Geneva. ISBN 978-92-4-

154761-1.


CHAPTER 11 DISTRIBUTION SYSTEMS

DISTRIBUTION SYSTEMS

11.1 Introduction .......................................................................................................... 11-1

11.2 Treated Water Pumping Stations .......................................................................... 11-1

11.2.1 Purpose and Types of Treated Water Pumping Stations ....................... 11-1




11.3 Treated Water Storage .......................................................................................... 11-4

11.3.1 Purpose and Types of Treated Water Storage Facilities ........................ 11-4




11.4 Distribution System Piping and Appurtenances ................................................... 11-8

11.4.1 Purpose and Types of Distribution System Facilities ............................ 11-8




11.5 Case Histories ..................................................................................................... 11-20

11.5.1 Region of Durham – Water Loss Control Strategy .............................. 11-20

11.5.2 Region of Niagara – Treated Water Pumping & Storage Optimization11-21

11.6 References .......................................................................................................... 11-22

CHAPTER 11. Distribution Systems 11-1


CHAPTER 11

DISTRIBUTION SYSTEMS

11.1 INTRODUCTION

Water distribution systems are designed and operated to provide a balance between hydraulic

water supply needs and water quality. The characteristics of a “high quality distribution

system” are defined in the report of the Walkerton Commission as “reliable, providing a

continuous supply of potable water at adequate pressure. Reservoirs within the system

balance pressure and cope with peak demands, fire protection and other emergencies without

causing undue water retention, while looped watermains prevent stagnation and minimize

customer inconvenience during repairs. Since water quality can decline with the length of

time the water remains in the system, and the rate of decline depends partly on the attributes

of the distribution system, a high-quality system has as few dead ends as possible and

maintains adequate flow and turnover” (O’Connor, 2002).

This chapter provides guidance on measures to optimize distribution system operation and

maintain water quality, system pressure and supply needs, while minimizing energy use and

water losses.

11.2 TREATED WATER PUMPING STATIONS

11.2.1 Purpose and Types of Treated Water Pumping Stations

High-lift pumps are used to discharge water from the treatment plant under pressure to the

distribution system. Booster pumps are used to increase pressure in the distribution system

and/or to supply elevated storage tanks.

High-lift pumping facilities are typically located at or near the water treatment plant. Booster

pumping stations are located throughout the distribution system and/or near storage facilities.


The performance of treated water pumping facilities is typically assessed based on the ability

to provide design flows at design pressures to the distribution system.

The minimum capacity of high-lift pumping facilities should be equal to the maximum day

demand for the system, with consideration given to the distribution system configuration and

storage capacity.

Booster pumping stations, either alone or in conjunction with storage, should be capable of

meeting the various demand requirements of the area being serviced, based on peak hourly

flows, night flows with refilling of remote storage facilities, fire flows, etc.

The discharge pressure from the pumping station should be adequate to ensure that the

pressure in the area to be served is within the range of 275 kPa to 700 kPa during peak and

minimum demand periods. In the case of fire flows, it may be acceptable to allow the

pressure in the system to drop to a level less than 275 kPa but maintain a minimum pressure

of 140 kPa.



Additional information that can be used to evaluate the performance of treated water

pumping facilities is provided in the Design Guidelines for Drinking Water Systems, 2008

(MOE, 2008).


Symptoms and causes of common problems encountered with high-lift and booster pumping

stations are presented in Table 11-1.

Table 11-1 – Treated Water Pumping – Symptoms and Causes of Common Problems


Potential Process Impacts Common Causes

Lack of hydraulic

capacity at the pump

station/pumps

Operating above firm capacity for

extended periods

Undersized pumps

Inadequate distribution system

storage

Frequent cycling of

pump operation Inconsistent flows and pressures

resulting in alternating periods of

flow and no-flow (and potential

flow reversals) in distribution

piping

Settling of solids in pipes during

no-flow or low flow conditions

Oversized pumps

Pumps not sized to meet the range of

demands

Pumps not equipped with variable

frequency drives (VFDs)


11.2.4.1 Pump Selection and Sizing

For high-lift pumping stations, the minimum number of pumps to be provided should be two,

to ensure redundancy, in addition to any pumps needed to provide fire flows. The minimum

capacity should be equal to the maximum day demand and the actual capacity will be dictated

by the distribution system and storage capacity (MOE, 2008).

Each booster pumping station should contain not less than two pumps with capacities such

that the firm station capacity can be satisfied with the largest pump out of service (MOE,

2008).

Oversized pumps will often operate in an on-off mode during low flow conditions, causing

uneven flows or periods of no-flow to downstream DWS components. This can cause settling

of suspended solids in downstream piping, flow reversals and other operational problems.

Improper design or the installation of oversized pumps (often to meet the ultimate design

capacity) can result in the requirement to throttle the pump discharge valve in order to reduce

cavitation. This can result in a significant waste of energy for pumping.

Problems with pump over-sizing are commonly encountered in new or newly expanded

facilities where the pumps were sized to be capable of handling the expected design flows at

build-out, without consideration of the demand at current conditions. The installation of



multiple, smaller capacity pumps, which operate according to a pressure or flow set point can

minimize the frequency of on-off cycling and provide consistent flows to the distribution

system throughout the day. Pump efficiency and operational energy savings should be

considered during pump selection.

11.2.4.2 Variable Frequency Drives

Where pumping station configuration does not allow for the installation of multiple, lower

capacity pumps in place of a single larger capacity pump, a VFD can be installed on the

existing pump(s). The installation of a VFD can optimize pump operation by providing

flexibility to operate over a range of flows. Additional information regarding VFDs is

provided in Section 5.5.3.2.

11.2.4.3 Control Strategies

The type of control for pump operation is an important consideration for pump specification

and selection, and depends on whether the pumps are part of an open or closed pumping

system.

In closed systems (e.g. a system that has no elevated storage and uses continuously running

pumps to provide pressure and meet water usage demands), a control valve is typically

provided to ensure proper operation of the pump. For very small systems, hydropneumatic

tanks (pressure tanks) may also be provided to maintain acceptable system pressures without

the need for frequent cycling of pumps.

Pressure control is commonly used for pump operation in both open systems and closed

systems. A combination of flow control and pressure control may be used in smaller systems.

Whatever control system is implemented, operation of the pumps near their maximum

efficiency points should be maintained.

11.2.4.4 Impeller Modification

Where a pump is undersized or oversized, or where downstream hydraulic conditions have changed,

impeller replacement or modification can potentially eliminate the need for pump replacement.

Modifying or replacing the impeller in a pump shifts the pump’s operating curve, effectively

changing the efficiency operating point of the pump. In addition to potentially avoiding costs

associated with pump replacement, impeller modification or replacement can allow for more

efficient operation of the pump, reducing operating costs.

Depending on the size of the pump volute and existing impeller, it may not always be

possible to replace the impeller with one of a larger or smaller size. In such cases, if a smaller

impeller is required for an oversized pump, the impeller can be trimmed to reduce its size.

Conversely, if a larger impeller is needed, total pump replacement may be required.

The selection or modification of a pump impeller is based on the size of the pump, the system

head curve, pump configuration, pump power and required capacity. The pump manufacturer

should be consulted when considering modification or replacement of an impeller to ensure

that the new or modified impeller will not negatively impact pump performance.



11.3 TREATED WATER STORAGE

11.3.1 Purpose and Types of Treated Water Storage Facilities

Treated water storage facilities are provided in a distribution system to maintain adequate

flows and pressure during periods of peak water demand, to meet critical water demands

during fire flow and emergency conditions, and to reduce the capacity required for the water

treatment plant.

There are several types of treated water storage facilities, which can be located either at the

water treatment plant or in the distribution system. Some of the most common types of

storage facilities in Ontario are listed below.

At the water treatment plant:

Clearwells;

Reservoirs;

Pumping wet wells; and

Pressure tanks.

In the distribution system:

Elevated tanks;

Standpipes; and

Reservoirs.

The type of water storage facility used in a drinking water system will depend on many

factors, such as function, the size of the service area, topography, costs, the balance between

water treatment capacity and demand, and the amount of storage required at the water plant

and in the distribution system.


The performance of treated water storage facilities is assessed based on the ability to meet

water demands that exceed the daily water supply capacity of the treatment plant, and where

fire protection is provided, fire flow demands.

The capacity of treated water storage facilities can be evaluated using the method described

in the Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008). This method

considers the need for fire storage, equalization storage and emergency storage in the system.

It should be noted that any volume required to provide storage for fire or equalization is not

available for contact time and should not be included in CT calculations. Additional

information on primary disinfection and contact time is provided in Chapter 9.



Storage facilities should also be designed to maintain water quality and prevent

contamination. Stagnation and detention times should therefore be minimized. Table 11-2

provides recommendations in terms of sampling locations and analyses, to monitor and

evaluate the performance of storage facilities with respect to maintaining treated water

quality.

Table 11-2 – Treated Water Storage – Recommended Monitoring to Evaluate

Performance


Treated water

(at a location where

water enters the

distribution system)


Disinfectant residual

Grab sample Microbial parameters

Influent to storage

facility

Continuous monitoring Flow rate or water level in tank

Grab sample Temperature

pH


Microbial parameters

Effluent from

storage facility

Continuous monitoring Flow rate or water level in tank


Grab sample Temperature

pH

Microbial parameters

Nitrate/nitrite1

Notes:

1. For systems using chloramination


Symptoms and causes of common problems encountered with treated water storage facilities

are presented in Table 11-3.



Table 11-3 – Storage Facilities – Symptoms and Causes of Common Problems



Deterioration in

water quality Loss of disinfectant residual

concentration

Increased microbiological growth

Increase in consumer complaints

related to colour, taste and/or odour

DBP formation (see Section

11.3.4.3)

Improper or poor control of

disinfectant dosage

Excessive detention time in storage

facility

Nitrification (see Section 11.4.4.4)

Elevated turbidity

in storage facility

effluent

Increase in customer complaints

related to turbid or coloured water

Frequent cleaning of storage

facilities required

Deposition of silt, calcium carbonate,

aluminum, iron or manganese

precipitates

Precipitation of solids caused by

changes in pH

Corrosion of metal surfaces

Floc carryover into clearwells

Freezing and ice

formation Loss of or inadequate flow Poor turnover of water and/or

inadequate mixing in storage facility

Excessive detention time in storage

facility


11.3.4.1 Storage Facility Cleaning and Maintenance

All storage structures should be inspected, and routine maintenance performed, every three to

five years. Regular maintenance of storage facilities includes draining, cleaning, painting and

repair, if necessary. The person inspecting the structure should look for deposition patterns on

the floors and walls to determine flow patterns and assess dead zones. Checks should also

include calibration and cleaning of critical instrumentation, and inspection of internal

structures and appurtenances (such as stairs, ladders, valve handles, sample lines, etc).

Internal inspection of reservoirs using submersible robots equipped with cameras is becoming

more common, as they do not require the reservoir to be taken out of service. The results of

the inspection can be used to determine the required frequency for regular maintenance on a

site-specific basis.

Periodic inspection of water storage facilities is needed to find any structural problems and

correct them before they become serious. Tanks should be inspected for corrosion and cracks

on both the inside and outside surfaces. Overflows and vents should be examined to ensure

they are not obstructed and that screens are clean and in place. The inspection should also

include checks of control valves and any instrumentation used in the operation of the facility.



Additional information is provided in AWWA Standard D101, Inspecting and Repairing

Steel Water Tanks, Standpipes, Reservoirs and Elevated Tanks for Water Storage.

After cleaning and/or painting are complete, water storage tanks must be disinfected before

being placed in service. Reference should be made to the most recent version of AWWA

Standard C652: Disinfection of Water Storage Facilities for more information.

11.3.4.2 Preventing Freezing in Storage Facilities

When freezing temperature conditions exist for several days, ice formation can occur in both

underground and elevated distribution storage reservoirs. In underground reservoirs, ice

formation is usually limited to surface ice. In elevated tanks, icing can be more severe and ice

can accumulate in thick layers on the sidewalls. Ice accumulation or falling ice can damage

walls and structures. As water freezes, expansion pressure can separate steel plates or panels

and the tank diameter can be altered resulting in damage to the interior coating. Interior

ladders, water level indicators, floats or electronic sensors can be damaged by ice.

Ice formation can be minimized by continuously fluctuating reservoir water levels. The

pumping and flow into and out of the reservoir should be adjusted to allow continuous water

circulation and to prevent ice from becoming attached to walls and columns. Storage tanks

can also be equipped with a small compressor and tank bubbler in order to circulate water in

the tank.

In most cases, the normal inflow and drawdown results in sufficient circulation to keep ice

formation to a minimum. In elevated tanks, the water level should be varied by 50 percent

every 24 hours. In underground reservoirs, 25 percent fluctuations in water levels every 24

hours are generally sufficient to minimize icing (California State University & USEPA,

1996). In arctic and sub-arctic areas, circulating water systems that continuously pump and

reheat the water in the system may be required to prevent severe icing.

If an excessive ice build-up inside an elevated distribution reservoir has occurred or the tank

malfunctions due to icing, a number of steps can be taken to restore operation. The affected

tank should be isolated and the distribution system pressurized using alternate means, such as

other storage tanks. The ice can be most effectively thawed by inserting a steam generator

equipped with a hose through one of the access hatches. Water storage tanks must be

disinfected before being placed back in service.

11.3.4.3 Maintaining Water Quality

Stagnation and excessive retention time in the distribution system and storage facilities may

result in a deterioration of water quality, which may be indicated by a loss of disinfectant

residual, formation of DBPs and bacterial regrowth.

It may be possible to improve hydraulic conditions within a storage facility by providing:

separate inlet and outlet piping; baffle walls; diffusers; and/or by locating the inlet and outlet

piping to promote water circulation.

In standpipes where only the upper portion of the storage provides useful system pressure, the

water should be circulated through the storage facility to maintain water quality and minimize

ice formation.



For smaller systems, high water temperatures can be alleviated by providing a circulation

system to prevent deterioration of water quality.

Where design limitations prevent sufficient turnover of water in a storage facility to maintain

water quality, a pumped recirculation system can be provided, with or without a booster

disinfection system.

Water quality deterioration in storage may be particularly rapid where sequestering agents are

used with hard water or where natural organic matter reacts rapidly with a free chlorine

residual. In such cases, the use of monochloramine as the secondary disinfectant should be

considered (see Section 11.4.4.3).

For systems using chloramination for secondary disinfection, nitrification can lead to the

formation of nitrate and nitrite in the distribution system, loss of chloramine residual,

decrease in dissolved oxygen concentration, reduction in pH and alkalinity, and increased

microbial growth. Mitigation methods are discussed later in Section 11.4.4.4.

Additional information on the operation of water storage facilities to maintain water quality is

provided in Kirmeyer et. al. (1999).

Hydraulic and water quality models can also be used to evaluate the conditions in existing

storage facilities and for selecting locations for re-chlorination facilities, if needed.

11.4 DISTRIBUTION SYSTEM PIPING AND APPURTENANCES

11.4.1 Purpose and Types of Distribution System Facilities

Water distribution systems consist of pipes, valves, pumps, meters, fire hydrants, storage and

other pieces of equipment that are used to convey water to consumers. The distribution

system is designed to ensure that a sufficient volume of water at adequate pressure is

available, while maintaining the quality of the water from the treatment plant to the end user.

There are three main distribution system configurations, including arterial-loop systems, grid

systems and tree systems, as shown in Figure 11-1.

Most distribution systems are actually a combination of grid and tree systems. Arterial-loop

and grid layouts are generally preferable to tree layouts, as they generally have fewer dead-

end mains than tree systems.



Figure 11-1 – Distribution Systems – Common Configurations

Adapted from Water Transmission and Distribution (AWWA, 1996)


Distribution systems are designed to provide a balance between hydraulic water supply needs

and acceptable water quality.

The hydraulic performance of a distribution system is evaluated on the basis of the pressures

that exist at various points in the system under specific operating conditions. While pressures

must be high enough to serve consumers, provide fire protection, and prevent the intrusion of

contaminants, excessive pressures will increase pumping energy costs and can have adverse

effects on private plumbing. Excessive pressures may also increase the potential for main

breaks.

A minimum pressure of 140 kPa should be maintained at ground level at all points in the

distribution system under maximum day demand plus fire flow conditions. The normal



operating pressure in the distribution system should be approximately 350 to 480 kPa and not

less than 275 kPa. Operating pressures outside of this range may be required based on

distribution system size and/or topography. The maximum pressures in the distribution

system should not exceed 700 kPa to avoid damage to household plumbing and unnecessary

water and energy consumption.

Additional information that can be used to evaluate the hydraulic capacity of distribution

systems is provided in the Design Guidelines for Drinking Water Systems, 2008 (MOE,

2008).

Water quality can deteriorate through interactions between the pipe wall and material on the

pipe wall and the water, and reactions within the bulk water itself. Depending on the retention

time in the system, water flow, treated water quality, pipe materials and condition, and

deposited materials (e.g. biofilms, iron, manganese, etc.), the water quality will change to a

greater or lesser extent.

Table 11-4 provides recommendations for monitoring, in terms of sampling locations and

analyses, in order to evaluate distribution system water quality.

Table 11-4 – Distribution Systems – Recommended Monitoring to Evaluate

Performance


Measurement


Treated Water

(at a location

where water

enters the

distribution

system)

Continuous monitoring Disinfectant residual

pH

Temperature

Turbidity

To monitor the

consistency of treated

water quality and for

comparison with

distribution system water

quality

Grab sample Bacteriological

parameters

Disinfection by-products

Metals (lead, copper,

aluminum, iron,

manganese)

Ammonia (for systems

using chloramination)

Colour, taste and odour



Table 11-4 – Distribution Systems – Recommended Monitoring to Evaluate



Measurement


Distribution

System


and/or grab samples Disinfectant residual

pH

Turbidity

Grab samples Bacteriological

parameters

Disinfection by-products

Ammonia, nitrate, nitrite

(if chloramination is

used)

Metals (lead, copper,

aluminum, iron,

manganese)

Colour, taste and odour

Note that the monitoring recommended in this table is in addition to the required regulatory

monitoring under the Drinking Water Systems Regulation (O. Reg. 170/03). The degree of

monitoring that is appropriate will depend on the size and complexity of the system, and the

variability in treated water quality.


There are several design and operational issues that can impact water quality in the

distribution system. Symptoms and causes of common problems encountered with

distribution systems are shown in Table 11-5.

Table 11-5 – Distribution Systems – Symptoms and Causes of Common Problems

Adapted from California State University (1996)

Problem Description

Mitigation

Cross Connections Physical connection between a

potable water supply with another

water supply of unknown or

contaminated quality

Can lead to contamination of the

potable water supply through

backflow or backsiphonage

Implement cross connection and/or

backflow prevention program or by-

law (see Section 11.4.4.10)

Maintain adequate system pressure to

prevent backflow or backsiphonage

Conduct regular water quality

sampling and testing to monitor for

indications of contamination




(cont’d.)


Problem Description

Mitigation

Corrosion Can lead to increased

concentrations of metals in water

supplied to consumers, causing

aesthetic and/or potential health

related problems

Can cause deterioration of

distribution system infrastructure

Implement internal corrosion control

program (Chapter 10)

Consider other corrosion control

techniques (e.g. cathodic protection),

if warranted (see Section 11.4.4.8)

Biological Growth

and Activity

(Biofilm formation)

Can accelerate corrosion in metal

pipes

Potential for reduced flow through

pipes as a result of greater

turbulence along pipe walls

Can cause taste and odour

problems as a result of sloughing

of biofilms and/or decay of

organisms

Potential loss of disinfectant

residual

Improve disinfection processes

during treatment (Chapter 9)

Maintain adequate secondary

disinfectant residual (see Section

11.4.4.3)

Nitrification For systems using chloramination

for secondary disinfection,

nitrification can lead to the

formation of nitrate and nitrite in

the distribution system, loss of

chloramine residual, decrease in

dissolved oxygen concentration,

reduction in pH and alkalinity,

and increased microbial growth

Control chlorine:ammonia dosage

ratio to reduce free ammonia levels

Monitor water temperatures and

other parameters to predict the onset

of nitrification events (see Section

11.4.4.4)

Improve operational practices to

prevent nitrification (see Section

11.4.4.4)

Changes in

Temperature Higher temperatures increase the

rate of chemical reactions,

biological growth and chlorine

demand, which can all result in a

loss of disinfectant residual

Very low temperatures can cause

freezing, potentially resulting in

more frequent main breaks and

loss of service




(cont’d.)


