FERRIC CHLORIDE AS COAGULANTS IN WATER...

EXPERIMENTAL INVESTIGATION ON FERRIC CHLORIDE AS COAGULANT IN WATER TREATMENT PROCESS

By

Manit Pongchalermporn

A research study submitted as a partial fulfillment of the requirements for the degree of Master of Engineering

Examination Committee Prof. C. Visvanathan (Chairperson) Prof. Samorn Muttamara Dr. Nguyen Thi Kim Oanh Nationality Thai Previous Degree Master of Science Mahidol University Bangkok, Thailand Scholarship Donor Asian Institute of Technology-Partial Scholarship

Asian Institute of Technology School of Environment, Resources and Development

Bangkok, Thailand August 2002

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Acknowledgement I would like to dedicate the success of this study to my parents, friends and Mahasawat Waterworks Authority (MWA), Special thanks for Mr. Nilcharat Koohirun, former deputy governer to Metropolitan Waterworks Authority, who already passed away, he always encourage me to study at AIT.

I would like to express the sincere gratitude and highly appreciation to my advisors, Prof. C. Visvanathan, Dr. Nguyen Thi Kim Oanh and especially Prof. Samorn Muttamara for their great contributions to enable me to accomplish this study. I also wish to express my thankful to Mr. Ittidej Boonyavit, the Department Director of Mahasawat Water Treatment Plant for his advice, understanding and strongly supporting my further study. Sincere thanks to Siam PVS Chemicals Co., Ltd. for providing Ferric Chloride for this experiment. Of course I have to thank to the staff of Mahasawat Water Treatment Plant for their support and good cooperation during the experiment. I feel indebt to all Professors at UEEM and everyone who involved for my success, there is no word to express my feelings to them except “Thank you”. It will be always in my mind and through out my life as well.

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Abstract

Pilot scale experiments were done for water treatment processes at Mahasawat Water Treatment Plant. Two phase of experiment were performed; 1) High turbidity raw water from Tha Chin River and 2) Low turbidity raw water from Mae Klong River. Raw water from each phase was treated by two coagulants, Aluminum Sulfate (Alum, which is the traditional coagulant for Metropolitan Waterworks Authority) and Ferric Chloride.

Phase I: average raw water turbidity was around 30 NTU, by applying 55 and 25

mg/L of Aluminum Sulfate and Ferric Chloride as coagulants, the overall treatment after filtration were 95.6 and 98.8%, respectively.

Phase II: average raw water turbidity was around 17 NTU, by applying 40 and 15

mg/L of Aluminum Sulfate and Ferric Chloride as coagulants, the overall treatment after filtration were 97.4 and 98.1% respectively.

Average filter run period for Aluminum Sulfate and Ferric Chloride were 23 and 34

hours, respectively. By using Ferric Chloride, filter run period can prolong 32.4%. Costs of drinking water production were 0.142 and 0.105 Baht/m3 when using

Aluminum Sulfate and Ferric Chloride, respectively. By using Ferric Chloride, chemical cost can be saved 26.0%.

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Table of Contents

Chapter Title Page Title page i Acknowledgement ii Abstract iii Table of contents iv List of figures vi List of tables vii List of abbreviations viii 1 Introduction 1 1.1 General 1 1.2 Objective of the study 2 1.3 Scope 2 2 Literature Review 3 2.1 Coagulation 3 2.2 Mechanisms of coagulation 3 2.3 Influence of mixing on coagulation 5 2.4 Conventional coagulants 6 2.5 Hydrolysis specification of inorganic metal salts 7 2.6 Coagulation Diagrams 10 2.7 Natural aquatic humic substances 10 3 Methodology 17 3.1 Introduction 17 3.2 Data collection 17

3.3 Experimental Set Up 17 3.4 Experimental Procedure 20

3.5 Sample Collection 20 3.6 Results Interpretation and Conclusion 22

4 Results and Discussion 23 4.1 Phase I: Tha Chin River Raw Water 23

4.1.1 Aluminum Sulfate as Coagulant 23 4.1.2 Ferric Chloride as Coagulant 26

4.2 Phase II: Mae Klong River Raw Water 30 4.2.1 Aluminum Sulfate as Coagulant 30 4.2.2 Ferric Chloride as Coagulant 34

4.3 Turbidity Treatment Efficiency Comparison 38 4.3.1 Phase I: Tha Chin River Raw Water (High Turbidity) 38 4.3.2 Phase II: Mae Klong River Raw Water (Low Turbidity) 39 4.4 Ferrous, Manganese and Residual Aluminum in filtered water 41 4.5 Total Solids 41 4.6 Filter Run Period 41

4.7 Expected Savings for Mahasawat Water Treatment Plant (MWTP) 42

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Chapter Title Conclusions and Recommendations 43 5.1 Conclusions 43 5.2 Recommendations 43

References 44 Appendices 46

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List of Abbreviations

Al Aluminum Alum Aluminum Sulfate AWWA American Water Works Association cm. Centimeter °C Degree Celcius DOC Dissolved Organic Carbon DOM Dissolved Organic Matter Fe Ferrous F:A Ferric Chloride : Aluminum Sulfate L/hr Litre per hour m. Meter mg/L milligram per litre mL MilliLitre mol wt Molecular Weight M Molar Mn Manganese MWA Metropolitan Waterworks Authority NTU Nephelometric Turbidity Unit pH Negative logarithm of the effective hydrogen-iron concentration rpm Revolutions per minute U Unit

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List of Figures

Figure Title Page 2.1 Stoichiometry of coagulation of fulvic acid 5 2.2 Reaction schematics of coagulation 7 2.3 Coagulation behavior of Fe(lII) polymeric species 9 2.4 Comparison of different coagulants 11 2.5 Design and operation diagram for alum coagulation 12 2.6 Design and operation diagram for ferric iron coagulation 13 3.1 Schematic Diagram for water treatment process 18 3.2 Experimental setup for pilot scale water treatment plant 19 3.3 Experimental setup 19 3.4 Jar test equipment 21 4.1 Logarithm graph from jar test for Aluminum Sulfate as coagulant, Phase I 24 4.2 Turbidity of raw water, clarified water and filtered water for Aluminum 24

sulfate as coagulant, Phase I 4.3 Alkalinity of raw water and clarified water for Aluminum sulfate as 25

coagulant, Phase I 4.4 pH of raw water, clarified water and filtered water for Aluminum sulfate 25

as coagulant, Phase I 4.5 Turbidity removal efficiency of clarified and filtered water for Aluminum 26

sulfate as coagulant, Phase I 4.6 Pressure drop of sand filter for Aluminum sulfate as coagulant, Phase I 26 4.7 Logarithm graph from jar test for Ferric Chloride as coagulant, Phase I 27 4.8 Turbidity of raw water, clarified water and filtered water for Ferric Chloride 28

as coagulant, Phase I. 4.9 Alkalinity of raw water and clarified water for Ferric Chloride as coagulant, 28

Phase I 4.10 pH of raw water, clarified water and filtered water for Ferric Chloride 29

as coagulant, Phase I 4.11 Turbidity removal efficiency of clarified and filtered water for Ferric Chloride 29

as coagulant, Phase I 4.12 Pressure drop of sand filter for Ferric Chloride as coagulant, Phase I 30 4.13 Jar test results for Aluminum Sulfate as coagulant, Phase II 31 4.14 Turbidity in raw water, clarified water and filtered water for Aluminum 32 Sulfate as coagulant, Phase II 4.15 Alkalinity in raw water and clarified water for Aluminum Sulfate as coagulant, 32 Phase II 4.16 pH in raw water, clarified water and filtered water for Aluminum Sulfate as 33 coagulant, Phase II 4.17 Turbidity removal efficiency clarified water and filtered water for Aluminum 33 Sulfate as coagulant, Phase II 4.18 Pressure drop for Aluminum Sulfate as coagulant, Phase II 34 4.19 Jar test result for Ferric Chloride as coagulant, Phase II 35 4.20 Turbidity in raw water, clarified water and filtered water for Ferric Chloride 35 as coagulant, Phase II

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Figure Title Page 4.21 Alkalinity in raw water and clarified water for Ferric Chloride as coagulant, 36 Phase II 4.22 pH in raw water, clarified water and filtered water for Ferric Chloride as 36 coagulant, Phase II. 4.23 Turbidity removal efficiency in clarified water and filtered water for Ferric 37 Chloride as coagulant, Phase II 4.24 Pressure drop for Ferric Chloride as coagulant, Phase II 37 4.25 Average turbidity in different sampling points of experiment Phase I 38 4.26 Average turbidity treatment efficiency in clarified and filtered water of 39 experiment Phase I 4.27 Average turbidity in different sampling points of experiment Phase II 40 4.28 Average turbidity treatment efficiency in clarified and filtered water of 40 experiment Phase II.

