CHEMICAL PRECIPITATION OF PALM OIL MILL EFFLUENT (POME)

CHEMICAL PRECIPITATION OF PALM OIL MILL EFFLUENT

SHAZANA BINTI MOHD IBRAHIM

UNIVERSITI TEKNOLOGI MALAYSIA

CHEMICAL PRECIPITATION OF PALM OIL MILL EFFLUENT

SHAZANA BINTI MOHD IBRAHIM

A dissertation submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Environmental Engineering)

Faculty of Chemical and Natural Resources Engineering

Universiti Teknologi Malaysia

FEBRUARY 2009

iii

To my beloved mother and father

who have provided me with love, guidance and support

iv

ACKNOWLEDGEMENTS

I wish to express my gratitude to my master’s dissertation supervisor, Dr.

Mohd. Ariffin bin Abu Hassan, for his guidance and encouragement during this

research. Without his help, I believe this research would have not been completed. I

learned many aspects of research methods and analysis. In addition, I learned

patience, dedication, humility and respect for others. His vision, creativity and

ongoing support are great assets.

My appreciation also goes to pollution laboratory assistants, Mrs. Noraidah

Zhwal and Mr. Mohd. Azri Mohd. Salleh for their guidance and their generosity in

giving useful suggestions and providing pleasant laboratory conditions to work in.

I greatly appreciated the contribution of Mr. Abu from Felda Palm Industries

Sdn. Bhd. for his help and insights throughout the experiments.

Lastly but certainly not the least, I am indebted to my parents for their endless

support.

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ABSTRACT

Many palm oil mills failed to comply with the standard discharge limits

especially BOD and TSS concentration although they have applied biological

treatment system. Hence, it is suggested that coagulation and flocculation process

will enhance the BOD and TSS removal so that the final discharge will meet the

Department of Environment (DOE) standards besides curtailing the large land area

required by the aerobic pond. A study using coagulation–flocculation method as a

pre-treatment for palm oil mill effluent (POME) has been carried out. The efficiency

of chitosan, polyacrylamide (PAM) and polyaluminum chloride (PACl) as

coagulants were explored in this study. Jar test method has been used to identify the

best coagulant in removing the organic matter. The reduction of turbidity, BOD, and

TSS were the main evaluating parameters. In coagulation–flocculation process,

coagulant dosage and pH played an important role in determining the coagulation

efficiency. Chemical cost estimation was done to determine the applicability of the

type of coagulant and its dosage. At the optimum chitosan dosage (250 mg/L) and

pH 5.0, turbidity reduction was found to be 94%, TSS removal was 97% and BOD

reduction was 61%. The optimum dosage and pH for PAM were 500 mg/L and 5.0,

respectively, at which it gave 44% reduction of turbidity, 94.8% of TSS removal and

63% of BOD reduction. At the optimum PACl dosage (500 mg/L) and pH 6.0,

turbidity reduction was found to be 76.3%, TSS removal was 96% and BOD

reduction was 59%. For PAM and PACl to obtain a comparable percentage of BOD

removal as performed by chitosan, the optimum dosages were 500 mg/L,

respectively, employing the same mixing speed and sedimentation time, and a pH

value of 5.0 and 6.0, respectively. Amongst the three types of sole coagulant, the

total chemical cost of PACl needed per tonne of crude palm oil produced was the

cheapest (RM0.85), followed by PAM (RM23.88) and chitosan (RM39.13).

vi

ABSTRAK

Kebanyakan kilang pemprosesan minyak kelapa sawit gagal menepati

piawaian pelepasan efluen terutamanya kepekatan BOD dan pepejal terampai (TSS)

walaupun telah menggunakan sistem rawatan biologi. Maka kaedah pengentalan dan

pengelompokan dicadangkan sebagai pilihan yang lebih baik dalam meningkatkan

pengurangan TSS dan BOD supaya efluen akhir menepati piawaian DOE di samping

mengurangkan keperluan tanah yang besar untuk kolam aerobik. Kajian

menggunakan kaedah pengentalan dan pengelompokan untuk pra-rawatan air sisa

kilang kelapa sawit (POME) telah dijalankan. Kecekapan chitosan, poliakrilamida

(PAM), dan poli-aluminium klorida (PACl) sebagai bahan pengental dikaji. Ujian

balang digunakan untuk mengenalpasti bahan pengental terbaik dalam

menyingkirkan bahan organik. Pengukuran pengurangan kekeruhan, TSS dan BOD

adalah parameter yang digunakan untuk justifikasi kecekapan rawatan pra-kimia

POME. Dalam proses tersebut, dos bahan pengental dan pH memainkan peranan

penting dalam menentukan kecekapan proses pengentalan. Analisis kos bahan kimia

dilaksanakan untuk menentukan aplikasi jenis bahan pengental dan dosnya. Pada

dos optima chitosan (250 mg/L) dan pH 5.0, pengurangan sebanyak 94% kekeruhan,

97% TSS dan 61% BOD berjaya dicapai. Dos dan pH optima bagi PAM ialah 500

mg/L and 5.0, dimana pengurangan sebanyak 44% kekeruhan, 94.8% TSS, dan 63%

BOD diperolehi. Pada dos dan pH optima PACl iaitu 500 mg/L dan pH 6.0,

penyingkiran 76.3% kekeruhan, 96% TSS dan 59% BOD dapat dicapai. Bagi PAM

dan PACl untuk mencapai peratusan pengurangan BOD yang setara dengan chitosan,

dos optima yang diperlukan ialah 500 mg/L, melalui halaju pengacauan dan tempoh

sedimentasi yang sama, dan nilai pH pada 5.0 dan 6.0, masing-masing. Kos PACl

bagi setiap tan penghasilan minyak sawit mentah adalah yang termurah (RM0.85),

diikuti PAM (RM23.88) dan chitosan (RM39.13).

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i DECLARATION ii DEDICATION iii ACKNOWLEDGEMENTS iv ABSTRACT v ABSTRAK vi TABLE OF CONTENTS vii LIST OF TABLES xii LIST OF FIGURES xiii LIST OF ABBREVIATIONS xv LIST OF APPENDICES xvi I INTRODUCTION

1.1 Introduction 1

1.2 Background of Research 3

1.3 Problem Statement 6

1.4 Objectives of Research 6

1.5 Scope of Research 7

1.6 Significance of Research 7

II LITERATURE REVIEW

2.1 Introduction 9

viii

2.2 Palm Oil Milling Process 10

2.3 Palm Oil Mill Effluent (POME) 13

2.4 Existing Palm Oil Wastewater Treatment Systems 17

2.4.1 Pretreatment 17

2.4.1.1 Sand and Oil Trap 17

2.4.1.2 Cooling System 17

2.4.2 Primary Treatment 18

2.4.2.1 Ponding Systems 18

2.4.2.2 Tank Digesters and Ponding Systems 20

2.4.2.3 Extended Aeration 21

2.4.3 Post-treatment 21

2.4.3.1 Land Treatment System 21

2.5 Previous Researches in the Field 22

2.6 Coagulation and Flocculation 28

2.6.1 Properties of Colloidal Systems 30

2.6.2 Colloidal Structure and Stability 30

2.6.3 Mechanism of Coagulation 31

2.6.3.1 Destabilization of Colloids 31

2.6.3.2 Bridging Mechanism 32

2.6.4 Influencing Factors 34

2.6.4.1 Coagulant Dosage 34

2.6.4.2 pH Value 35

2.6.4.3 Colloid Concentration and Zeta

Potential 35

2.6.4.4 Affinity of Colloids for Water 36

2.6.4.5 Mixing 36

2.6.5 Coagulants 37

2.6.5.1 Polymeric Inorganic Salts 37

2.6.5.2 Organic Polymers 38

2.6.6 Coagulation Aids 39

2.6.7 Coagulation Control 39

2.6.8 Jar Test 40

2.6.9 Rapid Mix 41

ix

2.6.10 Flocculation 41

2.7 Coagulation and Flocculation using Chitosan 42

2.8 Coagulation and Flocculation using Polyacrylamide

(PAM) 42

2.9 Coagulation and Flocculation using Polyaluminum

Chloride (PACl) 43

2.10 Efficiency of POME Treatment 44

2.10.1 Biochemical Oxygen Demand (BOD)

Analysis 44

2.10.2 Turbidity Analysis 45

2.10.3 Total Suspended Solids Analysis 45

2.11 Chemical Cost Estimation 46

III METHODOLOGY

3.1 Introduction 48

3.2 Materials and Methods 49

3.2.1 Experimental Materials 49

3.2.1.1 POME Sample Collection 49

3.2.1.2 Quantity 49

3.2.1.3 Containers 49

3.2.1.4 Representative Samples 50

3.2.1.5 Sample Preservation 50

3.2.1.6 Coagulants 50

3.2.2 Experimental Design 51

3.2.2.1 Laboratory Treatability Study 51

3.2.2.2 Reproducibility Studies 52

3.2.2.3 Characterization of POME 52

3.2.2.4 Optimum Dosage 53

3.2.2.5 Optimum pH Value 54

3.2.2.6 Jar Testing 55

3.2.3 Determination of the Response 56

3.2.3.1 Observation 56

x

3.2.3.2 Chemical Analyses 56

3.2.3.3 Biochemical Oxygen Demand (BOD)

Determination 56

3.2.3.4 Turbidity Determination 58

3.2.3.5 Total Suspended Solids

Determination 59

3.3 Comparison of the Performance of Chitosan, PAM

and PACl as Coagulants in POME Treatment 61


IV RESULTS AND DISCUSSIONS

4.1 Introduction 62

4.2 Characteristic Study of POME 63

4.3 Sole Coagulant for Coagulation

and Flocculation Processes 64

4.3.1 Chitosan as Sole Coagulant 64

4.3.1.1 Effect of Coagulant Dosage on BOD

Removal 64

4.3.1.2 Effect of Coagulant Dosage on TSS

Removal 66

4.3.1.3 Effect of Coagulant Dosage on

Turbidity Removal 67

4.3.2 Polyacrylamide (PAM) as Sole Coagulant 68


Removal 69


Removal 71



4.3.3 Polyaluminum Chloride (PACl) as Sole

Coagulant 74

xi


Removal 74


Removal 76



4.4 Optimum Dosage and Operating Condition Analysis 81

4.4.1 Chitosan Performance at Optimum Dosage 81

4.4.1.1 Effect of pH on BOD, TSS and


4.4.2 PAM Performance at Optimum Dosage 84



4.4.3 PACl Performance at Optimum Dosage 87



4.5 Comparison of the Performance of Chitosan, PAM

and PACl as Coagulants in POME Treatment 90


V CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction 96

5.2 Conclusions 96

5.3 Recommendations 98

REFERENCES 100

APPENDICES 109

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Properties of Palm Oil Mill Effluents 13

2.2 Chemical Properties of POME 14

2.3 Environmental Regulations for Watercourse Discharge

for POME

15

2.4 Palm Oil Mill Effluent Discharge Standards 16

2.5 Typical mixing times for various chemicals used in

wastewater treatment facilities

36

3.1 Reproducible data for BOD value of raw POME 52

3.2 Coagulants used in the study 53

3.3 B.O.D. Dilution Table 57

4.1 Characteristics of raw POME 63

4.2 Estimated costs to treat POME generated per tonne of

CPO produced at the optimum dosages of each

coagulants

94

4.3 Cost of coagulants required based on the amount of CPO

produced and POME generated monthly

95

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Mass Flow in Palm Oil Mill Process 12

2.2 Palm Oil Mill Processing Flow Chart 12

2.3 Mechanisms of Coagulation 33

2.4 Interparticle Bridging with Organic Polymers 33

3.1 (a) Jar Test Apparatus 55

3.1 (b) pH Meter and Magnetic Stirrer 55

4.1 The Percentage of BOD Removal for Different Dosage of

Chitosan

65

4.2 The Percentage of TSS Removal for Different Dosage of

Chitosan

66

4.3 The Percentage of Turbidity Removal for Different Dosage

of Chitosan

67

4.4 Coagulation using 250 mg/L Chitosan at pH 5 68


PAM

69


PAM

71


of PAM

72

4.8 Coagulation with PAM at optimum dosage and initial pH;

after 1 hour settling time

73


PACl

74

xiv

4.10 Schematic diagram showing the interaction of aluminium

species with initially negatively charged particles in water

75


PACl

76


of PACl

78

4.13 Coagulation with PACl at Optimum Dosage and Initial pH 79

4.14 The Percentage of BOD Removal vs. Dosage of Chitosan,

PAM and PACl

80

4.15 The Percentage of BOD, TSS and Turbidity Removal

Using 250 mg/L Chitosan at Different pH of POME

82

4.16 (a) Supernatant After Treatment with Chitosan at pH 3 83

4.16 (b) Supernatant After Treatment with Chitosan at pH 4 83

4.16 (c) Supernatant After Treatment with Chitosan at pH 6 83


Using 500 mg/L PAM at Different pH of POME

84

4.18 (a) PAM Performances at pH 3 86

4.18 (b) PAM Performances at pH 4 86

4.18 (c) PAM Performances at pH 6 86


Using 500 mg/L PACl at Different pH of POME

87

4.20 (a) PACl Performances at pH 3 88

4.20 (b) PACl Performances at pH 4 88

4.20 (c) PACl Performances at pH 6 88

4.21 BOD Removal Using Chitosan, PAM and PACl vs.

Different pH of POME

90

4.22 TSS Removal Using Chitosan, PAM and PACl vs.


91

4.23 Turbidity Removal Using Chitosan, PAM and PACl vs.


92

xv

LIST OF ABBREVIATIONS

BOD Biochemical Oxygen Demand COD Chemical Oxygen Demand CPO Crude Palm Oil DO Dissolved Oxygen DOE Department of Environment

EFB Empty Fruit Bunches FFB Fresh Fruit Bunches HCl Hydrochloric acid

HRT Hydraulic Retention Time

MRE Mixed Raw Effluent

NaOH Sodium Hydroxide

NTU Nephelometric Turbidity Units

PACl Polyaluminum Chloride PAM Polyacrylamide POME Palm Oil Mill Effluent

ppm Parts Per Million

RO Reverse Osmosis

rpm Rotation Per Minute

TN Total Nitrogen

TS Total Solids

TSS Total Suspended Solids

UASB Upflow Anaerobic Sludge Blanket

UF Ultrafiltration

v/v Volume Per Volume

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A POME Characteristic Study 109

B Sole Coagulant for Coagulation and Flocculation

Processes

110

C Parameter Optimization 114

D Photo of the Coagulants Application in POME

Treatment

117

CHAPTER I

INTRODUCTION

1.1 Introduction

Malaysia presently accounts for 51% of world palm oil production and 62%

of world exports, and hence also for 8% and 22% of the worlds total production and

exports of oils and fats. As the leading producer and exporter of palm oil and palm

oil products, Malaysia has a significant role to play in fulfilling the growing global

need for oils and fats in general.

The oil palm growth in Malaysia has been bright. The crop has developed to

the multi billion ringgit industry as what is witnessed today. In Africa the crop exists

wild in the groves facing various constraints in efforts towards domestication. It is in

Malaysia that the crop's full potential was utilized. This revolution from wild to

domesticated, growing under well managed plantations is not without cost. A great

deal of effort went into appreciating this new crop and means of fitting it to its new

home.

2

It was during this development that more was discovered about the crop and

its interaction with the environment. Success in the plantation development carried

the crop to a new challenge, which is in the processing technology. Malaysia had to

take the lead in this new endeavor and developed technologies which are

economically sound. Development of the palm industry in Malaysia has been

exceptional. From a mere 400 hectares planted in 1920 the area increased to 54 000

hectares in 1960. Many more areas were opened up for oil palm cultivation, either

from virgin jungles, or from conversion of plantations that originally supported

rubber or other crops since then (MPOB Website).

This increase in area is a direct result of the government’s policy on crop

diversification. The area under oil palm stood at a staggering 2.6 million hectares by

1996. A corresponding growth in the milling and refining sectors was the result of

this fast growth in oil palm planting. Encouraged further by the government

incentive to make use of the country's rich agro-based resources, oleochemical

processing from palm oil and palm kernel oil began to assume prominence in 1980's.

Today, 3.88 million hectares of land in Malaysia is under oil palm cultivation

producing 14 million tonnes of palm oil in 2004 (MPOB Website).

Throughout its entire development in Malaysia, both upstream and

downstream, the oil palm and its product have always been linked with the

environment. Such a rapid increase in both downstream and upstream activities

would result in uncontrollable environmental pollution.

To produce palm oil, a considerable amount of water is needed, which in turn

generate a large volume of wastewater. Palm oil mills and palm oil refineries are

two main sources of palm oil wastewater; however, the first is the larger source of

pollution and effluent known as palm oil mill effluent (POME). The palm oil

processing became synonymous to POME pollution. An estimated 30 million tonnes

of POME are produced annually from more than 300 palm oil mills in Malaysia.

The oxygen depleting potential of POME is 100 times that of domestic sewage.

3

Owing to the high pollution load and environmental significance of POME, an

emphasis ought to be placed on its treatment system.

The year 1978 witnessed the enactment of the Environmental Quality

Regulations detailing POME discharge standards. Biochemical Oxygen Demand

(BOD) was the key parameter in the standards. From the initial BOD of 25 000 ppm

of the untreated POME, the load was reduced to 5 000 ppm in the first generation of

discharge standard, down to the present BOD of 100 ppm (Malaysia, 1977).

1.2 Background of Research

Wastewater, also known as sewage, originates from household wastes, human

and animal wastes, industrial wastewaters, storm runoff, and groundwater infiltration

(Lin, 2001). An understanding of physical, chemical and biological characteristics of

wastewater is very important in design, operation and management of collection,

treatment, and disposal of wastewater. The nature of wastewater includes physical,

chemical and biological characteristics which depend on the water usage in the

particular industry.

Depending on the nature of the industry and the projected uses of the waters

of the receiving streams, various waste constituents such as soluble organics and

suspended solids, may have to be removed before discharge (Eckenfelder, 2000).

