^innovative applications of treatment processes for spent filter backwash

7/30/2019 ^Innovative Applications of Treatment Processes for Spent Filter Backwash

1/220

Innovative Applications

of Treatment Processesfor Spent Filter Backwash

Subject Area: Water Resources and Environmental Sustainability


2/220


3/220


4/220

About the Water Research FoundationThe Water Research Foundation (formerly Awwa Research Foundation or AwwaRF) is a member-supported,international, 501(c)3 nonpro t organization that sponsors research to enable water utilities, public healthagencies, and other professionals to provide safe and affordable drinking water to consumers.

The Foundations mission is to advance the science of water to improve the quality of life. To achieve thismission, the Foundation sponsors studies on all aspects of drinking water, including resources, treatment,distribution, and health effects. Funding for research is provided primarily by subscription payments fromclose to 1,000 water utilities, consulting rms, and manufacturers in North America and abroad. Additionalfunding comes from collaborative partnerships with other national and international organizations and theU.S. federal government, allowing for resources to be leveraged, expertise to be shared, and broad-basedknowledge to be developed and disseminated.

From its headquarters in Denver, Colorado, the Foundations staff directs and supports the efforts ofmore than 800 volunteers who serve on the board of trustees and various committees. These volunteersrepresent many facets of the water industry, and contribute their expertise to select and monitor researchstudies that bene t the entire drinking water community.

The results of research are disseminated through a number of channels, including reports, the Web site,Webcasts, conferences, and periodicals.

For its subscribers, the Foundation serves as a cooperative program in which water suppliers unite to pooltheir resources. By applying Foundation research ndings, these water suppliers can save substantial costsand stay on the leading edge of drinking water science and technology. Since its inception, the Foundationhas supplied the water community with more than $460 million in applied research value.

More information about the Foundation and how to become a subscriber is available on the Web atwww.WaterResearchFoundation.org .

2010 Water Research Foundation. ALL RIGHTS RESERVED


5/220

Innovative Applicationsof Treatment Processesfor Spent Filter Backwash

Jointly sponsored by:Water Research Foundation6666 West Quincy Avenue, Denver, CO 80235-3098

City of Cleveland, OHand

U.S. Environmental Protection AgencyWashington, D.C.

Published by:

Prepared by:

David A. Cornwell , John Tobiason , and Richard BrownEE&T, Inc.712 Gum Rock Court, Newport News, VA 23606



6/220

Copyright 2010

by Water Research Foundation

ALL RIGHTS RESERVED.No part of this publication may be copied, reproduced

or otherwise utilized without permission.

ISBN 978-1-60573-084-4

Printed in the U.S.A.

DISCLAIMER

is study was jointly funded by the Water Research Foundation (Foundation), the City of Cleveland, and the U.S. Environmental Protection Agency (USEPA) under Cooperative AgreementNo. CR-83110401. e Foundation, City of Cleveland, or USEPA assume no responsibility for the

content of the research study reported in this publication or for the opinions or statements of factexpressed in the report. e mention of trade names for commercial products does not represent or

imply the approval or endorsement of the Foundation, City of Cleveland, or USEPA. is report ispresented solely for informational purposes.



7/220

v

CONTENTS

TABLES ....................................................................................................................................... vii

FIGURES ....................................................................................................................................... xi

FOREWORD ............................................................................................................................... xix

ACKNOWLEDGMENTS ........................................................................................................... xxi

EXECUTIVE SUMMARY ....................................................................................................... xxiii

CHAPTER 1: BACKGROUND .................................................................................................... 1 Characteristics of SFBW..................................................................................................... 1

Quantity ........................................................................................................................ 1

Quality (Composition) ................................................................................................. 3

Options for SFBW Treatment ............................................................................................. 4 Equalization (With or Without SFBW Treatment) ..................................................... 4 Low-Rate (Standard) Quiescent Gravity Settling .................................................... 5 Plate (Lamella) or Tube Settlers .................................................................................. 6 Dissolved Air Flotation ................................................................................................ 6 High-Rate Solids Contact Clarification Processes ...................................................... 7 Membranes ................................................................................................................... 8

CHAPTER 2: LITERATURE REVIEWPREVIOUS STUDIES OF SFBW TREATMENT ...... 9 City of Durham, NC (DAF) ................................................................................................ 9 City of Boulder, CO (DAF) .............................................................................................. 14 City of Modesto, CA (Actiflo) .......................................................................................... 17 City of Phoenix, AZ (DAF) .............................................................................................. 21 City of Tempe, AZ (Actiflo) ............................................................................................. 22

Background ................................................................................................................ 22 ResultsCoagulant Screening .................................................................................. 22 Impact of Clarification Rate and Flocculation Time ................................................. 24 Impact of Polymer Dose Under Mixed Conditions ................................................... 24

East Bay Municipal Utility District, Walnut Creek, CA (Actiflo) ................................... 27 City of Cleveland, OH (DAF) ........................................................................................... 30 United Water (DensaDeg) ................................................................................................. 32

CHAPTER 3: PILOT- AND FULL-SCALE EVALUATIONS OF CLARIFICATIONAND FLOTATION FOR SFBW TREATMENT................................................................... 35

Introduction ....................................................................................................................... 35 City of Boulder (Boulder, CO) ......................................................................................... 35

Description ................................................................................................................. 35 Cold Weather Conditions (Spring 2007) ................................................................... 36 Warm Weather Conditions (Summer 2007) .............................................................. 38



8/220


9/220

vii

TABLES

ES.1 Summary of SFBW treatment results discussed in this report ....................................... xxv

1.1 High-rate SFBW treatment options .................................................................................... 4

2.1 Summary of standard-rate DAF testing results at Durham in 1999 .................................. 11

2.2 Summary of standard-rate DAF testing results at Boulder in 1999 .................................. 16

2.3 Summary of sand-ballasted coagulation (Actiflo) testing results at Modesto in 2005 ..... 18

2.4 Operational matrix during Actiflo testing at Modesto in 2005 ......................................... 18

2.5 Recommended future operational matrix for Actiflo used for SFBW

treatment at Modesto ................................................................................................... 18

2.6 Summary of standard-rate DAF testing results at Phoenix in 2000 .................................. 21

2.7 Summary of polymers tested with Actiflo at Tempe in 1997 (no alum added) ................ 23

2.8 Summary of sand-ballasted coagulation (Actiflo) testing results at Tempe in 1997 ........ 26

2.9 Summary of sand-ballasted coagulation (Actiflo) testing resultsat Walnut Creek in 1997 ............................................................................................. 30

2.10 Summary of standard-rate DAF testing results at Cleveland in 2000 .............................. 31

3.1 Impact of full-scale operating conditions on DAF particulate removal at Boulderin April and May 2007 ................................................................................................ 37

3.2 Impact of full-scale operating conditions on DAF particulate removal at Boulderin September 2007 ...................................................................................................... 38

3.3 Impact of operating conditions on ClariDAF performance during May 2007 testingin Utah (as measured by turbidity in treated water) .................................................... 46

3.4 Treated and untreated SFBW characteristics during May 2007 testing in Utah ............... 47

3.5 Metals, turbidity, and TOC samples collected on July 23, 2007 ...................................... 53

3.6 Summary of results using Trident HSC (tube portion preceding AC portion)at Utah Valley WTP in July and August 2007 ............................................................ 56

3.7 Summary of Utah studies with CONTRAFAST in July and August 2007 ...................... 57



10/220

viii | Innovative Applications of Treatment Processes for Spent Filter Backwash

3.8 Grab sample data during August and September pilot studies in Utah ............................ 64

3.9 Performance data of full-scale tube settler during spring and summer pilot test periods ....... 65

3.10 Estimated cost and footprint for high-rate SFBW treatment at Utah Valley WPP ........... 66

3.11 Impact of AquaDAF rate on particulate removal at Cleveland in May 2007 ................... 73

3.12 Impact of AquaDAF flocculation time and polymer dose on particulate removalat Cleveland in May 2007 ........................................................................................... 74

