HEAVY METALS IN LANDFILL

(1)

ENHANCEMENT OF LANDFILL DAILY COVER PERFORMANCE BY USING MIXTURE OF LOCAL SOIL, PRESSMUD AND EMPTY FRUIT BUNCH IN MINIMIZING THE MIGRATION OF

HEAVY METALS IN LANDFILL

MAHEERA BINTI MOHAMAD

UNIVERSITI SAINS MALAYSIA

2018

(2)

ENHANCEMENT OF LANDFILL DAILY COVER PERFORMANCE BY USING MIXTURE OF LOCAL SOIL, PRESSMUD AND EMPTY FRUIT BUNCH IN MINIMIZING THE

MIGRATION OF HEAVY METALS IN LANDFILL

by

MAHEERA BINTI MOHAMAD

Thesis submitted in fulfillment of the requirements for the degree of

Doctor of Philosophy

September 2018

(3)

ACKNOWLEDGEMENT

First of all, I would like to express my utmost gratitude to ALLAH (SWT). All praises belong to Him for giving me strength and keeping me healthy throughout my studies. Sincere appreciation to my supervisor, Prof. Ismail bin Abustan and my co- supervisor, Dr. Kamarudin bin Samuding (Malaysian Nuclear Agency) for their guidance and consistent help throughout the study. Without them, this thesis could not be completed in time.

Special thanks to my husband Ahmad Shaiful Yazam Ahmad Asri and both of my sisters Miss Nabilah Mohamad and Miss Amirah Mohamad for their technical support, valuable encouragement and guidance throughout my study. I am also thankful to the academic members, laboratory assistants; especially Mr. Mohammed Nizam Mohd Kamal and Mr Mohad Shukri Zambri, and all technical staff of School of Civil Engineering for their assistance and cooperation during my experimentation.

I would also like to express my deepest gratitude to the Ministry of Higher Education for the scholarship provided under MyBrain 15.

In addition, a big thank you to Seberang Perai Municipal Council, Penang and Malayan Sugar Manufacturing (MSM) Prai, Penang for granting the permission to use the landfill site for my studies. Last but not least, an immeasurable appreciation from the bottom of my heart to my parents; Mohamad bin Hashim and Roshadah binti Said, my sons; Akmal Aqeel and Muhammad Adeel, and to my brother;

Dzulfadzli Mohamad, my sister in-law; Fatimah Ahmad and also my family in-law for their continuous support, encouragement, and understanding during my study.

(4)

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF TABLES ix

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xvii

ABSTRAK xx

ABSTRACT xxii

CHAPTER ONE: INTRODUCTION

1.1 Background 1

1.2 Problem Statement 6

1.3 Objectives 7

1.4 Scope of Study 8

1.5 Outline of Thesis 9

CHAPTER TWO: LITERATURE REVIEW

2.1 Introduction 11

2.2 Landfills 11

2.3 The Migration of Contaminant in Landfill 15

2.3.1 Problem of Leachate in Landfill 16

2.3.1(a) Factors Affecting Leachate Quantity 17 2.3.1(b) Factors Affecting Leachate Quality 20 2.3.1(c) Impact on Groundwater and Surface Water 23

(5)

2.4 Overview of Daily Cover 24

2.4.1 Application of Daily Cover 26

2.4.2 Alternative Daily Cover 31

2.4.3 Characterization of Daily Soil Cover 38

2.5 Heavy Metals in Landfill 40

2.5.1 Immobilization of Heavy Metals 41

2.6 Adsorption 43

2.6.1 Factors Affecting the Adsorption 46

2.6.1(a) Precipitation of Heavy Metals 47

2.7 Adsorption Model 48

2.7.1 The Kd Model Concept and Its Use in Contaminant

Transport Modelling 49

2.7.2 Methods for Determining Kd Values 51

2.7.2(a) Laboratory Batch Method 51

2.7.2(b) Laboratory Flow-Through (Column)

Method 52

2.7.3 Adsorption Models 54

2.7.3(a) Constant Partition Coefficient (Kd) Model 55

2.7.3(b) Parametric K_d Model 57

2.7.3(c) Adsorption Isotherm Models 57 2.7.3(d) Adsorption Kinetic Models 65

2.8 Optimization of Soil Mixture Preparation 67

2.9 Agricultural Wastes 69

2.10.1 Empty Fruit Bunch (EFB) 69

2.10.2 Pressmud 71

(6)

2.10 Research Gap Analysis 73

CHAPTER THREE: MATERIALS AND METHODS

3.1 Introduction 74

3.2 Research Flowchart 75

3.3 Materials 76

3.4 Sampling 77

3.5 Laboratory Test 80

3.5.1 Preparation of Samples 80

3.5.2 Characterization of Samples 82

3.5.2(a) Particle Size Distribution Analysis of

Soil Sample 84

3.5.2(b) pH Analysis of Soil, Pressmud and EFB 85 3.5.2(c) Specific Surface Area and Pore Size

Analysis 85

3.5.2(d) Cation Exchange Capacity 85

3.5.2(e) Compaction Test 88

3.5.2(f) Permeability Test 89

3.5.2(g) Unconfined Compression Test 90 3.5.2(h) X-Ray Diffraction (XRD) Analysis 92 3.5.2(i) X-Ray Fluorescence (XRF) Analysis 92 3.5.2(j) Carbon, Hydrogen, Nitrogen and

Sulphur (CHNS) Analysis 93

3.5.2(k) Fourier Transform Infrared (FT-IR)

Analysis 94

3.5.2(l) Field Emission Scanning Electron

Microscopy (FESEM) Imaging 95

(7)

3.6 Batch Equilibrium Test (BET) 95 3.6.1 Preparation of Heavy Metals Stock Solution 95

3.6.2 Batch Equilibrium Test Procedure 96

3.6.2(a) Effect of Initial Concentration 99

3.6.2(b) Effect of Contact Time 99

3.7 Optimization Study by Central Composite Design (CCD) 100

3.8 Soil Column Test 102

3.8.1 Heavy Metals Solution Preparation 102

3.8.2 Experimental Setup for Soil Column Test 103 3.8.3 Determination of Heavy Metals Concentration 105

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Introduction 106

4.2 Concentration of Heavy Metals in Pulau Burung Landfill Leachate 107 4.3 Heavy Metals Content in Soil Profile of Top Soil Cover 108 4.4 General Characteristics of Samples 111

4.4.1 Physical Characterization 116

4.4.1(a) Surface Physical Morphology of

Individual and Mixed Samples 117 4.4.1(b) Permeability Test of Individual and

Mixed Samples 120

4.4.1(c) Compaction Test of Individual and

Mixed Samples 121

4.4.1(d) Stress Strain Behavior and Shear Strength of Individual and Mixed Samples 124

