1
THE USE OF LOW COST ZEOLITES FOR THE REMOVAL OF
SELECTED CONTAMINANTS AND COMBINATION WITH BIOLOGICAL
PROCESS FOR WASTEWATER TREATMENT
LEE KIAN KEAT
UNIVERSITI TEKNOLOGI MALAYSIA
iii
To my beloved mother, father, brother and sisters
iv
ACKNOWLEDGEMENT
I would like to thank my supervisor Prof. Dr. Alias Mohd. Yusof for giving
me the chance to work on his project as well as for his valuable guidance, support
and untiring patience.
I am grateful to Associate Professor Dr. Zaharah Ibrahim, Dr. Zaiton Abdul
Majid and Professor Dr. Noor Aini bt. Abdul Rashid for their constant vigilance and
valuable suggestions throughout this study. I would also express my appreciation to
all other faculty members and staff in the Department of Chemistry and Department
of Biology for their enormous help with my study.
I thank all of my friends, colleagues and laboratory personnel who extended
their time, expertise, generous advice, criticism, technical assistance and
encouragement during my research. I like to acknowledge everyone, but I am to be
constrained to a few in mentioning names as Mr. Ayob Jabal, Mr. Hanan Basri, Mr.
Azmi M. Rais, Mrs. Z. Ain Jalil, Mr. Hj. Yasin bin. M. Sirin, Miss. Nurul H.
Sapiren, Mr. M. Nazri Zainal, Mr. Dinda Hairul, Mr. Hamzah, Mr. Abdul Kadir,
Mrs. Mek zum, Mr. Amin Derani, Mr. Abdur Rahim, Mrs. Mariam Hassan, Mr.
Azani b. Ishak of Department of Chemistry, Mr. Awang, Mrs. Fatimah, Mrs. Radiah
and who indebted me most for their assistance in pursing laboratory work.
I owe thanks to my all family members, my mother, brothers and sisters for
their help and love without that I cannot continue my study here.
v
ABSTRACT
Two types of low cost zeolites, namely natural mordenite and synthetic
zeolite Y synthesized from a local agro-wastes, rice husk ash were applied to remove
various types of contaminants from water. Zeolite Y was synthesized under
hydrothermal conditions with appropriate seeding and aging methods, in which the
overall relative composition of Na2O: Al2O3: SiO2: H2O is 5.1: 1.0: 10.5: 184.0. The
physico-chemical properties of the zeolites were characterized using various
techniques. Ammonium removal studies were carried out with the raw mordenite
and as-synthesized zeolite Y. Pseudo first order kinetic model and pseudo second
order kinetic model were employed to understand the sorption kinetics, while several
isotherm equations such as Langmuir, Freundlich and Temkin to study the sorption
behavior. To bombard against oxyanions such as nitrate, sulfate and phosphate, the
surface chemistry of the zeolites were altered by a cationic surfactant, quaternary
amine HDTMA-Br in proportional to the external cation exchange capacity of the
zeolites. Both the surfactant-modified zeolites (SMZ) presented significant affinity
and adsorption capacity towards the oxyanions. Besides that, while the unmodified
zeolites had no affinity towards anionic organic, Acid Orange 7 (AO7), the SMZ
showed impressively high adsorption capacity with a rapid removal rate. Suitable
kinetics and isotherms models were employed to further understand the sorption
behaviors. Combination of the adsorption and biological treatment process in
wastewater treatment is interesting. Prior to the study of the combined process, the
powdered zeolites and its modified form were first fabricated to the small round
particle; several studies were carried out to study the physico-chemical
characteristics of the zeolite particles. Indigenous bacteria strains were isolated from
a wastewater source and the performance of the bacteria to remove different
contaminants was screened. Finally the use of zeolite particle in textile wastewater
treatment together with the mixed cultures of bacteria was studied in several
approaches.
vi
ABSTRAK
Dua jenis zeolit kos rendah, iaitu zeolit semula jadi mordenit dan zeolit Y
sintetik yang disintesis daripada sisa pertanian tempatan, iaitu abu sekam padi telah
digunakan untuk menyingkirkan beberapa jenis pencemar daripada air. Zeolit Y
yang disintesis dalam keadaan hidro-terma dengan kaedah pembenihan dan
penungguan, dengan kandungan keseluruhan bagi Na2O: Al2O3: SiO2: H2O ialah 5.1:
1.0: 10.5: 184.0. Ciri-ciri fisikal-kimia zeolit tersebut telah diperiksa dengan
pelbagai kaedah. Kajian penyingkiran ammonium telah dijalankan dengan mordenit
dan zeolit Y. Model pseudo kinetik tertib pertama dan model pseudo kinetik kedua
digunakan untuk meneliti kinetik penjerapan, sementara itu beberapa jenis
persamaan isoterma seperti Langmuir, Freundlich dan Temkin digunakan untuk
meneliti kelakuan penjerapan. Demi menjerap oksi-anion seperti nitrat, sulfat dan
fosfat, kimia permukaan zeolit tersebut perlu ditukarsuai dengan surfaktan kation,
heksadesiltrimetil ammonium (HDTMA-Br) dengan kandungan berkadar dengan
kapasiti penukaran kation luar. Kedua-dua zeolit ditukarsuai surfaktant (SMZ)
menunjukkan afiniti yang jelas dan kapasiti penjerapan terhadap oksi-anion.
Sementara zeolit asli tiada afiniti terhadap organik anionik, Oren Asid 7 (AO7),
SMZ menunjukkan kapasiti penjerapan tinggi yang memerangsangkan dengan kadar
penyingkiran laju. Model kinetik dan isoterma yang bersesuaian telah digunakan
untuk memahami kelakuan penjerapan tersebut. Gabungan penjerapan dan rawatan
biologi dalam rawatan air sisa adalah suatu proses yang menarik. Sebelum kajian
proses gabungan itu, zeolit dalam bentuk serbuk dan SMZ telah dibentuk kepada
bebola kecil; beberapa kajian telah dijalankan untuk memeriksa ciri-ciri bebola zeolit
tersebut. Bakteria tempatan telah dipisah daripada sumber air sisa dan keupayaan
bakteria-bakteria itu untuk menyingkir pelbagai pencemar telah diuji. Akhirnya,
penggunaan bebola zeolit dalam rawatan sisa air tekstil bersama dengan campuran
bakteria dalam beberapa pendekatan telah dikaji.
vii
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
THESIS STATUS DECLARATION
SUPERVISOR’S DECLARATION
1
2
TITLE PAGE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiv
LIST OF SYMBOLS
xx
LIST OF ABBREVIATIONS
xxii
INTRODUCTION
1.1
Background
1
1.2
Research Objectives
5
1.3
Scope and Outline of Thesis
5
LITERATURE REVIEW
2.1
Features of Zeolite
8
2.1.1 Zeolite Framework Topology
10
viii
2.2
Relationship of Synthetic Zeolite to Natural
11
Zeolite: A Brief Review
2.3
The Synthesis of Zeolite
14
2.3.1 General Aspects of Zeolite Synthesis
15
2.3.2 Rice Husk Ash (RHA) as a Silica Source
16
2.3.3 Synthesis of Zeolite Y
19
2.3.3.1 Effect of Aging of Amorphous
19
Gel on Crystallization
2.3.3.2 Effect of Seeding on
21
Crystallization
2.4
Zeolite Y
21
2.5
Mordenite
23
2.6
Surfactant Modified Zeolite
25
2.6.1 Adsorption of Cationic Surfactant at
29
Zeolite Surface
2.6.2 Mechanisms of Contaminants Sorption by
31
SMZ
2.6.3 Biological Toxicity of Surfactant and
33
SMZ
2.7
2.8
Adsorption Theory
34
2.7.1 Langmuir Adsorption Model
35
2.7.2 Freundlich Adsorption Model
37
2.7.3 Temkin Adsorption Model
37
Combination of Adsorption and Biological
38
Treatment
3
EXPERIMENTAL
3.1
Preparation of the Rice Husk Ash
42
3.2
Determination of Silica Content in Rice Husk
42
Ash
3.3
Detailed Description of Synthesis of Zeolite Y
43
from Rice Husk Ash
3.4
Characterization Techniques
45
ix
3.4.1 X-ray Diffraction (XRD)
45
3.4.2 Fourier Transform Infrared (FTIR)
46
Spectroscopy
3.4.3 Thermogravimetry-Differential Thermal
47
Analysis (TG-DTA)
3.4.4 Field-Emission Scanning Electron
47
Microscopy (FESEM) and Energy
Dispersive X-Ray Analysis (EDAX)
3.4.5 Surface and Porosity Analysis with
48
Nitrogen Adsorption
3.5
Determination of Cation Exchange Capacity and
48
External Cation Exchange Capacity
3.6
Preparation of Surfactant-Modified Zeolites
49
3.7
Adsorption Studies
50
3.7.1 Test and Standard Solutions
51
3.7.2 Kinetic Studies
52
3.7.3 Adsorption Equilibrium (Isotherm)
52
Studies
3.7.5 Chemical Analysis
55
3.8
Aseptic Working Condition
56
3.9
Preparation of Growth Medium
57
3.9.1 Nitrate Selective Agar
57
3.9.2 Sulfate Selective Agar
58
3.9.3 Phosphate Selective Agar
59
3.10
Isolation of Bacteria from Wastewater
59
3.11
Screening Studies of Bacteria for Contaminants
59
Removal
3.12
Preparation of Zeolite Particle
60
3.13
Use of Zeolite Particle for Wastewater Treatment
62
3.14
Laboratory Analysis
63
x
4
RESULT AND DISCUSSION PART I
4.1
Characterization of Rice Husk Ash (RHA)
65
4.2
Synthesis of Zeolite Y
67
4.3
Characterization of Zeolite Y
71
4.3.1 Fourier Transform Infrared (FT-IR)
71
Spectroscopy
4.3.2 Thermal Behavior
73
4.3.3 Textural and Physico-Chemical
78
Characterization
4.4
4.3.4 Cation Exchange Capacity
81
Characterization of Mordenite
81
4.4.1 Mineralogical Characterization
81
4.4.2 Fourier Transform Infrared (FT-IR)
85
Spectroscopy
4.4.3 Textural and Physico-Chemical
87
Characterization
4.5
5
92
Ammonium Removal Studies
92
4.5.1 Kinetic Studies
93
4.5.2 Batch Equilibrium Studies
99
RESULT AND DISCUSSION PART II
5.1
5.2
6
4.4.4 Cation Exchange Capacity
Oxyanions Removal Studies
103
5.1.1 Nitrate Removal
104
5.1.2 Sulfate Removal
