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EXPERIMENTAL STUDY ON THE FACTOR AFFECTING

COAGULATION AND FLOCCULATION

Helmi bin Mohamad Jamil

Bachelor of Engineering with Honors

(Civil Engineering)

2005

Faculty of Engineering

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EXPERIMENTAL STUDY ON THE FACTOR AFFECTING COAGULATION AND

FLOCCULATION

HELMI BIN MOHAMAD JAMIL

The thesis is represented to

Faculty of Engineering, University Malaysia Sarawak

As Fulfill a Part of Condition Award of Bachelor of Engineering

With Honors (Civil Engineering) 2005

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DEDICATION

To my parents Hj. Mohamad Jamil bin Bahatim @ Jaafar, Hjh. Normah bt. Hj Embi,

Ariffin bin Ishak, Allahyarhamah Che Mah bt. Ismail, my family and lovely friends.

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ACKNOWLEDGEMENTS

I would like to acknowledge and give thanks to my supervisor Mr. Jethro Henry Adam

who always encourage me to strive for higher performance, my lucky examiner Dr.

Law Poung Ling, Prof. Dr. F.J. Putuhena, oral examiner Prof. Dr. Nabil Bessaih,

Kuching Water Board Secretary Agatha Aham Suni, Senior Chemist Mr. Wong Soon

Sing, Batu Kitang Water Treatment Plant Officer Rahayu, all the great staff at Kuching

Water Board especially at Batu Kitang Water Treatment Plant and certainly not least

my parents and family who were always by my side. Thanks goodness for my helpful

friends Mohd Fadhil bin Musa (FSGK), Diana Michael Gawan (FSGK), Hamsiah bt

Rapaee (FSGK), Mohd Alfian bin Yusop (Master Degree of FSTS) and Mohd Sadeli

(FK).

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ABSTRAK

Laporan ini menumpukan kepada penyelidikan ke atas faktor yang

mempengaruhi pengentalan dan pemberbukuan dalam proses perawatan air. Analisis ini

secara mendalam memfokus ke atas air mentah di Batang Samarahan, Sg. Sarawak dan

Sg. Sarawak Kiri. Kecekapan dan ketepatan pengentalan dan pemberbukuan ini saling

bergantungan kepada banyak faktor. Kajian yang terdahulu menunjukkan pH,

kealkalian, kekeruhan, jenis dan jumlah bahan kimia pengental serta bahan kimia

pengental bantuan, cuaca, jangka masa pembentukan flok dan kadar kelajuan mesin

pencampur secara meluas mempengaruhi keberhasilan proses pengentalan dan

pemberbukuan. Laporan ini menumpukan kepada jumlah optimum Al(SO4)3 sebagai

bahan kimia pengental, Ca(OH)2 sebagai bahan kimia pengental bantuan dan

polyelectrolyte sebagai agen pengumpal untuk mencapai tahap perawatan yang penuh

bermakna, pengaruh pH, dan jangka masa pengumpulan flok. Penyelidikan dan hasil

yang tepat diperlukan untuk membolehkan air mentah dari ke semua sungai ini dirawat

dengan selamat untuk pengguna di sekitar kawasan Kuching. Masalah ini diselesaikan

terutamanya dengan menjalankan ujian kelalang. Selain itu, termasuk beberapa kaedah

eksperimen contohnya penentuan pH dan kekeruhan untuk mencapai hasil yang efisien.

Eksperimen ini dilaksanakan di Logi Rawatan Air, Lembaga Air Kuching, Batu Kitang,

Bau, Sarawak. Penyelidikan ini mendapati kualiti air mentah Batang Samarahan

memerlukan Al(SO4)3 sebanyak 95 ppm, Ca(OH)2 sebanyak 2 ppm dan polyelectrolyte

sebanyak 0.1 ppm. Sg. Sarawak memerlukan Al(SO4)3 sebanyak 20 ppm, Ca(OH)2

sebanyak 1 ppm dan polyelectrolyte sebanyak 0.05 ppm. Bagi Sg. Sarawak Kiri

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sebanyak 25 ppm Al(SO4)3, 1.2 ppm Ca(OH)2 dan 0.2 ppm polyelectrolyte diperlukan.