4.4.2 Chemical Characterization 126

4.4.2(a) Cation Exchange Capacity of Individual

(8)

and Mixed Samples 126 4.4.2(b) Surface Functional Group of Individual

and Mixed Samples 128

4.5 Removal of Heavy Metals 131

4.5.1 Removal Efficiency Tests 131

4.5.2 Initial Concentration Effect to the Removal Efficiency 139

4.6 Batch Equilibrium Test 152

4.6.1 Adsorption Isotherm Models 152

4.6.1(a) Soil 153

4.6.1(b) Pressmud 160

4.6.1(c) EFB 166

4.6.1(d) 50S:40P:10E 171

4.6.1(e) 50S:30P:20E 177

4.6.1(f) 50S:25P:25E 183

4.6.1(g) 50S:10P:40E 189

4.6.1(h) 50S:20P:30E 195

4.6.2 Adsorption Kinetics 201

4.6.2(a) Soil 201

4.6.2(b) Pressmud 203

4.6.2(c) EFB 204

4.6.2(d) 50S:40P:10E 206

4.6.2(e) 50S:30P:20E 208

4.6.2(f) 50S:25P:25E 209

4.6.2(g) 50S:10P:40E 210

4.6.2(h) 50S:20P:30E 212

4.6.3 Optimization Study 216

(9)

4.6.3(a) Statistical Analysis 217 4.6.3(b) Effects of Operating Variables 223 4.6.3(c) Optimization and Validation 226

4.7 Column Test 227

4.7.1 Soil 227

4.7.2 Pressmud 228

4.7.3 EFB 229

4.7.4 50S:40P:10E 230

4.7.5 50S:30P:20E 231

4.7.6 50S:25P:25E 233

4.7.7 50S:10P:40E 234

4.7.8 50S:20P:30E 235

4.8 Summary of Result 240

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATION

5.1 Conclusion 248

5.2 Recommendation 251

REFERENCES 252

APPENDICES

LIST OF PUBLICATIONS

(10)

LIST OF TABLES

Page Table 2.1 Summary of work done by previous researchers using 38

variety of material for cover improvements

Table 2.2 Landfill directive requirement 39

Table 2.3 Cation exchange capacities (CEC) for several clay 45 minerals

Table 3.1 List of chemical reagents that have been used in this 76 research study

Table 3.2 Individual material and mixture ratio 83 Table 3.3 Details of laboratory compaction methods 89 Table 3.4 Central composite design for two factors with their levels 101 Table 4.1 Heavy metals concentration in Pulau Burung Landfill 107

leachate

Table 4.2 Basic properties of local soil at landfill, pressmud and 115 EFB

Table 4.3 Results of permeability test 121

Table 4.4 Summary of maximum dry density and optimum water 123 content of the tested sample

Table 4.5 Summary of unconfined compressive test 124 Table 4.6 Result of cation exchange capacity 126 Table 4.7 List of the functional group in the soil-pressmud- 130

EFB mixtures

Table 4.8 Summary of the percentage removal of heavy metals 139 Table 4.9a Removal efficiency of Cd for all media 150 Table 4.9b Removal efficiency of Cr for all media 150 Table 4.9c Removal efficiency of Cu for all media 151

(11)

Table 4.9d Removal efficiency of Fe for all media 151 Table 4.9e Removal efficiency of Mn for all media 151 Table 4.9f Removal efficiency of Ni for all media 152 Table 4.9g Removal efficiency of Zn for all media 152 Table 4.10 Langmuir and Freundlich isotherm constants and 158

coefficients (Soil)

Table 4.11 Langmuir and Freundlich equations of soil adsorbent 159 Table 4.12 Langmuir and Freundlich isotherm constants and 165

coefficients (Pressmud)

Table 4.13 Langmuir and Freundlich equations of pressmud 165 adsorbent

Table 4.14 Langmuir and Freundlich isotherm constants and 170 coefficients (EFB)

Table 4.15 Langmuir and Freundlich equations of EFB adsorbent 170 Table 4.16 Langmuir and Freundlich isotherm constants and 175

coefficients (50S:40P:10E)

Table 4.17 Langmuir and Freundlich equations of 175 50S:40P:10E adsorbent

Table 4.18 Langmuir and Freundlich isotherm constants and 180 coefficients (50S:30P:20E)

(12)

Table 4.26 Kinetic constants for Pseudo-First Order and 201 Pseudo-Second Order Models of the sorption process

(Soil)

(Pressmud)

(EFB)

(50S:40P:10E)

(50S:30P:20E)

(50S:25P:25E)

(50S:10P:40E)

(50S:20P:30E)

Table 4.34 Summary of adsorption at equilibrium result from media 214 Table 4.35 Experimental design data with the corresponding 219

actual response

Table 4.36 Model validation for optimization procedures 225 Table 4.37 Summary of the breakthrough of heavy metals from 238

media

Table 4.38 Characterization of the materials that can be related to 242 the suitability as a good daily cover

(13)

Table 4.39 Summary of the results that obtained from batch 245 and column test

(14)

LIST OF FIGURES

Page

Figure 2.1 Cross section of an operating of sanitary landfill 14 Figure 2.2 Local soil as daily cover in Pulau Burung Landfill 28

Figure 2.3 Typical breakthrough curves 53

Figure 2.4 Four types of adsorption isotherm curves shown 61 schematically

Figure 3.1 Flowchart of research study 75

Figure 3.2 Location of leachate sampling 77

Figure 3.3 Location of collected soil profile in the study area 78 Figure 3.4 A typical soil covers in Pulau Burung Landfill 78 Figure 3.5 Site location of Pulau Burung Landfill 79

Figure 3.6 Soil sample 81

Figure 3.7 Pressmud sample 81

Figure 3.8 EFB sample 82

Figure 3.9 A) Sample trimming, B) Load and deformation dial 91 gauges, C) Compression device, and D) Sample during the testing

Figure 3.10 Centrifuge tube 96

Figure 3.11 Schematic drawing dimension of column test 103

Figure 3.12 Leaching of soil column test 104

Figure 4.1 Pb concentration in soil profile of top soil cover 109 Figure 4.2 Zn concentration in soil profile of top soil cover 110 Figure 4.3 Particle size distribution analysis for soil 116 Figure 4.4 Surface physical morphology of: a) soil, b) pressmud 118

and c) EFB

(15)

Figure 4.5 Surface physical morphology of: a) 50S:40P:10E, 119 b) 50S:30P:20E, c) 50S:25P:25E, d) 50S:10P:40E

and e) 50S:20P:30E

Figure 4.6 Compaction test graph 122

Figure 4.7 FTIR spectrums of soil 128

Figure 4.8 FTIR spectrums of pressmud 128

Figure 4.9 FTIR spectrums of EFB 129

Figure 4.10 FTIR spectrums of soil-pressmud-EFB mixtures 129 Figure 4.11 Removal percentage of Cd from the solution 132 Figure 4.12 Removal percentage of Cr from the solution 133 Figure 4.13 Removal percentage of Cu from the solution 134 Figure 4.14 Removal percentage of Fe from the solution 135 Figure 4.15 Removal percentage of Mn from the solution 136 Figure 4.16 Removal percentage of Ni from the solution 137 Figure 4.17 Removal percentage of Zn from the solution 138 Figure 4.18 Effect of initial Cd concentration on the removal efficiency 140 Figure 4.19 Effect of initial Cr concentration on the removal efficiency 142 Figure 4.20 Effect of initial Cu concentration on the removal efficiency 143 Figure 4.21 Effect of initial Fe concentration on the removal efficiency 145 Figure 4.22 Effect of initial Mn concentration on the removal efficiency 146 Figure 4.23 Effect of initial Ni concentration on the removal efficiency 147 Figure 4.24 Effect of initial Zn concentration on the removal efficiency 148

Figure 4.25 Langmuir isotherm model for Soil 154

Figure 4.26 Freundlich isotherm model for Soil 157 Figure 4.27 Langmuir isotherm model for Pressmud 161 Figure 4.28 Freundlich isotherm model for Pressmud 164