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List of Tables

Table Title Page 3.1 Parameters and their experimental procedures 21 4.1 Jar Test result for Aluminum Sulfate as coagulant, Phase I 23 4.2 Jar Test result for Ferric Chloride as coagulant, Phase I 27 4.3 Turbidity results(NTU) from Jar Test for Ferric Chloride as coagulant feeding 31

rate 25 mg/L 4.4 Jar test result for Ferric Chloride as Coagulant, Phase II 34 4.5 Residual chemicals concentration, comparing with the standard of filtered 41 water from the experiments. 4.6 Comparison conclusion of Ferric Chloride and Aluminum Sulfate 42

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Chapter 1

Introduction 1.1 General

Aluminum Sulfate, commonly know as Alum, has been widely used as coagulant in water treatment process in Thailand and around the world for over a century. Coagulation is one of the most important step in drinking water treatment. Its purpose is to destabilize the suspended colloidal and dissolved contaminants in water, so they may be removed by subsequent processes. Coagulation typically involves the addition of metallic salts to the water. The salts undergo complex hydrolysis reaction, and the reaction products cause the destabilization of contaminants in the water. The destabilization contaminants are then bought into contact with one another so that aggregation occurs. Metallic salts of aluminum sulfate and Fe(III) are typically used as coagulants, the most common being aluminum sulfate. Coagulation diagrams have been developed to assist the design engineers and plant operators in identifying conditions for the mechanisms of effective coagulation. The diagrams are based on the removal of turbidity and indicate the pH and coagulant dosage, it which this removal is effective. To be more applicable to natural surface water, the diagrams should also incorporate the removal of dissolved organic constituents. Regions of removal for natural aquatic humic substances have not been previously investigated using the coagulation diagram. Although numerous studies have addressed the removal of natural aquatic humic substances by alum coagulation, few studies have extensively investigated the effectiveness of Fe(III) coagulant.

Aluminum Sulfate has been used as a main chemical usage in Metropolitan Waterworks Authority (MWA) for water treatment process for more than 3 decades. This is because of its lowest price compare to other chemicals. However, Ferric Chloride becomes more acceptable for its application on water treatment process in many countries such as Australia, United States of America and Canada. Because it shows an effective solution for destablilization of particles, removal of dissolved organic matter, induction of flocculation and also improvement of filtration. In order to promote Ferric Chloride to be a real application in water treatment process, the comparison experimental study of Alum and Ferric Chloride was done in Mahasawat Water Treatment Plant. Further application of Ferric Chloride might be possible for all MWA’s water treatment plant if the study shows that using Ferric Chloride is better than Aluminum Sulfate.

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1.2 Objective of the Study The objective of this study is to investigate the effectiveness of ferric chloride for

turbidity and dissolved organic removal in water treatment process, through pilot scale experiment unit.

Specific objectives are as below:

To study the efficiency of Ferric Chloride, and To investigate the cost-effectiveness of Ferric Chloride compare with

Aluminum Sulfate. 1.3 Scope of the Study

Conducting the standard jar test as batch experiment in order to investigate the optimum operating condition, and

Setting up a pilot scale experimental unit for application of continuous flow experiment and measuring parameters involved.

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Chapter 2

Literature Review

2.1 Coagulation

Conventional water treatment typically involves the following sequence of physicochemical processes: rapid mixing; slow mixing, or flocculation; sedimentation; filtration; and disinfection. Variations in this sequence include direct filtration, which eliminates sedimentation, and in-line filtration, which eliminates both flocculation and sedimentation. In the treatment of drinking water, coagulation is considered a pretreatment process. Its effectiveness affects the efficiency of sedimentation and filtration.

Coagulation involves the addition of chemicals into water to produce chemical species

that act to destabilize contaminants and improve their removal. In water treatment, chemical coagulants are used to destabilize particles, remove dissolved organic matter, induce flocculation, and improve filtration (AWWA Coagulation Committee 1988). The processes of rapid mixing and flocculation are collectively known as coagulation. The purposes of rapid mixing are to provide quick and uniform dispersion of chemicals and to cause the destabilization of the particles in the raw water (AmirtharaJah and Mills, 1982). Slow mixing provides an opportunity for particles to aggregate and form a settleable or filterable mass.

Numerous reviews of the fundamental theory and mechanisms of coagulation have been

published (O'Melia, 1972; Dempsey, 1984; AWWA Coagulation Committee, 1988; Gray, 1988; Gregory, 1989; Amirtharajah and O'Melia, 1990). The purpose of this section is to provide a general overview of the mechanisms of coagulation, the influence of mixing on coagulation, typical coagulants, and coagulation diagrams. This overview is followed by a detailed review of the hydrolysis of inorganic metal salts, specifically ferric chloride, and the mechanisms by which humic substances are removed during coagulation with metal salts. 2.2 Mechanisms of Coagulation

Different mechanisms of destabilizing contaminants using chemical coagulants have been identified. These mechanisms include double layer compression, charge neutralization, sweep coagulation, and interparticle bridging (O'Melia, 1972; and Dempsey, 1984). The type of interaction between the chemical coagulant and the contaminants determines the mechanism of coagulation. Double Layer Compression

The theory of double layer compression has its foundation electrostatic repulsion between similarly charged particles. When oppositely charged ions surround the particles, the electrostatic repulsion is reduced. At a certain concentration of ions, the double layer will theoretically be compressed to an extent that enables attractive forces to hold the particles together. This mechanism is not considered to be significant for the treatment of most freshwaters (Dempsey, 1984).

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Adsorption-Charge Neutralization

Charge neutralization involves the interaction of a chemical coagulant and a charged contaminant (Stumm and O'Melia, 1968). Dempsey et al. (1984) reported that stoichiometry exists between the coagulant and the contaminant under conditions of charge neutralization. They demonstrated stoichiometry between aquatic fulvic acid and the coagulant polyaluminum chloride, as presented in Figure 2.1. The stoichiometry between coagulant dosage and concentration of a contaminant to be removed is indicative of adsorptive interactions (Tang and Stumm, 1987). Evidence of adsorptive interaction is the occurrence of charge reversal. Excessive coagulant concentrations may result in restabilization of particles by reversing the charge on the contaminant (O'Melia, 1972; Dempsey, 1984). Conditions leading to restabilization can be detected by monitoring the electrophoretic mobility or zeta potential of the particles. Sweep Coagulation

The removal of contaminants through the formation of a solid precipitate is referred to as sweep coagulation. This mechanism of coagulation is common when metal salts such as alum or ferric chloride are used as coagulants. Voluminous hydroxide precipitates formed because the water is supersaturated to several orders of magnitude above the solubility of the metal salt (AWWA Coagulation Committee, 1988). When aluminum and ferric salts are used, the solid precipitate species that typically formed are Al(OH)3 (aluminum hydroxide) and Fe(OH)3 (ferric hydroxide), respectively. Dissolved contaminants adsorb to the solid precipitate and are removed with it; particulate contaminants are removed by enmeshment or entrapment within a mass of the solid precipitate.

Dempsey (1984) pointed out that particulate contaminants are typically negatively

charged and that the solid precipitates formed during conditions of sweep coagulation are positively charged. He suggested that particulate contaminants are electrostatically attracted to the solid precipitates. Interparticle Bridging

Interparticle bridging is a mechanism of particle destabilization that involves the use of high molecular weight (mol wt > 106) polymers as coagulants. Some of the functional groups on the polymers bond to the surface of the contaminants, and others extend out and contact the surface of other particles in the solution. The polymer serves as a "bridge" between two or more particles (O'Melia, 1972).

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Aluminum Dosage (mg/L)

Note: C/Co = ratio of final to initial fulvic acid concentration; TOC = total organic carbon. Source: Dempsey, Ganho, and O'Melia, 1984.