The natural waters in streams, rivers, lakes, and reservoirs have a natural

waste assimilative capacity to remove solids, organic matter, even toxic chemicals in

the wastewater. However, it is a long process. Wastewater treatment facilities are

designed to speed up the natural purification process that occurs in natural waters and

4

to remove contaminants in wastewater that might otherwise interfere with the natural

process in the receiving waters (Lin, 2001). Methods of treatment consist of

physical, chemical and biological unit process.

The principal chemical unit processes used for wastewater treatment include

chemical coagulation, chemical precipitation, chemical disinfection, chemical

oxidation, advance oxidation processes, ion exchange, and chemical neutralization,

scale control, and stabilization (Metcalf and Eddy, 2004). Nevertheless, coagulation

(i.e. physicochemical destabilization of the colloidal system) and flocculation (i.e.

the aggregation of the particles) are most important in many water and sewage

treatment processes (Pawlowski, 1982).

There are quite a number of effluent treatment systems which are currently

used by the Malaysian palm oil industry. Among them are anaerobic/facultative

ponds, tank digestion and mechanical aeration, tank digestion and facultative ponds,

decanter and facultative ponds, and physicochemical and biological treatment.

Treatment of POME has also been tried using membrane technology, an up-flow

anaerobic filtration, an up-flow anaerobic sludge blanket and an up-flow anaerobic

sludge fixed film bioreactor. At present 85% of POME treatment is based on an

anaerobic and facultative ponding system, which is followed by another system

consisting of an open tank digester coupled with extended aeration in a pond

(Vijayaraghavan et al., 2007).

Chemical treatment of palm oil wastewater was investigated using

physicochemical treatment i.e. coagulation and flocculation. It is currently an

attractive option in POME treatment that numerous studies had been done on its

application in POME treatment system. The results showed that by applying alum,

93% suspended solid removal can be achieved (Ahmad et al., 2003a). Application of

chitosan as a coagulant showed the best performance as compared to activated

carbon and bentonite with more than 99% residual oil and suspended solid removal

(Ahmad et al., 2005b). Chitosan, besides being environmentally friendly, performed

5

better when compared to alum and polyaluminum chloride (PACl) (Ahmad et al.,

2006). Ariffin et al. (2005) concluded that cationic polyacrylamide (PAM) gave

99% turbidity and total suspended solid (TSS) removal, and 40% Chemical Oxygen

Demand (COD) removal. Bhatia et al. (2007a) studied the advantage of Moringa

Oleifera seeds usage. 99% TSS removal can be achieved when utilized with

flocculant (NALCO7751). The use of polymeric agent in the treatment of POME

was also considered (Ng et al., 1987; Ismail and Lau, 1987).

In the present scenario of POME treatment, anaerobic digestion is followed

by aerobic oxidation in facultative and algae ponds. Hence, in this study, the

coagulation and flocculation process is proposed as a pre-treatment before the

anaerobic digestion process with the intention of increasing the BOD and TSS

removal so that the final discharge will meet the Department of Environment (DOE)

standards besides curtailing the large land area required by the aerobic pond. The

efficiency of the coagulation and flocculation process was evaluated by treating the

mixed raw effluent obtained from the effluent treatment plant of Kilang Sawit

Penggeli, Felda Palm Industries Sdn. Bhd.

POME is a voluminous, high BOD liquid waste. It has total solids content of

5–7% which a little over half is dissolved solids, and the other half being a mixture

of various forms of organic and inorganic suspended solids. This property, coupled

with its high BOD loading and low pH, makes it not only highly polluting but also

extremely difficult to treat by conventional methods. The crude palm oil production

of 985,063 tonnes used 1,477,595m3 of water, and 738,797m3 was discharged as

POME (Bhatia et al., 2007a). A new and improved POME treatment technology

would be required in order to meet the requirements of DOE discharge limits (400

mg/L TSS and 100 mg/L BOD) and to curb watercourses pollution. There are many

processing plants failed to comply with the standard discharge limits even though

they have applied biological treatment system.

6

1.3 Problem Statement

A variety of coagulants has been studied to assess their ability to destabilize

the POME suspension and to flocculate the particulate matter. The conditions that

would allow for optimal use of the respective chemicals were noted especially for

suspended solid removal. However, the magnitudes of the increase in the BOD

removal rate by the application of the coagulants are still vague as there is currently

little published information on the use of coagulants in POME treatment for BOD

removal, with much of the information that is available being proprietary in nature.

Most studies performed did not carry out chemical cost analysis which is equally

important so as to determine the most cost effective process.

This study was designed to measure the effectiveness of chitosan, PACl and

PAM as coagulants for POME treatment by assessing the removal efficiency of TSS,

turbidity and BOD and to verify the most suitable and cost effective coagulant for

coagulation and flocculation of POME.

1.4 Objectives of Research

The project was aim to achieve the following objectives:

1. To study the potential and effectiveness of chitosan, PACl and PAM as

coagulants for POME treatment by assessing the removal efficiency of TSS,

turbidity and BOD.

2. To determine the optimum dosage of coagulant needed to achieve maximum

removal of TSS, turbidity and BOD.

7

3. To observe the influence of pH on the coagulation process and thus identify

the optimum pH which will give the highest removal.

4. To verify the most suitable and cost effective coagulant for coagulation and

flocculation of POME.

1.5 Scope of Research

The research primarily focused on the chemical pre-treatment of POME,

collected from Felda Palm Industries Sdn. Bhd (Kilang Sawit Penggeli), by using

chitosan, PACl and PAM as coagulants. TSS, turbidity and BOD removal efficiency

was determined in order to observe the performance of each coagulant.

Coagulation and flocculation process was carried out via jar test apparatus, in

which the optimum dosage of each coagulant to coagulate the mixed raw effluent at

the initial pH was identified. Alteration of the effluent’s initial pH was done so as to

verify the most optimum condition which will give the highest removal efficiencies.

This was followed by the chemical cost analysis with the purpose of selecting the

most suitable and cost effective coagulant.

1.6 Significance of Research

Palm mills in Malaysia is facing the challenge of balancing environmental

protection, their economic viability, and sustainable development after the DOE

enforced the regulation for the discharge of effluent from the crude palm oil industry,

under the Environmental Quality (Prescribed Premises) (Crude Palm Oil)

8

Regulations 1977. Quite a number of mills’ discharge did not meet the effluent

standards as stipulated by the DOE Malaysia. This indicates that up-grading of the

existing wastewater treatment plants has to be made in order to comply with the

effluent standards established by the authorities. The immediate implication of this

research is readily observable. By applying chemical pre-treatment in the POME

treatment system, it will significantly improve the treatment system and thus improve

the quality of the effluent discharge from the mill and reduce potential environmental

liabilities. The findings from this study will also provide way to the most feasible

and economical unit processes which can be further studied on a pilot plant scale.

CHAPTER II

LITERATURE REVIEW

2.1 Introduction

This chapter describes the palm oil milling process, POME and its chemical

properties, and environmental regulations for watercourse discharge for POME.

Existing palm oil wastewater treatment systems which are currently used by most

palm mill are also discussed in this chapter. Due to more stringent Environmental

Quality Regulations, various studies in POME treatment had been carried out by

many researchers. Previous studies in POME treatment were reviewed in this

chapter and detail discussions on physicochemical treatment (coagulation and

flocculation) of POME were made. Several coagulants were considered and the

parameters involved in evaluating the process efficiency were cited in this chapter.

10

2.2 Palm Oil Milling Process

Palm oil milling is the process that extracts crude palm oil from fresh fruit

bunches (FFB). In the extraction of oil from the oil palm fruits, no chemicals are

added, therefore making all generated wastes nontoxic to the environment. The

standard process consists of bunch sterilization, fruit stripping, digestion, screw

pressing for liquid extraction and centrifugation for oil separation (Teoh et al., 1980).

In order to inactivate the natural enzymes and loosen the fruits for easy

stripping the FFB is sterilized by steam. It is also to remove external impurities and

to detach the kernels from the shells. The sterilization process acts as the first

contributor to the accumulation of POME in the form of sterilizer condensate. Steam

condensate from the sterilizer contains palm oil and solid of 1% each. In normal

practice, it is discharged to the wastewater pond (Hassan et al., 2004).

A rotary thresher is used to strip off the fruits and then mashed in a digester.

The empty fruit bunches (EFB) can be recycled to the plantation for mulching or as

organic fertilizer. The digester consists of a cylindrical vessel equipped with stirrer

and expeller arms mainly to digest and press the fruitlets. Mixing water is added to

the digester, screw press and screening unit to improve extraction efficiency and flow

ability of the processing stream. The quantity of water has a direct effect on the

efficiency of the palm oil extraction process (Chungsiriporn et al., 2006).

Palm oil mixture, the extracted product, is a mixture of palm oil, water and

fine solid particles. Oil and pressed cake comprising nuts and fiber are produced at

the end of the process. The fiber and nuts are separated in the depericarper column.

The waste fiber is then burnt for energy generation inside the boiler. The nuts from

the digestion and pressing processes are polished before being sent to the nut-

cracking machine or ripple mill. The cracked mixture of kernels and shells is then

11

separated in a winnowing column using upward suction (hydrocyclone) and a clay

bath (Hassan et al., 2004).

The third source of POME is the washing water of the hydrocyclone. The

kernel produced is then stored before being transferred to palm kernel mill for oil

extraction. The palm oil mixture is continuously fed to the settling tank. Palm oil,

which is the lightest phase, overflows from the settling tank and is purified (by

moisture removal) for the final product called crude palm oil (CPO). Dirt and

impurities are removed from the oil by centrifugation. Before the CPO is transferred

to the storage tank, it is subjected to high temperatures to reduce the moisture content

in the CPO. This is to control the rate of oil deterioration during storage prior to

processing at the palm oil refinery (Hassan et al., 2004).

Bottom sludge from the settling tank consisting of water, solids and palm oil

residue of 7–10% is then passed through a decanter and a separator in series for oil

recovery. Water is added to the decanter and the separator to blend and balance the

phase for efficient oil recovery. POME that is a mixed stream of separator outlet,

sterilizer condensate and turbine cooling water is sent to a wastewater treatment

system (Chungsiriporn et al., 2006).

12

The schematic diagram of the palm oil milling process, without and with

refining process, is shown in Figure 2.1 and 2.2 respectively.

Figure 2.1 Mass flow in palm oil mill process (Chungsiriporn et al., 2006)

Figure 2.2 Palm Oil Mill Processing Flow Chart (MPOPC Website)

13

In most mills, all three wastewater streams, amounting to about 3 tonnes per

tonne of palm oil produced, are combined to give viscous brown liquid containing

fine suspended solids (Hassan et al., 2004). If discharged untreated, these solids can

cause considerable environmental problem. The characteristics of this mixed waste

are shown in Table 2.1.

Table 2.1 : Properties of Palm Oil Mill Effluents (Borja-Pardilla and Banks, 1994)

Parametera Sterilizer effluent

Hydrocyclone effluent

Centrifuge effluent

Mixed effluent

BOD 10-25 - 17-35 11-30 COD 30-60 - 40-75 38-70 TS 40-50 5-15 35-70 30-65 TSS 3-5 5-12 12-18 9-25 Oil and Grease 2-3 1-5 5-15 5-13 Ammonia N 0.02-0.05 - 0.02-0.05 0.02-0.05 TN 0.35-0.60 0.07-0.15 0.5-0.9 0.5-0.9 pH 4.5-5.5 - 3.5-4.5 3.5-4.5 a All in g dm -3 (except pH).

2.3 Palm Oil Mill Effluent (POME)

Oil palm (Elaeis guineensis) is one of the most versatile crops in the tropical

region, notably in Malaysia and Indonesia. The palm oil industry has become one of

the largest revenue earners and has contributed much toward Malaysia's development

and improved standard of living. About 11.9 million tonnes of CPO were produced

that amounted to RM 14.79 billion in the year 2002 (MPOPC Website). However,

the palm oil mills also have generated enormous amounts of highly polluting

effluent. It is estimated that about 1.5 m3 of water are needed to process one tonne of

FFB, half of this amount ends up as POME (MPOPC Website). It has been singled

out as the chief contributor to Malaysia's environmental pollution. Therefore, while

enjoying a most profitable commodity, the adverse environmental impact from the

palm oil industry cannot be overlooked.

14

POME is an oily wastewater generated by the palm oil processing mills in

Malaysia. It is a colloidal dispersion of biological origin and with an unpleasant

odour. POME is a voluminous, high BOD liquid waste. It is a colloidal suspension

that contains 95–96% of water, 0.6–0.7% of oil and grease and 4–5% of total solids

including 2–4% suspended solids originated from the mixture of sterilized

condensate, separator sludge and hydrocyclone wastewater. This property, coupled

with its high BOD loading and low pH, makes it not only highly polluting but also

extremely difficult to treat by conventional methods. It is a thick brownish color

liquid and discharged at a temperature between 80 and 90°C. It is fairly acidic with

pH ranging from 4.0 to 5.0 (Borja-Pardilla and Banks, 1994). Table 2.2 shows the

refined characteristics of raw POME.

Table 2.2 : Chemical Properties of POME (Hassan et al., 2004)

Chemical Property Average Range pH 4.2 3.4 – 5.2 BOD (mg/L) 25,000 10,250 – 43,750 COD (mg/L) 50,000 15,000 – 100, 000 Oil and Grease (mg/L) 6000 150 – 18,000 Ammoniacal Nitrogen (mg/L) 35 4 – 80 TN (mg/L) 750 180 – 1400 TSS (mg/L) 18,000 5000 – 54,000 TS (mg/L) 40,000 11,500 – 78,000

Apart from the organic composition, POME is also rich in mineral content,

particularly phosphorus (18 mg/L), potassium (2270 mg/L), magnesium (615 mg/L),

and calcium (439 mg/L) (Hassan et al., 2004). Thus, most of the dewatered POME

dried sludge (the solid end product of the POME treatment system) can be recycled

or returned to the plantation as fertilizer.

Based on the statistics of total CPO production in May 2001, the CPO

production of 985,063 tonnes used 1,477,595m3 of water, and 738,797m3 was

discharged as POME. In year 2004, more than 40 million tonnes of POME was

generated from 372 mills in Malaysia (Bhatia et al., 2007a). Without proper

15

treatment of POME, the effluent will pollute watercourses where this effluent is

discharged.

The palm oil mills traditionally have discharged their effluents into rivers

leading to the seas. They relied solely on nature to absorb large quantities of waste

products. With the rapid expansion of the industry and the public's increased

awareness of environmental pollution, the industry is obliged both socially and

aesthetically to treat its effluent before it is discharged. The Government also has

responded by enacting the environmental laws in 1976 to control the pollution

caused by the palm oil industry (Thanh et al., 1980). The laws require the POME to

be treated to a required standard before it can be discharged (Table 2.3).

Table 2.3 : Environmental Regulations for Watercourse Discharge for POME

(Malaysia, 1977)

Parameters Level BOD (mg/L) 100 Total Suspended Solids (mg/L) 400 Oil and Grease (mg/L) 50 Ammoniacal Nitrogen (mg/L) 150 Total Nitrogen (mg/L) 200 pH 5 - 9

16

The year 1978 witnessed the enactment of the Environmental Quality

Regulations detailing POME discharge standards. BOD was the key parameter in the

standards. From the initial BOD of 25 000 ppm of the untreated POME, the load

was reduced to 5 000 ppm in the first generation of discharge standard, down to the

present BOD of 100 ppm (Malaysia, 1977). Table 2.4 shows the Palm Oil Mill

Effluent Discharge Standards from 1978 to 1984.

Table 2.4 : Palm Oil Mill Effluent Discharge Standards (Malaysia, 1977)

Std A Std B Std C Std D Std E Std F Parameter 1/7/78 1/7/79 1/7/80 1/7/81 1/7/82 1/7/84 pH 5 - 9 5 - 9 5 - 9 5 - 9 5 - 9 5 - 9 BOD (mg/L) 5000 2000 1000 500 250 100 COD (mg/L) 10000 4000 2000 1000 - - TS (mg/L) 4000 2500 2000 1500 - - TSS (mg/L) 1200 800 600 400 400 400 Oil and Grease (mg/L) 150 100 75 50 50 50

Ammoniacal Nitrogen (mg/L) 25 15 15 10 150 100

TN (mg/L) 200 100 75 50 - - Temperature (°C) 45 45 45 45 45 45

The various effluent treatment schemes which are currently used by the

Malaysian palm oil industry are listed in descending order: (a) anaerobic/facultative

ponds (Rahim and Raj, 1982; Chan and Chooi, 1982), (b) tank digestion and

mechanical aeration, (c) tank digestion and facultative ponds, (d) decanter and

facultative ponds, and (e) physico-chemical and biological treatment (Andreasen,

1982). Treatment of POME has also been tried using evaporation technology

(Stanton, 1974).

Conventional biological treatments are most widely adopted. The current

treatment technology of POME typically consists of biological aerobic and anaerobic

digestion or facultative digestion. Nowadays, about 85% of POME treatment is

based on an anaerobic and facultative ponding system by Malaysian palm oil mills,

which is followed by another system consisting of an open tank digester coupled

17

with extended aeration in a pond (Hassan et al., 2004). The most cost effective

technology is anaerobic treatment.

2.4 Existing Palm Oil Wastewater Treatment Systems

2.4.1 Pretreatment

2.4.1.1 Sand and Oil Trap

Manually operated sand and oil traps were installed as pretreatment units in

many wastewater treatment systems. This would minimize sand being discharged

into the next unit as it will accumulate in the primary pond or tank digester thereby

reducing its effective volume and increasing the frequency of desludging of these

units (Thanh et al., 1980). The mixed raw effluent (MRE) is then pumped into the

cooling and mixing ponds for stabilization before primary treatment. No biological

treatment occurs in these ponds. However, sedimentation of abrasive particles such

as sand will ensure that all pumping equipment is protected (Hassan et al., 2004).