3.13 Impact of AquaDAF recycle on particulate removal at Cleveland in May 2007 ............. 74

3.14 Impact of DensaDeg rate on particulate removal at Cleveland in May 2007 ................... 80

3.15 Impact of DensaDeg polymer dose on particulate removal at Cleveland in May 2007 ... 80

3.16 Summary of grab samples during May 2007 testing in Ohio ........................................... 83

3.17 Summary of grab samples during September 2007 testing in Ohio ................................. 86

3.18 Treated and untreated SFBW characteristics during September 2007 testing in Ohio ..... 87

3.19 Estimated cost and footprint for retrofit of high-rate SFBW treatmentat Morgan WTP using different assumptions for recycle ........................................... 89

3.20 Morgan WTP SFBW EQ cost analysis for 5 and 10 percent recycle limits ..................... 90

3.21 Tube settler performance at Passaic Valley Water Commission ...................................... 92

4.1 Membrane performance: Operation and assessment ........................................................ 94

4.2 Properties of SFBW feed waters ....................................................................................... 94

4.3 Bench-scale test membranes ............................................................................................. 97

4.4 Membrane performance test conditions ............................................................................ 99

5.1 Summary of SFBW treatment results discussed in this report ....................................... 117

A.1 Summary of SFBW treatment results discussed in this report ....................................... 123

A.2 Estimated cost and footprint for high-rate SFBW treatment at Utah Valley WPP ......... 123

A.3 New ClariDAF SFBW treatment system cost analysis ................................................... 132



11/220

Tables | ix

A.4 Summary of Utah studies with CONTRAFAST in July and August 2007 .................... 136

A.5 New CONTRAFAST SFBW treatment system cost analysis ........................................ 138

A.6 Utah Valley WPP Trident HSC pilot data for SFBW ..................................................... 143

A.7 New Trident HSC SFBW treatment system cost analysis .............................................. 145

B.1 Summary of SFBW treatment results discussed in this report ....................................... 150

B.2 Estimated cost and footprint for high-rate SFBW treatment at Morgan WTP ............... 150

B.3 Morgan WTP operational assumptions ........................................................................... 155

B.4 Morgan WTP filter operations ........................................................................................ 158

B.5 Morgan WTP SFBW EQ cost analysis for 5 and 10 percent recycle limits ................... 160

B.6 Summary of Leopold pilot testing at Cleveland Morgan WTP in September 2007 ....... 162

B.7 10 percent SFBW recycle EQ and ClariDAF retrofit cost analysis ................................ 163

B.8 5 percent SFBW recycle EQ and ClariDAF retrofit cost analysis .................................. 163

B.9 10 percent SFBW recycle EQ and AquaDAF retrofit cost analysis ............................... 171

B.10 5 percent SFBW recycle EQ and AquaDAF retrofit cost analysis ................................. 171

B.11 Impact of loading rate on DensaDeg performance during May 2007 pilot studies ........ 172

B.12 Impact of polymer dose on DensaDeg performance during May 2007 pilot studies ..... 173

B.13 10 percent SFBW recycle EQ and DensaDeg retrofit cost analysis ............................... 174

B.14 5 percent SFBW recycle EQ and DensaDeg retrofit cost analysis ................................. 174



12/220



13/220

xi

FIGURES

1.1 Predicted backwash rate as a function of temperature ........................................................ 2

2.1 Impact of polymer dose on performance of DAF for SFBW treatmentat Durham in 1999 ...................................................................................................... 12

2.2 Impact of flocculation time during DAF testing at Durham in 1999 ................................ 12

2.3 SFBW treatment with DAF at Durham in 1999 ............................................................... 13

2.4 Comparison of turbidity reduction in plate settler vs. DAF for SFBWat Durham in 1999 ...................................................................................................... 13

2.5 SFBW treatment with Actiflo at Modesto in 2005 ........................................................... 19

2.6 SFBW treatment with Actiflo at Modesto in 2005 (turbidity) .......................................... 19

2.7 SFBW treatment with Actiflo at Modesto in 2005 (particles) .......................................... 20

2.8 Treated vs. untreated SFBW turbidity during studies with Actiflo at Modestoin 2005 ................................................................................................................... 20

2.9 Comparison of polymer type and dose for Actiflo treatment of SFBWat Tempe in 1997 ........................................................................................................ 23

2.10 Impact of polymer dose on Actiflo treatment of SFBW at Tempe in 1997 ...................... 24

2.11 Actiflo SFBW treatment at Tempe in 1997 under stable treatment conditions ................ 25

2.12 Reduction of SFBW turbidity during treatment with Actiflo under stable treatmentconditions at Tempe in 1997 ....................................................................................... 26

2.13 Comparison of polymers for Actiflo treatment of SFBW at Walnut Creek in 1997 (0.85 mg/L) .................................................................................................... 27

2.14 Impact of 2530TR polymer dose on Actiflo treated SFBW at Walnut Creek in 1997 ............. 28

2.15 SFBW treatment with Actiflo at Walnut Creek in 1997 ................................................... 28

2.16 Actiflo turbidity treatment of SFBW at Walnut Creek ..................................................... 29

2.17 Actiflo particle count treatment of SFBW at Walnut Creek ............................................. 29



14/220

xii | Innovative Applications of Treatment Processes for Spent Filter Backwash

2.18 DensaDeg treatment of 100 percent alum SFBW at Haworth andLake DeForest WTPs in 2005 ..................................................................................... 33

2.19 DensaDeg treatment of 100 percent PACl SFBW at Lake DeForest WTP ...................... 33

3.1 Seasonal water temperature at Betasso WTP (Lakewood Reservoir) .............................. 36

3.2 Turbidity testing at Boulder in April and May ................................................................. 37

3.3 Impact of full-scale testing of polymer dose on turbidity at Boulder in summer 2007 .......... 39

3.4 Utah Valley WPP process schematic ................................................................................ 41

3.5 Utah Valley WPP SFBW treatment facilities (WWW reclamation building) .................. 42

3.6 ClariDAF trailer provided by Leopold during May 2007 testing in Utah ........................ 43

3.7 ClariDAF schematic.......................................................................................................... 43

3.8 ClariDAF pilot schematic ................................................................................................. 44

3.9 Continuous and grab turbidity during 32-hour period at 14 gpm/ft 2 in Utah in May 2007 ................................................................................................... 48

3.10 Turbidity and DAF clarification rate during 48-hour period at 8 gpm/ft 2 in Utah in May 2007 ................................................................................................... 48

3.11 Photo of CONTRAFAST pilot during July and August 2007 in Utah ............................. 50

3.12 Schematic of CONTRAFAST pilot .................................................................................. 51

3.13 Photo of Trident HSC pilot during July and August 2007 in Utah ................................... 52

3.14 Schematic of Trident HSC pilot ........................................................................................ 52

3.15 Variability of turbidity in untreated SFBW during July and August 2007 study in Utah .... 54

3.16 Impact of spike in turbidity of untreated SFBW on performance of Trident HSC ............. 54

3.17 Impact of spike in particle count of untreated SFBW on performance of Trident HSC ...... 55

3.18 Impact of rate on turbidity removal in Trident HSC during July and August 2007testing in Utah ............................................................................................................. 57

3.19 Impact of rate on particle count in Trident HSC during July and August 2007testing in Utah ............................................................................................................. 58



15/220

Figures | xiii

3.20 Impact of rate on turbidity removal in tube section of Trident HSC ................................ 58

3.21 Impact of rate on combined turbidity removal from tubes and AC in Trident HSC ........ 59

3.22 Impact of rate on particle count in tube section of Trident HSC (see Table 3.7) ............. 59

3.23 Impact of rate on particle count in AC in Trident HSC (see Table 3.7 ) ........................... 60

3.24 Impact of rate on turbidity removal in CONTRAFAST during July and August 2007testing in Utah ............................................................................................................. 60

3.25 Impact of rate on distribution of turbidity in CONTRAFAST during July and August2007 testing in Utah .................................................................................................... 61

3.26 Impact of rate on particle count in CONTRAFAST during July and August 2007testing in Utah ............................................................................................................. 61

3.27 Impact of rate on distribution of particle count in CONTRAFAST during July andAugust 2007 testing in Utah ....................................................................................... 62

