PREPARATION AND CHARACTERIZATION OF

MODIFIED OIL PALM (Elaeis guineensis) FROND

FOR THE REMOVAL OF RHODAMINE B IN

WASTEWATER

LOW LING WEI

UNIVERSITI SAINS MALAYSIA

2016

PREPARATION AND CHARACTERIZATION OF

MODIFIED OIL PALM (Elaeis guineensis) FROND

FOR THE REMOVAL OF RHODAMINE B IN

WASTEWATER

by

LOW LING WEI

Thesis submitted in fulfillment of the requirements

for the degree of

Doctor of Philosophy

September 2016

ii

ACKNOWLEDGEMENT

First and foremost I offer my sincerest gratitude to my supervisors, Professor

Teng Tjoon Tow and Prof. Dr. Norhashimah Morad, whose encouragement;

excellent guidance; invaluable suggestions and support from the initial to the final

level enable me to develop an understanding of the subject, without them this thesis,

too, would not have been completed. I am heartily thankful to my co-supervisor,

Associate Prof. Dr. Baharin Bin Azahari for his assistance, help and advices during

my period of study. Associate Prof. Dr. Abbas F.M. Alkarkhi has offered much

advice and insight throughout my work on statistical part and publications.

I would like to acknowledge the financial support provided by Ministry of

Higher Education Malaysia under the program of MyBrain15 and the research

facilities of Universiti Sains Malaysia.

Great appreciation goes to all lab assistants at School of Industrial

Technology for their technical support in using the instruments required to complete

my research. In my daily work, I have been blessed with the encouragement from my

dearest friends, Claire Su Xin Hui, Chou Kian Weng, Dr. Carol Ang Chai Tew, Yeap

Kiew Lee, Li Zhimin, Dr. Ho Yeek Chia, Dr. Lee Khai Ern, Tan Kah Aik, Lim Yee

Ling, Tang Soke Kwan, Lim Han Khim, Chang Pei Xi, Dr. Wong Yee Shian, and Dr.

Amir Talebi.

I thank my parents and brother for supporting me throughout all my studies at

University. To my beloved husband, thank you for being understandable and your

companion have made this path more delightful. Finally, I dedicate this dissertation

to my lovely son, who came to my life just after I started my research journey.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENT ii

TABLE OF CONTENTS iii

LIST OF TABLES x

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS xvii

LIST OF SYMBOLS xix

ABSTRAK xxiii

ABSTRACT

xxv

CHAPTER 1 - INTRODUCTION

1.1 Background 1

1.2 Oil Palm Biomass (Elaeis guineensis Biomass ) 2

1.3 Problem Statement 3

1.4 Research Scope and Objectives

6

CHAPTER 2 - LITERATURE REVIEW

2.1 Dyes 8

2.2 Pollution Due to Dye Wastewater 9

2.2.1 Color 9

2.2.2 Chemical Oxygen Demand 9

2.3 Textile Wastewater Treatment Technologies 10

2.3.1 Adsorption 12

2.3.2 Classification of Adsorption 13

iv

2.3.2(a) Physisorption 14

2.3.2(b) Chemisorption 14

2.4 Kinetic Study 15

2.4.1 Pseudo-First Order Model 15

2.4.2 Pseudo-Second Order Model 16

2.5 Equilibrium Study 17

2.5.1 Langmuir Isotherm 17

2.5.2 Freundlich Isotherm 18

2.5.3 Temkin Isotherm 19

2.5.4 Dubinin-Radushkevich (DR) Isotherm 20

2.6 Activated Carbon 24

2.7 Development of Low-Cost Adsorbents 24

2.7.1 Types of Precursors 25

2.7.1(a) Organic Precursors 25

2.7.1(b) Inorganic Precursors 28

2.7.1(c) Use of Oil Palm Biomass in Adsorption Studies 29

2.7.2 Processing Methods 30

2.7.2(a) Carbonization 32

2.7.2(a)(i) Physical Activation 32

2.7.2(a)(ii) Chemical Activation 33

2.7.2(b) Nanomaterials Preparation Methods 36

2.7.2(b)(i) Co-Precipitation Method 38

2.7.3 Iron Oxide Nanomaterials 38

2.7.3(a)

2.7.3(b)

Types of Iron Oxide

Nano-Composite Material

40

40

v

2.7.3(c) Synthesis of Iron Oxide-Based Magnetic

Nanoparticles through Co-Precipitation Method

44

2.8 Design of Experiment 46

2.8.1 Mathematical Models 47

2.8.2 Response Surface Methodology (RSM)- Central Composite

Design (CCD)

48

CHAPTER 3 – MATERIALS AND METHODS

3.1 Materials and Chemicals 50

3.2 Dye Aqueous Solution 51

3.3 Preparation of Chemical Oxygen Demand (COD) Digestion Reagent 51

3.4 Equipments Used 52

3.5 Project Flow Chart 55

3.6 Preparation of Adsorbents 56

3.6.1 Pretreatment of Elaeis guineensis Frond Fiber (EGFF) 56

3.6.2 Preparation of Phosphoric Acid Modified Elaeis guineensis

Frond Fiber (A-EGFF)

57

3.6.3 Preparation of Carbonized Phosphoric Acid Modified EGFF

(AC-EGFF)

58

3.6.4 Preparation of Carbonized Phosphoric Acid Modified EGFF

Impregnated with Iron Oxide (AC-EGFF-Fe3O4)

59

3.7 Experimental Methods and Measurements 60

3.7.1 Adsorption Experiments 60

3.7.2 Chemical Oxygen Demand (COD) Measurement 61

3.7.3 Dye Concentration Measurement 61

3.8 Adsorbent Characterization 62

3.8.1 Fourier Transform Infra-Red (FTIR) 62

vi

3.8.2 The Scanning Electron Microscopy (SEM) 63

3.8.3 The Transmission Electron Microscopy (TEM) 64

3.8.4 Surface Analysis

64

3.8.5 X-Ray Diffraction (XRD) 64

3.8.6 Zeta Potential 65

3.8.7 pH Point of Zero Charge (pHzpc) 65

3.9 Regeneration Study 65

3.10 Experimental Design 66

3.10.1 Preparation of AC-EGFF Using Design of Experiment

(DOE)

66

3.10.2 Preparation of AC-EGFF-Fe3O4 Using Design of

Experiment (DOE)

67

3.10.3 Batch Adsorption Studies Using Design of Experiment

(DOE)

67

3.11 Treatment of Industrial Textile Wastewater 68

CHAPTER 4 - RESULTS AND DISCUSSION

4.1 Rhodamine B (RB) Dye Wavelength and Calibration Curve 70

4.2 Effect of Adsorbent Particle Size on RB Adsorption 70

4.3 Adsorption of RB Dye Using Conventional and Thorough Washing

of Raw EGFF

71

4.3.1 Screening of Process Variables for Raw EGFF Adsorption

Conditions

72

4.3.2 Face Centered Composite Design for Raw EGFF 77

4.3.3 Optimization of the Experiment for Raw EGFF 87

vii

4.4 Adsorption of RB Dye Using Acid Modified EGFF 89

4.4.1 Effect of Phosphoric Acid Concentration 89

4.4.2 Effect of Impregnation Ratio 91

4.4.3 Optimization of the RB Dye Adsorption Conditions Using

A-EGFF

92

4.5 Adsorption of RB Dye Using Carbonized Acid Modified EGFF 99

4.5.1 Statistical Analysis of Preparation Conditions of Carbonized

Acid Modified EGFF (AC-EGFF)