2.4.1.2 Cooling System

Small holding pond or aeration tower was commonly used to bring down the

raw wastewater temperature prior to discharge into any treatment system. The raw

wastewater was cooled down to a temperature less than 35°C before feeding it into

18

an anaerobic pond (Thanh et al., 1980). The retention time of MRE in the cooling

and mixing ponds is between 1 and 2 days (Hassan et al., 2004).

2.4.2 Primary Treatment

2.4.2.1 Ponding Systems

The ponding system comprised of a series of anaerobic, facultative, and algae

ponds. An anaerobic pond is the most economical and feasible means in treating a

high strength organic waste. Because of its simplicity of construction, operation and

maintenance, it has been adopted by most of the palm oil mills throughout Malaysia

for waste treatment. These systems also require less energy due to the absence of

mechanical mixing. Mixing is very limited and achieved through the bubbling of

gases; generally this is confined to anaerobic ponds and partly facultative ponds

(Thanh et al., 1980).

The ponding system requires a vast area to accommodate a series of ponds in

order to achieve the desired characteristics for discharge. Generally anaerobic ponds

are designed to be followed by facultative waste stabilization ponds. In constructing

the ponds, the depth is crucial for determining the type of biological process. The

sizing of most of anaerobic pond systems was arbitrarily done. For anaerobic ponds,

the optimum depth ranges from 5 to 7 m, while facultative anaerobic ponds are 1 -

1.5 m deep. The hydraulic retention time (HRT) ranged from 40 to 200 days. The

effective HRT of anaerobic and facultative anaerobic systems is 45 and 20 days,

respectively (Hassan et al., 2004).

19

A shallower depth of approximately 0.5 – 1 m is required for aerobic ponds,

with an HRT of 14 days. The shapes of the anaerobic ponds vary from square to

narrow ditch, with a length to width ratios varying from 1:1 to as high as 110:1. The

POME is pumped at a very low rate of 0.2 to 0.35 kg BOD/m3.day of organic

loading. Under these optimum conditions, the system should be able to meet the

requirement of DOE. The number of ponds will depend on the production capacity

of each palm oil mill (Hassan et al., 2004).

The area occupied by the ponding system varies from 1 ha to as high as 5 ha.

Even in a mill having the same processing capacity, the land area provided will never

be the same. The inlet and outlet structures vary from one pond to another, the slope

of the pond was not properly done, the embankment was not firmly compacted, and

neglect of proper maintenance was apparent (Thanh et al., 1980).

One problem faced by pond operators is the formation of scum, which occurs

as the bubble rise to the surface, taking with them fine suspended solids. This results

from the presence of oil and grease in the POME, which are not effectively removed

during the pretreatment stage. Another disadvantage of the ponding system is the

accumulation of solid sludge at the bottom of the ponds. Eventually the sludge and

scum will clump together in side the pond, lowering the effectiveness of the pond by

reducing the volumetric capacity and HRT. When this happens, the sludge may be

removed by either using submersible pumps or excavators (Hassan et al., 2004).

Most of the treated effluents from these systems did not comply in all

respects with the final effluent standard stipulated by the DOE. Quite a number of

pond systems had been found to be inefficient; this is mainly due to improper start-

up and lack of knowledge in monitoring programme. At times, the performance of

facultative waste stabilization ponds could be affected due to various reasons such as

overloading, the blackish color of the anaerobically treated effluent inhibits light

penetration into the algae culture system, and toxic effects of some trace elements

(Thanh et al., 1980).

20

2.4.2.2 Tank Digesters and Ponding Systems

This system is a combination of an open digester tank and a series of ponding

systems. The anaerobic digestion is carried out in the digester, then in the facultative

and algae ponds. The raw wastewater is mixed with the tank digester’s effluent in a

ratio of 1:1 before being fed into both the concrete and steel tank digester on a

continuous basis. The digesters are constructed at various volumetric capacities

ranging from 600 up to 3600 m3 (Hassan et al., 2004).

The system runs at a HRT of 20 days. In other treatment plant, the tank

effluent is discharged into an aerated lagoon for further treatment. The retention

time in tank digester and aerated lagoon is 20 days. It has been shown that by using

an open digester, a better reduction of BOD can be achieved in a shorter time.

However, it has a higher organic loading of 0.8 – 1.0 kg BOD/m3 .day compared to

anaerobic ponds. Using the same principle as anaerobic ponds, mixing of POME is

achieved via bubbling of biogas. Occasionally, the mixing is also achieved when the

digester is being recharged with fresh POME. The treated POME is then overflowed

into the ponding system for further treatment (Hassan et al., 2004).

Although the digester system has been proven to be superior to anaerobic

ponds, it also has similar problems of scum formation and solid sludge accumulation.

Another serious problem is the corrosion of the steel structures due to long exposure

to hydrogen sulfide. Incident such as burst and collapsed digesters have been

recorded. Accumulated solids could be easily removed using the sludge pipe located

at the bottom of the digester. The dewatered and dried sludge can then be disposed

for land application (Thanh et al., 1980).

21

2.4.2.3 Extended Aeration

To complement the previous systems, mechanical surface aerators can be

introduced at the aerobic ponds. BOD can be reduced effectively through aerobic

processes. The aerators are normally installed at the end of the ponding system

before discharge. Nevertheless, this happens only where land area is a constraint and

does not permit extensive wastewater treatment. Or else, aerators must be provided

to meet DOE regulations (Hassan et al., 2004).

2.4.3 Post-treatment

2.4.3.1 Land Treatment System

Raw or partially treated palm oil wastewater mainly by anaerobic pond

system is applied to land by either discharging to overland flow or applying directly

for irrigation. In spite of the fact that the application of wastewater to oil palm has

been found to provide immediate benefits, many schemes were designed and

implemented without the knowledge of the assimilative capacity of the soil in

relation to the pollutants, except in a few cases where depth of wastewater

application had been limited and annual nitrogen loading rates had been studied

(Hassan et al., 2004).

Raw palm oil waste would not be suitable for land disposal because of its

high content of total solids, low pH, and high concentrations of certain trace elements

such as Fe, Cu, Cd, and Mn, while the anaerobically treated palm oil waste seems to

be more favorable for land application provided the high concentrations of total

22

dissolved solids and some trace elements are removed from the wastewater (Hassan

et al., 2004).

However, the existing conventional biological treatment is characterized by

long HRT, often in an excess of 20 d, necessitating large areas of land or digesters.

There are many processing plants failed to comply with the standard discharge limits

even though they have applied biological treatment system (Bhatia et al., 2007). A

ponding system consisting of 8 ponds in series was studied to evaluate the efficiency

for treating 600m3 POME per day. Even with a HRT of 60 d, effluent COD and

BOD were still as high as 1,725 and 610 mg/L, respectively. Effluent quality was

unable to meet the discharge standard set by the Malaysian DOE, so further

treatment is needed (Chin et al., 1996).

2.5 Previous Researches in the Field

To shorten the treatment time and lessen the land required, high-rate reactors

such as anaerobic filter, anaerobic baffled reactor, anaerobic fluidized reactor,

upflow anaerobic sludge blanket (UASB), upflow anaerobic sludge fixed film

bioreactor, and other hybrid reactors were put forward and tested in treating POME

(Ng et al., 1985, 1987; Borja-Pardilla and Banks, 1994; Borja, 1995; Borja et al.,

1996a; Borja-Pardilla et al., 1996b; Setiadi et al., 1996; Faisal and Unno, 2001,

Najafpour et al., 2006; Yacob et al., 2005, 2006a; Vijayaraghavan et al., 2007,

Yejian et al., 2008, Zinatizadeh et al., 2007). In an anaerobic fluidized bed reactor,

the maximum organic loading rate (OLR) could reach as high as 40 kg COD/ (m3·d)

(Borja-Pardilla et al., 1996b). But all these biological treatment systems need proper

maintenance and monitoring as the processes solely rely on microorganisms to

degrade the pollutants. The microorganisms are very sensitive to the changes in the

environment and thus great care has to be taken to ensure that a conducive

environment is maintained for the microorganisms to thrive in. It requires skilful

23

attention and commitment. How to ensure the stability of the system deserves most

urgent concern.

As for UASB, several months may be required for the development of

anaerobic sludge granules (Najafpour et al., 2006). The process appears to be

particularly sensitive to the TSS loading which can be applied, and also to the nature

of the organic content of the wastewater. At high organic loadings or at low

temperatures the insoluble organic fraction of the wastewater tends to accumulate

within the granule or sludge blanket region of the reactor; this leads to granule

destabilization or inhibition of granule formation. Under these conditions

methanogenesis is affected, leading ultimately to reactor failure as a result of

increased acid concentrations (Najafpour et al., 2006).

Therefore, in order to eliminate the pollution of POME, many more treatment

and disposal methods have been investigated and proposed so as to improve the

existing treatment system. This includes crop irrigation, animal fodder; decanting

and drying (Jorgensen, 1982), evaporation, wet oxidation, land disposal,

centrifugation with or without flocculation (Stanton, 1974), land application (Tam et

al., 1982), ultrafiltration (Tusirin and Suwandi, 1981; Ahmad et al., 2003b, Yejian et

al., 2008), adsorption (Ahmad et al., 2003a, 2003b, 2005a, 2005b), solvent extraction

(Ahmad et al., 2003a), and membrane technology (Ahmad et al., 2003b, 2006;

Yejian et al., 2008). POME treatment using tropical marine yeast, Yarrowia

lipolytica NCIM3589 was also investigated (Oswal et al., 2002). Coagulation-

flocculation method was often employed to remove TSS and residual oil in POME

treatment. Many coagulants, including inorganic salts (AlCl3, Al2 (SO4)3, FeCl3,

FeSO4, etc.) and polyelectrolyte (PACl, PAM and other synthetic polymers), were

used in evaluating their efficiency (Ng et al., 1987; Ariffin et al., 2005; Ahmad et al.,

2005a, 2006b; Vijayaraghavan et al., 2007).

In membrane separation processes, GH and CE (GH) membranes gave 63%

and 49% reductions in TSS and residual oil respectively at pH 9.0 and pressure of

24

1000 kPa (Ahmad et al., 2003a). Yejian et al. (2008) reported that in the membrane

process unit, almost all the suspended solids were captured by ultrafiltration (UF)

membranes and reduced turbidity from 111 NTU to 0.79 NTU, while reverse

osmosis (RO) membrane excluded most of the organic matter from RO permeate.

Suspended solids and color were undetectable in RO permeate. Performance in

terms of turbidity, COD and BOD for each treatment process, consisting of two

stages of chemical treatments and adsorption process by granular activated carbon

treatment as a pretreatment process while UF and RO membranes were used for

membrane separation treatment was studied (Ahmad et al., 2003b). The

pretreatment process was able to remove organic matter and TSS in POME by

reducing 97.9% turbidity, 56% COD and 71% BOD. For the membrane separation

treatment, the turbidity value was reduced to almost 100%, with a 98.8% reduction in

COD and 99.4% BOD reduction.

However, membrane separation technology for treating POME has never

been applied on an industrial scale due to POME characteristics. Membrane

processes have some limitations in dealing with the high suspended solids effluent.

The membranes will suffer from fouling and degradation during use. In order to

apply membrane separation technology, pretreatment processes must be carried out

to reduce the high content of suspended solids and oil in the fresh sample of POME

(Ahmad et al., 2003a).

In the batch adsorption process, an 88% reduction in residual oil was obtained

at a mixing speed of 100rpm for 1 h, pH 9.0 and an adsorbent dosage of 300 g dm−3

(Ahmad et al., 2003a). Ahmad et al. (2005a) reported that chitosan powder, at a

dosage of 0.5 g/l, 15 min of contact time and a pH value of 5.0, presented the most

suitable conditions for the adsorption of residue oil from POME. The adsorption

process performed almost 99% of residue oil removal from POME. Chitosan could

successfully remove 99% of residual oil and minimize the TSS content to a value of

25 mg/l from POME at a dosage of 0.5 g and employing a mixing time of 30 min, a

mixing rate of 100 rpm, sedimentation for 30 min and a pH value of ranging from 4.0

to 5.0 (Ahmad et al., 2005b). For activated carbon and bentonite, the optimum

25

dosages were 8.0 and 10.0 g/l, respectively, 30 min of mixing time at 150 rpm, 80

and 60 min of settling time, respectively, and pH of 4.0–5.0 to obtain the same

percentage of removal as performed by chitosan and can only reduce the TSS values

up to 35 and 70 mg/l, respectively, at the optimized conditions.

Evaporation processes were also used to treat POME. About 85% (v/v) water

in the POME can be recovered as distillate that later could be reused as boiler feed

water or process water with minimal chemical treatment. Energy requirements were

the major concern in this process. It was reported that 1 kg of steam is used to

evaporate 1 kg of water from POME (Ahmad et al., 2003b). Stanton (1974) also

reported that evaporation is technically proven but expensive in terms of energy and

capital equipment. Open pan evaporation produces a highly caramelized solid in

which much of the original protein value is lost.

Coagulation method is widely used in water and wastewater treatments and

well known for its capability of destabilizing and aggregating colloids. There are

number of different mechanisms involved in a coagulation process, including ionic

layer compression, adsorption and charge neutralization, inter-particle bridging, and

sweep coagulation. These mechanisms are very important in forming flocs of

residue oil and suspended solid which could be easily settled and finally removed.

Numerous researches have reported the treatment of POME using coagulation,

flocculation and settling procedure (Ismail and Lau, 1987; Ng et al., 1987; Ahmad et

al., 2003a, 2003b; Ariffin et al., 2005; Ahmad et al., 2005a, 2005b, 2006; Bhatia et

al., 2007a, 2007b; Vijayaraghavan et al., 2007).

The reduction of pollution strength in POME using five inorganic salts and

nine polymers was investigated by Ismail and Lau (1987). Treatment of POME with

80–100 mg/L of Magnafloc LT22 polymer aided in coagulation and flocculation of

TSS, producing 96%, 63%, 53% and 93–94% reduction in the turbidity, COD, TS

and TSS respectively, of the effluent. Treatment with 200 to 300 mg/L FeCl3 and 70

to 100 mg/L Magnafloc LT22 polymer reduced COD, TS and TSS by 47 to 53%, 43

26

to 49% and 92 to 94%, respectively. The TSS of POME can be substantially reduced

by treating with coagulating and flocculating agents before discharging into other

treatment systems.

Ng et al. (1987) assessed the ability of a variety of coagulants to destabilize

the POME suspension and to flocculate the particulate matter. Synthetic polymers

were found to be more effective than lime or alum. Excessively large quantities of

the latter were required in order to achieve the same percentage of removal as

performed by synthetic polymers. This might affect the usefulness of the recovered

solids in animal feed formulation and also lead to a sludge disposal problem.

A pilot plant study of POME treatment using coagulation was found to be

very successful by Ahmad et al. (2003a). The optimum values of the process

parameters obtained in the flocculation process were an alum dosage of 4000 mg

dm−3, mixing speed of 150rpm for 1 h and sedimentation time of 270 min, resulting

in 93% TSS removal. Adopting coagulation, sedimentation and activated carbon

adsorption as a pretreatment stage for POME treatment resulted in removal

efficiencies of 97.9% turbidity, 56% COD and 71% BOD (Ahmad et al., 2003b).

High charge density cationic PAM (485 C/g) is the most effective polymer

(Ariffin et al., 2005). It obtains 98% turbidity removal, 98.7% TSS removal and

54% COD removal with a dosage as low as 32 mg/l at pH 3.0 of POME. Very low

charge density (48.2 C/g) cationic PAM is effective only at very high dosages up to

250 mg/l. To obtain 99% turbidity removal, 99% TSS removal and 40% COD

removal, high dosage (200 mg/L) of low density cationic PAM is required.

Using the optimum conditions from the flocculation, chitosan powder, at a

dosage of 0.5 g/l, 15 min of contact time and a pH value of 5.0, presented the most

suitable conditions for the adsorption of residue oil from POME (Ahmad et al.,

2005a). Chitosan has also been compared to activated carbon and bentonite as a

27

potential residual oil remover. Ahmad et al. (2005b) reported that chitosan showed

the best removal compared to the other adsorbents for all the parameters studied.

Chitosan could successfully remove 99% of residual oil and minimize the TSS

content to a value of 25 mg/l from POME at a dosage of 0.5 g and employing a

mixing time of 30 min, a mixing rate of 100 rpm, sedimentation for 30 min and a pH

value of ranging from 4.0 to 5.0. For activated carbon and bentonite, the optimum

dosages were 8.0 g and 10.0 g/l, respectively, 30 min of mixing time at 150 rpm, 80

and 60 min of settling time, respectively, and pH of 4.0–5.0 to obtain the same

percentage of removal as performed by chitosan. Activated carbon and bentonite can

only reduce the TSS values up to 35 and 70 mg/l, respectively, at the optimized

conditions.

The performance of chitosan was compared to alum and PACl, in a study

conducted by Ahmad et al. (2006). The results obtained proved that chitosan was

comparatively more efficient and economical to alum and PACl. At the defined

optimum experimental conditions (dosage: 0.5 g/l, contact time: 15 min, mixing rate:

100 rpm, sedimentation time: 20 min and pH 4.0) chitosan showed more than 95% of

TSS and residue oil removal. For alum and PACl the optimum dosages were 8.0 and

6.0 g/l, respectively, 30 min of mixing time at 100 rpm, 50 and 60 min of settling,

respectively, and pH of 4.5 to obtain the same percentage of removal as performed

by chitosan.

According to Vijayaraghavan et al. (2007), for an influent COD

concentration of 59 700 mg/L at an alum dosage of 1700 mg/L, the residual COD,

TSS removal, sludge volume and pH were found to be 39 665 mg/L, 87%, 260 mol/L

and 6.3, respectively.