3.28 Impact of polymer dose on turbidity removal in CONTRAFAST testing in Utah ........... 62

3.29 Impact of polymer dose on particle count during CONTRAFAST testing in Utah ......... 63

3.30 Morgan WTP facilities site plan ....................................................................................... 68

3.31 Morgan WTP SFBW treatment facilities site plan ........................................................... 69

3.32 Morgan WTP SFBW treatment facilities schematic ......................................................... 69

3.33 Schematic of AquaDAF process ....................................................................................... 70

3.34 Schematic of DensaDeg process ....................................................................................... 71

3.35 AquaDAF pilot (trailer in background) and DensaDeg pilot (blue skid next to car)and full-scale SFBW equalization basins during May 2007 testing in Ohio .............. 71

3.36 Float solids collected in AquaDAF pilot during May 2007 testing in Ohio ..................... 72

3.37 Impact of AquaDAF rate on turbidity during May 2007 testing in Ohio ......................... 75

3.38 Impact of AquaDAF rate on particle count during May 2007 testing in Ohio ................. 75

3.39 Impact of polymer dose and flocculation time on AquaDAF turbidity during May 2007 ...... 76



16/220

xiv | Innovative Applications of Treatment Processes for Spent Filter Backwash

3.40 Impact of polymer dose on AquaDAF turbidity at 5.7 min flocculation timeand 14 gpm/ft 2 clarification rate during May 2007 ..................................................... 76

3.41 Impact of polymer dose on AquaDAF turbidity at 11.3 min flocculation timeand 14 gpm/ft 2 clarification rate during May 2007 ..................................................... 77

3.42 Impact of DAF recycle on AquaDAF turbidity during May 2007 testing in Ohio ........... 77

3.43 Impact of flocculation time on AquaDAF turbidity during May 2007 testingin Ohio ................................................................................................................... 78

3.44 Impact of static mix on AquaDAF turbidity during May 2007 testing in Ohio ............... 78

3.45 Impact of rate on DensaDeg performance during May 2007 in Ohio .............................. 81

3.46 Impact of DensaDeg rate on turbidity during May 2007 testing in Ohio ......................... 81

3.47 Impact of DensaDeg rate on particle count during May 2007 testing in Ohio ................. 82

3.48 Impact of polymer dose on DensaDeg turbidity during May 2007 testing in Ohio ......... 82

3.49 Impact of clarification rate on turbidity removal using ClariDAF duringSeptember 2007 .......................................................................................................... 88

3.50 Continuous operation (48 hours) under constant conditions at Morgan WTPusing ClariDAF ........................................................................................................... 88

4.1 Bench-scale membrane test apparatus schematic ............................................................. 95

4.2 Photos of bench-scale membrane test apparatus ............................................................... 96

4.3 Permeate turbidity, Koch tubular membrane, simulated SFBW ..................................... 100

4.4 Normalized specific flux, Koch tubular, 8 psi TMP, simulated SFBW ......................... 101

4.5 Permeate turbidity, CeraMem ceramic membrane ......................................................... 102

4.6 Normalized specific flux, CeraMem ceramic, 5.2 ft/s cross-flow velocity, simulatedSFBW ........................................................................................................................ 102

4.7 Normalized specific flux, CeraMem ceramic, dead-end mode, simulated SFBW ......... 103

4.8 Specific flux and permeate turbidity, Koch hollow fiber, simulated SFBW .................. 103

4.9 Flux through ceramic membrane treating simulated and Trap Falls SFBW .................. 105



17/220

Figures | xv

4.10 Ceramic membrane performance with changing influent water quality while treatingTrap Falls SFBW ...................................................................................................... 105

4.11 Feed (raw) and permeate (filtered) TOC, Fe, and Mn while treating Trap Falls SFBWwith ceramic membrane operated at constant pressure and decreasing flux ............ 106

4.12 Koch hollow fiber membrane permeate flux, simulated and Trap Falls SFBW ............. 107

4.13 Hollow-fiber membrane performance while treating Trap Falls SFBW ........................ 107

4.14 Raw and filtered TOC, Fe, and Mn while treating Trap Falls SFBW with hollow-fiber membrane operated at constant pressure and decreasing flux ......................... 108

4.15 Flux through tubular membrane treating simulated and Trap Falls SFBW .................... 109

4.16 Flux and specific flux for ceramic membrane filtration of Trap Falls and Lake

Gaillard SFBW at ~constant flux and increasing pressure ....................................... 110

4.17 Pressure and specific flux for ceramic membrane filtration of Trap Falls and LakeGaillard SFBW at ~constant flux and increasing pressure ....................................... 111

4.18 Flux and specific flux for hollow-fiber membrane filtration of Trap Falls and LakeGaillard SFBW at ~constant flux and increasing pressure ....................................... 112

4.19 Specific flux and TMP, Koch hollow-fiber membrane filtration of Trap Falls andLake Gaillard SFBW at ~constant flux and increasing pressure .............................. 112

4.20 Specific permeate flux and TMP, Koch tubular membrane, Lake Gaillard SFBW,constant flux ~140 gfd/ft 2 ......................................................................................... 113

A.1 Utah Valley WPP site plan ............................................................................................. 124

A.2 Utah Valley WPP process schematic .............................................................................. 125

A.3 Utah Valley WPP SFBW treatment facilities schematic ................................................ 126

A.4 Utah Valley WPP SFBW treatment facilities (WWW reclamation building) ................ 127

A.5 Number of filter backwash events per month at the Utah Valley WPP(October 2005 through September 2006) ................................................................. 129

A.6 ClariDAF schematic........................................................................................................ 129

A.7 ClariDAF pilot trailer at Utah Valley WPP in May 2007 ............................................... 130

A.8 ClariDAF pilot schematic ............................................................................................... 130



18/220

xvi | Innovative Applications of Treatment Processes for Spent Filter Backwash

A.9 Utah Valley WPP ClariDAF loading rates for SFBW .................................................... 131

A.10 Utah Valley WPP ClariDAF polymer impact on SFBW ................................................ 131

A.11 Utah Valley WPP SFBW ClariDAF facilities site plan .................................................. 132

A.12 Utah Valley WPP ClariDAF SFBW treatment system(two units at 2,000 gpm for redundancy) .................................................................. 133

A.13 Utah Valley WPP ClariDAF SFBW treatment system(two units at 2,000 gpm for redundancy) .................................................................. 134

A.14 CONTRAFAST schematic ............................................................................................. 135

A.15 Siemens pilot equipment used at Utah Valley WPP in July and August 2007 ............... 136

A.16 Utah Valley WPP CONTRAFAST loading rates for SFBW .......................................... 137

A.17 Utah Valley WPP CONTRAFAST polymer impact on SFBW...................................... 137

A.18 Utah Valley WPP SFBW CONTRAFAST facilities site plan........................................ 138

A.19 Utah Valley WPP CONTRAFAST SFBW treatment system(two units at 2,000 gpm for redundancy) .................................................................. 139

A.20 Utah Valley WPP CONTRAFAST SFBW treatment system(two units at 2,000 gpm for redundancy) .................................................................. 140

A.21 Trident HSC schematic ................................................................................................... 141

A.22 Trident HSC process schematic ...................................................................................... 142

A.23 Impact of Trident HSC clarification rate on SFBW treated turbidity ............................. 144

A.24 Impact of polymer dose on Trident HSC treated turbidity ............................................. 144

A.25 Utah Valley WPP SFBW Trident HSC facilities site plan ............................................. 145

A.26 Utah Valley WPP Trident HSC 2,100 gpm system ........................................................ 146

A.27 Utah Valley WPP Trident HSC 2,100 gpm system P&ID.............................................. 147

B.1 Morgan WTP process schematic .................................................................................... 152

B.2 Morgan WTP facilities site plan ..................................................................................... 153



19/220

Figures | xvii

B.3 Morgan WTP SFBW treatment facilities site plan ......................................................... 153

B.4 Morgan WTP SFBW treatment facilities schematic ....................................................... 154

B.5 Morgan WTP SFBW full scale clarifier testing .............................................................. 154

