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PERFORMANCE STUDY ON DISSOLVED AIR FLOTATION (DAF) UNIT

AND PROCESS PERFORMANCE IMPROVEMENT STUDY IN THE PHYSICO-

CHEMICAL TREATMENT OF WASTEWATER

LEE SENG CHOW

A project report submitted in fulfillment of the

requirements for the award of the degree of

Master of Engineering

(Civil Wastewater Engineering)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

May 2007


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UNIVERSITI TEKNOLOGI MALAYSIA

BORANG PENGESAHAN STATUS TESIS

JUDUL : PERFORMANCE STUDY ON DISSOLVED AIR FLOTATION (DAF)

UNIT AND PROCESS PERFORMANCE IMPROVEMENT STUDY IN

THE PHYSICO-CHEMICAL TREATMENT OF WASTEWATER

SESI PENGAJIAN : 2006 / 2007 II

Saya

(HURUF BESAR)

mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan

Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:

1. Tesis adalah hakmilik Universiti Teknologi Malaysia.2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan

pengajian sahaja.3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi

pengajian tinggi.

4. ** Sila tanda ( )

SULIT (Mengandungi maklumat yang berdarjah keselamatan atau

kepentingan Malaysia seperti yang termaktud di dalam AKTA

RAHSIA RASMI 1972)

TERHAD (Mengandungi maklumat yang TERHAD yang telah ditentukanoleh organisasi/badan di mana penyelidikan dijalankan)

TIDAK TERHAD

Disahkan oleh

(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)

Alamat Tetap: NO. 67, JALAN 28,

DESA JAYA, KEPONG, PROF IR DR. MOHD. AZRAAI KASSIM

52100 KUALA LMPUR.. Nama Penyelia

Tarikh: 02 MAY 2007 Tarikh: 02 MAY 2007

CATATAN: * Potong yang tidak berkenaan.

** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi

berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai

SULIT atau TERHAD. Tesis dimaksudkan sebagai tesis bagi ijazah Doktor Falsafah dan Sarjana secara penyelidikan,

atau disertai bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek

Sarjana Muda (PSM).

LEE SENG CHOW


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I hereby declare that I have read this thesis and in

my opinion this thesis is sufficient in terms of scope and

quality for the award of the degree of Master of Engineering

(Civil- Wastewater Engineering)

Signature : ....................................................

Name of Supervisor : Prof. Ir. Dr. Mohd. Azraai Kassim

Date : 2nd May 2007


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I declare that this project report entitled Performance Study on Dissolved Air

Flotation (DAF) Unit and Process Performance Improvement Study in the Physico-

chemical Treatment of Wastewater is the result of my own research except as cited

in the references. The project report has not been accepted for any degree and is not

concurrently submitted in candidature of any other degree.

Signature : ....................................................

Name : Lee Seng Chow

Date : 2nd May 2007


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To my beloved parents and family


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ACKNOWLEDGEMENT

This study would not have been completed without the assistance and support

of those who guided me in the course of my masters project. In preparing this thesis,

I was in contact with many people, academicians and practitioners. They have

contributed towards my understanding and thoughts. In particular, I wish to express

my sincere appreciation to my honorable supervisor, Professor Ir. Dr. Mohd. Azraai

Kassim, for encouragement, support, guidance, critics and friendship. Without his

continued support and interest, this thesis would not have been the same as presented

here.

Secondly, I would like to extend my thankfulness to Universiti Teknologi

Malaysia (UTM) and librarians at UTM for their assistance in supplying the relevant

literatures.

My fellow postgraduate students should also be recognized for their support.

My sincere appreciation also extends to all my colleagues and others who have

provided assistance at various occasions. Their views and tips are useful indeed.

Unfortunately, it is not possible to list all of them in this limited space.

Lastly but not least, I am grateful to my family members for their love, care,

support and encouragement.


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ABSTRACT

From the time of the early 20th

century, Dissolved Air Flotation (DAF) had

been used in the separation process. In the DAF system, air is dissolved in the

wastewater under a pressure of several atmospheres, followed by release of the

pressure to the atmospheric level. In this case, the recycle flow system has been

studied. For this kind of system, a portion of the DAF effluent is being recycled,

pressurized and semi-saturated with air. The main study object is the DAF System in

HACO Asia Pacific Sdn. Bhd. In the first stage, process performance improvement

study was carried out to determine the most effective operating parameters and

conditions of the DAF. Then, a performance monitoring study was continued by

operating the DAF in the most effective and optimum condition. Samples were being

taken before and after the DAF treatment to determine its pollutant removal

efficiency. Results from the performance monitoring study showed that the DAF is

able to meet its original design specification of Total Suspended Solids (TSS)

removal efficiency up 85%-95%. At a later stage, an emerging design system known

as Band-pass Filter (BF) was brought in for a comparative performance study with

the DAF system. The BF is intended for mechanical filtering of wastewater in

situations where rejections of waste products in connection with processing plants

are required. To obtain optimum cleansing, the BF is tuned for the imminent

cleansing process. Results from the comparative performance study showed that the

BF can achieve a slightly higher average TSS and Chemical Oxygen Demand (COD)

removal efficiency, with 93.9% and 49.6% respectively. On the other hand, DAF can

achieve a slightly higher average Oil and Grease (O&G) removal efficiency up to

91.9%.


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ABSTRAK

Daripada abad kedua-puluhan, Dissolved Air Flotation (DAF) telah

digunakan dalam proses pengasingan. Di dalam sistem DAF, udara akan dilarutkan

dalam air sisa pada tekanan yang tertentu, diikuti dengan pembebasan tekanan udara

mengikuti tahap tekanan udara biasa. Di sini, sistem pengedaran pengaliran semula

akan dikaji. Bagi sistem ini, sebahagian air daripada rawatan DAF akan diedarkan

semula ke dalam sistem, ditambahkan tekanan angin dan dilarutkan separa dengan

angin. Bahan kajian utama ialah sistem DAF di HACO Asia Pacific Sdn. Bhd.. Pada

peringkat pertama, proses peningkatan prestasi DAF telah dikaji untuk mendapatkan

parameter dan keadaan operasi yang paling berkesan. Seterusnya, kajian prestasi

DAF telah dilanjutkan pada keadaan operasi yang paling baik dan berkesan. Sampel

air sisa sebelum dan selepas rawatan DAF telah diambil dan dianalisis untuk

mengenalpastikan keberkesanan pengasingan bahan-bahan pencemar oleh DAF.

Keputusan daripada kajian prestasi DAF menunjukkan bahawa DAF berupaya untuk

mencapai spesifikasi reka bentuk asalnya yang dapat mengurang Total Suspended

Solids (TSS) sebanyak 85% - 95%. Pada peringkat akhir, satu reka bentuk terbaru

yang dikenali sebagai Band-pass Filter (BF) telah dibawa masuk untuk

membandingkan prestasinya dengan DAF sistem. BF ini adalah digunakan untuk

penapisan air sisa secara mekanikal dalam keadaan di mana penyinggiran bahan-

bahan sisa berhubungan dengan kilang pemprosesan adalah ddiperlukan. Untuk

mencapai pencucian optima, BF ini telah diubahsuai untuk proses pencucian yang

cepat. Keputusan daripada kajian pembandingan prestasi ini telah menunjukkan

bahawa BF dapat mencapai purata keberkesanan penyinggiran TSS dan Chemical


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Oxygen Demand (COD) yang lebih tinggi , iaitu 93.9% dan 49.6%. Manakala, DAF

dapat mencapai purata keberkesanan penyinggiran minyak dan gris yang lebih tinggi,

dengan bacaan sebanyak 91.9%.