(16)

Figure 4.29 Langmuir isotherm model for EFB 167 Figure 4.30 Freundlich isotherm model for EFB 168 Figure 4.31 Langmuir isotherm model for 50S:40P:10E 172 Figure 4.32 Freundlich isotherm model for 50S:40P:10E 173 Figure 4.33 Langmuir isotherm model for 50S:30P:20E 177 Figure 4.34 Freundlich isotherm model for 50S:30P:20E 178 Figure 4.35 Langmuir isotherm model for 50S:25P:25E 183 Figure 4.36 Freundlich isotherm model for 50S:25P:25E 184 Figure 4.37 Langmuir isotherm model for 50S:10P:40E 189 Figure 4.38 Freundlich isotherm model for 50S:10P:40E 190 Figure 4.39 Langmuir isotherm model for 50S:20P:30E 195 Figure 4.40 Freundlich isotherm model for 50S:20P:30E 196 Figure 4.41 Maximum adsorption capacity of heavy metals onto media 199 Figure 4.42 a) Pseudo-first order and b) Pseudo-second order kinetics 201

of heavy metals on soil

Figure 4.43 a) Pseudo-first order and b) Pseudo-second order kinetics 203 of heavy metals on pressmud

Figure 4.44 a) Pseudo-first order and b) Pseudo-second order kinetics 204 of heavy metals on EFB

Figure 4.45 a) Pseudo-first order and b) Pseudo-second order kinetics 206 of heavy metals on 50S:40P:10E

(17)

Figure 4.50 Predicted versus actual values plot for heavy metals 221 Removal (%); a) Cd, b) Cr, c) Cu, d) Fe, e) Mn, f) Ni

and g) Zn

Figure 4.51 3D surface plot showing the effect of initial concentration 224 and contact time on the removal of heavy metals: a) Cd,

b) Cr, c) Cu, d) Fe, e) Mn, f) Ni and g) Zn

Figure 4.52 Breakthrough curve of heavy metals for soil 227 Figure 4.53 Breakthrough curve of heavy metals for pressmud 228 Figure 4.54 Breakthrough curve of heavy metals for EFB 229 Figure 4.55 Breakthrough curve of heavy metals for 50S:40P:10E 230 Figure 4.56 Breakthrough curve of heavy metals for 50S:30P:20E 231 Figure 4.57 Breakthrough curve of heavy metals for 50S:25P:25E 232 Figure 4.58 Breakthrough curve of heavy metals for 50S:10P:40E 234 Figure 4.59 Breakthrough curve of heavy metals for 50S:20P:30E 235

(18)

LIST OF ABBREVIATIONS

AAS Atomic Absorption Spectrometry ANOVA Analysis of Variance

ASTM American Society for Testing and Materials

ATSDR Agency for Toxic Substances and Disease Registry BDL Below Detection Limit

BET Batch Equilibrium Test BOD Biochemical Oxygen Demand BS British Standard

CCD Central Composite Design CEC Cation Exchange Capacity

CIRIA Construction Industry Research & Information Association COD Chemical Oxygen Demand

CV Coefficient of Variance DOE Department of Environment EDTA Ethylenediaminetetraacetic acid EFB Empty Fruit Bunch

EP Extraction Procedure

EPA Environmental Protection Agency

(19)

EQA Environmental Quality Act

ETPI Environmental Technology Program for Industry

FELCRA Federal Land Consolidation and Rehabilitation Authority FELDA Federal Land Development Authority

FESEM-EDX Field Scanning Electron Microscopy & Energy Dispersive X-Ray FRIM Forest Research Institute Malaysia

FTIR Fourier Transform Infra-Red GAC Granular Activated Carbon GRC Geotechnical Research Centre HDPE High Density Polyethylene

ICP-OES Inductively Coupled Plasma-Optical Emission Spectrometry IOI Industrial Oxygen Incorporated

LFG Landfill Gas

LOF Lack of Fit

MPC Maximum Permissible Concentration MPCA Minnesota Pollution Control Agency MPOB Malaysian Palm Oil Board

MPOC Malaysian Palm Oil Council MSM Malayan Sugar Manufacturing

(20)

MSW Municipal Solid Waste NRE Natural Red Earth

OM Organic Matter

PORIM Palm Oil Research Institute of Malaysia

PV Pore Volume

RCRA Resource Conservation and Recovery Act

RISDA Rubber Industry Smallholders Development Authority RSM Response Surface Methodology

SEPA Scottish Environmental Protection Agency TCLP Toxicity Characteristics Leaching Procedure TDS Total Dissolved Solid

TKN Total Kjeldahl Nitrogen TOC Total Organic Carbon

US United States

USEPA United State Environmental Protection Agency WHO World Health Organization

XRD X-Ray Diffraction System

(21)

PENAMBAHBAIKAN PRESTASI PENUTUP HARIAN TAPAK PELUPUSAN SISA PEPEJAL MENGGUNAKAN CAMPURAN TANAH TEMPATAN, KEK

LUMPUR DAN TANDAN SAWIT KOSONG DALAM MEMINIMAKAN PENGHIJRAHAN LOGAM BERAT DI TAPAK PELUPUSAN SISA

PEPEJAL

ABSTRAK

Peningkatan kepekatan logam berat dalam larut lesap tapak pelupusan sisa pepejal adalah membimbangkan kerana ia merupakan bahan utama kepada terjejasnys kualiti kesihatan manusia dan persekitaran sekitarnya. Pengubahsuaian penutup tanah harian tapak pelupusan sisa pepejal adalah pilihan yang baik untuk mengurangkan pergerakan logam berat di dalam sel pelupusan sampah. Dalam kajian ini, sampel tanah tempatan kemudian dicampur dengan pressmud iaitu bahan buangan daripada proses pembuatan gula dan tandan kosong buah kelapa sawit (EFB) dengan peratusan berat yang berbeza. Seterusnya, eksperimen penjerapan dilakukan secara kajian kelompok untuk mengkaji keberkesanan campuran tanah-pressmud-EFB dalam menyingkirkan logam berat. Keberkesananya dibandingkan dengan penggunaan tanah, pressmud dan EFB secara individu. Pencirian bagi tanah dan juga campuran tanah-pressmud-EFB secara fizikokimia dan geoteknikal, seterusnya ujian luluhlarut dijalankan. Kaedah ujian luruhlarut termasuk ujian keseimbangan kelompok dan ujian turus tanah. Daripada kajian pencirian, terdapat beberapa penambahbaikkan sifat fizikokimia dan pencirian kejuruteraan bagi campuran berbanding dengan tanah sahaja. Campuran tanah-pressmud-EFB berkeupayaan menyingkirkan lebih daripada 59% sehingga 98.9% kandungan Cd, Cr, Cu, Fe, Mn, Ni and Zn penyingkiran logam berat daripada larutan. Sementara itu, kecekapan

(22)

penyingkiran logam berat di dalam tanah adalah masing-masing daripada 1.6%

sehingga 33.3% sahaja manakala pressmud pula menunjukkan daripada 78.4%

sehingga 99.7% penyingkiran. EFB hanya menunjukkan 19.9% sehingga 56.2%

penyingkiran. Kaedah respon balas permukaan (RSM) mengenai reka bentuk komposit pusat (CCD) telah digunakan untuk mengoptimumkan pembolehubah operasi terhadap keberkesanan setiap respon daripada segi kecekapan penyingkiran kepekatan awal dan masa tindak balas. Berdasarkan hasil ujikaji, 4.05 mg/L kepekatan awal dan 30 minit masa tindak balas diperlukan untuk penyingkiran untuk semua logam berat. Keputusan ujian turus yang berdasarkan kepada kajian pencirian, kecekapan penyingkiran dan penjerapan bahan campuran tanah-pressmud-EFB khususnya 50S:40P:10E adalah lebih sesuai dan mempunyai potensi yang baik untuk digunakan sebagai bahan penutup tanah harian untuk meminimakan penghijrahan logam berat dalam larut lesap di tapak pelupusan sisa pepejal.