B.6 Morgan WTP SFBW production during 24-hour period assuming 55 mgd productionrate, three recycle rates (3, 5, and 10 percent), and 28 filter backwash events perday (0.26 MG per backwash event) .......................................................................... 157

B.7 Required SFBW equalization assuming 55 mgd production rate, three recycle rates(3, 5, and 10 percent), and nine filter backwash events per day (0.26 MG perbackwash event) ........................................................................................................ 157

B.8 Morgan SFBW schematic with new EQ and new SFBW treatment system .................. 159

B.9 Morgan WTP SFBW new EQ siteplan ........................................................................... 159

B.10 ClariDAF schematic........................................................................................................ 161

B.11 ClariDAF pilot schematic ............................................................................................... 161

B.12 Morgan WTP SFBW ClariDAF system plan view ......................................................... 164

B.13 Morgan WTP SFBW ClariDAF system profile view ..................................................... 165

B.14 AquaDAF schematic ....................................................................................................... 166

B.15 Impact of AquaDAF loading rates on SFBW turbidity at Morgan WTP ....................... 167

B.16 Impact of AquaDAF loading rates on SFBW particles at Morgan WTP ....................... 167

B.17 Morgan WTP SFBW AquaDAF system plan view ........................................................ 168

B.18 Morgan WTP SFBW AquaDAF system profile view .................................................... 169

B.19 Morgan WTP SFBW AquaDAF system P&ID .............................................................. 170

B.20 DensaDeg schematic ....................................................................................................... 172

B.21 Morgan WTP SFBW DensaDeg loading rate for SFBW ............................................... 173

B.22 Morgan WTP SFBW DensaDeg impact of polymer dose on SFBW ............................. 174

B.23 Morgan WTP SFBW DensaDeg 5,100 gpm system plan view ...................................... 175



20/220

xviii | Innovative Applications of Treatment Processes for Spent Filter Backwash

B.24 Morgan WTP SFBW DensaDeg 5,100 gpm system profile view .................................. 176

B.25 Morgan WTP SFBW DensaDeg 5,100 gpm system P&ID ............................................ 177

B.26 Morgan WTP SFBW DensaDeg system general arrangement ....................................... 178



21/220

xix

FOREWORD

The Water Research Foundation (Foundation) is a nonprofit corporation that is dedicatedto the implementation of a research effort to help utilities respond to regulatory requirements and

traditional high-priority concerns of the industry. The research agenda is developed through aprocess of consultation with subscribers and drinking water professionals. Under the umbrella of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projectsbased upon current and future needs, applicability, and past work; the recommendations areforwarded to the Board of Trustees for final selection. The Foundation also sponsors researchprojects through the unsolicited proposal process; the Collaborative Research, ResearchApplications, and Tailored Collaboration programs; and various joint research efforts withorganizations such as the U.S. Environmental Protection Agency, the U.S. Bureau of Reclamation, and the Association of California Water Agencies.

This publication is a result of one of these sponsored studies, and it is hoped that itsfindings will be applied in communities throughout the world. The following report serves not

only as a means of communicating the results of the water industry's centralized researchprogram but also as a tool to enlist the further support of the nonmember utilities and individuals.Projects are managed closely from their inception to the final report by the Foundation's

staff and large cadre of volunteers who willingly contribute their time and expertise. TheFoundation serves a planning and management function and awards contracts to otherinstitutions such as water utilities, universities, and engineering firms. The funding for thisresearch effort comes primarily from the Subscription Program, through which water utilitiessubscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufacturers subscribe based on their annual billings.The program offers a cost-effective and fair method for funding research in the public interest.

A broad spectrum of water supply issues is addressed by the Foundation's research

agenda: resources, treatment and operations, distribution and storage, water quality and analysis,toxicology, economics, and management. The ultimate purpose of the coordinated effort is toassist water suppliers to provide the highest possible quality of water economically and reliably.The true benefits are realized when the results are implemented at the utility level. TheFoundation's trustees are pleased to offer this publication as a contribution toward that end.

David Rager, P.E. Robert C. Renner, P.E.Chair, Board of Trustees Executive Director

Water Research Foundation Water Research Foundation



22/220



23/220

xxi

ACKNOWLEDGMENTS

The authors would like to thank City of Cleveland Division of Water and the CentralUtah Water Conservancy District for providing staff, logistical support, and other assistance

during pilot studies at their facilities in Spring and Summer of 2007. The City of Cleveland alsoprovided a cash contribution of $20,000 to the project. The City of Boulder contributed similarstaff time and logistical support during full-scale testing of DAF for SFBW treatment at one of their facilities. Two other utilities listed below (South Central Connecticut Regional WaterAuthority and Passaic Valley Water Commission) provided full-scale data from evaluations of plate or tube settlers for SFBW treatment at their facilities. Utility staff providing direction andsupport for these activities at each of these utilities are listed below:

City of Cleveland, Division of Water, Morgan Water Treatment Plant, Cleveland,OH Maggie Rodgers, Tyrone Butler, Bob Mehota, and Dr. Edwin Guasp

Central Utah Water Conservancy District, Utah Valley Water Purification Plant,

Orem, UT David Hardy and Monica Hoyt City of Boulder, Betasso Water Treatment Plant, Boulder, CO Suzanne Givler andRandy Crittenden

South Central Connecticut Regional Water Authority, New Haven, CT Passaic Valley Water Commission, Clifton, NJ Santa Fe Irrigation District, Rancho Santa Fe , CA - Cor Shaffer Aquarion Water Company, Monroe, CT

Infilco-Degremont (IDI), ITT WWW Leopold (Leopold), and Siemens WaterTechnologies provided equipment and staff, and other logistical support for pilot studiesconducted during this project at the Cleveland, OH and Orem, UT locations listed above. These

three manufacturers also provided staff time to provide information used to develop drawingsand cost estimates for the tested high-rate processes. Pilot test reports were provided by I.Kruger, Inc. (Actiflo), Leopold (standard-rate DAF), and Infilco-Degremont (DensaDeg). Bench-scale membrane modules were provided by Koch Membrane Systems and CeraMem Corporation(purchased in April 2008 by Veolia Water Solutions, now part of HPD Membrane TechnologyCenter). Manufacturer support was provided by the following:

IDI, Richmond, VA Dr. Robert Kelly Leopold, Zelienople, PA James Farmerie and Christopher Falbo Siemens Water Technologies, Ames, IA - Rohan Wikramanayake Koch, Wilmington, MA, Brian Kilcullen

CeraMem, Waltham, MA, Dr. Bruce BishopThe Foundation Project Manager for this project was Hsiao-wen Chen. Members of the

Foundation project advisory committee (PAC) reviewing project findings include David Hardy(Central Utah Water Conservancy District), Abhay Tadwalkar (City of Toronto, ON), and JoeNattress (CH2M HILL).



24/220

xxii | Innovative Applications of Treatment Processes for Spent Filter Backwash

EE&T staff, in addition to authors, included Nick Pizzi (coordination and oversightduring testing in Cleveland), Venkat Balasubramanian (data evaluation and oversight of testingin Utah), Timothy Natoli (data evaluation, report preparation, and webtool development), andWilliam Cornwell (webtool development and programming). Studies at the University of Massachusetts were conducted by Kenneth Mercer and Hai Anh Nguyen, under the direction of

Dr. Tobiason, in Amherst, MA.



25/220

xxiii

EXECUTIVE SUMMARY

INTRODUCTION

The report includes a description of options available for spent filter backwash (SFBW)treatment, including a discussion of characteristics and performance of some of these alternativeprocesses. The project was particularly designed to evaluate high rate treatment processes thatgenerally require smaller footprints than conventional settling. The information available prior tothis project was limited to gravity clarification processes (quiescent settling, with or withouttubes and plates) and some standard-rate dissolved air flotation (DAF) studies (defined in thisreport as DAF processes with rates


26/220

xxiv | Innovative Applications of Treatment Processes for Spent Filter Backwash

summer 2007. Findings included evaluations of the impacts of clarification rate, polymer typeand dose, initial mix and flocculation, and internal recycle rate (when appropriate) on high-rateSFBW treatment processes. Evaluations at two drinking water plants included comparison of cost and footprint requirement estimated for the high-rate processes pilot tested at these locationsAlthough each manufacturer expresses clarification rate a little differently, typically loading rates

are based on the relative clarification area. In this report the rate is also expressed relative to thetotal footprint required to implement the process, including the area for flocculation, chemicalfeed, and other ancillary facilities. The Appendices to the report include preliminary designreports discussing details regarding costs and footprint for the two facilities where pilot studieswere conducted.