Bhatia et al. (2007a, 2007b) studied the advantage of Moringa Oleifera seeds

usage. Moringa oleifera seeds, an environmental friendly and natural coagulant are

an effective coagulant with the removal of 95% TSS and 52.2% reduction in the

COD (Bhatia et al., 2007b). The combination of MOAE with flocculant (NALCO

28

7751) resulted in 99.3% TSS removal and 52.5% COD reduction. It also reduced the

sludge volume index (SVI) to 210 mL/g with higher recovery of dry mass of sludge

(87.25%) and water (50.3%). At pH 5.0 and 120 min settling time, 99% TSS

removal can be achieved when utilized with flocculant (NALCO7751) (Bhatia et al.,

2007a).

The objective of this research was to investigate the performance of

physicochemical process as a chemical pretreatment in treating POME based on the

BOD, TSS and turbidity removal efficiency. A technological shift from biological

treatment to integrated biological and chemical process with environmental friendly

coagulants could result in improving the POME treatment system. It is intended to

increase the BOD and TSS removal efficiency so that the final discharge will meet

the DOE standards besides curtailing the large land area required by the aerobic

pond.

It is believed that physicochemical treatment will be able to treat POME in a

more beneficial way. This technology is increasingly being used for treating water

and wastewater. Several advantages in using coagulation and flocculation process

are: its wide applicability across a wide range of industries, the quality of the treated

water is more uniform regardless of the influent variations, and the plant can be

highly automated and does not require highly skilled operators (Metcalf and Eddy,

2004).

2.6 Coagulation and Flocculation

Coagulation and flocculation constitute the backbone processes in most water

and wastewater treatment plants. Their purpose is to improve the separation of

particulate species in downstream processes such as sedimentation and filtration.

29

Colloidal particles and other finely divided matter are brought together and

agglomerated to form larger size particles that can subsequently be removed in a

more efficient fashion. The coagulation process consists of three sequential steps

which are coagulant formation, particle destabilization and interparticle collisions

(Shammas, 2005).

Coagulant formation and particle destabilization are generally quick and

occur in a rapid-mixing tank. However, interparticle collisions, is a slower process

that is achieved by fluid flow and slow mixing. This is the process that causes the

agglomeration of particles and it takes place in the flocculation tank (Shammas,

2005).

Coagulation is usually accomplished through the addition of inorganic

coagulants such as aluminium- or iron-based salts, or synthetic organic polymers

commonly known as polyelectrolytes or natural organic polymers. Flocculant or

coagulant aids are available to help in the destabilization and agglomeration of

difficult and slow to settle particulate material (Metcalf and Eddy, 2004).

Coagulation is applied in water treatment, municipal wastewater treatment,

industrial waste treatment, and combined sewer overflow. It is used in the industrial

waste treatment to improve removals from secondary effluents, control of color,

handling seasonal wastes and providing treatment to meet stream and disposal

requirements at lower capital cost (Metcalf and Eddy, 2004).

30

2.6.1 Properties of Colloidal Systems

Colloidal particles are bigger than atoms and ions but are small enough that

they are usually not visible to the naked eye. They range in size from 0.001 to 10 µm

resulting in a very small ratio of mass to surface area. Colloids are tremendously

tiny particles that have very large surface area. The consequence of this smallness in

size and mass and largeness in surface area is that in colloidal suspensions

gravitational effects are insignificant, and surface phenomena predominate.

Colloidal particles have the affinity to adsorb various ions from the surrounding

medium that impart to the colloids an electrostatic charge relative to the bulk of the

surrounding water because of their tremendous surface. The developed electrostatic

repulsive forces prevent the colloids from coming together and, thus, contribute to

their dispersion and stability (Shammas, 2005).

2.6.2 Colloidal Structure and Stability

The stability of colloidal particulate matter is dependent on their

electrokinetic property. Colloidal particles acquiring similar primary charges

develop repulsive forces that keep them apart and prevent their agglomeration. The

primary electrical charges could be either negative or positive. However, the

majority of colloids that exist in aqueous systems are negatively charged (Metcalf

and Eddy, 2004).

A colloidal system as a whole does not have a net charge. Negative primary

charges on colloidal particles are balanced by positive counter-ions near the solid-

liquid interface and in the adjoining dispersion medium. In a similar fashion,

positively charged particles are counterbalanced by negative ions present in the

surrounding water. This natural inclination toward achieving electrical neutrality and

31

counterbalance of charges results in the formation of an electric double layer around

colloidal particles (Metcalf and Eddy, 2004).

2.6.3 Mechanism of Coagulation

2.6.3.1 Destabilization of Colloids

Destabilization of colloidal particles is accomplished by coagulation through

the addition of hydrolyzing electrolytes such as metal salts and/or synthetic organic

polymers. Upon being added to the water, the action of the metal salt is complex. It

undergoes dissolution, the formation of complex highly charged hydrolyzed metal

coagulants (hydroxyoxides of metals), interparticle bridging, and the enmeshment of

particles into flocs. Polymers work either on the basis of particle destabilization or

bridging between the particles (Shammas, 2005).

The destabilization process is achieved by the following four mechanisms of

coagulation: (1) double-layer compression, (2) adsorption and charge neutralization,

(3) entrapment of particles in precipitate, and (4) adsorption and bridging between

particles (Sincero and Sincero, 1996).

The addition of high-valence cations depresses the particle charge and the

effective distance of the double layer, thereby reducing the zeta potential. As the

coagulant dissolves, the cations serve to neutralize the negative charge on the

colloids. This occurs before visible floc formation, and rapid mixing which “coats”

the colloid is effective in this phase. Microflocs are then formed which retain a

positive charge in the acid range because of the adsorption of H+. These microflocs

also serve to neutralize and coat the colloidal particle. Flocculation agglomerates the

32

colloids with a hydrous oxide floc. In this phase, surface adsorption is also active.

Colloids not initially adsorbed are removed by enmeshment in the floc (Eckenfelder,

2000).

2.6.3.2 Bridging Mechanism

Polymers become attached at a number of adsorption sites to the surface of

the particles found in the wastewater. A bridge is formed when two or more particles

become adsorbed along the length of the polymer. Bridged particles become

intertwined with other bridged particles during the flocculation process. The size of

the resulting three-dimensional particles grows until they can be removed easily by

sedimentation (Shammas, 2005).

Where particle removal is to be achieved by the formation of particle-

polymer bridges, the initial mixing of the polymer and the wastewater containing the

particles to be removed must be accomplished in a matter of seconds. The mixing

intensity must be sufficient to bring about the adsorption of the polymer onto the

colloidal particles. If in adequate mixing is provided, the polymer will eventually

fold back on itself, in which case, it is not possible to form polymer bridges (Metcalf

and Eddy, 2004).

33

Figure 2.3 and 2.4 show the mechanisms of coagulation and interparticle

bridging with organic polymers.

Figure 2.3 Mechanisms of coagulation (Eckenfelder, 2000)

Figure 2.4 Interparticle bridging with organic polymers (Metcalf and Eddy, 2004)

34

2.6.4 Influencing Factors

Many factors affect the coagulation process. This includes colloid

concentration, coagulant dosage, zeta potential, affinity of colloids for water, pH

value and mixing (Shammas, 2005).

2.6.4.1 Coagulant Dosage

Aluminum and iron coagulant dosage effect on coagulation was reported by

Shammas (2005) and the relationship has been divided into four zones starting with

the first low-dosage zone and increasing the dosage progressively to the highest

dosage that is applied in zone four.

Zone 1 Not enough coagulant is present for the destabilization of the colloids.

Zone 2 Sufficient coagulant has been added to allow destabilization to take

place.

Zone 3 Excess concentration of coagulant can bring about charge reversal and

restabilization of particles.

Zone 4 Oversaturation with metal hydroxide precipitate entraps the colloidal

particles and produces very effective sweep coagulation.

The range of coagulant dosage that triggers the start, end, or elimination of

any of the above zones is dependent on colloidal particle concentration and pH value

(Shammas, 2005).

35

2.6.4.2 pH Value

The presence of H+ and OH- ions in the potential determining layer may

cause particle charge to be more positive or less negative at pH values below the

isoelectric point. pH value affects radically the solubility of colloidal dispersions.

The influence of pH on the polymer’s behaviour and effectiveness in coagulation is

vital because of the interaction between pH and the charge on the electrolyte. The

extent of charge change with pH is a function of the type of active group on the

polymer (carboxyl, amino, etc.) and the chemistry of those groups (Shammas, 2005).

2.6.4.3 Colloid Concentration and Zeta Potential

Colloidal concentration has a great impact on the dosage needed and the

efficiency of the coagulation process itself. The dosage of coagulants required for

the destabilization of a colloidal dispersion is stoichiometrically related to the

amount of colloidal particles present in solution (Shammas, 2005).

The zeta potential represents the net charge of colloidal particles. Therefore,

the higher the value of the zeta potential, the greater is the magnitude of the repulsive

power between the particles and hence the more stable is the colloidal system

(Metcalf and Eddy, 2004).

36

2.6.4.4 Affinity of Colloids for Water

The stability of hydrophilic dispersion depends more on their affinity for

water than on their electrostatic charge. Hydrophilic colloids are very stable and due

to their hydration shell, chemicals cannot readily replace sorbed water molecules

and, consequently, they are difficult to coagulate and remove from suspension.

Suspensions containing such particles require 10-20 times more coagulant than what

is normally needed to stabilize hydrophobic particles. Typical example is organic

colloids present in wastewater. The bulk of colloidal particles in turbid water usually

exhibit a mixture of hydrophobic-hydrophilic properties resulting in suspensions that

are intermediate in the degree of their difficulty to coagulate (Shammas, 2005).

2.6.4.5 Mixing

The optimal time for mixing can vary from a fraction of a second to several

seconds or more. Typical mixing times for the chemicals used in wastewater

treatment facilities are reported in Table 2.5.

Table 2.5 : Typical mixing times for various chemicals used in wastewater treatment

facilities (Metcalf and Eddy, 2004)

Chemical Applications Recommended mixing times, s

Alum, Ferric chloride Coagulation of colloidal particles

< 1

Lime Chemical precipitation 10-30 Cationic polymer Destabilization of

colloidal particles < 1

Anionic polymers Particle bridging 1-10 Nonionic polymers Filter aids 1-10

37

2.6.5 Coagulants

Coagulant is the chemical that is added to destabilize the colloidal particles in

wastewater so that floc formation can result (Metcalf and Eddy, 2004). The choice

of coagulant chemical depends upon the nature of the suspended solid to be removed,

the raw wastewater conditions, and the cost of the amount of chemical necessary to

produce the desired result. Final selection of the coagulant (or coagulants) should be

made following thorough jar testing. Considerations must be given to required

effluent quality, cost, method and cost of sludge handling and disposal, and net

overall cost at the dose required for effective treatment (Metcalf and Eddy, 2004).

According to Shammas (2005), lime is the most commonly used chemical

because of its lower cost. However, soda ash has an advantage over lime in that it

does not increase water hardness. Ferric salts (ferric chloride and ferric sulfate)

when added to water, behave in a similar fashion to alum. Ferric coagulants may

have some advantages. Coagulation is effective over a wider pH range, a strong and

heavy floc is produced, which can settle rapidly. Sodium aluminate is also used as

coagulant. The main difference between sodium aluminate and other common

coagulants is its being alkaline rather than acidic in solution. Sodium aluminate can

be produced by dissolving alumina in sodium hydroxide. The main deterrent to the

wide scale use of this coagulant is its relatively high cost (Shammas, 2005).

2.6.5.1 Polymeric Inorganic Salts

Polymeric ferric and aluminum salts are increasingly being used to coagulate

turbid waters and are applied in conventional wastewater treatment systems as well.

This is because of their effectiveness, cheap, easy to handle and availability. They

forms positive charged Al species that adsorb to negatively charged natural particles

38

resulting in charge neutralization (Ahmad et al., 2006). PACl, a prehydrolized

inorganic salt is one of the examples (Metcalf and Eddy, 2004).

2.6.5.2 Organic Polymers

Synthetic organic polymers are long–chain molecules made up of small

subunits or monomeric units. Polyelectrolytes are polymers that contain ionizable

groups such as carboxyl, amino or sulfonic groups. Due to their ability to destabilize

particles by charge neutralization, interparticle bridging, or both, polymers function

as excellent coagulants. Cationic polymers are capable of destabilizing and

coagulating particles by both charge neutralization and interparticle bridging.

Anionic and nonionic polymers, on the other hand, destabilize negatively charged

colloidal particles through their bridging effect (Shammas, 2005).

Natural organic polymer like chitosan, has excellent properties, such as

biodegradability, biocompability, adsorption property, flocculating ability,

polyelectrolisity and its possibilities of regeneration in number of applications

(Ahmad et al., 2005b).

The effectiveness of polymers in accomplishing their function as coagulants

depends on several factors, which includes polymer properties and solution

characteristics. Among the polymer properties are functional groups on polymers,

charge density, molecular weight and degree of branching. Solution characteristics

take account of pH value and concentration of divalent cations (Shammas, 2005).

There is a constricted range for maximum performance. Concentrations

lower than essential will not generate effective coagulation, whereas overdosing of

39

polymers will results in charge reversal and restabilization of the colloidal system.

In addition polymers are more expensive compared to metallic salts. However, this

is usually more than compensated for by the lower polymer dosage as well as the

reduced sludge production (Metcalf and Eddy, 2004).

2.6.6 Coagulation Aids

Coagulation aids or flocculant are occasionally applied to attain optimum

conditions for coagulation and flocculation. The intention is to obtain faster floc

formation, produce denser and stronger flocs, decrease the coagulant dosage, broaden

the effective pH band, and improve the removal of turbidity and other impurities.

Alkalinity addition, polymers, particulate addition and pH adjustment are the four

typical types of coagulant aids (Shammas, 2005).

Acids and alkalis are used to adjust the pH of the water to fall within the

optimal pH range for coagulation (Sincero and Sincero, 1996). pH reduction is

usually accomplished by the addition of sulfuric or hydrochloric acid. Increasing the

pH is achieved by the addition of lime, sodium hydroxide, or soda ash.

2.6.7 Coagulation Control

Theoretical analysis of coagulation is essential for understanding the process,

for knowing how it works and what it can achieve as well as for discerning how to

obtain the maximum performance out of it. However, because the process is so

complex and the number of variables is so large, in most cases it is not feasible either

40

to predict the best type of coagulant and optimum dosage or the best operating pH.

The most practical approach is to simulate the process in a laboratory setting using

the jar test (Shammas, 2005).

2.6.8 Jar Test

The jar test is the most precious tool available for developing design criteria

for new plants, for optimizing plant operations, and for the evaluation and control of

the coagulation process. A jar test apparatus is a variable speed, multiple station or

gang unit that varies in configuration depending on the manufacturer. The

differences, such as the number of test stations (usually six), the size (commonly

1000 mL) and shape of test jars (round or square), method of mixing (paddles,

magnetic bars, or plungers), stirrer controls, and integral illumination, do not have a

significant impact on the performance of the unit. The jar test can be run to select

type and dosage of coagulants, coagulant aid and its dosage, optimum operating pH,

optimum energy and mixing time for rapid and slow mixing (Sincero and Sincero,

1996).

For dosage optimization, samples of wastewater are filled into a series of jars,

and different dosages of the coagulant are fed into the jars. The coagulants are

rapidly mixed at a speed of 60-80 rpm for a period of 30-60 s then allowed to

flocculate at a slow speed of 25-35 rpm for a period of 15-30 min. The suspension is

finally left to settle for 20-60 min under quiescent conditions. The appearance and

size of the flocs, the time for floc formation, and the settling characteristics are noted.

The supernatant is analyzed for turbidity, color, suspended solids, and pH. The

optimum chemical dosage is chose on the basis of best effluent quality and minimum

coagulant cost (Sincero and Sincero, 1996).

41

2.6.9 Rapid Mix

Rapid mixing is used to distribute the chemicals immediately (Sincero and

Sincero, 1996). In order to achieve instantaneous, uniform dispersion of the

chemicals through the wastewater body, rapid mixing is needed. It is not only

sufficient, but also desirable because the production of effective coagulant species

greatly depends on being able to achieve a uniform dispersion of the added

chemicals. The adsorption rate for the various coagulants products is also very fast.

It may be wise to achieve the required dispersion through a less intense mixing over

a longer time interval, when dealing with fragile colloidal particles (Shammas,

2005).

2.6.10 Flocculation

The function of flocculation is to optimize the rate of contact between the

destabilized particles, hence increasing their rate of collision and bridging about the

attachment and aggregation of the particles into larger and denser floc (Shammas,

2005). In consequence, the flocculation process permits the colloidal particles to

come together and build into bigger flocs that are more amenable to separation by

settling, or filtration. Optimal mixing must be supplied to bring particles into contact

and keep them from settling. Slow mixing can be attained mechanically or

hydraulically (Metcalf and Eddy, 2004).

42

2.7 Coagulation and flocculation using chitosan

Chitosan is a high molecular weight carbohydrate polymer manufactured

from chitin. It is a natural cationic polyelectrolyte formed by N-acetyl-D-

glucosamine units with β (1–4) glycosidic bounds. Chitosan owes its cationic nature

to the free amino groups obtained by removing some of the acetyl groups of chitin.

Chitin is widely distributed in marine nature, occurring in the insects, yeasts, fungi

and exoskeletons of crustaceans (Ahmad et al., 2006). Chitosan is a linear

polyelectrolyte at acidic pH and it has a high charge density, one charge per each

glucosamine unit. It is an excellent flocculant due to its high number of NH3+ groups

that can interact with negatively charged colloids and it forms complexes with many

metal ions (Pinotti et al., 2001).

Chitosan, a natural deacetylated marine polymer has been used in a variety of

practical fields including wastewater management, pharmacology, biochemistry, and

biomedical. Its largest use is still as a non-toxic flocculent in the treatment of

organically polluted wastewaters. Chitosan has high proportions of amino functions

that provide novel binding properties for many heavy metals in wastewater (Ahmad

et al., 2005a). Chitosan is not a health threatening material because it is a

biodegradable and biopolymeric material (Ahmad et al., 2005b).