99

4.5.2 Effect of Carbonization Temperature on AC-EGFF for The

Removal of RB Dye

105

4.5.3 Effect of Heating Rate on AC-EGFF for The Removal of

RB Dye

109

4.5.4 Effect of Nitrogen Gas Flow Rate on AC-EGFF for The

Removal of RB Dye

109

4.5.5 Optimization of the RB Dye Adsorption Conditions Using

AC-EGFF

110

4.6 Adsorption of RB Dye Using AC-EGFF-Fe3O4 Composite

Adsorbent

116

4.6.1 Statistical Analysis for the Preparation Conditions of AC-

EGFF-Fe3O4

116

4.6.2 Effect of Fe2+

/Fe3+

Ratio for AC-EGFF-Fe3O4 on Color

Removal and COD Reduction of RB Dye

119

4.6.3 Effect of Iron Oxide Solution pH on Color Removal and

COD Reduction of RB Dye

124

4.6.4 Effect of Reaction Temperature on Color Removal and

COD Reduction of RB Dye

126

4.6.5 Optimization of the RB Dye Adsorption Conditions Using

AC-EGFF-Fe3O4

127

4.7 Individual Effects of Process Variables 132

4.7.1 Effect of pH on RB Adsorption 132

4.7.2 Effect of Initial RB Dye Concentration on RB Adsorption 135

viii

4.7.3 Effect of Adsorbent Amount on RB Adsorption 137

4.7.4 Effect of Temperature on RB Adsorption 139

4.7.5 Effect of Ionic Strength on RB Adsorption 140

4.8 Adsorption Kinetics for the Removal of RB Dye 141

4.9 Adsorption Isotherm for The Removal of RB Dye Aqueous

Solutions

146

4.9.1 Langmuir Isotherm 146

4.9.2 Freundlich Isotherm 147

4.9.3 Temkin Isotherm 148

4.9.4 Dubinin-Radushkevich (DR) Isotherm 149

4.9.5 Summary of The Adsorption Isotherms 150

4.10 Adsorption Thermodynamics 151

4.11 Adsorbent Characterization 153

4.11.1 Scanning Electron Microscopy (SEM) Spectroscopy

Analysis

153

4.11.2 Energy Dispersive X-Ray (EDX) Analysis 157

4.11.3 Transmission Electron Microscopy (TEM) Analysis 159

4.11.4 Fourier Transform Infra-Red (FTIR) Spectroscopy Analysis 161

4.11.5 X-Ray Diffraction (XRD) Analysis 168

4.11.6 Surface Area, Average Pore Diameter, and Total Pore

Volume Analysis

170

4.12 Adsorbent Regeneration 171

4.13 Treatment of Industrial Textile Wastewater 173

4.14 Comparison of AC-EGFF-Fe3O4 with Other Agricultural Byproduct

Based Adsorbents in Dye Wastewater Treatment

174

ix

CHAPTER 5 – CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 177

5.2 Recommendations 181

REFERENCES 182

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

224

226

227

228

LIST OF PUBLICATIONS

x

LIST OF TABLES

Page

Table1.1 Typical characteristics of textile industry wastewater 1

Table 2.1 Distinctive dyes used in textile dyeing process 8

Table 2.2 Properties and characteristics of physisorption and

chemisorption

14

Table 2.3 Kinetic and isotherm studies of textile dye adsorption 22

Table 2.4 Adsorption capacities (mg/g) of organic precursor based

adsorbents

27

Table 2.5 Compilation of various natural inorganic materials and

their adsorption capacity (mg/g) in dye removal

28

Table 2.6 Malaysian palm oil biomass output 29

Table 2.7 Oil palm biomass and their adsorption capacities (mg/g)

for dye removal

30

Table 2.8 Chemical activation of various by-products 35

Table 2.9 Nanomaterials synthesis techniques 37

Table 2.10 Synthesis of nanomaterials using co-precipitation method 38

Table 2.11 Comparison of the synthesis methods of iron oxide

magnetic particles

43

Table 2.12 Application of iron oxide composite materials through co-

precipitation synthesis method in dye wastewater

treatment

45

Table 3.1 Materials and Chemicals 50

Table 3.2 General specifications of Rhodamine B dye 51

Table 3.3 Equipments used throughout the experimental works 53

Table 3.4 Independence factors and corresponding levels used for

optimization

66

Table 3.5 Factors and levels used for AC-EGFF-Fe3O4 preparation 67

Table 3.6 Factors and levels used for screening experiment 68

xi

Table 3.7 Factors and levels used for optimization study 68

Table 4.1 The results of 26 factorial design for screening experiment

using raw EGFF

74

Table 4.2 The results of FCCD for percentage of color removal and

COD reduction using raw EGFF

81

Table 4.3 The results of ANOVA for percentage of color removal

and COD reduction using thorough washing method of

raw EGFF.

85

Table 4.4 Optimum conditions using raw EGFF 89

Table 4.5 Parameter levels and coded values for optimization of

adsorption process using A-EGFF

93

Table 4.6 FCCD for percentage of color removal and COD

reduction using A-EGFF

93

Table 4.7 ANOVA for percentage of color removal and COD

reduction using A-EGFF

96

Table 4.8 Validation of test results for the adsorption of RB dye

using A-EGFF

98

Table 4.9 The results of statistical analysis for the preparation of

AC-EGFF

101

Table 4.10 ANOVA for color removal and COD reduction for AC-

EGFF preparation conditions

102

Table 4.11 Characteristics of the EGFF chars prepared under various

carbonization temperatures

108

Table 4.12 FCCD for percentage of color removal and COD

reduction using AC-EGFF

110

Table 4.13 ANOVA for percentage of color removal and COD

reduction using AC-EGFF

113

Table 4.14 Validation of test results for the adsorption of RB dye

using AC-EGFF

115

Table 4.15 FCCD in natural variables with the experimental data

values of % color removal and % COD reduction for the

preparation of AC-EGFF-Fe3O4

117

Table 4.16 ANOVA for percentage of color removal and COD

reduction for the preparation of AC-EGFF-Fe3O4

118

xii

Table 4.17 Validation of test results for the preparation conditions of

AC-EGFF-Fe3O4

119

Table 4.18 Effect of Fe2+

/Fe3+

ratio for AC-EGFF-Fe3O4 on color

removal and COD reduction of RB dye

120

Table 4.19 Effect of pH on color removal and COD reduction of RB

dye

124

Table 4.20 Effect of reaction temperature on color removal and COD

reduction of RB dye

126

Table 4.21 FCCD for percentage of color removal and COD

reduction using AC-EGFF-Fe3O4

128

Table 4.22 ANOVA for percentage of color removal and COD

reduction using AC-EGFF-Fe3O4

130

Table 4.23 Validation of test results for the adsorption or RB dye

using AC-EGFF-Fe3O4

132

Table 4.24 Comparison of the pseudo-first order and pseudo-second

order adsorption rate constants and calculated and

experimental qt values obtained at different initial RB

concentrations at different times (All values are average

of three replications)