Another focus of this report was to evaluate membrane treatment alternatives for SFBWin bench-scale studies. Membrane technologies evaluated included low pressure MF/UF types,such as hollow fiber membranes, tubular membranes, and ceramic membranes.

SFBW TREATMENT ALTERNATIVES

SFBW treatment alternatives discussed in this report include the following: (a) low-rate(i.e., standard) quiescent gravity settling (e.g., standard clarifiers, lagoons, stilling basins, andother processes involving gravity settling in quiescent basins), (b) plate (lamella) or tube settlers,(c) standard-rate DAF (4 to 6 gpm/ft 2). (d) high-rate DAF (up to 18 gpm/ft 2), (e) high-rate solidscontact clarification processes (including process tradenames DensaDeg, CONTRAFAST,Trident HSC, and Actiflodiscussed in more detail in report), and (f) membranes. The first twoof these alternatives have already been addressed in previous studies (e.g., Cornwell et al. 2001),and so new information in this report is limited to some data collection from existing full-scalegravity clarifiers containing tubes or plates. The other processes are discussed in more detail inthis report including: (1) a literature review of existing pilot study reports for standard rate DAFand two high-rate solids contact processes, (2) data from full-scale DAF used for SFBWtreatment, (3) pilot-scale evaluations plus cost and footprint estimates for new or retrofittedfacilities at two drinking water plants, and (4) bench-scale data on membranes.

PERFORMANCE OF ALTERNATIVE TECHNOLOGIES FOR SFBW TREATMENT

Findings regarding effectiveness of different alternative treatment technologies, exceptmembranes (which are discussed later), summarized below are based on the review of data fromexisting pilot-scale studies and new full-and pilot-scale studies conducted as part of this project.Processes performance objectives included the reduction of the 95 th percentile turbidity to


27/220

Table ES.1Summary of SFBW treatment results discussed in this report

City State Year

Medianuntreatedturbidity

(ntu)

Clarificationrate

(gpm/ft2

)

Residualsconcentration

(percent solids)

Information

source

Polym

neededStandard-rate DAFDurham NC 1999 100 up to 5 3.5 mfr records yes Boulder CO 1999 10 up to 7 3.5 mfr records yes Phoenix AZ 2000 not reported up to 6 4 to 6 mfr records *

Cleveland OH 2000 20 up to 6 2 to 3 mfr records yes Boulder CO 2007 10 up to 3 up to 3 this study yes

High-rate DAFOrem UT 2007 100 12 4.4 this study yes

Cleveland OH 2007 20 16 3 this study yes Cleveland OH 2007 20 15 3.6 this study yes

Sand-ballasted coagulation/clarificationModesto CA 2005 20 up to 30 Not reported mfr records

Tempe AZ 1997 10 up to 20 Not reported mfr records

W. Creek CA 1997 100 up to 20 0.45 mfr records

Solids contact + tubesW. Nyack NJ 2005 ~50 ~12 2 to 3 mfr records

Oradell NJ 2005 ~50 ~12 2 to 3 mfr records

Orem UT 2007 100 12 >5 this study yes Cleveland OH 2007 20 16 3 this study yes

TubesOrem UT 2007 100 0.45 ~0.5 this study

Orem UT 2007 100 0.92 ~0.5 this study

Tubes + upflow buoyant mediaOrem UT 2007 100 18 ~0.3 this study yes

*Ok without polymer, but more stable with polymerImpact of treatment without flocculation and without polymer not reported

2 0 1 0 Wat er R es ear c h F ound at i on.A L L R I GH T S R E S E R V E D


28/220

xxvi | Innovative Applications of Treatment Processes for Spent Filter Backwash

A summary of these findings include the following (see also Table ES.1 ):

Polymer type and dose With rare exceptions, testing showed that SFBW treatment processes generally

did not work when no polymer was present, and yet significantly improved

performance could be demonstrated with addition of appropriate polymers. Evenin the few cases when the above turbidity performance objectives could beachieved without polymer, the processes always worked better when an optimalpolymer dose was used.

Cationic polymer was often demonstrated to be optimal, but this was not alwaysthe case. Consequently, optimal polymer for any location is site specific and thebest course of action when evaluating treatment is to evaluate a number of different polymer types.

Optimal polymer dose was typically


29/220

Executive Summary | xxvii

solids contact or flocculation area needed to process the water prior toclarification, nor accounting for ancillary processes such as chemical feed).

Acceptable performance was typically demonstrated with standard-rate DAF atrates up to 4 to 6 gpm/ft 2. For high-rate DAF and solids contact processes (likeDensaDeg and CONTRAFAST) it was typically about 15 gpm/ft 2 or higher.

Clarification rates listed for sand-ballasted coagulation systems were typically>20 gpm/ft 2. When taking into account total footprint (including chemical feed, flocculation,

and other ancillary equipment), and not just the clarification area as in the ratesexpressed above, the clarification rates for the three high-rate solids contact andtwo high-rate DAF processes evaluated in the pilot studies was about 1 gpm/ft 2,ranging from 0.8 to 1.5 gpm/ft 2 (see Appendices A and B). Cost and footprintestimates for standard-rate DAF, sand-ballasted coagulation, and other processeswere not developed during this project, so it was not possible to compareclarification rates calculated in a similar manner to the above high-rate processes.

Removal of particulates, turbidity, and other solids in untreated SFBW

Optimal conditions for each process were able to achieve desired objectives forturbidity (median of continuous data or steady-state grab samples


30/220

xxviii | Innovative Applications of Treatment Processes for Spent Filter Backwash

Robustness of SFBW treatment alternatives Some of the high-rate solids contact and DAF processes appear to be more able to

resist spikes in flow and particulate content than are lower rate processes. SFBW treatment performance is typically more sensitive to fluctuations in

particulate content than to fluctuations in flow rate.

Mixing of equalization basins can improve robustness of SFBW treatmentprocesses. Solids can settle out in unmixed or poorly mixed equalization basins.Subsequent backwash events stir up these settled solids, creating short-termspikes in particulate concentrations leaving the equalization basins and enteringSFBW treatment. As noted above, SFBW is sensitive to fluctuations in influentparticulate content. Therefore, not only is equalization of flow important, butequalization of particulates and other contaminants is also an importantconsideration. The latter can best be addressed by providing adequate mixing inthe equalization basins.

At some locations using some processes, SFBW treatment without polymer couldachieve acceptable performance, but this performance was not as robust with

respect to flow and particulate concentration fluctuations as when optimalpolymer doses were used.

The results of bench-scale studies of SFBW treatment using three types of low pressuremembranes (tubular, ceramic, hollow fiber) lead to the following main conclusions:

Treatment of SFBW at high specific permeate flux rates of 10 to 200 gfd/psi usingeither hollow fiber or ceramic membranes appears technically feasible. Pilot-scaletesting is needed to reach a firm conclusion.

Although SFBW has a relatively high solids level, it does not appear necessary to usea large bore (i.e., 1 cm) tubular membrane such as tested in this study for treatment of

SFBW. The inherent lower pore size (resulting in higher transmembrane pressure(TMP) for a desired flux) and lower membrane surface area per volume or area of theoverall membrane system make this type of membrane less likely to be selected ascompared to the other types tested, despite being technically feasible to utilize.

Utilization of continuous cross-flow decreased the rate of flux decline for constantpressure filtration of simulated SFBW compared to dead-end filtration yet did noteliminate the need for periodic backflushing to maintain a desired permeate flux;however the specific permeate production prior to backflushing may be relativelyhigh, in the range of 5 to 15 gal/ft 2 of membrane.