Problem Description

Mitigation

Changes in Flow Changes in velocity and flow

reversals can cause accumulated

sediment to be stirred up and

carried to consumers

Low flow and stagnation can

result in microbial growth,

deposition of sediment and

increased tastes and odours

Conduct hydraulic modelling to

evaluate flow conditions in a specific

area and identify options for

improving system flows (Chapter 4)

Conduct regular flushing and

periodic swabbing of distribution

system to remove sediment and

biofilm (see Section 11.4.4.5)

Excessive Water

Age and/or Presence

of Dead-End Mains

Excessive water age can lead to

increased DBP concentrations,

taste and odour problems, loss of

disinfectant residual and increased

microbial growth

Consider use of blow-offs or bleeders

on oversized mains or mains with

very low usage/flow

Conduct hydraulic modelling to

evaluate flow conditions in a specific

area and identify options for

improving system flows

Consider “looping” dead-end mains

to improve circulation (see Section

11.4.4.7)

Improve turnover in storage facilities

to minimize water age (see Section

11.3.4.3)

Excessive Water

Loss or

“Unaccounted for

Water”

Water loss results in additional

costs associated with treatment

and pumping (energy and

chemicals)

Small leaks can accelerate pipe

deterioration and lead to larger

breaks, which are more costly to

repair

Undetected leaks increase the

potential for contamination in the

distribution system

Conduct a water audit and/or

implement a leak detection program

(see Section 11.4.4.9)


The operation and optimization of a distribution system can be very complex due to the size,

layout, construction and age of the system. The five step approach presented in Lauer (2005)

can be used to prevent or mitigate water quality problems. The five steps include:

1. Understanding the distribution system and defining the problem;



2. Establishing water quality goals and preliminary performance objectives;

3. Evaluating alternatives and selecting the best approach;

4. Implementing good management practices and monitoring effectiveness; and

5. Finalizing performance standards and developing standard operating procedures.

Many of the approaches to optimizing distribution system water quality and solutions to

water quality problems involve improvements in water quality monitoring, operations and

maintenance, water treatment, management practices and/or system design (e.g. minor

modifications).

A discussion of all of the approaches that can be used to optimize distribution system

operation is beyond the scope of this manual. An overview of common optimization

techniques is provided in the following subsection. Additional information is available in

Lauer (2005), California State University (1996) and Friedman et. al. (2005).

11.4.4.1 Improving Treated Water Quality

In many cases, distribution system water quality can be improved by optimizing water

treatment. Improving nutrient removal (e.g. iron, manganese, sulphide, methane, assimilable

organic carbon (AOC), biodegradable organic carbon (BDOC), etc.) (see Chapter 10) and

disinfection (see Chapter 9), providing corrosion control (see Chapter 10) and maintaining an

adequate secondary disinfectant residual (see Section 11.4.4.3) can help to minimize

biological activity and regrowth in the distribution system. Similarly, improving the removal

of natural organic matter (see Chapter 6 and Chapter 10) during treatment can reduce DBP

formation and biological regrowth in the distribution system.

11.4.4.2 Enhancing Distribution System Monitoring

Under O. Reg. 170/03, drinking water systems are required to conduct regular monitoring

throughout the distribution system for a number of parameters. Additional monitoring can

also be conducted to identify the source and magnitude of a distribution system water quality

problem, such as nitrification or corrosion, by targeting specific parameters. A list of

parameters recommended for monitoring to identify a particular water quality issue was

presented in Table 11-4. Additional information is provided in Lauer (2005).

11.4.4.3 Disinfectant Residual Maintenance (Secondary Disinfection)

Secondary disinfection involves the maintenance of a disinfectant residual in the distribution

system. The maintenance of a persistent disinfectant residual protects the water from

microbiological re-contamination, reduces bacterial re-growth, controls biofilm formation

and serves as an indicator of distribution system integrity. Only chlorine, chlorine dioxide

and monochloramine provide a persistent disinfectant residual.

For drinking water systems that are required to provide secondary disinfection under O. Reg.

170/03, the system must be operated such that at all times and at all locations within the

distribution system there is a minimum free chlorine residual of 0.05 mg/L (at pH 8.5 or

lower), or chlorine dioxide residual of 0.05 mg/L, or a combined chlorine residual of 0.25

mg/L where chloramination is used.



The Procedure for Disinfection of Drinking Water in Ontario (MOE, 2006) also establishes

operational targets for free chlorine residual and combined chlorine residual at 0.2 mg/L and

1.0 mg/L, respectively, at all locations in the distribution system.

The maximum disinfectant residual at any time and at any location within the distribution

system should not exceed 4.0 mg/L as free chlorine, 0.8 mg/L as chlorine dioxide and 3.0

mg/L as combined chlorine.

It should be noted that higher disinfectant residual concentrations (i.e. greater than the

operational objectives) may be needed to control microbial activity, nitrification and to

provide a persistent residual throughout the system, depending the size, and layout of the

distribution system and water quality characteristics. Higher free chlorine residuals may

increase the rate of DBP formation if organic precursors are present; therefore, the balance

between the need to ensure adequate secondary disinfection and minimizing DBP formation

should be considered.

In larger distribution systems, booster or re-chlorination systems may be needed at one or

more points in the distribution system to improve secondary disinfection.

11.4.4.4 Controlling Nitrification

Nitrification is a microbiological process by which ammonia is oxidized to nitrite and nitrate

by ammonia oxidizing bacteria (AOB) and archaea (AOA). The use of chloramine as a

secondary disinfectant and the presence of nitrifying bacteria in the distribution system are

the main causes of nitrification in water distribution systems.

Ammonia-nitrogen is converted to chloramine-nitrogen at the point of chloramine formation

during treatment. The chloramine-nitrogen is converted back to ammonia-nitrogen as

chloramines degrade in the distribution system.

There are several symptoms of nitrification that can impact water quality, including loss of

disinfectant residual, nitrite and nitrate formation, dissolved oxygen depletion, reduction in

pH and alkalinity, and an increase in heterotrophic plate count (HPC) bacteria, total coliforms

and ammonia-oxidizing bacteria and/or nitrite oxidizing bacteria.

A number of water quality factors contribute to nitrification, including the chlorine to

ammonia weight ratio, inadequate initial chloramine residual at the plant or booster station,

the availability of nutrients for nitrifying bacteria, and physical water quality characteristics

that may favour bacterial growth and/or hinder inactivation (e.g. temperature, pH and

alkalinity).

Operations and maintenance activities that can help to control nitrification events include:

Minimizing water age;

Improving turnover in storage facilities;

Flushing of distribution mains can be used to reduce water age, to maintain adequate

disinfectant residual concentrations and to remove accumulated biofilm or sediment;

and



Periodic free chlorination either of the entire system or affected areas of the

distribution system.

If nitrification is a recurring problem in a drinking water system, consideration should be

given to the development of a site specific nitrification assessment and response plan.

Additional information on the causes, prevention and control of nitrification is provided in

AWWA (2006).

11.4.4.5 Improving Distribution System Operation and Maintenance

Three primary operational goals are used to maintain water quality: minimizing water

detention time in the system; maintaining positive pressure; and purposefully controlling the

direction and velocity of flow (Lauer, 2005). Table 11-6 provides a list of optimization

activities that can be undertaken in support of these objectives.

Table 11-6 – Operational Changes for Distribution System Optimization

Adapted from Lauer (2005)

Minimize Detention Time Maintain Positive Pressure Control Flow Direction and

Velocity

Hydraulic and water quality

modelling to predict water

age, DBP and disinfectant

residual concentrations

Improve reservoir turnover


Develop standard operating

procedures for reservoir

and system operation

Water quality monitoring


Looping of dead-ends (see

Section 11.4.4.7)

Hydraulic modelling to predict

water pressure

Implement cross connection

control program

Inspect valve positions

Avoid hydraulic surges

(improve control of pump

startup and shutdown; open

and close valves slowly)

Hydraulic modelling to evaluate

flow conditions in the system as

a result of power failure, fire

fighting and hydrant flushing

Control on/off cycles at well

pumping stations, if several

sources of supply are used in

the system

Avoid hydraulic surges

(improve control of pump

startup and shutdown; open and

close valves slowly)

Common distribution system maintenance activities include flushing, cleaning and repairs.

Watermain flushing is an important tool for helping to reduce the amount of sediment in the

distribution system and to remove stagnant water. Issues to consider when developing a

sampling program include: the type of flushing program (i.e. targeted flushing or system-

wide); unidirectional flushing versus conventional flushing of specific areas; the frequency of

flushing; the target velocity needed; monitoring of water quality before and after flushing; as

well as recording the procedures and results of the flushing program.

A variety of cleaning techniques can be used for watermains, including mechanical scraping,

pigging, swabbing, chemical cleaning and flow jetting. Each technique has advantages and

disadvantages that should be considered before being implemented. When a cleaning

technique is used, it may or may not be followed by relining of the pipe. If the pipe will not



be relined following cleaning, special consideration should be given to the pipe material and

its condition so that corrosion of the newly exposed surface does not rapidly occur and

impact water quality.

11.4.4.6 Minor Modifications

Where limitations in distribution system performance are due to design factors,

reconfiguration of the existing system can be considered to improve system hydraulics and

water quality. The following measures can be implemented to optimize distribution system

performance:

Hydraulic and water quality models can be used to estimate water age and

disinfectant residuals at various points in the distribution system;

Pressure zones can be planned or reconfigured to reduce water age and maintain

water quality;

Consideration can be given to the installation of booster chlorination facilities;

Rehabilitation of deteriorated pipelines can be used to restore capacity and/or

improve water quality in targeted areas; and

Eliminating or looping of dead-end water mains (see Section 11.4.4.7).

11.4.4.7 Eliminating Dead-End Watermains

Dead-ends in a distribution system can be eliminated by making appropriate tie-ins or

looping whenever practical. Looping can provide increased reliability of service, and reduce

stagnation and loss of disinfectant residual.

Where dead-end mains cannot be avoided, a means for adequate flushing should be provided

that will help to prevent stagnation, such as the installation of a fire/flushing hydrant, or a

blow-off valve or “bleeder”.

Historically, bleeders have been used to prevent freezing in small diameter watermains or

service lines. The use of bleeders results in large volumes of water being wasted throughout

the year, increasing treatment and energy costs. Two options are available to reduce the

amount of water wasted from bleeders when their primary purpose is for preventing freezing:

1. Timers: Timers are used to turn bleeders on and off automatically. For example, they

can be set to clear water from a pipe before the water reaches ice-forming

temperatures. The capital cost is relatively low, but the system still wastes large

volumes of water.

2. Temperature sensors: These sensors are more expensive to install and maintain but

waste less water than bleeders with or without timers. The sensors should be installed

in the coldest sections of the supply pipes. When the sensor reads below a preset

temperature (usually just above freezing), the sensor triggers the opening of the

bleeder. The bleeder closes when the sensor reads above another preset temperature.



Another alternative to providing a bleeder on a dead-end main is to install a recirculation

system, in which a pump and smaller diameter pipe are used to recirculate unused water in

dead-ends to prevent freezing and maintain water quality. The installation costs for

circulation systems are typically more expensive than for bleeders; however, there are

significant cost savings due to reduced water demand, energy consumption and wastewater

generation.

Site specific studies are needed to evaluate the various options available and select the

preferred alternative for improving water quality and preventing freezing in dead-end

watermains.

11.4.4.8 External Corrosion Control

Treatment processes commonly used for internal corrosion control are presented in Chapter

10. Other techniques that can be used to prevent corrosion in distribution systems include:

Coatings: These can be applied to the interior surface of watermains and tank surface

to protect against interior corrosion.

Cathodic Protection: This type of protection consists of a sacrificial anode made of

zinc or magnesium. These anodes are buried in the ground in close proximity to the

pipe and in areas that are prone to external corrosion. These metals deteriorate first

and thus protect the pipe material from deterioration. The anodes must be replaced on

a regular basis to maintain the desired level of protection.

Impressed Current Systems: These systems apply a low current through the pipe or

tank in a controlled circuit. This type of system is common for metal tanks and above

ground installations.

11.4.4.9 Leak Detection

Leaks may originate from any weakened joint or fitting connection, or from a damaged or

corroded part of the pipe. Leaks are undesirable not only because they waste water, but

because they can undermine pavements and other structures. Another undesirable effect of

leaks is that they create a potential for backflow contamination if pressure is lost in the pipe.

Leak detection programs are an effective means for water utilities to reduce operating and

maintenance costs. If a leak detection crew can reduce water loss and produce cost savings

greater than the cost of maintaining the field crew, then the leak detection program is

economically justified. Leak detection programs can also be justified in terms of the early

detection and repair of leaks while they are small, before serious failure occurs with resulting

property damage, crew overtime, delays of other projects and other similar problems.

Methods used to determine the location of leaks include sound rods, audio phones and

commercially available leak detection equipment, which intensifies the sound as a means of

locating leaks.

Water operators can also undertake a water audit of water supplied compared to the water

consumed in each area or zone of the system. The amount of “unaccounted for water” can be

compared against industry standards to identify the areas of the system that require a more

detailed street by street leak detection survey.



Additional information is provided in AWWA (2009) and National Guide to Sustainable

Municipal Infrastructure (2003).

11.4.4.10 Backflow Prevention and Cross Connection Control

Backflow is the flow of any water, foreign liquids, gases or other substances, back into a

potable water supply. Two conditions that can cause backflow are backpressure and

backsiphonage.

A cross connection is any connection between a potable water system and any other water

source or system through which backflow can occur.

Cross connections must either be removed or some means provided to protect the potable

water supply from possible contamination. The preventive measure chosen depends on the

degree of hazard involved, the accessibility of the premises where the cross connection exists

and the type of water distribution system. Some commonly used backflow prevention devices

include:

Air gaps;

Reduced-pressure-zone backflow preventers;

Double check valve assemblies;

Vacuum breakers (atmospheric and pressure); and

Barometric loops.

When developing a cross connection control program, the owner/operator of a drinking water

system should consider provincial codes and regulations, municipal by-laws and the size of

the community. An effective cross connection control program should include the following

elements:

Adherence to or creation of plumbing and cross connection control by-laws;

Identification of an organization or agency with overall responsibility and authority

for administering the program, with adequate staff;

Systematic inspection of new and existing installations;

Follow-up procedures to ensure compliance;

Backflow prevention device standards, as well as standards for inspection and

maintenance;

Cross connection control training; and

A public awareness and information program.



Additional information on the development of cross connection control and backflow

prevention programs is provided in AWWA (2004) and National Guide to Sustainable

Municipal Infrastructure (2005).

11.5 CASE HISTORIES

11.5.1 Region of Durham – Water Loss Control Strategy

The following case study is based on information presented in Hobbs & Dejan (2010).

System Description

The Region of Durham (the Region) operates and maintains six surface water treatment

plants, 25 groundwater wells, 22 reservoirs, 19 pumping and booster stations and almost

2,400 km of watermains.

The Region regularly undertakes a number of water loss management activities, including a

leak detection program, meter change-out program, hydrant inspections, valve inspection and

maintenance, service repairs and replacement, as well as a cathodic protection program.

In 2006, a Water Loss Control Strategy was developed to:

Assess existing Regional practices;

Evaluate data sources;

Understand the significance and scale of water loss;

Understand the economics of leakage;

Evaluate potential savings or maximized revenue;

Outline benefits to water loss control for maintenance, rehabilitation and demand

control; and

Recommend a strategy for water loss management.

The objective of the study was to incorporate the Region’s existing water loss activities into a

more comprehensive program.


A water balance was conducted to quantify water losses. Conducting the water balance

before embarking on leakage detection or management projects allowed the Region to

determine if water loss reduction was economical. The water balance was conducted by

comparing the System Input Volume (production from the six surface water plants and eight

well systems) to authorized consumption. The difference, deemed water loss, was further

analyzed to determine apparent losses (e.g. meter inaccuracies) and real losses (i.e. leakage).

The results of the water balance indicated that, depending on the method used, real losses

accounted for up to 21 percent of the total system input. The estimated cost of real losses was



determined to be approximately $1 million per year. The total cost of apparent losses was

estimated between $513,400 and $657,700 per year. The Region determined that a potential

annual savings of approximately $760,000 could be achieved by reducing real losses.

As a result, several strategies were recommended to manage water loss, including the

implementation of:

Annual water loss assessment;

Improvements to metering strategies, including meter installations at system

interconnection points, sub-metering for larger zones, installation of Smart Meters

for large volume users, and at reservoir inlets;

Improving the billing database;

Customer meter replacement;

Calibration of meters at sources of supply;

Development of a Bulk Water Strategy; and

Improved tracking of unbilled authorized consumption.

Summary

As part of the water loss management study, the Region learned that detailed analysis of

water demands would require sub-metering on a district or pressure zone basis. In addition,

the accuracy of billing data and customer meter replacement would be required to more

accurately evaluate billed authorized consumption. Measures were also put into place to

investigate methods to reduce unauthorized consumption. The strategy will be reviewed on

an annual basis to evaluate the annual costs of the program versus the annual reduction in

water lost to recognize when it is no longer economical to further reduce leakage.

11.5.2 Region of Niagara – Treated Water Pumping & Storage Optimization

The following case study is based on information presented in Tracy (2009).

System Description

The Grimsby WTP is a conventional surface water treatment plant and supplies water to the

towns of Grimsby, Lincoln and West Lincoln. It is owned and operated by the Region of

Niagara (the Region).

Treated water storage facilities are typically sized to provide a portion of the maximum day

demand, water for fire protection and to provide balancing storage. In practice, operations

staff often maintain storage levels fairly high to keep pressures in the system and to maximize

emergency storage. This results in water treatment facilities having to operate towards peak

hour rates rather than maximum day rates, and frequent changes in the production rate are

often required. Ultimately, this operating scheme requires earlier expansion or upgrading of

WTPs earlier than planned or necessary.




The Region of Niagara conducted a pilot program applying OPIR® software to optimize

water treatment plant production and balance storage in the Grimsby drinking water system.

OPIR® is control software developed to optimize water system production through

intelligent control. The software continuously monitors actual diurnal demand by mass

balance calculations of consumption. It then forecasts the demand and sets the WTP

production rate to make full use of available balancing storage to minimize the number of

production set point changes.

The production rate set point is calculated using three steps:

1. Configuration: A database of storage capacities and operating levels, WTP

production increments, and flow and level instrumentation information is assembled.

2. Data capture: The software continuously calculates demand or consumption, derives

diurnal demand patterns for each day of the week based on the previous seven weeks,

and continuously moves the seven week window to capture seasonal variations.

3. Forecasting: The program forecasts demand in each control zone, forecasts levels in

all storage facilities, and displays historical performance and forecasts for the next

two days. It then derives cumulative demand and storage curves to determine a

“constant” production rate set point based on available WTP capacity increments.

By pumping at average day rates rather than peak rates, energy costs can be reduced by an

estimated 10 to 15 percent. The program can also be used to skew WTP production hours to

off-peak hydro hours, resulting in a potential energy savings of up to 20 percent.

Summary

Current energy costs at the Grimsby WTP are approximately $280,000 per year. It is

anticipated that by optimizing balancing storage and WTP production rates, the potential

energy savings would be between $30,000 and $50,000 per year. It should be noted that by

operating the WTP for average day demand rather than peak hour demand, the most

significant savings may be realized by delaying the expansion of the Grimsby WTP by

several years.

11.6 REFERENCES

American Water Works Association (1996). Water Transmission and Distribution –

Principles and Practices of Water Supply Operations. Second Edition. AWWA. Denver, CO.

ISBN 0-89867-821-8.

American Water Works Association (2004). Manual of Water Supply Practices M14:

Recommended Practice for Backflow Prevention and Cross Connection Control. Third

Edition. AWWA. Denver, CO. ISBN 1-58321-288-2.

American Water Works Association (2006). Manual of Water Supply Practices M56:

Fundamentals and Control of Nitrification in Chloraminated Drinking Water Distribution

Systems. Third Edition. AWWA. Denver, CO. ISBN 1-58321-419-4.