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viii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS viii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF ABBREVIATIONS xiv

LIST OF SYMBOLS xv

1 INTRODUCTION

1.1 General Overview in the Environmental

Control of Industrial Wastewater 1

1.2 Physico-Chemical Treatment ofIndustrial Wastewater 4

1.2.1 History and Concept of Flotation 5

1.2.1.1 Type of Flotation Process 6

1.2.2 History and Concept of Filtration 9

1.3 Problem Statements 11

1.4 Objectives of the Study 12


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1.5 Scope of the Study 13

1.6 Significance of the Study 13

2 LITERATURE REVIEW

2.1 Coffee Production and Manufacturing

Factory Production Process Description 15

2.2 Wastewater Treatment Plant Design 192.2.1 Wastewater Treatment Plant

General Description 21

2.2.2 Wastewater Treatment Plant

Detailed Process Description 22

2.3 Chemical Treatment Process 282.3.1 pH Adjustment 30

2.3.2 Coagulation and Flocculation 31

2.4 Dissolved Air Flotation (DAF) System 342.5 Band-pass Filter (BF) System 35

3 RESEARCH METHODOLOGY

3.1 Wastewater Treatment Plant Site Survey,

Study and Planning 39

3.2 Dissolved Air Flotation (DAF) Unit 413.2.1 Site Operation Aspects of Installed DAF 45

3.2.2 Start-up of DAF 47

3.2.3 Shutting Down of DAF 49

3.3 Band-pass Filter (BF) Unit 50

3.3.1 Site Operation Aspects of BF Unit 53

3.3.2 Start-up of BF 54

3.3.3 Shutting Down of BF 55

3.4 Sampling at the Wastewater Treatment Plant 56

3.5 Analysis of Wastewater Samples 58

3.6 Jar Tests and Chemical Selection 59

3.7 Monitoring and Testing Design 59

3.7.1 Process Performance Improvement Study 60


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3.7.2 Performance Monitoring and Study of DAF 61

3.7.3 Comparative Performance Study between

DAF and BF 61

4 RESULTS AND ANALYSIS

4.1 Characterization of Soluble Coffee Production

Wastewater 63

4.2 Jar Test Results and Discussion 66

4.3 Process Performance Improvement Study on DAF 70

4.3.1 Design Calculation Review 70

4.3.1 Design Calculation Explanation 73

4.3.2 Analysis on the Mechanical Tuning

Adjustment Study 74

4.3.3 Analysis on the Chemical Tuning

Adjustment Study 76

4.4 Performance Monitoring of DAF 79

4.4.1 Analysis on the Wastewater Pollutant

Removal Efficiency 80

4.5 Comparative Performance Study between DAF and

BF 83

5 CONCLUSIONS AND RECOMMENDATIONS 86

REFERENCES 89

APPENDICES

Appendix A 92

Appendix B 95

Appendix C 97

Appendix D 100

Appendix E 102

Appendix F 104

Appendix G 106


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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 WWTP design input and output 20

3.1 Recommended operating condition for DAF 47

3.2 Recommended operating condition for BF 54

4.1 Average values of incoming wastewater characteristics

at the equalization tank (results abstracted from

Appendix A) 64

4.2 Average values of incoming wastewater characteristics

at the equalization tank (results abstracted from

Appendix B) 64

4.3 Range of values for the incoming wastewater

characteristics at the equalization tank (results

abstracted from Appendix A & B) 66

4.4 Wastewater characteristics before and after chemical

treatment 67

4.5 Average characteristics and removal efficiency for pH,

COD, BOD5, TSS and O&G 80


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xii

LIST OF FIGURES

CHAPTER TITLE PAGE

1.1 Dispersed-Air Flotation Unit. Air is induced anddispersed into the liquid by pumping action of the

inductors 8

2.1 Soluble coffee production process flow chart 16

2.2 WWTP flow diagram 23

2.3 Small flocs formation during the coagulation process

at the coagulation reaction tank 33

2.4 Bigger flocs formation during the flocculation process

at the flocculation reaction tank 33

2.5 DAF system with recycle, in which only therecycle flow pressurized 35

2.6 Process flow diagram for BF System 36

2.7 True unit of BF system 37

3.1 WWTP layout plan 40

3.2 The whole process equipments involve in

DAF treatment 42

3.3 C&F Reactor 42

3.4 Flotation tank with skimmer 43

3.5 Pressure vessel 43

3.6 Recirculation pump 44

3.7 Air injection valve 44


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3.8 P&ID of the studied DAF at the site 46

3.9 Overflow adjustment valve located at the discharge

collection basin 49

3.10 Roller filter with gear motor 51

3.11 Control panel 52

3.12 C&F reactor 52

3.13 Water jet system 53

3.14 Incoming sampling point at the equalization tank 57

3.15 Treated effluent after BF 58

4.1 TSS removal efficiency in relation to the differences

in recycle system pressure 75

4.2 TSS removal efficiency in relation to coagulant dosage 77

4.3 TSS removal efficiency in relation to polymer dosage 78

4.4 Wastewater pollutants removal efficiency (%) vs. date

for the 12 weeks of samples 82

4.5 Wastewater pollutant removal efficiency (%) after DAFAnd BF treatment vs. date 84


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LIST OF ABBREVIATIONS

BF - Band-pass Filter

BOD5 - 5-days Biochemical Oxygen Demand

C&F - Coagulation and FlocculationCOD - Chemical Oxygen Demand

DOE - Department of Environment

DAF - Dissolved Air Flotation

IESWTR - Interim Enhanced Surface Water Treatment Rule

LT1ESWTR - Long Term 1 Enhanced Surface Water Treatment Rule

O&G - Oil and Grease

P&ID - Process and Instrumentation Diagram

SI - System International

SBR - Sequencing Batch Reactor

SWTR - Surface Water Treatment Rule

TSS - Total Suspended Solids

US - United States

USEPA - United States Environmental Protection Agency

WWTP - Wastewater Treatment Plant


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xv

LIST OF SYMBOLS

% - Percent

g/d - Gram per day

g/m3

- Gram per cubic metergpd - Gallons per day

kg/d - Kilogram per day

lit. - Liter

lit./min - Liter per minute

lit./m2/min - Liter per meter square per minute

lit./hr - Liter per hour

lit./d - Liter per day

mm - Millimeter

m - Meter

m2

- Meter square

m3

- Cubic meter

m3/hr - Cubic meter per hour

m3/d - Cubic meter per day

mg/l - Milligram per liter

mL/mg - Milliliter per Milligram

oC - Degree of Celsius

sec - Seconds


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Malaysia. In the United States, the discharge of process wastewater from this kind of

food and beverage industry has fully emphasized on the removal of constituents that

may cause long-term health effects and environmental impacts since 1980. In here,

the important US federal regulation that govern the control of wastewater issues, and

have brought about the changes in the planning and design of wastewater treatment

facilities in the US are as follows:

i. Clean Water Act (CWA)(Federal Water Pollution Control ActAmendments of 1972)

Establishes the National Pollution Discharge Elimination System(NPEDS), a permitting program based on uniform technological

minimum standard for each discharger.

ii. Water Quality Act of 1987 (WQA) (Amendment of the CWA) Strengthen federal water quality regulations by providing changes

in permitting and adds substantial penalties for permit violations.

(U.S.EPA, 1997)

As one of the fast developing countries, Malaysia has also planned and

implemented its environmental protection management policy and activities in the

control of the industrial wastewater discharge by referring to the control strategies as

presently adopted in the US. In Malaysia, the achievements and progress in the

works of pollution abatement and control is mainly via the enforcement of pollution

control and regulations under the Environmental Quality Act, 1974 carried out by the

Department of Environment (DOE). The enforcement of the existing environmental

laws and legislation is essential and has been stepped up so as to ensure the

capability of the industrial sector, in particular to control the production of


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environmental pollutants and to practice effective storage and disposal systems.

Some technological progress has been noted in treating and controlling pollution

resulting from the agro-based industries. However, on the whole, performance

records show that the status of compliance of these industries is still far from

satisfactory. The problems are attributed to improper management of treatment

systems, the use of under-sized system as well as increased milling capacity (Abu

Bakar Jaafar, KMN, 1992).

More concerted efforts are needed to curb down pollution problems resulting

from all these manufacturing industries. With stricter enforcement of the Environ-

mental Quality (Sewage and Industrial Effluents) Regulations 1979, it is envisaged

that the river pollution problems can be minimized. Strict revision on the issuance of

contravention licenses made under the Section 22(1) and Section 25(1) of the

Environmental Quality Act, 1974 will help to facilitate further the compliance to

these regulations. In addition, factors that aggravate or increase non-compliance,

such as the incompetence of some waste management consultants in designing

effective treatment systems, have been recognized, and efforts initiated to address

and resolve these problems. The implementation and enforcement of the mandatory

environmental impact assessment (EIA) procedure and requirements under the

Environmental Quality (Prescribed Activities)(Environmental Impact Assessment)

Order 1987 have been stepped up in tandem with the country's increasing rate of

development and inclination to industrialize (Laws of Malaysia, 2003)


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1.2 Physico-chemical Treatment of Industrial Waste Water

Premises other than those prescribed (crude palm oil and raw natural rubber

mills) i.e. largely manufacturing industries, are subjected to the Environmental

Quality (Sewage and Industrial Effluents) Regulations 1979, the Environmental

Quality (Clean Air) Regulations 1978 and the Environmental Quality (Scheduled

Wastes) Regulations 1989 (Laws of Malaysia, 2003). As a coffee production and

manufacturing factory that have a great production capacity, HACO Asia Pacific Sdn.