(23)

ENHANCEMENT OF LANDFILL DAILY COVER PERFORMANCE BY USING MIXTURE OF LOCAL SOIL, PRESSMUD AND EMPTY FRUIT BUNCH IN MINIMIZING THE MIGRATION OF HEAVY METALS IN

LANDFILL

ABSTRACT

An increase of heavy metals concentration in landfill leachate is a concern as it is a major threat to human health and surrounding environment. Landfill daily soil cover amendment is a good option to reduce the mobility of heavy metals in the landfill cell. In this study, local soil samples were mixed with waste from sugar manufacturing process, pressmud and empty fruit bunch (EFB) of palm oil at different percentage of weight ratio. Then, batch adsorption experiments were performed to evaluate the effectiveness of soil mixtures in removing the heavy metals. Their performances were compared to the individual performance of the soil, pressmud and EFB. The physicochemical and geotechnical properties of the soil, pressmud, EFB and soil-pressmud-EFB mixtures characterization as well as leaching test were carried out. The leaching test method included batch equilibrium test and soil column test. From the characterization study, there were some improvements on the physicochemical and engineering properties of mixtures compared to soil alone.

Batch equilibrium test showed that the soil-pressmud-EFB mixtures have the capability to remove more than 59% to 98.9% Cd, Cr, Cu, Fe, Mn, Ni and Zn metals from solution. Meanwhile, the removal efficiency of heavy metals from solution in the soil alone was ranged from 1.6% to 33.3%. Pressmud alone, however, showed 78.4% to 99.7% heavy metals removal while EFB indicated 19.9% to 56.2%

removal. The response surface methodology (RSM) concerning Central Composite Design (CCD) was used to optimize the experimental condition in the removal of

(24)

heavy metals. According to the results, initial concentration of 4.05 mg/L and 30 minutes contact time were required to effectively remove all heavy metals. Based on the characterization study, the removal efficiency and the column test, the soil- pressmud-EFB mixture particularly 50S:40P:10E was the most suitable combination and possessed great potential as daily cover to reduce heavy metals migration in landfill leachate.

(25)

CHAPTER ONE

INTRODUCTION

1.1 Background

A landfill is defined as that system designed and constructed to contain discarded waste so as to minimize releases of contaminants to the environment.

Landfills are necessary because (1) other waste management technologies such as source reduction, recycling and waste minimization cannot totally eliminate the waste generated and (2) waste treatment technologies such as incineration and biological treatment produce residues (LaGrega et al, 2001). Landfills are the most widely used facilities for solid waste disposal all over the world (Aziz et al, 2016;

Aljaradin, 2015; El-Salam and Abu-Zuid, 2015).

Nowadays, increasing population growth and industrial development in Malaysia have increased the generation of municipal solid waste (MSW). MSW can be defined as the wastes generated from domestic, commercial, industrial and institutional activities (Ravindra et al., 2015). Most landfills in Malaysia do not have proper covers which resulted in potential problems of groundwater and surface water contamination because of the leachate generated from solid waste in landfill (Aziz et al., 2016). Therefore, due to these arising environmental issues regarding landfilling, cover system implementation should be taken into consideration. The landfill cover system can be used to minimize exposure on the surface of the waste facility, and prevent vertical infiltration of water into wastes that would create contaminated leachate (EPA, 1991).

Landfilling practice is basically a process of dumping waste in trenches after manual sorting and followed by covering it with 0.5 m thick of soil on a daily basis.

(26)

This means that the daily cover remains within the landfill after the next lift of waste and often ends up as the final cover of the landfill. For this reason, it is vital to select the appropriate type of cover to promote drainage. In general, the thickness of waste within the landfill ranges from 6 to 20 m (Chopra, 2001; Aljaradin and Persson, 2010). The dumped waste includes solid waste and liquid waste with a high water content that can generate more leachate with more toxicity. Generation of leachate from MSW landfill has been long neglected with the assumption that minimal leachate could be formed in the absence of precipitation. Many studies, on the other hand, have identified the potential of contamination occurrence is due to uncontrolled landfilling (e.g., Teta and Hikwa, 2017; Kamaruddin et al., 2015). In addition, Aljaradin and Persson, (2015) found that the water held in the surface soils by capillary action can infiltrate through the solid waste. As a result, the leachate will eventually migrate toward the water table beneath the landfill contaminating the soil and the aquifer system.

The use of soil cover in landfills is important in protecting health and the environment, leading to less landfill volume available for compacted waste and providing good operational practice to prevent scattering of waste. As a result of these concerns, there is a great interest worldwide in ways to minimize the amount of soil cover used in landfills and to execute different cover types. For example, in some countries, less space demanding geotextiles, foams or other forms of waste (e.g., recycled tyres) have been used in place of cover soil. However, these types of daily cover alternatives are prohibitively expensive and impractical within developing countries. Using local soils or blends of them as daily cover is a much more accessible way to minimize the environmental consequences of waste disposal.

Therefore, in order to have a low cost and sustainable landfilling process, it is

(27)

necessary to execute the most efficient cover from the native soils (Aljaradin and Persson, 2015). In landfill technology, landfill soil needs to be amended or mixed with other materials in order to enhance the performance of soil stabilization in terms of geotechnical and physicochemical properties as well to reduce the pollutant in landfill. This is because soil cover in landfill acts as a medium for the migration of pollutant in leachate, especially heavy metals, before seeping to the surface water.

There are several materials that can be used for landfill cover system like sand, clay, silt and sludge generated from industrial wastewater treatment plants. The functions of covering systems are to promote drainage, minimize erosion of the cover, accommodate settling and have hydraulic conductivity less than or equal to that of any bottom liner system or natural soil present (Aziz et al., 2016 and Chabuk et al., 2018). There are three types of cover that can be used in a landfill which are daily cover, intermediate cover and final cover. Daily cover is placed over the entire working face at the end of each working day. Typically, daily cover uses soil, however, other daily cover alternatives may also be approved. Normally, 15 cm of soil is used as daily cover. Intermediate cover must be placed on areas with received waste but then will be inactive for a period of longer than 180 days. Intermediate cover must be at least 30 cm in thickness. Lastly, final cover is placed over areas of the landfill that have reached full capacity and final design waste grades. The final cover system typically consists of multiple layers of materials. A final layer of cover material is used when the fill reaches the final design height (Peavy et al., 1985).