American Water Works Association (2009). Manual of Water Supply Practices M36: Water

Audits and Loss Control Programs. AWWA. Denver, CO. ISBN 1-58321-631-6.

American Water Works Association Research Foundation and Japan Water Works

Association (1993). Instrumentation & Computer Integration of Water Utility Operations.

ISBN 0-89867-630-4.

California State University and USEPA Office of Drinking Water (1996). Water Distribution

System Operation and Maintenance. 3rd Ed. California State University, Sacramento

Foundation. ISBN 1-884701-16-7.

Friedman, M., G.J. Kirmeyer, G. Pierson, S. Harrison, K. Martel, A. Sandvig and A. Hanson

(2005). Development of Distribution System Water Quality Optimization Plans. AwwaRF.

Denver, CO. ISBN 1-58321-388-0.

Hobbs, E. and C. Dejan (2010). “A Systematic Approach to Undertaking Water Loss

Management”, presented at the OWWA/OMWA Joint Annual Conference, Windsor,

Ontario.

Kirmeyer, G.J. et. al. (1999). Maintaining Water Quality in Finished Water Storage

Facilities [Project #254]. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-983-4.

Lauer, W.C. (2005). Water Quality in the Distribution System. AWWA. Denver, CO. ISBN

1-58321-323-6.

National Guide to Sustainable Municipal Infrastructure (2003). Water Use and Loss in

Distribution Systems. Federation of Canadian Municipalities and National Research Council.

National Guide to Sustainable Municipal Infrastructure (2005). Methodology for Setting a

Cross Connection Control Program. Federation of Canadian Municipalities and National

Research Council.

O’Connor, D. R. (2002). Part Two Report of the Walkerton Inquiry: A Strategy for Safe

Drinking Water. Toronto: Publications Ontario. ISBN: 0-7794-2621-5.

Tracy, H. (2009). “Water System Optimization & Energy Savings Using Predictive Control”,

presented at the OWWA/OMWA Joint Annual Conference, Toronto, Ontario.


CHAPTER 12 RESIDUALS AND RECYCLE STREAMS

RESIDUALS AND RECYCLE STREAMS

12.1 Introduction .......................................................................................................... 12-1

12.2 Water Treatment Process Residuals ..................................................................... 12-1

12.3 Residuals Treatment Processes ............................................................................ 12-3

12.3.1 Sludge Thickening ................................................................................. 12-4

12.3.2 Sludge Dewatering ................................................................................. 12-8

12.4 Case Histories ..................................................................................................... 12-11

12.4.1 City of Brantford – Residuals Management Facility ........................... 12-11

12.4.2 Charleston, W.Va. – Kanawha Valley WTP Recycle Stream

Evaluation ............................................................................................ 12-12

12.5 References .......................................................................................................... 12-14

CHAPTER 12. Residuals and Recycle Streams 12-1


CHAPTER 12

RESIDUALS AND RECYCLE STREAMS

12.1 INTRODUCTION

Most water treatment process residuals require treatment. The degree of treatment provided

depends on: regulatory requirements; the disposal method; the assimilative capacity of the

receiving water body in the case of discharge to the environment; and treatment/disposal

costs.

A discussion of all types of residuals and treatment technologies is beyond the scope of this

Manual, however, a brief overview of the types of plant waste residuals and treatment options

commonly used in Ontario is provided in this chapter.

Measures to optimize treatment processes to minimize the quantity of residuals produced are

presented elsewhere (e.g. Chapter 6 and Chapter 8). Reducing the quantity of residuals

requiring treatment and/or disposal will also decrease the costs associated with waste

handling.

12.2 WATER TREATMENT PROCESS RESIDUALS

Table 12-1 presents a summary of specific water treatment process residuals, as well as

treatment and/or disposal options. Additional information on the types of water treatment

plant wastes is provided in Cornwell et. al. (1987).

Table 12-1 – Specific Water Treatment Process Residuals Treatment and Disposal

Options

Process Type of Residual Treatment and/or

Disposal Options

Comments

Sedimentation/

Clarification

Sludge Mechanical dewatering

(centrifuges, rotary drum

thickeners, filter presses)

Disposal to sanitary

sewer1

Mechanical methods

are typically used for

larger treatment plants

Sewer and sewage

treatment plant

capacity need to be

considered




Options (cont’d)


Disposal Options

Comments

Chemically-

assisted Granular

Media Filtration

Backwash wastewater Surge/equalization tank

with disposal to sanitary

sewer1

Equalization/decant tank

with disposal of

supernatant to sanitary

sewer1 (or receiving

water body, where

acceptable) and sludge

removed for further

treatment

Recycling of supernatant

from backwash

treatment facilities to the

WTP intake or

headworks2

Sewer and sewage

treatment plant

capacity need to be

considered

Treatment may be

required when

discharging to a

receiving water body

Granular media may be

lost over time in

backwash waste

streams; impacts of

solids loading and

presence of media on

sludge thickening

equipment should be

considered

Membrane

Filtration

Membrane reject water May be discharged

without treatment to a

suitable surface water

body provided effluent

quality criteria are met

Membrane backwash

residuals Discharge to sanitary

sewer1

Treatment with

supernatant recycle and

solids disposal

Discharge of supernatant

to a suitable surface

water body if applicable

regulations or standards

are met

Membrane chemical

cleaning residuals On-site treatment

(quenching,

neutralization, etc.)

followed by discharge to

sanitary sewer1 or

holding tank for proper

disposal

The use of surfactants

or other proprietary

cleaning agents may

result in a requirement

for additional treatment




Options (cont’d)


Disposal Options

Comments

Iron and

Manganese

Removal

Backwash wastewater

and sludge Discharge to sanitary

sewer1

Holding tank with

supernatant recycle1 to

head of plant and solids

disposal

Ion Exchange Brine waste Discharge to sanitary

sewer1, where permitted

Holding tank for off-site

disposal

Discharge to sanitary

sewer may require use

of equalization tank

with discharge flow

control

Precipitative

Softening

Sludge Lagoons

Land application

Mechanical dewatering

Landfilling

Notes:

1. Discharges to sanitary sewers should meet all applicable local sewer-use bylaws.

2. Specific operating and monitoring requirements may apply when backwash water recycling is

practiced to minimize hazards associated with the potential for increased concentration of

pathogens in the water. Refer to the Design Guidelines for Drinking Water Systems, 2008

(MOE, 2008) for further information.

12.3 RESIDUALS TREATMENT PROCESSES

The type of residuals treatment process used at a water treatment plant will depend on the

type, quality and quantity of residuals produced as well as the discharge and ultimate disposal

requirements.

The recycling of waste streams can impact treated water quality or cause process upsets,

consideration of specific measures to minimize the concentrations of pathogenic organisms

and other contaminants in the recycle streams is required. Additional information is provided

in MOE (2008) and Cornwell & Lee (1993).

Processes commonly used in Ontario for handling water treatment process residuals include

flow equalization, sedimentation/clarification, sludge thickening and dewatering.

Methods for evaluating and improving the performance of equalization tanks and clarification

processes are presented in Chapter 7. Information on sludge treatment processes (thickening

and dewatering) is presented in the following subsections.



12.3.1 Sludge Thickening

12.3.1.1 Purpose and Types of Sludge Thickeners

Sludge thickening is the process of removing free water not bound within the sludge flocs.

The result of removing a portion of the free water is a higher solid content, typically between

four (4) and 14 percent depending on the type of thickener. Thickening is typically

undertaken in order to reduce the volume of solids that will require subsequent treatment or

disposal.

There are a number of types of sludge thickeners that utilize different mechanisms to increase

the solids concentrations of the sludge including; gravity settlers, gravity belt thickeners

(GBTs), rotary drum thickeners (RDTs), thickening centrifuges, and DAF thickeners.

Gravity settlers use settling processes usually accompanied by a slowly revolving sludge

collector. GBTs thicken sludge by placing the sludge in between two fabric belts which move

and allow the water to separate from the sludge by gravity. RDTs act by straining free water

from the sludge through a rotating cylindrical screen.

Thickening centrifuges apply a strong centrifugal force to the sludge which separates the

sludge and water as a result of the density differences. The lighter liquids remain near the

center of rotation and exit by overflowing a weir. There are three types of centrifuges; basket,

solid-bowl and disc centrifuges. Basket centrifuges are rotating vertical chambers with a weir

at the top. Solid-bowl centrifuges bring sludge into a fast rotating bowl using a screw-type

conveyor. Within the bowl, the solids move to the walls while the liquid is decanted or

drawn-off. In disc centrifuges, the solids move toward the wall where stacks of discs are

located that collect the liquid. The collected liquid then flows to a discharge chamber. Solid

bowl centrifuges are most commonly used for sludge thickening.

Thickening of sludge using DAF occurs by introducing air to the sludge in a unit that has an

elevated pressure. When the sludge is depressurized, fine air bubbles are formed which, when

attached to the solid floc, carry thickened sludge to the top where it can be removed.

Further information on the purpose and type of thickeners can be found in MOE (2008),

Wang et al. (2007), and Metcalf & Eddy (2003).

12.3.1.2 Evaluating Process Performance

Typically, sludge thickener performance is evaluated based on the solids captured and the

total solids content achieved. Table 12-2 presents typical process performance results for the

various types of sludge thickeners.



Table 12-2 – Sludge Thickening – Typical Process Performance

Adapted from MOE (2008) and Metcalf & Eddy (2003)

Thickening Method

Expected Performance

Total Solids (%) Solids Capture (%)

Basket centrifuges 8-10 1

80-90

Disc-nozzle centrifuges 4-6 1 80-90

Solid bowl centrifuges 5-8 1 70-90

GBT 4-8 ≥ 95

RDT 4-9 93-98

Gravity thickeners 5-10 n/a

DAF 4-6 ≥ 95 2

Notes:

1. Lower solids concentrations expected without use of polymers.

2. Using flotation aids.

Table 12-3 presents recommended monitoring, in terms of sampling locations and analyses,

in order to evaluate the performance of sludge thickeners.

Table 12-3 – Sludge Thickening – Recommended Process Monitoring to Evaluate

Performance



Influent sludge Composite

recommended Flowrate

Sludge volume index

(SVI)

Total solids (TS)

Thickening units Continuous

monitoring Polymer dosage

Overflow rate

Underflow rate

For process control



Table 12-3 – Sludge Thickening – Recommended Process Monitoring to Evaluate

Performance (cont’d)



Centrate/supernatant/

subnatant

Composite


Total suspended solids

(TSS)

Chlorine residual

Other parameters may

be required based on C

of A or DWWP/License

if discharged to the

environment or Sewer

Use By-Law limits if

discharged to the

municipal sewer system

Thickened sludge Composite


TS

For performance

measurement

Figure 12-1 presents a process schematic of a sludge thickening process, along with

recommended sampling locations.

Thickeners

Centrate/Supernatant/Subnatant

Sample Location

Influent

Sludge

Influent Sludge

Sample LocationThickened Sludge

Sample Location

Thickening Unit

Centrate/

Supernatant

Thickened

Sludge

Figure 12-1 – Sludge Thickening – Process Schematic and Recommended Sampling

Locations

12.3.1.3 Common Problems and Potential Process Impacts

Symptoms and causes of common problems encountered with the sludge thickening process

are presented in Table 12-4.



Table 12-4 – Sludge Thickening – Common Problems and Impacts



Thickened sludge has

low solids content Lower than expected TS in the

thickened sludge

Higher than expected TS in the

centrate/supernatant/subnatant

Inadequate polymer dosing

(Section 12.3.1.4)

Inadequate sludge storage

Thickener is hydraulically

overloaded due to poor feed pump

controls

Short circuiting through the

thickener

Septic thickened

sludge Thickened sludge is odorous

High sludge blanket (gravity

thickeners)

Floating of sludge (gravity

thickeners)

Ineffective pump controls resulting

inconsistent or infrequent sludge

feeding

Low hydraulic overflow or

underflow rate

Long retention time of solids

within thickener

12.3.1.4 Options to Enhance Thickening

Optimizing the performance of thickeners begins with ensuring that the operation of the unit

is as close to the manufacturer’s recommended operating conditions as possible. Consultation

with the process supplier can be useful in ensuring the unit is operating optimally.

In addition, thickening can be improved by optimizing the use of polymers. Dosing polymers

can improve the solids capture and increase the solids content in the thickened sludge. Both

the polymer dosage and dosing point(s) should be reviewed as in some cases multiple dosing

points can improve performance. Jar testing can be used to optimize polymer type, dosage

and mixing. Full scale tests can be performed during plant operation to further optimize

polymer dosage. As polymer effectiveness depends on the polymer dose per unit of solids

(mg of polymer per kg dry solids in the sludge feed) not on dose per litre of sludge flow,

dosing polymer based on flow only will not be optimal unless sludge concentration is

relatively constant.

Thickening can be improved by ensuring that influent flows and concentrations are

maintained relatively constant which will prevent wide variations in solids load and polymer

dose. Minimizing the variability of feed flows and concentrations can be accomplished by a

number of ways including the implementation of online instrumentation and control systems

that can measure feed solids concentration and flow. In addition, implementation of mixed

storage tanks prior to mechanical thickening equipment can also be used to minimize

variability rather than feeding directly from clarifier underflows to thickeners.

Stress testing of the thickening process can be undertaken in order to determine the maximum

throughput, optimal operating settings, polymer dosage requirements, and the impact on the



thickened sludge concentration and centrate quality. Procedures for stress testing are presented

in Chapter 4.

Further information on enhancing thickening processes can be found in WERF (2009).

12.3.2 Sludge Dewatering

12.3.2.1 Purpose and Types of Sludge Dewatering

The purpose of dewatering is to remove the floc-bound and capillary water from sludge prior

to further processing or off-site disposal. Sludge dewatering is similar to sludge thickening

(Section 12.3.1) but a much higher TS concentration in the dewatered sludge is achieved

compared to a thickening process. In order to improve sludge dewatering, chemical

conditioning is typically used to improve the solids capture and increase the solids content in

the dewatered sludge.

There are numerous dewatering processes available, a number of which can be employed to

increase the solids content of the sludge to between 10 to 50 percent depending on the

process. The processes include: solid bowl centrifuges, belt filters presses, filter presses, and

vacuum filters. Solids bowl centrifuges were described in Section 12.3.1.1.

Belt filter presses are continuously fed units that dewater chemically conditioned sludge first

in a gravity drainage section where the free water is removed. After the free water is

removed, low pressure is applied by porous belts to remove a portion of the bound water

from the sludge. Filter presses dewater by the application of high pressure to remove bound

water. Vacuum filters remove water from sludge by application of a vacuum.

Further information on the purpose and type of dewatering processes can be found in MOE

(2008), Wang et al. (2007), and Metcalf & Eddy (2003).

12.3.2.2 Evaluating Process Performance

Typically, sludge dewatering process performance is evaluated based on the solids captured

and the total solids content achieved. Table 12-5 presents typical process performance for the

various types of sludge dewatering processes.



Table 12-5 – Sludge Dewatering – Typical Process Performance

Adapted from MOE (2008) and Fournier Inc. (2010)

Dewatering Method

Expected Performance

Total Solids (%)1 Solids Capture (%)

Solid bowl centrifuges 15-30 95-99

Belt filter press 10-25 85-95

Filter press 25-50 90-95

Vacuum filter 10-25 90-95

Notes:

1. Values presented in this table assume the use of conditioning chemicals (i.e. polymers). If no

conditioning chemicals are used, cake solids and solids capture values may be reduced.


in order to evaluate the performance of dewatering processes.

Table 12-6 – Sludge Dewatering – Recommended Process Monitoring to Evaluate

Performance


Influent sludge Composite recommended Flowrate

TS

Centrate/filtrate Composite recommended Flowrate

TSS

Chlorine residual

Dewatered sludge Composite recommended Flowrate

TS

Figure 12-2 presents a process schematic of a dewatering unit, along with recommended

sampling locations.



Thickeners

Centrate/Filtrate

Sample Location

Influent

Sludge

Influent Sludge

Sample LocationDewatered Sludge

Sample Location

Dewatering Unit

Centrate/

Supernatant

Dewatered

Sludge

Figure 12-2 – Sludge Dewatering – Process Schematic and Recommended Sampling

Locations

12.3.2.3 Common Problems and Potential Process Impacts

Symptoms and causes of common problems encountered with the sludge dewatering process


Table 12-7 – Sludge Dewatering – Common Problems and Impacts



Dewatered sludge

has low solids

content

Lower than expected TS in the

dewatered sludge

Higher than expected TSS in the

centrate/filtrate

Inadequate polymer dosing

(Section 12.3.1.4)

Dewatering process is hydraulically

overloaded

Short circuiting through the unit

Septic dewatered

sludge Dewatered sludge is odorous

Inconsistent or infrequent sludge

feeding

Hydraulic overflow or underflow

rates lower than design rates

Long retention time of solids

within unit



12.3.2.4 Options to Enhance Dewatering

As dewatering is a process similar to thickening, optimizing dewatering process performance

involves similar techniques. Possible techniques to enhance dewatering are listed below with

additional information available in Section 12.3.1.4:

Consultation with the process supplier to ensure that there are no equipment or

operating issues;

Jar testing to optimize polymer type, dosage and mixing rate;

Conducting full scale studies to optimize polymer dosing locations and dosage;

Installation of online instrumentation to measure and control the feed flow and solids

density to minimize feed fluctuations;

Implementation of mixed storage tanks prior to dewatering units to minimize feed

variability; and

Stress testing to determine optimal operating settings and maximum throughput.

Further information on enhancing dewatering processes can be found in WERF (2009).

12.4 CASE HISTORIES

12.4.1 City of Brantford – Residuals Management Facility

The following case study is based on information presented in Yohannes (2010).

System Description

The City of Brantford WTP process consists of an ActifloTM

high rate clarification process,

followed by dual media filtration and chlorination. In 2003, a new residual management

facility (RMF) was constructed to replace the existing lagoons.

Prior to the commissioning of the RMF, sludge was directed into a settling pond and the

supernatant overflowed into the Grand River. The bottom of the pond was dredged

periodically to remove the excess solids and maintain its effective settling capacity. Problems

associated with the operation of the lagoon included limited dredging time in winter months

because of ice formation, solids carryover into the Grand River during periods of heavy

rainfall, and disturbances in settling causing elevated suspended solids and aluminum levels.

Various studies were undertaken to evaluate waste handling systems for the wastewater

produced from filter backwashes and pretreatment processes (sludge from ActifloTM

process).

Both rotary drum thickeners and gravity settling thickeners were evaluated. Based on the data

obtained during the studies, gravity settling thickeners were selected as the preferred

alternative and two units were installed.

As part of the RMF operation, backwash water and pre-treatment sludge is collected into an

equalization tank before being pumped to the thickeners. An anionic polymer is applied to the

waste stream at the inlet of the thickeners in a flocculation tank. The supernatant from the

thickeners is dechlorinated and discharged to the Grand River. Thickened sludge is collected



in a sludge storage tank until it is pumped to belt presses for dewatering. A cationic polymer

is added to the incoming sludge to enhance the dewatering process. Excess water is pumped

back into the equalization tank for further processing.

Upon commissioning of the RMF, it was determined that the thickeners did not perform

according to the design specifications because of significant problems with operation and

maintenance.


To address the problems with the operation of the thickeners, full scale trials were undertaken

to determine if the thickeners could meet performance requirements for the overflow and

underflow when operated at the design loadings.

Several trials were conducted at various flow rates and at anionic polymer dosages of up to

3.0 mg/L. The results showed that the thickeners were challenged at the flow rate of 35 L/s

and were incapable of processing 52 L/s. It was determined that the units were overloaded

due to their small surface area. As a result, a third thickener was commissioned in 2006.

It was also noted that during winter months, turbidity levels in the raw water were very low,

resulting in low solids concentrations in the feed to the thickeners. Low solids in the residuals

process resulted in difficulties during the dewatering process, which caused the sludge to

become very “sloppy”. Careful monitoring and routine adjustments to belt speed, polymer

dose and sludge flow are required to ensure the proper operation of the belt presses.

Summary

The RMF had a number of advantages compared to the lagoon system, including an increase

in residuals treatment capacity and improvements in the discharge water quality (no chlorine

residual, lower suspended solids concentration, etc.). Proper operation of the RMF did

require additional monitoring and maintenance compared to the lagoon system.