Bhd. should be categorized under a general term known as Food & Beverages

manufacturing industries.

This kind of industry does contribute significantly to water pollution in the

country. Their non-compliance is largely due to the absence of a proper wastewater

treatment system, under capacity of the existing treatment system to cater for the

increased production capacity of the industry and lack of maintenance of the

wastewater treatment system. For the year 1991, about 32 industries have applied for

the contravention license under Section 25(1) of the Environmental Quality Act. This

constitutes about 39.5 per cent of the total contravention licenses issued under

Section 25(1) of the Environmental Quality Act for that year (Abu Bakar Jaafar,

KMN, 1992).

In order to implement a proper wastewater treatment system and to avoid any

ineffective treatment system design that was mentioned previously, physico-chemical

treatment system has always be a wise choice to be adopted in the primary treatment

stage. Common physico-chemical treatment systems normally adopted in the

wastewater treatment plant design are Dissolved Air Flotation Systems and

Sedimentation Tank Systems. Due to advances in the material developing technology,


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some kind of filtration system known as the Band-pass Filter can even breakthrough

the cost constraints and is beginning to be adopted in the primary treatment stage for

small WWTP. The main focus of this study is on the DAF which is operated based

on the concept of flotation. At the latter part of this thesis, a preliminary study on the

BF which functions based on the concept of filtration is also included.

1.2.1 History and Concept of Flotation

Over 2000 years ago, the ancient Greeks used a flotation process to separate

the desired minerals from the gangue, the waste material (Gaudin, 1957). Crushed

ore was dusted onto a water surface, and mineral particles were retained at the

surface by surface tension while the gangue settled. In 1860, Haynes patented a

process in which oil was used for the separation of the mineral from the gangue

(Kitchener, 1984). The mineral floated with the oil when the mixture was stirred in

water.

In 1905, Salman, Picard, and Ballot developed the froth flotation process by

agitating finely divided ore in water with entrained air. A small amount of oil was

added, sufficient enough to bestow good floatability to the sulfide grains (Kitchener,

1984). The air bubbles, together with the desired mineral, collected as foam at the

surface while the gangue settled. The first froth flotation equipment was developed

by T. Hoover in 1910 (Kitchener, 1984), and except for size, it was not much

different than the equipment used today.


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Elmore suggested in 1904 the use of electrolysis to produce gas bubbles for

flotation. This process, although not commercially used at that time, has been

developed into electrolytic flotation (Bratby, 1976). Elmore also invented the

dissolved-air (vacuum) flotation (DAF) process, whereby air bubbles are produced

by applying a vacuum to the liquid, which releases the air in the form of minute

bubbles (Kitchener, 1984). The original patent for the dissolved-air pressure flotation

process was issued in 1924 to Peterson and Sveen for the recovery of fibers and

white water in the paper industry (Lundgren, 1976).

1.2.1.1Type of Flotation Process

Flotation is a unit operation used to separate solid or liquid particles from a

liquid phase. Separation is brought about by introducing fine gas (usually air)

bubbles into the liquid phase. The bubbles attach to the particulate matter, and the

buoyant force of the combined particle and gas bubbles is great enough to cause the

particle to rise to the surface. Particles that have a higher density than the liquid can

thus be made to rise. The rising of particles with lower density than the liquid can

also be facilitated (e.g., oil suspension in water). Different methods of producing gas

bubbles give rise to different types of flotation processes. These are electrolytic

flotation, dispersed-air flotation, and dissolved-air flotation (Lundgren, 1976).

i. Electrolytic Flotation:The basis of electrolytic flotation, or electrolytic flotation, is the

generation of bubbles of hydrogen and oxygen in a dilute aqueous

solution by passing a DC current between two electrodes (Barrett, 1975).


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The bubble size generated in electrolytic flotation is very small, and the

surface loading is therefore restricted to less than 4 m/h (13.3 ft/h). The

application of electrolytic flotation has been restricted mainly to sludge

thickening and small wastewater treatment plants in the range 10 to 20

m3/h (50,000 to 100,000 gpd).

ii. Dispersed-air FlotationTwo different dispersed-air flotation systems are foam flotation and

froth flotation (Sherfold, 1984). Generally, dispersed-air flotation is

seldom used in municipal wastewater treatment, but it is used in

industrial applications for the removal of emulsified oil and suspended

solids from high volume of waste or process waters. In dispersed-air

flotation systems, air bubbles are formed by introducing the gas phase

directly into the liquid phase through a revolving impeller. The spinning

impeller acts as a pump, forcing fluid through disperser openings and

creating a vacuum in the standpipe (see Fig. 1.1). The vacuum pulls air

(or gas) into the standpipe and thoroughly mixes it with the liquid. As

the gas/liquid mixture travels through the disperser, a mixing force is

created that causes the gas to form very fine bubbles. The liquid moves

through a series of cells before leaving the unit. Oil particles and

suspended solids attach to the bubbles as they rise to the surface. The oil

and suspended solids gather in dense froth at the surface and are

removed by skimming paddles (Tchobanoglous et al, 2003). The

advantages of a dispersed-air flotation system are: (1) compact size, (2)

lower capital cost, and (3) capacity to remove relatively free oil and

suspended solids. The disadvantages of induced-air flotation include

higher connected power requirements than the pressurized system;

performance is dependent on strict hydraulic control, and less

flocculation flexibility. The quantities of float skimming are


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significantly higher than the pressurized unit: 3 to 7 percent of the

incoming as compared to less than 1 percent of dissolved-air systems

(Eckenfelder, 2000).

Figure 1.1: Dispersed-air flotation unit. Air is induced and dispersed into the liquid

by pumping action of the inductors. (Courtesy Eimco) (Tchobanoglous et al, 2003).

iii. Dissolved Air Flotation (DAF)There are three main type of DAF, and it is known as vacuum flotation

(Zabel and Melbourne, 1980), microflotation (Hemming, Cottrell, and

Oldfelt, 1977), and pressure flotation (Barrett, 1975). Of these three,

pressure flotation is currently the most widely used. In pressure flotation,

air is dissolved in water under pressure. Three basic pressure DAF

processes can be used: full-flow, split-flow, and recycle-flow pressure


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flotation (Zabel and Melt, 1980). For water treatment applications

requiring the removal of fragile floe, recycle flow pressure flotation is

the most appropriate system. Further details on the DAF description will

be explained later in Section 2.4.

1.2.2 History and Concept of Filtration

Filtration is a process that is widely used for removing particulate matter

from water. Besides raw water treatment, the filtration concept is beginning to be

popularly utilized in wastewater treatment process. In raw water treatment, nearly all

surface water treatment facilities and some groundwater treatment facilities employ

some form of filtration. Most surface waters contain algae, sediment, clay, and other

organic or inorganic particulate matter, and filtration improves the clarity of water by

removing these particles. More importantly, all surface waters contain

microorganisms that can cause waterborne illnesses, and filtration is nearly always

required in conjunction with chemical disinfection to assure that water is free of

pathogens. Groundwater is often low in microorganisms and particles but may

require filtration when other treatment processes (such as oxidation or softening)

generate particles that must be removed. In wastewater treatment, filtration is

commonly being used to achieve supplemental removals of suspended solids

(including particulate BOD) from wastewater effluents of biological and chemical

treatment processes to reduce the mass discharge of solids and perhaps more

importantly, as a conditioning step that will allow for the effective disinfection of the

filtered effluent.


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Filters have been used to clarify water for thousands of years. Medical lore

written in India, dating to perhaps 2000 BC, mentions filtration through sand and

gravel as a method of purifying water. Venice, Italy, used rainwater stored in cisterns

as a freshwater supply but drew the water from wells in sand that surrounded the

cisterns (Baker, 1948). In 1852, the first regulation mandating filtration was passed,

required all river water supplied by the Metropolitan District of London to be filtered.

The regulation was prompted by rampant pollution in the Thames River and

suspicions that cholera was transmitted by water (Fuller, 1933), a suspicion

confirmed by Dr. John Snow in his famous investigation of a cholera outbreak in

London just 2 years later.