144

Table 4.25 Langmuir isotherm model constants and correlation

coefficients for RB dye adsorption

147

Table 4.26 Freundlich isotherm model constants and correlation

coefficients for RB dye adsorption

147

Table 4.27 Temkin isotherm model constants and correlation

coefficients for RB dye adsorption

148

Table 4.28 DR isotherm model constants and correlation coefficients

for RB dye adsorption

149

Table 4.29 Thermodynamic parameters for the adsorption of RB dye

from the aqueous solution using AC-EGFF-Fe3O4

153

Table 4.30 Functional groups associated with certain specific bands 161

Table 4.31 BET surface area, average pore diameter, and total pore

volume for the raw EGFF, Fe3O4, AC-EGFF, and AC-

EGFF-Fe3O4

170

xiii

Table 4.32 Comparison of fresh and regenerated adsorbents on color

removal and COD reduction on RB dye

172

Table 4.33 Characteristics of collected industrial textile wastewater 173

Table 4.34 Comparison of AC-EGFF-Fe3O4 with other agricultural

byproduct based adsorbents in dye wastewater treatment

175

xiv

LIST OF FIGURES

Page

Figure 2.1 Definitions of adsorbent and adsorbate 13

Figure 3.1 Overall project flow chart of the present study 55

Figure 3.2 Oil palm frond 57

Figure 3.3 Schematic diagram of the experimental set-up of a

carbonization unit

59

Figure 4.1 Effect of adsorbent particle size on percentage of color

removal at fixed 200 mg/L RB concentration, 5000 mg/L

adsorbent dosage, 150 rpm, 27±1 oC, contact time 2 h, pH

7

71

Figure 4.2 Normal probability plot of (a) percentage of color removal

(b) percentage of COD reduction using conventional

washing method of raw EGFF

78

Figure 4.3 Normal probability plot of (a) percentage of color removal

(b) percentage of COD reduction using thorough washing

pretreatment method of raw EGFF

79

Figure 4.4 Removal/reduction of RB dye using various phosphoric

acid concentrations at fixed impregnation ratio of 1:1 at

adsorption conditions of pH 7, 150 rpm, 27±1 oC, 40

minutes, 0.5 g/100 mL adsorbent dosage with 500 mg/L

RB dye concentration

90

Figure 4.5 Removal of RB dye using various impregnation ratios at

fixed adsorption conditions of pH 7, 150 rpm, 27±1 oC, 40

minutes, 0.5 g/100 mL adsorbent dosage with 500 mg/L

RB dye concentration

92

Figure 4.6 Plot of the experimental and predicted (a) color removal

(b) COD reduction for AC-EGFF preparation conditions

104

Figure 4.7 N2 adsorption isotherm of AC-EGFF prepared under

different carbonization temperatures at fixed carbonization

duration of 1 h, heating rate of 10 oC/min, nitrogen gas

flow rate of 100 cm3/min

106

Figure 4.8 Color of AC-EGFF-Fe3O4 prepared under different

Fe2+

/Fe3+

ratios

121

xv

Figure 4.9 TEM images of AC-EGFF-Fe3O4 at various Fe2+

/Fe3+

ratios

123

Figure 4.10 Fe3O4 prepared at (a) pH 9 (b) pH 12 125

Figure 4.11 Effect of pH on color removal and COD reduction of RB at

fixed RB concentration of 500 mg/L, 150 rpm, 0.5 g

adsorbent at 27±1 oC for 30 minutes

133

Figure 4.12 Initial pH versus final pH for determination of pHzpc of

AC-EGFF-Fe3O4

133

Figure 4.13 Zeta potential measurements for AC-EGFF-Fe3O4 as a

function of RB pH

134

Figure 4.14 Effect of initial dye concentration on (a) color removal and

(b) COD reduction at fixed 0.5 g/100 mL adsorbent

dosage, 150 rpm, 27±1 oC, pH 9

136

Figure 4.15 Effect of adsorbent amount on (a) color removal and (b)

COD reduction at fixed initial dye concentration of 500

mg/L, 27±1 oC, 150 rpm, and pH 9

138

Figure 4.16 Effect of temperature on the adsorption capacity at fixed

0.5 g adsorbent, 150 rpm, pH 9, 40 min equilibrium time

139

Figure 4.17 Effect of ionic strength NaCl on RB adsorption at fixed

500 mg/L initial RB concentration, 27±1 oC, pH 9, 40 min,

150 rpm and 0.5 g adsorbent

140

Figure 4.18 Pseudo-first order plot for kinetic study of RB adsorption 142

Figure 4.19 Pseudo-second order plot for kinetic study of RB

adsorption

142

Figure 4.20 The linear plots of Langmuir Isotherm for RB adsorption 146

Figure 4.21 The linear plots of Freundlich Isotherm 148

Figure 4.22 The linear plots of Temkin Isotherm 149

Figure 4.23 The linear plots of Dubinin-Radushkevich (DR) Isotherm 150

Figure 4.24 Plot of ln qe/Ce versus 1/T for the adsorption of the RB dye

aqueous solution using AC-EGFF-Fe3O4

152

xvi

Figure 4.25 SEM micrograph of (a) raw EGFF, (b) AC-EGFF, (c)

Fe3O4, (d) AC-EGFF-Fe3O4, and (e) spent AC-EGFF-

Fe3O4 with a magnification of 1000 x, (f) AC-EGFF-Fe3O4

with magnification of 50000x.

154

Figure 4.26 Energy Dispersive X-ray (EDX) spectra of (a) raw EGFF

(b) AC-EGFF-Fe3O4.

158

Figure 4.27 TEM image of (a) Fe3O4 at magnification 66000 x, (b)

Fe3O4 at magnification 110000 x, and (c) AC-EGFF-Fe3O4.

159

Figure 4.28 FTIR spectra of (a) raw EGFF, (b) Rhodamine B dye, (c)