Figure 2.1 Stoichiometry of coagulation of fulvic acid. 2.3 Influence of Mixing on Coagulation

Charge neutralization requires rapid and uniform mixing of the chemicals added to the water and contact between the charged contaminant particulates and the hydrolysis species of the coagulant (Amirtharajah and Mills, 1982). This contact must occur before the hydrolysis speciation reaches the state where solid hydroxide precipitate is formed (O'Melia, 1972). The purpose of rapid mixing is to provide quick and uniform dispersion of the chemicals added to the untreated water, creating the coagulant species that cause destabilization.

Slow mixing is an important step when the mechanism is sweep coagulation. A report

prepared by the AWWA Coagulation Committee (1988) reviewed the fundamentals of slow mixing and flocculation. The process of slow mixing promotes contact between the solid

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hydroxide precipitate and the particulate matter to be removed. Collisions between particles occur by Brownian motion, fluid motion, and differential sedimentation. The frequency of collisions is dependent on properties of the water and the particles as well as the type of mixing. Properties of the water include temperature, viscosity, and density. Properties of the particles to be removed include number concentration, density, and size. Mixing conditions may vary depending on detention time, flow conditions, and mixing intensity. 2.4 Conventional Coagulants

Metal salts and high molecular weight organic polymers can induce coagulation under appropriate conditions. The selection of a coagulant is based on the characteristics of the raw water to be treated and the desired mechanism of coagulation. Raw water characteristics that must be considered are turbidity, temperature, concentration of DOM, pH, buffer capacity, ionic strength, and calcium concentration. Jar testing is a valuable technique for evaluating the effectiveness of coagulants.

Inorganic Metal Salts

Because of their ionic charge, all simple salts present in natural waters can affect the stability of colloidal particles. However, simple salts are not effective as coagulants because they do not promote the formation of strong aggregates that are resistant to shear (Gregory, 1989). Salts that release adsorbing counterions are more effective coagulants. When these salts are added to water, counterions are released and adsorb to the particle surfaces. The charge on these particles is reduced to nearly zero.

The mechanism of coagulation for metal salts of aluminum and iron involves either the

adsorption of coagulant species to the contaminant to be removed or the entrapment of the contaminant within a hydroxide precipitate (O'Melia, 1972; Gregory, 1978). The reaction schematics are shown in Figure 2.2.

Dempsey (1984) reported that alum is the most commonly used coagulant for water

treatment in the United States and that polyaluminum chloride is widely used in Japan. Fe(III) salts are also used as coagulants in drinking water treatment but are more commonly used in wastewater treatment The effective pH range for Fe(III) salts is reportedly broader than that for aluminum salts (Gregory, 1989; Hall and Packham, 1965). Polymeric Coagulants

Polyelectrolytes that have nonionic, anionic, or cationic character have been developed as coagulants. These high molecular weight products interact with the surfaces of particles in the water through hydrophobic and hydrogen bonding (Gregory, 1989). The primary mechanism of coagulation with polyelectrolytes is interparticle bridging. These products tend to produce flocs that are more resistant to high shear stresses than are flocs formed with inorganic coagulants. High shear stresses during mixing or flow within pipes and channels may cause floc breakup.

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Source: Amirtharajah and Mills, 1982.

Figure 2.2 Reaction schematics of coagulation. 2.5 Hydrolysis Speciation of Inorganic Metal Salts

When a metal salt is added to water, a series of complex hydrolysis reactions occur. Gregory (1989) described the hydrolysis of a metal salt as the progressive replacement of water molecules in the hydration shell with hydroxyl groups. The positive charge is reduced until the formation of the solid hydroxide precipitate occurs. The hydrolysis speciation is continuously changing and is influenced by many factors. Dempsey (1984) provided as many of these factors, which include the pH and temperature of the water, the presence of particulate and dissolved matter, the mixing conditions, and the time of reaction. Other factors sometimes considered are the concentration and age of the coagulant solution. Impact of Hydrolysis Speciation

When inorganic metal salts are used as coagulants, the mechanism of coagulation is controlled by the hydrolysis speciation. The efficiency of charge neutralization as a mechanism of coagulation depends upon the speciation of the coagulant. Amirtharajah and Mills (1982) stressed that the intensity of rapid mixing is of utmost importance for charge neutralization because the coagulant species must come in contact with the charged contaminants before the solid hydroxide precipitate forms. The hydrolysis of the coagulant influences the efficiency of contaminant removal and the settleability of fIoc (AWWA Coagulation Committee, 1988). Hydrolysis of Fe(III) Salts

The mechanisms of coagulation for Fe(III) salts are a function of the hydrolysis speciation of Fe (III) in water (Stumm and Morgan, 1962; Stumm and O'Melia, 1968; Black, 1967; Johnson and Amirtbarajah, 1983; Matijevic and Janauer, 1966). The hydrolysis of a metal salt is primarily

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dependent on the characteristics of the raw water and is affected by the intensity and duration of rapid mixing. The process that hydrolyzes Al (III) is essentially identical to that for Fe(lII).Al(III) speciation was reviewed in detail by Baes and Mesmer (1976), and many of the major species formed during hydrolysis are shown in Figure 2.2.

The following possible hydrolysis reactions of Fe(III) in aqueous solution were reported

by Stumm and coworkers (Stumm and Morgan, 1962; Stumm and O'Melia, 1968; Tang and Stumm, 1987):

Fe3+ + H2O <=> Fe(OH)2+ + H+

Fe3+ + 2H2O <=> Fe(OH)2 + + 2H+

2Fe3+ + 2H2O <=> Fe2(OH)2

4+ + 2H+

3Fe3+ + 4 H2O <=> Fe3(OH)4

5+ + 4H+

Fe3+ + 3 H2O <=> Fe(OH)3 + 3H+

Similar reactions were reported by Snoeyink and Jenkins (1980). All of these reactions

follow the general expression

xFe3+ + yH2O <=> Fex(OH)y (3x-y)+ + yH+

Fe3+ does not exist in natural waters as a simple ion but exists as an aquocomplex species,

such as Fe(H2O)63+ (O'Melia, 1972). However, to simplify the reaction expressions, the water

molecules are typically not shown. Tang and Stumm (1987) evaluated the speciation of ferric chloride and presented several

reactions that can form complexes between Fe(III) and Cl-.

These were given as

Fe3+ + Cl- <=> FeCl2+

Fe3+ + 2Cl- <=> FeCl2+

Fe3+ + 3Cl-<=>FeCl3

o

Fe3+ + 4Cl- <=>FeCl4

After an extensive evaluation of factors controlling the hydrolysis speciation of Fe (III),

Tang and Stumm (1987) proposed the hydrolysis-polymerization-precipitation scheme presented in Figure 2.3. This scheme incorporates those previously proposed by Dousma and de Bruyn (1976) and Knight and Sylva (1974) and shows the chemical species expected to be present during various stages of hydrolysis. The extent of hydrolysis of a coagulant is dependent on the age of the coagulant solution as well as its concentration. In addition, elevated temperature promotes hydrolysis reactions (Tang and Stumm, 1987). In the Tang and Stumm scheme, type A

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solutions contain monomers, oligomers, and complexes with chlorides that occur during the initial stages of hydrolysis. At low OH-:Fe ratios, rapid precipitation is favored under conditions characteristic for type B solutions.

Note: am = amorphous species of iron; B = [OH-a] I [FeT]; B* = [OH-b] [FeT]; [FeT] = total iron concentration. Source: Adapted from Water Research, Vol 21, H.X.-Tang and W. Stumm, The Coagulating Behaviors of Fe(III) Polymeric Species-/ and II, pages 115-128, Copyright 1987, with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington OX5 1 GB, UK.

Figure 2.3 Coagulation behavior of Fe(III) polymeric species.

When OH- is more abundant, polymerization characteristic of type C solutions is more likely to occur than is precipitation. The formation of high level polymers is characteristic of type D solutions. A decrease in the charges of type D species occurs because of deprotonation and leads to precipitation characteristic of type E solutions.