2.8 Coagulation and flocculation using polyacrylamide (PAM)

Acrylamide is a crystalline, relatively stable monomer that is soluble in water

and in many organic solvents. It undergoes polymerization by conventional free-

radical methods, but can also be polymerized photochemically. All current industrial

production is believed to be free-radical polymerization. The pH of the reaction

medium is also important, since hydrolysis of amide groups can take place at high

43

pH, whereas imidization is favored at low pH and high temperature. By far the

greatest current interest is in those PAMs having very high molecular weights (> 5 x

106) (Pinotti et al., 2001).

Synthetic polyelectrolytes are known to be as much as 80 times more

efficient (weight for weight) in the removal of suspended colloidal particles than the

traditional water treatment agents. Their effectiveness as flocculants increases with

increasing molecular size, the limit of which is only dictated by problems in

solubility. The use of PAMs has been found to have extensive commercial

application in the clarification of water in industrial and municipal municipal

processes. However, the basis of the physicochemical interactions at the solid-

solution interface is still little understood (Ariffin et al., 2005).

2.9 Coagulation and flocculation using polyaluminum chloride (PACl)

PACl, an inorganic coagulant, has become more popular as the alternative

coagulants in recent years. The advantages over traditional coagulants are obvious

due to their stable preformed polymeric species and less pH dependence. Among the

available coagulants, aluminum sulphate (alum) and PACl are the most extensively

used coagulant for sludge conditioning and dewatering coagulation processes. The

most significant usage of aluminum coagulants are usually overdosed in order to

ensure coagulation efficiency. They are more effective at lower temperatures, a

broader pH range and forms positive charged Al species that adsorb to negatively

charged natural particles resulting in charge neutralization (Ahmad et al., 2006).

44

2.10 Efficiency of POME treatment

2.10.1 Biochemical Oxygen Demand (BOD) Analysis

The BOD determination is an empirical test in which standardizes laboratory

procedures is used to determine the relative oxygen requirements of wastewaters,

effluents, and polluted waters. The test has its widest application in measuring waste

loadings to treatment plants and in evaluating the BOD-removal efficiency of such

treatment systems. The test measures the molecular oxygen utilized during a

specified incubation period for the biochemical degradation of organic material

(carbonaceous demand) and the oxygen used to oxidize inorganic material such as

sulfides and ferrous iron (Standard Methods, 2005).

The most widely used parameter of organic pollution applied to both surface

water and wastewater is the 5-day BOD (BOD5). The method consists of filling with

diluted and seeded sample, to overflowing, an airtight bottle of specified size and

incubating it at the specified temperature for 5 d. Dissolved oxygen is measured

initially and after incubation, and the BOD is computed from the difference between

initial and final dissolved oxygen (Metcalf and Eddy, 2004).

BOD test results are used (1) to determine the approximate quantity of

oxygen that will be required to biologically stabilize the organic matter present, (2)

to determine the size of waste treatment facilities, (3) to measure the efficiency of

some treatment processes, and (4) to determine compliance with wastewater

discharge permits (Metcalf and Eddy, 2004).

45

2.10.2 Turbidity Analysis

The clarity of a natural body of water is an important determinant of its

condition and productivity. Turbidity in water is caused by suspended and colloidal

matter such as clay, silt, finely divided organic and inorganic matter, and plankton

and other microscopic organisms. Turbidity is an expression of the optical property

that causes light to be scattered and absorbed rather than transmitted with no change

in direction or flux level through the sample (Standard Methods, 2005).

Electronic nephelometers are the preferred instruments for turbidity

measurement. Nephelometers are relatively unaffected by small differences in

design parameters and therefore are specified as standard instrument for

measurement of low turbidities. Its precision, sensitivity, and applicability over a

wide turbidity range make the nephelometer method preferable to visual methods.

Formazin suspensions are used as the primary standard. The results of turbidity

measurements are reported as nephelometric turbidity units (NTU). Colloidal matter

will scatter or absorb light and thus prevent its transmission. It should be noted that

the presence of air bubbles in the fluid will cause erroneous turbidity readings. In

general, there is no relationship between turbidity and the concentration of total

suspended solids in untreated wastewater. There is, however, a reasonable

relationship between turbidity and total suspended solids for the settled and filtered

secondary effluent from the activated sludge process (Metcalf and Eddy, 2004).

2.10.3 Total Suspended Solids (TSS) Analysis

A well-mixed sample is filtered through a weighed standard glass-fiber filter

and the residue retained on the filter is dried to a constant weight at 103 to 105°C.

The increase in weight of the filter represents the total suspended solids (Standard

46

Methods, 2005). Because a filter is used to separate the TSS from the TDS, the TSS

test is somewhat arbitrary, depending on the pore size of the filter paper used for the

test. Filters with nominal pore sizes varying from 0.45 μm to about 2.0 μm have

been used for the TSS test (Metcalf and Eddy, 2004).

The measured values of TSS are dependent on the type and pore size of the

filter paper used in the analysis. Depending on the sample size used for the

determination of TSS, autofiltration, where the suspended solids that have been

intercepted by the filter also serve as a filter, can occur. Autofiltration will cause an

apparent increase in the measured TSS value over the actual value. Depending on

the characteristics of the particulate matter, small particles may be removed by

adsorption to material already retained by the filter. TSS is a lumped parameter,

because the number and size distribution of the particles that comprise the measured

value is unknown (Metcalf and Eddy, 2004).

Nevertheless, TSS test results are used routinely to assess the performance of

conventional treatment processes and the need for effluent filtration in reuse

applications. TSS is one of the two universally used effluent standards (along with

BOD) by which the performance of treatment plants is judged for regulatory control

purposes (Metcalf and Eddy, 2004)

2.11 Chemical Cost Estimation

Before the profitability of a project can be assessed, an estimate of the

investment required and the cost involved are needed. An estimate of the operating

costs is needed to judge the viability of a project, and to make choices between

possible alternative processing schemes (Sinnott, 1996).

47

The price of each coagulant is best obtained by getting quotations from

potential suppliers, but in the preliminary stages of a project, prices can be taken

from the literature or published prices. Open market prices for some chemical

products can fluctuate considerably with time (Smith, 2005).

The coagulant costs were based on the application of the coagulants at their

respective optimum dosage for the treatment of 1 cubic meter of POME fed. The

cost of each coagulant was also calculated based on the volume of mixed raw

effluent generated for each tonne of CPO produced. The cost is then compared to the

revenue earned from the CPO production to evaluate the viability of chemical pre-

treatment in treating POME.

Chemical cost analysis is equally important so as to determine the most cost

effective process. The cost of each coagulant needed to treat the amount of POME

generated monthly from the production of CPO is compared against the revenue

earned from the amount of CPO produced monthly (based on the latest market price

of palm oil).

CHAPTER III

METHODOLOGY

3.1 Introduction

This chapter describes the process and procedure involved in carrying out this

research. This includes POME sample collection and preservation, and chemical i.e.

coagulants preparation. Experimental design consists of POME characterization,

determination of optimum coagulant dosage and evaluation of optimum pH value via

jar testing, determination of the response through chemical analyses which includes

BOD, TSS and turbidity analysis, and chemical cost estimation.

49

3.2 Materials and Methods

3.2.1 Experimental Materials

3.2.1.1 POME Sample Collection

Samples of raw POME were collected from Kilang Sawit Penggeli, Felda

Palm Industries Sdn. Bhd., Kluang, Johor, at a temperature ranging from 80 to 90°C.

Samples may vary day to day depending on the discharge limit of the factory, climate

and condition of the palm oil processing.

3.2.1.2 Quantity

A 30-40 liter sample was sufficient for analysis. The storage containers were

filled completely to exclude air.

3.2.1.3 Containers

Samples were collected and stored in wide-mouthed bottles made of

polyethylene. All bottles were provided with stoppers, caps or plugs which should

resist the attack of material contained in the vessel. Sample bottles were carefully

cleaned before each use. Before filling, the sample bottles were rinsed out two or

three times with the effluent to be sampled.

50

3.2.1.4 Representative Samples

Sampling of the effluent was carried out at the designated point of discharge.

This technique was carried out so as to ensure that the samples obtained were

representative samples.

3.2.1.5 Sample Preservation

The POME was preserved at a temperature less than 4°C, but above the

freezing point in order to prevent the wastewater from undergoing biodegradation

due to microbial action (Standard Methods, 2005). Sample preservation as well as

the experimental works was carried out in Pollution Control Laboratory, Faculty of

Chemical and Natural Resources Engineering.

3.2.1.6 Coagulants

Chitosan was supplied by ACRŌS Organics, New Jersey, U.S.A. in the form

of a fine off-white powder with molecular weight between 100,000 and 300,000.

PAM and PACl were obtained from the Pollution Control Laboratory. The viscosity

of PAM is about 280cP (0.5% aqueous solution at 25°C). Its molecular weight is

more than 5,000,000. Both PAM and PACl were in powder form.

Distillated water was used to dilute hydrochloric acid solution (Merck,

Germany) and dissolve sodium hydroxide pellets (Merck, Germany) to obtain

51

solutions of 5 M. These solutions were then used for pH adjustment during the

treatment process.

3.2.2 Experimental Design

3.2.2.1 Laboratory Treatability Study

Treatability study is a laboratory test designed to provide critical data needed

to evaluate and, ultimately, to implement one or more economical treatment

technologies to treat and manage such wastes to meet the regulatory criteria for safe

disposal and/or reuse (USEPA Website). This study generally involves

characterizing untreated waste and evaluating the performance of the technology

under different operating conditions. These results may be qualitative or

quantitative, depending on the level of treatability testing. Yielded data can be used

as indicators of a technology’s potential to meet performance goals and can identify

operating standards for investigation during bench-or pilot-scale testing. These

studies are necessary to determine specific treatment as well as capital and operating

costs.

The physicochemical treatment ability study which was carried out consists

of POME characterization, determination of optimum coagulant dosage and

evaluation of optimum pH value via jar testing, determination of the response

through observations and chemical analyses, and chemical cost estimation.

52

3.2.2.2 Reproducibility Studies

The turbidity, BOD and TSS content in the suspension was determined for

each sample of POME both before and after experiment. Eight replicates of each test

were undertaken with the mean value obtained for turbidity, BOD and TSS content

being calculated from the replicates. Table 3.1 shows an example of eight

reproducible data for BOD of the raw POME from characterization study. The mean

values of the BOD data tested was 25,840 mg/L which is close to the BOD value

from literature studied by Ahmad et al. (2005b) and Vijayaraghavan et al. (2006) i.e.

25,000 mg/L. The BOD data can be up to 25,840 ± 1,965.4 mg/L. Reproducible

data for initial pH, turbidity and TSS of raw POME were shown in Appendix A.

Reproducible data for turbidity, BOD and TSS of treated POME were shown in

Appendix B and C.

Table 3.1 : Reproducible data for BOD value of raw POME

No of test 1 2 3 4 5 6 7 8

BOD value (mg/L)

23,040 26,700 24,900 25,620 27,900 23,800 25,900 28,860

3.2.2.3 Characterization of POME

Raw effluent sludge collected from the palm oil mill was viscous, oily, dark

brown in colour with an obnoxious odour. Samples of POME were collected at a

temperature ranging from 80 to 90 °C and were cooled to room temperature. The

characteristics of POME were obtained following APHA Standard Methods of

Examination of Water and Wastewater.

53

Characterization of the wastewater is the most critical step. Portions of this

suspension were withdrawn and analyzed for their initial BOD, TSS, turbidity and

pH properties. Although the characteristics of POME could vary but, in order to

minimize the effect of different characteristics of POME, the experiments were

repeated with different samples of POME to obtain the average results that can be

applied to the treatment of different POME samples.

3.2.2.4 Optimum Dosage

The experiment involved the usage of three different types of coagulants, as

listed below in table 3.2.

Table 3.2 : Coagulants used in the study

Type Name

Inorganic Salt PACl

Synthetic Organic Polymer PAM

Natural Organic Polymer Chitosan

The experimental works was initiated by the determination of the optimum

dosage of each coagulant via jar test which will be explained in later part. In order to

determine the optimum dosage required to treat the POME sample, the concentration

of chitosan was varied in the range of 100-1000 mg/L, while the concentration of

PACl and PAM were varied in the range of 500-2500 mg/L. The main parameters

that were considered were turbidity, TSS, and BOD. The concentration of

coagulants which gave the highest BOD removal was elected as the optimum dosage.

54

Reason behind the selection of BOD removal in determining the optimum

dosage is because it is the most critical parameter. Current regulatory requirement

stated the final BOD levels must be below 100 mg/L. However, most mills which

are currently using conventional biological treatment system do not comply with the

DOE standards in terms of BOD level.

3.2.2.5 Optimum pH Value

Once the optimum dosage for each coagulant was determined, pH adjustment

was carried out to find the most suitable pH value which will give the best BOD

removal. pH value of the POME was adjusted in the range of 3-6, as POME achieve

good removal at acidic condition. Ahmad et al., (2005a, 2005b and 2006) found that

chitosan performed best at pH 4.0 and 5.0. PACl are effective at broader pH range

(Ahmad et al., 2006). Ariffin et al. (2005) adjusted the pH of POME to 3.0 prior to

flocculation to achieve the best performance.

Because a number of chemicals are available that can be used for pH

adjustment, the choice will depend on the suitability of a given chemical for a

particular application and prevailing economics. Sodium Hydroxide (NaOH) was

used to raise pH of POME. It is convenient and is widely used for treatment where

small quantities are adequate (Metcalf and Eddy, 2004). NaOH pellets were

dissolved in distillated water on hot plate before being used. Hydrochloric acid

(HCl) was used to lower the pH of POME. It is recommended to use concentrated

HCl as small amount will be sufficient.

55

3.2.2.6 Jar Testing

Coagulation–flocculation process was carried out via jar test apparatus.

1. A conventional jar test apparatus (Phipps and Bird 6 Paddle Stirrer Model)

was used in the experiments.

2. Different amounts of chitosan were added as primary coagulant to five 1 L jar

with 1000 ml sample water of each under a rapid mixing at 250 rpm for 3

min, followed by a slow mixing at 30 rpm for 30 min, and then settlement for

60 min.

3. The samples were analyzed with different dosages of chitosan 100 - 1000

mg/L, PACl and PAM 500 - 2500 mg/L.

4. In the pH adjustment for coagulation, the sample water pH was adjusted by 5

M NaOH or 5 M HCl before the coagulant was added.

5. pH adjustments from 3 to 6, were done to obtain the best pH condition for

BOD5, turbidity, and suspended solids removal from POME.

6. The normal procedure for primary coagulant test was then followed.

7. At the end of the settling period, water samples were taken from the

supernatants and analyzed for the residual turbidity, suspended solids, BOD5

and pH values.

8. The jar test was repeated using PACl and PAM as coagulants.

(a) (b)

Figure 3.1 Jar Test Apparatus (a) and pH Meter and Magnetic Stirrer (b)

56

3.2.3 Determination of the Response

3.2.3.1 Observation

After the stirring is stopped, the nature and settling characteristics of the flocs

were observed and recorded qualitatively as poor, fair, good, or excellent. A hazy

sample denotes poor coagulation; a properly coagulated sample is manifested by

well-formed flocs that settle rapidly with clear supernatant above the flocs (Sincero

and Sincero, 1996).

3.2.3.2 Chemical Analyses

Accurate analysis is important not only to determine the efficacy of the

treatment but also to ascertain compliance with the standards. The BOD, turbidity

and TSS content of the supernatant was determined using methods recommended by

Standard Methods (2005). The reproducibility of the experimental data was

analyzed by repeating each experimental runs for eight times.

3.2.3.3 Biochemical Oxygen Demand (BOD) Determination

Wheaton BOD bottles, vitro ‘800’ with ground glass pennyhead stopper and

caps were used. The advantage of these bottles is the water seal which prevents air

bubbles being formed in the BOD bottles. The cap prevents evaporation of the water

57

seal during incubation. The bottles were cleaned with chromic acid mixture and then

washed out several times with clean water.

Dilution depends on the strength of the sample. Unless the BOD of the

sample is already known approximately, the required degree of dilution was not

known and more than one dilution was set up in duplicate. Table 3.3 shows the BOD

dilution table used in this study.

Table 3.3 : BOD Dilution Table

A B C

Dilution Aliquot of Sample Taken Second Dilution from (B)

1/10000 1 ml make up to 1000 ml

1/5000 2 ml make up to 1000 ml



1/1000

10 ml make up to 100 ml

with dilution water





1/100


with dilution water




1/25


with dilution water 80 ml make up to 1000 ml

In the standard BOD test, a small sample of the wastewater to be tested was

placed in a 300mL BOD bottle. The bottle was then filled with dilution water

saturated in oxygen and containing the nutrients required for biological growth. To

ensure that meaningful results are obtained, the sample must be suitably diluted with

specially prepared dilution water so that adequate nutrients and oxygen will be

available during the incubation period.

58

Before the bottle was stoppered, the oxygen concentration in the bottle was

measured. After the bottle was incubated for 5 days (120 ± 1 hr) at 20°C ± 1°C, the

dissolve oxygen (DO) concentration was measured again. Longer time periods

(typically 7 days), which correspond to work schedules, are often used, especially in

small plants where the laboratory staff is not available on the weekends. The BOD

of the sample is the difference in the dissolve oxygen concentration values, expressed

in milligrams per liter, divided by the decimal fraction of sampled used. BOD

concentration and BOD removal efficiency were determined as equation 3.1 and 3.2

respectively.

BOD (mg/L) = P

DD 21 − (3.1)

Where D1 = DO of diluted sample immediately after preparation, mg/L

D2 = DO of diluted sample after 5-day incubation at 20°C, mg/L

P = fraction of wastewater sample volume to total combined volume

)2.3(%100% ×−

=POMErawforBOD

POMEtreatedforBODPOMErawforBODefficiencyremovalBOD

3.2.3.4 Turbidity Determination

Turbidity was determined as soon as possible after the sample is taken. All

samples were gently agitated before examination to ensure a representative

measurement. Formazin polymer was used as the primary standard reference

suspension. The turbidity of a specified concentration of formazin suspension is

defined as 4000 NTU.