111
5.1.3 Phosphate Removal
117
Acid Dye Removal Studies
125
RESULT AND DISCUSSION PART III
6.1
Isolation and
Screening
of Bacteria
from
132
Wastewater
6.1.1 Nitrate Removal Test
135
6.1.2 Sulfate Removal Test
138
xi
6.2
6.1.3 Phosphate Removal Test
140
Use of Zeolite Particle for Textile Wastewater
142
Treatment (I)
6.3
6.2.1 pH Change
143
6.2.2 Color Removal
144
6.2.3 Nitrate Removal
147
6.2.4 Sulfate Removal
148
6.2.5 Phosphate Removal
149
6.2.6 Ammonium Removal
150
Use of Zeolite Particle for Textile Wastewater
151
Treatment (II)
7
6.3.1 pH Change
152
6.3.2 Color Removal
153
6.3.3 Ammonium Removal
154
6.3.4 Nitrate Removal
155
6.3.5 Sulfate and Phosphate Removal
155
CONCLUSIONS AND SUGGESTIONS
7.1
Conclusions
157
7.2
Contributions
159
7.3
Suggestions for Future Studies
160
REFERENCES
162
xii
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Chemical source and their function in zeolite synthesis
15
3.1
The annotations of the prepared surfactant-modified
50
zeolites
3.2
Conditions of kinetic studies
54
3.3
Conditions of adsorption equilibrium studies
54
3.4
Composition of nitrate selective agar
58
3.5
Composition of sulfate selective agar
58
3.6
Composition of phosphate selective agar
59
3.7
The materials and mixing ratio for the preparation of zeolite particle
61
4.1
Silica content and LOI in RHA
67
4.2
X-ray diffraction data of as-synthesize zeolite Y,
70
commercial zeolite Y and PDF 43-0168
4.3
Infrared adsorption bands for zeolite Y
72
4.4
Chemical composition of the zeolite Y from EDAX
79
analysis
4.5
CEC and ECEC data of synthesized zeolite Y
81
4.6
X-ray diffraction data of powdered mordenite, granular
84
mordenite and PDF 29-1257, , (Na2, Ca, K2)Al2Si10O24
4.7
X-ray diffraction data of powdered mordenite, granular
85
mordenite and PDF 46-1045 (quartz, SiO2)
4.8
Infrared adsorption bands for mordenite
87
4.9
Chemical composition of the zeolite Y from EDAX
91
analysis
xiii
4.10
CEC and ECEC data of mordenite samples
92
4.11
Kinetic parameters for the removal of ammonium by
97
different adsorbents
4.12
Isotherm parameters for ammonium removal by zeolites
102
5.1
Kinetic parameters for the removal of nitrate by different
109
adsorbents
5.2
Freundlich isotherm parameters for NO3- removal by SMZ
111
5.3
Kinetic parameters for the removal of sulfate by different
115
adsorbents
5.4
Isotherm parameters for SO42- removal by SMZ
118
5.5
Kinetic parameters for the removal of phosphate by
122
different adsorbents
5.6
Isotherm parameters for PO43- removal by SMM
126
5.7
Kinetic parameters for the removal of ammonium by
131
different adsorbents
5.8
Isotherm parameters for AO7 removal by SMZ
133
6.1
Screening of bacteria in selective media
135
6.2
Systems used in the wastewater treatment
145
xiv
LIST OF FIGURES
FIGURE NO.
1.1
TITLE
PAGE
Overview of all water on earth. The amount of fresh
liquid is less than 1 %
2
1.2
Outline of the thesis
7
2.1
The Secondary Building Unit (SBU) and their symbols in
10
zeolite framework. Number in parenthesis = frequency
occurrence
2.2
Faujasite framework illustrating the oxygen position and
23
cation site
2.3
(a) The schematic illustration of mordenite framework.
25
The small black and large gray balls in the framework
show Si/Al and O atoms, respectively. (b) The two kinds
of Na cation sites are shown by the large black and
striped balls.
2.4
The structure of hexadecyltrimethyl ammonium bromide
27
(HDTMA-Br)
2.5
Cationic surfactants adsorb on solid surface and form the
30
hemimicelle (a) and admicelle (b)
2.6
Schematic diagram of sorption mechanisms for anions,
32
cations, and non-polar organics on SMZ.
3.1
Structural formula of AO7
52
4.1
XRD pattern of RHA
66
4.2
FT-IR spectrum of RHA
66
xv
4.3
X-ray diffractogram for mixture of zeolite Y and zeolite P
68
4.4
X-ray diffractogram of synthetic zeolite Y
69
4.5
X-ray diffractogram of synthesized zeolite Y and
69
commercial zeolite Y
4.6
IR spectrum of the synthesized zeolite Y
72
4.7
TG and DTA curve of the zeolite Y synthesized from
74
RHA
4.8
TG and DTA curve of the commercial zeolite Y,
75
CBV100
4.9
XRD patterns of the heat-treated zeolite Y
77
4.10
XRD patterns of the heat-treated commercial zeolite Y
77
4.11
FESEM image of the zeolite Y at magnification of
78
1000 ×
4.12
FESEM image of the zeolite Y at magnification of
78
5000 ×
4.13
Typical EDAX spectrum of zeolite Y
4.14
N2
adsorption-desorption
isotherms
79
of
zeolite
Y
80
X-ray diffractograms of powdered mordenite (upper
82
synthesized from RHA
4.15
pattern) and granular mordenite (lower pattern)
4.16
X-ray diffractograms of powdered mordenite with PDF
83
29-1257, mordenite and PDF 46-1045, quartz (peaks with
black dot)
4.17
IR spectrum of the powdered mordenite
86
4.18
IR spectrum of the granular mordenite
86
4.19
Typical topographic images for the granular modernite by
88
FESEM at magnification of 1000 × (a) and 5000 × (b)
4.20
Typical topographic images for the powdered modernite
89
by FESEM at magnification of 1000 × (a) and 5000 × (b)
4.21
Typical EDAX spectrum of powdered mordenite
90
4.22
Typical EDAX spectrum of granular mordenite
90
4.23
N2
adsorption-desorption
(powder)
isotherms
of
mordenite
91
xvi
4.24
Kinetic profile of ammonium uptake by zeolites
94
4.25
Plot of pseudo first-order kinetic model for NH4+ sorption
96
into P-M
4.26
Plot of pseudo first-order kinetic model for NH4+ sorption
96
into G-M
4.27
Pseudo second-order kinetic plot for the ammonium
97
removal by P-M
4.28
Pseudo second-order kinetic plot for the ammonium
98
removal by G-M
4.29
Pseudo second-order kinetic plot for the ammonium
98
removal by Y
4.30
Langmuir isotherm plots for removal of NH4+ by various
100
sorbents (pH = 7, temperature = room temperature, Co =
10 to 500 mg/L, zeolite dosage = 2.5 g/L)
4.31
Freundlich isotherm plots for removal of NH4+ by various
100
sorbents (pH = 7, temperature = room temperature, Co =
10 to 500 mg/L, zeolite dosage = 2.5 g/L)
4.32
Temkin isotherm plots for removal of NH4+ by various
101
sorbents (pH = 7, temperature = room temperature, Co =
10 to 500 mg/L, zeolite dosage = 2.5 g/L)
5.1
Kinetic profile of nitrate removal by SMM
106
5.2
Kinetic profile of nitrate removal by SMY
107
5.3
Plot of pseudo second order kinetic for NO3- sorption into
107
SMM
5.4
Plot of pseudo second order kinetic for NO3- sorption into
108
SMY
5.5
The adsorption isotherm of NO3- sorption on unmodified
109
mordenite (UM) and SMM
5.6
The adsorption isotherm of NO3- sorption on unmodified
110
zeolite Y (UY) and SMY
5.7
The maximum adsorption capacity of nitrate by the
112
various sorbents
5.8
Kinetic profile of sulfate removal by SMM
113
xvii
5.9
Kinetic profile of sulfate removal by SMY
114
5.10
Pseudo-second order kinetic model for the removal of
114
sulfate by SMM
5.11
Pseudo-second order kinetic model for the removal of
115
sulfate by SMY
5.12
Adsorption isotherm of SO42- removal by SMM
116
5.13
Adsorption isotherm of SO42- removal by SMY
117
5.14
Langmuir isotherm for SO42- removal by SMM
117
5.15
Langmuir isotherm for SO42- removal by SMY
118
3-
5.16
Kinetic profile of PO4 removal by SMM
120
5.17
Kinetic profile of PO43- removal by SMY
120
5.18
Pseudo-second order kinetic model for the removal of
121
PO43- by SMM
5.19
Pseudo-second order kinetic model for the removal of
121
PO43- by SMY
5.20
Adsorption isotherm of PO43- removal by SMM
122
5.21
Adsorption isotherm of PO43- removal by SMY
123
5.22
Langmuir isotherm for PO43- removal by SMM
124
5.23
Langmuir isotherm for PO43- removal by SMY
125
5.24
Freundlich Isotherm for PO43- Removal by SMM
125
PO43-
5.25
Freundlich Isotherm for
5.26
Kinetic profile of AO7 uptake by SMM
127
5.27
Kinetic profile of AO7 uptake by SMY
127
5.28
Pseudo second order kinetic plot for the AO7 removal by
128
Removal by SMY
126
SMM
5.29
Pseudo second order kinetic plot for the AO7 removal by
129
SMY
5.30
Langmuir isotherm plots for removal of AO7 by SMM
130
5.31
Langmuir isotherm plots for removal of AO7 by SMY
131
5.32
Freundlich isotherm plots for removal of AO7 by SMM
131
5.33
Freundlich isotherm plots for removal of AO7 by SMY
132
6.1
Nitrate reduction test (initial NO3- concentration = 15.6
135
mg/L)
xviii
6.2
Sulfate reduction test (initial SO42-concentration = 153
136
mg/L)
6.3
Phosphate reduction test (initial PO43- concentration =
137
5.72 mg/L)
6.4
Time course of NO3- removal (aerobic, initial
138
concentration = 15.2 mg/L)
6.5
Time course of NO3- removal (facultative, initial
138
concentration = 15.2 mg/L)
6.6
Nitrate removal by bacteria A2-1-2 (comparison between
139
aerobic and facultative condition)
6.7
Nitrate removal by bacteria A4-7-1 (comparison between
139
aerobic and facultative condition)
6.8
Nitrate removal by bacteria A4-2-3 (comparison between
140
aerobic and facultative condition)
6.9
Percentage of SO42- removal (aerobic, initial
141
concentration = 60 mg/L)
6.10
Percentage of SO42- Removal (facultative, initial
141
concentration = 60 mg/L)
6.11
Sulfate removal by bacteria A1-1-3 (comparison between