Fe3O4, (d) AC-EGFF-Fe3O4, and (e) spent AC-EGFF-

Fe3O4

162

Figure 4.29 XRD spectra of Fe3O4, AC-EGFF, and AC-EGFF-Fe3O4 169

xvii

LIST OF ABBREVIATIONS

A-EGFF Phosphoric acid modified Elaeis guineensis frond fiber

AC-EGFF Carbonized phosphoric acid modified EGFF

AC-EGFF-Fe3O4 Carbonized phosphoric acid modified EGFF impregnated

with iron oxide

ANOVA Analysis of variance

APHA American public health association

BBD Box behnken design

BDDT Brunauer-Deming-Deming-Teller

BET Brunauer, Emmett and Teller

BOD Biochemical oxygen demand

CCD Central composite design

COD Chemical oxygen demand

C.I. Color index

Davg Average diameter

DOE Design of experiment

DR Dubinin-Radushkevich

EDX Energy dispersive X-ray

EGFF Elaeis guineensis frond fiber

FCCD Face centered composite design

FTIR Fourier transform infra red

IUPAC International union of pure and applied chemistry

RB Rhodamine B

RSM Response surface methodology

SEM Scanning electron microscopy

xviii

TEM Transmission electron microscopy

XRD X-ray diffraction

xix

LIST OF SYMBOLS

A Initial solution pH -

A1 RB stock solution concentration mg/L

A2 Required final RB concentration mg/L

AT Temkin isotherm constant L/g

Ag2SO4 Silver sulphate -

B Agitation speed rpm

bT Temkin isotherm constant related to heat of

adsorption

J/mol

C Initial dye concentration mg/L

Ce Concentration of dye at equilibrium mg/L

Co Initial dye concentration mg/L

Ct Dye concentration at respective time, t mg/L

-CH= Methane group -

C=O Carbonyl group -

D Temperature oC

E Contact time min

F Adsorbent dosage g/100 mL

FeCl3.6H2O Iron (III) chloride hexahydrate -

Fe3O4 Iron oxide -

FeSO4.7H2O Iron (II) sulphate heptahydrate -

HCl Hydrochloric acid -

HgSO4 Mercury sulphate -

H2O2 Hydrogen peroxide -

H3PO4 Phosphoric acid -

xx

H2SO4 Sulphuric acid -

KBr Potassium bromide -

KCl Potassium chloride -

K2CO3 Potassium carbonate -

K2Cr2O7 Potassium dichromate -

KOH Potassium hydroxide -

KF Freundlich isotherm constant mg/g(L/mg)1/n

KL Langmuir isotherm constant related to the

affinity of the binding sites

L/mg

k1 Pseudo-first order rate constant min-1

k2 Pseudo-second order rate constant g/mg.min

M1 Fe2+

:Fe3+

ratio -

M2 Heating time min

M3 Heating temperature oC

MnO4 Permanganate -

NaOH Sodium hydroxide -

NH4OH Ammonium hydroxide -

-NO2 Nitro group -

-N=N- Azo group -

NR2 Amino group -

1/n Adsorption intensity -

OH Hydroxyl group -

QDR Dubinin-Radushkevich constant -

Qo Amount of adsorbate adsorbed by unit mass of

adsorbent that is required to cover an adsorbent

surface completely as a monomolecular layer

mg/g

xxi

pHzpc pH point of zero charge -

qe Amount of dye uptake at equilibrium mg/g

qt Amount of dye adsorbed at any time, t mg/g

R Universal gas constant J/mol.K

RL Dimensionless constant -

r2 Coefficient of determination -

Sa Initial COD concentration mg/L

Sb Equilibrium COD concentration mg/L

SBET BET surface area -

T Absolute solution temperature K

V Volume of the dye solution L

V1 Known volume of RB stock solution mL

V2 Total volume of required final RB concentration mL

Vmicro Micropore volume -

Vtotal Total volume -

W Weight of the adsorbent g

X1 Carbonization temperature oC

X2 Carbonization duration h

X3 Heating rate oC/min

X4 Nitrogen gas flow rate cm3/min

xi Coded variables

y1 color removal or decolorization %

y2 COD reduction %

ΔGo Gibbs free energy kJ/mol

ΔHo Standard entalpy kJ/mol

xxii

ΔSo Standard entropy J/mol.K

ε Constant for Dubinin-Radushkevich isotherm -

βo, βi, βii, βij Regression coefficients -

η Response surface area -

ξi Natural variable

xxiii

PENGHASILAN DAN PENCIRIAN PELEPAH KELAPA SAWIT (Elaeis

guineensis) TERUBAHSUAI DALAM PENGOLAHAN AIR SISA

RHODAMINE B

ABSTRAK

Proses penjerapan telah diaplikasikan dalam pelbagai rawatan air sisa,

termasuk air sisa pewarna. Walau bagaimanapun, kajian mengenai penggunaan sisa

pertanian seperti pelepah kelapa sawit dan pelepaj kelapa sawit terubahsuai masih

tidak dikaji dengan menyeluruh. Dalam kajian ini, penjerapan Rhodamine B (RB) ke

atas pelepah kelapa sawit (a) mentah (EGFF), (b) yang diubahsuai dengan asid

fosforik (A-EGFF), (c) yang diubahsuai dengan asid fosforik dan dikarbonisasikan

(AC-EGFF), (d) yang diubahsuai dengan asid fosforik dan dikarbonisasikan serta

dikandungkan dengan oksida ferik (AC-EGFF-Fe3O4) telah dikaji. Untuk

menyingkirkan sebatian organik yang menyumbang kepada keperluan oksigen kimia

(COD), proses pencucian penjerap dengan menggunakan air suling didih telah

dilaksanakan sebagai pengganti kepada air suling pada suhu bilik. Proses penyediaan

penjerap telah dikaji dan dioptimumkan dengan menggunakan metodologi

permukaan sambutan (RSM)- rekabentuk ujikaji gabungan pusat (FCCD). Kesan pH,

kelajuan pergaulan, dos penjerap, kepekatan awal pewarna, tempoh pergaulan dan

suhu ke atas penyahwarnaan dan penurunan peratus COD telah dikaji dan

dioptimumkan. Keputusan menunjukkan AC-EGFF-Fe3O4 mempunyai luas

permukaan BET yang luas dan lebih berkesan dalam penyahwarnaan dan penurunan

COD bagi pewarna RB berbanding dengan EGFF, A-EGFF, dan AC-EGFF.

Keadaan penjerapan optimum bagi AC-EGFF-Fe3O4 diperolehi pada 550 mg/L

xxiv

kepekatan awal pewarna, pH 8.49, 28.43 oC, 27 min dan 0.97 g dos penjerap dengan

98.63 % penyahwarnaan dan 98.06 % penurunan COD. Luas permukaan BET bagi

AC-EGFF-Fe3O4 ialah 797.68 m2/g iaitu lebih tinggi daripada EGFF mentah (13.80

m2/g), A-EGFF (31.67 m

2/g), dan AC-EGFF (555.53 m

2/g). Isoterma penjerap,

kinetik, dan termodinamik untuk penjerapan zat warna RB telah dikaji. Data

isotherma penjerap pewarna RB dengan menggunakan AC-EGFF-Fe3O4 didapati

mengikuti model isoterma Langmuir dan Freundlich. Kinetik penjerapan mengikuti

model kinetik tertib pseudo-kedua. Kajian termodinamik menunjukkan proses

penjerapan adalah proses endotermik. AC-EGFF-Fe3O4 yang telah digunakan boleh

diregenerasikan dengan menggunakan 0.1 M NaOH. Kajian menunjukkan bahawa

sisa agrikultur EGFF terubahsuai adalah bahan penjerap yang sesuai digunakan

untuk merawat air sisa berwarna.

xxv

PREPARATION AND CHARACTERIZATION OF MODIFIED OIL PALM

(Elaeis guineensis) FROND FOR THE REMOVAL OF RHODAMINE B IN

WASTEWATER

ABSTRACT

The adsorption process has been applied in various wastewater treatments,

including dye wastewater. However, research on the use of agricultural waste such as

oil palm frond and modified oil palm frond is still not thoroughly investigated. In this

research, the adsorption of Rhodamine B (RB) from the aqueous solutions onto (a)

raw Elaeis guineensis frond fiber (EGFF), (b) phosphoric acid modified EGFF (A-

EGFF), (c) carbonized phosphoric acid modified EGFF (AC-EGFF), and (d)

carbonized phosphoric acid modified EGFF impregnated with ferric oxide (AC-

EGFF-Fe3O4) have been investigated. In order to remove organic compounds and to

improve the reduction of chemical oxygen demand (COD), the raw EGFF was

thoroughly washed with boiling distilled water instead of using room temperature

distilled water. The preparation conditions of the adsorbents were optimized using

response surface methodology (RSM)-face centered composite design (FCCD). The

effects of pH, shaking speed, adsorbent dosage, initial dye concentration, contact

time and temperature on color removal and COD reduction were studied and

optimized. The results showed that the AC-EGFF-Fe3O4 has higher BET surface area

and was more effective in terms of color removal and COD reduction of RB dye than

the raw EGFF, A-EGFF, and AC-EGFF. The optimal adsorption conditions for AC-

EGFF-Fe3O4 were obtained at 550 mg/L initial RB dye concentration, pH 8.49, 28.43

oC, 27 min, and 0.97 g adsorbent with 98.63 % color removal and 98.06 % COD

xxvi

reduction. The BET surface area for AC-EGFF-Fe3O4 was 797.68 m2/g which was

higher than that of raw EGFF (13.80 m2/g), A-EGFF (31.67 m

2/g), and AC-EGFF

(555.53 m2/g). Adsorption isotherms, kinetics and thermodynamics for the

adsorption of RB dye were determined. The equilibrium data for the adsorption of

RB dye using AC-EGFF-Fe3O4 was best represented by Langmuir isotherm model,

followed by Freundlich isotherm model. The adsorption kinetics was found to follow

the pseudo-second-order kinetic model. The thermodynamic study showed that the

adsorption process was endothermic. Spent AC-EGFF-Fe3O4 can be effectively

regenerated using 0.1 M NaOH. The results indicated that modified agricultural

waste EGFF is suitable to be used as adsorbent for the treatment of dye wastewater.

1

CHAPTER ONE

INTRODUCTION

1.1 Background

The textile industry is one of the most highly-consuming water and energy

industries, causing severe pollution. Indeed, the impact of textile effluents on the

aquatic medium has been traditionally of immense concern because its high variation

in composition with strong color, high chemical oxygen demand (COD), varying pH

values and relatively low biodegradability with large amount of dissolved salts and

suspended solids (Merouani et al., 2010; Blanco et al., 2014; Pang and Abdullah,

2013a,b). A typical example of the characteristics of textile industry wastewater is

given in Table 1.1.