SFBW quality is likely to have a significant impact on membrane performance, sosite-specific pilot testing is needed. Type of coagulant(s), organic matter levels, metal

(Fe, Al) content, pH, solids concentration, and prior SFBW processing (storage,pumping) may all be important. Due to the very high quality of the permeate from membrane treatment of SFBW,

selection of membrane treatment of SFBW may be desirable for utilities withpathogen impacted source waters that need or choose to recycle SFBW to the head of the treatment plant.



31/220

Executive Summary | xxix

It is important to note that the membranes in this study were small modules, oftenoperated at constant TMP, very high specific flux levels (10 to 200 gfd/psi), at high throughputprior to backflush (5 to 20 gal/ft 2) as compared to conventional dead-end, recirculation or singlepass mode MF/UF treatment of surface waters (typically 2 to 8 gfd/psi specific flux and only 0.5to 2 gal/ft 2 prior to backflush). Operation at somewhat lower fluxes, yet still high in comparison

to typical dead-end or recirculation operation, may provide even better performance. Thepreliminary results of this work indicate potential promise for very high flux, low footprint,membrane processes for SFBW treatment prior to recycle.

Ultimately, the best choice for SFBW treatment will include considerations of size, costand the mode of operation of a process. Energy costs in terms of pressure required will becomemore important in the future. Cleaning costs and membrane replacement costs are two other costconsiderations that affect selection of membrane treatment of SFBW. Key aspects of membraneoperation that should be considered include the specific flux rate (i.e., the pressure normalizedflux rate) and the specific throughput (i.e. the surface area normalized flux rate). Measures of performance should include filtrate quality, TMP and fouling, as well as recovery afterbackflushing and cleaning procedures to control membrane fouling (reversible and irreversible).

UTILITY RECOMMENDATIONS

The following observations and information items are provided for utilities wishing toevaluate SFBW treatment, including high-rate treatment options, for their facilities:

Equalization

Equalization will reduce the hydraulic impact of recycle return to the main process, plusit will improve performance of any SFBW treatment systems utilized prior to recycle.Furthermore, equalization will minimize the size of any SFBW treatment needed, therebyminimizing the cost of the SFBW treatment facilities. Equalization basins must be designed withsufficient mixing to keep solids from settling out in the equalization basin. The only exception tothis is for large plants with many filters such that the instantaneous backwash flow is low relativeto the influent flow. Still a small mixed equalization basin will reduce slug particulate loading toa treatment device.

Pre-Treatment

Polymer addition and provision of sufficient flocculation time are often necessary forachievement of desired performance in high rate SFBW treatment systems. In some instances,performance objectives can be met without adding polymer or without providing anyflocculation prior to clarification, although even in these cases high rate clarification processesperform better when polymer addition and sufficient flocculation time are provided.Furthermore, even though all SFBW clarification processes evaluated were sensitive tofluctuations, especially spikes in the amount of particulate material in the incoming untreatedSFBW, the use of proper polymer at optimal dose, and allowance for sufficient flocculation time,made SFBW treatment processes more robust with respect to these fluctuations. As in otherprocesses involving chemical addition, if polymer is added then it is also important to providesufficient rapid mix.



32/220

xxx | Innovative Applications of Treatment Processes for Spent Filter Backwash

Performance Criteria

Each utility needs to set its treatment objective for the treated water quality whether thewater is to be recycled or discharged. For discharge situations the state will dictate the qualityrequirement. For a recycle situation one approach to SFBW treatment would be to reduce

contaminants, including particulate matter, to levels equal to or below levels in raw water atpoint of recycle return. In this way the recycle cannot increase contaminants entering the plantabove that initially present in the raw water. Reducing some contaminants like manganese tolevels below raw water levels can require the production of a very low turbidity water.

Area Requirements

Lower-rate clarification processes (e.g., quiescent gravity settling as described in thisreport) for SFBW treatment need to include sufficient surface area to produce surface loadingrates low enough to reliably achieve the treatment objectives. Furthermore, additional area forchemical addition and flocculation could be needed in some instances to properly prepare the

SFBW prior to clarification. It may not be possible to obtain enough area at space-limited sites tomeet treatment objectives using the lower rate processes. Consequently, high-rate processes withsmaller footprint (like those discussed in this report) may need to be evaluated.

Retrofitting

If existing SFBW treatment facilities are undersized either under current conditions orunder conditions projected after a planned expansion of filtration capacity, it may be possible toretrofit components of high-rate processes to replace existing lower rate processes, therebyproviding sufficient treatment capacity to reliably treat more SFBW without requiring more areaat space-limited sites. Appendix B includes examples of high-rate processes retrofitted into spaceoccupied by existing lower rate SFBW treatment processes.

Residuals Handling

Some of the SFBW clarification processes evaluated (standard- and high-rate DAF, solidscontact clarification with solids recycle) produced residuals with 3 to 5 percent solidsconcentration, or higher, under conditions tested. These residuals may not need furtherthickening prior to dewatering. Other low- and high-rate processes evaluated (quiescent gravitysettling with or without plates or tubes, sand ballasted coagulation, upflow clarification in a bedof buoyant media) produced residuals that are typically 0.3 percent solids concentration or lower,and rarely exceed 1 percent solids concentration under most conditions. These residuals willprobably need some thickening prior to dewatering. Consequently, utilities without existingSFBW treatment who plan to install systems producing the less concentrated residuals will notonly have to provide sufficient area for the processes themselves (including equalization,chemical addition, flocculation, and clarification), but may also need to install thickeningfacilities or expand existing thickening capacity.



33/220

Executive Summary | xxxi

Pilot Testing

Pilot testing of low- or high-rate clarification processes is strongly encouraged in orderfor a utility to evaluate site specific conditions on performance of different alternative treatmenttechnologies. Piloting is not only important to evaluate the clarification technology itself, but

also to evaluate chemical addition and flocculation conditions preparing the SFBW prior toclarification.

Additional Information

Water Research Foundation subscribing utilities are also encouraged to review thewebtool produced for this project in order to find additional information to help in their efforts toevaluate SFBW treatment alternatives. The webtool includes example drawings for differentfacility sizes using the technologies evaluated in this project, as well as a calculation tool toestimate facility cost and footprint for different sizes of high-rate clarification facilities. Thewebtool is available at the following link:

http://www.waterresearchfoundation.org/research/TopicsAndProjects/resources.aspx?type=WebTool



34/220



35/220

1

CHAPTER 1BACKGROUND

The driving force for installation of SFBW treatment systems is often attributed to the

USEPA Filter Backwash Recycle Rule (FBRR). However, the FBRR does not mandate SFBWtreatment prior to recycle. Rather, there are two other drivers for SFBW treatment. One of themajor driving forces for utilities to increase the efficiency of existing SFBW treatment or to installnew treatment is a proactive concern over process or water quality impacts associated with recycle.According to previous survey studies (Cornwell et al. 2001, Cornwell 1998) about 45 percent of the plants practicing recycle do not have SFBW treatment for solids removal. While in many casesutilities can successfully meet water quality goals without treatment of recycled SFBW, others arefinding that more stringent goals and regulations are making it economically desirable to evaluateSFBW treatment. Previous research (Cornwell and Lee 1993, Cornwell et al. 2001) has shown thatuntreated SFBW can contain elevated levels of Giardia , Cryptosporidium, TOC, DBPs, DBPprecursors, and manganese. These research efforts have also shown that removal of solids from

SFBW, if efficient enough, eliminates most of the contaminant carryover (particularly, in the caseof manganese, if solubilization can be prevented).

A second driver for utilities to install SFBW treatment may well result from the newNPDES guidelines being developed by USEPA. These guidelines will be the first time thatUSEPA has addressed the discharge of water plant residuals, though some states already have suchrequirements in place. These rules could require treatment where none exists (such as the recentconsent order between USEPA and the US Army Corps of Engineers for the Washington, DCtreatment plants) or additional efficiencies in treatment to meet the new discharge guidelines.

Some information is known about the emphasis of this projectinnovative/high-ratetreatment processesbut enough critical performance and cost data were not available prior to thisproject to allow for ease of evaluation and implementation by utilities.