142
aerobic and facultative condition)
6.12
Percentage of PO43- Removal (aerobic, initial
143
concentration = 6 mg/L)
6.13
Percentage of PO43- Removal (facultative, initial
143
concentration = 6 mg/L)
6.14
PO43- removal by bacteria A1-1-2 (comparison between
144
aerobic and facultative condition)
6.15
pH change during 7-day treatment
146
6.16
Comparison of color removal by zeolite particle (ZP) and
147
bio-zeolite particle (Bio-ZP)
6.17
Comparison of color removal by Bio-SMY and SMY
148
6.18
Comparison of color removal by Y and SMY
149
6.19
Removal of NO3- by ZP and Bio-ZP
150
6.20
2-
Removal of SO4 by ZP and Bio-ZP
151
xix
6.21
Removal of PO43- by ZP and Bio-ZP
152
6.22
Removal of NH4+ by ZP and Bio-ZP
153
6.23
pH Change during Treatment
155
6.24
Comparison of ADMI removal by different systems
156
6.25
Comparison of ammonium removal by different systems
156
6.26
Comparison of NO3- Removal by different systems
157
6.27
Comparison of SO42- Removal by different systems
158
6.28
Comparison of PO43- Removal by different systems
158
xx
LIST OF SYMBOLS
°C
-
Degree Celsius
Co
-
Initial concentration
Ce
-
Equilibrium concentration
cm
-
Centi meter
dm
-
Deci meter
g
-
Gram
h
-
Hour
kg
-
Kilo gram
kJ
-
Kilo Joule
kPa
-
Kilo Pascal
kV
-
Kilo Volt
L
-
Liter
lb
-
Pound
m
-
Meter
M
-
Molar
mA
-
Mili ampere
meq
-
Mili equivalent
mg
-
Mili gram
min
-
Minute
mL
-
Mili Liter
mm
-
Mili meter
mmol
-
Mili mol
N
-
Normal
nm
-
Nano meter
ppm
-
Part per million
xxi
ppb
-
Part per billion
rpm
-
Revolutions per minute
Å
-
Angstrom
µg
-
Micro gram
µm
-
Micro meter
µL
-
Micro Liter
xxii
LIST OF ABBREVIATIONS
AAS
-
Atomic Absorption Spectroscopy
ADMI
-
American Dye Manufacturers Institute
AlPO4
-
Aluminophosphates
ANA
-
Analcime
AO7
-
Acid Orange 7
ASAP
-
Accelerated Surface Area and Porosimeter
APHA
-
American Public Health Association
BEA
-
Zeolite Beta
BET
-
Brunauer, Emmet, and Teller
BJH
-
Barrett-Joyner-Halenda
BTEX
-
Benzene, Toluene, Ethylene and Xylene
CCA
-
Chromated Copper Arsenate
CEC
-
Cation Exchange Capacity
CHA
-
Chabazite
CMC
-
Critical Micelle Concentration
COD
-
Chemical Oxygen Demand
CQ
-
Chloroquin
DDTMA
-
Decadecyltrimethylammonium
DHA
-
Dehydroabietic Acid
DNA
-
Deoxyribonucleic Aid
ECEC
-
External Cation Exchange Capacity
EDAX
-
Energy-Dispersive X-ray Spectroscopy
EDI
-
Edingtonite
EPA
-
Environmental Protection Agency
ERI
-
Erionite
xxiii
ETFE
-
Ethylenetetrafluroethylene
FAU
-
Faujasite
FEP
-
Fluorinated Ethylene Propylene
FER
-
Ferrierite
FESEM
-
Field Emission Scanning Electron Microscopy
FT-IR
-
Fourier Transform Infrared
GIS
-
Gismondine
HDTMA
-
Hexadecyltrimethylammonium
HEU
-
Clinoptilolite
ICDD
-
International Centre for Diffraction Data
IIS
-
Ibnu Sina Institute for Fundamental Science Studies
ISO
-
International Organization for Standardization
IUPAC
-
International Union of Pure and Applied Chemistry
IZA
-
International Zeolite Association
LOI
-
Lost of Ignition
LTA
-
Linde Type A
LTL
-
Linde Type L
MeAPO
-
Metal-substituted Aluminophosphates
MER
-
Merlinoite
MFI
-
Zeolite Socony Mobil – five
MOR
-
Mordenite
MTT
-
Zeolite Socony Mobil – twenty-three
PAC
-
Plug Flow Combustor
PDF
-
Powder Data File
PHI
-
Phililipsite
QAC
-
Quaternary Ammonium Compounds
RHA
-
Rice Hush Ash
SAPO
-
Silicoaluminophosphates
SBU
-
Secondary Building Unit
SCF
-
Surface Complex Formation
SIRIM
-
Standards and Industrial Research Institute of
Malaysia
SMC
-
Surfactant Modified Clay
xxiv
SMM
-
Surfactant Modified Mordenite
SMY
-
Surfactant Modified Zeolite Y
SMZ
-
Surfactant Modified Zeolite(s)
SOC
-
Synthetic Organic Chemicals
TDTMA
-
Tetradecyltrimethylammonium
TG-DTA
-
Thermogravimetry-Differential Thermal Analysis
US
-
United States
USA
-
United States of America
UV
-
Ultra Violet
UV-Vis
-
Ultra Violet-Visible
WHO
-
World Health Organization
XRD
-
X-Ray Diffraction
XRF
-
X-Ray Flourescence
ZSM
-
Zeolite Socony Mobil
xxv
CHAPTER 1
INTRODUCTION
1.1
Background
Water is essential for all life on earth. Including human beings, all life uses
water as the basic medium of metabolic functioning. The removal and dilution of
most natural and human-made wastes are also accomplished almost entirely by
water.
In addition, water possesses several unique physical properties that are
directly responsible for the evolution of our environment and the life that functions
within it. It seems that water is in abundance with two thirds of the planet covered
by oceans. However, it is not quantity but quality that counts (Figure 1.1) (Fischer,
2001).
Obviously, humans have been polluting water since the early days of
civilization. The development of towns and cities in close proximity to rivers also
caused the rivers to become polluted by human waste and effluents. Indeed whole
civilization has disappeared not only because of water shortages resulting from
changes in the climate but also because of water-borne diseases such as cholera and
typhoid (Lee and Speight, 2000). The industrial revolution of nineteenth century,
rapid growth in human population has placed strains to environment for instance
adding more chemical contaminants into the aquatic system. The presence of a wide
range of synthetic organic chemicals (SOC) was confirmed by the Environmental
Protection Agency (EPA) of USA in finished drinking water, in many locations, even
2
those are from ground water supply (Cotruvo et al., 1983). This survey breaks the
historical concept of viewing ground water as a relatively uncontaminated resource,
unspoiled by the human activities that affect surface waters. The presence of even
trace quantities of SOC in finished drinking water should be encountered as a major
future threat to the supply water for the existing mechanism of contamination of the
source by man-made pollution. Especially in densely populated or industrial areas
the quality of water can become a problem. These areas have a high demand of clean
water while at the same time produce large amounts of wastewater. Beyond a certain
point the natural occurring purification processes are no longer sufficient and ground
water quality will start to decrease, causing both environmental en economical
problems.
Figure 1.1: Overview of all water on earth. The amount of fresh liquid water is less
then 1 %.
Concerned for sustaining healthy water resources, the public are calling for
more and more environmental restrictions. Consequently, industries and scientists
are searching for economic and efficient methods in protecting water resources from
pollution.
Using the sorption process for the removal of contaminants from
wastewater has a relatively shorter history if compared to other water purification
processes. The earliest documented use of carbon for the removal of impurities in
solutions was made by Lowitz, he observed that charcoal would decolorize many
liquids in 1785 (Clark and Lykins, 1989). Nowadays adsorption on activated carbon
is a recognized method for the removal of organics and harmful metals from
3
wastewater while the high cost of activated carbon production and application limits
its use in adsorption. A search for low cost and easily available adsorbents has led to
the investigation of materials of agricultural and biological origin as potential metal
sorbents (Hammaini, et al., 1999).
Zeolites were proven as potential sorbents in aquatic pollution control
especially in the removal of water hardness, ammonium and toxic metals. Besides
the natural occurring zeolites, the efficiencies of low cost synthetic zeolites in the
water treatment have been evaluated.
Generally, the sources should have high
content of silica or alumina. In addition, these compositions should be highly
reactive aiming towards cost-effective synthesis. Mineralogists have studied zeolites
for two and half centuries beginning with the first member, stilbite, which was
discovered in 1756 (Barrer, 1982). However their applications in industry have been
developed only in the last 50 years. The openness of the anionic frameworks ensures
the easier mobility both of cations in ion exchangers and of water molecules or other
guest species.
Among the available local natural materials, rice husk which contains high
percentage of silica has drawn the attention of researchers worldwide. Rice husks
are natural sheaths that form on rice grains during their growth; it is a nonbiodegradable fibrous material with high silica content. These husks are removed
during the refining of rice. The world beneficiation of rice generates as by-product
rice husk in significant quantities that corresponds to about 20 % of its initial weight
(Della et al., 2002). Among the population consume the rice as main daily food,
South and South East Asia countries account for over 90 % of world’s rice
production (Wang et al., 1998). In Malaysia, rice husk is produced in abundance
after rice harvesting season, the annual production of rice leaves behind about 2.4
million tonnes of husk as waste product (Hamdan et al., 1997).