Tang and Stumm (1987) monitored changes in the color of the ferric chloride solutions

during hydrolysis. According to these researchers, the color of the solution indicates the extent of hydrolysis. A yellow color indicates the presence of monomers oroligomers of Fe(III) hydrolysis; a brown color indicates the polynuclear species present after extended hydrolysis. The addition of base to an Fe(III) solution causes the hydrolysis reactions to proceed, as indicated by the change in color of the solution from clear yellow to cloudy red-brown.

The effect of Fe(III) concentration on the coagulation of kaolinite suspensions with FeCl3

(ferric chloride) as the coagulant was also investigated by Tang and Stumm (1987). FeCl3 solutions of greater than 0.1 M concentration behaved as type A solutions, and concentrations near 0.01 M behaved as type B solutions. Solutions below 0.005 M acted as type C, and those below 0.0001 M acted as type D. The concentration of the coagulant and conditions of the untreated water, such as pH, affected the chemical speciation of the coagulant. This speciation

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determines the mechanism and efficiency of coagulation. Tang and Stumm (1987) suggested that concentrated FeCl3 solutions (>=O.1 M, or type A) are more advantageous for coagulation than more dilute concentrations. Type B solutions are typical of sweep coagulation conditions, which require higher coagulant dosages.

Other investigations by Tang and Stumm (1987) identified differences in coagulation with aluminum and iron salts. Positive charges were higher for hydrolysis species of aluminum salts than iron salts, which indicate that lower dosages of aluminum salts are required for charge neutralization. Based on residual turbidity, coagulation with aluminum salts was less efficient after charge neutralization occurred. Iron salts were found to require slightly higher dosages for charge neutralization. However, even though charge reversal occurred at the highest iron dosages, optimum turbidity removal was still achieved. Therefore, Tang and Stumm (1987) suggested that iron salts are more suitable for coagulation by charge neutralization than aluminum salts because of their hydrolysis speciation. Under similar conditions, iron salts exhibited higher OH:metal ion ratios than aluminum salts, which implies lower charge density and higher binding ability. A 0.3 MFeCl3 solution was found to be much more effective than AlCl3 (alum) and 0.01 M FeCl3 based on turbidity removal. These results are presented in Figure 2.4. 2.6 Coagulation Diagrams

Coagulation diagrams for effective turbidity removal were developed by superimposing treatment data on thermodynamic stability diagrams for the inorganic coagulant (Amirtharajah and Mills 1982; Johnson and Amirtharajah 1983). The diagrams are based on the speciation of aluminum and iron salts with respect to the solubility of solid precipitates-Al(OH)3 for aluminum salts and Fe(OH)3 ferric salts. These diagrams also indicate the mechanism of coagulation responsible for panicle removal depending on the pH and coagulant dosage. Coagulation diagrams for Al(III) and Fe(III) salts are presented in Figures 2.5 and 2.6, respectively. Additional information about coagulation diagrams can be found in Amirtharajah and O 'Melia (1990). 2.7 Natural Aquatic Humic Substances

Humic substances are complex, organic polycondensate mixtures that exist in all soil and

aquatic environments. These substances have been studied extensively because of their environmental significance. Because of extreme complexity of humic substances, many researchers studying them have focused their efforts on functional group characterization, metal complexation properties, and acidic properties.

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Note: PACI = polyaluminum chloride; PFC = polyferric chloride; 0 = days. Source: Adapted from Water Research, Vol 21, H.x. Tang and W. Stumm, The Coagulating Behaviors of Fe(lII) Polymeric Species and II, pages 115-128, Copyright 1987 with kind permission from Elsevier Science Ltd. The Boulevard, Langford Lane, Kidlington OX5 1 GB. UK.

Figure 2.4 Comparison of different coagulants.

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This section comprehensively reviews the current understanding of the origin, classification, molecular size, elemental composition, molecular structure, and characteristic properties of humic substances. Methods for isolating DOM and the impact of humic substances on water treatment are also discussed. Much of the material presented in this section focuses on humic substances from the Suwannee River because humic substances from this source were used in the research project. Overview

Humic substances are extremely complex mixtures of randomly condensed organic compounds that originate from the decomposition of plant and animal residues (MacCarthy and Suffet 1989). Aquatic humic substances are classified as fulvic acids, humic acids or humic according to their aqueous solubility under varying pH conditions. Fulvic acids are soluble in water at all pH conditions. Humic acids are not soluble in water below a pH of 2. Humic is not soluble in water at any pH. The molecular weight of fulvic acids typically ranges between 500 and 2,000 Daltons (Thurman et al., 1982). Humic acids have molecular weights greater than 2,000 Daltons. The elemental composition of humic substances provides information about their nature, and source. Through various analytical and chemical techniques, functional groups in the structure of humic substances have been characterized. These functional groups determine the geochemical behavior of humic substances. Humic substances have a significant impact on the processes used in the treatment of drinking water.

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Source: Amirtharajah and Mills, 1982. . - .

Figure 2.5 Design and operation diagram for alum coagulation Origin of Humic Substances

Hall and Packham (1965) stated that the color in surface waters is caused by complex organic compounds of natural origin derived from water soluble peptizable components of soil humus and peat. They suggested that humic substances in the soil result from the polymerization of polyphenolic units from bacterial synthesis or the breakdown of lignin residues of higher plants. More recently, MacCarthy and Suffet (1989) stated that humic substances are extremely complex mixtures of organic materials resulting from the decomposition of plant and animal tissues.

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Source: Johnson and Amirtharajah 1983.

Figure 2.6 Design and operation diagram for ferric iron coagulation

Stevenson (1985) reviewed the polyphenol theory, which is currently widely accepted as an explanation of the origin of humic substances in soils. This theory suggests that humic substances are formed by a multistage process. According to this theory, plant materials decompose into simple monomers. The metabolism of these monomers increases the biomass of the soil. The biomass carbon is repeatedly recycled by the synthesis of new cells. Concurrently, reactive monomers are polymerized into high molecular weight polymers. The various pathways by which humic substances are formed vary with environmental conditions such as the moisture, temperature of the soil, and type of surrounding vegetation. The dissolved organic carbon (DOC) found in surface waters is predominantly allochthonous (originating elsewhere), entering the water through runoff from the soil within a watershed. This DOC is derived from the decay of Vegetation. Malcolm (1985) stated that humic substances in mineral soils typically originate from the decay of higher plants, which contain cellulose and lignin. Whereas allochthonous humic substances are prevalent in rivers, bogs, and swamps, autochthonous humic substances are common in clear lakes (Steinberg and Muenster 1985). The autochthonous humic substances result from the decomposition of aquatic plants and animals (Malcolm 1985). Diatoms and algae, which contain hemicellulose and proteins, and also aquatic animals, which contain protein and chitinous substances, contribute to the composition of aquatic humic substances.

Thurman and Malcolm (1983) suggested that the fulvic acid found in the Suwannee River originated from recent degradation of terrestrial plant materials (within a 25-year period) and not from older organic matter from the swamp peats.

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The composition of humic substances varies depending on their source and method of extraction. In natural waters, dissolved humic substances are mixed with amino acids, sugars, and aliphatic and aromatic acids (MacCarthy and Suffet, 1989). Humic substances are also associated with various metal ions, clays, and amorphous oxides of aluminum and iron (Thurman et al., 1982). Humic substances may be separated from these materials by passing the mixture through a hydrophobic resin. Hydrophilic compounds such as amino acids and simple sugars pass through the column, whereas hydrophobic humic substances sorb to the resin. However, the isolation and separation processes may alter the natural state of the humic substances and change their molecular size (Thurman et al., 1982).

Malcolm (1985) estimated that 50 percent of the DOC in uncolored surface waters in the

United States consists of humic substances. The average concentration of carbon in these surface waters is 2.2 mg/L, which translates into 4.4 mg humic substance/L based on an average elemental weight of 50 percent carbon. The DOC for colored surface waters may range from 5 to more than 50 mg/L, and humic substances may contribute up to 80 percent of the DOC.

It is proposed to use Ferric Chloride instead of Aluminum Sulfate (Alum) during

pretreatment of Raw Water in Bangkok. It is anticipated that modifying water treatment plants to use both Alum and Ferric Chloride will enable savings in the cost of chemicals at the treatment plants. Raw water is treated by the following steps to produce Drinking Water (Austin, 1975):

1. Pretreatment - In a contact basin, potassium permanganate is added to the water. This

removes iron and manganese and improves the color. Carbon dioxide in combination with lime is used to recarbonate the Raw Water. The Raw Water in its natural state is too soft for domestic use.