12.4.2 Charleston, W.Va. – Kanawha Valley WTP Recycle Stream Evaluation

The following case study is based on information presented in Cornwell & Lee (1993).

System Description

The Kanawha Valley WTP is located in Charleston, W.Va., and draws water from the Elk

River. Treatment consists of polymer, lime and chlorine addition, followed by upflow

clarification and dual media filtration.

Sludge from the upflow clarifiers is discharged to the sanitary sewer. Spent filter backwash

water is pumped from an equalization tank into the raw water line upstream of the chemical

application point. Recycle pumping lasts for two to three hours and occurs one to three times

per day. The recycle flow typically ranges from 10 to 20 percent of the raw water flow.




A sampling program was undertaken to evaluate the impact of the recycle stream on finished

water quality, specifically in regards to turbidity, total THMs and THMFP concentrations.

Two rounds of sampling were performed. For each round, sampling was conducted over a

two-day period, with one set of samples collected each day. The water quality parameters

included in the study were: total THMs, THMFP, TOC, turbidity, chlorine residual and pH.

The following samples were collected:

Raw water

Mixed water without recycle

Settled water without recycle

Filtered water without recycle

Mixed water with recycle

Settled water with recycle

Filtered water with recycle

Recycle water (unsettled spent backwash)

The results of the sampling indicated that the introduction of the recycle stream to the

treatment process had a significant effect on total THM levels throughout the treatment

process. Filtered water total THM concentration increased from 73 to 95 µg/L during the first

round of sampling, and from 25 to 38 µg/L during the second round.

THMFP levels in the recycle water were found to be twice those of the raw water. The results

from this sampling showed a slight increasing trend of THMFP levels throughout the

treatment process during the recycle operation. The mixed, settled, and filtered water samples

all increased by similar percentages. The results also showed that settling the recycle water

could significantly reduce the THMFP values.

Sampling from both rounds of testing indicated that the recycle stream had substantial effects

on the turbidity of the mixed water; however, there was no impact on clarified or filtered

water. The treatment process was able to handle the increased turbidity loading without an

impact on finished water turbidity.

Summary

At the Kenawha Valley WTP, the influent water total THM concentration increased from 14

to 29 µg/L with the introduction of spent backwash water. This approximately 20 µg/L

differential was carried through the plant; such that the filtered water had a greater total THM

concentration with recycle than without.



12.5 REFERENCES

Cornwell, D.A., M.M. Bishop, R.G. Gould and C. Vandermeyden (1987). Water Treatment

Plant Waste Management. AwwaRF & AWWA. Denver, CO. ISBN0-89867-404-2.

Cornwell, D.A. and R.G. Lee (1993). Recycle Stream Effects on Water Treatment. AwwaRF

& AWWA. Denver, CO. ISBN 0-89867-689-4.

Fournier Inc. (2010). “List of Advantages of the Rotary Press versus the Belt Filter Press”.

Metcalf & Eddy (2003). Wastewater Engineering: Treatment and Reuse, 4th ed. Toronto:

McGraw Hill. ISBN 0-07-041878-0.

MOE (2008). Design Guidelines for Sewage Works. ISBN 978-1-4249-8438-1.

Wang, L.K., N.K. Shammas, and Y-T Hung (2007). Volume 6 Handbook of Environmental

Engineering: Biosolids Treatment Processes. Humana Press Inc. ISBN: 978-59259-996-7.

Water Environment Research Federation (WERF) (2009). Integrated Methods for

Wastewater Treatment Plant Upgrading and Optimization. IWA Publishing. Document

Number: 04-CTS-5.

Yohannes, Y. (2010). “City of Brantford Residuals Management – An Environmentally

Friendly Process of Treating Sludge”, presented at the OWWA Spring Treatment Seminar,

“The Waste of Water”. Toronto, ON, March 2010.

CHAPTER 13 REPORTING RESULTS

REPORTING OF RESULTS

13.1 Introduction .......................................................................................................... 13-1

13.2 Interim Reports – Technical Memoranda ............................................................. 13-1

13.3 Workshops ............................................................................................................ 13-2

13.4 Final Report .......................................................................................................... 13-3

13.5 Implementation of Recommendations and Follow-up ......................................... 13-5

CHAPTER 13 . Reporting of Results 13-1


CHAPTER 13

REPORTING OF RESULTS

13.1 INTRODUCTION

Reporting of results is an important part of an optimization study and can be used to present

findings and conclusions at key points during the study, and also to provide guidance for

facility administrators and operators and, if applicable, regulatory personnel. Internal studies

should be documented for future reference or in support of other activities.

The degree of detail and frequency of progress reports will vary with the scope of the study.

The following subsections present information on interim and final reports, as well as other

reporting tools, such as workshops, that can be developed as part of an optimization study.

13.2 INTERIM REPORTS – TECHNICAL MEMORANDA

Preparation of Technical Memoranda after completion of key activities are an effective

means of ensuring that all participants in the optimization study (owner, operations staff,

consulting team, etc.) are kept informed of project progress, have an opportunity to review

and understand project findings at an early stage, and provide input to the overall project

direction. Each Technical Memorandum (TM) should include:

An introduction describing the overall objective of the project;

The specific objective of the TM and how it relates to the overall project;

A discussion of the methodology, approach and key sources of information used;

The results of the specific activity described in the TM; and

Conclusions and recommendations.

Relevant data (e.g. modelling and simulation results, tracer test results, stress test results, etc.)

should be appended to the TM.

Table 13-1 presents some possible Technical Memoranda that could be prepared during a

comprehensive drinking water system optimization project. TMs prepared to describe the

findings of field investigations will depend on the specific field investigations undertaken.

These Technical Memoranda should be issued as drafts for review by the project team

responsible for the optimization study. Comments on the TM should be compiled and the TM

appropriately revised and issued as final. These Technical Memoranda can be incorporated

into the final report.



Table 13-1 – Possible Technical Memoranda

TM Title TM Contents

#1: Existing Conditions Description of Drinking Water System.

Historic Data Review.

Desk-top Capacity Assessment.

#2: Field Investigations

Work Plan Outlines Work Plan for suggested field investigations based on

findings of TM#1.

Provides detailed description of test methodology, sampling and

analytical requirements, operations staff support requirements,

notification requirements, and any health and safety considerations.

#3: Filter Stress Testing Methodology, results and conclusions of filter stress testing to

determine filter performance efficiency and capacity.

#4: Tracer Testing to Verify

Clearwell Conditions Methods used for tracer testing for determination of actual hydraulic

detention time and test findings.

#5: Process and Distribution

System Modelling and

Simulation

Methodology used to calibrate and verify the simulation model,

conditions modelled, and the model outcomes.

#6: Options to Optimize

Plant Performance and

Distribution System

Operation

Description of options being considered.

Criteria considered in the assessment.

Evaluation of each option against the criteria.

Selection of preferred option and justification for selection.

13.3 WORKSHOPS

Workshops can be an effective means of communicating findings to all project participants,

including plant administration, management and operations staff, and regulators, at key

points in the project and soliciting input on key decisions.

The objectives and desired outcomes of the Workshop must be clearly communicated to the

participants. Important technical information that will be discussed at the Workshop should

be provided to the participants in advance to ensure that informed feedback and input can be

obtained.

Key points in the project where Workshops can prove useful are:

At project initiation, to introduce the project participants, review project background

and objectives, and provide a brief overview of the work plan to be executed and the

project schedule;

After completion of the historic data review, to present the findings of the desk-top

analysis, identify process or capacity limitations, and discuss the proposed field

investigations; and



After the analysis of options, to present the findings of the field investigations,

proposed solutions to achieve the project objectives, the evaluation of options and to

obtain input to the selection of the preferred option(s).

Additional workshops may be beneficial depending on the study scope and duration.

Workshops should not replace regular project meetings with plant management and

operations staff to discuss specific activities, particularly field investigations.

Workshop notes should be compiled and included as an Appendix to the final project report.

13.4 FINAL REPORT

The outcome of an optimization study should be a comprehensive report that concisely

presents:

The project background and the rationale for the optimization study;

The project objectives;

A concise description of the drinking water system including a summary of the

design flows and water quality objectives, the process design of unit processes, a

process flow diagram, a distribution system schematic, and a summary of the

regulatory requirements that must be met or specific performance objectives that

have been set;

A summary of key information sources used during the investigation (e.g. historic

data; preliminary design reports, Certificate of Approval (C of A) or Drinking Water

Works Permit (DWWP) /Municipal Drinking Water Licence (Licence), MOE

inspection reports, annual reports, etc.);

A summary of historic operating conditions and performance for a period of at least

one year (refer to Section 3.3.3);

A desk-top analysis of the capacity and capability of each major drinking water

system component (refer to Section 3.2.1);

The methodology and findings of all field investigations such as stress tests, tracer

tests, jar tests, etc.;

An analysis of options to address capacity, performance or operational limitations, or

increase rated capacity to meet the project objectives;

The conclusions of the study; and

Any recommendations for follow-up investigations or implementation of the

findings.

Table 13-2 presents a suggested Table of Contents for a Drinking Water System Optimization

Final Report. The level of detail included in the final report should be consistent with the

project objectives and the target audience. For example, if an objective of the optimization

study is to support an application for a new C of A or DWWP/Licence to re-rate the plant

capacity, sufficient detail must be provided in the report for the MOE review engineer to

confirm that the proposed changes will consistently and reliably meet regulatory

requirements at the re-rated flow.



Table 13-2 – Example Table of Contents for Drinking Water System Optimization

Report

Item Content

Executive Summary A concise (2 to 3 page) summary of the project objectives, key findings,

conclusions and recommendations.

Table of Contents Identifies key sections and subsections by title and includes a list of tables,

figures and appendices.

Introduction and

Background

Provides the rationale for the study and any background information

relevant to understanding the need for the process optimization. Should

include a list of key information sources used in the study.

Project Objectives Concisely states the key objective(s) of the study.

System Description Provides a process flow diagram of the WTP and/or distribution system,

including the locations of chemical addition points. Key design parameters

(e.g. average day flow, maximum day flow, CT requirements, etc.) and

sizing of key unit processes/mechanical equipment should be provided.

Historic Data Review A review of key operating and performance information for a period of at

least one year, including flows, raw water characteristics, treated water

quality, water quality at intermediate points in the process where available

and applicable (e.g. settled water, filtered water, etc.), and critical

operating parameters (e.g. surface overflow rates, settled water turbidity,

chemical dosages, etc.).

Desk-top Capacity

Assessment

Results of the desk-top analysis of the capacity of each major drinking water

system component study, based on the historic data and comparison to

typical design standards and guidelines, including a performance potential

graph (see Figure 3-2).

Results of Field

Investigations

Methodology and findings of any field investigations undertaken to

confirm the capacity assessment or determine the optimum approach to

achieve the project objectives.

Assessment of Options Identification and evaluation of alternative approaches to optimize the

system to meet the project objectives, including both operational and

design changes. Should include consideration of constructability,

integration with existing system, capital and operating costs, risks,

complexity, etc.

Conclusions Concise summary of the key findings.

Recommendations Recommendations for implementation of the conclusions or for further

investigations.

References Listing of key reference material.

Appendices Contains all supporting documentation such as Cs of A or

DWWP/Licence, modelling outputs, data from field investigations, details

of cost analysis if any, etc.



13.5 IMPLEMENTATION OF RECOMMENDATIONS AND FOLLOW-UP

The time required to implement the recommendations from the optimization study will

depend on the nature of the recommendations. Operational changes such as increasing the

frequency of filter backwashing, increasing chemical dosage, or modifying sludge pumping

rates can be implemented quickly by operations staff. Design changes such as installing

baffles in clarifiers, retrofitting filters with new underdrains, or changing chemical dosage

points can be more time-consuming, likely requiring a detailed design phase, C of A or

DWWP/Licence amendment, tendering and construction.

Regardless of the nature of the upgrade, it is important to ensure that there is follow-up

monitoring to determine how effective the recommended upgrade was in achieving the

original optimization objective. If performance enhancement was the primary objective, a

post-implementation monitoring program should be undertaken to compare the performance

of the unit process after implementation with the performance achieved prior to

implementation. If cost reduction or energy efficiency was the primary objective,

comparative operating cost or energy use data, pre- and post-implementation, should be

collected.

Documentation of the success of the optimization project is critical to ensure on-going

support from management for further optimization activities.

APPENDICES


APPENDICES

APPENDIX A: Classification System, Factor Checklist and Definitions


APPENDIX A

CLASSIFICATION SYSTEM, FACTOR CHECKLIST AND DEFINITIONS

FOR ASSESSING PERFORMANCE LIMITING FACTORS

APPENDIX A: Classification System, Factor Checklist and Definitions A-1


APPENDIX A: CLASSIFICATION SYSTEM, FACTOR

CHECKLIST AND DEFINITIONS

CPE SUMMARY SHEET TERMS

Plant Type Brief but specific description of type of plant (e.g. conventional

with flash mix, flocculation, sedimentation, filtration and chlorine

disinfection or direct filtration with flash mix, flocculation and

disinfection).

Raw Water Source Brief description of water source (e.g. surface water including

name of river or ground water including geologic formation).

Plant Performance Summary Brief description of plant performance as related to desired water

quality.

Ranking Table A list of the major causes of decreased plant performance and

reliability.

Ranking Causes of decreased plant performance and reliability, with the

most critical ones listed first (typically only "A" and "B" factors

are listed).

Type A or B Identify factors as to A (major effect on a long term repetitive

basis) or B (minimum effect on a routine basis or major effect on a

periodic basis).

Performance Limiting Factors

and Category

Items identified from the Checklist of Performance Limiting

Factors. Identify factor category (e.g. administration, design,

operations, or maintenance).



CPE SUMMARY SHEET FOR RANKING PERFORMANCE LIMITING

FACTORS

Plant Name/Location: __________________________________________________

CPE Performed By: ______________________________Date: _________________

Plant Type: ___________________________________________________________

Raw Water Source: ____________________________________________________

Plant Performance Summary:

RANKING TABLE

RANKING TYPE A or B PERFORMANCE LIMITING FACTOR/CATEGORY

1 ____________ ______________________________________________________

2 ____________ ______________________________________________________

3 ____________ ______________________________________________________

4 ____________ ______________________________________________________

5 ____________ ______________________________________________________

6 ____________ ______________________________________________________

7 ____________ ______________________________________________________

8 ____________ ______________________________________________________

9 ____________ ______________________________________________________

10 ____________ ______________________________________________________

11 ____________ ______________________________________________________

12 ____________ ______________________________________________________

A – Major effect on a long term repetitive basis.

B – Minimum effect on a routine basis or major effect on a periodic basis.

C – Minor effect.



CHECKLIST OF PERFORMANCE LIMITING FACTORS

FACTOR RATING COMMENTS

A. Administration

1. Plant Administrators

a. Policies ____________ ____________________________________________

b. Familiarity with plant

needs ____________ ____________________________________________

c. Supervision ____________ ____________________________________________

d. Planning ____________ ____________________________________________

2. Plant Staff

a. Manpower

i) Number ____________ ____________________________________________

ii) Plant coverage ____________ ____________________________________________

iii) Workload distribution ____________ ____________________________________________

iv) Personnel turnover ____________ ____________________________________________

b. Morale

i) Motivation ____________ ____________________________________________

ii) Pay ____________ ____________________________________________

iii) Work environment ____________ ____________________________________________

c. Staff Qualifications

i) Aptitude ____________ ____________________________________________

ii) Level of education ____________ ____________________________________________

iii) Certification ____________ ____________________________________________


d. Productivity ____________ ____________________________________________



3. Financial

a. Insufficient funding ____________ ____________________________________________

b. Unnecessary spending ____________ ____________________________________________

c. Indebtedness ____________ ____________________________________________

B. Maintenance

1. Preventive

a. Lack of Program ____________ ____________________________________________

b. Spare parts inventory ____________ ____________________________________________

2. Corrective ____________ ____________________________________________

a. Procedures ____________ ____________________________________________

b. Critical parts

procurement ____________ ____________________________________________

3. General ____________ ____________________________________________

a. Housekeeping ____________ ____________________________________________

b. References available ____________ ____________________________________________

c. Staff expertise ____________ ____________________________________________

d. Technical guidance ____________ ____________________________________________

e. Equipment age ____________ ____________________________________________




C. Design

1. Raw Water

a. THM precursors ____________ ____________________________________________

b. Turbidity ____________ ____________________________________________

c. Seasonal variation ____________ ____________________________________________

d. Watershed management ____________ ____________________________________________

2. Unit Design Adequacy

a. Pretreatment

i) Intake structure ____________ ____________________________________________

ii) Presedimentation ____________ ____________________________________________

iii) Prechlorination ____________ ____________________________________________

b. Low lift pumping ____________ ____________________________________________

c. Flash mix ____________ ____________________________________________

d. Flocculation ____________ ____________________________________________

e. Sedimentation ____________ ____________________________________________

f. Filtration ____________ ____________________________________________

g. Disinfection ____________ ____________________________________________

h. Sludge treatment ____________ ____________________________________________

i. Residuals disposal ____________ ____________________________________________

j. Fluoridation ____________ ____________________________________________




3. Miscellaneous

a. Process flexibility ____________ ____________________________________________

b. Process controllability ____________ ____________________________________________

c. Process automation ____________ ____________________________________________

d. Lack of standby units for

key equipment ____________ ____________________________________________

e. Flow proportioning to

unit processes ____________ ____________________________________________

f. Alarm systems ____________ ____________________________________________

g. Alternate power source ____________ ____________________________________________

h. Lab space/ equipment ____________ ____________________________________________

i. Sample taps ____________ ____________________________________________

j. Plant inoperability due to

weather ____________ ____________________________________________

k. Return process stream ____________ ____________________________________________

D. Operation

1. Testing

a. Performance monitoring ____________ ____________________________________________

b. Process control testing ____________ ____________________________________________




2. Process Control Adjustments

a. Water treatment

understanding ____________ ____________________________________________

b. Application of concepts

and testing to process

control ____________ ____________________________________________

c. Technical guidance ____________ ____________________________________________

d. Training ____________ ____________________________________________

e. Insufficient time on job ____________ ____________________________________________

3. O&M Manual

a. Adequacy ____________ ____________________________________________

b. Use ____________ ____________________________________________

4. Distribution System ____________ ____________________________________________

E. Miscellaneous

1. ____________ ____________________________________________

2. ____________ ____________________________________________

3. ____________ ____________________________________________

4. ____________ ____________________________________________

5. ____________ ____________________________________________

6. ____________ ____________________________________________

7. ____________ ____________________________________________

8. ____________ ____________________________________________



DEFINITIONS OF PERFOMRANCE LIMITING FACTORS

A. ADMINISTRATION

1. Plant Administrators

a. Policies Do operating staff members have authority to make

required operation (e.g., adjust chemical feed),

maintenance (e.g. hire electrician), and/or

administrative (e.g. purchase critical piece of

equipment) decisions, or do policies cause critical

decisions to be delayed which in turn affect plant

performance and reliability? Does any established

administrative policy limit plant performance (e.g. non-

support of training; or plant funding too low because of

emphasis to avoid rate increases)?

b. Familiarity with plant needs Do administrators have a first-hand knowledge of plant

needs through plant visits or discussions with operators?

If not, has this been a cause of poor plant performance

and reliability through poor budget decisions, poor staff

morale, or limited support for plant modifications?

c. Supervision Do management styles, organizational capabilities,

budgeting skills, or communication practices at any

management level adversely impact the plant to the

extent that performance is affected?

d. Planning Does lack of long range plans for facility replacement,

alternative source waters, emergency response, etc.

adversely impact the plant performance?