Table1.1 Typical characteristics of textile industry wastewater (Tan et al., 2000; Lim

et al., 2010; Pang and Abdullah, 2013a).

Parameters Values

pH 6.9-11.6

Temperature (oC) 35-58

Color Point (PtCo) 735-8100

Chemical Oxygen Demand (COD)

(mg/L)

675-3190

Suspended Solids (mg/L) 530-3000

In addition, these effluents reduce the aesthetic value of the receiving water

and pose significant threat to human health and the ecosystem (Sun et al., 2007; Pang

and Abdullah, 2013b).

In Malaysia, the Department of Environment under the Ministry of Natural

Resources and Environment has established an international water quality standard.

2

Tables A1 and A2 in Appendix A list the parameter limits of effluent of Standards A

and B as stated in the Fifth Schedule of Environmental Quality (industrial effluent)

Regulations 2009 (Environmental Quality Act and Regulation, 2010). Standards A

and B list the limits that ought to be abided by effluent that is discharged into any

inland waters within the catchment areas and any other inland waters, respectively

(Environmental Quality Act and Regulation, 2010).

During the past few decades, a wide range of wastewater treatment

techniques has been used. The adsorption process is one of the most effective and

widely used techniques in decolorizing different types of coloring materials (Crini,

2006; Su et al., 2014; Low et al., 2014). Currently, there are many studies on the

development of adsorbents using natural materials, biomass, and agricultural waste

materials.

1.2 Oil Palm Biomass (Elaeis guineensis Biomass )

Generally, biomass can be defined as compounds or organic matters either

produced from marine life, forestry or crops (Awalludin et al., 2015). Biomass can

also be defined as a type of hydrocarbon material comprises of oxygen, hydrogen,

carbon, and nitrogen, and sometimes sulphur and small proportion of inorganic

substances (Yaman, 2004).

Oil palm (Elaeis guineensis) is nurtured at an enormous scale as a source of

oil in Central and West Africa (where it is originated), and in Thailand, Indonesia

and Malaysia (Wan Rosli et al., 2004). In Malaysia, oil palm is one of the most vital

commercial crops with world production of 19.22 million tons in year 2013 (MPOB,

2014). The growth of oil palm plantation in Malaysia has generated large amounts of

3

waste, generating problems in replanting operations, and tremendous environmental

concerns (Wan Rosli et al., 2004). In the palm oil mill, 10% of the total biomass

consists of palm oil, while the remaining 90% is discarded as waste (Abdullah et al.,

2013).

The high demand for palm oil is due to its nutritional value and cheaper price

as compared with other vegetable oils (Ramli, 2011). Besides food uses, palm oil is

also widely applied in non-food applications, such as in cosmetics, pharmaceuticals,

lubricants, and various products of the oleo-chemical industries (Nurfahisza et al.,

2014).

The oil palm is a lignocellulosic rich material containing cellulose,

hemicelluloses, and lignin. Oil palm frond contains a high composition of

hemicelluloses (83.13 %), cellulose (47.76 %) and lignin (20.15 %) (Ahmad, et al.,

2011) which has made it a suitable precursor as adsorbent in wastewater treatment.

The oil palm biomass was found to contain high amount of calcium, silica, aluminina

and potassium that can be used to synthesize active compounds that are responsible

for adsorption of various pollutants on the surface of the adsorbents (Zainudin et al.,

2005; Ghazali et al., 2006; Ahmad et al., 2011).

1.3 Problem Statement

Adsorption process has been widely used in dye wastewater treatment

because this process proved to be more effective than other wastewater treatment

technologies in terms of low cost, flexibility and simplicity of design, ease of

operation and insensitivity to toxic pollutants (Crini, 2006). However, the use of

commercially available activated carbon has been limited due to high cost (1-2

4

US$/pound) (Babel and Kurniawan, 2004; Tsang et al., 2008). Activated carbons are

normally made from petroleum coke, bituminous coal, lignite, wood products, etc.

(Drovac and Skipton, 2008). These materials are expensive and non-renewable,

which is unjustified in pollution control applications (Ahmad and Hameed, 2010).

Therefore, inexpensive agro-lignocellulosic material (Elaeis guineensis frond) has

been used as adsorbent for the removal of Rhodamine B (RB) dye from aqueous

solutions.

In Malaysia, the most vital agro-industry is the palm oil industry (Sumathi et

al., 2008). Starting from this decade, replanting of palm oil is likely to increase

rapidly. Presently, Elaeis guineensis frond, a major lignocellulosic rich, agricultural

solid waste are regularly abandoned in the field on pruning and replanting (Hameed

and El-Khaiary, 2008) which leads to environmental issues. There are no significant

commercial applications for the fronds, unlike trunk, empty fruit bunches (EFB), oil

palm fibers and shells; are used as construction materials. Annually, 44.8 million

tones of oil palm fronds were generated (Ng et al., 2012). The high chemical

compositions of oil palm frond (83.13 % hemicellulose, 47.76 % cellulose, and

20.15 % lignin) have made it suitable to be used as adsorbent in the wastewater

treatment. Consequently, economic exploitation of these fibers in wastewater

treatment will be favorable and the disposal problem will be solved.

Rhodamine B (RB) is an important water-soluble organic dye. RB has been

widely used as a colorant in the textile and food industries as well as a biological

stain in biomedical laboratories. RB has been banned to use in the food industry for

many years due to its suspected carcinogenic nature. However, with the development

of industry and the illegal discharge, RB still has the chances to enter the food chain

to hazard human health. RB can cause permanent injury to the humans’ eyes,

5

irritation to the gastrointestinal tract with symptoms such as nausea, vomiting and

diarrhea and also cause methemoglobinemia, cyanosis, convulsions and skin

irritation (Xue et al., 2009; Muthuraman and Teng, 2009). Thereby, the removal of

RB from aqueous solutions is of utmost importance prior to their discharge into the

receiving water bodies.

Many researchers use raw agricultural waste or acid modified adsorbent for

the treatment of dye aqueous solutions (Hameed and Daud, 2008; Jalil et al., 2012;

Heibati et al., 2015; Aboua et al., 2015; Elmoubarki et al., 2015) which are unable to

achieve high Brunauer, Emmett and Teller (BET) surface area. Adsorbent with high

BET surface area gives high adsorption capacity. The present study not only used the

conventional carbonization method (only involved two variables, i.e. carbonization

temperature and carbonization duration of the process) to increase the BET surface

area of the adsorbent (Li et al., 2008; Kim et al., 2012), the influence of heating rate

and nitrogen gas flow rate in the carbonization process were also studied. Magnetic

nano-composite adsorbent has shown to increase the efficiency of the adsorbent in

the adsorption of dye aqueous solutions (Panneerselvam et al., 2011; Konicki et al.,

2013).

Although filtration and centrifugation have been used to remove adsorbents

from aqueous solutions, magnetic separation provides a promising method to

perform solid-liquid separation. For magnetic separation, a magnetic component,

such as iron oxide, is added in the composite particles. Then, once dispersed in the

water solution during adsorption, an external magnet is used to gather the composite

particles that were dispersed in water. When the magnet is removed, these composite

particles may redisperse in water without any undesired magnetic aggregation

(Zhang et al., 2014).

6

Most previous studies (Zhang et al., 2012; Lin et al., 2013; Hazzaa and

Hussein, 2015; Tan et al., 2015a, b; Maneerung et al., 2016) applied the univariate

method (changing one factor at a time and keeping the others constant) in adsorption

studies, which might not attain the authentic optimal operational conditions and also

energy and time consuming. Response surface methodology (RSM), an

amalgamation of mathematical and statistical techniques has been used in the present

study to develop, improve, optimize and study the interactions of two or more

variables in the adsorption process.