2. Coagulation and flocculation any mineral and organic compounds present in the water must be bound together to facilitate their removal by filtration. The particles are destabilized (coagulation) in a flash mixer, by adding alum and then agglomerated into bulky floccules, called "flocs". This occurs inside a coagulation tank (flocculation).

3. Filtration - Flocculated water is passed through a filter, to remove the impurities. A

nonionic polymer is added in a low energy mixer to act as a filtration aid. This slows penetration of very fine flocs into the filter bed. The filters are composed of coal and sand over 0.1 m of gravel. The filters are regulated to maintain equal flow to each one.

4. Post-treatment - Lime combined with carbon dioxide is added to control the pH and

prevent scaling in the distribution network. Chlorine is used to disinfect the water prior to distribution. To protect treated water from contamination during distribution to consume, ammonia is also added to form monochloramine.

5. Residuals - Waste by-products (residuals) are collected by washing the filters

(backwash). The washwater is sent to thickeners. Residuals are treated with a non-ionic polymer in centrifuges, and then taken by truck to drying beds. Water from the thickeners (supernatant) is recycled upstream of the plant.

This project will test the practicality of replacing alum in the coagulation and flocculation step (Step 2) with ferric chloride. The ferric chloride will coagulate mineral and organic compounds in the Raw Water to allow flocculation.

14

The use of ferric chloride and other iron compounds for coagulation in water treatment was first patented in 1884 (Carnduff, 1971). Issiah Smith Hyatt proposed using perchloride of iron or ferric chloride in the treatment of New Orleans water.

In a similar study for the Metropolitan Toronto water supply (Carnduff, 1976), it was

found that dosages of ferric chloride necessary to produce high-quality water were smaller than required for alum treatment. However, the cost savings were a function of fluctuating commodity prices. The study recommended that plant design should allow the use of either compound when commodity prices favoured it. The study also recommended the use of chemically resistant plastics for ferric chloride tanks, pipes and pumps. These were considered significantly cheaper than tantalum and titanium alternatives.

Treatment by using ferric chloride is also a way of avoiding the clogging of mains by

postprecipitation of aluminium complexes. This problem occurs when treating Raw Water with a high pH with alum.

The Toronto study (Carnduff, 1976) used jar tests and plant scale testing to determine the

effectiveness of flocculation and the quality of filtered water produced. A similar methodology was used for this study. The objectives of the study are to determine the effectiveness of flocculation; the dosage range required for treatment; the quality of the filtered water produced with respect to turbidity, taste and colour; and a cost comparison with a similar treatment using alum.

The Woronora Water Filtration Plant, near Sydney Australia uses ferric chloride for

coagulation of mineral and organic impurities (General Water Australia, 2001). The Raw Water quality and Treated Water quality (shown below) are comparable to Bangkok:

Table 2.1 Raw water quality parameters and their ranges Raw Water Quality Parameters Range

Turbidity 0.5-10.7 NTU Apparent Color 2-70 CU Iron 0.02-1 mg/L Manganese 0.003-0.07 mg/L Aluminium 0.069-0.4 mg/L Hardness 2.6-22.8 mg/L as CaCO3Alkalinity 0.5-12.5 mg/L as CaCO3pH 5.06-7.54 Temperature 10-26.6°C Algae 0-5,000 U/mL

15

Table 2.2 Treated water quality parameters and their ranges Treated Water Quality Parameters Range

Turbidity <0.3 NTU True Color <5 HU Iron <0.2 mg/L Manganese <0.03 mg/L Aluminium <0.2 mg/L Coliforms 0 Trihalomethanes <0.2 mg/L pH 7.7-8.1 Calcium Carbonate -3.5 to -0.5

Table 2.3 Raw water quality parameters and their ranges Precipitation Potential Range

Fluoride 1 mg/L Chlorine Residual 0.5-1.7 mg/L

The Woronora plant supplies up to 160 million litres of drinking water per day (General Water Australia).

16

Chapter 3

Methodology 3.1 Introduction Aluminum sulfate is a traditional coagulant for coagulation process in Thailand. Ferric chloride is to be an alternative coagulant for this process. In order to compare these coagulants, the experiment was established to investigate the efficiency and cost-effectiveness comparisons. The activities in this study are:

• Data collection • Experimental set up • Sample collection and • Result interpretation and conclusion

3.2 Data Collection

The data about coagulation was collected from previous studies and researches worldwide.

The main topics for data collection are:

• Coagulation and its mechanisms • Coagulants • Coagulation diagrams • Natural aquatic humic substances

3.3 Experimental Set Up

The experimental module of simulated water treatment system was established as shown in Figure 3.1. Raw water from the Tha Chin River and also Mae Klong River were feed into the mixing tank together with the coagulant solution. Circulating pump was employed for rapid mixing. The mixed water-coagulant would then flows to flocculating tank which paddles were employed for completely agitation. The third tank was settling tank, which flocs were settled and the clarified water would overflow and flow to the sand filter. Settled flocs would be drained through the drained valve. Sand filter with 120 cm. sand bed was used for filtration. Totally 13 sets of tubes were used for head loss detection. Filtered water was drained at the bottom of the sand bed.

17

MIXING TANK

RA

W

WA

TER

OUT LET

ROTAMETER

ROTAMETER

SETTLING TANK

DRAIN VALVE

WASH WATER

AGITATOR MOTOR MIXING

VOLT 220 V OUTPUT 20/30 W

PMASR SINGLE AMPERE 0.24/0.26 A

CYCLE 50/60 Hz RPM 2830/3300

INPUT 45/55 W CAP 1UF FOCCULATING TANK

OVER FLOW

Cm.

Cm.

Cm.

Cm.

Cm.

Cm.

Cm.

Cm.

Cm.

Cm.

Chemical Solution Tank

DIAPHRAGM DOSING PUMP

ROMINENT ELECTROMO TYPE G 41 0216SS

GEGAN 2 BAR 10 L/h

SAND FILTER

Cm.

2

18

1

3Legend: 1: Influent 2: Clarified Water 3: Effluent (Filtered Water) Figure 3.1 Schematic Diagram for water treatment process

Manometer

CIRCULATING PUMP PIPE 17 MM.

HEAD (MAX) 3.5/4.5 M.

CAPACITY

Figure 3.2 Experimental setup for pilot scale water treatment plant

Figure 3.3 Experimental setup.

19

3.4 Experimental Procedure 3.4.1 Chemicals Preparation

Aluminum Sulfate Solution was prepared by diluting 189.7 mL (50% w/w) to 20 L of tap water.

Ferric Chloride Solution was prepared by diluting 214.3 mL (40% w/w) to 20 L of tap water.

3.4.2 Experimental Procedure

Adjust the flow rate of chemical feeding pump to the calculated dosage,

Adjust the flow rate of raw water to 150 l/hr, Start circulating pump, Mixed water-chemical will flow to the flocculating tank, start

agitator motor, adjust to 20 rpm., After flocculation tank, water will overflow to settling tank for

sedimentation. If the sludge is filled up to the “HIGH” level, all sludge will be drained,

Clarified water will overflow to the sand filter column, with 120 cm. sand bed and fixed water level of 100 cm. above sand level, with filtration rate of 90 l/hr. The left-over water will overflow out of the sand filter,

There are 13 pores on the side of filter column, distance between each pore is 10 cm., as shown in Figure 3.1,

3.4.3 Scenarios

Raw water from 1) Tha Chin River and 2) Mae Klong River, were used as influent to the system. These 2 sources of raw water had different turbidity, which were had around 30 and 20 NTU for Tha Chin and Mae Klong River, respectively. Two scenarios were set up to investigate the performance of coagulants: Phase I: Tha Chin River raw water: High Turbidity, and Phase II: Mae Klong River raw water: Low Turbidity. 3.5 Sample Collection

Jar test was performed prior to the experimental run to investigate the feeding rate of coagulants, as shown in Figure 3.4.

20

Figure 3.4 Jar test equipment.