One of the possible ways to reduce the migration of heavy metals in leachate is by enhancing daily soil cover material with local soil as a mixture of daily cover in landfill. Nowadays, researchers are not only focusing on the hydraulic transport of contaminants, but also on reducing the diffusion of contaminants through daily soil

(28)

cover and the chemical processes. All of these cover materials are emerging to increase the sorption capacity of daily soil covers especially through the application of mixtures in the soil materials (Aljaradin, 2015; Ng and Lo, 2010). Every landfill requires a large amount of cover materials, however, it is essential to begin the transition from open dumping to sanitary landfilling since it has huge environmental benefits (Aljaradin, 2015; Aljaradin and Persson, 2010).

In Malaysia, the environmental challenge for the local sugar mills is associated with liquid waste, gaseous emission and solid waste. There are three major departments in sugar manufacturing namely mill house, process house and boiler house. Main sources of solid waste are from mill house (bagasse), process house (pressmud and molasses), and boiler house (fly ash) (ETPI, 2001).Pressmud is the compressed sugar industry waste produced from the vacuum filtration of the cane juice. It is a good source of fertilizer. Sugar mills produce millions of tons of pressmud (filter cake) as a waste from double sulphitation processes. The precipitated impurities contained in the cane juice, after removal by filtration, form a cake of varying moisture content known as pressmud or filter mud. This cake contains much of the colloidal organic matter anions that precipitate during clarification, as well as certain non-sugars occluded in these precipitates (Akhtar et al., 2017). Pressmud contains, on a dry basis, about 1 percent by weight of phosphate (P₂O₅) and about 1 percent of nitrogen. Therefore, it has been used as a fertilizer (James and Pandian 2017). It contents 50–70 % moisture, which is most favorable for soil micro-organisms, especially earth-worms (Dominguez, 1997). The composition of pressmud is also affected by variety, fertility status of soil, and also the recovery process of industries. It contains significant amounts of iron, manganese, calcium, magnesium, silicon, and phosphorus, and enhanced the

(29)

suitability of pressmud as a source of nutrient (Yadav and Solomon, 2006).

Pressmud, an end product of the sugar industry, is used as one of the substrates in bio-composting (Chand et al., 2011). The pressmud is also generated from the alcohol distillation originating from the fermentation of sugarcane molasses; it contains a huge volume of water and plant nutrients. Therefore, it is a necessity for treating pressmud to a valuable bio-fertilizer for agricultural crop production (Dotaniya et al., 2016 and Patil et al., 2013).

Malaysia is among the top most important oil palm producers in the world and experiencing a robust development in new plantations and palm oil mills through giant government companies (FELDA, FELCRA, and RISDA) and private estates (Guthrie, IOI Plantations, Genting Plantations, and Sime Darby) (Faizi et al., 2017).

EFB supply is available and its continuous production at palm oil mills makes it a great prospect for commercial exploitation. Thus, these materials have been widely used in agriculture and industry. The fresh EFB from the mill usually contains 30.5%

lignocellulose, 2.5% oil, and 67% water; and the main constituents of the lignocellulose are cellulose, hemicellulose, and lignin. Those constituents are physically hard and strong. Hence, the EFB basically possess qualities promising for further applications. In Malaysia, for an example, the EFB has been used to produce a medium density fiberboard. However, to be able to further use the EFB fiber, particularly for an engineering application, it is necessary to quantify the fiber mechanical properties (Gunawan et al., 2009). A potential use of EFB, which has received little attention, is in soil stabilization. Shredded EFB can be mixed with soil to improve their engineering properties for specific applications (Samuding, 2010).

Pressmud and EFB can be mixed with soil to improve their engineering properties for specific utilizations and capability to remove heavy metals from the leachate in

(30)

landfill. The spread of pollutants or contaminants in soil can be hindered by the soil stabilization technique (Edao, 2017; Onyelowe and Chibuzor, 2012).

1.2 Problem Statement

Most of the landfill in developing countries does not have any covers which results in the potential problems of ground water/surface water contamination due to the leachate generated from the solid waste landfill. Therefore, landfills must be separated away from the surrounding environment. Some environmental aspects for landfilling should be considered such as cover or capping system. The landfill capping system can be used to minimize exposure on the surface of the waste facility, and prevent vertical infiltration of water into wastes that would create contaminated leachate (Aziz et al., 2016 and EPA, 1991).

Several materials can be used for landfill cover system like sand, clay, silt and sludge generated from industrial waste water treatment plants. Cover materials should restrict surface water infiltration into the contaminated subsurface to reduce the potential for contaminants to leach from the site. Covering systems must function with minimum maintenance, promote drainage, minimize erosion of the cover, accommodate settling, and have hydraulic conductivity less than or equal to that of any bottom liner system or natural soil present (Aziz et al., 2016 and We and, 2010).

In humid climates, cover and/or re-vegetation are usually required for erosion protection and infiltration control. The regulations do, however, permit alternative designs if they can achieve erosion and infiltration protection equivalent to an acceptable conventional cover system. This indicates the significance of searching different alternatives to compacted clay-based covers or barriers in arid areas and evaluates their performance under various environmental conditions (Fatta and

(31)

Loizidou, 2011). Many laboratory tests are needed to ensure that the materials being considered for each of the landfill cover components are suitable. Landfill instability can be solved by understanding the interface friction properties between all material layers, natural or synthetic (Aziz et al., 2016).

A variety of heavy metals are found in landfill leachate such as iron, zinc, copper, cadmium, lead, nickel, chromium and mercury. They are either soluble components of the refuse or are products of physical processes such as corrosion.

Heavy metal concentrations in leachate increase over a period of time as they are non-biodegradable and accumulated in living tissues and finally became a threat to human health. Therefore, by introducing and amending the daily cover with other materials that have the capability of adsorbing metals, it can reduce the migration of heavy metals pollutants in landfill cells.

In this proposed study, local soil cover was enhanced by mixing soil with 2 types of wastes namely pressmud, which was obtained from sugar manufacturing waste, and empty fruit bunch (EFB) of palm oil at different ratio in order to improve the capability of daily soil cover in minimizing the migration of heavy metals in landfill. This study introduced pressmud and EFB as new admixture materials in landfill daily cover to reduce the migration of heavy metals in landfill.

1.3 Objectives

The main objectives of this study are as follows:

1. to determine physico-chemical properties and geotechnical properties of the local soil and soil-pressmud-EFB mixtures.

2. to determine the migration of heavy metals in the proposed soil mixtures.

(32)

3. to evaluate the suitability and the significance of the proposed landfill daily cover with optimal mixture of local soil, pressmud and EFB.

1.4 Scope of Study

This research investigates and evaluates the ability of pressmud and EFB mixed with soil to reduce and minimize the migration of heavy metals in landfill leachate. It involves field samples collection and laboratory experiments. The field sampling involves the collection of leachate from municipal solid waste disposal site and fresh soil from several areas in Nibong Tebal, Penang, while laboratory experiments involve physico-chemical analysis and characterization of soil and suitability of the soil implemented at the specific landfill site.

Physico-chemical, geotechnical, batch equilibrium test (BET) and column tests were conducted on the materials. BET was performed to evaluate the removal efficiency of heavy metals. In order to determine the suitability of the soil-pressmud- EFB mixtures usage from industrial waste material, column tests were carried out to investigate the removal of heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni) and zinc (Zn) which were among the significant pollutants present in the Pulau Burung landfill leachate plume.