Tahap kealkalian air mentah adalah faktor terbesar yang menyebabkan perbezaan dalam

penggunaan jumlah bahan kimia pengental dan bahan kimia pengental bantuan. Nilai

pH untuk proses pengentalan dan pemberbukuan yang optimum dicapai sekitar 7.

Eksperimen juga mendapati pembentukan flok yang lebih besar memerlukan masa yang

lebih singkat untuk mendap ke bawah kerana kepekatan bahan lekit adalah tinggi

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ABSTRACT

The report is concentrate on the investigation of factor affecting coagulation and

flocculation. The analysis is profoundly focusing on the raw water at Batang

Samarahan, Sg. Sarawak and Sg. Sarawak Kiri. The effective and efficiency of

coagulation and flocculation is interrelated on many factors. Previous studies indicated

that the pH, alkalinity, turbidity, types and amount of coagulant and coagulant aids,

temperature, detention time for flocs formation and the rate of speeding mixture are

affecting the huge consequence of coagulation and flocculation process. The thesis is

concentrate on the optimum amount of Al(SO4)3 as a coagulant, Ca(OH)2 as a coagulant

aids and polyelectrolyte as a flocculent to achieve significant treatment, influence of

pH, and detention time for flocs agglomeration. The adequate examination and results

are required to enable the raw water from all these rivers are treated with save haven for

end user around the Kuching region. The problem is solved by first and foremost

conducting the laboratory jar test. There are also included several experiment

procedure, for instance pH determination and turbidity to achieve the efficient results.

The experiment is implemented at Water Treatment Plant, Kuching Water Board, Batu

Kitang, Bau, Sarawak. The investigation are found that the quality of raw water at

Batang Samarahan required Al(SO4)3 in the range of 95 ppm, Ca(OH)2 in the range of

2.0 ppm and polyelectrolyte in the range of 0.1 ppm. The Sg. Sarawak required 20 ppm

of Al(SO4)3, 1.0 ppm of Ca(OH)2 and 0.05 ppm of polyelectrolyte. For Sarawak Kiri 25

ppm of Al(SO4)3, 1.2 ppm of Ca(OH)2 e and 0.2 ppm of polyelectrolyte required. The

alkalinity of the raw water is a dominant factor that causing the differences in applying

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the amount of coagulant and coagulant aid. The pH value for optimum coagulation and

flocculation is achieved around 7. The experiment also found that larger flocs formation

needed the smaller time for settling because the colloidal concentration is highest.

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CONTENTS

Page number

List of Chart and Figure xi

List of Table and Schedule xiii

List of Abbreviations xiv

Chapter 1 INTRODUCTION

1.1 General 1

1.2 Study Objective and Scope of Study 5

Chapter 2 LITERATURE REVIEW

2.1 Coagulation 6

2.2 Flocculation 8

2.3 Alkalinity 11

2.4 Chemical Reaction 11

2.4.1 Aluminum Sulfate Reaction 12

2.4.2 Reaction of Lime 14

2.4.3 Polymers 15

2.5 Coagulation Practice 17

2.6 The Laboratory Jar Tests 19

Chapter 3 METHODOLOGY

3.1 Chemicals 24

3.1.1 Coagulants 24

3.1.2 Coagulant Aids 25

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3.2 The Experimental Study 25