In 1880, rapid filtration had its origin in the United States. Elements of

modern design, such as mechanical or hydraulic systems to assist with cleaning the

media during backwashing, appeared during that decade. The first municipal plant

employing coagulation and other critical elements of rapid filtration was in

Somerville, New Jersey, in 1885 (Fuller, 1933). Both slow sand and rapid filters

were common in early filter installations (Fuller, 1933), but by the middle of the

twentieth century, rapid filters were commonplace and slow sand filters were rarely

used.

By the latter part of the twentieth century, most surface water was filtered

before municipal distribution. Nevertheless, the Surface Water Treatment Rule

(SWTR), passed in 1989, was the first regulation in the United States requiring

widespread (but not universal) mandatory filtration of municipal water (U.S. EPA,

1989), with the recognition that chemical disinfection alone was ineffective for

protozoa such as Giardia lamblia and Cryptosporidium parvum. Rapid filters were

used in almost all cases (99 percent), but the SWTR caused a resurgence of interest

in slow sand filter, particularly among small utilities that had unfiltered water


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Since passage of the SWTR and more recently the Interim Enhanced SWTR

(IESWTR) (U.S. EPA, 1998) and Long Term 1 Enhanced SWTR (LT1ESWTR)

(U.S. EPA, 2002), finished water turbidity requirements have become more stringent

and the remaining utilities with unfiltered surface water supplies have been under

increasing pressure to install filtration. In short, filtration is and will continue to be a

central feature in surface water treatment plants.

1.3 Problem Statements

DAF, being one of the important physico-chemical separation devices, is

being used currently in the primary treatment stage of industrial WWTP at the

coffee production factory, HACO Asia Pacific Sdn. Bhd. Since the actual pollutant

concentration and loading discharged from the factory is higher than the designed

loading, this physico-chemical separation device is facing a great challenge to

remove the pollutant concentration up to the expected requirement. Furthermore,

due to the upset of the bacteria in the secondary biological treatment system after

the DAF treatment at the early stage of the operation, it is very important to ensure a

sufficient and consistent pollutant removal before the wastewater is being

transferred into the biological treatment system. As such, a process performance

improvement study and performance monitoring needs to be carried out on the DAF.

Firstly, it is important to carry out a process performance improvement study to

maximize the performance of the DAF and to determine the most effective

operating parameters; then, to analyze the pollutant concentrations before and after

the DAF treatment. The results from this study were very important for the plant

designer, i.e. CST Engineering Sdn. Bhd. to propose solutions to the clients.


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At the later stage of the study, a newly invented equipment, the Band-pass

Filter (BF) test unit will be tested out for its performance. This test unit performs the

same functions as DAF and had been brought in by CST from Denmark. A

comparative performance study shall be carried out between the DAF and the BF

due to the availability of the facility at the site.

1.4 Objectives of the Study

This study is aimed at improving and monitoring the performance of the

installed DAF and the existing physico-chemical treatment system and process. The

objectives of the study are as follows:-

i. To determine the most effective operating parameters of the existing DAF.

ii. To determine methods to improve the performance of DAF process.

iii. To determine the effectiveness of DAF in the primary treatment stage ofthe WWTP in the coffee production factory.

iv. To compare the performance effectiveness between the DAF and BF inthe primary treatment stage.


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1.5 Scope of the Study

The first target of the study was to perform a process performance

improvement study on the DAF and to determine the most effective operating

parameters. This is to find out all the possible design improvement modification if any.

Then, it was followed by a performance monitoring study on DAF. The study consists

of a through on-site monitoring works at Haco Asia Pacifics factory at Kota

Kemuning, Shah Alam using the installed DAF unit in the wastewater treatment plant.

The study shall focus on the determination of the Chemical Oxygen Demand (COD),

Biochemical Oxygen Demand (BOD5), Total Suspended Solids (TSS) and Oil and

Grease (O&G) reduction efficiencies of the DAF.

At the later stage of the study, a BF test unit shall be brought to HACO Asia

Pacific S/B, Shah Alam. A comparative performance study was carried out between

the DAF and the BF to compare the removal efficiencies of COD, O&G and TSS.

1.6 Significance of the Study

In the portion of the process improvement study, the results from the study can

be used to operate the DAF more effectively and always in the peak performance.

These effective operating parameters shall be determined and adjusted during the

performance monitoring works.


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As previously stated, this performance monitoring study was very important

especially in determining the COD, BOD5, TSS and O&G. before and after the DAF

treatment. By measuring and knowing these values, the removal efficiencies can be

determined and a judgment can be made on the performance of the DAF unit.

At the later stage of the study, the BF offers a very good opportunity to study

an emerging design from overseas. It will give an alternative choice that can be

adopted in the WWTP design. More importantly, the results from the comparative

performance study between the DAF and BF are very helpful for the project design

and management team of CST Engineering Sdn. Bhd. in the WWTP design decision

making.


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CHAPTER 2

LITERATURE REVIEW

2.1 Coffee Production and Manufacturing Factory Production Process

Description

Since this study is focusing on the coffee production and manufacturing

factory, it is very important to understand the coffee and wastewater production

process before going into the details of the WWTP process. Figure 2.1 captures a

general idea of the soluble coffee production process. In this flow chart, coffee

production mainly consists of 8 main production processes namely:

i. Process (1): Green Coffee Cleaning:In this first process, green beans are received in 60 kg sacks, big bags or

loose in containers. In here, there is a cleaning unit used to separate all

foreign material such as metal, wood, stones and dust from the green

beans. It is a clean physical separation process with metal detection,


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Figure 2.1: Soluble coffee production process flow chart


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sieve and vacuum system (de-stoner). The cleaned coffee beans are

stored in compartment silos or big bags.

i. Process (2): Roasting:In this process, the different origins are now blended together according

to the confidential recipes. In this step, the end product quality is

influenced depending on the type of green beans used. The beans are

now filled into the drum-roasting chamber and with induction heated to

more than 200C. This phase lasts for about 15 minutes and in this time

period, the cell structure is breaking open, and the typical coffee flavor

and aesthetic oils are created. The volume of the beans increases by

more than 30%. The roasting process must be interrupted fast and in two

stages, the beans are cooled down to temperatures below 80C in order

to stop all chemical reactions. After this cooling process and de-stoner,

the beans are pneumatically transported to the roast Coffee Silos.

ii. Process (3): High Pressure Extraction:The roasted beans are now divided in batch sizes and pass through a

coffee granulator. Before the extraction process, the granulated coffee

must be pre-moistured. The extraction batteries (percolators) are under

16 bar working pressure and the extraction temperature can exceed more

than 180C. The aroma-extract stream is stripped in a distillation process

to save the premium flavor. This aroma concentrate is given back to the

process directly before the drying process to optimize the flavor profile

of the end product. Before entering the tank farm, the stripped aroma

and hydrolyze extract must be cleaned and concentrated in a vacuum-

fall-stream process.


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iii. Process (4): Tank farm:The purpose of the tank farm is to store concentrated extract ready to

spray dry. The storage temperature is kept below 15C to prohibit

microbiological growth. The Rework station is used to blend non

conforming product back to the main product stream.

iv. Process (5): Liquid Coffee Concentrated (S):Concentrated Coffee can also be sold as finished goods mainly for

industrial purpose. The coffee is filled and packed in cans or containers.

v. Process (6): Spray Drying (A):The spray drier is changing the liquid concentrated extract into dry

soluble coffee. The feed tank system adjusts the pH. After the pre-

pressure pump, the liquid extract must be foamed in order to control the

density and color of the finished product. The high-pressure system is

important to stabilize the product dispersing through the nozzles. Inside

the drying chamber, the extract is spread into a hot air stream. The

moisture content of the end product is less than 3.5%. The spray-dried

product is stored in hermetic closed containers and forwarded to the

product on hold area. All sensorial, analytical and bacteriological

analysis must be completed before the product is released to the

packaging area.

vi. Process (7): Bulk Packaging & Process (8):Packaging in Pouches:As the word imply, packaging of the finished product is being carried

out in here and the product to be sold out.

(CST, 2007)


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In here, process (2) to process (6) is the major processes that waste materials

to the environment. Gas emissions discharge to the atmosphere is normally

contributed by process 2, 3, 4 and 6. In terms of the solids waste generation, it is

purely generated by process 3. However, in terms of the waste water generation, it is

mainly contributed by process 3, 4, 5 and 6.