The utilization of RHA as an alternative source of active silica towards the
preparation of zeolites has been reported since the early of 1980’s by Rao and coworkers (Bajpai et al, 1981; Dalal et al.; 1985; Rawtani, 1989). In the pioneering
work of Rao’s group, several type of zeolites such as mordenite, zeolite NaX and
zeolite ZSM-5 have been successfully synthesized. Apart from that, zeolite A and
4
zeolite Y (Hamdan, 1997), zeolite ZSM-48 (Wang, 1998) were also successfully
synthesized. It is trusted that other kinds of zeolite and mesoporous silica will be
synthesized from time to time in the light of the early work.
Zeolites possess a net negative structural charge due to the isomorphic
substitution of cations in the crystal lattice. Thus, ordinary zeolites have little or no
affinity for neutral and anionic solutes. Consequently, in order to treat oxyanions
and anionic organic contaminants, the surface chemistry of zeolite was altered by
attaching appropriate quaternary ammonium cationic surfactants. At the maximum
surfactant sorption, the surfactant molecules form bilayers on zeolite surfaces with
the lower layer held by electrostatic interaction between the negatively charged
zeolite surfaces and the positively charged surfactant headgroups in both layer.
Under the surfactant bilayer configuration, the zeolite reverses its surface charge
resulting in a higher affinity for negatively charged anionic contaminants.
Adsorption and biological treatment are two common methods applied in
wastewater treatment.
In general, these two approaches have been used either
separately, but in same process (e.g., an activated sludge treatment followed by
adsorption on activated carbon as polishing step), or as an alternative to each other.
However, it has also shown that adsorption and biotreatment can be used
simultaneously. For example, microorganisms can be used as an adsorbing material
(biosorption) as well as active degraders of the target organic compounds
(Armenanta et al., 1996). The biomass is first contacted with the wastewater to
promote adsorption of the dissolved organics on the surface of microbial flocs prior
to biodegradation of the same microorganisms. In such cases, the biomass is also the
adsorbing material. In other cases, the adsorbing material may be a sorbent such as
zeolite added to a microbial process to improve the overall performance of the
system and increase the removal of recalcitrant materials from the wastewater. Thus,
it is of special interest to examine the sorbents developed in this study to combine
with biological treatment.
5
1.2
Research Objectives
The goal of this research is to examine the low cost zeolite, e.g. rice husk ash-
synthesized zeolite Y and natural mordenite, and their modified forms towards the
removal of various contaminants in water including cation, inorganic oxyanions and
anionic organic.
Finally, small round shape particles were fabricated from the
sorbents and applied together with microbial species to perform cleaning in
wastewater treatment. The specific objectives of this research are:
•
To synthesize zeolite Y by using rice husk ash as the silica source.
•
To characterize the prepared zeolite Y and natural mordenite by a variety of
method.
•
To prepare surfactant-modified zeolites at different cationic surfactant loading.
•
To examine the efficiency of the raw zeolites and modified zeolites for the
removal of various contaminants of NH4+, NO3-, SO42-, PO43- and Acid Orange 7
in terms of kinetics and equilibrium studies.
•
To isolate and screen the suitable bacteria from wastewater for contaminant
removal.
•
To fabricate zeolite particle (raw and modified forms) and use together with
microbial community for wastewater treatment.
1.3
Scope and Outline of Thesis
This thesis consists of seven chapters. Chapter 1 presents the general research
background and scope of the work. Chapter 2 presents extensive review of research
relevant to the present study. The third chapter describes the materials and the
experimental details employed in this study, while Chapters 4 to 6 are results and
discussions, it can be viewed as an independent study of each chapter, while in a
broader sense, the three chapters together provide an overall picture of this research
with significant relevancy. Finally, the concluding remarks can be found in Chapter
6
7. The outline of the thesis is discussed in more detail below. The relations between
the various chapters are visualized in Figure 1.2.
•
In Chapter 1, the general research background, research objectives, scope and
outlines of thesis were presented.
•
In Chapter 2, background knowledge and extensive review were provided in
relevant to the present study.
Basic background of zeolite was discussed in
terms of physical features, framework topology, relationship of natural zeolite
and synthetic zeolite. Then, hydrothermal synthesis of zeolite was discussed
which include the general aspects, rice husk ash as an alternative silica source
and in particular the methods of preparing synthetic zeolite Y. Extensive reviews
were made on the previous developments of surfactant modified zeolites
covering the fundamental aspects of surfactant and zeolite relationship,
adsorption mechanism of SMZ, and previous applications of SMZ. Finally the
synergistic advantages on the combination of adsorption and biological treatment
are briefly reviewed.
•
In Chapter 3, materials consumed, instruments applied and detailed experimental
procedures in this study are described. The experiments consist of the preparation
of zeolite and it’s modified form, characterization methods of materials,
adsorption kinetics and equilibrium studies in batch mode, isolation and
screening of pure colony of bacteria, zeolite particle preparation, the use of
zeolite particle in wastewater treatment in combination with bacterial
degradation.
•
In Chapter 4, results and discussion on synthesis, characterization and
ammonium removal studies of zeolite are presented. It includes characterization
of RHA, synthesis of zeolite from RHA, characterization of zeolite by XRD, FTIR, FESEM, EDAX, nitrogen adsorption studies, ammonium removal studies in
which suitable kinetics and isotherms models were employed to investigate the
adsorption behavior.
•
In Chapter 5, results and discussion on the preparation of surfactant-modified
zeolite and anionic contaminants removal studies are deliberated.
Anionic
contaminants investigated are nitrate, phosphate, sulfate and acid dye (Acid
Orange 7). Pseudo second order kinetic was found fit to the adsorption kinetics
7
of SMZ towards anionic contaminants. Langmuir and Freundlich isotherms are
employed to obtain the important adsorption parameters.
•
In Chapter 6, results and discussion on the development of zeolite particle for
wastewater treatment are presented. This chapter covers the performance of
several types of bacteria to remove different contaminants, optimization and
preparation of zeolite particle, and finally the use of zeolite particle (raw zeolite
and SMZ) in textile wastewater treatment in coupling with mixed cultures of
bacteria.
•
In Chapter 7, the concluding remarks and some recommendations for further
research can be found.
Chapter 1
Introduction
Chapter 2
Literature Review
Chapter 4
Result and Discussion
Synthesis,
characterization and
NH4+ removal studies
of zeolite
Chapter 3
Experimental
Chapter 5
Result and Discussion
Preparation of SMZ &
anionic contaminants
removal studies
Chapter 7 Conclusions
Figure 1.2: Outline of the thesis
Chapter 6
Result and Discussion
Development of
zeolite particle with
bacteria for
wastewater treatment
CHAPTER 2
LITERATURE REVIEW
2.1
Features of Zeolite
Zeolites are crystalline microporous aluminosilicates containing pores and
cavities of molecular dimensions. Many occur as natural minerals, but it is the
synthetic varieties which are among the most widely used sorbents, catalysts and ionexchange materials (Cundy and Cox, 2003).
Zeolite crystals are porous on a
molecular scale, their structure revealing regular arrays of channels and cavities, (ca.
3-15 Å), creating a nanoscale labyrinth which can be filled with water or other guest
molecules. The history of zeolites began in 1756 when the Swedish mineralogist,
Baron Cronstedt discovered the first zeolite, stilbite (Barrer, 1978). Owing to the
crystals exhibited water vapors when gently heated, he named the mineral zeolite,
which derived from two Greek words, zeo and lithos meaning “to boil” and “stone”.
Breck further defined that:
Zeolites are crystalline, hydrated aluminosilicates of group I and
group II elements as formed in nature or synthesized, higher
polyvalent ions, e.g., rare earths, are readily introduced by cation
exchange, in particular, sodium, potassium, magnesium, calcium,
strontium, and barium. Structurally the zeolites are “framework”
aluminosilicates which are based on an infinitely extending three-
9
dimensional network of AlO4 and SiO4 tetrahedra linked to each other
by sharing all of the oxygens.
(Breck, 1974: 4)
Zeolites are the members of tectosilicate family of minerals and a
representative empirical formula of a zeolite is M2/nO.Al2O3.xSiO2.yH2O where M
represents the exchangeable cation of valence n, x is generally equal to or greater
than 2 since AlO4 tetrahedra are joined only to SiO4 tetrahedra (Smith, 1984). The
SiO4 tetrahedron readily shares all four oxygen atoms at the corners with other TO4
tetrahedra with one central Si atom to form three-dimensional framework. The
overall Si/O ratio is 2, thus the structure is neutralized electrically with Si having 4+
surrounded by four O of 1-. Nevertheless, the inclusion of small enough Al3+ to
occupy the central position of the tetrahedra disrupts the balance of charges. The
presence of alkaline metal ion such as Na+ and K+ or alkaline earth ion such as Ca2+
compensate the charge deficiency to maintain electrical neutrality.
Such
exchangeable cations usually close to the O of the Al substituted tetrahedra where is
the deficiency of charge occurs.
The channels and interconnected voids formed by the anionic framework are
occupied by the guest cation and water molecules. The cations are mobile and
ordinary undergo ion-exchange while the water may be removed continuously and
reversibly.
An accurate representative of zeolite structure is formulated for the
crystallographic unit cell as:
Mx/n[(AlO2)x(SiO2)y]. yH2O
The total number of tetrahedra in the unit cell is given by (x+y) and the portion with [
] denotes the framework composition.
10
2.1.1 Zeolite Framework Topology
The chemistry of zeolite is based on the tetrahedron TO4 where basically T
may be Si, Al etc. Zeolites are diverse due to the secondary building unit (SBU, Fig.
2.1), based on small groupings linked tetrahedra are needed in describing and
classifying their topologies. The non-chiral SBU are invented on the assumption that
each zeolite framework can be generated from one type of SBU only (Koningsveld,
1991).