3.2.1 The Procedure of Preparation of

Stock Solutions 25

3.2.2 Jar Test Procedure 26

3.2.2.1 Equipment 26

3.2.2.2 Jar Test Experiment 26

Chapter 4 DATA AND ANALYSIS

4.1 Sg. Batang Samarahan. 28

4.1.1 Jar Test by Using Al(SO4)3 28

4.1.2 Jar Test by Using Al(SO4)3 and

Ca(OH)2. 32

4.1.3 Jar Test by Using Al(SO4)3, Ca(OH)2

and Polyelectrolyte. 35

4.2 Sg. Sarawak 38


4.2.2 Jar Test by Using Al(SO4)3 and Ca(OH)2. 42



4.3 Sg. Sarawak Kiri 48


4.3.2 Jar Test by Using Al(SO4)3 and Ca(OH)2. 51



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4.4 Discussion 58

Chapter 5 CONCLUSION 61

REFERENCES 63

APPENDIX 64

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LIST OF CHART AND FIGURE

Chart Page number

1 The analysis of optimum dose of Al(SO4)3

required to treat the Sg. Batang Samarahan raw water. 31

2 The analysis of optimum dose of Ca(OH)2


3 The analysis of optimum dose of polyelectrolyte


4 The analysis of optimum dose of Al(SO4)3 required

to treat the Sg. Sarawak raw water. 41

5 The analysis of optimum dose of Ca(OH)2 required

to treat the Sg. Sarawak raw water. 44


required to treat the Sg. Sarawak raw water. 47

7 The analysis of optimum dose of Al(SO4)3 required

to treat the Sg. Sarawak Kiri raw water. 50

8 The analysis of optimum dose of Ca(OH)2 required

to treat the Sg. Sarawak Kiri raw water. 53


required to treat the Sg. Sarawak Kiri raw water. 57

4.1 Standard Floc Size. 30


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Figure

1.1 Schematic diagram of a coagulation process. 2

2.1 Reaction schematics of coagulation. 13

2.2 Interparticle bridging with polymers. 16

2.3 Diagram of jar testing device. 20

2.4 Results of jar test at increasing turbidities. 21

2.5 Coagulant dosage as a function of turbidity. 23

Picture

1 Experimental study on the factor affecting coagulation

and flocculation at Batu Kitang Trearment Plant, Bau, Sarawak. 64

2 Experimental study on the factor affecting coagulation

and flocculation at Batu Kitang Trearment Plant, Bau, Sarawak. 65

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LIST OF TABLE AND SCHEDULE

Schedule Page number

1 The result of Batang Samarahan by using Al(SO4)3 28

2 The result of Batang Samarahan by using Al(SO4)3

and Ca(OH)2. 32

3 The result of Batang Samarahan by using Al(SO4)3,

Ca(OH)2 and polyelectrolyte. 35

4 The result of Sg. Sarawak by using Al(SO4)3 38

5 The result of Sg. Sarawak by using Al(SO4)3 and Ca(OH)2. 42

6 The result of Sg. Sarawak by using Al(SO4)3, Ca(OH)2

and polyelectrolyte. 45

7 The result of Sg. Sarawak Kiri by using Al(SO4)3 48

8 The result of Sg. Sarawak Kiri by using Al(SO4)3

and Ca(OH)2. 51

9 The result of Sg. Sarawak Kiri by using Al(SO4)3,

Ca(OH)2 and polyelectrolyte. 54

Table

1 Settling time for various diameters of particle 1

2 The stages in agglomeration 8

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LIST OF ABBREVIATIONS

Al(SO4)3 - Aluminum Sulfate

Ca(OH)2 - Calcium Hydroxide

NTU - Nephlometric Turbidity Unit

ppm - part per million

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CHAPTER 1

INTRODUCTION

1.1 General

Coagulation and flocculation is an essential process in raw water treatment.

Surface water sources may contain suspended and colloidal solids as a result of soil

erosion, decaying vegetation, and microorganisms. Coarser materials such as silt and

sand can usually be eliminated by gravity settling. However, it is the long settling time

of finer particles to settle under the influence of gravity alone and shown in Table 1.

Table 1: Settling time for various diameters of particles.

Particle diameter Type of Particle Settling time through 1m of

water mm um

0.0001 0.1

0.00001 0.01

0.000001 0.001

0.0000001 0.0001

Colloid

Colloid

Colloid

Dissolved Matter

2 years

20 years

200 years

Infinity

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Therefore, finer particles must be chemically coagulated to form larger particles

which more easily removed in subsequent sedimentation and filtration steps. A

schematic flow diagram of a typical treatment process is shown in Fig. 1.1

Figure 1.1: Schematic diagram of a coagulation process

Coagulation is accomplished by the addition of a chemical coagulant which

neutralizes the surface charge usually negative found on colloidal material. Elimination

of the repulsive forces between suspended solid particles allows them to stick together

and form flocs upon contact. The process where coagulant is added to facilitate the

destabilization of particles is called the rapid mixing.