2.2 Wastewater Treatment Plant Design

Although the main scope of study in this thesis is focused on the DAF, it is

better to understand the whole process design of the WWTP before going into details

of DAF. The proposed treatment plant is designed to produce secondary effluent of a

quality that will meet the requirements of the Malaysian Government for discharge

according to DOE Standard B provided that the influent is having the wastewater

characteristics shown in Table 2.1.


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Table 2.1: WWTP design input and output

Parameter Raw influent Treated effluent (DOE

Std. B)

Flow Rate (m3/day) 600

-

Peak Flow (m3/hour) 30 (max. 2 hours) -

BOD5 ( mg/L)1000 - 2200 < 50

COD (mg/L) 4000 - 6500 < 100

TSS (mg/L) 700 < 100

O&G ( mg/L) 50 < 10

Temperature (oC) < 60 < 40

pH 4 7 6 9

Plant Operating Hours 20 -

WWTP Operating Hours 24 -

(Laws of Malaysia, 2003)


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2.2.1 Wastewater Treatment Plant General Description

First of all, the industrial wastewater from the factory is discharged into the

pump sump and consequently, pumped to the WWTP. In the WWTP, the proposed

treatment process comprises of the following main steps, namely physical, chemical

and biological treatment:

i. Physical Treatment:

The physical pretreatment involves a solid screening system. The

wastewater stream passes through a static fine screen that will remove

any solid particles in excess of 1.0 mm.

ii. Chemical Treatment:After the static fine screen and equalization tank, the wastewater is

being treated by chemical means through coagulation and flocculation

in a Dissolved Air Flotation (DAF) unit. Efficient removal of

emulsified oil and grease, fine solids and certain dissolved proteins

will be achieved in this step.

iii. Biological Treatment:Organic pollutants are removed aerobically in a Sequencing Batch

Reactor (SBR) to a level required by the DOE. The mechanism

involved microbial metabolism that will transform BOD and COD into

environmentally inoffensive compounds. Adequacy of COD removal,

however, will depend on overall biodegradability of the wastewater.


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2.2.2 Wastewater Treatment Plant Detailed Process Description

In this section, the detailed process design of the WWTP will be explained.

By referring to the WWTP flow diagram as shown in Figure 2.2, a better conceptual

understanding can be obtained when reading through the process description as

follows:

i. Pump Sump:

This sump receives different wastewater sources from the processing

plant. The wastewater will then be pumped by submersible pumps into

subsequent high load damping system and equalization tank

respectively after passing a screening system for solid and particle

removal, depending on the effluent quality from the processing plant.

This unit has two chambers with a volume of 20 m3

for normal load

and 5 m3 for high load wastewater.

ii. Screening System:

It is proposed that the wastewater to be directed into a static fine

screen with aperture size approximately 1.0 mm. Particles with size

greater than 1.0 mm, which may cause operational problems

downstream, will be retained in the screen. The screened wastewater

will flow by gravity into the high load tank and equalisation tank

downstream. The solids on the screen will be removed and stored in a

bin prepared by client. The designed screening system is capable to

handle wastewater of 600 m3/day.


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LI

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i. High Load Dumping System:

During the factories processing, maintenance and cleaning schedule or

change of process system in the plant, high organic loading (COD &

BOD) wastewater will be dampened by this specially designed system

to avoid organic shock to the wastewater treatment plant. High loading

wastewater will be held temporary in a High Load Damping Tank

(HLDT) to avoid abrupt increment in organic loading, which will pose

detrimental effect to aerobic system. During the time of normal

loading, wastewater in HLDT will be fed gradually into the

equalisation tank. A floating surface aerator is installed in the tank to

ensure proper mixing, to equalise the high loading wastewater from

different sources and to enhance the temperature level.

ii. Equalization Tank:

During the normal operation of the processing plant, the equalisation

tank is used to overcome the operational problems caused by flow rate

variations and organic loading fluctuation, thus improve the

performance of downstream processes. Therefore the subsequent

processes will be steady hydraulically. A floating surface aerator is

used to keep the wastewater properly mixed and enhance the

temperature reduction prior to be transferred into the following

chemical treatment system. This unit has a total volume of 600 m3.

iii. DAF System:

Our design calculations are based on chemical assistance be provided

to alter the physical state of dissolved proteins, dispersed fine solids

and/or emulsified oil droplets to facilitate their removal in the DAF

unit. With proper chemical dosing, the DAF unit and scraper system


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will be able to achieve the stated COD removal. A flocculator and

coagulator reactor system shall be installed as part of the DAF unit to

facilitate the injection of chemicals for treatment of the wastewater.

iv. Intermediate Holding / Hydrolysis Tank:

The chemical pre-treated wastewater will be held temporarily in an

intermediate holding tank cum hydrolysis reactor prior to being

transferred to the biological treatment system at the reaction phase of

the sequencing batch reactor. This tank will have a capacity of 1000 m3

.

v. Sequencing Batch Reactor (SBR):

The biological treatment involves a Sequencing Batch Reactor, which

has a total volume of 1700 m3. This design is done to meet the

optimum removal of the COD and BOD in the influent wastewater to

meet local government required standard.

In the SBR process, the tank serves as both aeration and

sedimentation basins for the system. This is achieved by operating the

SBR in a sequential mode instead of the standard continuous mode

commonly adopted for conventional activated sludge processes. This

mode of operation is ideal for the type of processing plant in question

due to its batch operation, and the undulating flow pattern

characterized by periods of high flow followed by sustained periods of

low or no flow.

The SBR cycle will be structured so that filling of the reactor will be

done mostly during high flow periods. Aeration (REACT phase) will


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be carried out for most of the FILL phase and for a short period after

filling has stopped.

Upon completion of REACT, the biomass will settle for a nominal

period of an hour (SETTLE phase). At the end of SETTLE, the reactor

will be decanted (DECANT phase), leaving most of the sludge mass

behind for the next cycle. The end of DECANT will incorporate an

IDLE phase when excess sludge is drawn off by a submersible

centrifugal pump to the sludge holding tank to await dewatering and

final disposal.

The SBR serves to reduce the concentration of soluble organic

compounds in the wastewater that survived the upstream treatment

steps. Removal of these compounds is done mainly through oxidation

by aerobic micro-organisms. To ensure proper performance, it is

essential that sufficient oxygen be supplied to the activated sludge

biomass. Oxygen will be supplied in this proposed scheme by floating

surface aerator. The micro-organisms in the tank will convert the

organic contaminants (substrate) by biochemical reaction to CO2, H2O

and mineral compounds and, as a result, reduce the concentration of

BOD5 and COD. At the same time, the micro-organisms multiply

themselves, producing a growing amount of activated sludge which

has to be withdrawn from the system as excess sludge.

Other than the aeration, the SBR can also provide an anoxic period for

the Denitrification system during the operating cycle. Hence, the NO3-

generation from the Nitrification system during aeration can be

reduced to required standard. For nitrification, SBR aerobic react times

may range from 1.0 to 3.0 h (WEF, 1998). A submersible mixer will be


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used to promote the good mixing of wastewater during the

Denitrification stage.

vi. Sludge Holding Tank:

The sludge holding tank has a volume of 160 m3. Settled sludge from

the clarifier will be stored temporarily in this tank for 1-2 days before

sludge is transferred to sludge conditioning tank downstream. The tank

will be provide by a submersible mixer/aerator used to keep the sludge

properly mixed and prevent potential odour problem.

vii. Sludge Conditioning & Dewatering System:

This system comprises a sludge-conditioning unit and a semi-

automatic chamber filter press. In the sludge-conditioning unit a

polymer conditioner (to be selected during commissioning of the plant)

will be added into a sludge conditioning tank to improve water

expulsion characteristics of the sludge. Polymer can bind with sludge

to become bigger in size and heavier particles for considerable gravity

sedimentation. An air diaphragm feed pump will be used to feed the

sludge into the chamber filter press.

Filter press is a type of filtration devices to separate solid and liquid. A

chamber of vertical filter plate, in series arrangement, is playing the

role of filtration by retaining solid or sludge on its surface. Filter press

is operating at 2-3 cycles per day at the operating pressure of 7 bars

and capable to handle sludge dry solid content of 53.4 kg SS/d. Sludge

in the holding tank is assumed to contain 1- 2% dry solids. Dry solids

content of the dewatered sludge cake will be about 30-40%, depending


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on the sludge characteristics. Dewatered sludge cake will be stored in a

bin prepared by client prior to final disposal.

