Faculty of Engineering

EXPERIMENTAL STUDY ON THE FACTOR AFFECTING COAGULATION AND FLOCCULATION

Helmi bin Mohamad Jamil

Bachelor of Engineering with Honors (Civil Engineering) 2005

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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 5

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 7

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

Chapter 2

Chapter 3

INTRODUCTION 1.1

General

1

1.2

Study Objective and Scope of Study

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LITERATURE REVIEW 2.1

Coagulation

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2.2

Flocculation

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2.3

Alkalinity

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2.4

Chemical Reaction

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2.4.1

Aluminum Sulfate Reaction

12

2.4.2

Reaction of Lime

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2.4.3

Polymers

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2.5

Coagulation Practice

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2.6

The Laboratory Jar Tests

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METHODOLOGY 3.1

Chemicals

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3.1.1

Coagulants

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3.1.2

Coagulant Aids

25

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3.2

The Experimental Study 3.2.1

3.2.2

Chapter 4

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The Procedure of Preparation of Stock Solutions

25

Jar Test Procedure

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3.2.2.1 Equipment

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3.2.2.2 Jar Test Experiment

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DATA AND ANALYSIS 4.1

Sg. Batang Samarahan.

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4.1.1

Jar Test by Using Al(SO4)3

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4.1.2

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

4.1.3

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Jar Test by Using Al(SO4)3, Ca(OH)2 and Polyelectrolyte.

4.2

Sg. Sarawak

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4.2.1

Jar Test by Using Al(SO4)3

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4.2.2

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

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4.2.3

Jar Test by Using Al(SO4)3, Ca(OH)2 and Polyelectrolyte.

4.3

35

45

Sg. Sarawak Kiri

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4.3.1

Jar Test by Using Al(SO4)3

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4.3.2

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

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4.3.3

Jar Test by Using Al(SO4)3, Ca(OH)2 and Polyelectrolyte.

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4.4

Chapter 5

Discussion

58

CONCLUSION

61

REFERENCES

63

APPENDIX

64

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LIST OF CHART AND FIGURE Chart 1

Page number The analysis of optimum dose of Al(SO4)3 required to treat the Sg. Batang Samarahan raw water.

2

The analysis of optimum dose of Ca(OH)2 required to treat the Sg. Batang Samarahan raw water.

3

41

The analysis of optimum dose of Ca(OH)2 required to treat the Sg. Sarawak raw water.

6

44

The analysis of optimum dose of polyelectrolyte required to treat the Sg. Sarawak raw water.

7

50

The analysis of optimum dose of Ca(OH)2 required to treat the Sg. Sarawak Kiri raw water.

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The analysis of optimum dose of Al(SO4)3 required to treat the Sg. Sarawak Kiri raw water.

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37

The analysis of optimum dose of Al(SO4)3 required to treat the Sg. Sarawak raw water.

5

34

The analysis of optimum dose of polyelectrolyte required to treat the Sg. Batang Samarahan raw water.

4

31

53

The analysis of optimum dose of polyelectrolyte required to treat the Sg. Sarawak Kiri raw water.

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4.1

Standard Floc Size.

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4.2

Standard Floc Size.

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4.3

Standard Floc Size.

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4.4

Standard Floc Size.

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4.5

Standard Floc Size.

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4.6

Standard Floc Size.

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4.7

Standard Floc Size.

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4.8

Standard Floc Size.

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4.9

Standard Floc Size.

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1.1

Schematic diagram of a coagulation process.

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2.1

Reaction schematics of coagulation.

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2.2

Interparticle bridging with polymers.

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2.3

Diagram of jar testing device.

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2.4

Results of jar test at increasing turbidities.

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2.5

Coagulant dosage as a function of turbidity.

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Figure

Picture 1

Experimental study on the factor affecting coagulation and flocculation at Batu Kitang Trearment Plant, Bau, Sarawak.

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Experimental study on the factor affecting coagulation and flocculation at Batu Kitang Trearment Plant, Bau, Sarawak.

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LIST OF TABLE AND SCHEDULE

Schedule

Page number

1

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

2

The result of Batang Samarahan by using Al(SO4)3 and Ca(OH)2.

3

28

32

The result of Batang Samarahan by using Al(SO4)3, Ca(OH)2 and polyelectrolyte.

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4

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

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5

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

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6

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

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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.

9

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

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1

Settling time for various diameters of particle

1

2

The stages in agglomeration

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Table

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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

Colloid

2 years

0.00001

0.01

Colloid

20 years

0.000001

0.001

Colloid

200 years

0.0000001

0.0001

Dissolved Matter

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 filtercapture 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,

Hydrolysis

ionization hydrolysis and polymerization 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

Perikinetic Flocculation

- Dissipated energy

Orthokinetic Flocculation

- Differential Settling

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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