In fact, sometimes more than one SBU is involved in generating the
framework (Barrer, 1982). For instance, faujasite is made up from 4-, 6-, 8-rings and
4-4 cubic units.
Figure 2.1: The Secondary Building Unit (SBU) and their symbols in zeolite
frameworks. Number in parenthesis = frequency of occurrence (Baerlocher et al.,
2001).
11
Based on the pore size (the number of T-atoms in the ring opening), zeolites
are referred to as small (8 member-ring), medium (10 member-ring) and large (12
member-ring) pore zeolite. Based on the framework Si/Al composition, zeolites are
classified as low silica zeolites (Si/Al less than 2), medium silica zeolites (Si/Al = 25), high silica zeolites (Si/Al ~10-100) and pure silica molecular sieves. The Si/Al
ratio is one of the important properties of zeolites. Generally, by increasing the Si/Al
ratio, the thermal stability, acid strength and hydrophobicity are increasing, whereas
the ion exchange capacity decreases.
Unlike the two-dimensional aluminosilicate, the rigid three-dimensional
frameworks of zeolites do not undergo significant dimensional changes with ion
exchange. In addition, the high selectivity shown by particular zeolites for certain
cations can assist in the isolation and recovery of such ions.
For instance,
clinoptilolite and mordenite showed their good selectivity towards cesium-137 and
strontium-90, two of the troublesome by-products of nuclear fission (Faghihian et al.,
1999; Komarneni and Rustum, 1981).
There are approximately 75 molecular sieve structures as assigned by the
Structure Commission of the International Zeolite Association (Meier and Olson,
1987). The designations are three-letter code to each framework topology, these are
based on the connectivity of the tetrahedral atoms using the maximum topological
symmetry, regardless of the changes in unit cell size and symmetry that may result
from differences in chemical composition (Davis and Lobo, 1992).
2.2
Relationship of Synthetic Zeolite to Natural Zeolite: A Brief Review
The discovery of natural zeolites since 50 years ago as large, widespread,
mineable, near-monomineralic deposits in tuffaceous sedimentary rocks in the world
open another chapter in the book of useful industrial minerals whose exciting surface
and structural properties have been exploited in various fields of technology (Barrer,
1982).
12
The attractive adsorption, cation-exchange, dehydration-hydration and
catalysis properties of zeolite open the multitude usages such as application in
pozzolanic cement; as light weight aggregates; in the drying of acid gases; in the
separation of oxygen from air; in the removal of NH3 from wastewater; in the
extraction of Cs and Sr from nuclear wastes and the mitigation of radioactive fallout;
as dietary supplements to improve animal production; as soil amendments to improve
cation exchange capacities and water adsorption capacities; as soilless zeoponic
substances for greenhouses and space missions; in the deodorization of animal litter,
barns, ash trays, refrigerators, and athletic footwear; in the removal of ammoniacal
nitrogen from saline haemodialysis solutions; and as bactericides, insecticides, and
antacids for people and animals (Mumpton, 1999).
According to many geological explorations, zeolite formation is consisted to
include the following genetic types (Barrer, 1982; Hay, 1986)
1. Crystals resulting from hydrothermal or hot-spring activity involving
reactions between solutions and basaltic lava flows.
2. Deposits formed from volcanic sediments in closed alkaline and saline lakesystems.
3. Similar formations from open freshwater-lake or groundwater systems acting
on volcanic sediments.
4. Deposits formed from volcanic materials in alkaline soils.
5. Deposits formed from hydrothermal or low-temperature alteration of marine
sediments.
6. Formation which are the result of low-grade burial metamorphism.
Some zeolites deposits appear to have formed with no direct evidence that the parent
material was of volcanic origin. Different types of zeolite formation may pose
different characteristic features (Barrer, 1982).
Sedimentary zeolitic tuffs are generally soft, friable, light weight and
commonly contain 50-95% of a single zeolite phase (Barrer, 1982; Mumpton, 1999).
However, several zeolites may coexist along with the un-reacted volcanic glass,
quartz, K-feldpar, montmorillonite, calcite gypsum, and cristobalite/ trimidymite
13
(Mumpton, 1999). Among the >63 natural zeolites, only six of them commonly
occur in large beds: analcime (ANA), chabazite (CHA), clinoptilolite (HEU), erionite
(ERI), mordenite (MOR), phillipsite (PHI) while ferrierite (FER) occurs in a few
large beds. Each of the seven also has been synthesized but only mordenite and
ferrierite are manufactured in large quantity (Sherman, 1999).
Significantly
synthetic mordenite has large pores whereas natural mordenite has small pores.
Besides mordenite and ferrierite, the principal synthetic aluminosilicate
zeolites in commercial use are Linde Type A (LTA), Linde Type X and Y (FAU),
Silicalite-1 and ZSM-5 (MFI) and Linde Type B (zeolite P) (GIS). Other commercial
available synthetic zeolites include Beta (BEA), Linde Type F (EDI), Linde Type L
(LTL), Linde Type W (MER), and SSZ-32 (MTT). All are pure aluminosilicates or
pure silica analogs.
Since 1948, Barrer’s synthesis of zeolite species P and Q (these material were
later found to have KFI structure) at high temperatures and pressures heralded the era
of synthetic zeolite (Cundy, 2003). From 1949 through out the early 1950, the
commercial significantly zeolite A (Milton, 1959a), X (Milton, 1959b), Y (Breck,
1964a), were discovered by Milton and Breck at the laboratories of the Linde Air
Products Division of Union Carbide Corporation (Milton, 1989). These zeolites
were synthesized from readily available raw materials (freshly precipitated
aluminosilicate gels) which were more reactive at much lower temperature and
pressure than used earlier (Breck, 1964b). By 1953, Milton, Breck and colleagues
had synthesized 20 zeolites including 14 unknown as natural zeolites.
In 1953, Linde Type A zeolite became the first commercial zeolite as an
adsorbent to remove oxygen impurities from argon. Later, synthetic zeolites were
introduced by Union Carbide as a new class of industrial adsorbent and as
hydrocarbon-conversion catalysts in 1959. New zeolites and new applications
continue to appear steadily after 1960.
As mentioned by Flanigen (1991), an
explosion of new molecular structures and compositions occurred in the 1980-1990s
from the aluminosilicate zeolites to the microporous silica polymorphs to the
microporous aluminophosphate-based polymorphs and metallo-silicate composition.
Recently, new non-aluminosilicate, synthetic molecular sieves became available
14
commercially
including
aluminophosphates
(family
of
AlPO4
structures),
silicoaluminophosphates (SAPO), and various metal-substituted aluminophosphates
(MeAPO). Molecular sieves now served the petroleum refining, petrochemical, and
chemical process industries as selective catalysts, adsorbent, and ion-exchangers.
Many synthetic zeolites have framework topologies not found to date among
the natural zeolites. The natural zeolite faujasite has the same framework (FAU) and
similar framework composition to the Type X and Y zeolites but is rare in nature.
Where both natural and synthetic form of the same zeolite are available in
commercial quantity, the variable phase purity of the natural zeolite and the chemical
impurities, which are costly to remove, can make the synthetic zeolite more attractive
for specific applications. Conversely, where uniformity and purity are not important,
the cheapness of a natural zeolite may favor its application. Hence, natural and
synthetic zeolites seldom compete for the same applications.
2.3
The Synthesis of Zeolite
Early investigations were carried on to duplicate the hydrothermal processes
by which zeolite minerals were assumed to be formed in nature. Zeolite synthesis
was pioneered by Barrer who in the early 1940s initially investigating the conversion
of known mineral phases under the action of strong salt solutions at fairly high
temperatures (ca. 170-270 °C).
Later, fascinating achievements were made by
Milton, Breck, Flanigen in Union Carbide laboratory; their approach was to use a
freshly prepared, highly reactive aluminosilicate “gel” (the term “gel” means a
hydrous, metal aluminosilicate mixture which is prepared from either aqueous phase
or reactive solid phase) (Breck, 1964b). Consequently, a wealth of zeolites and
related microporous materials have been synthesized and novel materials of this class
will continue to be discovered. In almost all instances, hydrothermal synthesis is the
method of choice for preparing zeolites. The techniques for hydrothermal synthesis
of zeolites have reached a high level of sophisticated yet the scientific understanding
of the very complex series of chemical events on route from the low molecular
weight reagents to the inorganic macromolecule remained somewhat obscure. The
15
International Zeolite Association (IZA) had reviewed the verified recipes for the
synthesis and characterization (Robson, 2001).
2.3.1 General Aspects of Zeolite Synthesis
The synthesis of zeolite is typically carried out in batch systems in which a
caustic aluminate solution and a caustic silicate solution are mixed together. The
temperature held at some level above ambient at autogenous pressure for certain
period in order to achieve high yield of crystals in an acceptable period of time. Most
commercially interesting synthesis is preceded by the formation of an amorphous gel
phase which dissolves to replace reagents consumed from the solution by crystal
growth (Thompson, 2001). It is common for the original mixture to become
somewhat viscous immediately due to the formation of an amorphous gel phase.
The chemical sources which are principle needed for hydrothermal synthesis
of zeolite are given in Table 2.1 (Jansen, 1991):
Table 2.1: Chemical source and their function in zeolite synthesis
Sources
Functions
SiO2
Primary building units of the framework
AlO2
Origin of framework charge
OH-
Mineralizer, guest molecule
Alkali cations, template
Counter ion of framework charge, guest molecule
Water
Solvent, guest molecule
Zeolite crystals are formed by a nucleation step as the synthesis proceeds at
elevated temperature. These zeolite nuclei grow larger by assimilation of
aluminosilicate material from the solution phase. An induction period may exist
during the early synthesis in which no apparent nucleation. The dissolution of
Al(OH)3 or soluble aluminate in alkali gives tetrahedral Al(OH)4- anions, which is a
dominant species under alkaline conditions. In soluble silicates as well, polymeric
16
silicate anions was found as mononuclear species such as Si(OH)4, Si(OH)3- and
SiO2(OH2)22-in dilute solution under alkaline condition. It is noteworthy that either
Al or Si is in tetrahedral coordination with respect to oxygen under alkaline medium
consequently built up the zeolite tectosilicate from hydrous gels and mixtures.