2. Plant Staff

a. Manpower

i) Number

Does a limited number of people employed have a

detrimental effect on plant operations or maintenance

(e.g., not getting the necessary work done)?

ii) Plant coverage Is plant coverage adequate such that necessary

operational activities are accomplished? Can

appropriate adjustments be made during the evenings,

weekends or holidays? For example, is staff available to

respond to changing raw water quality characteristics

during periods of operation?

iii) Work load

distribution

Does the improper distribution of adequate manpower

(e.g. a higher priority on maintenance tasks) prevent

process adjustments from being made or cause them to



be made at inappropriate times, resulting in poor plant

performance?

iv) Staff turnover Does a high personnel turnover rate cause operation

and/or maintenance problems that affect process

performance or reliability?

b. Morale

i) Motivation Does the plant staff want to do a good job because they

are motivated by self-satisfaction?

ii) Pay Does a low pay scale or benefit package discourage

more highly qualified persons from applying for

operator positions or cause operators to leave after they

are trained?

iii) Environment Does a poor work environment create a condition for

more "sloppy work habits" and lower operator morale?

c. Staff Qualifications

i) Aptitude Does the lack of capacity for learning or understanding

new ideas by critical staff members cause improper O &

M decisions leading to poor plant performance or

reliability?

ii) Education Does a low level of education result in poor O & M

decisions? Does a high level of education cause needed

training to be felt unnecessary?

iii) Certification Does the lack of adequately certified personnel result in

poor O & M decisions?

d. Productivity Does the plant staff conduct the daily operation and

maintenance tasks in an efficient manner? Is time used

efficiently?

3. Financial

a. Insufficient funding Does the lack of available funds (e.g. inadequate rate

structure) cause poor salary schedules, insufficient stock

of spare parts that results in delays in equipment repair,

insufficient capital outlays for improvements or

replacement, lack of required chemicals or chemical

feed equipment, etc.?

b. Unnecessary spending Does the manner in which available funds are utilized

cause problems in obtaining needed equipment, staff,

etc.? Are funds spent on lower priority items while

needed, higher priority items are unfunded?



c. Indebtedness Does the annual debt payment limit the amount of funds

available for other items such as equipment, staff, etc.?

4. Water Demand Does excessive water use caused by declining rate

structure, concessions to industry, or high unaccounted

for use exceed the capability of plant unit processes and

therefore degrade plant performance?

B. MAINTENANCE

1. Preventive

a. Lack of Program Does the absence or lack of an effective scheduling and

recording procedure cause unnecessary equipment

failures or excessive downtime, which results in plant

performance or reliability problems?

b. Spare parts inventory Does a critically low or nonexistent spare parts

inventory cause unnecessary long delays in equipment

repairs that result in degraded process performance?

2. Corrective

a. Procedures Are procedures available to initiate maintenance

activities on observed equipment operating irregularities

(e.g. work order system)? Does the lack of emergency

response procedures result in activities that fail to

protect process needs during breakdowns of critical

equipment (e.g., maintaining disinfectant or coagulant

feeds during equipment breakdowns)?

b. Critical parts

procurement

Do delays in getting replacement parts caused by

procurement procedure result in extended periods of

equipment downtime?

3. General

a. Housekeeping Does a lack of good housekeeping procedures (e.g.

unkempt, untidy, or cluttered working environment)

cause an excessive equipment failure rate?

b. References available Does the absence or lack of good equipment reference

sources result in unnecessary equipment failure and/or

downtime for repairs (includes maintenance portion of

O & M Manual, equipment catalogs, etc.)?

c. Staff expertise Does the plant staff have the necessary expertise to keep

the equipment operating and to make equipment repairs

when necessary?



d. Technical guidance Does inappropriate guidance for repairing, maintaining,

or installing equipment from a technical resource (e.g.

equipment supplier or contract service) result in

equipment downtime that adversely affects

performance? If technical guidance is necessary to

decrease equipment downtime; is it available and

retained?

e. Equipment age Does the age or outdatedness of critical pieces of

equipment cause excessive equipment. downtime and/or

inefficient process performance and reliability (due to

unavailability of replacement parts)?

C. DESIGN

1. Raw Water Does the presence of raw water quality characteristics

over and above what the plant was designed for, or over

and above what is thought to be tolerable, cause

degraded process performance by any of the items (a-c)

listed below?

a. THM precursors

b. Turbidity

c. Seasonal variation

d. Watershed management Do facilities exist to control raw water quality entering

the plant (e.g. can intake levels be varied, can chemicals

be added to control aquatic growth, do watershed

management practices adequately protect raw water

quality)?

2. Unit Design Adequacy

a. Pretreatment Do the design features of any pretreatment unit cause

problems in downstream equipment or processes that

have led to degraded plant performance?

i) Intake structure Does the design of the intake structure result in

excessive clogging of screens, a build-up of silt, or

passage of solids that damages downstream processes?

ii) Presedimentation Does a deficient design cause poor sedimentation that

results in poor plant performance (e.g., inlet

configuration, size, type, or depth of the basin; or

placement or length of the weirs)?

iii) Prechlorination Does prechlorination cause excessive finished water

disinfection byproducts?



b. Low lift pumping Does the existence of high volume constant speed

pumps cause undesirable hydraulic loadings on

downstream unit processes?

c. Flash mix Does a lack of or inadequate mixing result in excessive

chemical use or insufficient coagulation to the extent

that it impacts plant performance?

d. Flocculation Does the performance of the flocculation unit process

contribute to problems in downstream unit processes

that have degraded plant performance? Does a lack of

flocculation time or flocculation stages with variable

energy input result in poor floc formation and degrade

plant performance?

e. Sedimentation Does a deficient design cause poor sedimentation that

results in poor filter performance (e.g., inlet

configuration, size, type, or depth of the basin; or

placement or length of the weirs)?

f. Filtration Does the size of filter, or the type, depth, and effective

size of filter media hinder its ability to adequately treat

water? Are the surface wash and backwash facilities

adequate to maintain a clean filter bed? Have the

underdrains or support gravels been damaged or

disturbed to the extent that filter performance is

compromised?

g. Disinfection Do the facilities have any design limitations that

contribute to poor disinfection (e.g. proper mixing,

detention time, feed rates, proportional feed, etc.)?

h. Sludge treatment Does the type or capacity of sludge treatment processes

cause process operation problems that degrade plant

performance?

i. Residuals disposal Are the sludge and backwash water facilities and

disposal area of sufficient size and type to ensure that

poor plant performance does not occur or applicable

permits regulating the discharge are not violated?

j. Fluoridation Do the fluoridation facilities have any design limitations

that result in an inability to achieve regulated fluoride

levels (e.g. feed rates, proportional feed, etc.)?

3. Miscellaneous The design "miscellaneous" category covers areas of

design inadequacy not specified in the previous design

categories. (Space is available in the Checklist to

accommodate additional items not listed.)



a. Process flexibility Do chemical feed facilities have various feed points to

optimize treatment (e.g. feed alum and cationic

polymers at flash mix, feed non-ionic or anionic

polymers at points where mixing is gentle)? Do

facilities exist to feed the types of chemicals required to

produce a high quality stable finished water (e.g.

coagulant aids, flocculant aids, filter aids, stabilization

chemicals)?

b. Process controllability Do the existing process control features provide

adequate adjustment and measurement of plant flow

rate, backwash flow rate, filtration rate, and flocculation

mixing inputs? Do chemical feed facilities provide

adjustable feed ranges that are easily set for operation at

all required dosages? Do chemical feed controls remain

set once adjusted or do they vary? Are chemical feed

rates easily measured?

c. Process automation Does the lack of needed automatic monitoring or

control devices (streaming current detector, continuous

recording turbidimeter, etc.) cause excessive operator

time for process control and monitoring? Does the

automatic operation of critical unit processes degrade

plant performance during startup and shut-down?

d. Lack of standby units for

key equipment

Does the lack of standby units for key equipment cause

degraded process performance during breakdown or

during necessary preventive maintenance activities (e.g.

backwash pumps and chemical feeders, etc.)?

e. Flow proportioning to

unit processes

Does inadequate flow proportioning or flow splitting to

duplicate units cause problems or partial unit overloads

that degrade effluent quality or hinder achievement of

optimum process performance?

f. Alarm systems Does the absence or inadequacy of an alarm system for

critical pieces of equipment or processes cause

degraded process performance (e.g. raw or finished

water turbidity)?

g. Alternate power source Does the absence of an alternate power source cause

problems in reliability of plant operation leading to

degraded plant performance?

h. Lab space/ equipment Does the absence of an adequately equipped laboratory

limit plant performance?

i. Sample taps Does a lack of sample taps on key process flow streams

(e.g. individual filters, sedimentation basin solids,

backwash recycle streams) for sampling prevent needed



information from being obtained?

j. Plant inoperability due to

weather

Are certain units in the plant extremely vulnerable to

weather changes and, as such, do not operate at all or do

not operate as efficiently as necessary to achieve the

required performance? Do poor roads leading into the

plant cause it to be inaccessible during certain periods

of the year for chemical or equipment delivery or for

routine operation?

k. Return process stream Does excessive volume and/or a highly turbid return

process flow stream (e.g. backwash return flow) cause

adverse effects on process performance, equipment

problems, etc.? Does the inability to measure or sample

these streams degrade plant performance?

D. OPERATION

1. Testing

a. Performance monitoring Are plant and distribution system monitoring tests truly

representative of performance?

b. Process control testing Does the absence or wrong type of process control

testing cause improper operational control decisions to

be made (e.g. does filter performance evaluation

support finished water turbidity data)?

2. Process Control Adjustments

a. Water treatment

understanding

Is the operator's lack of basic understanding of water

treatment (e.g. limited exposure to terminology, lack of

understanding of the function of unit processes, etc.) a

factor in poor operational decisions and poor plant

performance or reliability?

b. Application of concepts

and testing to process

control

Is the staff deficient in the application of their

knowledge of water treatment and interpretation of

process control testing such that improper process

control adjustments are made?

c. Technical guidance Does inappropriate operational information received

from a technical resource (e.g. design engineer,

equipment representative, regulatory inspector) cause

improper operational decisions to be implemented or

continued?

d. Training Does non-attendance at available training programs

result in poor process control decisions by the plant

staff or administrators?



e. Insufficient time on job Does the short time on the job and associated

unfamiliarity with plant needs result in the absence of

process control adjustments or in improper process

control adjustments being made (e.g., opening or

closing a wrong valve, turning on or off a wrong

chemical feed pump, backwashing a filter incorrectly,

etc.)?

3. O&M Manual

a. Adequacy Does inappropriate guidance provided by the O & M

manual/procedures result in poor or improper operation

decisions?

b. Use Does the operator's failure to utilize a good O & M

manual/procedures cause poor process control and poor

treatment that could have been avoided?

4. Distribution System Are distribution system operating procedures adequate

to protect the integrity of finished water quality (e.g.

flushing, reservoir management, etc.)?

E. MISCELLANEOUS

The "miscellaneous" category allows addition of factors

not covered by the above definitions. Space is available

in the Checklist to accommodate these additional items.

APPENDIX B. Data Collection Forms


APPENDIX B

DATA COLLECTION FORMS

APPENDIX B. Data Collection Forms B-1


APPENDIX B: DATA COLLECTION FORMS

FORM A – KICK OFF MEETING

A. MEETING OUTLINE

1. Purpose of CPE

a. Background

b. Assess plant potential for achieving compliance

c. Identify current factors limiting performance

d. Outline follow-up activities.

2. Schedule of Events DAY TIME

a. Kickoff Meeting _________________________ _________________________

b. Plant Tour _________________________ _________________________

c. Review Budget/User

Fees/Revenues _________________________ _________________________

d. Onsite Data Collection _________________________ _________________________

e. Personnel Interviews _________________________ _________________________

f. Exit Meeting _________________________ _________________________

3. Information Resources (availability):

As built drawings

O & M Manual

Monitoring records

Equipment literature

Process control records

Budget records

Design consultant



FORM A – KICK OFF MEETING (cont’d.)

B. ATTENDANCE LIST

Municipality: ___________________________________________ Date: ____________________

Name Title/Dept. Telephone No.

1. ________________________ _________________________ _________________________

2. ________________________ _________________________ _________________________

3. ________________________ _________________________ _________________________

4. ________________________ _________________________ _________________________

5. ________________________ _________________________ _________________________

6. ________________________ _________________________ _________________________

7. ________________________ _________________________ _________________________

8. ________________________ _________________________ _________________________

9. ________________________ _________________________ _________________________

10. _______________________ _________________________ _________________________

11. _______________________ _________________________ _________________________

12. _______________________ _________________________ _________________________

13. _______________________ _________________________ _________________________

14. _______________________ _________________________ _________________________

15. _______________________ _________________________ _________________________

16. _______________________ _________________________ _________________________

17. _______________________ _________________________ _________________________

18. _______________________ _________________________ _________________________

19. _______________________ _________________________ _________________________

20. _______________________ _________________________ _________________________



FORM A – KICK OFF MEETING (cont’d.)

C. PERSONNEL INTEVIEWS SCHEDULING SHEETINGS *

Name Title/Dept. Day Time

1. ________________________ _________________________ ___________ ___________

2. ________________________ _________________________ ___________ ___________

3. ________________________ _________________________ ___________ ___________

4. ________________________ _________________________ ___________ ___________

5. ________________________ _________________________ ___________ ___________

6. ________________________ _________________________ ___________ ___________

7. ________________________ _________________________ ___________ ___________

8. ________________________ _________________________ ___________ ___________

9. ________________________ _________________________ ___________ ___________

10. _______________________ _________________________ ___________ ___________

11. _______________________ _________________________ ___________ ___________

12. _______________________ _________________________ ___________ ___________

13. _______________________ _________________________ ___________ ___________

14. _______________________ _________________________ ___________ ___________

15. _______________________ _________________________ ___________ ___________

16. _______________________ _________________________ ___________ ___________

17. _______________________ _________________________ ___________ ___________

18. _______________________ _________________________ ___________ ___________

19. _______________________ _________________________ ___________ ___________

20. _______________________ _________________________ ___________ ___________

* Includes offsite administrators/owners, budgeting personnel, laboratory personnel,

maintenance personnel, plant administrators, shift personnel, operators, etc.



FORM B – ADMINISTRATION DATA

A. NAME AND LOCATION:

Name of Facility _______________________________________________________

Owner _______________________________________________________

Administrative Office: _______________________________________________________

Mailing Address _______________________________________________________

Primary Contact _______________________________________________________

Title _______________________________________________________

Telephone No. _______________________________________________________

Treatment Plant:

Mailing Address _______________________________________________________

Primary Contact _______________________________________________________

Title _______________________________________________________

Telephone No. _______________________________________________________



FORM B – ADMINISTRATION DATA (cont’d.)

B. ORGANIZATION:

1. Governing Body (Name and Schduled Meetings):

2. Structure:

From Governing Body to Plant:

Within Plant:

3. Staff Meetings (formal/informal):




B. ORGANIZATION (cont’d.):

4. Reporting Requirements (formal/informal):

5. Public Relations/Education:

6. Observations (openness, awareness of plant needs, management style, etc.):




C. PERSONNEL:

PLANT

No. Title/Name Certification Pay Scale % Time at

Plant

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

____ _________________________ _________________________ ___________ ___________

OFF SITE

No. Title/Name Pay Scale % Time Allocated to Plant

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________

____ _________________________ ___________ ________________________________________




D. TRAINING:

Operator Training Budget _______________________________________________________

_______________________________________________________

_______________________________________________________

Training Incentives _______________________________________________________

_______________________________________________________

_______________________________________________________

Training Over Last Year _______________________________________________________

_______________________________________________________

_______________________________________________________

E. PLANT COVERAGE:

Weekdays (shift times/overlap/number per shift):

Weekends and Holidays:

Alarms (on what process? Auto-dailer?):




F. PLANT BUDGET/EXPENDITURES:

(Attach copy of actual budget and/or expenditures if available.)

Budget year _____________________ to ___________________________________

Expenditure period _______________ to ___________________________________

CATEGORY BUDGET AMOUNT EXPENDITURE AMOUNT

Administrative Salaries _________________________ _________________________

Plant Staff Salaries _________________________ _________________________

Utilities _________________________ _________________________

Electric _________________________ _________________________

Gas _________________________ _________________________

Chemicals _________________________ _________________________

Vehicles _________________________ _________________________

Training _________________________ _________________________

_________________________ _________________________ _________________________

_________________________ _________________________ _________________________

_________________________ _________________________ _________________________

_________________________ _________________________ _________________________

OPERATIONS TOTAL _________________________ _________________________




G. CAPITAL OUTLAYS:

1. Capital Improvement Reserve (Self-sustaining utility? Master Plan? Replacement philosophy?)

2. Capital Replacement Plan (Available? Items scheduled for replacement? Attach if available.)

3. Expansion History and Proposed Modifications (historical studies, current evaluations, long range

plans, etc.).




H. REVENUE:

1. User Charges:

2. Connection Fees:

3. Other Sources of Revenue (interest income, bulk water sales, etc.):

4. Total Revenue for Evaluation Period (compare to expenditures):

5. Miscellaneous:

Are rates and budget reviewed annually?

When was the last rate increase (how much)?

Proposed Increases?



FORM C – DESIGN DATA

A. PLANT FLOW DIAGRAM

(Attach if Available, include solids handling and chemical addition points.)

B. FLOW DATA

Design Flow

Average Daily Flow = ____________ m3/d

Maximum Hydraulic Capacity = ____________ m3/d

Operating Flow

Peak Instantaneous Operating Flow = ____________ m3/d



FORM C – DESIGN DATA (cont’d.)

C. UNIT PROCESSES

FLOW MEASUREMENT

Flow Stream Measured Meter Type Calibration

Frequency Comments

Raw Water:

Finished Water:

Backwash:

Other (Describe):

Accuracy Check During

CPE (Describe)




C. UNIT PROCESSES (cont’d.)

SCREENING

Travelling Bar Screen:

Bar Screen Width = ____________ cm

Bar Opening = ____________ cm

Screening Disposal:

Operation Problems:

Hand Cleaned Bar Screen:

Bar Screen Width = ____________ cm

Bar Opening = ____________ cm

Cleaning Frequency = ___________________________

Screening Disposal:

Operation Problems:

Other (Describe):





PUMPING

Flow Stream Pumped Pump Description # of Pumps Rated Capacity

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

Flow Control Method (Describe):


________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________



________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________

________________________ _________________________ ___________ ___________






PRESEDIMENTATION

Type (e.g. concrete or earthen) ___________________________________________

Number of Basins _____________ Surface Dimensions ______________________

Water Depth (shallowest) = _____________ m Water Depth (deepest) =_____ m

Weir Location ____________________ Weir Length = ____________ m

Total Surface Area = ____________ m2 Total Volume ____________ m

3

FLOW:

Design Flow = ________________ m3/d Operating Flow

*_________ m

3/d

DETENTION TIME:

At Design Flow = _______________ hr At Operating Flow* ________ hr

WEIR OVERFLOW RATE:

At Design Flow = _____________ m3/m/d Operating Flow

* = ___________ m

3/m/d

SURFACE OVERFLOW RATE:

At Design Flow = _____________ m3/m

2/d Operating Flow

* = __________ m

3/m

2/d

CHEMICAL FEED CAPABILITY:

Type of Chemicals: ____________________________________________________

Operating Range (Describe) _____________________________________________

Schematic:

* Peak instantaneous operating flow.