After coagulation, gentle mixing of the water sample, called flocculation,

promotes contact between the neutralized suspended solid particles. This results in the

flocs form which can be more easily settled from solution. Flocs settling velocity is not

constant as is discrete settling, but increases as particles agglomerate.

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Optimum coagulation treatment of raw water represents the achievement of very

complex constancy in which many variables are involved. Investigation by Corbitt,

(1990) for certain water, there will be interrelated optima of conditions, such as pH,

turbidity, chemical composition of the water, types of coagulant, and such physical

factors as temperature and mixing conditions.

The previous experimental establish that highly turbid water or highly pH

relatively easy to treat. Turbid water normally requires higher coagulant dosage. Water

with low pH or low alkalinity, necessary to add caustic soda or lime as a coagulant aids

to raise the pH and to balance the acidity of metal ion coagulants which strongly

influences the adsorption properties of coagulation.

Low temperature has effect on the efficiency of treatment processes. From the

previous study increasing in temperature caused decreasing in detention time.

According to the Stokes law, discrete settling in laminar region is inversely proportional

to viscosity. Viscosity is lower at higher temperatures meaning that flocs settling

velocity decreases at lower temperatures.

Different chemicals may be used as a coagulant in coagulation depending on the

characteristics of the water being treated. In certain waters, a combination of two or

more chemicals produces better results than any one chemical alone. The optimum

coagulant dose is also a function of chemical and physical composition of water.

Overdosing cause destabilization of destabilized particles.

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Rapid mixing for a few seconds is required to separate the coagulant during

coagulation. However gentle mixing of the suspension is then undertaken to promote

particle contact during flocculation. Longer times will allow more contact between

particles and thus promotes the agglomerate to form larger solids called floc.

The jar test is a laboratory procedure used to determine the optimum operating

conditions for raw water treatment by trial and error. This method allows adjustments in

pH, variations in coagulant or polymer dose, alternating mixing speeds, or testing of

different coagulant or polymer types, on a small scale in order to predict the functioning

of a large scale treatment operation. A jar test simulates the coagulation and flocculation

processes that encourage the removal of suspended colloid and organic matter which

can lead to turbidity, odor and taste problems.

Aluminum sulfate [Al(SO4)3], ferrous sulfate [FeSO4], ferric chloride [FeCl3],

ferric sulfate [Fe2(SO4)3], calcium hydroxide [Ca(OH)2], and calcium hardness

[Ca(HCO3)2] were usually used as coagulants. Lime [Ca(OH)2], soda ash [Na2CO3],

caustic soda or lye [NaOH] and sulfuric acid were usually used as coagulant aids.

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1.2 The Objective and Scope of Study.

The objective of the project is to determine the factors affecting coagulation and

flocculation. The objective is specified to the analysis of the optimum dosage required

to treat the raw water. The raw water samples are collected from Batang Samarahan, Sg.

Sarawak and Sg. Sarawak Kiri. The briefing objective is mainly concentration on jar

test experiment and several procedures related. Generally, the factor affecting

coagulation and flocculation is more influenced by alkalinity of the raw water or the

quality of the raw water.

The detail investigation is using the Al(SO4)3 as a coagulant, Ca(OH)2 as a

coagulant aid and polyelectrolyte as a flocculent. The experiment enable to acquire the

optimum dose of Al(SO4)3, Ca(OH)2 and polyelectrolyte required to attain the

significant treatment for each raw water from Batang Samarahan, Sg. Sarawak and Sg.

Sarawak Kiri. The study of factor Ca(OH)2 as a coagulant aid and polyelectrolyte as a

flocculent on the flocs formation is performed with added to the appropriate Al(SO4)3

determine previous in the jar test.

The study also explore the factor of pH, turbidity and the temperature of each

raw water with their relationship to the dose of Al(SO4)3. The investigation is expanded

to the factor of Al(SO4)3, Ca(OH)2 and Polyelectrolyte and its influence to the form

flocs upon contact. The turbidity of raw water is measured by 2100N Turbidimeter and

the pH value by pH meter. The size of flocs is measure by sighting or eye and compare

with their standard size.