It was proposed that hydrated alkali cations templated or stabilized the
formation of the zeolite structure subunits. The unique structural characteristics of
zeolite frameworks containing polyhedral cages had led to the postulate that the
cation stabilizes the formation of structural subunits that were the precursors or
nucleating species in crystallization. The addition of quaternary ammonium cations
to alkali aluminosilicate gels was reported to produce the high silica zeolite and “all
silica” molecular sieves.
Temperature, pH, ratio of reactants, reactivity of reactants and pretreatment
of the amorphous gel can affect the crystallization kinetic and determine the type of
zeolite formed.
Nutrient concentration and temperature are the two key factors
determined the degree of supersaturation which is the principal driving force for
nucleation. As the nutrient concentration increases, the degree of supersaturation
increases while as the temperature increases, the degree of supersaturation decreases
due to the increase of nutrients solubility. However, the elevated temperature induce
the greater kinetic of reaction, thus the nucleation and crystal growth rate may be
accelerated. The nature of the reactants is critical to nucleation process, for instance
chemical impurities and physical impurities in the reactants can increase the
nucleation potential of a given system. In addition, other factors such as the role of
added salts, aging of the reaction mixtures, and the order of reactant are mixed and so
forth during zeolite formation may influence the course of reaction.
2.3.2 Rice Husk Ash (RHA) as a Silica Source
Rice husks are natural sheaths that form on rice grains during their growth; it
is a non-biodegradable fibrous material with high silica content. These husks are
removed during the refining of rice. The world beneficiation of rice generates as by-
17
product rice husk in significant quantities that corresponds to about 20 % of its initial
weight (Della et al., 2002). Among the population consume the rice as main daily
food, South and South East Asia countries account for over 90 % of world’s rice
production (Wang et al., 1998). In Malaysia, rice husk is produced in abundance
after rice harvesting season, the annual production of rice leaves behind about 2.4
million tonnes of husk as waste product (Hamdan et al., 1997).
The major constituents of rice husk are cellulose, lignin and ash. Though the
actual composition is variable, the following values may be considered typical: ash,
20 %; lignin, 22 %; cellulose, 38 %; pentosans, 18 %, and other organics, 2 % (James
and Rao, 1986). Efforts to utilize rice husk has been handicapped by their tough,
woody, abrasive nature; low nutritive properties; resistance to degradation; great
bulk; and high ash content. Such efforts have resulted in minor usage, mostly in lowvalue applications in agricultural areas or as fuel.
An increasing application of rice husk in some regions is as fuel in heat
generation for rice drying, due to its high calorific power (ca. 16720 kJ/kg) (Della et
al., 2002). Nevertheless, in other countries they are treated as waste that causing
pollution and disposal problem. Due to environmental concern and the need to
conserve energy, the rice husk was usually burnt under controlled conditions and the
resultant ash was further utilized. The ash is largely constituted of silica with minor
amounts of alkalis and other trace elements.
RHA contain high concentration of silica was investigated in the early 1950’s
by ceramic engineers as a source of raw material. Since the early investigation, rice
husk ash has been widely utilized in lime-pozzolana mixes and for Portland cement
replacement, as an additive for cement and concrete fabrication due to its highly
reactive pozzolanic properties (Payá et al., 2001). Besides, many researchers have
concluded that RHA is an excellent source of high grade amorphous silica. This
conclusion leads to the versatile applications of rice husk ash in the past few decades
including as a source for metallurgical as well as semiconductor-grade silicon (James
and Rao, 1986), adsorbent, solar cells for photovoltaic power generation,
semiconductors, synthesis of silicon carbide or silicon nitride, adsorbent, catalyst
support and so forth (Real, 1996).
18
The content of silica and all impurities in rice husk ash vary depending on the
variety, climate, geographic location and also the preparation conditions. According
to literature, raw rice husk ash contains 87-99 % SiO2 (Bajpai et al.; 1981; Real et
al., 1996; Hamdan et al., 1997; Sun and Gong, 2001). The high purity of silica in
RHA provides a cheap alternative source for zeolite synthesis.
However, the
reactivity of the silica depends on the preparation method from the raw rice husk.
The properties of silica in rice husk are strongly influenced by the temperature of
combustion and the duration of heating. When the RHA is produced by uncontrolled
combustion, the ash is generally crystalline. However, combustion of the rice husks
under controlled temperature and atmosphere, highly reactive amorphous silica can
be obtained for the zeolite synthesis, whereas crystalline silica is inactive. However,
not all amorphous silica is an active silica source for zeolite synthesis.
The silica in RHA obtained by combustion below 800 °C was found to be
amorphous. At combustion temperatures above 900 °C, the oxidation of rice husks
results in a physical structural change of silica from its original amorphous state to
crystalline state thereby encapsulating residual carbons. The phase transformation
began with the appearance of the cristobalite phase at 800 °C and the next
transformation to tridymite started at about 1000 °C and became quite pronounced
above 1200 °C (Sun and Gong, 2001). Hamdan et al. (1997) also showed that RHA
prepared by open field burning of rice husk without control of temperature for 24 h
contained the cristobalite and tridymide indicates that prolong burning time may
produce crystalline RHA.
The utilization of RHA as an alternative source of active silica towards the
preparation of zeolites has been reported since the early of 1980’s by Rao and coworkers (Bajpai et al, 1981; Dalal et al.; 1985; Rawtani, 1989). In the pioneering
work of Rao’s group, several type of zeolites such as mordenite, zeolite NaX and
zeolite ZSM-5 have been successfully synthesize. Apart from that, zeolite A and
zeolite Y (Hamdan, 1997), zeolite ZSM-48 (Wang, 1998) were also successfully
synthesized. It is trusted that other kinds of zeolite and mesoporous silica will be
synthesized from time to time in the light of the early work. However, it should be
noted that due to the different properties of the rice husk ash and commercial silica
(e.g. sodium silicate solution, colloidal silica), modifications on the present method
19
of synthesis such as reactant compositions might be required. For instance, Bajpai et
al. showed that for the synthesis of mordenite using silica from RHA, relatively less
Na2O or a greater SiO2 content in the starting mixture is required.
2.3.3 Synthesis of Zeolite Y
Zeolite Y is one of the earliest commercially significant synthetic zeolite
discovered by Breck (1964b and 1967). Typically, zeolite Y is crystallized from
sodium aluminosilicate gels prepared by mixing aqueous sodium aluminate, sodium
hydroxide and sodium silicate solutions. This mixture forms an amorphous gel and it
is agitated to produce a homogenous mixture. The mixture is further heated at an
appropriate temperature until the crystallization is completed as evidenced visibly by
the separation of an extensive supernatant solution and the settling of the solids into a
compact layer of crystals at the bottom of the reactor.
Zeolite Y has been
crystallized from aluminosilicate gels prepared from sodium hydroxide, sodium
aluminate, and colloidal silicas, commonly in the form of aqueous sol or reactive
amorphous solids (Breck, 1964b). After gel formation, it is a common practice to
age the reaction mixture at room temperature prior to the subsequent crystallization
at higher temperature (Breck, 1974).
The preliminary aging step improves the
crystallization process and even yields a zeolite Y of greater purity.
2.3.3.1 Effect of Aging of Amorphous Gel on Crystallization
After its preparation, the aluminosilicate gel is usually kept for a certain
period of time below the crystallization temperature. This aging period is often
crucial for obtaining a given product at a desired rate. The primary effects of the gel
aging are the shortening of the induction period and the acceleration of the
crystallization process (Ginter et al., 1992; Feijen et al., 1994). Besides, in certain
cases, the gel aging also influences the types of zeolite formed (Feijen et al., 1994;
Zhao et al., 1997).
20
It is well known that zeolite NaP can co-crystallized with zeolite NaX and
NaY (faujasite) if the aluminosilicate gel are not aged (Breck, 1974; Zhao et al.,
1997). If the crystallization was carried out using gels aged at ambient temperature
for 1-10 days, zeolite NaX appeared as the first crystalline phase, after that zeolite
NaP co-crystallized with zeolite NaX. After the maximum yield of zeolite NaX
attained, the fraction of zeolite NaX decreased due to the transformation of zeolite
NaX into more thermodynamically stable zeolite NaP. These results are consistent
with the typical reaction sequence under the appropriate synthesis conditions;
amorphous-faujasite-gismondine (Barrer, 1982; Dalal et al., 1985). Nevertheless in
some other cases, zeolite NaP appears as the first crystalline phase when freshly
prepared gel has been heated at the appropriate temperature commonly higher than
temperature for zeolite NaX synthesis (Breck, 1974).
The solid phase of freshly prepared gel contained a number of very small
particles of quasi-crystalline phase having a structure resemble the cubic
modification of zeolite P, this particles probably resulting from polycondensation
processes during the precipitation of the gel matrix (Feijen et al., 1994; Nishi and
Thompson, 2002). During aging, structural transformation takes place in the solid
phase of the gel, it is generally assumed that the structural change related to the slow
formation of particles of six-membered aluminosilicate rings, their ordering into
sodalite cages, and a possible formation of quasi-crystalline particles resembling the
faujasite structure.
In accordance to zeolite NaX, the synthesis of zeolite NaY from gels also
requires room temperature aging of the synthesis gel prior to crystallization. Such
aging step suppresses the formation of other zeolite phases such as zeolite P, zeolite
R (chabazite type) and zeolite S (gmelinite type).
This step also fastens the
crystallization rate, increases the yield of zeolite and enables the synthesis from
batches of smaller amounts of excess silica and base.
Ginter et al. (1992)
investigated the effects of gel aging on the synthesis of NaY zeolite from colloidal
silica. A gel was immediately formed on the initial mixing of the colloidal silica and
sodium aluminate due to the flocculation of silica particles in the sol. During aging,
the silica particles slowly dissolved releasing monomeric silicate anions to form
amorphous aluminosilicate precipitates; further aging resulted in the dissolution of
21
remaining silica and forming of aluminosilicate solid; prolonged aging resulted the
incorporation of additional Si into the initially Al-rich aluminosilicate solid,
converting it to a less-hydrated solid. Thus smaller nuclei were created and a higher
final yield of zeolite NaY was achieved.