59

Laboratory or process nephelometer consisting of a light source for

illuminating the sample and one or more photoelectric detectors with a readout

device to indicate intensity of light scattered at 90° to the path of incident light was

used. The sensitivity of the instrument should permit detecting turbidity differences

of 0.02 NTU or less in the lowest range in waters having a turbidity of less than 1

NTU. Sample cells or tubes of clear, colorless glass were used.

Cells were kept scrupulously clean, both inside and out, and were discarded if

scratched or etched. Tubes with sufficient extra length, or with a protective case,

were used so that they may be handled properly. Cells were filled with samples and

standards that have been agitated thoroughly and sufficient time was allowed for

bubbles to escape. Because small differences between sample cells significantly

impact measurement, matched pair of cells or the same cell for both standardization

and sample measurement was used. Turbidity removal efficiency was determined as

equation 3.3.

)3.3(%100×−

=POMErawforTurbidity

POMEtreatedforTurbidityPOMErawforTurbidity

Turbidity Removal

Efficiency %

3.2.3.5 Total Suspended Solids (TSS) Determination

Samples containing an excessive amount of suspended matter and those

containing colloidal matter are often difficult to filter. When it is impracticable to

use the filtration method, the centrifugal method should be used. Of the suspended

matter inclusive volatile oil, the following procedure only measures the non-volatile

part. The centrifugal method is not applicable if any part of the suspended matter

floats. The filter used most commonly for the determination of TSS is the Whatman

60

glass fiber filter disk, which has a nominal pore size of about 1.58 μm. Disk was

inserted with wrinkled side up in filtration apparatus. Vacuum was applied and disk

was washed with 10 mL of distilled water. Suction was continued to remove all

traces of water, and discard washings and was dried in an oven at 103°C to 105 °C

for 1 hour and cooled in desiccator to balance temperature and weighed.

Sample was stirred with magnetic stirrer, and while stirring, a measured

volume was pipet onto the seated glass fiber filter and was dried for at least 1 h at

103°C to 105 °C in an oven, and cooled in a dessicator to balance temperature and

weigh. The cycle of drying, cooling, desiccating, and weighing was repeated until a

constant weight was obtained or until the weight change was less than 4% of the

previous weight or 0.5 mg, whichever was less.

It is desirable to use the maximum volume of the well-mixed sample that can

be passed through the crucible without clogging the filter pad. 25 ml of the well

shaken sample was filtered, using gentle suction and the whole was dried at 100°C to

105 °C for 1 hour, cooled and weighed. The result was expressed in milligram of

suspended solids per liter of sample. TSS concentration and TSS removal efficiency

were determined as equation 3.4 and 3.5 respectively.

TSS (mg/L) = mLvolumesample

BA,

1000)( ×− (3.4)

Where A = weight of crucible + paper + solids (mg) and

B = weight of crucible + paper (mg)

)5.3(%100% ×−

=POMErawforTSS

POMEtreatedforTSSPOMErawforTSSefficiencyremovalTSS

61

3.3 Comparison of the Performance of Chitosan, PAM and PACl as

Coagulants in POME Treatment

Chitosan, PAM and PACl were compared to each other to determine the most

potential BOD, TSS and turbidity remover. The coagulant which projected the

highest removal efficiencies were selected as the best coagulant.


The formula for calculating the cost of chemicals involved in the chemical

pre-treatment of one cubic meter of POME is given in equation 3.6 and the formula

for estimating the total chemical cost for each tonne of CPO produced is given in

equation 3.7.

Chemical cost (POMEmRM

3 ) = Selected coagulant dosage (L

mg ) x mg

g1000

1 xg

kg1000

1

x Price of chemical (kg

RM ) x 311000

mL (3.6)

Total cost )(CPOoftonne

RM = Chemical (POMEmRM

3 ) x (CPOoftonne

m3

)

(3.7)

Volume of POME

generated per tonne of CPO

cost

CHAPTER IV

RESULTS AND DISCUSSIONS

4.1 Introduction

This chapter presents the findings of this research and the interpretations of

the results obtained. Mainly, there were four parts of experiments were executed.

In the first part, characterization of raw POME were done in which the initial pH

value, turbidity, BOD, TSS concentration were verified. Subsequently, 1000 mL of

POME was used for each of the jar test which was conducted at 27ºC. Using

chitosan, PAM and PACl as sole coagulant, with a dosage range from 100 mg/L to

2500 mg/L at pH 5.0 (initial pH) under controlled rapid and slow mixing conditions,

jar test were performed. The performance of the coagulation and flocculation

processes of POME were evaluated by measuring supernatant turbidity, BOD, and

TSS of the POME at the end of the jar test. The results of these jar tests were used to

define the experimental condition i.e. optimum coagulant dosage which affect the

coagulation and flocculation processes.

The third part of the experiment was the pH optimization. Coagulation and

flocculation of POME were carried out with the optimum dosage of coagulants

obtained from part two but with varying pH. pH values varies between 3 and 6.

63

Upon completion of the jar test, the supernatant of POME were measured for its

turbidity, BOD and TSS value. The best set of the data for the organic removal were

selected to perform the final part of the study.

The final part was the economic evaluation. Based on the results obtained

from part two and three, the chemical cost analysis was then performed. Chemical

cost analysis were studied to validate set of operating conditions and concentrations

to be used for further lab or pilot plant scale studies.

4.2 Characteristic Study of POME

POME characterization was carried out once the samples collected cooled to

room temperature and the results are shown in Table 4.1. The initial BOD, TSS,

turbidity and pH properties were analyzed. POME contains about 18,000 to 22,000

mg/L TSS. The pH value varied between 4.9 and 5.25, whereas the BOD varied

between 23,000 and 29,000 mg/L due to its high organic content. Turbidity was also

taken into consideration and was measured to be between 5800 and 6900 NTU.

Table 4.1 : Characteristics of raw POME

Parameters Value Standard Deviation

pH 5.0 0.1

BOD5 (mg/L) 25840 1965.4

TSS (mg/L) 19340 1277.7

Turbidity (NTU) 6548 430.5

In comparison, Ahmad et al. (2005b) and Vijayaraghavan et al. (2006) have

reported that POME contains a high concentration of organic matter, average BOD

64

concentration around 25,000 mg/L and average TSS around 17,000 to 18,000 mg/L.

Detail results are presented in Appendix A.

4.3 Sole Coagulant for Coagulation and Flocculation Processes

Chitosan, PAM and PACl were used as sole coagulant in the dosage

optimization process. The experiments were conducted at pH 5.0 which was the

initial pH of the raw POME. Sets of data for the analysis are shown in Appendix B.

4.3.1 Chitosan as Sole Coagulant

Each beaker was filled with 1 liter of POME. After adding chitosan powder

into the suspension, the beakers were rapidly mixed at 3 min contact time and were

slowly mixed for 30 min for different weight dosages of chitosan (0.1–1 g). POME

was allowed to sediment for 1 hour with the supernatant being analyzed for its

turbidity, BOD and TSS concentration after sedimentation.

4.3.1.1 Effect of Coagulant Dosage on BOD Removal

Fresh POME was treated with 5 different weight dosages of chitosan powder.

The BOD concentration before and after treatment were analyzed. The initial BOD

concentration in POME was about 25,840 mg/L.

65

Figure 4.1 shows the effect of chitosan dosage towards the percentage of

BOD removal. It was noticed that the maximum BOD removal i.e. 60.7 % was

achieved at a dosage of 250 mg/L and pH 5.0. The lowest removal was achieved at

500 mg/L i.e. 51.1%. For all the chitosan dosage studied, it can be seen that there

was a drop in the percentage reduction of BOD at the dosage of 500 and 1000 mg/L.

After the fall, the reduction efficiency of BOD increased until the next value and then

decreased towards the following dosage.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 250 500 750 1000 1250Dosage (mg/L)

BO

D Re

mov

al (%

)

pH 5 (initial pH)

Figure 4.1 Percentage of BOD Removals for Different Dosage of Chitosan

The properties of chitosan, including its cationic behavior and molecular

weight, may be used both for charge neutralization (coagulating effect for anionic

compounds) and for particle entrapment (flocculating effect) (Roussy et al., 2005a).

These characteristics enhanced the performance of the coagulation and flocculation

of suspended particles. Wan Ngah and Musa (1998) reported that chitosan is fully

protonated at a pH of close to 5, and this protonation gives it the possibility of

attracting organic compounds. However, increase in chitosan dosage produced

excessive number of cationic charges contributed by the protonated amine groups led

to restabilization of the suspension and a decrease in coagulation–flocculation

efficiency, which explains the decrease in removal efficiency at a dosage of 500 and

1000 mg/L.

66

4.3.1.2 Effect of Coagulant Dosage on TSS Removal

The initial TSS concentration in POME was about 19,340 mg/L. Figure 4.2

shows the percentage of TSS removal after being treated with chitosan powder.

0.0

20.0

40.0

60.0

80.0

100.0

0 250 500 750 1000 1250

Dosage (mg/L)

TSS

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.2 Percentage of TSS Removal for Different Dosage of Chitosan

Chitosan at 250 mg/L and pH 5.0 produced the best removal efficiency.

Almost 97% reduction in TSS concentration was achieved. The flocs produced by

chitosan appeared rapidly and grows very fast to form a larger size which can be

easily sedimentated. The flocs were fibrous and forms large entangled mass

resembling cobwebs (Ahmad et al., 2006). This was due to the bridging mechanism.

Chitosan bridged the flocs more rigid and tight. Suspended solid values reduced as

the bridged particles and flocs started to settle to the bottom of the beaker and this

effect was mainly influenced by the gravitational force. The flocs formed by

chitosan were bigger and denser causing the suspended solid to settle more rapidly.

This proves that chitosan is a successful coagulant to coagulate suspended solid in

POME. Nevertheless in Figure 4.2, it was also noticed that when the applied dosage

was higher than the optimum amount, the TSS removal efficiency decreased to

67

between 87.2 and 93%. This could be due to restabilization of colloid complex in

POME, thus causing complete charge reversal.

4.3.1.3 Effect of Coagulant Dosage on Turbidity Removal

Figure 4.3 shows the percentage of turbidity removal at different chitosan

dosages.

0

20

40

60

80

100

0 250 500 750 1000 1250Dosage (mg/L)

Turb

idity

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.3 Percentage of Turbidity Removal for Different Dosage of Chitosan

The initial POME turbidity value was about 6548 NTU. After treatment with

250 mg/L chitosan at initial pH, the value decreased to 424 NTU i.e. 93.5% turbidity

removal which was the maximum removal efficiency. Figure 4.3 shows that the

turbidity removal and TSS reduction trends were similar to each other. Turbidity

analysis represents the suspended solid removal in POME. At higher chitosan

dosage i.e. 500 mg/L and initial pH, the removal efficiencies were slightly lower i.e.

79.6%.

68

However, it increased again subsequently but not as high as the maximum

one. At high doses of coagulant, a sufficient degree of over-saturation occurs to

produce a rapid precipitation of large quantity of coagulant (Ahmad et al., 2006).

This clarifies the increase in TSS and turbidity removal efficiencies at 1000 mg/L

chitosan. Figure 4.4 shows the flocs formed by chitosan and turbidity of the

supernatant.

Figure 4.4 Coagulation using 250 mg/L Chitosan at pH 5

4.3.2 Polyacrylamide (PAM) as Sole Coagulant

Each beaker was filled with 1 liter of POME. After adding PAM powder into

the suspension, the beakers were rapidly mixed at 3 min contact time and were

slowly mixed for 30 min for different weight dosages of PAM (0.5–2.5 g). POME

was allowed to sediment for 1 hour with the supernatant being analyzed for its

turbidity, BOD and TSS concentration after sedimentation.

69


Fresh POME was treated with 5 different weight dosages of PAM powder.

Figure 4.5 shows the effect of PAM dosage towards the percentage of BOD removal.

It was noticed that maximum BOD removal efficiency i.e. 63 % removal was

achieved at a dosage of 500 mg/L at initial pH.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 500 1000 1500 2000 2500 3000

Dosage (mg/L)

BO

D Re

mov

al (%

)

pH 5 (initial pH)

Figure 4.5 Percentage of BOD Removal for Different Dosage of PAM

BOD reduction efficiencies decreased with the increase in coagulant dosage.

1000 mg/L of PAM resulted in poorest BOD removal i.e. 47.5%. Further increase in

the dosage did not improve the reduction efficiency. This behavior suggests that floc

breakup occured due to charge reversal phenomenon of coagulant; where colloidal

stability gets destabilized once the coagulant charge concentration was higher than

the total charge of the colloids present in POME, and dispersion when there was an

excessive or overdosing of coagulants.

The percentage reduction of BOD with PAM was very significant at the

lowest dosage of 500 mg/L. According to Ariffin et al. (2004), the molecular weight

70

of a polymer can affect polymer adsorption and particle flocculation. The PAM used

in this study was of high molecular weight PAM (5 million gmol-1). The size of the

polymer can affect the rate of collisions. The capture of particles was enhanced by

the length of the loops and tails of adsorbed polymer molecules. The formation of

more loops of sufficient length to bridge the “gap” between the colliding particles led

to a stronger bridging effect between aggregating particles.

High molecular weight polyelectrolyte would enhance the unevenness of the

surface charge distribution which would boost “electrostatic patch” attraction and the

amount of polymer loops of sufficient length to allow interparticle bridging.

The use of PAM resulted in more than 50% reduction of BOD at all dosages

used, except for 1000 mg/L. These results suggest that the use of PAM reduces the

amount of coagulant required for the treatment and lowers the cost of the

coagulation–flocculation process. Stabilization of PAM involves a combined

coagulation-flocculation reaction.

The PAM molecules first act as a coagulant by reducing the forces of

repulsion between the particles and then a flocculent in bridging (Gill and

Herrington, 1988). Cationic polyelectrolyte favors the bridging action and strong

electrostatic attraction which subsequently leads to increased mass, compactness and

supernatant viscosity.

71


The percentage removal of TSS using PAM at various dosages is shown in

Figure 4.6. The optimum dosage of the PAM in the removal of TSS was 1500mg/L

with almost 96% removal. However, the removal efficiencies of TSS with PAM

were more than 90% at each dosage applied and even at a dosage as low as 500 mg/L

except for PAM with 2000 mg/L which shows 89% TSS removal. This was

probably due to the fact that the flocculation efficiency is dependent on the original

concentration of suspended solids of the wastewater (Wong et al., 2006). For the

optimum aggregation of more concentrated suspensions, a lower amount of polymer

is needed, and the addition of this amount results in a high degree of flocculation

(Barany and Szepesszenentgyorgyi, 2004). The effects of PAM dosage on TSS

reduction were not significant within the range of dosage studied. The TSS

reduction was between 89 and 96%.

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000Dosage (mg/L)

TSS

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.6 Percentage of TSS Removal for Different Dosage of PAM

Acrylamide is a polyfunctional molecule that contains a vinylic carbon–

carbon double bond and an amide group. The flocculations of the suspended

particles occur via the double bond. The wastewater that was used in this process

72

contained very high concentration of suspended solids. The high efficiency of the

PAM in the TSS removals may be due to the high collision frequency between the

PAM and the suspended solid particles.


The results in figure 4.7 show that a large number of PAM molecules were

needed to acquire high removal efficiency. The turbidity reduction efficiencies

increase with increase in coagulant dosage at initial pH till it reached its highest

value, optimum dosage, after which the reduction and removal efficiencies started to

decrease. It required 2000 mg/L PAM to obtain 58.5% turbidity removal. The

lowest removal i.e. 44% was attained at the lowest dosage i.e. 500 mg/L. However,

500 mg/L was chosen as the optimum dosage as it gave the highest BOD and TSS

removal efficiencies.

0

20

40

60

80

0 500 1000 1500 2000 2500 3000Dosage (mg/L)

Turb

idity

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.7 Percentage of Turbidity Removal for Different Dosage of PAM

73

However, flocs obtained by PAM treatment had a mucous aspect, being oily

to the touch; they adhered to the vessel walls and were difficult to filtrate. Cationic

polyelectrolyte used as a coagulant in this study actually replaced the anionic groups

on POME colloidal particles. The application of polyelectrolyte (PAM) in doses

higher than those giving the minimum turbidity led to emulsion restabilization,

consequently hindered the formation of flocs, and increased the turbidity. The

emulsion restabilization was accompanied by a reversal of the colloidal charge

(Pinotti et al., 2001). Figure 4.8 shows the tiny flocs formed by coagulation using

PAM. It can hardly be seen as the supernatant was quite turbid.

Figure 4.8 Coagulation with PAM at optimum dosage and initial pH; after 1 hour

settling time

Nonetheless, Ariffin et al. (2004) suggested that very high molecular weight

PAM will result in poor floc formation and yielded reduced removal efficiency

because polyelectrolytes with very high molecular weights do not dissolve readily

but tend to form gel lumps known as “fish eyes”. This explains the formation of gel

lumps during the study and the reduction in removal efficiency as the dosage of

PAM increase.

74

4.3.3 Polyaluminum Chloride (PACl) as Sole Coagulant

Each beaker was filled with 1 liter of POME. After adding PACl powder into

the suspension, the beakers were rapidly mixed at 3 min contact time and were

slowly mixed for 30 min for different weight dosages of PACl (0.5–2.5 g). POME

was allowed to settle for 1 hour with the supernatant being analyzed for its turbidity,

BOD and TSS concentration after sedimentation.