These data (from characterization and adsorption behavior) were used to evaluate the potential use of soil-pressmud-EFB mixtures as a daily soil cover. Physico-chemical characterizations and geotechnical properties were studied in this research, focusing on the pattern and trend in removal capability of the new materials namely pressmud and EFB.

(33)

1.5 Outline of Thesis

This thesis contains 5 chapters (including this chapter) as follows;

Chapter 1: Introduction: This chapter introduces the background of the study, presents the problem statement, list of objectives, scope of the research and outline of thesis.

Chapter 2: Literature Review: This chapter discusses and elaborates on the groundwater aspects such as the groundwater status in terms of quality and quantity, groundwater pollution and the sources of groundwater pollution. It discusses about the solid waste disposal site and emphasizes more on the leachate quality and quantity. Besides, this chapter provides information on the overview of subsurface containment that contained the daily cover development, function and nature of engineered covers, as well as characterization and improvement of the cover materials. This research emphasizes more on the behavior of the heavy metals studied. This chapter also discusses about the adsorption model concept, optimization by using response surface methodology (RSM) and column study.

Chapter 3: Materials and Methods: This chapter presents the field sampling techniques, laboratory experimental programed and analytical equipment that were used in this study. Field sampling involved the collection of leachate and soil profile at the study site. The methods to characterize the samples are also presented in this chapter. Experimental procedures of the batch equilibrium test, including optimization sequence using RSM and column test were also discussed.

Chapter 4: Results and Discussion: This chapter contains analytical data obtained from the experimental work. The concentrations of leachate or contaminant species at the waste disposal site are presented. The characterization of the proposed

(34)

materials as adsorbent are also investigated. The removal efficiencies of heavy metals such as Cd, Cr, Cu, Fe, Mn, Ni and Zn from the contaminant in batch tests using soil, pressmud, EFB and soil-pressmud-EFB mixtures are determined.

Adsorption isotherm models, Langmuir and Freundlich isotherms, are plotted to determine the best fit models. Adsorption kinetic models i.e. Pseudo-first order and Pseudo-second order model are plotted using the results and presented. Optimum removal efficiency of heavy metals involved are also obtained from RSM.

Breakthrough curves of the pollutant species from the column test data are plotted and discussed.

Chapter 5: Conclusion and recommendations: This chapter summarizes all of the findings of the research and makes conclusion based on them. Besides that, future work is also recommended.

(35)

CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction

This chapter is divided into several subtopics. The first topic discusses the general information on landfills. The second topic presents the solid waste disposal site and further focuses on the problem of landfill leachate. The third topic discusses in detail on the overview of containment landfill daily cover in order to minimize the migration of landfill leachate plume. The fourth topic explains about the selected heavy metals in more details. The fifth section discusses the adsorption concept and mechanism involved for the proposed daily cover. Finally, the sixth section extensively discusses about the statistical analysis used in this study including the principles and application of RSM and CCD approaches, accordingly. Besides, the regeneration of adsorbent is also discussed in detail.

2.2 Landfills

Prosperous lifestyles and continuing industrial and commercial growth in many countries around the world during the past decades have been accompanied by rapid increases in both municipal and industrial solid waste production (Jumaah et al., 2015). Municipal solid waste (MSW) generation continues to grow both in per capita and overall terms (Wang et al., 1982). Methods such as recycling, composting and incineration are promoted as alternatives to landfill method. However, even the most incineration method creates residue of approximately 10-20 % that must be ultimately landfilled (Johansson and Nils, 2014). Currently, modern landfills are complex engineered facilities designed to eliminate or minimize the adverse environmental impact of the waste on the surrounding areas (Jumaah et al., 2016).

(36)

In spite of the fact that many alternative methods of MSW treatment was introduced, sanitary landfilling is currently the most common municipal solid waste disposal method in many countries due to its relatively simple procedure and low cost (Norma et al., 2012; Jumaah and Othman 2015b). Up to 95 % of the total MSW collected worldwide is being disposed of in landfills (Adamcová et al., 2016). After landfilling, solid waste undergoes physico-chemical and biological changes.

Consequently, the degradation of the organic fraction of the wastes in combination with percolating rainwater leads to the production of a dark colored and highly polluted liquid called “leachate”.

The Fukuoka method semi-aerobic system was developed more than 20 years ago at the Fukuoka University but it is not widely known to many countries around the world. It is a proven technology practically tested in many places in Japan, and in a few developing countries such as Malaysia, Iran and China. Generally, the Fukuoka method semi-aerobic landfill system can be explained as a system where the leachate and gas are continuously removed from the waste mass using leachate collection and gas venting systems, with proper engineering designs in which the ambient air flows into the waste body naturally through the leachate collection pipes, and subsequently improves the waste stabilization process and increases the leachate quality due to the enhancement of the micro-organisms activities in the waste body (Amiri et al., 2016).

A sanitary landfill is an engineered method in which solid wastes are disposed of by spreading them in thin layers, compacting them to the smallest practical volume and covering them with earth each day in a manner that minimizes environmental pollution. The disposal site shall: (1) be easily accessible in any kind of weather to all vehicles expected to use it; (2) safeguard against water pollution originating from the disposed solid waste; (3) safeguard against uncontrolled gas

(37)

movement originating from the disposed solid waste; (4) have an adequate quantity of earth cover material that is easily workable, compactible, free of large objects that would hinder compaction, and does not contain organic matter of sufficient quantity and distribution conducive to the harborage and breeding of vectors; (5) conform with land use planning of the area (EPA, 1971).

Landfill plays the most important role in the solid waste disposal because it is economical and is usually used as the final resort. Solid waste leachate with its high organic and inorganic strength and quantities are however containing more major polluting substances compared with wastewater (Ozel et al., 2008; Ozel et al., 2012).

Leachate is generated by water passing through solid wastes with biological and chemical constituents leaching into the subsoil (Tchobanoglous et al., 1993; Koerner and Soong, 2000). Leachate discharge into the subsoil causes groundwater pollution, so landfill technology needs to be implemented in preventing and controlling the leachate problems. Therefore, barrier or cover systems are used in order to mitigate the negative effects of the leachate. The technology of modern sanitary landfilling includes cover systems over the waste to control nuisances, to protect the environment, and to protect the health and safety of workers and the public.

Depending on the location of the fill and the phase of the construction and operation, the cover systems employed are categorized as daily, intermediate, and final. Figure 2.1 shows the cross section of an operating of sanitary landfill.

(38)

Figure 2.1: Cross section of an operating of sanitary landfill (UNEP, 2005) The daily and intermediate covers are placed more or less continuously during the active phase of the filling operation, or in other words, they consist of compressed soil or earth which is laid on top of a day's deposition of waste on an operational landfill site. The final cover is usually applied after the landfill or a single landfill cell has reached its final capacity. First the waste needs to be covered by an intermediate cover layer, which is insensitive to settlements of the landfill surface. In the context of economically developing countries, the design and materials selection for the construction of each of the three types of cover systems are subjected to short- and long-term risks posed by the operation of the fill, the availability of suitable materials, and financial resources (ISWA, 2013).