RAPID MIXING

RAPID MIX:

Type ________________________________________________________________

(mechanical, in-line mechanical, in-line static)

Number of mixers _____________ Power Rating ___________________________

Number of Basins _____________ Surface Dimensions = ____________________

Water Depth = ____________ m Total Volume = ___________________

m3

FLOW:


* = _______ m

3/d

DETENTION TIME:

At Design Flow = _______________ hr At Operating Flow* = ______ hr

G VALUE (see Chapter 6 and Appendix G):

At Design Flow = _______________ s-1

At Operating Flow* =_______ s

-1

Operating Problems:






FLOCCULATION

Type (e.g. paddle wheel, turbine, hydraulic) _________________________________

Control (e.g. constant or variable speed) ____________________________________

Stage Surface

Dimensions Depth Volume Power G Value

1 ________________ _____________ _____________ _____________ _____________

2 ________________ _____________ _____________ _____________ _____________

3 ________________ _____________ _____________ _____________ _____________

4 ________________ _____________ _____________ _____________ _____________

Total ________________ _____________ _____________ _____________ _____________

FLOW:


*_________ m

3/d

DETENTION TIME:


Operating Problems:

Schematic:






CLARIFICATION

Number of Basins _____________ Surface Dimensions ______________________

Water Depth (shallowest) = _____________ m Water Depth (deepest) = _____m

Weir Location ____________________ Weir Length = ____________ m

Total Surface Area = ____________ m2 Total Volume = __________ m

3

FLOW:


* = _______ m

3/d

DETENTION TIME:


WEIR OVERFLOW RATE:

At Design Flow = _____________ m3/m/d Operating Flow

* = ___________ m

3/m/d

SURFACE OVERFLOW RATE:

At Design Flow = _____________ m3/m

2/d Operating Flow

* = __________ m

3/m

2/d

Inlet/Outlet Conditions (describe and/or schematic):

Operating Problems:






FILTRATION

Type of Filters (media type, pressure, gravity, etc.) ___________________________

Number of filters _________________ Surface Dimensions __________

Total Surface Area ________________ m2

MEDIA CHARACTERISTICS:

Media Type Depth Uniformity

Coefficient Effective Size Specific Gravity

________________ _____________ _____________ _____________ _____________

________________ _____________ _____________ _____________ _____________

________________ _____________ _____________ _____________ _____________

________________ _____________ _____________ _____________ _____________

FLOW:


* = _______ m

3/d

FILTRATION RATE:

At Design Flow = ______________ m/h At Operating Flow* = _____ m/h

Filter control (e.g. declining or constant rate/level, etc.): _______________________

Available Headloss = ____________ m

SURFACE WASH:

Type (e.g. rotary, fixed, manual) ____________________________________

Water Flow Rate = _______ m3/d Surface Wash Rate = ________m

3/m

2/d

Wash duration = ____________ min

BACKWASH:

Wash Water Rate:

At Design Flow = _______ m3/m

2/d At Operating Flow

* = ____ m

3/m

2/d

Wash duration = ____________ min






FILTRATION (cont’d.)

AIR WASH RATE :

At Design Flow = ___________ m3/m

2/d At Operating Flow

* = _______ m

3/m

2/d

CONTROL/OPERATING PROBLEMS:

Mud Balls:

Dirty media:

Uneven media:

Backwash rate control/Procedure (e.g. gradual start/stop):

Filter Rate Control/Procedure (e.g. gradual changes):

Hydraulic Loading During Backwash (e.g. reduce flow to remaining filters):

Air Bubbles During Backwash:

Surface Wash Control/Procedure:

Other:

Availability of Sample Taps (e.g. backwash and individual filters):






DISINFECTION

Contact Basin(s) Available (e.g. clearwell) __________________________________

Basin Surface Dimensions Depth Volume

____________________ ________________________ _______________ _______________

____________________ ________________________ _______________ _______________

____________________ ________________________ _______________ _______________

TOTAL: _______________

DETENTION TIME (see Chapter 9 and Appendix G):

Theoretical1 = ____________ min

Functional2 = ____________ min

1. Based on total available volume and peak instantaneous operating flow.

2. Based on evaluation of operating variables such as basin baffling, minimum operating depth

and transmission line length to first user.

CHLORINATORS:

No. of Chlorinators ___________________________________

Description (make/type, etc.) ___________________________

Capacity _______________ to __________________ kg/d

Flow Proportioned ___________________________________

FLOW:


* = _______ m

3/d

MAXIMUM DOSAGE CAPABILITY:

At Design Flow = _____________ m3/d At Operating Flow

* = ____ m

3/d

Operating Problems:






CHEMICAL FEED SYSTEMS

METAL SALTS

DRY:

Type Design Feed

Range (kg/h)

Dosage Range at Design Flow

(mg/L)

Dosage Range at Operating*

Flow (mg/L)

Min. Max. Min. Max.

________________ ___________ ___________ ___________ ___________ ___________

________________ ___________ ___________ ___________ ___________ ___________

LIQUID:

Type

Design Feed

Range

(mL/min)

Dosage Range at Design Flow

(mg/L)

Dosage Range at Operating*

Flow (mg/L)

Min. Max. Min. Max.

________________ ___________ ___________ ___________ ___________ ___________

________________ ___________ ___________ ___________ ___________ ___________

Dosage Control (describe):

Operating Problems:

Accuracy Check During CPE (describe):







POLYMERS

Type

Design

Feed

Range

(mL/min)

Stock1

Solution

(%w/v)

Recom-

mended1

Dilution

(%w/v)

Dosage Range at

Design Flow (mg/L)

Dosage Range at

Operating* Flow (mg/L)

Min. Max. Min. Max.

____________ _________ ________ ________ ________ ________ ________ ________

____________ _________ ________ ________ ________ ________ ________ ________

____________ _________ ________ ________ ________ ________ ________ ________

____________ _________ ________ ________ ________ ________ ________ ________

1. Obtain from manufacturer’s data sheet


Operating Problems:

Accuracy Check During CPE (describe):







pH/ALKALINITY ADJUSTMENT:

Chemicals Used:


Operating Problems:

FLUORIDATION:

Fluoride Compound Used:


Operating Problems:

SOFTENING:

Chemicals Used:


Operating Problems:

POWDERED ACTIVATED CARBON:


Operating Problems:

OTHER:





SOLIDS HANDLING

PRESEDIMENTATION SLUDGE:

Description of Pumping Procedure (e.g. time clocks, variable speed pumps):

Method of Waste Volume Measurement:

Sampling Location:

Sampling Procedure:

Operating Problems:

CLARIFICATION SLUDGE:

Description of Pumping Procedure (e.g. time clocks, variable speed pumps):

Method of Waste Volume Measurement:

Sampling Location:

Sampling Procedure:

Operating Problems:

RETURN SLUDGE (Solids Contact Unit):

Description of Sludge Movement:

Controllable Capacity Range: Low = ___________ m3/d High = ____________ m

3/d

Method of Control:

Sampling Location:

Sampling Procedure:

Operating Problems:





SOLIDS HANDLING (cont’d.)

SLUDGE DRYING BEDS/LAGOONS:

No. of Beds/Lagoons ___________ Dimensions ____________________________

Total Volume _______________ Subnatant Drain To ______________________

Dewatered Sludge Removal:

Mode of Operation (depth of sludge draw, seasonal operation, schematic):

Operating Problems:

OTHER DEWATERING UNIT(S):

Type of Unit(s) __________________________________ No. of Units ________

Loading Rate:

At Design Flow = _____________ mg/L At Operating Flow* = __________ mg/L

Polymer Used ________________________ Dosage ________________ g/kg dry wt.

Cake Solids __________________________ % solids

Hours/Week of Operation

Design ___________________________ Operating ________________________

Operating Problems:

ULTIMATE SLUDGE DISPOSAL:

Description

_________________________________________________________________

Operating Problems:





D. MISCELLANEOUS DESIGN INFORMATION

Process Automation (describe existing systems):

Standby Units (chemical feed, backwash pumps):

Flow Proportioning to Units:

Alarm Systems (description of systems, units covered):

Alternate Power Source:

Weather Inoperability:

Return Process Streams:



FORM D – OPERATIONS DATA

A. PROCESS CONTROL STRATEGY AND DIRECTION

Who sets major process control strategies and decisions?

Who makes process control decisions when lead process control person is not at

plant?

Where is help sought when desired performance is not achieved?

Are staff members asked their opinions?

How is communication conducted between laboratory, operations and maintenance

staff?

B. SPECIFIC PROCESS CONTROL PROCEDURES

SAMPLING AND TESTING:

Sampling Locations (add to plant flow schematic):

PRESEDIMENTATION:

Sludge Removal (method of control/adjustment):

Performance Monitoring:

Other:



FORM D – OPERATIONS DATA (cont’d.)

B. SPECIFIC PROCESS CONTROL PROCEDURES (cont’d.)

CLARIFICATION:

Performance Monitoring (tests used, solids balance):

Sludge Removal (method of control/adjustment):

Sludge Recycle (contact sedimentation):

Other:

FILTRATION:

Hydraulic Loading Rate Control (method of control/adjustment):

Backwash Control (test used, method of determining frequency):

Filter Monitoring:

Influent turbidity:

Effluent turbidity:

Headloss:

Loading rate:

Length of run:

COAGULATION:

Feed Rate Control (method of control/adjustment):

Performance Monitoring:

Jar testing:

Pilot filter:

Zeta meter:

Streaming current detector:

Turbidity:




B. SPECIFIC PROCESS CONTROL PROCEDURES (cont’d.)

DISINFECTION:

Performance Monitoring (tests used):

Feed rate Control (method of control/adjustment):

FLUORIDATION:



pH/ALKALINITY ADJUSTMENT:



SOFTENING/RECARBONATION:



TASTE AND ODOUR:



SLUDGE HANDING AND DISPOSAL:

Sludge Dewatering (monitoring, process control/optimization):

Sludge Disposal (meet requirement, monitoring, options):




C. PROCESS CONTROL REFERENCES

Specifically note sources (e.g. publications or personnel) that are the cause of poor

process control decisions or strategies, suspected or definitely identified.

D. OPERATIONS AND MAINTENANCE MANUAL

Adequacy:

Use:




E. LABORATORY CAPABILITY

1. Facilities

Adequate

Comments

Yes No

Bench space __________ __________ ______________________________

Storage space __________ __________ ______________________________

Floor area __________ __________ ______________________________

Lighting __________ __________ ______________________________

Electricity __________ __________ ______________________________

Potable water supply __________ __________ ______________________________

Compressed air __________ __________ ______________________________

Vacuum __________ __________ ______________________________

Chemical fume hood __________ __________ ______________________________

Air conditioning __________ __________ ______________________________

Desk __________ __________ ______________________________

Records storage __________ __________ ______________________________

2. Equipment & Instruments

Adequate

Comments

Yes No

Turbidimeter __________ __________ ______________________________

Core sampler __________ __________ ______________________________

pH meter __________ __________ ______________________________

Centrifuge __________ __________ ______________________________

Distilled water __________ __________ ______________________________

Drying oven __________ __________ ______________________________

FC water bath incubator __________ __________ ______________________________

Coliform water bath incubator __________ __________ ______________________________

Hot air oven __________ __________ ______________________________




E. LABORATORY CAPABILITY (cont’d.)

2. Equipment & Instruments

Adequate

Comments

Yes No

Refrigerator __________ __________ ______________________________

Autoclave __________ __________ ______________________________

Analytical balance __________ __________ ______________________________

Microscope __________ __________ ______________________________

Desiccator __________ __________ ______________________________

Automatic samplers __________ __________ ______________________________

Spectrophotometer __________ __________ ______________________________

Conductivity meter __________ __________ ______________________________

Jar test apparatus __________ __________ ______________________________

Titration burets __________ __________ ______________________________

Erlenmeyer flasks __________ __________ ______________________________

Volumetric flasks __________ __________ ______________________________

Beakers __________ __________ ______________________________

Evaporating dishes __________ __________ ______________________________

Zeta meter __________ __________ ______________________________

Particle counter __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________





3. Analytical Capability

Adequate

Comments

Yes No

Calcium __________ __________ ______________________________

Magnesium __________ __________ ______________________________

Hardness __________ __________ ______________________________

Sodium __________ __________ ______________________________

Alkalinity __________ __________ ______________________________

Temperature __________ __________ ______________________________

pH __________ __________ ______________________________

Turbidity __________ __________ ______________________________

Iron __________ __________ ______________________________

Manganese __________ __________ ______________________________

Chlorine __________ __________ ______________________________

Sulphate __________ __________ ______________________________

Nitrate __________ __________ ______________________________

Total coliform __________ __________ ______________________________

Heterotrophic plate count __________ __________ ______________________________

Conductivity __________ __________ ______________________________

Total dissolved solids __________ __________ ______________________________

Trace inorganics __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________





3. Analytical Capability

Adequate

Comments

Yes No

Organics __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

________________________ __________ __________ ______________________________

4. Miscellaneous

Quality Control:

Reference Standards:

Duplicate Tests (schedule, records, etc.):

Standard Procedures/References:

Standard Methods:

Site Specific Procedures:

Training:



FORM E – MAINTENANCE DATA

A. PREVENTIVE MAINTENANCE PROGRAM

Program Description:

Method of Scheduling:

Method of Documenting Work Completed:

Method of Factoring Costs for Parts/Equipment Into Budgeting Process:

Spare Parts Inventory:

References:

O & M Manual:

Accurate Record Drawings:

Manufacturer’s Literature:

Adequacy of Following Resources:

Outside Support:

Tools/Lubricants:

Work Areas:



FORM E – MAINTENANCE DATA (cont’d.)

B. EMERGENCY MAINTENANCE PROGRAM

Priority Setting (relationship to process control decisions):

Extent of On-Site Capability:

Method of Initiating Work Activities

Critical Parts Procurement (policy restrictions, sources):

Comments:

C. GENERAL

Equipment or Processes Out of Service Due to Breakdowns (identify equipment or

process, description of problem, length of time out of service, what has been done,

what remains to be done, estimated time before repair, how it affects performance) :

During the CPE (list and explain):

During the Last 12 Months (list and explain):



FORM F – PERFORMANCE DATA

A. SOURCE OF DATA:

(e.g. plant records, MOE DWSP reports)

B. FLOW DATA

Month/Year Minutes

Flow Operating

Time

Inst. Peak

Operating

Flow Average Maximum

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

____________ ____________ ____________ ____________ ____________ ____________

Average: ____________ ____________ ____________ ____________ ____________

Peak: ____________ ____________

Instantaneous plant operating flow is the peak flow rate that the unit processes

experience on a sustained basis. For example, if a plant treats 5,000 m3 during its

daily 12 hour (0.5 day) operating period, then the instantaneous peak operation flow

would be 5,000 m3 ÷ 0.5 d = 10,000 m

3/d. Judgment of the evaluator is essential in

selecting the instantaneous peak operating flow because of variations in flow that can

occur by operating different pumps or changing unit processes that are in service.



FORM F – PERFORMANCE DATA (cont’d.)

C. DEMAND EVALUATION

Number of Service Connections ____________ Population Served _____________

Major Industrial Users (include name and volume used):

Per Capital Consumption:

Average:

Peak:

Typical per capita water consumption values are shown below (Fair, Geyer and

Okun, 1971):

Type of Consumption Lpcd (range) Lpcd (average)

Domestic/Residential 76 – 340 208

Commercial 38 – 492 76

Industrial 76 – 303 189

Public 19 – 76 38

Unaccounted for Water 19 – 114 57

227 – 946 568

D. UNACCOUNTED FOR WATER EVALUATION

Total production of plant ____________ m3

Total metered water in system ____________ m3

Difference ____________ m3

% Unaccounted = Difference/Total Production x 100 = ____________ %

Typical unaccounted for water is approximately 10%.

E. BACKWASH WATER EVALUATION

Total volume filtered water _________ m3 Total volume backwash water _____ m

3

Difference ____________ m3

% BW Water = Difference/Total volume filtered water x 100 = ____________ %

Typical amount of backwash water is 2% to 6% for conventional plants. Direct

filtration plants often exceed this depending on raw water quality.




F. RAW WATER QUALITY

Month/Year

Turbidity

Temperature pH Alkalinity

Min. Ave. Max.

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

Average ________ ________ ________ __________ ________ __________




G. REPORTED OPERATING DATA FOR PREVIOUS 12 MONTHS

Month/Year

Settled Water Turbidity Finished Water Turbidity

Min. Ave. Max. Min. Ave. Max.

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

___________ ________ ________ ________ __________ ________ __________

Average ________ ________ ________ __________ ________ __________




H. CHEMICAL CONSUMPTION

Type of Chemical _____________________________________________________

Unit Cost _____________________________________

Month/Year Chemical Use per Month

(L or kg/month) Comments

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

Total ________________________

Type of Chemical _____________________________________________________

Unit Cost _____________________________________

Month/Year Chemical Use per Month

(L or kg/month) Comments

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

___________________ ________________________ ________________________________

Total ________________________




I. MOE DRINKING WATER SURVEILLANCE PROGRAM (DWSP)

If available, review previous three years of DWSP data to identify water quality

concerns, including the distribution system, that are not evident from the review of

in-plant monitoring data.

J. PERFORMANCE ASSESSMENT

Develop graphs to depict plant performance, such as:

1. Plant effluent turbidity versus time for week or months with maximum

recorded turbidities. Isolate shorter time frames on graph after reviewing

dates.

2. Filter effluent turbidity versus time to assess recovery time following

backwashing a filter or starting a dirty filter.

3. Probability plots to show percentage of time turbidity exceeds desired

objective.

4. Long term plots of raw water and finished water turbidities to assess process

control.

5. Long term plots of finished water turbidity to assess stability of operation.

K. PERFORMANCE VIOLATIONS WITHIN LAST 12 MONTHS:



FORM G – INTERVIEW DATA

A. INTERVIEW CONCERNS

Interviews are used to obtain feedback in the four categories of administration,

design, operation and maintenance. The following items are presented to assist the

interviewers in obtaining this feedback.

1. Administration

Owner Responsibility:

Attitude toward staff? Regulatory agency? Consultants?

Self-sustaining facility attitude?

Policies?

Communications (formal/informal)?

Performance Goal

Is plant in compliance?

o If yes, what’s making it that way?

o If no, why not?

Is regulatory pressure felt for performance?

What are performance requirements?

Administrative Support

Budget

o Within range of other plants?

o Covers capital improvements?

o Unnecessary expenditures?

o Sufficient?

o Attitude toward rates?

Personnel

Within range of other plants?

Allows adequate time?

Motivation, pay, supervision, working conditions?

Productivity? Turnover? Training support?

Involvement

Visits to treatment plant?

Awareness of facility performance?

Request status reports (performance and cost-related)?

Familiarity with plant needs?



FORM G – INTERVIEW DATA (cont’d.)

A. INTERVIEW CONCERNS (cont’d.)

2. Design

Raw water quality problems?

Equipment problems?

Status of warranties?

Return process streams?

Preliminary treatment?

Coagulation/flocculation?

Sedimentation?

Filtration?

Chemical feed?

Advanced treatment techniques?

Disinfection?

Sludge handling and disposal?

Flow measurement?

Flow splitting?

Alarms or alternate power?

3. Operation

Communication of decisions?

Key control parameters?

Involvement of staff?

Laboratory quality?

Administrative support?

Staffing?

Performance problems?

Unit process optimization?

External support?

Process control testing/adjustments?

O & M manual/references?

4. Maintenance

How are priorities set?

Attitude toward program?

Emergency versus preventative?

Reliability (spare parts or critical part procurement)?

Staffing?

Equipment accessibility?



FORM G – INTERVIEW DATA (cont’d.)

B. PERSONNEL INTERVIEWS

Name: _______________________________________________________________

Title:

____________________________________________________________________

Certification: _________________________________________________________

Years at plant: ____________ Years of experience: _____________________

Area of Responsibility: _________________________________________________

Training: ____________________________________________________________

Concerns/Recommendations (Administration, Design, Operation & Maintenance):



FORM H – EXIT MEETING

ATTENDANCE LIST

Municipality: ___________________________________________ Date: ____________________

Name Title/Dept. Telephone No.

1. ________________________ _________________________ _________________________

2. ________________________ _________________________ _________________________

3. ________________________ _________________________ _________________________

4. ________________________ _________________________ _________________________

5. ________________________ _________________________ _________________________

6. ________________________ _________________________ _________________________

7. ________________________ _________________________ _________________________

8. ________________________ _________________________ _________________________

9. ________________________ _________________________ _________________________

10. _______________________ _________________________ _________________________

11. _______________________ _________________________ _________________________

12. _______________________ _________________________ _________________________

13. _______________________ _________________________ _________________________

14. _______________________ _________________________ _________________________

15. _______________________ _________________________ _________________________

16. _______________________ _________________________ _________________________

17. _______________________ _________________________ _________________________

18. _______________________ _________________________ _________________________

19. _______________________ _________________________ _________________________

20. _______________________ _________________________ _________________________

Attach copy of Exit Meeting Handouts

APPENDIX C. Example CPE Report

APPENDIX C

EXAMPLE CPE REPORT

APPENDIX C. Example CPE Report C-1


APPENDIX C: EXAMPLE CPE REPORT

RESULTS OF THE COMPREHENSIVE PERFORMANCE EVALUATION OF THE

ABC WATER TREATMENT PLANT

MUNICIPALITY OF XYZ

XYZ, ONTARIO

NOVEMBER 2010



INTRODUCTION

Composite Correction Program

The Composite Correction Program (CCP) is an approach developed by the U.S.

Environmental Protection Agency (USEPA) to improve surface water treatment plant

performance and to achieve compliance with their Surface Water Treatment Rule (SWTR).