2.3.3.2 Effect of Seeding on Crystallization
In order to avoid the co-crystallization of competing phases such as zeolite P,
seeding is another method usually employed for synthesis of zeolite Y (Zhao et al.,
1997; Robson and Lillerud, 2001).
Adding pre-formed crystals or pre-aged
nucleating slurry to a crystallization system can reduce the incubation time thus
increase the rate of crystallization, and improve the purity of the crystal products.
Such seeds are also known as “directing agents” and they serve the purpose of
promoting the rate of formation of the desired phase. The seeds need not be large but
may be quite small even undetectable to the naked eye, Kasahara et al. (1986) found
that it was possible to synthesize pure faujasite in shorter crystallization times by
adding a “clear aqueous nuclei solution”. Upon investigation, it is usually found that
the nucleating mixture (pre-aged slurry) is x-ray amorphous and the seeding
properties of the aged precursors are strongly time dependent and reach a
reproducible optimum.
2.4
Zeolite Y
Zeolite X, Y and faujasite have similar aluminosilicate framework topology.
Zeolite X and Y are synthetic analogues of the natural mineral faujasite. The unit
cells are cubic with a nearly 25 Å of unit cell dimension and contain 192 TO4 (T = Si
or Al) tetrahedra. The remarkable stable and rigid framework structure contains the
largest void space any known zeolite and amounts to about 50 volume % of the
dehydrated crystals. The zeolites are varied on chemical composition, structure, and
their related physical and chemical properties (Breck, 1974).
22
The composition of the unit cell of zeolite X and Y is Nax[(AlO2)x(SiO2)192-x],
where 96 ≥ x ≥ 0. Zeolite X or Y is distinguished depending on their framework
aluminum density [x, x = 192/ (1+R) where R = NSi/NAl]. Zeolite X has a framework
aluminum density between 96 and 77 aluminum atoms per unit cell whereas zeolite
Y contains fewer than 77 framework aluminum atoms per unit cell. In the Si/Al ratio
(R) form, the value of R for zeolite X varies from 1 to 1.5 and greater than 1.5 for
zeolite Y . For the hydrated zeolite NaX and NaY, a0 increased from 24.6 to 25.0 Å.
The holosymmetry of the faujasite (FAU) framework is cubic with space
group Fd3m (all face-centered cubic lattices, there are diamond glide reflections
perpendicular to the crystallographic a, b, and c axes). The entire framework of
faujasite made up from 4, 6, 6-2 and 6-6 secondary building units in such a way as to
form three different cavities or cages; the large supercage, the sodalite cage (24tetrahedra cuboctahedral units) and the double 6-ring (hexagonal prisms).
It is
conveniently visualized as being formed from sodalite cages, joined through double
6-ring. The structure can be viewed as the diamond structure, with the sodalite cages
playing the role of carbon atoms, and the double 6-rings the role of C-C bonds
(Baerlocher, 2001). The pore structure is characterized by large supercages 13 Å in
diameter, which are linked through windows about 7.4 Å in diameter, composed of
rings of 12 linked tetrahedra (12-rings) as projected in Figure 2.2. Thus threedimensional, interconnecting channels of equidimensional 7.4 Å are created by the
interconnection of the supercages along the (110) dimension. These channels permit
access to quite large molecules, making this structure useful in catalytic applications.
Thus, zeolites in this group system are also known as large pore zeolites. Zeolites can
be grouped into six categories according to the number of O-atoms in their largest
ring. The faujasite family including zeolite Y is categorized into the 12-membered
oxygen ring systems (Chen et al., 1994).
Several extra framework sites are commonly populated in cation-exchanged
faujasites (Fig. 2.2). Five sites will be found to be occupied (Kaduk and Faber,
1995):
I:
at the center of the double 6-rings
I':
in the sodalite cage, adjacent to a hexagonal ring shared by the
sodalite cage and a double 6-ring
23
II:
in the supercage, adjacent to an unshared hexagonal face of a sodalite
cage
II':
in the sodalite cage, adjacent to an unshared hexagonal face
V:
near the center of the 12-ring apertures between supercages
supercage
sodalite cage
large cavity
double 6-ring
Figure 2.2: Faujasite framework illustrating the oxygen position and cation site
(Kaduk and Faber, 1995)
2.5
Mordenite
The unit cell chemical formula of Na-type mordenite is given by
Na8[(Al2O3(SiO2)40]H2O, with a constant Si/Al ratio of 4.17-5.0 is known as the
siliceous zeolite material. This constant ratio indicates an ordered distribution of Si
and Al in the framework structure. The framework is composed of Si, Al and O. For
24
the charge balance to the negatively charged framework, Na, K and Ca cations are
distributed in the nano-spaces.
The holosymmetry of the mordenite (MOR) framework is orthorhombic with
space group Cmcm. The entire framework of mordenite made up of complex chains
of 5-rings crosslinked by 4-rings chains consist of 5-rings of SiO2 tetrahedra and
single AlO4 tetrahedra. The chains were crosslinked by the sharing of neighboring
oxygens while each tetrahedron belongs to one or more 5-rings in the framework.
The high degree of thermal stability shown by mordenite is probably due to
the large number of 5-rings which are energetically favored in terms of stability. For
the diffusion of small molecules, the dehydrated zeolite has a two-dimensional
channel system but for larger molecules the channel system is one dimensional and
may be subjected to diffusion blocks produced by crystal stacking faults in the cdirection or the presence of amorphous material or cation in the channel.
Fig. 2.3 shows the mordenite framework structure schematically. The dashed
line in Fig. 2.3(a) shows the unit cell. The lattice constants are 18.1, 20.5 and 7.5 Å
for a-, b- and c-axis, respectively (Baerlocher et al., 2001). The mordenite has two
kinds of elliptical channels running along c-axis, indicated by A and B in Fig. 2.3(a).
The size of the channels A and B are 7.0 × 6.5 and 5.7 × 2.6 Å, respectively. The
small black and large gray balls of the framework show Si or Al and O atoms,
respectively. Cations are known to be distributed in the two sites, Na1 and Na2, in
the channel B, indicated by the large black and striped balls in Fig. 2.3(b). The
positions of 4 of the 8 sodium ions in the hydrated crystal have been determined.
Locations of the remaining 4 sodium ions and water molecules are not known. Large
cations such as caesium cannot occupy the positions determined for sodium. It
appears doubtful that water molecules are located in fixed positions at room
temperature. The fibrous nature and prismatic cleavage of mordenite crystal is
explained on the basis of the structure.
25
Figure 2.3: (a) The schematic illustration of mordenite framework. The small black
and large gray balls in the framework show Si/Al and O atoms, respectively. (b) The
two kinds of Na cation sites are shown by the large black and striped balls.
2.6
Surfactant Modified Zeolite
The research on surfactant modification of zeolites was in fact inspired and
stimulated by earlier works on surfactant modification of clay minerals and soils,
which showed that the minerals modified with cationic surfactant can substantially
enhance the removal of nonionic organic solutes from aqueous solutions (Boyd et al.,
1988a; Boyd et al., 1988b; Boyd et al., 1988c; Lee et al., 1989; Cadena, 1989; Zhang
et al., 1993; Stapleton, 1994). Similarly surfactant-modified zeolites have been
shown to remove chlorinated aliphatic compounds and benzene derivatives from
aqueous solution by means of a partitioning-like mechanism (Haggerty and Bowman,
1994). However, such treatment with quaternary amines does not lower the zeolites
naturally high sorption affinity for transition metals cations such as Pb2+ (Bowman et
al., 1995; 1996; 2000).
26
Zeolites possess a net negative structural charge due to the isomorphic
substitution of cations in the crystal lattice. Subsequently, ordinary zeolites have a
little or no affinity for neutral and anionic solutes. In fact, anions are repelled by the
negatively-charge zeolite. Thus the use of ordinary zeolites for water treatment are
primary limited to removal of cations, particularly relatively small cations such as
metal ions.
Surfactant is an abbreviation for surface active agent, which are amphipathic
molecules that consist of a non-polar hydrophobic portion commonly a straight or
branched hydrocarbon or fluorocarbon chain containing 8-18 carbon atoms, which is
attached to a polar or ionic portion (hydrophilic) (Tadros, 2005). The hydrophilic
portion can be nonionic, ionic or zwitterionic and accompanied by counter ions in the
latter two cases. The major classification of surfactants is made on the basis of the
charges of the polar head portion, thus it can be divided into the classes anionics,
cationics, non-ionics, and zwitterionics. Cationic surfactants are mostly based on the
nitrogen atom carrying the cationic charges; the most common cationic surfactants
are the quaternary ammonium compounds (Jungermann, 1969). Cationic surfactants
with only one long alkyl group are generally water soluble and the prime use of
cationic surfactant is their tendency to adsorb at negatively charged surfaces.
In the previous works on surfactant modified soil and clay minerals, it was
observed that the longer the tail group of the cationic surfactant, the more stable the
surfactant retained on the surface (Lee, 1989; Zhang, 1993). Ersoy and Çelik (2003)
compared the adsorption behavior of quaternary ammonium cationic surfactants with
different hydrocarbon chain lengths, i. e. HDTMA (hexadecyltrimethylammonium,
C16H33(CH3)3NBr), TDTMA (tetradecyltrimethylammonium, C14H33(CH3)3NBr),
DDTMA (dodecyltrimethylammonium, C12H33(CH3)3NBr) onto zeolite clinoptilolite
and observed that the effectiveness of both ion exchange and hydrophobic
interactions increases with increasing chain length. Thus the greatest surfactant
adsorption onto zeolite was obtained by HTDMA.
These literatures reveal the
rationality to apply the HDTMA instead of others for surface modification of various
minerals. The structure of the HDTMA is illustrated in Figure 2.4. The HDTMA
structure consists of permanently charged trimethylammonium head group attached
to a 16-carbon chain. It can be obtained as common salts such as HDTMA-Br and
27
HDTMA-Cl. Since these surfactants are bulky products to use in shampoo, hair
conditioner, mouthwash and fabric softeners, it is assumed that low levels of
HDTMA will not be harmful to the environment. The critical micelle concentration
(CMC) is the minimum concentration of the surfactant needed to form a micelle and
for HDTMA-Br is 0.9 mmol/L.