Using daily cover on landfills helps to control odors, reduce windblown litter and inhibit fires, as well as minimizing the percolation of water through the waste which leads to the generation of leachate. Placing soil over freshly disposed waste is time consuming and requires large volume of soil. The potential saver of time and

(39)

material at specific sites is the motivating force behind the consideration to the usage of alternative daily cover materials. Using local soils or blends of them as daily cover is a much more accessible way to minimize the environmental consequences of waste disposal. Therefore, in order to have a low cost and sustainable landfilling process, it is necessary to execute the most efficient cover from the native soils (Aljaradin, 2015). A growing variety of alternative materials are available to site operators in lieu of soil. These include spray applied foams and cellulose/polymer mixtures, geotextiles, modified soils, and waste-based materials (Medne et al., 2015).

The decision to use an alternative daily cover material is a site-specific procedure.

The benefits of using these materials can become striking from both the labor and material savings and the landfill volume saving aspects (Medne et al., 2015; Carson, 1992).

2.3 The Migration of Contaminant in Landfill

Engineered soil daily covers constitute important components of general landfill cover systems because of their ability to attenuate contaminant transport through the system when the proper choice of soil materials is made. Apart from its low cost, natural materials can retard the flow of leachates and chemically attenuate contaminant transport through various sorption processes. The most suitable types of soils are those which possess high cation exchange capacities (CEC), large specific surface areas, and high chemical buffering capacities (Yong et al., 2001 and 1999).

The use of clay soils as impermeable or attenuating barriers is becoming more popular as the material of choice in landfill liner systems. Many researchers (Ige, 2013; Griffin et al., 1976; Yanful et al., 1988; Yong et al., 1992; Yong and Phadungchewit, 1993, etc.) had discussed the different aspects and potential use of

(40)

soil material not only for liners, but also as substrate material under landfills. Heavy metals such as Pb, Cu and Zn that are commonly found in leachate from landfills can be effectively attenuate by such soils. The amount of heavy metals retained depends on the pH of the soil-water (leachates) and they are retained in soils by hydroxide and carbonate when the pH of the soil solution is higher than 4 (Yong et al., 2001;

Yong et al., 1999). The primary mechanism for Pb, Cu and Zn retention in clay soils is through precipitation of the metal ions with carbonates and amorphous oxides or hydroxides (Griffin et al., 1976). Yong and Phadungchewit (1993) have shown that the presence of carbonates in a soil contributes significantly to the retention capability of the soil (Yong et al., 2001).

Leachate is known as a liquid that passes through the waste refuse and water generated within the landfill site (Fard et al., 2017). The solid waste management facility regulations require that a groundwater protection system (commonly referred to as a cover and liner system) be installed at all new or expanding landfills. The purpose of cover or a liner system is to prevent leachate from reaching groundwater by collecting leachate for treatment and disposal. By preventing the movement of leachate into groundwater, the cover serves to protect groundwater and surface water from pollution. A cover of landfill is intended to be a low permeable barrier, which is laid down above wastes in engineered landfill sites (Mahmud and Alamgir, 2014).

2.3.1 Problem of Leachate in Landfill

Landfill leachate is one of the main sources of groundwater and surface water pollution if it is not properly collected, treated and safely disposed. It may percolate through soil reaching water aquifers (Bashir et al., 2009; El-Salam and Abu-Zuid, 2015). The risk of groundwater contamination by leachate is determined by many

(41)

factors, including precipitation, hydrogeological conditions of the area, the toxicity, concentration and chemical composition of contaminants, solid waste composition, degree of compaction, absorptive capacity of the waste, landfill chemical and biological activities, landfill temperature, age of waste, and depth and distance from the pollution source or the direction of groundwater flow (Koda et al., 2016). In Malaysia, groundwater quality at Ampar Tenang landfill sites showed that the value for various parameters are higher than standards. This indicates that the groundwater within and surrounding the landfill is contaminated by the leachate (Yusoff et al., 2013). Heavy metals are the most dangerous pollutant group that are present in leachates and they are able to contaminate water resources (groundwater and surface water) that are close to the landfill sites, making this as one of the most serious environmental concerns. Although some of the heavy metals such as Zn, Mn, Ni and Cu act as micronutrients at lower concentrations, they become toxic at higher concentrations (Awaz, 2015).

2.3.1 (a) Factors Affecting Leachate Quantity

Several factors influencing leachate quantity are precipitation, groundwater intrusion, moisture content of the waste, refuse condition and final cover of the landfill (Mukherjee et al., 2014; Baziene et al., 2013; Aziz et al., 2004a; 2004b, El- Fadel et al., 2002). Daily cover meant to minimize leachate quantity as well to reduce the contaminant content in leachate seeping through it.

(i) Precipitation

The amount of rain and snow falling on the landfill influences leachate quantity significantly. In Malaysia, a country with high rainfall rate, the amount of leachate is very significant at all landfills. As rainwater filtrated through a waste

(42)

layer by the procedure of penetration, it dissolves and leaches out a wide spectrum of organic and inorganic components (Mukherjee et al., 2014). According to Baziene et al., (2013), different quantities of leachate with different concentrations are accumulated during different seasons of the year due to an unequal amount of precipitation (less precipitation – more pollutants).

(ii) Groundwater Intrusion

Sometimes the base of a landfill is constructed below the groundwater table.

In this case, the groundwater intrusion may increase the leachate quantity especially at the unlined landfills. As a part of naturally occurring process, it is common for landfill to be constructed below the groundwater table. As a result, landfills that are unlined and untreated may contribute to groundwater intrusion. In this context for instance, leachate may happen (Ibrahim et al., 2017).

(iii) Moisture Content of Waste

The waste especially organic waste will produce leachate through aerobic or anaerobic reactions. In Malaysia, the moisture content of the waste is high. So, leachate quantity will increase if the waste releases pore water during the compaction activity when it is squeezed. Gaps between soils and waste contain both water and air in the unsaturated zone. Regardless of considerable amount of water exist in this zone, the water is unable to be compacted through landfill cell as they are hold tightly by the capillary forces (Matsin, 2017). Unsaturated waste continues to absorb water until it reaches field capacity. Thereby dry waste will reduce leachate formation. Co-disposal of sludge or liquid waste will increase the leachate quantity in a landfill (Samuding, 2010).

(43)

Landfill moisture can be influenced by many factors such as rainfall, groundwater intrusion, initial moisture content, irrigation, recirculation, liquid waste co-disposal and also refuse decomposition (El-Fadel, 1997). Most Asian countries have biodegradable and moisture content solid waste composition such as food waste, paper, plastic/foam and agriculture waste (Tarmudi et al., 2012). Those are the factors that affect the leachate or moisture distribution within the landfill. Generally, as more water flows through the solid wastes, more pollutants are leached. Therefore, it is important to know methods that can be used to estimate the amount of leachate generation at a landfill site (Ibrahim et al., 2017; Qasim and Chiang 1994).

(iv) Final Cover/Daily Cover

To prevent leachate generation or infiltration, the surface and stormwater flows should be managed by using suitable cover materials, as well as saving the material with high liquid content away from the waste management facility (Chabuk et al., 2018). Leachate volume is reduced significantly after the landfill is covered.

Application of soil as a final or daily cover will reduce infiltration. Low permeability of the final or daily covered material can also cause reduction in percolation.

Basically, good design of the final or daily cover will reduce leachate quantity significantly. However, sometimes cracks appear on the surface of cover materials due to several factors such as waste settlement and wet and dry processes (Aziz et al., 2016; Samuding, 2010 and Albright et al., 2004). Addition of fibers has been found to improve toughness, reduce cracking from plastic shrinkage and decrease crack width and transfer stress across cracks. The potential benefit gained by adding fibers is that the fibers can reduce small crack width in shrink-swell soils. While fibers do not stop the formation of cracks, they can reduce the extent of cracking by decreasing

(44)

crack width and growth, thereby improving the overall performance of the grout (Saradar et al., 2018 and Allan et al., 1995).