Chemical oxygen demand (COD) is used to measure the capacity of water to

consume oxygen during the decomposition of organic matter. COD is the primary

index used to evaluate organic pollution in aqueous solutions (Metcalf and Eddy,

2004; Narayanan, 2015). COD has close relation with dye concentration. However,

many previous studies (Gil et al., 2011; Madrakian et al., 2012; Pathak et al., 2015)

only emphasize on the color removal but no COD measurement was done. In this

study, COD is considered as a crucial parameter to be reduced throughout the

adsorption process.

1.4 Research Scope and Objectives

Application and reuse of wastes have gained attention and have also been

widely applied in various areas by researchers. The present study uses an agricultural

waste - Elaeis guineensis frond fiber in dye wastewater treatment. Synthesis of

effective adsorbents in terms of color removal, COD reduction and BET surface area

for the treatment of RB dye aqueous solutions is the primary focus in this study.

Various adsorbent modification methods such as phosphoric acid modification

7

method (A-EGFF), carbonized phosphoric acid modification method (AC-EGFF),

and impregnation of iron oxide on AC-EGFF through co-precipitation method (AC-

EGFF-Fe3O4) were carried out and were analyzed using a statistical tool- Response

Surface Methodology (RSM)- Faced centered composite design (FCCD). Optimal

conditions of the adsorption process using various adsorbents (raw EGFF, A-EGFF,

AC-EGFF, AC-EGFF-Fe3O4) were determined. To examine the practicability of the

prepared adsorbent, the adsorbent was later on used in the treatment of textile

industry wastewater.

The objectives of the present study include:

(a) To produce and characterize adsorbents for RB color removal and COD

reduction using an agricultural waste- Elaeis guineensis frond fiber, through

different adsorbent modification methods such as phosphoric acid

modification, carbonization, and co-precipitation.

(b) To optimize the adsorbent preparation processes and the adsorption activities

using statistical design of experiment (DOE)-Response surface methodology

(RSM).

(c) To determine the efficiency of using nano-composite adsorbent for the color

removal and COD reduction of Rhodamine B dye aqueous solutions and

industrial textile wastewater.

(d) To determine the kinetics and propose the mass transfer mechanisms

involved in the adsorption process.

8

CHAPTER TWO

LITERATURE REVIEW

2.1 Dyes

Textile industry ranks first among other industries such as rubber, paper,

cosmetic, plastic, etc. in usage of dyes for fiber coloration (Grag et al., 2003). A dye

is a colored, aromatic organic substance that absorbs light in the visible spectrum

from 400-800 nm (Rangabhashiyam et al., 2013). The dye molecule contains

delocalized electron systems with conjugated double bonds which comprise the

chromophore and the auxochrome. The chromophore is a group of atoms principally

responsible for the color of dye. The most imperative chromophores are the azo (-

N=N-), carbonyl (C=O), methane (-CH=), and nitro (-NO2) groups (Christie, 2001).

The auxochrome intensifies the color of the chromophore by providing solubility of

the dye through modification of the overall energy in the electron system. The

common auxochrome groups are hydroxyl (OH), and amino (NR2) groups (Christie,

2001). The distinctive dyes used in textile dyeing process are listed in Table 2.1.

From Table 2.1, most of the dyes are water soluble except disperse and vat dyes.

Table 2.1 Distinctive dyes used in textile dyeing process (Demirbas, 2009;

Rangabhashiyam et al., 2013).

Dye class Description

Acid Anionic compounds; water soluble

Basic Cationic compounds; water soluble; used in weakly acidic dye

baths; very bright color

Direct Anionic compounds; water soluble; can be used directly to

cellulosic without mordant

Disperse Non-ionic aromatic compounds; Water insoluble

Reactive Anionic compounds; water soluble; largest dye class

Sulfur Contain sulfur or sodium sulfide

Vat Water insoluble; oldest dyes; contain complex chemical structure

9

2.2 Pollution Due to Dye Wastewater

2.2.1 Color

Colored wastewater is a corollary of batch processes both in the dye

manufacturing and dye-consuming industries. According to Easton (1995), 10% of

the dyes are lost during textile coloration process due to incomplete exhaustion of

dyes onto the fibre. Type of dyestuff, the depth of shade needed, and the application

route are the dependent factors that determined the amount of dye lost (Pearce et al.,

2003).

Color pollution in aquatic environments is an escalating problem. The

toxicity, abnormal coloration and carcinogenic properties of dyes cause severe

effects on exposed organisms and hinder the photosynthesis reaction (Slokar and Le

Marechal, 1998; Pearce et al., 2003). Moreover, the color of water greatly influences

the public perception of water quality, where the presence of colors in water is

aesthetically unpleasant and is often associated with contamination (Waters, 1995;

Pearce et al., 2003). The recalcitrant nature of dyes causes dyes to be persistent in the

water, leading to the imposition of strict environmental regulations.

2.2.2 Chemical Oxygen Demand

In environment chemistry, chemical oxygen demand (COD) is generally used

to evaluate the concentration of organic contaminants in water bodies. As

degradation of organic compounds involves oxygen, their concentrations can be

represented by the amount of oxygen needed (Li et al., 2003). COD concentration in

the unit of mg/L is largely dependent on initial dye waste concentration, chemical

10

structure of the dye and treatment duration (Tanja et al., 2003). The COD value

indicates the amount of oxygen required for the complete oxidation of a substance in

specific volume of aqueous solutions. When organic pollutants are high in a water

sample, concentration of COD is high; more oxygen is required to completely

oxidize a substance. Therefore, wastewater with high COD concentration denotes

high pollution level (Tanja et al., 2003).

2.3 Textile Wastewater Treatment Technologies

High volumes of textile industrial effluent discharge and increasing stringent

legislation make the search for appropriate treatment technologies a must. On the

whole, textile industrial wastewater treatment encompasses four processes i.e.

pretreatment, primary treatment, secondary treatment, and tertiary treatment (Perry et

al., 1997). Pretreatment process comprises of equalization and neutralization. In the

primary treatment, physical or chemical separation techniques are employed to

remove suspended solids in the textile wastewater (Gupta and Suhas, 2009).

Secondary treatment, also known as biological treatment, exploits microorganisms to

stabilize the dyes components before tertiary treatment (i.e. adsorption, ion-exchange,

stripping, chemical oxidation, and membrane separation) takes place. The last steps

for the textile wastewater treatment process are the sludge processing and disposal

steps (Gupta and Suhas, 2009).

In general, textile wastewater treatment methods include physical, chemical

and biological treatments. These methods can be applied either individually or

together in various combinations.

11

Physical treatment involves only particle separation processes and there is no

chemical or biological changes carried out (Metcalf and Eddy, 2004). Example of the

treatment processes are adsorption (Low et al., 2011; Lin et al., 2013), sedimentation

(He et al., 2015; Walker and Narbaitz, 2016), aeration (Wu and He, 2012), filtration

(Zuo et al., 2015; Zhao et al., 2016), etc.

Chemical treatment mainly involves the use of oxidizing agents such as

ozone (O3), hydrogen peroxide (H2O2), and permanganate (MnO4) to modify the

chemical composition of dyes (Metcalf and Eddy, 2004). The cost of this treatment

process is largely dependent on the chemical used. Chemical treatment process has a

satisfactory result in removing disperse, sulfur, and vat dyes (Verma et al., 2012).

The disadvantages of the treatment process are large quantities of concentrated

sludge produced, pH dependent, not effective for highly soluble dyes and not

effective in treating acid and basic dyes (Hai et al., 2007). Examples of chemical

treatment processes are ozonation (Tehrani-Bagha et al., 2010; Hu et al., 2016),

coagulation-flocculation (Yeap et al., 2014; Lau et al., 2014), liquid-liquid extraction

(Muthuraman and Teng, 2009, 2010), and sonolysis (Vassilakis et al., 2004; Khataee

et al., 2015).