Filtrate and from the filter press and excess water in sludge bin will be

drained back to the equalization tank for further treatment.

viii. Filtration System:

This filtration system comprises of a supernatant holding tank, a disc

filter and pump system and a treated water tank. Treated water from

the SBR tank will be discharged into the supernatant holding tank with

a volume of 600 m3, where the water will be held temporary in this

tank before going through the filtration system for water reuse at

selected areas of the factory or drained off for final discharge.

2.6 Chemical Treatment Process

Before going into details about the DAF and the BF, it is important to first

understand the chemical treatment process. It is vital and important because the

wastewater will be treated chemically first before it goes through the 2 process unit

for separation purpose. Chemical processes, in conjunction with various physical

operations, have been developed for the complete secondary treatment of untreated

(raw) wastewater, including the removal of either nitrogen or phosphorus or both.

Chemical processes have also been developed to remove phosphorus by chemical

precipitation, and are designed to be used in conjunction with biological treatment.

Other chemical processes have been developed for the removal of heavy metals and


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for specific organic compounds and for the advanced treatment of wastewater

(Tchobanoglous et al, 2003), in case, chemical pretreatment prior to filtration is more

critical to success than the physical facilities at one plant. This was fully agreed and

reported by Cleasby et al (1989) who recommended that the plant staff used a well-

defined coagulant chemical control strategy that considers variable raw-water quality

(Cleasby et al, 1989).

The concern here is in the pH adjustment, coagulation and flocculation

process. Before going into details of each, it is important to differentiate the 2

confusing terms- Coagulation and Flocculation. The terminology of coagulation

has not been standardized. However, in most of the water treatment literature,

coagulation refers to all the reactions and mechanisms that result in particle

aggregation in the water being treated, including in situ coagulant formation (where

applicable), particle destabilization, and physical inter-particle contacts. The physical

process of producing interparticle contacts is termed Flocculation (Camp, 1955).

However, in the colloidal sciences literature, LaMer (1964) considered only chemical

mechanisms in particle destabilization and used the term coagulation and

flocculation to distinguish between two of them. LaMer defined destabilization by

simple salts such as NaCl (a so-called indifferent electrolyte) as coagulation.

Destabilization of particles by adsorption of large organic polymers and the

subsequent formation of particle-polymer-particle bridges was termed flocculation

(LaMer, 1964).

The water treatment literature sometimes makes a distinction between the

terms coagulant and flocculant. When this distinction is made, a coagulant is a

chemical used to initially destabilize the suspension and is typically added in the

rapid-mix process. In most cases, a flocculant is used after the addition of a

coagulant; its purpose is to enhance floc formation and to increase the strength of the


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floc structure. It is sometimes called a coagulant aid. Flocculants are often used to

increase filter performance (they may be called filter aids in this context) and to

increase the efficiency of a sludge dewatering process. In any case, depending on

how and where it is used and at what dosage, a coagulant is sometimes a flocculant

and vice versa.

2.3.1 pH Adjustment

The removal of excess acidity or alkalinity by treatment with a chemical of

the opposite composition is termed neutralization. In general, all treated wastewater

with excessively low or high pH require neutralization before they can be dispersed

to the environment. In a variety of waste water treatment operation and processes,

there is often a need for pH adjustment. Because a number of chemicals are available,

the choice will depend on the suitability of a given particular application and

prevailing economics.

Neutralization of acidic wastewater in small plants or for treatment where

small quantities are adequate commonly employ sodium hydroxide (NaOH, also

known as caustic soda) and sodium carbonate, although somewhat expensive, are

convenient and used widely by these small plants. Lime, which is cheaper but

somewhat less convenient and slower in reaction rate, is the most require widely

used chemicals.


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Alkaline wastes are less of problem than acid but nevertheless often require

treatment. If acidic waste streams are not available or are not adequate to neutralize

alkaline waste, sulfuric acid is commonly employed. In some treatment plants,

carbon dioxide in the form of flue gas had been used to neutralize alkaline

wastewater.

Most importantly, chemical neutralization or pH adjustment also functions to

be used in the chemical precipitation reaction. Adjustment of pH will cause the

adjustment of solubility of different constituents in the wastewater and can be used to

precipitate out the necessary pollutants especially heavy metals. Besides that, pH

adjustment of the wastewater is required in getting the best floc during the

coagulation/ flocculation process (Tchobanoglous et al, 2003). In this case, caustic

soda (NaOH) is used to achieve a pH range of 4.3 to 4.8, in which a best floc can be

gotten.

2.3.2 Coagulation and Flocculation

Colloidal particles found in wastewater typically have a net negative surface

charge. The size of colloids (about 0.01 to 1 m) is such that the attractive body

forces between particles are considerably less than the repelling forces of the

electrical charge. Under these stable conditions, Brownian motion keeps the particles

in suspension. Brownian motion (i.e. random movement) is brought about by the

constant thermal bombardment of the colloidal particles by the relatively small water

molecules that surround them. The term chemical coagulation used in here

includes all of the reactions and mechanisms involved in the chemical destabilization


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of colloidal particles so that particles growth can occur as a result of particle

collisions, which means that in the formation of larger particles through perikinetic

flocculation (aggregation of particles in the size range from 0.01 to 1 m).

In general, a coagulant is the chemical that is added to destabilize the

colloidal particles in wastewater so that the floc formation can result. A flocculant is

a chemical, typically organic, added to enhance the flocculation process. Typical

coagulants and flocculants include natural and synthetic organic polymer, metal salts

such as alum or ferric sulfate, and pre-hydrolized metal salts such as polyaluminium

chloride (PACl) and polyiron chloride (PICI). Flocculents, especially organic

polymers, are also used to enhance the performance of granular medium filters and in

the dewatering of digested biosolids. In these applications, the flocculant chemicals

are often identified as filter aids.

In the aspect of flocculation, there are two types of flocculation: (1)

microflocculation (also known as perikinetic flocculation), in which particle

aggregation is brought about by the random thermal motion of fluid molecules

known as Brownian motion or movement and (2) macroflocculation (also known as

orthokinetic flocculation), in which particle aggregation is brought about by inducing

velocity gradients and mixing in the fluid containing the particles to be flocculated.

Another form of macroflocculation is brought about by differential settling in which

large particles overtake small particles to form larger particles. The purpose of

flocculation is to produce particles, by means of aggregation, that can be removed by

inexpensive particle-separation procedure such as gravity sedimentation and

filtration. To further emphasize on this, macroflocculation is ineffectual until the

colloidal particles reach a size of 1 to 10 m through contacts produced by Brownian

motion and gentle mixing (Tchobanoglous at al, 2003)(To have a general idea on


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how the flocs formation during coagulation and flocculation, refer to Figure 2.3 and

Figure 2.4).

Figure 2.3: Small flocs formation during the coagulation process at the

coagulation reaction tank.


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Figure 2.4: Bigger flocs formation during the floculation process at the

flocculation reaction tank..

2.4 Dissolved Air Flotation (DAF) System

DAF is a unit operation for the separation of solids and semisolid (floc)

particles from a liquid phase that has been used for the clarification of potable water

for over 40 years (Edzwald, 1995). Besides potable water, this concept is also widely

applicable in wastewater treatment. In here, air bubbles are introduced near the

bottom of the basin containing the water to be treated. As the bubbles move upward

through the water, they become attached to the particulate matter and floc particles,

and the buoyant force of the combined particles and air bubbles will causes the

particles to rise to the surface.

To achieve efficient clarification by DAF, particles and natural color present

in the water must be coagulated and flocculated effectively prior to the introduction

of micro-bubbles to form bubble-floc aggregates. Floatable bubble-floc agglomerates

might form by any of three distinct mechanisms: entrapment of bubbles within

condensing network of floc particles, growth of bubbles from nuclei within the floc,

and attachment of bubbles of floc during collision. All three mechanisms can occur

but that the principal mechanism in DAF for the potable water treatment is the

attachment mechanism (Kitchener and Gochin, 1981).

On the other hand, for the treatment of industrial waste and concentration of

solids, recycle-flow pressurized system is being considered and utilized in here and it

is shown in Figure 2.5. In this kind of system, a portion of the DAF effluent is

recycled, pressurized and semi-saturated with air. The recycled flow is mixed with

the un-pressurized main stream just before admission to the flotation tank, with the


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result that the air comes out of solution in contact with particulate matter at the

entrance to the tank. A pressure release device is being utilized in here to control the

entrance of the pressurized recycle water. Here, the pressure is reduced to

atmospheric pressure, releasing the air in the form of fine bubbles (10 to 100m in

diameter). The air bubbles attach themselves to the flocs, and the aggregates float to

the surface. The floated material (the float) is removed from the surface, and the

clarified water is taken from the bottom of the flotation tank.