Figure 4.9 shows the results obtained when PACl was used as coagulant. The

BOD removal decreased with increase in coagulant dosage till it reached its lowest

value, after which the removal efficiency started to increase. The highest BOD

reduction was 51.4% at the lowest PACl dosage i.e. 500 mg/L and the lowest BOD

reduction achieved by using PACl was 37.4% at 2000 mg/L.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0 500 1000 1500 2000 2500 3000

Dosage (mg/L)

BOD

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.9 Percentage of BOD Removal for Different Dosage of PACl

75

Compared with chitosan and PAM, however, PACl behaved differently

owing to the preformed Al13 species with relatively high stability. The oligomers

and polymers component in PACl may facilitate the removal of organic matters via

charge neutralization due to their high charge density in the coagulation process (Yu

et al., 2007). PACl exhibited strong charge-neutralization ability due to fast

adsorption process due to high positive charge. Optimum destabilization occurred

when only very small portion of POME surface are covered. The destabilized

particles were likely to be removed by both the electrostatic patch coagulation and

also bridge-aggregation.

Duan and Gregory (2003) believed that some form of sweep flocculation is

operating when using pre-hydrolysed coagulants like PACl, since the volume of

hydroxide precipitate would be expected to depend on the amount of coagulant

added and that PACl products give more rapid flocculation and stronger flocs. This

process has become known as ‘sweep flocculation’ since impurity particles are

enmeshed in a growing amorphous hydroxide precipitate and are effectively removed

from suspension and can be observed from figure 4.10 below.

Figure 4.10 Schematic diagram showing the interaction of aluminium species with

initially negatively charged particles in water (Duan and Gregory, 2003)

76

The particles on the right hand side were initially stable and then become

destabilized by charge neutralisation. At higher coagulant dosages they became

restabilised by charge reversal and incorporated in a flocculent hydroxide precipitate

‘sweep flocculation’. Optimum coagulation appeared at the lowest dosage at 500

mg/L and re-stabilization occurred with further dose for PACl. As studied by Wu et

al. (2007), surface coverage indicates adsorption behaviors of PACl on particles.

The surface coverage increased with the aluminum dosage and reached the plateau

when restabilization was completed. This explains the almost plateau trend shown in

figure 4.9 that happened between 1000-2500 mg/L.


Figure 4.11 shows that the TSS removal trend was similar to BOD reduction

trends.

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000Dosage (mg/L)

TSS

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.11 Percentage of TSS Removal for Different Dosage of PACl

77

This may be due to the high organic contents of the suspended solid particles.

The effect of increasing the PACl dosage only reveals minor impacts on the

reduction/removal efficiency of TSS. The TSS removal efficiency decreased from

95% to 87.5% as the dosage of coagulant increased. Although at a dosage of

1000mg/L, PACl gave the highest removal i.e. 95.4%, 500mg/L was chosen as the

optimum dosage as it resulted in 95.1% TSS removal efficiency at pH 5 (initial pH of

POME). These results were better than those of ref. (Ahmad et al., 2006), who

found that under the optimal conditions of pH 4.5 and initial PACl dosage of 6000

mg/L, about 95% of TSS reduction was obtained in the treatment of palm oil mill

wastewaters.

The strong charge-neutralization and bridging ability with its aggregated

species, as commented by Wu et al. (2007), make PACl an efficient coagulant in

destabilizing and aggregating suspended particles and colloids. It is therefore very

reasonable to suggest that for PACl, the electrostatic interaction is the main driving

forces for the adsorption process forming ‘electrostatic patches’ to induce

electrostatic patch coagulation and highly charged larger size aggregated polycations

can also attract particles through electrostatic forces and bridging.

Nevertheless in figure 4.11, it was also noticed that when the applied dosage

was higher than the optimum amount, the suspended solid removal value decreased.

This shows restabilization of POME. At 1000mg/L of PACl there was an increase in

suspended solid reading. At high doses of coagulant, a sufficient degree of over-

saturation occurred to produce a rapid precipitation of large quantity of coagulant.

78


The turbidity reduction efficiencies increased with increase in coagulant

dosage till it reached its highest value, optimum dosage, after which the reduction

and removal efficiencies started to decrease. From figure 4.12, it can be observed

that the turbidity reduction efficiency started to drop at 2000 mg/L. The highest

turbidity reduction was 87.7%, achieved at 1500mg/L dosage while the lowest

turbidity reduction attained by PACl was 72% at 1000 mg/L.

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000Dosage (mg/L)

Turb

idity

Rem

oval

(%)

pH 5 (initial pH)

Figure 4.12 Percentage of Turbidity Removal for Different Dosage of PACl

The outstanding behavior of turbidity removal by PACl at the optimum

dosage may attribute to its relatively high content in the colloidal hydroxides

component. It is recognized that the colloidal hydroxide, can aggregate rapidly to

form positively charged patches on the negatively charged surfaces of particles in

wastewater. Wang et al. (2004) suggested that turbidity removal via coagulation

using cationic polymer can be achieved through patch coagulation.

79

Wu et al. (2007) commented that the electrostatic patch coagulation and

bridge- aggregation can be used to explain the effective turbidity removal of PACl.

As the dose of PACl increased further, restabilization appeared after the maximum

turbidity removal. It was implied that particles repelled to each other due to the

strong electrostatic repulsion forces caused by adsorbed polycations.

Although the flocs formed by PACl were large and dense, as can be seen in

figure 4.13, the flocs that have been formed by PACl seemed to be easily dispersed

in the sample. The breakage of the flocs caused the sample to be turbid again. This

indirectly caused the suspended solid to disperse in the sample. Therefore, it is

clearly noticed that PACl acts only as a coagulant which flocs the suspended solid in

POME and settled it by gravity settling.

Figure 4.13 Coagulation with PACl at optimum dosage and initial pH

80

Figure 4.14 below sums up the results for sole coagulant application in the

pre-treatment of POME analysis for three different coagulants studied in terms of

BOD removal efficiencies. The optimum dosage of a coagulant was determined

when there was no significant increase in the BOD removal efficiency with further

addition of coagulants. The optimum chitosan dosage at pH 5 (initial pH) was 250

mg/L. A removal of BOD at approximately 61% can be achieved. This result

reveals that the optimum coagulant dosage for chitosan was less than that of PAM

and PACl at the same pH value. 500 mg/L PAM was required to achieve BOD

reduction as high as that of chitosan. At initial pH, the usage of PAM at its optimum

dosage resulted in 63% BOD removal. By using PACl, BOD removal efficiency was

the lowest compared to chitosan and PAM. The highest BOD removal that can be

achieved via PACl application was 51.4% at the lowest dosage tested i.e. optimum

dosage.

0

10

20

30

40

50

60

70

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750

Dosage (mg/L)

BOD

Rem

oval

(%)

Chitosan PAM PACl

Figure 4.14 Percentage of BOD Removal vs. Dosage of Chitosan, PAM and PACl

81

4.4 Optimum Dosage and Operating Condition Analysis

Further optimum analysis for coagulation and flocculation was performed

based on the highest BOD removal efficiency achieved using chitosan, PAM and

PACl as coagulants. The dosage of coagulants was obtained from the previous

results. 250 mg/L was the optimum dosage of chitosan which gave 60.7% BOD

removal. For PAM and PACl, 500 mg/L was chosen as they resulted in 63 % and

51.4% BOD removal respectively.

In this section, further study on the optimum pH for coagulation and

flocculation process was evaluated. The pH values range between 3 and 6. POME is

an acidic suspension, therefore pH adjustments were only done between pH 3 and 6

(acidic regent to neutral). Furthermore, based on literature, chitosan, PAM and PACl

perform well at acidic pH (Ahmad et al., 2005a, 2005b, 2006; Ariffin et al., 2005;

Roussy et al., 2005a). The effect of pH value on the removal of BOD, TSS and

turbidity was analyzed with the optimized coagulants dosage determined in Section

4.3 with a mixing rate of 250 rpm (rapid mixing), 30 rpm (slow mixing), and

sedimentation time of one hour.

4.4.1 Chitosan Performance at Optimum Dosage

4.4.1.1 Effect of pH on BOD, TSS and Turbidity Removal

To study the effects of the pH value on the turbidity reduction, TSS removal

and BOD reduction in POME using chitosan, jar tests were conducted with pH

adjusted from 3.0 to 6.0.

82

The results obtained are shown in figure 4.15. The turbidity reduction, TSS

removal and BOD reduction efficiencies increased with increase in pH value till it

reached its highest value, optimum pH, after which the reduction and removal

efficiencies started to decrease. The TSS reduction efficiency started to drop at pH

6.0. The highest TSS reduction was 98% and the lowest TSS reduction achieved by

chitosan was 90.5%. pH value showed significant effects on the BOD removal and

turbidity reduction between 5.0 and 6.0. The BOD removal efficiency decreased

from more than 60.7% to below 50.5%. The turbidity reduction efficiency decreased

from more than 93.5% to below 64.2%. The optimum chitosan dosage and pH were

250 mg/L and 5.0, respectively.

0102030405060708090

100

2 3 4 5 6 7pH value

Rem

oval

(%)

BOD Removal TSS Removal Turbidity Removal

Figure 4.15 Percentage of BOD, TSS and Turbidity Removal Using 250 mg/L

Chitosan at Different pH of POME

Chitosan properties allow charge neutralization (coagulation) and particle

entrapment (flocculation) which were the double effect of chitosan in the process.

The contribution of each mechanism depends on the pH of the suspension (Roussy et

al., 2005a). Chitosan is a positively charged linear polyelectrolyte at acidic

conditions. POME is naturally an acidic suspended effluent. Therefore, this

condition could easily stimulate chitosan to destabilize the negatively charged

colloids in POME. Strong acidic condition aggravates POME to destabilize

83

suspended solid in the suspension. Thus, enhances the coagulation of suspended

solids which explains the satisfactory BOD, TSS and turbidity removal between pH 4

and 5. Figure 4.16 shows the clarity of the supernatant after treatment and pH 4

indicates the best turbidity removal as compared to pH 3 and 6.

(a) (b) (c)

Figure 4.16 Supernatant after treatment with chitosan at (a) pH 3, (b) pH 4, and (c)

pH 6

Amine functional group of chitosan which attracts anionic ions to bind and

bridge (Osman and Arof, 2003) helps to coagulate negatively charged colloids in

POME. The protonation of amine groups in chitosan is also responsible for the

polymer dissolving in acidic solutions, with the notable exception of sulfuric acid

solutions (Roussy et al., 2005a). At pH more than 5, BOD, TSS and turbidity

removal efficiency started to decrease. Ahmad et al. (2005b) reported that the

optimum pH for coagulation using chitosan was around 4.0 to 5.0 and that pH 6.0

showed the poorest removal efficiency (Ahmad et al., 2006). The very low

efficiency of chitosan at slightly alkaline pH (pH 6.0) also confirmed that, at least

partial protonation of the biopolymer’s amine groups was required to achieve

efficient coagulation–flocculation of these organic suspensions. At pH 3, the

excessive number of cationic charges contributed by the protonated amine groups led

to restabilization of the suspension and a decrease in coagulation–flocculation

efficiency. Ahmad et al. (2006) reported that chitosan showed more than 95% of

TSS removal at 500 mg/L and pH 4.0. Nevertheless, this study proved that at only

84

250 mg/L chitosan and at pH between 4 and 5, 97-98% TSS removal can be

accomplished.

4.4.2 PAM Performance at Optimum Dosage


The pH of the reaction medium is also important, since hydrolysis of amide

groups can take place at high pH, whereas imidization is favored at low pH (Pinotti

et al., 2001). Figure 4.17 indicates the effect of pH adjustment on BOD, TSS and

turbidity removal using PAM as sole coagulant. BOD reduction increased with

increase in pH value till it reached its highest value, optimum pH, after which the

reduction and removal efficiencies started to decrease.

0102030405060708090

100

2 3 4 5 6 7pH value

Rem

oval

(%)


Figure 4.17 Percentage of BOD, TSS and Turbidity Removal Using 500 mg/L PAM

at Different pH of POME

85

The maximum BOD removal achieved was 63% at pH 5 while the lowest

removal occurred at pH 6 with 44% BOD reduction. The BOD reduction drop-off at

pH 6 was due to the concentration of OH− ions, which was high enough to compete

with organic molecules from POME for adsorption process. In addition, at high pH

the charge of the coagulating species will become less positive and as a result, less

attracted to anionic organic compounds. But, at low pH the anionic organic

molecules from POME reacted directly to form insoluble complexes.

PAM with charges opposite of the suspended solids was added to the POME

wastewater to neutralize the negative charges on dispersed non-settleable solids.

When the charges were neutralized, the small suspended particles were capable to

interact together through rapid mixing. Once the coagulation process was completed,

flocculation processes started to take place. The PAM used has high molecular

weight containing a long chain of polyelectrolyte. This polyelectrolyte could

generate a ‘macroflocs’ particles with slow mixing, resulting in the interaction with

the suspended solids. Finally, when the floc reached its optimum size and strength,

the wastewater was subjected to the sedimentation process.

The effects of pH on TSS reduction were not significant within the range of

pH studied as each pH resulted in 94 to 95% TSS removal. 95% TSS removal was

achieved at pH 4 and 5. At low pH, the solution appeared clear but showed the

presence of very small colloidal particles. As the pH increased towards alkaline

value, the POME turned into a darker color due to the presence of higher suspended

solids and the removal became poorer. Bhatia et al. (2007b) used NALCO 7751 as

high molecular weight which contains long chain of polyelectrolyte, resulting in the

interaction with the suspended solids and reported that 98% TSS removal can be

attained at pH 5.

pH 3 and 4 gave the highest turbidity removal i.e. 79.1 and 79.3%

respectively. However, the removal efficiency dropped drastically to 44% at pH 5.

From figure 4.17 it can be observed that the removal trends of BOD and turbidity

86

were dissimilar to each other. Pinotti et al. (2001) reported that pH 3.5 gave

minimum turbidity when treating emulsion with PAM.

This agrees with the results shown in figure 4.17 and 4.18 which indicates

that maximum turbidity removal was achieved between pH 3 and 4. pH 5 was

chosen as the optimum pH, although the turbidity removal was at the lowest as it was

compensated by the highest BOD and TSS removal.

The result above also shows that the charges of suspended solids present in

the POME probably not effective in coagulation process with pH changes and

thereby the suspended solids removal decreased with the increase of pH. At higher

pH, the colloidal particles were negatively charged while at lower value of pH, the

particles were positively charged. Nik Norulaini et al. (2001) suggested that the

charge balance is actually associated with changes in H+ and OH− ions to maintain

the ion balance with water at different pH.

(a) (b) (c)

Figure 4.18 PAM performances at (a) pH 3, (b) pH 4, and (c) pH 6

87

4.4.3 PACl Performance at Optimum Dosage


Figure 4.19 shows the effect of different pH on BOD, TSS and turbidity

removal using PACl as sole coagulant. pH shows significant effects on the BOD

reduction at pH 6. At pH 6, the BOD removal increased from 51 to 59% which was

the maximum reduction achieved. The effects of pH on TSS reduction were not

significant within the range of pH studied. All pH values show 95% TSS removal

except for pH 6 which showed 96% TSS removal i.e. the greatest reduction. pH 3

and 6 resulted in the highest turbidity removal which were 78 and 76% respectively.

The lowest turbidity reduction was 71% which was attained at pH 4. It can be seen

that an optimum range of pH exists between 5.0 and 6.0 beyond which effluent

quality deteriorates.

0102030405060708090

100

2 3 4 5 6 7pH value

Rem

oval

(%)


Figure 4.19 Percentage of BOD, TSS and Turbidity Removal Using 500 mg/L PACl

at Different pH of POME

88

The optimum PACl dosage and pH were 500 mg/L and 6.0, respectively. At

lower pH and lower coagulant dosage, the only mechanism for destabilization of

particles was charge neutralization. At low pH, because the aggregates were small in

size, the mechanism of colloidal destabilization was mainly charge neutralization. At

lower dosage, PACl behaves like the alum salt; therefore, charge neutralization is the

principal mechanism for destabilization (Huang and Pan, 2002). Figure 4.20 shows

the performance of PACl at pH 3, 4, and 6.

.

(a) (b) (c)

Figure 4.20 PACl performances at (a) pH 3, (b) pH 4, and (c) pH 6

According to Ahmad et al. (2006), the optimal condition of coagulation using

PACl was around pH 4.0–5.0 and a dosage of 6000 mg/L to obtain the same

percentage of TSS removal as performed by chitosan and that pH 6 showed the

poorest removal efficiency. Nevertheless, in contrast, this study proved that at a

dosage as low as 500 mg/L, and pH 4 and 5, PACl could give 95% TSS removal.

The formation of PACl floc particles at different pH condition was studied by

Van Benschoten and Edwzwald (1990a, 1990b) and concluded that PACl is least

soluble between pH 6 and 7 which agreed with the results obtained from this study

89

for PACl application. Highest amount of PACl was converted to solids phase flocs

particles at those pH.

Pre-hydrolyzed coagulants like PACl are often more effective than simple Al

and Fe salts. Part of the reason has to do with highly charged cationic species, such

as Al13, which are rather stable and have a better opportunity to adsorb on negative

colloids and neutralize their charge.

As a summary for this section, all the coagulants showed a good potential of

BOD, TSS and turbidity removal at initial pH value (pH 5). These results can be

clearly seen in figure 4.15, 4.17 and 4.19. This encouraging fact could bring to a

conclusion that pH adjustment on POME in the real treatment system can be

discarded in order to remove the suspended solid by using any of these coagulants.

However, when the pH was adjusted to a higher value i.e. pH 6, only PACl showed

the best removal for all parameters compared to the acidic condition with 59% BOD

removal, 96% TSS removal and 76% turbidity reduction. PAM and chitosan

application resulted in poorer removal at pH 6 but portrayed best removal at pH 5.

By using chitosan, 61% BOD removal, 97% TSS removal and 94% turbidity

reduction can be achieved. At optimum dosage and pH, PAM gave 63% BOD

removal, 95% TSS removal and 44% turbidity reduction.

90

4.5 Comparison of the Performance of Chitosan, PAM and PACl as

Coagulants in POME Treatment

Figure 4.21 shows the BOD removal efficiency using chitosan, PAM and

PACl at different pH of POME. Chitosan could successfully remove 61% of BOD

concentration from POME at a dosage of 250 mg/L and employing a rapid mixing at

250 rpm for 3 min, slow mixing at 30 rpm for 30 min, sedimentation for 60 min and

a pH value of 5.0.