Two coagulants were used for coagulation of raw water:

1) Aluminum Sulfate 2) Ferric Chloride

Sampling was performed in accordance with procedure described in Standard

Methods of Water and Wastewater Examination (AWWA, 1992). The water samples were collected as a representative of 1) influent, 2) clarified water and 3) filtered water as illustrated in Figure 3.1. All samples were analyzed at the Mahasawat Water Treatment Plant Laboratory. The analytical parameters and their methods were presented in Table 3.1.

Table 3.1 Parameters and their experimental procedures.

Parameters Units Method Point of sampling Frequency pH pH pH Meter 1, 2 and 3 Every 4 hours Turbidity NTU Turbidimeter 1, 2 and 3 Every 2 hours Alkalinity mg/L Test Kit 1 and 2 Every 4 hours Total Solid (TS) mg/L Conductivity

Meter Drained sludge Once a day

Aluminum ion mg/L AWWA* 3 Once a day Ferrous ion mg/L AWWA* 3 Once a day Manganese ion mg/L AWWA* 3 Once a day

*Note: Standard as standard method (AWWA, 1992) Total Solids (TS) were analyzed for sludge concentration, moreover residual Aluminum Ferrous and Manganese were only analyzed for contamination of drinking water fro the process.

21

All system equipment and status, which were pumps, motors, inlet, outlet and sludge quantity were checked every 2 hours. 3.6 Results Interpretation and Conclusion The results from experiments were analyzed to compare the performance and removal efficiency of two coagulants: 1) Aluminum Sulfate and 2) Ferric Chloride. Moreover, the cost-effectiveness and filter run period of those two coagulants were also calculated.

22

CHAPTER 4

Results and Discussion Aluminum Sulfate is the main coagulant for MWA water treatment. Ferric Chloride would be the comparative coagulant. Jar test was performed by using the water from Tha Chin and Mae Klong River. According to MWA standard of water treatment, water after clarified should have turbidity lower than 5 NTU and water after sand bed filtration should have turbidity lower than 2 NTU.

The total experimental period was separated into 2 phases according to the feeding rate: Phase I: Raw water from Tha Chin River (high turbidity) and Phase II: Raw water from Mae Kong River (low turbidity). 4.1 Phase I: Tha Chin River Raw Water

4.1.1 Aluminum Sulfate as Coagulant The result of jar test in phase I showed that 55 mg/L of Alum feeding rate were

appropriate. Aluminum Sulfate feeding rate of 55 mg/L was applied to the experiment totally 14 hours (excluding system preparation). As shown in Figure 4.2, turbidity in raw water were high, 26 – 31 NTU and after clarification and filtration, turbidity were reduced to 4.0 – 6.7 and 0.68 – 1.55 NTU, respectively, and the average treatment efficiency were 82.4 and 95.6%, respectively. (Figure 4.5)

Alkalinity in raw water were in a range of 100 – 108 mg/L, after clarification they

were reduced to 52 – 60 mg/L (Figure 4.3) or around 47.5% removal efficiency. pH was reduced from 7.81 – 8.17 in raw water to 6.75 – 7.29 and 6.80 – 7.24 after

clarification and filtration, respectively, as shown in Figure 4.4. Effluent water quality as well. Moreover, jar test was performed only a guideline

for practical application of coagulant to the raw water. Figure 4.6 shows the pressure drop in sand bed filter for the lowest pipe,

extrapolated pressure drop up to 50 cm. were used for filter run expectation. Filter run period for Aluminium Sulfate for Phase I was calculated to be 18 hours.

Table 4.1 Jar Test result for Aluminum Sulfate as coagulant, Phase I.

Alum Dose (mg/L) Turbidity(NTU) pH Alkalinity (mg/L) 0 29.0 8.12 104 35 15.5 7.30 92 40 13.2 7.21 92 45 9.7 7.11 88 50 6.8 7.04 86 55 4.5 6.95 86 60 3.1 6.87 82

23

30

35

40

45

50

55

60

65

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0Tubidity (NTU)

Alum

Dos

e (m

g/L)

Figure 4.1 Logarithm graph from jar test for Aluminum Sulfate as coagulant, Phase I.

Tha Chin, Alum

05

101520253035

0 2 4 6 8 10 12 14Run Time, Hour

Turb

idity

, NTU

Raw WaterC larified WaterF iltered Water

Figure 4.2 Turbidity of raw water, clarified water and filtered water for Aluminum sulfate as coagulant, Phase I.

24

Tha Chin, A lum

50

60

70

80

90

100

110

0 2 4 6 8 10 12 14Run Time, Hour

Alk

alin

ity (m

g/L)

Raw WaterC larified Water

Figure 4.3 Alkalinity of raw water and clarified water for Aluminum sulfate as coagulant,

Phase I.

Tha Chin, A lum

6

7

8

9

0 2 4 6 8 10 12 14Run Time, Hour

pH


Figure 4.4 pH of raw water, clarified water and filtered water for Aluminum sulfate as

coagulant, Phase I.

25

Tha Chin, A lum

7580859095

100

0 2 4 6 8 10 12 14Run Time, Hour

% T

urbi

dity

Re

mov

al

C larified WaterF iltered Water

Figure 4.5 Turbidity removal efficiency of clarified and filtered water for Aluminum

sulfate as coagulant, Phase I.

Tha Chin/ Alum

y = 0.3798x - 1.2617R2 = 0.9632

0

5

10

15

20

25

0 10 20 30 40 50 60Total Pressure Drop, cm.

Run T

ime, H

our

Figure 4.6 Pressure drop of sand filter for Aluminum sulfate as coagulant, Phase I.

4.1.2 Ferric Chloride as Coagulant The result from jar test is illustrated in Table 4.2 and Figure 4.7, 25 mg/L of Ferric Chloride feeding rate was selected.

During experiment, turbidity of raw water were 30 – 34 NTU, and reduced to 4.0 – 5.8 and 0.08 – 0.90 NTU after clarification and filtration respectively as shown in Figure 4.8, with the average treatment efficiency of 84.7 and 98.8%, respectively (Figure 4.11).

Alkalinity in raw water were in a range of 96 – 104 mg/L, after clarification they were reduced to 76 – 90 mg/L (Figure 4.9) or around 16.4% removal efficiency.

26

pH was reduced from 7.82 – 8.14 in raw water to 7.19 – 8.04 and 7.16 – 7.86 after

clarification and filtration, respectively. (Figure 4.10) Figure 4.12 shows the pressure drop in sand bed filter for the lowest pipe, with the

same method of extrapolation, filter run period for Ferric Chloride for Phase I was calculated to be 25 hours.

Table 4.2 Jar Test result for Ferric Chloride as coagulant, Phase I.

Ferric Chloride Dose (mg/L) Turbidity(NTU) pH Alkalinity (mg/L) 0 30.0 8.17 98 15 8.2 7.10 84 20 6.5 6.94 78 25 5.2 6.88 78 30 3.6 6.81 72 35 2.9 6.76 70 40 2.4 6.68 64

10

15

20

25

30

35

40

45

0 1 2 3 4 5 6 7 8 9Turbidity (NTU)

FeC

l 3 D

ose

(mg/

L)

Figure 4.7 Logarithm graph from jar test for Ferric Chloride as coagulant, Phase I.

27

Tha Chin,FeCl3

0

10

20

30

40

0 2 4 6 8 10 12 14 16 18 20Run T ime, Hour

Turb

idity

, NTU


Figure 4.8 Turbidity of raw water, clarified water and filtered water for Ferric Chloride as

coagulant, Phase I.

Tha Chin, FeCl3

70

80

90

100

110

0 5 10 15 20Run Time, Hour

Alka

linity

(mg/

L)


Figure 4.9 Alkalinity of raw water and clarified water for Ferric Chloride as coagulant,

Phase I.

28

Tha Chin, FeCl3

77.27.47.67.8

88.2

0 2 4 6 8 10 12 14 16 18 20Run T ime, Hour

pH


Figure 4.10 pH of raw water, clarified water and filtered water for Ferric Chloride as

coagulant, Phase I.

Tha Chin, FeCl3

80

85

90

95

100

0 2 4 6 8 10 12 14 16 18 20Run Time, Hour

%Tu

rbid

ity R

emov

al


Figure 4.11 Turbidity removal efficiency of clarified and filtered water for Ferric Chloride

as coagulant, Phase I.