The approach consists of two components, the Comprehensive Performance Evaluation (CPE)

and the Comprehensive Technical Assistance (CTA). A CPE is a thorough evaluation of an

existing treatment plant, resulting in a comprehensive assessment of the unit process

capabilities and the impact of the operation, maintenance, and administrative practices on

performance of the plant. A CTA is used to improve performance identified during the CPE.

Therefore, the CCP approach can be utilized to evaluate the ability of a water filtration plant

to meet turbidity and disinfection requirements and then to facilitate the achievement of cost-

effective compliance.

In recent years the CCP has gained in prominence as a mechanism that can be used to assist in

optimizing the performance of existing surface water treatment plants to levels of

performance that exceed regulatory requirements.

The Municipality of XYZ and the Ontario Ministry of Environment (MOE) recognized that

optimizing performance of its surface water treatment plants was an important safeguard that

could be pursued to ensure the protection of the public health. As such, they developed a

partnership to pursue the development of CCP capability within the municipality and the

Province. As a first component of this partnership effort, selected personnel are being trained

to conduct CPEs at two surface water treatment plants within the municipality. The training

that is being provided for the municipality and the MOEE was arranged by the project

consultant. The training was led by Process Applications, Inc. who developed the CCP

approach for the U.S. EPA. It is envisioned that use of CCP components will be an integral

part of the effort to optimize the performance of the municipality's surface water treatment

plants.

The following report documents the findings of a CPE conducted at the ABC water treatment

facility from September 18 - 21, 2010. The CPE was the first of the two training CPEs to be

conducted.

General Facility Information

The ABC WTP comprises two conventional treatment trains, essentially two plants, with a

common raw water source and treated water reservoir. Plant 1 was constructed around 1926;

Plant 2 was added in 1958 for an additional 25% capacity. The coagulation/sedimentation

process train in Plant 1 was modified in 1980 to provide more flocculation capacity.

Treatment includes coagulant chemical feed (alum or acidified alum and seasonal powdered

activated carbon (PAC», flocculation, sedimentation and dual media filtration - there is one

multimedia filter - and chlorination (prechlorination when PAC is not used and post

chlorination when the PAC is added).

The total design capacity is 109 ML/day with Plant 1, providing approximately 82 ML/day of

treatment capacity and Plant 2 providing about 27 ML/day of treatment capacity.



Raw water is supplied from an old canal which is basically a backwater of the "new" canal.

The old canal can act as a major raw water settling basin as the water flows from the new

canal to the plant and then into an adjacent river.

Raw water quality is generally good with more variability in the winter months, when

turbidities average 4 NTU with periodic excursions to a maximum between IS and 20 NTU.

The summer months have more stable raw water quality with turbidities around 2-3 NTU.

A flow schematic of the plant is presented in Figure 1.

Figure 1 – Plant Flow Schematic



FACILITY DESIGN DETAILS

Key design data were collected during the three-day CPE and are presented in Table 1. The

plant was evaluated against the 102 ML/day Peak Instantaneous Operating Flow (PIOF) as

identified from the records for the last ten years. It is worth noting that the plant's PIOF over

the previous 12 months had been 86.5 ML/day and that the design flow is higher than the

PIOF at 109 ML/day.

Table 1 – Facility Design Details

Type of Flow Design Parameters

Design Flow 109 ML/d

PIOF 102 ML/d

Raw Water Intake Five (5) Pumps: 32.7 ML/d

26 ML/d

39 ML/d

14.4 ML/d

34 ML/d

For a total of 146.1 ML/d

Raw Water Flow Measurement Venturi meters to each plant

Flocculation Plant 1 Two identical trains for a total volume of 1200 m3

Flocculation Plant 2 388 m3

Sedimentation plant 1 Two identical trains for a total surface area of 625.54 m2

Sedimentation plant 2 Two “stacked” basins with an effective settling area of 446 m2

Filtration Plant 1 Six dual media filters with a total area of 343 m2

Filtration Plant 2 One dual media and one multi-media (with garnet sand) filters with a

total area of 96 m2

Backwash Two pumps each rated at 56.16 ML/d (650 L/s)

Reservoir Volume of 3241 m3; serpentine baffled basins

Treated Water Pumps Seven (7) Pumps: Two 19.6 ML/d

Two 5.42 ML/d

2.75 ML/d

34.66 ML/d

32.7 ML/d

For a total of 120.15 ML/d

Chemical Feed Pumps (duty and

standby)

Liquid alum

Liquid hydrofluosilicic acid

Liquid sodium hypochlorite

Powdered activated carbon slurry

PERFORMANCE ASSESSMENT



During the CPE the capability of the ABC was evaluated to assess whether the facility, under

existing conditions, could comply with the turbidity and disinfection requirements that are

used to define optimized performance. Optimized performance, for purposes of this CPE,

represents performance criteria that exceed the Ontario Drinking Water Standards, Objectives

and Guidelines. A preliminary definition of optimized performance was established by the

project Partners during a Protocol Development Workshop held in August 2010.

The optimized performance values were as follows:

1. Sedimentation:

< 2 NTU as average

< 5 NTUs as peaks

2. Filtration

< 0.1 NTU as average

< 0.2 NTUs as peaks

3. Disinfection

To be based on CT concept described in the Procedure for Disinfection of Drinking Water in

Ontario.

Based on this preliminary protocol, optimized performance would require that the facility take

a raw water source of variable quality and consistently produce a high quality, finished water.

Multiple treatment processes (flocculation, sedimentation, and filtration) are provided in

series to remove turbidity, cysts, and other microorganisms followed by disinfection to

inactivate any remaining microorganisms. Each of these processes represents a barrier to

prevent the passage of cysts and other microorganisms through the plant. By providing

multiple barriers, any microorganisms passing one process will be removed in the next,

minimizing the likelihood of microorganisms passing through the entire treatment system and

surviving in water supplied to the public. All treatment processes in the plant must be capable

of providing a barrier at all times because even temporary loss of a barrier could result in the

passage of microorganisms into the distribution system and represents a potential health risk

to the community.

A major component of the CPE process is an assessment of past and present performance of

the plant. This performance assessment is intended to identify if specific unit treatment

processes are providing multiple barrier protection through optimum performance. The

performance assessment is based on data from plant records and data collected during special

studies performed during the CPE.

The ABC operations staff measures the turbidity of the raw, settled, and finished waters

throughout each day and records this information on daily log sheets. The data then serves as

the basis of the monthly monitoring reports. During the CPE, raw water turbidity values from

the monthly reports for the most recent twelve months (e.g., September 1, 2009 through

August 31, 2010) were used to assess raw water quality. Performance out of the combination



sedimentation units and filtered water from the plant c1earwells were also evaluated based on

data from the daily log sheets. Individual filter performance is not routinely monitored. It is

noted that the evaluation of settled and finished water quality was based on the maximum

turbidity values measured each day. Maximum values were used to assess if these unit

processes were providing the consistent performance needed for optimized performance and

maximum public health protection.

The raw water turbidities for the most recent twelve months show that the average raw water

turbidity was less than 5 NTU, which indicates that the plant routinely receives a relatively

good quality raw water. However, variability in raw water quality was noted, which requires

process control adjustments to maintain consistent treatment.

The daily maximum settled turbidity for the sedimentation basins associated with each plant

are also varied widely for each of the units. Often the turbidity values were in excess of the

desired maximum of 2 NTU. The variability in settled water also seemed to trend with the

variability of the raw water indicating that process adjustments are not optimized.

The daily maximum finished water turbidity also shows variability. The level of performance

depicted meets the Provincial Drinking Water Objectives but does not meet the optimized

performance goal of 0.1 NTU or less on a consistent basis.

Since the end of March 2010, the raw water turbidity improved from that of the winter

months, averaging less than 4 NTU. This improved raw water quality was again reflected in

the treated water with values of filtered water averaging less than 0.2 NTU. From the end of

June 2010, the treated filtered water was consistently less than 0.05 NTU. This excellent

performance coincides with a number of recent changes to the plant operation. Firstly, a new

laboratory turbidimeter was purchased; secondly the coagulant used was changed from alum

to acidified alum (Clarion A7) and, as already discussed, the raw water quality improved

significantly. Therefore, it is difficult to attribute one specific reason for the consistent high

quality treated water nailed performance over the four months from June to September.

A study of the turbidity output of Filter #7 was carried out during the three week period

before the CPE. The filter effluent was passed through a continuous monitoring turbidimeter

(Hach 172OC) and the results recorded on a circular 7-day chart. The data on the recordings

indicated that a turbidity spike up to 0.35 NTU occurred immediately after each backwashing

of the filter.

The week before the CPE filtered water data indicated that following backwashing the filtered

water peaked to 0.15 NTU with a duration of perhaps 15 to 20 minutes before dropping below

0.1 NTU; often these peaks only reached 0.1 NTU. This represents excellent filtration

operation. During this period the raw water turbidity averaged 1.3 NTU.

Prior to June 2010, the plant performance suggests that there is opportunity for performance

optimization to achieve a more consistent, higher quality finished water (i.e. 0.1 NTU which

minimizes public health risk) at a potentially lower operating cost.



MAJOR UNIT PROCESS EVALUATION

The capacities of the major unit processes were determined based on recognized design

criteria. Disinfection capacity was determined based on the requirements of the Procedure for

Disinfection of Drinking Water in Ontario (MOE, 2006) with respect to Giardia cyst

inactivation. The capacity assessment applies the concentration*time (CT) concept for the

cyst inactivation. The standard required reduction for a reasonable quality raw water source is

3 logs (99.9% removal/inactivation) and it was judged that the conventional treatment at the

ABC WTP would receive a removal "credit" of 2.5 logs for Giardia. This results in the

requirement for the ABC WTP achieve a further 0.5 log reduction through inactivation.

Since the plant's treatment processes must provide an effective barrier at all times, a peak

instantaneous operating flow (PIOF) was also determined. The PIOF represents those

conditions where the treatment processes are the most vulnerable to the passage of cysts and

microorganisms.

If the treatment processes are adequately sized to operate at the PIOF and are within

performance goals, then the major unit processes are likely capable of providing the necessary

effective barriers at lower flow rates. A peak instantaneous operating flow rate of 102 ML/day

was used to assess the plant's physical facilities.

The design criteria on which the estimated unit process capacities were based were as follows:

1. Flocculation

estimated capacity based on 20 minute Hydraulic Detention Time (HDT)

2. Sedimentation

estimated capacity based on 58 m3/m

2/d Surface Overflow Rate (SOR)

3. Filtration

estimated capacity based on 290 m3/m

2/d Hydraulic Loading Rate (HLR)

4. Disinfection

3 log removal/inactivation required

plant 2.5 log removal credit

pH 8.0

Temp 0.5°C

Assumes 90% plug flow (0.9 X usable volume) and 1.85 m effective depth in

reservoir

1.5 mg/L free chlorine residual is max. allowed at clearwell outlet



Required CT = 54.5 mg/L min. (need at least 36.3 minutes detention at the

PIOF)

Unit process capability was assessed using a performance potential graph format where the

estimated treatment capacity of each major unit process was compared against the current

PIOF rate. The calculations that were conducted to complete the graph and major unit process

evaluation are shown below.

Flocculation

Plant 1 Flocculation Tanks Total Volume = 1200 m3

Rated by evaluator for HDT = 20 min (see Chapter 6)

Rated Capacity = 1200 m3 ÷ 20 min x (60 min/h x 24 h/d) = 86,400 m

3/d = 86.4 ML/d

Plant 2 Flocculation Tank Volume = 388 m3

Rated by evaluator for HDT = 20 min (see Chapter 6)

Rated Capacity = 388 m3 ÷ 20 min x (60 min/h x 24 h/d) = 27,936 m

3/d = 27.9 ML/d

Sedimentation

Plant 1 Settling area = 625.54 m2

Rated by evaluator at 59 m3/m

2/d or 2.45 m/h (see Chapter 7)

Rated Capacity = 59 m3/m

2/d x 625.54 m

2 = 39,907 m

3/d = 39.9 ML/d

Plant 2 Settling area = 446 m2


2/d or 2.45 m/h (see Chapter 7)


2/d x 446 m

2 = 26,314 m

3/d = 26.3 ML/d

Filtration

Plant 1 Filtration area = 343 m2


2/d or 12 m/h (see Chapter 8)


2/d x 343 m

2 = 99,470 m

3/d = 99.5 ML/d

Plant 2 Filtration area = 96 m2


2/d or 12 m/h (see Chapter 8)


2/d x 96 m

2 = 27,840 m

3/d = 27.8 ML/d



Disinfection

Plants 1 & 2 Combined Calculate required detention time

Required HDT = 54.5 mg/L·min ÷ 1.5 mg/L = 36.3 min

Calculate effective volume of clearwell

Effective volume = 3,241 m3 x 0.9 = 2,917 m

3

Calculate rated capacity at required detention time

Rated capacity = 2,917 m3 ÷ 36.3 min x (60 min/h x 24 h/d)

= 115,716 m3/d = 116 ML/d

The performance potential graphs prepared for the two plants are shown in Figures 2 and 3.

The combined disinfection performance potential graph is shown in Figure 4. The unit

processes evaluated are shown on the left side of the graphs and the various flow rates against

which the processes were assessed are shown across the top.

Figure 2 – Plant 1 Performance Potential Graph



Figure 3 – Plant 2 Performance Potential Graph

Figure 4 – Combined Plant Disinfection Performance Potential Graph

Horizontal bars on the graph represent the estimated peak capability of each unit process that

would support achievement of desired process performance. These capabilities were estimated

based on the combination of the CPE team's experience with. other similar processes, industry

design guidelines, and regulatory standards. The shortest bar represents the unit process which

limits plant capability relative to achieving the desired plant performance.



The unit processes were assigned a rating indicated by the number at the end of the bar. Each

major unit process was then categorized as indicated below:

Type 1 – Are Adequate

A Type 1 unit process is adequately sized. Any necessary performance improvement is

most likely to be achieved through implementation of non-construction oriented

follow up technical assistance.

Type 2 – Are Marginal

Type 3 – Are Inadequate

From the performance potential graphs, it can be seen that Plant 1, which processes 75 % of

the raw water flow, has adequately sized Type 1 flocculation and filtration facilities with the

sedimentation unit process being about half the size theoretically needed. The 1980 plant

upgrade used some of the sedimentation tankage, assuming that the plant could operate in the

direct filtration mode – there is a by-pass directly from the flocculation to the filters. As a

result, the Plant 1 sedimentation process was not considered to be a major performance

limiting impact.

In Plant 2, which processes 25% of the raw water flow, all processes were categorized as

Type 1.

The common disinfection facility was also adequate and categorized as Type 1.

A special study was carried out to determine backwash efficiency and filter media depth. The

backwash rate supplied by the backwash pumps was sufficient to expand the bed by about

20% and adequately clean the bed. Filter media depth was as indicated in plant design

specifications.

PERFORMANCE LIMITING FACTORS

The areas of design, operation, maintenance, and administration were evaluated in order to

identify factors which limit performance. These evaluations were based on information

obtained from the plant tour, interviews, performance and design assessments, special studies,

and the judgment of the evaluation team. Each of the factors were classified as A, B, or C,

according to the following guidelines:

A – Major effect on a long-term, repetitive basis

B – Minimal effect on a routine basis or major effect on a periodic basis

C – Minor effect.

Of the five factors identified, three were "B" factors and two were "Cs". These ratings reflect

the relatively high level of performance of the plant. The "B" factors were prioritized in terms

of relative importance; "C" factors are merely listed. Of the four categories evaluated, there

was one "B" Factor each in the areas of administration, operations and design. Maintenance

factors were not felt to impact on the plant performance.



The factors identified were prioritized as to their relative impact on performance and are

summarized below:

1. Administrative Policies (B-1)

Issues in this category were noted in. several areas including:

The performance target or goal of 0.1 NTU is not clearly established for plant staff

nor clearly communicated to them by plant management. As a result, there is no

commitment from staff to ensure that this goal is consistently met.

There is no incentive to try to continue to improve the plant operation in terms of

producing the highest quality of finished water at the lowest cost.

There is no procedure to ensure that new operating staff have opportunity to

acquire sufficient skills from knowledgeable staff before being given operating

responsibility.

2. Operator Application of Concepts and Testing to Process Control - Operations (B-2)

This factor relates to the ability of operations staff to apply their water treatment

knowledge to interpret process test results and adjust process conditions to support

optimum performance. This factor was demonstrated in a number of ways:

Very high quality raw water has led to complacency on the part of plant staff in

terms of process control. There is little need to adjust conditions to produce a high

quality finished water. As a result, technical skills such as jar testing, to respond to

even small changes in raw water quality are not used. As such the capability to

respond to process changes may not be adequate.

Filtered water turbidimeters are not repaired or replaced so that the ability to

optimize or even to monitor performance of this key barrier does not exist.

The link between turbidity spikes from key unit processes, especially filtration,

and potential public health impact, does not appear to be clearly understood.

The plant staff could not discern whether low raw water turbidities, changes in

coagulant or different turbidity reading from a new turbidimeter led to improved

performance in June 2010.

3. Lack of Process Flexibility - Design (B-3)

There is no ability to independently control chemical feed rates to different filters, no

ability to apply a filter aid or to dose chlorine at different rates to the two plants. The

fact that there are two plants with different designs make control more difficult, but at

the same time more necessary. Operation of the two plants at the optimum is difficult

to establish.



The final two factors are both "C" factors, those having a minor effect. Both are design factors

which are not presented in any particular order.

The sedimentation capacity is limited in Plant 1 which results in floc carryover to

the filters under peak hydraulic loading;

There is a lack of sludge treatment processing to permit routine cleaning of the

sedimentation tanks which can lead to sludge accumulation and consequent solids

carryover to the filters.

In developing this list of factors limiting performance, 65 potential factors were reviewed and

their impact on the performance of the ABC Water Treatment Plant was assessed. These

factors are outlined in Optimization Guidance Manual for Drinking Water Systems (this

Manual). Five factors were identified, and numerous other factors were not felt to be

impacting plant performance. Most notably, the administration acted in a professional manner

and was genuinely committed to learning about methods to optimize existing plant

performance. This type of attitude represents a solid foundation for future plant optimization

activities.

SUMMARY

Comprehensive Technical Assistance (CTA) is a formal and comprehensive program that

systematically addresses the factors identified in a CPE as limiting the plant's performance.

Activities during a CTA normally focus on improving performance through the transfer of

process control capabilities to the plant operators. Administrative and minor design factors are

also resolved as they relate to their impact on plant performance. Typically, all changes

during a CTA are implemented by local personnel under the guidance of a facilitator external

to the plant staff. The facilitator can be a consultant or other qualified person.

Many of the factors identified by this CPE could be addressed by a CTA. For example, as the

municipal administration moves to address the first B factor identified – In the area of

administrative policies – it will be expected that the enthusiasm and tenacity to achieve the

higher operational standard will positively affect the second B factor, the operator application

of concepts and testing to process control.

The finished water at the ABC WTP meets Ontario drinking water objectives. The plant

performance since June of 1995 suggests that there is capability for performance optimization

to achieve more consistent, higher quality finished water (i.e. less than 0.1 NTU, which

minimizes public health risk) at a lower operating cost. This capability represents a viable and

worthwhile challenge for ABC WTP staff.

APPENDIX D. Example CPE Scheduling Letter and Letter to MOE

Regarding Project Approval


APPENDIX D

EXAMPLE CPE SCHEDULING LETTER AND LETTER TO MOE REGARDING

PROJECT APPROVAL


Regarding Project Approval D-1


APPENDIX D: EXAMPLE CPE SCHEDULING LETTER AND

LETTER TO MOE REGARDING PROJECT APPROVAL

EXAMPLE CPE SCHEDULING LETTER

(From CPE Team)

Date

Address of Municipality

Re: Evaluation of the XYZ Drinking Water Treatment Plant on Month/Day/Year

Dear Official:

This letter is intended to provide you with some information on the evaluation and

describe the activities in which you will be involved. We expect that this evaluation

will enable your water plant to attain significantly improved performance.

The evaluation procedure that will be used is the first phase of the Composite

Correction Program (CCP) approach. The CCP approach has been successfully used

in Ontario and the United States to bring existing plants into compliance with their

regulations. In this first phase, which is known as the Comprehensive Performance

Evaluation (CPE), all aspects of the design, operation, maintenance, and

administration of the plant will be reviewed and evaluated with respect to their

impact on performance.