Biological treatment involves the use of microorganisms to decompose

organic matters during wastewater treatment. It is the most economical alternative

treatment compared to the physical and chemical processes. Examples of biological

treatments generally used for the treatment of textile industrial effluents are

microbial degradation, adsorption by living or dead microbial biomass and

bioremediation systems using microorganisms (McMullan et al., 2001).

12

The biological process can be aerobic (in the presence of oxygen) (Franca et

al., 2015; Liu et al., 2015), anaerobic (without oxygen) (Wong et al., 2009; Hahn and

Figueroa, 2015) or combined aerobic-anaerobic (Yang et al., 2016). The main

drawbacks of the biological treatment are less feasibility in design and operation,

sensitivity to some chemicals, low biodegradability of the COD and dyes, larger land

area requirement and longer time required for decolorization-fermentation processes

(Dilaver and Kargi, 2009).

The present study focuses on the adsorption of Rhodamine B dye on a locally

available biomass.

2.3.1 Adsorption

The process of adsorption involves accumulation of a substance at the

interface between two phases such as solid and liquid or solid and gas. It can also be

defined as a process that transfers pollutants from the effluent to a solid phase

thereby reducing the bioavailability of toxic species to living organisms (Bhatnagar

and Sillanpaa, 2009; Ribas et al., 2014). Solids have been widely used for substance

removal from either gaseous or liquid phase since biblical times. This process

involves the preferential partitioning of substances from the gaseous or liquid phase

onto the surface of a solid substrate. Thus, adsorption is different from absorption, a

process in which materials are transferred from one phase (liquid phase or gaseous

phase) to another interpenetrates the second phase to form a solution (Weber, 1972).

Figure 2.1 shows the definitions of adsorbent and adsorbate.

13

Figure 2.1: Definitions of adsorbent and adsorbate.

The substance to be removed from liquid or gaseous phase at the interface is called

adsorbate. Adsorbent can be defined as the solid, liquid, or gas phase onto which the

adsorption takes place (Butt et al., 2011).

Generally, transformation of adsorbate to the porous media adsorbent follows

four steps, (i) bulk solution transport; i.e. transportation of adsorbate from bulk

solution to the hydrodynamic boundary layer (liquid-solid interface) surrounding the

adsorbent. (ii) external diffusion; i.e. transportation of the asorbate from the bulk to

the external surface of the adsorbent. (iii) intraparticle diffusion. (iv) adsorption; i.e.

adsorbate is attached onto the available active sites on the adsorbent surface (Wang

et al., 2008).

2.3.2 Classification of Adsorption

On the whole, adsorption process largely depends on the nature of force

existing between adsorbate molecules and adsorbent. Adsorption can be categorized

into physical adsorption (physisorption) and chemical adsorption (chemisorption).

14

2.3.2(a) Physisorption

Physisorption involves intermolecular forces such as van der waals and

dipole forces between the adsorbent and the adsorbate. This process is completely

nonspecific reversible under high temperature and pressure. A physisorption

molecule is not attached to a specific site on the solid surface, spontaneously it can

leave the surface after a certain time (Sawyer et al., 2003).

2.3.2(b) Chemisorption

Chemisorption occurs as a result of the formation of a chemical linkage

(often covalent) between the adsorbent and adsorbate giving a shorter bond length

and higher bond energy (Montgomery, 1985). Table 2.2 presents the properties and

characteristics of physisorption and chemisorption.

Table 2.2 Properties and characteristics of physisorption and chemisorption (Atkins,

1994).

Properties/

Characteristics

Physisorption Chemisorption

Adsorption temperature Adsorption process

decreases with the

increase of temperature

Adsorption process

increases with the increase

of temperature

Adsorption energy Exothermic or

endothermic,

40-200 kJ/mol

Merely exothermic

< 40 kJ/mol

Nature of adsorption Non-dissociative and

reversible

Frequently dissociative

and irreversible

Adsorption site Monolayer or multilayer Monolayer

Adsorption process Non-activated and fast Activated and slow

Desorption process Desorption is possible Desorption is impossible

15

For chemisorption, the adsorption process is irreversible and increases with

temperature. The adsorption energy is merely exothermic with the value of less than

40 kJ/mol. However, for physisorption, the adsorption process is reversible and

decreases with the increases of temperature. The adsorption energy has the value

between 40-200 kJ/mol.

2.4 Kinetic Study

Adsorption kinetic study is a vital characteristic in wastewater treatment as it

illustrates the adsorbate uptake rate, which in turn controls the residence time of the

adsorbate uptake at solid-liquid interface (Dąbrowski, 2001). The pseudo-first order

and pseudo-second order models are the most commonly used kinetic models for

studying solid-liquid interactions. In pseudo-first order kinetic model, adsorption

process is controlled by diffusion and mass transfer of the dye molecules to the

adsorption site, whereas in pseudo-second order kinetic model, chemisorption is the

rate limiting step (Crini and Badot, 2008; Nair et al., 2014).

2.4.1 Pseudo-First Order Model

Pseudo-first order model was proposed by Lagergren (1898). The pseudo-

first-order equation can be written as Equation (2.1):

)(1 tet qqk

dt

dq (2.1)

Integrating Equation (2.1) for the boundary conditions, t=0 to t=t and qt=0 to qt=qt,

generates Equation (2.2):

16

tkq

q

e

t1)1ln( (2.2)

where 1k is the rate constant of pseudo-first order model (min-1

), eq (mg/g) is the

amount of equilibrium uptake, tq (mg/g) is the amount of solute adsorbed at any time

t, and is given by Eq. (2.3). The value of k1 can be obtained by plotting )1ln(e

t

q

q

versus t.

W

VCCq t

t

)( 0 (2.3)

where C0 (mg/L) is the initial solute concentration, Ct (mg/L) is the solute

concentration at respective time, t, V is the volume of the dye solution (L), and W is

the weight of the adsorbent (g).

2.4.2 Pseudo-Second Order Model

Pseudo-second-order equation (Ho and McKay, 1998) based on equilibrium

adsorption can be expressed as Equation (2.4):

tqkqqeet

2

2

111 (2.4)

where 2k (g/mg.min) is the pseudo-second order rate constant. This equation can also

be written as Equation (2.5):

tqkqqeet

2

2

111 (2.5)

17

The value of k2 can be obtained by plotting et qq

11 versus

t

1.

2.5 Equilibrium Study

The adsorption isotherm gives the relationship between mass of adsorbate

adsorbed per unit weight of adsorbent in equilibrium and the concentration of

adsorbate at liquid-phase equilibrium (Lata et al., 2007). It is a basic requirement for

the design of adsorption system. A number of isotherms have been proposed and

these include Langmuir isotherm, Freundlich isotherm, Temkin isotherm, and

Dubinin-Radushkevich (DR) isotherm.

2.5.1 Langmuir Isotherm

Langmuir adsorption model (Langmuir, 1918) is based on the assumption that

maximum adsorption takes place at specific homogeneous sites within the adsorbent.

Langmuir model is given by Equation (2.6):

eL

eLe

CK

CKQq

1

0 (2.6)

where eC is the concentration of adsorbate remaining in the solution at equilibrium

(mg/L), 0Q is the amount of adsorbate adsorbed by unit mass of adsorbent that is

required to cover an adsorbent surface completely as a monomolecular layer (mg/g),

and LK (L/mg) is the Langmuir constant related to the affinity of the binding sites.

The values of 0Q and LK are determined from intercept and slopes of the linear plots

18

of e

e

q

Cversus eC . The Langmuir model can be represented in the linear form as

shown in Equation (2.7):

00

1

Q

C

KQq

C e

Le

e (2.7)

A linear plot of e

e

q

C versus eC suggests the applicability of the Langmuir model for

the system.