29

Tha Chin/ FeCl3

y = 0.5683x - 2.762R2 = 0.9843

05

1015202530

0 10 20 30 40 50 60Total Pressure Drop, cm.WC

Run T

ime,

Hour

Figure 4.12 Pressure drop of sand filter for Ferric Chloride as coagulant, Phase I.

4.2 Phase II: Mae Klong River Raw Water

4.2.1 Aluminum Sulfate as Coagulant

The same method was used. Jar test was performed with the water from Mae Klong River. Results of jar test are as shown in Table 4.3 and Figure 4.13, and found that the appropriate Aluminum Sulfate feeding rate was selected to be 40 mg/L in order to get a better water quality. Figure 4.14 shows the result of turbidity in raw water, clarified water and filtered water. Turbidity of raw water ranged from 16 – 20 NTU, while turbidity of clarified and filtered water were ranged from 2.2 – 5.6 and 0.24 – 0.53 NTU, respectively. The average efficiency of turbidity treatment after clarified and filtered were 80.3 and 97.4%, respectively. (Figure 4.17) The Alkalinity of raw water and clarified water are shown in Figure 4.15, with the value of 98 – 104 and 46 – 90 mg/L, respectively. The average efficiency of alkalinity treatment after clarified was 30.1% pH of raw water, clarified water and filtered water were shown in Figure 4.16, the ranges were 6.83 – 7.97, 5.43 – 7.53 and 5.96 – 7.66, respectively.

Figure 4.18 shows the pressure drop in sand bed filter for the lowest pipe, with the same method of extrapolation, filter run period for Aluminum Sulfate for Phase I was calculated to be 23 hours.

30

Table 4.3 Turbidity results(NTU) from Jar Test for Ferric Chloride as coagulant feeding rate 25 mg/L.

Aluminum Sulfate Dose (mg/L) Turbidity(NTU) pH Alkalinity (mg/L) 0 15.0 7.50 92 15 11.3 7.30 82 20 8.6 7.26 80 25 6.4 7.18 78 30 5.0 7.10 78 35 3.5 7.04 76 40 3.3 6.93 72

y = -18.887Ln(x) + 60.518R2 = 0.982

10

15

20

25

30

35

40

0.0 2.0 4.0 6.0 8.0 10.0 12.0Turbidity (NTU)

Alu

m D

ose

(mg/

L)

Figure 4.13 Jar test results for Aluminum Sulfate as coagulant, Phase II.

31

Mae K long, A lum

0

5

10

15

20

25

0 2 4 6 8 10 12 14Run Time, Hour

Turb

idity

, NTU


Figure 4.14 Turbidity in raw water, clarified water and filtered water for Aluminum

Sulfate as coagulant, Phase II.

Mae K long, A lum

40

60

80

100

120

0 2 4 6 8 10 12 14Run Time, Hour

Alk

alin

ity (m

g/L)


Figure 4.15 Alkalinity in raw water and clarified water for Aluminum Sulfate as

coagulant, Phase II.

32

Mae K long, Alum

5

6

7

8

9

0 2 4 6 8 10 12 14Run Time, Hour

pH

Raw WaterClarified WaterFiltered Water

Figure 4.16 pH in raw water, clarified water and filtered water for Aluminum Sulfate as


Mae K long, Alum

60

70

80

90

100

0 2 4 6 8 10 12 14Run T ime, Hour

% T

urbi

dity

Rem

oval

Clarified Water

Filtered Water

Figure 4.17 Turbidity removal efficiency clarified water and filtered water for Aluminum

Sulfate as coagulant, Phase II.

33

Mae Klong/Alum

y = 0.5404x - 456 4. 5R2 = 0.

0

5

10

15

20

25

0 10 20 30 40 50 60

9973

Total Pressure Drop, cm.

Run T

ime,

Hour

Figure 4.18 Pressure drop for Aluminum Sulfate as coagulant, Phase II.

4.2.2 Ferric Chloride as Coagulant

According to jar test, as shown in Table 4.4 and Figure 4.19, 15 mg/L of Ferric Chloride feeding rate was selected to obtain the same water quality as using Aluminum Sulfate.

During phase II, the turbidity of raw water was dropped down to 15 – 19 NTU, and the analyzed results from clarified and filtered water were 1.6 – 4.3 and 0.14 – 0.80 NTU, respectively (Figure 4.20), with the average turbidity treatment efficiency of 85.0 and 98.1%, respectively (Figure 4.23). The Alkalinity of raw water and clarified water are shown in Figure 4.21, with the value of 100 – 110 and 62 – 86 mg/L, respectively. The average efficiency of alkalinity treatment after clarified was 30.3%. pH of raw water, clarified water and filtered water were shown in Figure 4.22, the ranges were 7.54 – 8.24, 6.97 – 7.55 and 5.71 – 7.70, respectively.

Figure 4.24 shows the pressure drop in sand bed filter for the lowest pipe, with the same method of extrapolation, filter run period for Ferric Chloride for Phase I was calculated to be 34 hours.

Table 4.4 Jar test result for Ferric Chloride as Coagulant, Phase II. Ferric Chloride Dose (mg/L) Turbidity(NTU) pH Alkalinity (mg/L)

0 15.0 7.39 92 5 7.0 7.22 84

10 3.5 7.14 82 15 2.7 7.08 78 20 2.1 7.07 70 25 1.3 6.91 68 30 1.0 6.48 62

34

0

5

10

15

20

25

30

35

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Turbidity (NTU)

FeCl

3 D

ose

(mg/

L)

Figure 4.19 Jar test result for Ferric Chloride as coagulant, Phase II.

Mae Klong, FeCl3

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16 18 20 22 24 26Run Time, Hour

Turb

idity

, NTU

Raw WaterClarified WaterFiltered Water

Figure 4.20 Turbidity in raw water, clarified water and filtered water for Ferric Chloride as


35

Mae Klong, FeCl3

50

70

90

110

0 2 4 6 8 10 12 14 16 18 20 22 24 26Run Time, Hour

Alk

alin

ity (m

g/L)


Figure 4.21 Alkalinity in raw water and clarified water for Ferric Chloride as coagulant,

Phase II.

Mae Klong, FeCl3

5

6

7

8

9

0 2 4 6 8 10 12 14 16 18 20 22 24 26Run Time, Hour

pH

R aw WaterC larified WaterFiltered Water

Figure 4.22 pH in raw water, clarified water and filtered water for Ferric Chloride as


36

Mae Klong, FeCl3

70

80

90

100

0 2 4 6 8 10 12 14 16 18 20 22 24 26Run T ime, Hour

% T

urbi

dity

Rem

oval

Clarified WaterFiltered Water

Figure 4.23 Turbidity removal efficiency in clarified water and filtered water for Ferric

Chloride as coagulant, Phase II.

Mae Klong/ FeCl3

y = 0.8096x - 6.5443R2 = 0.9764

05

10152025303540

0 10 20 30 40 50 60Total Pressure Drop, cm.

Run T

ime,

Hour

Figure 4.24 Pressure drop for Ferric Chloride as coagulant, Phase II.

37

4.3 Turbidity Treatment Efficiency Comparison

The results of experiment for water treatment process by using Aluminum Sulfate and Ferric Chloride were discussed in section 4.1 and 4.2. 4.3.1 Phase I: Tha Chin River Raw Water (High Turbidity)

The obtained results show that during Phase I, the average raw water for both

cases were high, 32.3 and 28.0 NTU for Ferric Chloride and Aluminum Sulfate, respectively, as shown in Figure 4.25. The final effluent or filtered water from Ferric Chloride as coagulant had a better quality with an average turbidity of 0.4 NTU. Ferric Chloride and Aluminum Sulfate were fed 25 and 55 mg/L, respectively, or can be calculated to a ratio of F:A = 1:2.2.

Figure 4.26 illustrates the average treatment efficiency of turbidity in clarified

and filtered water of both experiments with Ferric Chloride and Aluminum Sulfate, with the final effluent achieved 98.8 and 95.6%, respectively.

RawWater C larified

Water F ilteredWater

32.3

28.0

4.9 4.9

0.4 1.20

5

10

15

20

25

30

35

Ferric C hlorideAluminum Sulfate

Turbidity (NTU)

Figure 4.25 Average turbidity in different sampling points of experiment Phase I.