The CPE will begin with a brief kickoff meeting on _______________ at

approximately 8:00 a.m. or 4:00 p.m. The purpose of the kickoff meeting is to explain

to the operations staff and plant administration the methods used in conducting the

evaluation and the types of activities which will occur during the three days. Any

questions and concerns regarding the CPE can also be raised at this time. It is

important that the plant administrators and those persons responsible for plant

budgeting and planning be present because the CPE will focus a significant effort in

reviewing these aspects of the plant. Following the kickoff meeting, which should last

approximately 30 minutes, the plant staff will be requested to take the CPE team on

an extensive plant tour. After the plant tour, the team will begin collecting

performance and design data. Please make arrangements so that the operating records

and any design information for the plant are available. These activities will be

continued through the second day.

As far as the types of information and records that will be reviewed during the CPE,

we will first need to review your monitoring reports for the last 12 months. Any

laboratory and plant log sheets covering this same period will be useful as well as any

drawings and specifications for the treatment plant. We will also need budget and

financial information. This will centre around the budget for the treatment plant and

information on salaries, operating funds available, etc. It is our experience that the

information we need is usually readily available from existing reports. We usually




work with the information available and do not request the administration staff

prepare additional summaries of the information.

On the third day the CPE team will be involved in several different activities. The

major involvement of the plant staff will be in individual interviews. The plant

administrators will also be interviewed and the financial records of the plant

reviewed. Several special studies may also be completed by the CPE team to

investigate the performance capabilities of the plant's different unit treatment

processes. We request that each member of the operations staff be available some

time during the day for the interviews. We would also appreciate having an operator

available to answer questions about the plant and to operate the plant during the

special studies. We will be flexible in working these interviews and special studies

around the other required duties of you and your staff.

The last day of the CPE will consist of an exit meeting. During the exit meeting the

results of the evaluation will be discussed with all of those who participated. The

performance capabilities of the treatment processes will be presented and any factors

found to limit the performance of the plant discussed. The CPE team will also answer

any questions regarding the results of the evaluation. The results presented in the exit

meeting will form the basis of the final report, which will be provided in about six

weeks. We expect to begin the exit meeting at 8:00 a.m. on and it should last

approximately one hour.

Yours Very Truly,




EXAMPLE LETTER TO MOE REGARDING PROJECT APPROVAL

(From CPE Team or Municipality/Utility. Please note that this letter is written as if a

CPE has already been completed and a CTA is planned. If contact is made with MOE

before the CPE begins, the letter must be changed to reflect the timing.)

Date

Addresses of MOE District Office and MOE Approvals Branch

Re: Certificate of Approval Requirements for Technical

Assistance Program at the XYZ Water Treatment Plant

Dear District Manager/Water and Wastewater Manager:

This letter is intended to provide you with general information on the evaluation that

was done at the XYZ plant on and the follow-up technical assistance that is planned.

The evaluation procedure that was used at the XYZ plant was the Comprehensive

Performance Evaluation (CPE) approach, which has been successfully used

elsewhere to bring existing plants into compliance. During this evaluation, all aspects

of the design, operation, maintenance, and administration of the XYZ plant were

reviewed and evaluated with respect to their impact on performance.

The next phase of our work will involve on-site technical assistance to address the

maintenance, administrative, operations, and design-related factors that are adversely

affecting finished drinking water quality. This work will likely require us to make

some equipment and/or operational changes, and the on-site assistance should last for

six months. We anticipate the following changes will be made:

(List here in bullet format)

Please respond soon and let us know which changes will require an amended

Certificate of Approval and what we are responsible for. I can be reached at (xxx)

yyy-zzzz if you require more information.

Yours Very Truly,

APPENDIX E. Example Special Study


APPENDIX E

EXAMPLE SPECIAL STUDY

APPENDIX E. Example Special Study E-1


APPENDIX E: EXAMPLE SPECIAL STUDY

TITLE: Reduce Plant Flow

HYPOTHESIS: A reduction in peak instantaneous operating flow will decrease

finished water turbidity.

APPROACH:

1. Reduce peak instantaneous operating flow to plant to 3,000 L/min by

adjusting valve at raw water pump.

2. Relocate pressure gauge to location upstream of throttling valve.

3. Reduce chemical feed rate in proportion to flow.

4. Measurements: (One week prior to change/one week after change.)

a. Raw water turbidity every four hours during operation.

b. Settled water turbidity every four hours during operation.

c. Effluent turbidity from each filter every four hours during operation.

d. Continuous measurement of finished turbidity with existing

turbidimeter.

e. Influent water temperature on daily basis.

DURATION: One week under current conditions and one week under

changed conditions. If raw water quality changes dramatically,

repeat.

EXPECTED RESULTS:

1. Reduction in settled water turbidity and in variations.

2. Reduction in filter water turbidity and in variations.

3. Reduction in finished water turbidity to <0.1 NTU on continuous basis.

4. Increase in filter run time.

CONCLUSIONS: To be completed after study.

IMPLEMENTATION: To be completed after study.

APPENDIX F. Example CTA Summary Report


APPENDIX F

EXAMPLE CTA SUMMARY REPORT

APPENDIX F. Example CTA Summary Report F-1


APPENDIX F: EXAMPLE CTA SUMMARY REPORT

SUMMARY REPORT

WATER TREATMENT PLANT X

COMPREHENSIVE TECHNICAL ASSISTANCE

(Note: this report was written for a CTA conducted at a U.S water plant in the early

1990s, hence the reference to the Surface Water Treatment Rule)



INTRODUCTION

The CCP approach is a proven procedure for improving performance of water

treatment plants. This approach consists of two components, the CPE phase and the

CTA phase. A CPE is a thorough review and analysis of a plant's design capabilities

and associated administrative, operation, and maintenance practices. It is conducted to

identify factors that may be adversely impacting a plant's capability to achieve optimal

performance. Its major objective is to determine if significant improvements in

performance can be achieved without major capital improvements. A CTA is a

performance improvement phase that may be implemented if results from the CPE

indicate that improved performance can be achieved. During the CTA phase, factors

identified by the CPE are systematically eliminated. The major benefit of a CTA is

that it optimizes the capability of existing facilities without the expense of major

capital improvements.

A CPE was conducted at plant X on August 21-24. It revealed that the plant had some

performance problems and that the top ranked factors identified were process control

related. It was felt that operator training, conducted as a portion of a CTA, would

improve plant performance. This report summarizes the results of the CTA, which was

initiated in the following April.

CPE RESULTS

A CPE was conducted August 21-24 at water treatment plant X. The plant is a direct

filtration facility constructed in 1978. Treatment includes coagulant chemical feed

(alum and cationic polymer), flocculation in a reaction basin, non ionic polymer filter

aid feed, filtration through four dual media filters, post chlorination, and gravity flow

from the plant to storage and distribution. Raw water is supplied from a multiple use

lake located several miles northwest of the plant. Raw water quality is generally good

in winter months, with turbidities in the 5 to 10 NTU range; but prevailing westerly

winds often stir up sediments in the relatively shallow lake in other seasons, resulting

in peak raw water turbidities as high as 50 to 280 NTU.

A review of operating data for the previous year revealed that the plant was generally

producing water of less than 1.0 NTU, but would not meet the Surface Water

Treatment Rule (SWTR) (USPEA, 1989) requirements of 0.5 NTU 95 percent of the

time. Further performance evaluation included a special study to determine the

turbidities before and after backwashing. Results indicated that filter effluent

turbidities increased to 3.2 NTU and did not drop below 1.0 NTU for over two hours.

Optimum performance would be a 0.2 NTU increase for less than 10 minutes and a

return to operating turbidities of less than 0.1 NTU.

A performance potential graph projected that the design-rated 11,400 m3/d facility

would have to be de-rated to 5,700 m3/d because of a severe air binding problem

identified with the filters. This problem was exacerbated by the design of the filter

effluent header, which allowed the formation of negative pressure in the filter

underdrains. A short detention time in the reactor/flocculation basin also resulted in a

projected capacity less than design for this unit process. A longer time was felt to be

necessary because of the longer reaction time needed with cold water during winter

operation.



The plant's performance limiting factors were assessed and prioritized in order of

significance as follows:

1. Operator Application of Concepts and Testing to Process Control – Operation

The plant had no formal process control program to provide information from

which operational decisions could be made. Although the operators had a good

understanding of water treatment, they were not applying their knowledge to

operation of the plant. Because of the highly variable raw water quality it was

essential that the plant be monitored continuously and coagulant dosages

changed to maintain a consistent high quality finished water.

2. Process Control Testing – Operation

The lack of process control testing resulted in insufficient data being collected

to properly assess plant performance (e.g. jar testing was not being conducted

to optimize the coagulation process).

3. Filtration – Design

Turbidity measurements taken at the time of the evaluation demonstrated that

the filters were not performing optimally. The presence of filter media in the

clearwell was an indication that the filters may have been damaged by

backwashing or the release of air from the severely air-bound filters. More

involved evaluations were felt to be necessary to determine if the support

gravels were damaged. Filter capacity was also being affected by air binding

and periodic high raw water turbidities, necessitating frequent backwashing.

4. Raw Water Turbidity – Design

The turbidity of the raw water often exceeded that normally recommended for

the direct filtration process. During periods of high turbidity it was projected

that it would be necessary to reduce plant flow rates to produce an acceptable

water.

5. Plant Coverage – Administration

The plant was not attended on weekends and the operators were often

conducting other duties away from the plant during weekdays. It was assessed

that this practice would result in undetected periods of poor finished water

quality.

6. Lack of Standby Units – Design

There were no standby alum and polymer feed pumps. Failure of one of the

units would result in poor plant performance.

7. Reactor/Flocculation Basin – Design

The reactor basin was too small to provide adequate time for flocculation

during cold water conditions in winter months. It was projected that the plant



flow rate would have to be reduced during winter to ensure adequate

flocculation.

8. Plant Inoperability Due to Weather – Design

Drought severely impacted the availability of water from the lake in 1985. An

engineering study had been completed to assess relocation of the intake to a

deeper part of the lake.

The CPE report recommended that a follow-up CTA be conducted because the top

ranked factors identified were process control related and it was felt that operator

training would improve plant performance. Also, since the historical peak day demand

was only about 5,700 m3, it was concluded that the plant could be operated at a lower

flowrate for a longer period to address the design-related limitations of the filters and

reactor/flocculation basin.

CTA SIGNIFICANT EVENTS

The CTA was initiated in the following April. Major activities are briefly summarized

below.

Consultant Initial Site Visit (April 3-6)

Implemented a process control sampling and testing schedule and developed a

daily data sheet to record results.

Implemented policies/procedures approach.

o Developed procedures for calibrating chemical feeders and calculating

chemical dosages so that chemicals could be accurately applied.

o Developed procedures for calibrating effluent turbidimeter.

o Developed procedure for process control testing and sampling.

Initiated a special study to determine the effect of operating the plant at a

reduced flow rate and operating the filters without a negative pressure. At the

conclusion of the visit, the plant was operated at 4,000 L/min (~5,700 m3/d)

rather than at 7,900 L/min (~11,400 m3/d) and a plug was removed from the

filter effluent header to allow the negative pressure to be released from the

filter.

Identified special studies to be conducted in the future including: analysis of

dissolved oxygen and temperature in raw water including transmission line to

determine causes of filter air binding, evaluation of effect of rapid mix on

coagulant feed, an analysis of effect of alum and polymer feed points.

Developed action/implementation plan and made assignments to the operating

staff and administrators with due dates to ensure activity continued until next

site visit.



Chemical feed rates were not changed during the visit because it was desirable

to have the plant staff operate the plant following feeder calibration to evaluate

plant performance with the newly calculated dosages.

Evaluation Period (April – July)

Continued process control testing on plant as presented in sampling and testing

schedule procedure.

Operated plant at reduced flow rate (4,000 L/min) and without negative

pressure on filter effluent header.

Initiated weekly transmission of data to consultant and initiated weekly phone

calls between plant staff and consultant.

Consultant developed computer spreadsheet to analyze plant data.

Installed accurate pressure gauges on lake intake pumps to relate pump

discharge pressure to pump output.

Sent finished water turbidimeter to factory service centre for repair.

Plant staff modified daily data sheet based on operating experience.

Purchased dissolved oxygen meter for special study on filter air binding.

Welded sample taps and chemical feed taps on plant influent line before and

after orifice plate in preparation for chemical feed special study. The plant staff

hired a local welder to make the welds.

Consultant Site Visit (June 26-27)

Conducted jar tests using filter paper and established new chemical feed rates

for alum and cationic polymer. Plant performance improved dramatically prior

to the end of the site visit.

Developed a procedure for jar testing using filter paper to correlate results with

plant performance. Explained the conduct and interpretation of the jar

testing/filter paper procedure to the operating staff.

Expanded process control program to include jar testing/filter paper testing to

establish chemical feed rates.

Reviewed chemical feed calculations with plant staff.

Investigated filter backwash and determined that additional wash time would

be required to adequately clean the filters.



Updated the special study on relocation of alum and cationic polymer feed

points.

Updated the action-implementation plan.

Evaluation Period (July – October)

Implemented full plant process control program including evaluating raw water

quality and determining the correct coagulant and filter aid feed rates. Jar tests

were used to determine required chemical doses when raw water quality

changed.

Continued weekly transmission of data to consultant and weekly phone calls

between plant staff and consultant.

Consultant developed monthly data sheet to analyze plant data.

Relocated the feed points for alum and cationic polymer addition to take

advantage of a hydraulic flash mix at the orifice plate located in the influent

piping. Completed special study on relocation of the chemical feed points.

Convinced administrators to allow time for the operating staff to remain at the

plant to conduct process control testing and to make plant adjustments.

Purchased additional laboratory supplies for conducting jar tests.

Extended filter backwash time to allow more complete cleaning of filters.

Staff investigated cost of monitoring raw water quality with a turbidimeter and

alarm at raw water pumping station, an alarm on the existing turbidimeter at

the plant, and a streaming current monitor with automatic control of coagulant

feeders.

Consultant Site Visit (October 17 - 19)

Reviewed process control program.

Conducted jar tests to evaluate alum replacement products.

Reviewed chemical feed calculations.

Completed CTA assistance.

CTA RESULTS

Significant improvement in plant performance was achieved during the conduct of the

CT A. This is depicted graphically in Figure 1. It is noted that while plant operation

improved after reducing the plant flow rate and eliminating the negative pressure on



the filters in April, performance remained erratic until process control, including

chemical adjustments, was implemented in July. After July, plant finished water

turbidities remained very consistent at about 0.1 to 0.2 NTU through the duration of

the project. This consistent performance was achieved even though raw water

turbidities, shown in Figure 2, varied widely. Plant finished water quality remained

below 0.3 NTU even when the raw water turbidities reached 70 NTU because the

operating staff consistently monitored varying raw water quality and responded by

changing chemical feed rates. The plant performance is especially impressive since

influent turbidities frequently exceeded values thought to be treatable with direct

filtration (e.g. > 50 NTU). Another indication of improved performance was that filter

effluent turbidity following a backwash did not exceed 0.3 NTU and returned to 0.15

NTU within minutes after the wash.

The improved performance was achieved primarily through improved process control

activities and lowering plant loadings that were more in line with unit process

capability. The primary process control tool utilized was the jar test, which proved to

be valuable in allowing the operators to predict chemical doses required when raw

water quality varied. The jar test was used in conjunction with filter paper to correlate

results with the direct filter plant conditions. The test provided a very accurate

indication of required chemical dose.

Figure 1 – Finished Water Turbidity for Plant X



Figure 2 – Raw Water Turbidity for Plant X

The plant staff became very adept at evaluating raw water quality and adjusting

chemical feed rates to produce a high quality finished water on a continuous basis. The

staff exhibited a great deal of expertise and professionalism during the CTA, and

quickly learned chemical feed calculations and implemented the necessary process

control activities.

The process control activities took additional operator time at the plant. Prior to the

CTA, operators would check the plant daily; however, during the CTA, operators were

at the plant a minimum of four hours each day. If plant raw water quality was

changing rapidly operators would be at the plant making adjustments whenever the

plant was operating. Administrators had to be convinced that the additional time was

necessary to achieve and maintain improved plant performance.

Only minor physical plant modifications were required to improve plant performance.

The modifications included removing a threaded plug from the filter effluent header to

relieve negative pressure on the filters, and adding additional alum and cationic feed

points prior to an orifice which was used as a flash mix. All minor modifications were

made by the plant staff.

The administrators were favourably impressed by the level of performance achieved

by the plant. Major plant (e.g. construction of a sedimentation basin) and raw water

intake modifications were being planned prior to the successful implementation of the

CTA. These major modifications were placed on hold based on the ability of the plant

to perform within the SWTR requirements. The intake modifications may eventually

be made because they will potentially reduce the turbidity load (e.g. draw water from

deeper points in the lake) to the direct filtration plant allowing it to operate at higher

hydraulic loading rates.



CONCLUSIONS

Implementation of a CTA at water treatment Plant X was highly successful. The CTA

proved that the plant could achieve compliance with SWTR turbidity requirements

without major capital improvements. City administrators had planned on spending an

estimated one million· dollars on construction of sedimentation basin facilities and

related improvements. After the CTA they decided to delay any construction until

water demands required the plant to be operated at higher rates. The plant staff

developed increased confidence that excellent quality water could be produced despite

high raw water turbidities, and they developed a level of pride that did not allow them

to accept marginal finished water quality. In addition, the jar test/filter paper

procedure proved to be a valuable process control tool that allowed accurate selection

of coagulant doses. The City will have to continue the commitment to water treatment

in order to sustain the level of performance obtained during the CTA. Continued

production of high quality water will require a commitment to allowing adequate

operator time at the plant to make necessary chemical feed adjustments. If operators

are not at the plant whenever it is operating, a turbidimeter with alarm should be

installed at the raw water pumps to give the operators continuous notice of raw water

changes. The use of a streaming current monitor that would automatically adjust the

alum feed rate if raw water quality changes could be investigated.

APPENDIX G. Equations and Calculations


APPENDIX G

EQUATIONS AND CALCULATIONS

APPENDIX G. Equations and Calculations G-1


APPENDIX G: EQUATIONS AND CALCULATIONS

A. COAGULATION AND FLOCCULATION CALCULATIONS

Velocity Gradient, G

21

V

PG

Where:

P = power input to the fluid (J/s)

V = volume of the flocculator (m3)

µ = dynamic viscosity of the water (N·s/m2)

Dynamic Viscosity of Water versus Temperature

Temperature (°C) Dynamic Viscosity (kg/m*s)

0 1.794 x 10-3

5 1.519 x 10-3

10 1.308 x 10-3

15 1.140 x 10-3

20 1.005 x 10-3

25 8.940 x 10-4

30 8.010 x 10-4

Jar Testing – Sampling Time

)(

000,1min

440,1)(dim1.0

(min)3

2

dLrateflowplant

m

L

dmareasurfaceentationsem

timeSampling

APPENDIX G. Equations and Calculations G-2


B. DISINFECTION CALCULATIONS

Required Detention Time, T

)/(Retansin

)min/((min)

LmgsidualtfecDi

LmgCTT

req

req

Where:

Treq = Required detention time in post-disinfection unit process

CTreq = CT requirements from tables in Disinfection Procedure for post-

disinfection conditions

Disinfectant Residual = Selected operating residual maintained at the discharge

point from the disinfection unit process

Flow Rate, Q (Post-Disinfection)

(min)

)(min)/(

3

3

req

post

T

mVmQ

Where:

Q = Flow rate where required CT can be met

Vpost = Effective volume for post-disinfection unit processes

Treq = Required detention time in post-disinfection unit process, as determined

using equation shown in Section 9.6.1

Flow Rate, Q (Pre- and Post-Disinfection)

(min)

)(

(min)

)(min)/(

33

3

postreq

post

prereq

pre

T

mV

T

mVmQ

Q = Flow rate where required CT can be met

Vpre = Total effective volume for pre-disinfection unit processes

Vpost = Total effective volume for post-disinfection unit processes

Treq = Required detention time in pre- or post-disinfection unit process, as

determined using equation shown in Section 9.6.1