Figure 2.5: DAF system with recycle, in which only the recycle flow is pressurized.

(Tchobanoglous et al, 2003).

.

2.5 Band-pass Filter (BF) System

BF is purely a chemical-mechanical filtration system with a proper electrical

device used in the controlling process. Before going through the unit in detail,


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understanding of the BF process flow diagram is important. The process flow

diagram of a BF is shown in Figure 2.6 and the picture for the true unit is shown in

Figure 2.7.

Figure 2.6: Process flow diagram for BF System (CST, 2007)


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flocculation as an integral part of those mechanisms governing filtration (Janssens et

al, 1985). In here, the target of coagulation-flocculation as a separate stage from filter

is to obtain a floc designed to penetrate the bed in depth and to resist the shear

forces, as a results, the different sizes of filter medium are necessary for sieving

flocs of different size. (Vigneswaran, 1989)

.

The concept of filtration is strictly connected to an idea of clearness, which in

turn is connected with a subjective sensory perception. The instruments commonly

employed to measure the turbidity of water are ineffective in providing objective

values of immediate application. This is the reason for the necessity to know the

concentration of suspended solids and the distribution of particle sizes. For instance,

the comparison between the turbidity value in formazine turbidity units (FTU) and

the concentration of suspended matter can provide useful information which is

known as fitness coefficient, i.e., the colloidal degree of suspension. Rather than

turbidity itself, this factor makes it possible to anticipate the coagulant quantity to be

employed for the treatment, thus rendering Direct Filtration feasible (Brathy, 1980).

What differentiates BF from common direct filtration and microstraining

method is its filtering materials and method. The BF has a constantly moving

polyethylene endless filter which means that the purchase, fitting and disposal of

expensive rolls of paper cloth can be avoided. When the water is passed through the

filter, the particles are carefully retained on the belt without breaking up into fine

particles. They are then lifted out of the water and deposited into a skid. The filter

belt is being flushed either intermittently or constantly with clean or recirculated

water in order to avoid the perforations from being blocked (CST Engineering, 2007).

As compared to other filtration system, BF utilize a very suitable filter media since

polyethylene is some kind of plastic media that are economical and have good

chemical resistance and weathering characteristics (Cheremisinoff, 2003).


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CHAPTER 3

STUDY METHODOLOGY

3.1 Wastewater Treatment Plant Site Survey, Study and Planning

Planning at the site has been carried out to determine the most suitable study

methods and set-up procedure for the equipment. Figure 3.1 shows the WWTP

Layout Plan. In here, the most important study object would be the DAF and it is

represented by S1 in Figure 3.1. It has already been constructed at the site and it was

used back during the study. For the BF study, the test unit was brought to the site and

being located at C09- Filtration Feed Tank, near the V4- Azud Filter. It is shown in

red color in Figure 3.1.

During the performance monitoring and process performance improvement

study on the DAF, sampling will be carried out at C04 (Equalization Tank) and S1

(DAF). In the comparative performance study, sampling will be carried out together

at three different locations at the same time.


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3.2 Dissolved Air Flotation (DAF) Unit

The DAF is the most important physico-chemical separation equipment in the

primary treatment design stage of the WWTP to knock down the residual TSS and

O&G, in order to enable the success of the downstream biological treatment process

functional ability. The DAF in this case study is of the rectangular type and the

whole process equipment of DAF is shown in Figure 3.2. The constructed DAF at

the WWTP consists of the following compartments:

i. Coagulation and Flocculation (C & F) Reactor (Figure 3.3)

ii. Flotation tank with skimmer (Figure 3.4)

iii. Pressure vessel (Figure 3.5)

iv. Recirculation pump (Figure 3.6)

v. Air injection valve (Figure 3.7)

vi. Chemical Dosing System


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Figure 3.2: The whole process equipment involved in DAF treatment

Figure 3.3: Coagulantion & Flocculation Reactor


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Figure 3.4: Flotation tank with skimmer

Figure 3.5: Pressure Vessel


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Figure 3.6: Recirculation pump

Figure 3.7: Air injection valve


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3.2.1 Site Operation Aspects of Installed DAF

Before going into details of the operation of DAF, it is better to have an

overall idea of the process flow of the DAF by looking at the detailed Process and

Instrumentation Diagram (P&ID) shown in Figure 3.8. By referring to this figure; the

equalized wastewater is pumped to the C & F reactor where Coagulant and flocculant

are added into the reactor. The contaminating solid is separated from the wastewater

in the C & F reactor. From the reactor, wastewater is overflowed into the flotation

tank. On top of the flotation tank a scraper chain conveying system is installed,

which intermittently scrapes the sludge into the sludge compartment tank, by a motor.

The purified effluent is discharged in the bottom of the flotation tank and

passed on to an outlet collection basin attached to the DAF. By means of overflow

control, the water level can be adjusted in the flotation tank. Both flotation tank and

outlet basin are made of stainless steel. Wastewater in the flotation tank can be

emptied by opening a bottom drain valve.

The dispersion system consists of a dispersion tank (Pressure Vessel),

compressed air, recirculation pump and pressure reducing valve. Dispersed water is

made continually and automatically. Dispersed water is made from recirculated water

and compressed air is mixed to supersaturation. The amount of water fed into the

flotation tank is adjustable by a manual valve.

The dispersed fluid is injected into the flotation tank forming microscopic air

bubbles, which would carries flocs to the surface. Sludge layer is formed on the


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surface and is scrapped intermittently to the sludge compartment. During the study

periods, the DAF was operated with parameters shown in Table 3.1.

Table 3.1: Recommended operating condition for DAF:

Operating Parameter Unit Operating/

Recommended Range

1. Feed pump flow rate m3/hr 300 - 450

2. Recirculation pump flow rate m3/hr 5 - 10

3. Recirculation pump

pressure

Bar 2.6 - 3.0

4. Air pressure Bar 2.0 - 4.0

5. Caustic dosing pump

rate

lit./hr 3.0 5.0

6. Coagulant dosing pump

rate

lit./hr 24 36

7. Flocculant dosing pump

rate

lit./hr 90 -180

3.2.2 Start-up of DAF

During the time of performance study, start-up of the DAF system needed to

be done and the following procedure had been carried out as followed:

i. Recirculation pump, DAF skimmer and dosing pumps selectorswitch were set to Auto Mode.


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ii. Water was then filled into the flotation tank.

iii. Coagulant and flocculant were being prepared

iv. Recirculation pump was started and the pressure vessel was filled

v. Air pressure for the pressure vessel was being set to the ranges from2.0 bars to 4.0 bars.

vi. Flotation manual feed valve and recirculation pump suction valvewere being adjusted until the desired flow rate approximately 10 -50%

of the main flow rate.

vii. Pressure reducing valve and the manual gate valve were adjusted untilthe desired fine bubble.

viii. Dosage of coagulant and flocculant were adjusted as per Jar Testresults.

ix. When the flotation tank was filled, the water level was adjusted byadjusting the overflow of the discharge collection basin (refer Figure

3.9).

x. Pressurized air or fluid in the pressure vessel should be released if theair pressure in the vessel build up beyond setting requirement and

design pressure during start up. It was carried out by releasing the air

from the pressure vessel using the manual air release valve. The

incoming air pressure must be regulated as well to reduce the air

supply and if necessary use the manual valve to shut off the air supply.

The liquid in the pressure vessel can be drained off by opening the


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bottom drain off valve should the water overflow to the air line

system.

xi. The recirculation pump to be shut off if abnormality of over pressureoccurred during start up as indicated on the pressure vessel pressure

gauge pressure build up and over 5 bars

Figure 3.9: Overflow adjustment valve located at the discharge collection basin.