CHARACTERISTICS OF SFBW

Quantity

Important considerations, particularly when SFBW is recycled, include understanding boththe quantity and quality of the SFBW. The amount of water used for backwash, and the frequencyand duration of backwash events producing the SFBW, are important in sizing equalization andtreatment facilities. Furthermore, quantification of SFBW is also important to evaluate the potentialhydraulic impact on the main process stream when SFBW is recycled. If SFBW recycle is notcurrently used, an understanding of the quantities of backwash water involved indicates the

potential increased efficiency and increased production possible if the SFBW is recovered andrecycled. Utilities are often faced with the dilemma of finding enough source water of any kind tohandle all of their systems needs, particularly enough source water of suitable quality. Manyutilities have found that it is easier to recover and recycle SFBW, typically enough to representabout 5 percent of the plants filtered water production, than it is to find other new sources toprovide a comparable volume of water for their filter plant. Even when other alternative sourcesare potentially available, they may not be as easy to treat or as easy to access as the SFBW that theutility already has in its control (i.e., that it does not have to purchase or have public hearings or



36/220

2 | Innovative Applications of Treatment Processes for Spent Filter Backwash

environmental impact statements to obtain). Therefore, though this report focuses a great deal onthe necessary considerations for appropriate treatment of SFBW, the fundamentals of the treatmentprocesses involved are still fairly straightforward and generally focus on the separation of particlesfrom water, concepts that are well understood by most drinking water treatment practitioners.

When evaluating quantity of backwash generated it is important to evaluate seasonal

impacts on SFBW generation. For example, in colder weather, the system demand is often lowerand consequently a filtration plant may not need to operate as many filters, and those that are inservice may be operated at lower rates. Conversely, in summer many filtration plants often arerunning all filters at as high a rate as possible, consequently resulting in greater frequency of backwash events. In addition to increasing the frequency of backwash events the backwash ratemay also increase in order to properly fluidize the filter media. In order to achieve the same degreeof media fluidization, the backwash rate may need to be as much as 1/3 higher, or more, when thewater temperature is higher. For example, Figure 1.1 illustrates the required backwash ratepredicted for sand media with a density of 2.65 g/cm 3, an effective size (d 10) of 0.7 mm, and auniformity coefficient (d 60 /d10) of 1.51 using relationships developed by Wen and Yu (1966). Inthis example, the required rate at 5C is about 21 gpm/ft 2 and about 28 gpm/ft 2 at 20C, or an

increase in backwash rate by a factor of 1.33 from the colder water temperature.In 2001 (USEPA 2001), USEPA published federal requirements for recycle of SFBW andother residuals streams at drinking water treatment facilities in the Filter Backwash Recycle Rule(FBRR). This rule requires that recycle flows be returned to the front of the treatment process (e.g.,before coagulation). However, although the FBRR does not regulate the quantity of SFBW andother residuals streams that can be recycled, some individual states do have such limits. Therecommended recycle limit for utilities that volunteer to follow Partnership for Safe Waterguidelines is less than 5 percent, though utilities in the partnership can recycle more water if theycomplete studies verifying that a higher rate does not impact performance of main treatmentprocess. The literature recommends that recycle flows be limited to at most 10 percent of plantflow (USEPA 2001, Cornwell and Lee 1993).

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30

Temperature (C)

B a c

k w a s

h R a t e R e q u

i r e

d f o r

F l u i d i z a

t i o n

( g p m

/ f t 2 )

Figure 1.1 Predicted backwash rate as a function of temperature



37/220

Chapter 1: Background | 3

Quality (Composition)

The principal issue with respect to SFBW composition that is most often of concern fortreatment and recycle of SFBW is particulate content. This is reflected in total solids (TS) andtotal suspended solids (TSS) content of the SFBW. Measurements for TS and TSS require

collection of samples and heating samples to drive off water to determine the amount of dry solidmaterial present. This requires heating for several hours in a drying oven, or perhaps a fewminutes in a moisture balance. In any event, these measurements do not provide on-linecontinuous data so on-line instruments such as particle counters and turbidimeters are used assurrogates for TS/TSS. Turbidimeters are suitable for monitoring turbidity in both treated anduntreated SFBW. However, particle counters can provide valuable information when used intreated SFBW. The large amount of particulate material in untreated SFBW generally does notallow reliable particle counting of untreated SFBW, and consequently, particle counters are notrecommended prior to treatment of SFBW.

Turbidity of untreated SFBW depends on the raw source water at the plant and the typeof treatment facility. In this project two facilities were selected for pilot studies that are believed

to represent the range of typical conditions found in US filtration plants, based on a previousstudy of SFBW conditions in US (Cornwell et al. 2001). One facility uses a raw water sourcefrom Lake Erie with little particulate content, treated in a filtration plant with clarification priorto filtration. In this case, much of the particulate material that is present in the raw water orproduced by the coagulant is removed in clarification, leaving much less material to be removedduring filter backwash. Direct filtration facilities, even though they are necessarily located onsources with low particulate content, have larger particulate content in SFBW than the aboveexample because all the solids in raw water are removed in filters, and consequently end up inSFBW. River sources, even if they have clarification prior to filtration, are expected to haveparticulate levels comparable to those observed at direct filtration plants. SFBW particulatelevels in the first example (raw water with low particulate content, treated with clarification priorto filtration) are about the lowest seen at filtration plants, about 20 ntu or TSS about 50 to 60mg/L. The high end of the spectrum, as would be expected in clarification plus filtration plantson river sources or direct filtration plants on any source could have turbidity about 200 ntu andseveral hundred mg/L for TSS and TS.

Other contaminants of concern include: (a) regulated and non-regulated microbialcontaminants (e.g., Cryptosporidium , Giardia , algae), (b) manganese, (c) iron and other tracemetals, (d) DBP precursor and other organic material, (e) regulated and non-regulated DBPs, (f)color/taste/odor-causing substances, and (g) filter media (due to excessive media fluidization).Most of these contaminants can be removed by the SFBW treatment processes described in thisreport, particularly contaminants composed of or sorbed onto particulate material, since SFBWtreatment processes specifically target particulate material. However, these processes do not doas well and are not targeted at removal of dissolved and soluble contaminants. Particulate metalsand organic matter can be removed by most SFBW treatment processes, including thosedescribed in this report, but dissolved contaminants will remain in the treated SFBW recycled tothe main plant.

One issue for facilities with manganese in raw water, or with manganese added as a tracecontaminant in metal-salt coagulants or other treatment chemicals, is that solid materialcontaining particulate manganese (either originating in particulate forms in the raw water orproduced when soluble manganese is converted to insoluble forms due to oxidation during the



38/220


preceding treatment processes) is collected in the clarification basins or in the filters prior tobackwash. If the manganese-containing solids are not removed quickly enough and if reducingconditions develop in the filters or clarification basins, then the collected solid manganese maybe converted to more soluble forms due to reducing conditions, thereby allowing soluble reducedmanganese to pass through the filters and end up in the finished water. In this instance, the

manganese can re-settle out in the distribution system or in customer plumbing fixtures when thereduced manganese is later oxidized.

OPTIONS FOR SFBW TREATMENT

There are several poss ible innov ative high-rate processes that could be considered forSFBW treatment as shown in Table 1.1 . These will be briefly described below. Note that rateslisted are relative to clarification area, but these processes may have different total footprintimpacts (e.g., additional space if flocculation or air saturators are required, for example, or if solidsproduced require additional thickening prior to dewatering). These total footprint impacts aredescribed in more detail later. The discussion below describes different options for SFBW

treatment, starting with equalization and then comparing different particle separation alternatives.Table 1.1

High-rate SFBW treatment options

TypeClarification rate

(gpm/ft 2)

Plate/tube settler (surface) 1 2Standard dissolved air flotation (DAF) 4 6High-rate DAF 12 18High rate clarifiers (e.g., Trident HSC/DensaDeg/CONTRAFAST) 8 10

Sand ballast (e.g., Actiflo) 15 30

Equalization (With or Without SFBW Treatment)

Due to the nature of backwash operations, SFBW is generated sporadically.Consequently, even without SFBW treatment, flow equalization prior to recycle to the mainprocess is desirable in order to avoid contributing flow surges which could disrupt the mainfiltration process. Flow equalization becomes essential if SFBW treatment is involved prior torecycle. This was investigated in Cornwell et al. (2001). Therefore, while flow equalization is nottreatment per se, application of proper flow equalization is recommended, if not essential,preparatory process prior to recycle to the main treatment system or prior to SFBW treatmentpreceding recycle. In particular, in the latter case when SFBW treatment is used, equalizationprovides the additional benefit of minimizing the size of SFBW treatment facilities needed,thereby minimizing cost of these treatment processes as well.