38


84.7

82.4

98.8

95.6

70

75

80

90

95

100

85


Turbidity Treatment Efficiency (%)

Figure 4.26 Average turbidity treatment efficiency in clarified and filtered water of

experiment Phase I. 4.3.2 Phase II: Mae Klong River Raw Water (Low Turbidity) Phase II had lower turbidity, 16.3 and 18.3 NTU for Ferric Chloride and Aluminum Sulfate, respectively, as shown in Figure 4.27, with the turbidity in filtered water of 0.4 and 0.5 NTU, respectively. For this experiment, feeding rate of Ferric Chloride was reduced to 15 mg/L, while that of Aluminum Sulfate was increased up to 40 mg/L. The ratio of feeding rate of F:A increased to 1:2.67 while Ferric Chloride achieved a better water quality.

Figure 4.28 illustrates the average treatment efficiency of turbidity in clarified and filtered water of both experiments with Ferric Chloride and Aluminum Sulfate, with the final effluent achieved 98.1 and 97.4%, respectively.

39

RawWater C larified

Water F ilteredWater

16.318.3

2.8 3.5

0.4 0.502468

1012

161820

14


Turbidity (NTU)

Figure 4.27 Average turbidity in different sampling points of experiment Phase II.


85.080.3

98.1 97.4

01020304050

8090

100

6070


Turbidity Treatment Efficiency (%)

Figure 4.28 Average turbidity treatment efficiency in clarified and filtered water of

experiment Phase II.

4.4 Ferrous, Manganese and Residual Aluminum in filtered water The standard of MWA indicated that Ferrous and Manganese in drinking water should not more than 0.3 and 0.1 mg/L, respectively. Average Ferrous and Manganese in drinking water after filtration when using Ferric Chloride as coagulant were 0.06 (max 0.27) and 0.01 (max 0.05) mg/L, respectively. The analyzed apparent colors were below the standard.

40

Average residual Aluminum in filtered water when using Aluminum Sulfate was 0.15 mg/L (max 0.39). The standard of MWA allows 0.5 mg/L for drinking water. All data is concluded as shown in Table 4.5. Table 4.5 Residual chemicals concentration, comparing with the standard of filtered water

from the experiments. Coagulant Parameter Range Average Standard

Ferrous ion 0.00 – 0.27 0.06 0.30 Manganese ion 0.00 – 0.05 0.01 0.10 Ferric Chloride Apparent color < 5.0 < 5.0 < 15.0

Aluminum Sulfate Aluminum ion 0.00 – 0.39 0.15 0.20 4.5 Total Solids Sludge generated from flocs, drained from the bottom of sedimentation tank was analyzed for Total Solids in order to investigate the sludge concentration. The results show that the average Total Solids (TS) of sludge from Ferric Chloride and Aluminum Sulfate as coagulant were 39.9 and 28.7 mg/L, respectively. Higher TS indicated that the sludge is denser in term of mass per volume. In order to dispose the sludge, denser sludge can be handled easier such as by dewatering or transportation. Moreover, it can be noted here that the sludge generated from using Aluminum Sulfate as coagulant is bulky sludge, which can disturb the efficiency of the system and also lead to the clogging or fouling of the system. 4.6 Filter Run Period

From the study, Ferric Chloride could prolong the filter run up to 34 hours. While Aluminum Sulfate could utilize filter for 23 hours, which means 32.4% of backwashing water can be saved. 4.7 Cost Comparison The price of each coagulant (2002) is;

1) Aluminum Sulfate: 3,550 Baht/ton (Dry weight) 2) Ferric Chloride : 7,000 Baht/ton (Dry weight)

Calculation of unit price of treatment per cubic meter of raw water shows below (according to the best ratio from pilot scale experiment; F:A = 1:2.67);

40 mg/L of Aluminum Sulfate = 1,000 (L/m3) * 40 (mg/L) * 3,550 (Baht/ton) / 109 (mg/ton) = 0.142 Baht/m3

15 mg/L of Ferric Sulfate

41

= 1,000 (L/m3) * 15 (mg/L) * 7,000 (Baht/ton) / 109 (mg/ton) = 0.105 Baht/m3

According to this study, 26.0% of money can be saved by using Ferric Chloride instead of Aluminum Sulfate. 4.7 Expected Savings for Mahasawat Water Treatment Plant (MWTP)

Nowadays, MWTP utilized around 25 tons of Aluminum Sulfate and 8,000 m3 of backwashing water daily (in 16 filter units). According to the results of this study, if Ferric Chloride is to be used substitute to Aluminum Sulfate;

• 26.0% of chemical cost can be saved (Aluminum Sulfate = 3,550

Baht/ton) = 25 tons/day * 3,550 Baht/ton * 0.260 = 23,075 Baht/day • 32.4 % of backwashing water also can be saved (Backwashing water =

1.30 Baht/m3) = 8,000 m3/day * 1.30 Baht/m3 * 0.395 = 3,370 Baht/day Totally 26,445 Baht per day or around 10 million Baht per year can be saved, if MWTP decides applying Ferric Chloride as coagulant in water treatment process. However, for more practical values of saving money, real application of Ferric Chloride to water treatment process at MWTP is highly suggested. In the year 2022, MWTP will expand the size of this plant up to 64 filter units or 4 times of the size nowadays. The water production will expand from 600,000 m3/d to 3,200,000 m3/d. The saving amount can be calculated to be: = (3,200,000/600,000)*23,075 + (64/16)*3,370 = 136,547 Baht/day Totally around 50 million Baht per year can be saved beyond the year 2022 if Ferric Chloride is applied in MWTP. Table 4.6 concludes the comparisons of water treatment by using Ferric Chloride and Aluminum Sulfate.

Table 4.6 Comparison conclusion of Ferric Chloride and Aluminum Sulfate Ferric

Chloride Aluminum

Sulfate % Advantages of Ferric Chloride

over Aluminum Sulfate TS of sludge (mg/L) 39.9 28.7 28.1 Filter Run Period (hrs) 34 23 32.4 Cost (Baht/m3 raw water) 0.105 0.142 26.0

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Chapter 5

Conclusions and Recommendations 5.1 Conclusions

Raw water from Tha Chin and Mae Klong Rivers were used as feeding influent for the pilot scale experiment;

Phase I: Raw water from Tha Chin River, average turbidity of 30 NTU

o Clarification and Filtration efficiency in term of Turbidity with Aluminium Sulfate as coagulant were 82.4 and 95.6%, respectively. Average turbidity concentration in filtrated water was 1.2 NTU.

o Clarification and Filtration efficiency with Ferric Chloride in term of Turbidity as coagulant were 84.7 and 98.8%, respectively. Average turbidity concentration in filtrated water was 0.4 NTU.

Phase II: Raw water from Mae Klong River, average turbidity of 17 NTU

o Clarification and Filtration efficiency in term of Turbidity with Aluminium Sulfate as coagulant were 80.3 and 97.4%, respectively. Average turbidity concentration in filtrated water was 0.5 NTU.

o Clarification and Filtration efficiency with Ferric Chloride in term of Turbidity as coagulant were 85.0 and 98.1%, respectively. Average turbidity concentration in filtrated water was 0.4 NTU.

By using Aluminum Sulfate as coagulant, average residual Aluminum was 0.15,

less than the standard. Average residual Ferrous and Manganese ions from coagulation of Ferric Chloride were 0.06 and 0.01, respectively, which lower than the standard values (0.30 and 0.10 mg/L).

Average filter run period for Aluminum Sulfate and Ferric Chloride were 23 and 34

hours, respectively. By using Ferric Chloride, filter run period can prolong 32.4%.

Costs of drinking water production were 0.142 and 0.105 Baht/m3 when using Aluminum Sulfate and Ferric Chloride, respectively. By using Ferric Chloride, chemical cost can be saved 26.0%.

5.2 Recommendations

This study’s result can be used as a guideline for substitution of Ferric Chloride to Aluminum Sulfate, longer period of pilot scale experiments shall be performed, in order to gain more data for interpretation.

Dual media of sand filter may be applied for filtration to study the results. For more practical results, real application of Ferric Chloride in water treatment

process shall be performed at MWTP. Sludge generated from both coagulants have to be analyzed in more parameters to

investigate their characteristics.

43

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