An essential characteristics of the Langmuir isotherm can be expressed in

terms of separation factor or equilibrium parameter, LR , a dimensionless constant

(Weber and Chakkravarti, 1974), which is given by Equation (2.8):

)1(

1

0CKR

L

L

(2.8)

A value of 0< LR <1 shows unfavourable adsorption conditions;

LR <1 shows unfavourable adsorption conditions;

LR =1 shows linear adsorption conditions; and

0LR shows irreversible adsorption conditions.

2.5.2 Freundlich Isotherm

Freundlich model is an empirical equation that assumes heterogenous

adsorption due to the diversity of adsorption active sites (Freundlich, 1907). The

Freundlich equation is given as Equation (2.9):

19

n

eFe CKq /1 (2.9)

where FK is Freundlich isotherm constant (mg/g (L/mg)1/n

), an indicator for

adsorption capacity and 1/n is the adsorption intensity. A value of 0 < 1/n < 1 shows

adsorption surface homogeneity, as the value gets closer to 0 the adsorption process

is heterogeneous (Hameed et al., 2007). A value for 1/n < 1 shows a normal

Langmuir isotherm while 1/n >1 indicates cooperative adsorption (Fytianos et al.,

2000). The linear form of Freundlich equation is given in Equation (2.10):

ln qe = ln KF + (1/n) ln Ce (2.10)

The values of FK and n are calculated from the intercept and slope of the plot of

eqln versus eCln .

2.5.3 Temkin Isotherm

Temkin isotherm (Temkin and Pyzhev, 1940) discussed on the adsorbent-

adsorbate interactions. Based on the isotherm, the heat of adsorption of all the

molecules in the layer would decrease linearly with coverage due to adsorbent-

adsorbate interactions. The adsorption is described by a consistent distribution of

binding energies, up to some maximum binding energy. The Temkin isotherm can be

expressed as Equation (2.11):

)(ln eT

T

e CAb

RTq (2.11)

where Tb is Temkin isotherm constant related to heat of adsorption in J/mol, TA is

the Temkin isotherm constant in L/g. R is the universal gas constant with the value of

20

8.314 J/mol.K and T is the absolute solution temperature in K. The values of Tb

RTand

TA are calculated from the intercept and slope of the plot of qe versus ln Ce

2.5.4 Dubinin-Radushkevich (DR) Isotherm

Dubinin-Radushkevich (DR) Isotherm is used for the analysis of isotherms of

a high degree of rectangularity (Dubinin and Radushkevich, 1947). DR isotherm can

be expressed as Equation (2.12):

qe = QDR exp (-Bε2) (2.12)

where can be correlated in Equation (2.13):

)1

1ln(eC

RT (2.13)

The constant B establishes the mean free energy E of adsorption per molecule of the

adsorbate when it is transferred to the surface of the solid from infinity in the

solution. DRQ is the Dubinin-Radushkevich constant. The equation for mean free

energy is expressed as Equation (2.14):

BE

2

1 (2.14)

The values of DRQ and E are calculated from the intercept and slope of ln qe versus

2 . Table 2.3 presents the compilation of results of the applicability of kinetic and

isotherm models for dye adsorption. Most of the dye adsorption studies followed

pseudo-second order kinetic model and Langmuir isotherm where chemisorptions is

21

the rate limiting step and maximum adsorption takes place at specific homogeneous

sites within the adsorbent.

Table 2.3 Kinetic and isotherm studies of textile dye adsorption.

Adsorbent Dye Kinetic model Isotherm model Reference

Bagasse fly ash Orange-G Pseudo-second order Freundlich Mall et al., 2006

Chitosan Remazol black 13 Pseudo-first and second

order

Langmuir Annadurai et al., 2008

Basic oxygen furnace

slag

Reactive Blue 19

Reactive Black 5

Reactive Red 120

Pseudo-first order Langmuir and

Redlich–Peterson

Xue et al., 2009

Tunisian olive waste cake Lanaset grey G Pseudo-first order Langmuir Baccar et al., 2010

Coconut coir Malachite green Pseudo-second order Langmuir and

Freundlich

Uma et al., 2013

Rice husk Methylene blue Pseudo-second order Langmuir Chen et al., 2013

MgO decked multi-

layered grapheme

Safranin O Pseudo-second order Langmuir Rotte et al., 2014

Poly(methacrylic

acid)/zeolite hydrogel

composites

Basic yellow 28 Pseudo-first order Langmuir and Temkin Panic and Velickovic, 2014

Spent coal based

activated carbon

Methylene blue Pseudo-second order Langmuir Duan et al., 2014

Macore fruit shell Methylene blue,

Methyl orange

Pseudo-second order Langmuir and

Freundlich

Aboua et al., 2015

activated carbon/γ-Fe2O3

nano-composite

Alizarin red S Pseudo-second order Langmuir Fayazi et al., 2015

Ag-doped hydroxyapatite Congo red Pseudo-second order Langmuir Srilakshmi and Saraf, 2016

Malt bagasse orange solimax TGL Pseudo-second order Langmuir Fontana et al., 2016

Cerastoderma lamarcki

shell

Malachite green Pseudo-second order Freundlich Kazemi et al., 2016

22

Table 2.3 (continued)

Adsorbent Dye Kinetic model Isotherm model Reference

Bagasse Methylene blue Pseudo-second order Langmuir and

Freundlich

Low et al., 2011

Cogongrass Methylene blue Pseudo-second order Langmuir Su et al., 2014

Raphia hookerie fruit

epicarp

Rhodamine B Pseudo-second order Freundlich Inyinbor et al., 2016

MIL-68(In)-

NH2/graphite oxide (GO)

composites

Rhodamine B Pseudo-second order Langmuir Yang et al., 2016

Aleurites Moluccana

seeds

Rhodamine B Pseudo-second order Sips isotherm Postai et al., 2016

Gum Ghatti/Fe3O4 Rhodamine B Pseudo-second order Langmuir Mittal and Mishra, 2014

Kaolinite Rhodamine B Pseudo-second order Langmuir Khan et al., 2012

Carnauba palm leaves Rhodamine B Pseudo-second order Freundlich Lacerda et al., 2015

Lythrum salicaria L. with

pyruvic acid

Rhodamine B Pseudo-second order Langmuir Huang et al., 2016

23

24

2.6 Activated Carbon

Activated carbon is a crude form of graphite, which has a highly porous,

random or amorphous structure with broad range of pore sizes, from visible cracks,

crevices and slits of molecular dimensions (Sun et al., 2013). In the 1940s activated

carbon was employed as an adsorbent for wastewater treatment (Gupta and Ali,

2013). Typically, activated carbon includes a broad range of carbonaceous materials,

possess high surface area (that can reach 2000 m2/g), well defined microporous

structure (average pore opening is about 1.5 nm), and high degree of surface

reactivity (Streat et al., 1995). Commercial activated carbons are mainly prepared

from coal and pine wood. However, activated carbon is expensive. This situation

compelled scientists toward the development of low cost adsorbents i.e. alternatives

of activated carbon (Ali et al., 2012).

2.7 Development of Low-Cost Adsorbents

Currently, there are many studies on the development of low-cost adsorbents

using natural materials, biomass, and agricultural waste. In general, an adsorbent can

be assumed to be “low-cost” if it requires little processing and is abundant in nature.

It could also be waste material from an industry or it's by-products, which have lost

economic value even after further processing (Yagub et al., 2014). The use of waste

products which have little or no economic value for developing low-cost adsorbents

gives advantages in waste minimization, recovery and reuse. In other words, waste

treatment by adsorption using low-cost adsorbent is a demanding area as it has

benefits in both water treatment and waste management (Yagub et al., 2014).