Furthermore, in addition to equalization of flow, equalization of particulates andcontaminants is also important prior to recycle. Without mixing in equalization basins,particulate material can settle out in the basin. If this particulate material builds up then each



39/220


succeeding backwash event can stir up this settled material and it can create sporadic spikes of particulate content in the equalized SFBW flow leaving the basin. Consequently, a SFBWequalization basin not only needs to function to reduce hydraulic spikes, it also needs to reduceor eliminate fluctuations of particulates and other contaminants. This latter function can best beachieved by keeping equalization basins well mixed. The case studies described in this report

include instances where temporary mixing was provided to existing basins that do not havepermanent mixing. Some of these temporary mixing facilities did not function sufficiently wellto normalize contaminant spikes. However, permanent mixing facilities can be designed andoperated to function more satisfactorily.

Low-Rate (Standard) Quiescent Gravity Settling

Treatment processes for SFBW include standard clarifiers, lagoons, stilling basins, andother processes involving gravity settling in quiescent basins. These are generally simple andstraightforward to operate, particularly for utilities that already use standard clarification basinsin the main process prior to filtration. These have lower loading rates and consequently require a

larger footprint to operate effectively compared to the higher rate processes that are the subjectof this report.Deficiencies in existing standard quiescent gravity settling facilities, or factors that

need to be incorporated into optimized versions of new facilities to evaluate in comparison tohigh-rate processes, include the following factors:

1. Settling AreaThe surface loading rate for properly operating quiescent settlingfacilities should be 0.2 gpm/ft 2 or lower in the main process. However, since SFBWtreatment requirements are less severe, a somewhat higher rate could be tolerated forSFBW clarification. Nevertheless, even allowing for the possibility of higher rates atSFBW clarifiers, many existing SFBW clarification processes are operated at too higha rate, and consequently achieve poorer performance than they otherwise could.Therefore, in order to improve the quality of treated SFBW, many treatment plantsmay need to operate at a lower rate and add more clarification area. Alternatively,space-limited locations that can not add more clarification area could convert to oneof the higher rate clarification processes discussed in this report.

2. FlocculationFlocculation would improve clarification, but may existing facilitiesgenerally do not have them.

3. Chemical AdditionSFBW has routinely been coagulated, particularly with respectto charge neutralization, and consequently does not often require addition of metalsalts during treatment. However, polymer addition often is highly desirable, and mayeven be essential to make SFBW clarification processes function satisfactorily.Polymer addition can typically allow smaller settling area than without polymer (i.e.,higher clarification rates). Many existing processes may not incorporate polymeraddition. Processes with polymer addition will also need to provide appropriate staticor flash mixing.

4. EqualizationExisting facilities may not incorporate equalization, or if they do theydo not incorporate mixed equalization. However, proper equalization is typicallyessential for optimized SFBW treatment using any process (see previous discussion).



40/220


5. Operator AttentionUtilities may be able to get better performance from any processwith greater level of operator attention. However, in many cases utilities may make atrade-off and decide that they are willing to accept below optimal performance if theprocess can be left to function with less operator attention.

Consequently, realistic assumptions about the above factors for lower rate alternativesmay need to be incorporated in order to make appropriate comparisons with some of the higherrate processes described in this report. Another important factor to note when comparing the highrate processes discussed in this report versus new or existing lower rate processes is that thehigher rate processes may incorporate more capacity to respond to particulate or flow ratespiking than lower rate processes, especially existing ones.

Plate (Lamella) or Tube Settlers

Plate (lamella) or tube settlers also remove particulate matter via conventional gravitysedimentation. However, these devices significantly reduce the distance required for particulate

matter to settle out, which reduces the minimum time required for particle collection andconsequently these devices can be operated at apparent surface overflow rates that are severaltimes higher than the lower rate conventional gravity settling basins described above. There are anumber of facilities in the US employing these devices for SFBW treatment, including threeutility participants in this project (Central Utah Water Conservancy District, Passaic ValleyWater Commission, and South Central Connecticut Regional Water Authority). Full-scale datafrom these facilities were collected during this project, as well as pilot-scale data from the tubemodule of a high-rate processes piloted in Utah (see later discussion). Since plate and tubesettlers are widely used and have been reported in the literature (e.g., Cornwell et al. 2001),further pilot studies were not considered necessary for this project.

The surface loading rate for these processes is typically expressed relative to the area of basin, but do not take into account the total impact on plant footprint due to flocculation,chemical feed, etc. In addition, since the solids produced by these and the lower rate processesare typically limited to 0.3 percent or lower, adding these processes for SFBW treatment mayconsequently require additional thickening capacity, or may use up more of the plants existingthickening capacity.

Dissolved Air Flotation

Dissolved air flotation (DAF) is certainly a high-rate process even in the traditionalclarification rate range of 4 to 6 gpm/ft 2 (called standard-rate DAF in this report). Four pilotstudies investigating standard-rate DAF for SFBW treatment were conducted prior to this projectand are described in this report using information provided by the manufacturer, plus additionaldata from two of these studies supervised by members of the project team. In addition, one of these four pilot study sites installed a full-scale DAF plant for SFBW (Boulder, CO). Full-scalestudies at this facility were conducted during this project and are described in this report.However, prior to this study there were no pilot- or full-scale data on the use of high-rate DAFprocesses (capable of operating up to 18 gpm/ft 2), and so high-rate DAF was evaluated at twotest sites during this project using pilot facilities supplied by two different manufacturers (seeChapter 3). As in other high-rate processes discussed below, the manufacturer expresses rates



41/220


relative to clarification area, but in this report the total footprint impact will be evaluated anddiscussed, including area required for flocculation, chemical addition, air saturation, etc.Available data from both standard- and high-rate DAF processes indicate that solids produced bythese processes are on the order of 3 to 5 percent solids, meaning solids may be able to go directto dewatering without having to undergo further thickening.

High-Rate Solids Contact Clarification Processes

A group of technologies that are described here as high-rate solids contact clarifiers havehad limited reported use for SFBW treatment in US. Four different solids contact clarifiers arediscussed in this report regarding their potential for SFBW treatment. The DensaDeg processmanufactured by Infilco-Degremont, Inc. (IDI, Richmond, VA) and the CONTRAFAST processmanufactured by Siemens Water Technologies (Ames, IA) are similar to one another and slightlydifferent from the other two. The DensaDeg and CONTRAFAST processes both involve internaland external recirculation of solids originating in the untreated water. Untreated water andtreatment chemicals first enter a mixed solids contact module, followed by a gravity clarification

module using tubes. Clarified water passes through the tubes and a portion of the solids collectedin the clarification module are recirculated to the solids contact module. Loading rates cited bythe manufacturer typically are expressed relative to the surface area of clarification, but do nottake into account total footprint. This report discusses findings relative to the clarification area,and also relative to total footprint. Solids produced from these processes are typically on theorder of 3 to 5 percent or perhaps higher. As with DAF, these solids may not need thickeningprior to dewatering, which is of course desirable and will reduce the net impact on plant footprintdue to adding one of these processes for SFBW treatment.

The Actiflo process manufactured by I. Krueger, Inc. (Cary, NC) is a sand ballastedflocculation/clarification system. This system has a flocculation stage, analogous to the contactstage described above, followed by a clarification step. The microsand added prior to theflocculation stage provides additional surfaces for collisions with particulate material inuntreated water and the resulting particulate and microsand floc create large, heavy particles thatsettle rapidly, allowing the clarification step to be operated at a high surface overflow rate. Acyclone separates the higher density microsand particles from other solids so the sand can berecycled. There are data available from three US Actiflo pilot studies. There is also one full-scalefacility in California designed to treat SFBW

^innovative applications of treatment processes for spent filter backwash

Documents