30

35

40

45

50

55

60

65

2 3 4 5 6 7pH value

BO

D R

emov

al (%

)

Chitosan (250mg/L) PAM (500mg/L) PACl (500mg/L)

Figure 4.21 BOD removal using chitosan, PAM and PACl vs. different pH of

POME.

For PAM and PACl, the optimum dosages were 500 mg/L, respectively,

employing a rapid mixing at 250 rpm for 3 min, slow mixing at 30 rpm for 30 min,

sedimentation for 60 min, and a pH value of 5.0 and 6.0, respectively to obtain a

comparable percentage of BOD removal as performed by chitosan. This proves

chitosan to be the best coagulant. Predominant mechanisms of coagulation with

chitosan were charge neutralization and bridging mechanism by amine group. The

main mechanisms for PACl during coagulation process were charge-neutralization,

91

electrostatic patch coagulation and bridge-aggregation, while bridging mechanism

was the dominant mechanism involved for high molecular weight PAM.

Chitosan and PAM showed almost similar trend for BOD removal. Due to

the concentration of OH− ions, which was high enough to compete with organic

molecules from POME for adsorption process, the BOD removal decreased at pH 6

when chitosan and PAM were used. However, PACl showed excellent BOD

removal at pH 6. At pH 6-7, Al3+ has limited solubility because of the precipitation

of an amorphous hydroxide which leads to sweep flocculation. As a result, impurity

become enmeshed in growing precipitate and effectively removed.

Figure 4.22 shows that chitosan, PAM and PACl have a good removal of

suspended solid at acidic pH. Chitosan was still the best. The removal of TSS with

chitosan resulted in 97-98% removal within the range of original pH of POME, i.e.,

pH 4.0–5.0.

90919293949596979899

100

2 3 4 5 6 7pH value

TSS

Rem

oval

(%)


Figure 4.22 TSS removal using chitosan, PAM and PACl vs. different pH of POME

92

Normally, the original pH value of POME is about pH 4 to 5 and from figure

4.22, it shows that at this pH value, the removal was very satisfying and achieved

95% and above of TSS removal at this pH for all the coagulants. Furthermore, the

supernatant was visually very clear. This encouraging observation leads to a

conclusion that pH adjustment of POME would be unnecessary under real-process

treatment conditions for removing TSS using chitosan, PAM and PACl.

At acidic pH, the Al3+ exists in significant amount; therefore the coagulation

using PACl was also good. At low pH, because the aggregates were small in size,

the mechanism of colloidal destabilization was mainly charge neutralization. As for

PAM, at lower pH value, the particles were positively charged. This caused an ion

balance with the negatively charged colloids in the wastewater, which in turn

enhanced the TSS removal at acidic pH. Based on figure 4.23, chitosan again

showed the most excellent turbidity removal between pH 4 and 5. The turbidity

reading of chitosan was as low as 64 NTU and 424 NTU i.e. 99% and 94% removal,

respectively, when the pH value of the suspension was at 4 and 5.

40

50

60

70

80

90

100

2 3 4 5 6 7pH value

Turb

idity

Rem

oval

(%)


Figure 4.23 Turbidity removal using chitosan, PAM and PACl vs. different pH of

POME

93

PACl also showed good turbidity removal at the same pH, with 71 to 72%

removal. However, PAM showed the best removal at pH 4 i.e. 79%, but the poorest

reduction at pH 5 i.e. 44%. It appears that at pH value of 4.0, the removal of

turbidity was at the maximum, and this pH value contributes to the most favorable

removal for all the coagulants. This explains the clarity of the supernatant that was

observed visually at this pH.

PAM and chitosan showed poor BOD, TSS and turbidity removal at pH 6 due

to the destabilization of the coagulants itself at weaker acid conditions. Furthermore,

at this pH, the adsorption process itself is very unstable due to the characteristic of

POME, which has changed drastically with the change of pH. Therefore, the most

excellent coagulant for coagulation and flocculation of POME at initial pH is

chitosan. In order to justify the usage of chitosan, PAM and PACl in industrial scale,

other factors, such as the price difference has to be thoroughly investigated.


Chemical cost estimation were performed for each of the coagulants. The

coagulant costs were based on the application of the coagulants at their respective

optimum dosage for the treatment of 1 cubic meter of POME fed. The chemical

costs were also estimated based on the volume of POME generated per tonne of CPO

produced. Evaluation of the operating costs is essential and needed and to make

choices between possible alternative processing schemes and to determine the most

cost effective process. The calculation of costing in this section serves only as a

preliminary study and a reference for the future study as the price varies from one

supplier to another.

94

Table 4.2 : Estimated costs to treat POME generated per tonne of CPO produced at

the optimum dosages of each coagulants

Type of coagulant Chitosan PAM PACl

Dosage (mg/L) 250 500 500

BOD removal (%) 60.7 63.0 58.8

Price/kg (RM) 50.00 15.25 0.54

Quantity needed (kg/m3 of POME) 0.25 0.5 0.5

Chemical cost (RM/m3 of POME) 12.50 7.63 0.27

Total cost (RM/tonne of CPO) 39.13 23.88 0.85

Costing of each coagulant at their optimal dosage can be observed from table

4.2 above. This data was taken from the analysis in Section 4.3 of a sole coagulant

for coagulation and flocculation processes. Chitosan gave the most excellent

performance out of the three types of sole coagulant selected. Almost 61% of BOD

removal was achieved by using only 250 mg/L dosage. It was estimated that

RM39.13 of chitosan was needed per tonne of CPO produced. Amongst the three

types of coagulant, the total chemical cost of PACl needed per tonne of CPO was the

cheapest (RM0.85), followed by PAM (RM23.88) and chitosan.

In order to judge the viability of introducing chemical pretreatment in POME

treatment system, an estimation of chemical costs required to treat the effluent

generated from the production of CPO per month was carried out. These costs were

then compared against the revenue earned from the CPO production. This estimation

is necessary to evaluate if the treatment scheme proposed is practical and cost

effective.

95

Table 4.3 shows the analysis of coagulant costs required based on the amount

of CPO produced and POME generated monthly.

Table 4.3 : Cost of coagulants required based on the amount of CPO produced and

POME generated monthly

Cost (RM) Chemical cost / CPO

revenue (%) Quantity per

month Chitosan PAM PACl Chitosan PAM PACl

POMEa

(m3) 14,013.66 0.18x106 0.11x106 3.78x103

Revenueb (RM) CPOa

(tonne) 4,474.46

6.48 x 106

2.56 1.56 0.06

a Based on the amount of FFB processed in Kilang Sawit Penggeli in November

2008. b Based on CPO market price in November 2008 (MPOC Website).

From the table above, it can be seen that the cost of chemicals involved in the

chemical pretreatment of POME is very cheap. The percentages of chemical costs

are very small when compared to the profit earned from the CPO production i.e. less

than 3% for all coagulants studied. Therefore, coagulation-flocculation process

using either of these coagulants is a very promising option to be introduced as a

pretreatment in the existing POME treatment system. Besides producing an

excellent performance in terms of the BOD and TSS removal, it is also cost efficient.

CHAPTER V

CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction

This chapter concludes the findings from the studies conducted. The aim,

results of this study, implications of the findings for practice and the overall

importance of the research to the field and recommendations for future research or

practices are reiterated and highlighted here.

5.2 Conclusions

The results showed that chitosan proved to be the best coagulant as it

performed exceptionally well. Chitosan showed the best removal compared to the

other coagulants for all the parameters studied. The following optimum parameters

were found necessary for the reduction of tubidity, BOD and TSS value from an

influent with a concentration of 6548 NTU, 25840 mg/L and 19340 mg/L,

respectively to 423.75 NTU (93.5% turbidity removal), 10147.5 mg/L (60.7% BOD

97

removal), and 603.25 mg/L (96.9% TSS removal), correspondingly: chitosan as the

best coagulant with a dosage of 250 mg/L; POME suspension initial pH value of 5.0;


and sedimentation for 60 min. However, the estimated cost of chitosan needed per

tonne of CPO produced was quite high i.e. RM39.13.

For PAM and PACl, the optimum dosages were 500 mg/L, respectively,


sedimentation for 60 min, and a pH value of 5.0 and 6.0, respectively to obtain a

comparable percentage of BOD removal as performed by chitosan. The cost of

PACl required per tonne of CPO was the cheapest i.e. RM0.85. In addition, it

resulted in an excellent TSS removal (96%) and good BOD (58.8%) and turbidity

reduction (76.3%). Although the price of PAM was also cheap, its application

resulted in average performance (63%, 94.8% and 44% removal in BOD, TSS and

turbidity value correspondingly). On the whole, in terms of performance, chitosan is

the best option in treating POME via coagulation-flocculation process, followed by

PACl and PAM.

All the coagulants showed a good potential of removal at initial pH value.

This encouraging fact could bring to a conclusion that pH adjustment on POME in

the real treatment system can be discarded in order to remove the turbidity, BOD and

TSS concentration by using any of these coagulants, thus keeping the treatment cost

lower and the quality of treated waste better compared to the conventional

coagulation.

By applying chemical pre-treatment i.e. coagulation and flocculation in the

POME treatment system, it will significantly improve the treatment system and

improve the quality of the effluent discharge from the mill. Hence, it is strongly

recommended to introduce coagulation and flocculation process as a chemical pre-

treatment in the POME treatment system.

98

5.3 Recommendations for future studies

Several recommendations for future studies are listed as follows:

First of all, it is recommended to conduct a study on integrated chemical and

biological system for treating POME so as to verify the effects the pre-chemical

treatment has in enhancing the BOD and TSS removal efficiencies which will

ultimately meet the Department of Environment Standards requirement for effluent

discharge. The anaerobic digester/ponds, facultative and algae ponds that are being

used in most mills at times fail to reduce the BOD and TSS concentration to below

100 and 400 mg/L, respectively. The study can be carried out by using the results

obtained from this research.

The suspended particles in POME will settle on its own after a period of time

even without physicochemical treatment. Thus, it is recommended to conduct the

coagulation-flocculation process on raw POME samples without the addition of

coagulants (as a control) but employing the same mixing speed and time to

investigate the effects it has on BOD, TSS and turbidity removal.

Manually operated sand and oil traps are installed as pretreatment units in

many wastewater treatment systems in palm oil mill. It is recommended to conduct

the study on samples (effluent) collected from this pretreatment unit so as to analyze

the difference between pretreated effluent and mixed raw effluent in terms of BOD,

TSS and turbidity removal.

Next, studies on coagulant dosage lower than the lowest dosage considered in

this research should also be considered to investigate if higher removal efficiency for

BOD, TSS and turbidity can be achieved at lower dosage. The samples can be

99

analyzed with different dosages of chitosan (0.01–0.1 g/l), PAM and PACl (0.05–0.5

g/l).

It is also recommended to study the effect of varying the mixing time,

sedimentation time, and mixing rate/speed in enhancing the removal efficiencies.

Effect of sedimentation time can be analyzed at different sedimentation time (5-

80min) at optimum dosage of chitosan, PAM and PACl at a fixed mixing time and

mixing rate. The effect of mixing speed can be analyzed using two different mixing

times at various mixing speed (20-200rpm) for all the coagulants with optimized

coagulant dosages, at initial pH and sedimentation time of 60 min. The effect of

mixing time can be conducted by varying the mixing time (5-60min) at a fixed

mixing rate. The sample can then let to settle for 1 h. Dosage of chitosan, PAM and

PACl should be fixed at their optimum values.

The sludge produced in the physical–chemical treatment is due to the amount

of organic matter and total solids in suspension that are removed and the compounds

formed from the coagulant used, since practically almost all of the latter will form

part of the sludge solids. In general, the amount and characteristics of the sludge

produced during the coagulation–flocculation process depend on the coagulants used

and on the operating conditions. Thus, it is recommended to determine the SVI with

the purpose of observing the volume and settling characteristics of the sludge

produced.

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APPENDIX A

POME CHARACTERISTIC STUDY

Table A1 : Analysis Results for Raw POME

Parameters pH BOD

(mg/L)

Turbidity

(NTU)

TSS

(mg/L)

Run 1 4.9 23040 5900 18480

Run 2 4.9 26700 5840 19000

Run 3 4.9 24900 6684 20540

Run 4 5.0 25620 6786 18000

Run 5 5.0 27900 6680 20100

Run 6 5.1 23800 6972 19200

Run 7 5.21 25900 6680 17900

Run 8 5.25 28860 6842 21500

Average 5.0 ± 0.1 25840 ± 1965.4 6548 ± 430.5 19340 ± 1277.7

APPENDIX B

SOLE COAGULANT FOR COAGULATION AND FLOCCULATION

PROCESSES

B1 Analysis results for Chitosan used as Sole Coagulant and Flocculant

Constant parameter:

pH : 5.0

Coagulation mixing speed : 250 rpm

Coagulation mixing time : 3 min

Flocculation mixing speed : 30 rpm

Flocculation mixing time : 30 min

Table B1.1 : Analysis results for POME treated with chitosan

A B C D E Dosage (mg/L) Parameter 100 250 500 750 1000

Turbidity (NTU) 2695 424 1338 780 563

Percent removal (%) 58.8 93.5 79.6 88.1 91.4

BOD (mg/L) 11070 10148 12630 10590 11043 Percent removal (%) 57.2 60.7 51.1 59.0 57.3

TSS (mg/L) 1720 603 2480 1520 1360 Percent removal (%) 91.1 96.9 87.2 92.1 93.0

111

Table B1.2 : Reproducible data for turbidity, BOD and TSS removal of POME

treated using 250 ppm chitosan at pH 5.0

Run Parameter 1 2 3 4 5 6 7 8 Mean

Turbidity (NTU) 548 388 506 536 440 314 323 335 424

Percent removal (%)

92 94 92 92 93 95 95 95 93.5

BOD (mg/L) 8130 8085 9870 10875 8520 11670 11790 12240 10148

Percent removal (%)

69 69 62 58 67 55 54 55 60.7

TSS (mg/L) 620 560 640 820 640 340 490 716 603 Percent removal (%)

97 97 97 96 97 98 97 96 96.9

B2 Analysis results for Polyacrylamide (PAM) used as Sole Coagulant and

Flocculant

Constant parameter:

pH : 5.0





Table B2.1 : Analysis results for POME treated with Polyacrylamide (PAM)


Turbidity (NTU) 3665 3078 2928 2718 3453

Percent removal (%) 44.0 53.0 55.3 58.5 47.3



112


treated using 500 ppm PAM at pH 5.0


Turbidity (NTU) 4193 4055 3972 3994 4070 3064 2906 3066 3665

Percent removal (%) 36 38 39 39 38 53 56 53 44.0

BOD (mg/L) 9045 8595 5550 6495 7560 12375 14025 12750 9549 Percent removal (%) 65 67 79 75 71 52 46 51 63.0

TSS (mg/L) 1000 940 760 860 1040 1260 1140 1060 1008 Percent removal (%) 95 95 96 96 95 93 94 95 94.8

B3 Analysis results for Polyaluminum Chloride used as Sole Coagulant and

Flocculant

Constant parameter:

pH : 5.0





Table B3.1 : Analysis results for POME treated with Polyaluminum Chloride


Turbidity (NTU) 1825 1836 805 1100 1555

Percent removal (%) 72.1 72.0 87.7 83.2 76.3



113


treated using 500 ppm PACl at pH 5.0


Turbidity (NTU) 1792 1584 1708 1752 1516 2080 2080 2088 1825

Percent removal (%)

73 76 74 73 77 68 68 68 72.1

BOD (mg/L) 13326 12287 13065 11973 12806 12290 12031 12662 12555

Percent removal (%)

48 52 49 54 50 52 53 51 51.4

TSS (mg/L) 760 820 820 840 1320 1140 920 980 950

Percent removal (%)

96 96 96 96 93 94 95 95 95.1

APPENDIX C

PARAMETER OPTIMIZATION

C1 Optimization of Chitosan as coagulant

Constant parameter:

Dosage : 250 mg/L





Table C1.1 : pH optimization for chitosan at 250 mg/L as the constant dosage

pH Parameter 3 4 5 6

Turbidity (NTU) 1176 64 424 2343

Percent removal (%) 82.0 99.0 93.5 64.2

BOD (mg/L) 12340 11415 10148 12800 Percent removal (%) 52.2 55.8 60.7 50.5

TSS (mg/L) 1090 380 603 1830 Percent removal (%) 94.4 98.0 96.9 90.5

115

C2 Optimization of Polyacrylamide as coagulant

Constant parameter:

Dosage : 500 mg/L





Table C2.1 : pH optimization for PAM at 500 mg/L as the constant dosage


Turbidity (NTU) 1369 1355 3665 3064

Percent removal (%) 79.1 79.3 44.0 53.2



116

C3 Optimization of Polyaluminum Chloride as coagulant

Constant parameter:

Dosage : 500 mg/L





Table C3.1 : pH optimization for PACl at 500 mg/L as the constant dosage


Turbidity (NTU) 1418.5 1869 1825 1554

Percent removal (%) 78.3 71.5 72.1 76.3



APPENDIX D

PHOTO OF THE COAGULANTS APPLICATION IN POME TREATMENT

0 min 15 min

30 min 60 min

Figure D1 Coagulation at optimum dosage of chitosan (250 mg/L) at different

settling time

118

0 min 15 min

30 min 60 min

Figure D2 Coagulation at optimum dosage of PAM (500 mg/L) at different settling

time

0 min 30 min

Figure D3 Coagulation at optimum dosage of PACl (500 mg/L) at different settling

time

119

60 min

Figure D3 (continued)

15 min 60 min

Figure D4 Coagulation at optimum chitosan dosage at pH 3, at different settling time

15 min 60 min

Figure D5 Coagulation at optimum chitosan dosage at pH 4, at different settling time

Documents

CHEMICAL PRECIPITATION OF PALM OIL MILL EFFLUENT (POME)