2.3.1 (b) Factors Affecting Leachate Quality

The extent of variation in leachate quality can be attributed to many interacting factors such as waste composition, depth of waste, availability of moisture, availability of oxygen, temperature and age of landfill. Scientists and researchers have mentioned the following factors for variation in leachate quality in general (Adhikari et al., 2014; Aziz et al. 2004a, 2004b, El-Fadel et al., 2002).

(i) Waste Composition

In general, the composition of waste determines the extent of biological activity within the landfill sites (Adhikari et al., 2014; Wimalasuriya et al., 2011;

Zouboulis et al., 2004). The waste such as food and garden wastes, and crop and animal residues contribute to the organic material in leachate in most of the cases and, inorganic constituents in leachate are often derived from ash wastes and construction and demolition debris derived from different sources (Adhikari et al., 2014; Christensen et al., 2001). Bagchi, (1994) noted that the leachate quality variation is higher for putrescible waste (food, paper and textile) than that for non- putrescible waste (glass, metal and plastic).

(ii) Depth of Waste

Some researchers (Adhikari et al., 2014; Tatsi and Zouboulis, 2002; Kang et al., 2002; and WHO, 2004; Qasim and Chiang, 1994) found that the concentrations of the pollutants are higher in leachate sample from deeper landfills under similar conditions of precipitation and percolation. Deeper fills require more water to reach

(45)

saturation, require longer time to decompose and distribute the leached material over a longer period of time (Qasim and Chiang, 1994; Lu et al., 1985). Deep landfills give greater contact time between the liquid and solid phases which increase the leachate concentration (Trankler et al., 2005; McBean et al., 1995).

(iii) Availability of Moisture

Water is the most significant factor influencing waste biodegradability and leachate quality. Moisture within the landfill serves as reactant in the hydrolysis reactions, transports the nutrients and enzymes, dissolves metabolites and dilutes inhibitory compounds (Adhikari et al., 2014; Shuokr et al., 2010; Noble and Arnold, 1991). The quantity of the moisture is important because it directly affects stabilization rate within the landfill (Mor et al., 2006; Silva et al., 2004). High moisture flow rates can flush soluble organic and inorganic out of the landfill (Tatsi and Zouboulis, 2002; WHO, 2004 and Shuokr et al., 2010). The optimum amount of moisture content reported ranges from 40 to 70 percent (Trankler et al., 2005; Barlaz et al., 1990).

(iv) Availability of Oxygen

The quantity of oxygen in landfill dictates the type of decomposition (aerobic or anaerobic). Aerobic decomposition occurs during the initial placement of waste, when oxygen is available. Aerobic degradation may continue to occur in the upper layers of the waste (Adhikari et al., 2014; Amokrane et al., 1997; McBean et al., 1995). Chemical release as a result of aerobic decomposition differs greatly from those produced during anaerobic degradation (Kiliç et al., 2007 and Bagchi, 2004).

During the process of aerobic decomposition, microorganisms degrade organic matter to CO₂, H₂O, and produce considerable amount of heat. Generally, high

(46)

concentrations of organic acids, ammonia, hydrogen, carbon dioxide, methane, and water are produced during anaerobic degradation (Bagchi, 1990). During bio- degradation, different phases occur in the landfills as a result of reductions in the quantity of oxygen. As for example, a transitional change takes place when oxygen is depleted and an anaerobic environment develops in the bio-degradation of landfills (Adhikari et al., 2014).

(v) Temperature

Landfill temperature is considered as an uncontrolled factor that influences leachate quality. Temperature affects bacterial growth and chemical reactions within the landfill. Each microorganism has an optimum growth temperature and any deviation from the temperature will decrease its growth due to enzyme deactivation and cell wall rupture. Solubility of compounds in leachate such as CaCO3 and CaSO4

decreases with increasing of temperature (Adhikari et al., 2014; Christensen et al., 1996; Lu et al., 1985).

(vi) Age of Landfill

Leachate quality is greatly influenced by the length of time which has elapsed since waste placement. The quantity of chemicals in the waste is finite and therefore, leachate quality reaches a peak after approximately two or three years followed by a gradual decline in the following years (Adhikari et al., 2014; Asadi, 2008; McBean et al., 1995). All contaminants do not peak at the same time (Tchobanoglous et al., 1993). Organic compounds decrease more rapidly than inorganics with increasing age of the landfill (Chiang et al., 2001 and Adhikari et al., 2013).

(47)

2.3.1 (c) Impact on Groundwater and Surface Water

Landfill leachate is one of the main sources of groundwater and surface water pollution if it is not properly collected and treated and safely disposed as it may percolate through soil reaching water aquifers (Bashir et al., 2009). Contamination of groundwater by landfill leachate is considered being a major environmental concern.

The landfill leachate generally contains hundreds of different inorganic and organic chemicals at some finite concentration beside a large microbial population and may be heavily contaminated with pathogenic organisms (Kumari et al., 2017; Samuding, 2010).

Leachate generation continues in a cyclic pattern in active and closed landfill as precipitation groundwater may enter the cell in landfill then finally will directly correspond to the net infiltration rates, modified by runoff evapotranspiration patterns (Oweis and Khera, 1988). Mostly, high concentration of heavy metals, organic matters and suspended solids are present in landfill leachate (Jokela et al., 2002). A lot of cases of leachate contaminated groundwater and surface water have been documented (Maiti et al., 2016; Murray and Beck, 1990; Nasir and Chong, 1999).

Documentation of the movement of leachate plumes originally at waste dumps moreover landfills is becoming increasingly abundant. Under certain hydrologic conditions, leachate plumes can shift considerable distances and degrade groundwater throughout wide areas.

Pollution of water bodies and natural streams by leachate can causes serious problem to humans and environment including animals and plants. High concentration of heavy metals such as zinc, lead, copper, cadmium and chromium

(48)

can cause serious water pollution and threaten the environment (Kamaruddin et al., 2017; Aziz et al., 2004). Therefore it is very important to remove the contaminants from the leachate in order to minimize the contaminants movement towards the surface water and groundwater.

Leachate must be treated prior to discharge and it must meet the discharge limits of treated effluents. Generally, these limits vary from country to country, depending on the various factors such as treatment cost and economic situation of the country.

Leachate treatment is costly and requires multiple processes (Ozturk and Bektas, 2004). Numerous factors need to be considered when designing the leachate treatment system. Leachate treatment is required during the landfill operation and after the landfill closure. During life cycle of the landfill, leachate characteristics will change, thus an improvement in treatment system may be required. One of the possible landfill leachate treatment systems is the use of landfill daily soil cover system. The details of landfill soil cover system are discussed in the subsequent topic.

2.4 Overview of Daily Cover

The use of cover material is an essential element of landfilling operations and performs a number of important functions to minimize the impact on the environment of the landfill. The type, quantity and method of application of the cover material used at each landfill must be appropriate to achieve the overall objective of controlling potential nuisances that may arise (Medne et al., 2015).

Operational landfills represent a very dynamic and changing work environment that must be managed on a continuous basis to achieve good overall environmental