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CHAPTER 2

LITERATURE REVIEW

2.1 Coagulation.

Tchobanoglous and Burton, (1991) state that raw water colloidal suspension

consists of negatively charged particles. When particles are similarly charged, the

resulting repulsive forces tend to stabilize the suspension and prevent particle

agglomeration. In order to destabilize the colloids, that is to neutralize the negative

surface charge positive ions are introduced into it through coagulation process and form

a layer around the colloids.

According to Heinke and Henry, (1989) coagulation is a chemical process used

to destabilize colloidal particle by add a chemical which has positively charged colloids

to water containing negatively charged colloids. The process will neutralize the negative

charge on the colloids and thus reduce the tendency for the colloids to repel each other.

The process is also known as colloid destabilization. Rapid mixing for a few seconds is

required to disperse the coagulant.

Experiment study by Eilbeck and Mattock, (1987), Tchobanoglous and Burton,

(1991), McGhee, (1991), and Casey, (1997) found that the most commonly used

coagulants-flocculants in raw water treatment are the trivalent salts of iron [FeCl3,

Fe2(SO4)3] and aluminum sulfate [Al(SO4)3]; ferrous sulfate [FeSO4]; and calcium

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hydroxide [Ca(OH)2]. There are often used with various coagulant aids, such as

synthetic polyelectrolyte (anionic, cationic, or non-ionic polymers), fly ash and clay.

The choice of a specific coagulation reagent is firstly governed by its effectiveness.

The choice of coagulants is dependent on the raw water quality. Generally,

aluminum sulfate [Al(SO4)3] is used for high turbidity raw water. Aluminum sulfate

[Al(SO4)3] and sodium aluminate are used for colored water. Most of waters in Sarawak

have insufficient natural alkalinity, so soda carbonate (soda ash) or hydrated lime is

added to react with the coagulants to form their hydroxides. More waterworks in

Sarawak are used polyelectrolyte to replace aluminum sulfate [Al(SO4)3] as a coagulant

for treating colored water with significant success.

The choice of coagulant is also dependent on the following factors:

a. Maintenance of optimum coagulation pH for coagulation.

b. Application of optimum chemical dosages, which can be determined by

conducting a series of jar tests.

c. Attainment of uniform dispersion of chemical throughout the mass of

water being treated.

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2.2 Flocculation.

Flocculation is the physical process of bringing the destabilized particles in

contact to form larger flocs that can be more easily removed from suspension. The

process is accomplished by slow mixing of the destabilized suspension to provide an

opportunity for the particles to come into contact with one another and bridge together.

Therefore, flocculation enhances subsequent sedimentation or the performance of

filtration systems by increasing particle size, resulting in increased settling and filter-

capture rates. The stages in agglomeration are summarized in Table 2.

Table 2: The stages in agglomeration

Stage Factors Term

Addition of coagulant Reaction with water,

ionization hydrolysis and

polymerization

Hydrolysis

Destabilization - Double layer

compression.

- Specific absorption of

ions from the coagulant on

the surface of the particles.

- Specific linkage between

ions or species on the

surface of the particles.

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- Inclusion of the colloid in

a hydroxide precipitate.

- Interparticular linking by

polymeric species of

coagulant.

Transport - Brownian Movement

- Dissipated energy

- Differential Settling

Perikinetic Flocculation

Orthokinetic Flocculation

Orthokinetic Flocculation

The three major mechanisms of flocculation are:

a. Aggregation resulting from Brownian movement of fluid molecules

(perikinetic flocculation). When particles move in water under Brownian

motion, they collide with other particles. On contact, they form large

particles and continue until they become too large to be affected by

Brownian motion. Perikinetic flocculation is predominant for sub-micron

particles. A large initial concentration of particles in the suspension will

cause faster floc formation, since the opportunity for collision is high.

b. Aggregation made by velocity gradient in the fluid (orthokinetic

flocculation). Orthokinetic flocculation that involves particles movement

with gentle motion water considers that particles will agglomerate if they

collide and become close enough to be within a zone of influence of one

another. It also considers that particles have negligible settling velocity

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