3.2.3 Shut-down of DAF

Shutting down of the system needed to be carried out by our own self if the

operator is not in at that moment. These procedures were followed during the shut-

off time:


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i. The overflow was adjusted to raise the sludge level.

ii. Then, the sludge layer was being scraped off.

iii. Inlet compressed air was shut off.

iv. The skimmer and dosing pumps were shut off..

v. The recirculation pump for the pump to be serviced was shut off.

vi. Pressurized air or fluid in the pressure vessel was released if the airpressure in the vessel build up beyond design pressureduring shut

down.time

vii. Inlet valve to the DAF was shut off.

viii. Recirculation feed valve was shut off after the recirculation pump wasswitch off.

ix. Drain valve in the DAF was opened

x. In servicing the Pressure vessel, the air pressure in the vessel wasrelease until it reaches zero, and the water in the vessel was being

drain out using bottom drain off line.

3.3 Band-pass Filter (BF) Unit

The BF fulfill the requirements of the laws of the Member States on the

safety of the machines 98/37/EEC. In operational condition, the requirements of the


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Figure 3.11: Control panel

Figure 3.12: C&F reactor


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Figure 3.13: Water jet system

3.3.1 Site Operation Aspect of BF Unit

During the actual site operation, Table 3.2 shows the recommended operating

condition.


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Table 3.2: Recommended operating condition for BF.

Operating Parameter Unit Operating/

Recommended Range

1. Feed pump flow rate m

3

/hr 1 22. Band-pass filter

rotational speed

m/min 5 7

3. Flocculation mixer

speed

rpm 60 90

4. Caustic dosing pump

Rate*

lit./hr 3.0 6.0

5. Coagulant dosing

pump rate

lit./hr 2.0 4.0

6. Flocculant dosing

pump rate

lit./hr 6.0 -14.0

* 10 times dilution of caustic (50%) chemical is required because the existing

chemical pump is more accurate at greater dosing rates.

3.3.2 Start-up of BF

During the performance study period, start-up of the BF system had to be

done and the following procedures must be followed:

i. First, the Power supply is connected.

ii. Then, the feed pump flow rate, BF rotational speed, flocculationmixer speed and chemical dosing rate was set manually according to

the recommended operating condition.


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iii. Water is filled into the system and water jet systems that utilizethe water to flush the BF roller filter all the while is turned on.

iv. Coagulant and flocculant were then prepared.

v. Feed pump (submersible pump) is switched on and the system shouldbe filled up at that moment.

vi. Influent valve is adjusted until the recommended influent flow rateis achieved.

vii. Dosing rate of coagulant and flocculant is adjusted as per Jar Testresults.

viii. The BF rotational speed is adjusted until the observed flocs removalcapacity and clear water is achieved.

3.3.3 Shut-down of BF

Shutting down of the system in here is very straight forward. We just needed

to turn off all the equipment at that moment except the BF filter roller and let it to

run for a while to clear the balance flocs inside the tank. Then, the discharge valve

can be opened at the bottom of the C & F reactor tank. Finally, the water jetting

systems that clean the BF roller filter can be turned off when the appearance of the

band-pass filter roller was clean at that moment.


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3.4 Sampling at the Wastewater Treatment Plant

There are 3 major sampling points in our study. They are:

i. Incoming sampling point at the equalization tank (Figure 3.14).

ii. Treated effluent after DAF (Figure 3.9).

iii. Treated effluent after BF (Figure 3.15).

For all these 3 sampling points, we were collecting the sample based on composite

sampling methods, in which 4 samples would be collected during an operational

testing of 4 hrs and then mixed together before sending to the laboratories.


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Figure 3.14: Incoming sampling point at the equalization tank


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Figure 3.15: Treated effluent after BF

3.5 Analysis of Wastewater Samples

For the temperature reading, it can be directly recorded from the monitoring screen

of the Eutech pH controller that is equipped with a built-in temperature sensor installed at

the coagulation tank. Meanwhile, the pH at the Equalization tank and after the DAF

treatment can be measured directly with a portable HANNA pH Tester- model no: HI

96107 (pHep). For the other parameters, it was tested when the entire wastewater sample

was sent to the third party laboratory and all the analysis on the wastewater was done in

accordance with Standard Methods (APHA, 1998).


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3.6 Jar Tests and Chemical Selection

The purpose of the jar test is to simulate, to the extent possible, the expected or

desired conditions in the coagulation-flocculation facilities. Refer to the American Society

for Testing and Materials procedure (ASTM, 1976) for a review of the experimental

protocols. Generally, the test consists of a rapid-mix phase (high mixing intensity) with

simple batch addition of the coagulant or coagulants followed by a slow-mix period to

stimulate flocculation. Normally, flocs were allowed to settle and samples would be takenfrom the supernatant. But in our case, since the operating equipment is a DAF, jar test was

to be simulated like DAF, in which air bubbles were being injected into the water at the

moment to ensure that all the flocs formed are floated to the surface of the beaker (Zakariya,

1998). The jar test was carried out by the water treatment chemical supplier.

3.7 Monitoring and Testing Design

Design of the testing and study would be firstly focused on the process performance

improvement study. By getting the optimum operating parameters, it was then possible to

carry out the performance monitoring study of the DAF by operating the DAF under

optimum conditions. Lastly and finally, the comparative performance study between the

DAF and the BF was designed to determine the superior removal functions of each

equipment.


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3.7.1 Process Performance Improvement Study

Before any testing was carried out, the original design based on the original design

input was first reviewed back. Then, based on the actual condition, a design calculation

simulation was carried out. From this, a general idea on what to focus in the process

performance improvement study can be obtained.

In the aspect of the mechanical tuning of the DAF, variation of the recycle system

pressure on the DAF performance was studied. In here, the valve after the recycle pumpwas adjusted to obtain the required pressure during the study. Performance of the DAF at

every different recycle pressure can be observed from the appearance of the effluent from

the DAF. To confirm about the observation results, 15 wastewater samples before and after

the DAF treatment were collected for analysis during the 3 days testing and commissioning

study.

In the aspect of the chemical tuning adjustment, it was mainly focused on the

chemical dosing pump capacity adjustment to determine the most effective and efficient

operating condition. The optimum pH condition would be based on the jar test results.

During the process performance improvement study, it was strictly required to vary

the studied operating parameters and maintain the other operating parameters as usual

(constant) (Ng, et al, 1988)


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3.7.2 Performance Monitoring and Study of DAF

This monitoring and study work was carried out at the WWTP of HACO Asia

Pacific Sdn. Bhd. and the WWTP layout plan is shown in Figure 3.1. The wastewater will

be pumped from the Equalization Tank into the DAF as what was happening during the

normal operation periods. Then, the operating parameter of the DAF being set according to

the optimum operating parameter obtained from the process performance improvement

study. Sample of wastewater was collected from the Equalization Tank and after the DAF

treatment. This sampling activity had to be carried out once every week during the

operation of the DAF and the sample taken will be sent out to a third party laboratory for

analysis. The sampling method was based on composite sampling during the operation of

the DAF for a period of 4 hrs. In this way, performance of the DAF can be monitored every

week.

3.7.3 Comparative Performance Study between DAF and BF

The BF was transported to the site and located near the Filtration Feed Tank

(C09)(Its location is shown in Figure 3.1). Then, a submersible pump was temporary

installed at the Equalization Tank and connected with a rubber hose to the BF. Test runs of

the BF ware carried out before the actual comparative study until the best treated water

condition was obtained. After that, the actual comparative study can be carried out. In this

study, the BF was operated to match the design flow of 1m3/hr, with the flocculation mixer

set to 80rpm to get the best flocs. Meanwhile, rotational speed of the band-pass filter roller

was set to 6m/min. (maximum speed of the system is 7m/min). For the DAF, it was


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operated with 15m3/hr, and the other operating parameters were set to match the optimum

operating parameter determined during the process performance improvement study.

In the chemical dosing part, the 2 process units were operated with the same

chemical concentration based on their own operational flow rate.


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CHAPTER 4

RESULTS AND ANALYSIS

1.3 Characterization of Soluble Coffee Production Wastewater

Incoming wastewater at the equalization tank was analyzed at 2 different time

frames, one was analyzed during the performance monitoring of DAF, and the other

was analyzed during the comparative performance study between the DAF and the

BF. Both of the results are tabulated separately in Appendix A and Appendix B.

These results are summarized separately in Tables 4.1 and 4.2.

.


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Table 4.1: Average values of incoming wastewater characteristics at the

equalization tank (results abstracted from Appendix A):

Waste water testing

parameters

Unit Reading

(Average Value)

1. Color - Dark brown

2. TemperatureoC 31

3. pH - 4.1

4. COD mg/l 13,281

5. BOD5 at 20oC mg/l 3,759

6.

06 tesis tratamiento de aguas

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