The individual surfactant molecules will self
associate into micellular clusters above the CMC.
+
hydrophobic tail
16 chain
hydrocarbon
(hexadecyl)
Br-
bromide anion
as counter ion
hydrophilic head
trimethylammonium
Figure 2.4: The structure of hexadecyltrimethyl ammonium bromide (HDTMA-Br)
Ion exchange of a quaternary amine and extrastructural cations (typically
Na+, K+, Ca2+, and Mg2+) on the zeolite’s external surface may dramatically alter
their surface chemistry, it happens to neutralize the surface negative charge or further
reverse it depend on the ion exchange conditions (Haggerty and Bowman, 1994).
These quaternary amines exchange quantitatively and essentially irreversibly with
inorganic cations on the external surface of the zeolite, but the long chain quaternary
amines are too large to enter the internal pore structure of the zeolite. For instance,
the diameter of HDTMA’s N(CH3)3 headgroup is about 7 Å, making it too large to
enter zeolite’s channel opening (Bowman et al. 2000). The surfactant loading on the
zeolite depends on both the external cation exchange capacity of the zeolite and the
chain length of the cationic surfactant (Li and Bowman, 1997; Li, 1999). Thus the
sorption of long chain quaternary amines is limited exclusively to external surfaces
of zeolite particles (Bowman et al., 1995). The internal or zeolitic exchange sites
potentially remain available for smaller inorganic cations. Surface exchange the
chemistry of the zeolite’s external surface; while remaining hydrophilic, the surface
becomes enriched in organic carbon acquires a positive charge and displays anionexchange properties.
28
Recently studies on the properties of surfactant-modified zeolite indicate that
it is an effective sorbents for different classes of contaminants including non-polar
organics, cations, oxyanions and anionic organics.
For the removal of organics, research groups of Li and Bowman made
extensive studies on the removal of perchloroethylene (Li and Bowman, 1998;
Bowman et al., 2000; Li and Bowman, 2001; Zhang et al., 2002; Bowman, 2003;
Burt et al. 2005) and gasoline components such as benzene, toluene, and p-xylene
(Bowman et al., 1995; Fuierer et al., 2001; Bowman, 2003; Karapanagioti et al.,
2005; Ranck et al., 2005). Besides that, Bouffard and Duff (2000) applied SMZ as
adsorbents for the removal of dehydroabietic acid (DHA); Hayakawa et al. (2000)
used zeolite P and X that modified with various kind of cationic surfactant as a drug
carrier and the release of chloroquin (CQ); Tomasevic-Canovic et al. (2003) applied
SMZ as the new efficient adsorbents for mycotoxins.
In addition to non-polar
organics, there were studies carried out to remove the anionic dyes by applying SMZ
by Celik and co-workers (Armagan et al., 2003, 2004; Benkli et al., 2005).
For the removal of oxyanions, chromate (CrO42-) was among the most
extensive investigated for various aspects particularly by Bowman’s group and Li’s
group (Haggerty and Bowman, 1994; Bowman et al., 1995, 1996, 2000; Li and
Bowman, 1997; Li et al., 1998a Sullivan et al., 1998b; Li, 2004; Bowman, 2003).
Besides chromate,
SMZ has also been proven to remove other oxyanions such as
sulphate (SO42-) (Haggerty and Bowman, 1994; Bowman et al., 1995, Li et al., 1998a
Vujaković et al., 2000), selenate (SeO42-) (Haggerty and Bowman, 1994; Bowman et
al., 1995, 1996) , AsO43-
(Bowman et al., 1996), hydrogenchromate (HCrO4-)
(Vujaković et al., 2000), dihydrogenphosphate (H2PO4-) (Vujaković et al., 2000),
nitrate (NO32-) (Li et al., 1998a Li et al., 2003).
Besides as a sorbent for
environmental remediation, SMZ was used as fertilizer carriers to control release of
nitrate and other anions (Li, 2003). Bowman et al. (2000) reported that cation
exchange by SMZ is reduced compared to the unmodified zeolite. They observed
that the reduction in metal cation uptake by the SMZ is controlled by the surfactant
loading on the zeolite surface and by the type of metal cations. For instance, most
exchange capacity of zeolite for Sr2+ uptake was lost after treatment with HDTMA
but in contrast, the uptake of Pb2+ remained essentially the same for untreated zeolite
29
the SMZ. Thus the zeolite surface seems to have a much greater affinity for the
transition metal cation Pb2+ that for the alkali-earth cation Sr2+. Davis et al. (1998)
commented that transition metal cations such as Pb2+ can bind to mineral surfaces by
specific complexation or precipitation reactions as well as by cation exchange.
Besides battles on chemical contaminants, recent studies were carried out to
evaluate the use of surfactant-modified zeolite to remove biological pathogens such
as viruses and bacteria from ground water (Schulze-Makuch et al., 2002, 2003,
2004). At typical groundwater pH, most virions have a net negative surface charge
thus it can be adsorbed by SMZ. The most intriguing result is the complete removal
of E. coli by SMZ during field tests.
2.6.1 Adsorption of Cationic Surfactant at Zeolite Surface
Surfactant adsorption is generally determined by two main factors. The first
is the interaction of the surfactant with the surface and the second is the
hydrophobicity of the surfactant, giving rise to what is known the hydrophobic effect
(Tadros, 2005). This latter driving force is of course closely related to the surfactants
in water. Besides that, other mechanisms attributed to sorption of cationic surfactant
onto solid surfaces are ion-pairing, acid-base interaction, polarization of π electrons
and dispersion force (Li, 1999). In the case of polar surface such as clay and zeolite
minerals, the sorption of a cationic surfactant involves cation exchange (interaction
of the surfactant with the surface) and hydrophobic bonding.
The surfactants at low concentration or below its critical micelle
concentrations (cmc) are retained by ion exchange in contact with the solid surface.
This leads to the formation of a monolayer or “hemimicelle” at the solid-aqueous
interface via strong Coulombic (ionic) bonds (Figure 2.5a) (Holmberg et al., 2003).
The size of the surfactant head group and the extent of interaction of the tail group
with the surface or with other surfactant molecules are expected to be significant in
determining the monolayer density on the surface at low solution concentration
(Sullivan et al., 1998b). If the surfactant concentration in solution exceeds the critical
30
micelle concentrations, two different structures at the surface are possible. If there is
a strong attraction between the surfactant head group and the surface, a monolayer is
formed, where the surfactant head groups are in contact with the surface and the
hydrocarbon moieties are in contact with the solution. This adsorption structure will
create a hydrophobic surface, which in turn will adsorb further surfactants with the
same configuration as described above for hydrophobic surfaces, thus a surfactant
bilayer is formed (Figure 2.5 b) (Xu and Boyd, 1995). However, if the attraction
between the surfactant head groups and the surface is intermediate in strength, then
“admicelle” (Figure 2.5b) or will form at the surface. In the case of solids with high
surface charge density such as clay and zeolite minerals, previous studies (Xu and
Boyd, 1995; Li and Bowman, 1997; Li et al.; 1998) suggested that as the amount of
surfactant increases, interactions among the hydrocarbon tails cause the formation of
a bilayer or patchy bilayer.
a.) C < CMC
b.) C > CMC
Figure 2.5: Cationic surfactants adsorb on solid surface and form the hemimicelle (a)
and admicelle (b)
Li and Bowman (1997) further stated that the force and interaction balance
for the surfactant bilayer sorption is the summation of (1) the electrostatic attraction
between the negatively charged zeolite surfaces and the positively charged head
group, (2) the tail-tail hydrophobic interaction between the first layer and the second
layer, which is of London-van der Waals type, (3) the electrostatic attraction between
31
the positively charged head groups of the second layer and the negatively counterion,
(4) the electrostatic repulsion between the head groups of the first layer and the
second layer, and (5) the electrostatic repulsion between the negatively charged
zeolite surface and the negatively charged counterions in solution. Their study
indicated the importance of counterion in stabilizing quaternary amine bilayer
sorption.
Sullivan et al. (1998) conducted detailed studies on the sorption mechanism
of HDTMA to zeolite clinoptilolite by using sorption isotherms and calorimetry as
complement to their previous HDTMA sorption studies (Haggerty and Bowman
1994; Bowman et al., 1995). They commented that the observation of counterion
and co-ion sorption is crucial to fully understand the surfactant process while the use
of very sensitive microcalorimetric methods allowed them to investigate details of
the sorption process not observable in the sorption isotherm study.
From their
extensive study, they proposed a conceptual model for the sorption of HDTMA onto
zeolite: early sorption of HDTMA onto zeolite is fast then slows some time after half
hour; for the monomer system, it appears that sorption below the external cationic
exchange capacity (ECEC) in the form of individual monomers which may either
interact with the surface, or form coiled tail group. When available surfactant is
greater, a monolayer forms and tail group interaction increases as a small amount of
surfactant is sorbed as a bilayer or patchy bilayers (disperse admicelles). Sorption in
the form of admicelles which later rearrange to a monolayer for the micellar system
below the ECEC while above the ECEC, micelle sorbing initially may rearrange to
the extent of the ECEC, with the remainder forming patchy bilayers or admicelles on
the surface. At high loading levels, sorbed micelles are stable and later may coalesce
to a full bilayer.
2.6.2 Mechanisms of Contaminants Sorption by SMZ
As mentioned in the previous section, at sufficient cationic surfactant loading
for the zeolite, a bilayer or patchy bilayer of surfactant molecules forms.
The
formation of this bilayer reverses the charge on the zeolite from negative to positive,
32
and provides sites for exchange of anions (Bowman et al. 2000; Sullivan et al.
1998a). The counterions sorbed on the outer layer of the surfactant bilayer were
readily exchange following a lyotropic series (Li and Bowman, 1997). Detailed
investigations showed that the sorption of chromate and other anionic contaminants
and desorption of surfactant counterions were stoichiometric, proposed that anion
exchange (Li et al., 1998a, 2003; Li and Bowman, 1997) instead of surface
precipitation ((Haggerty and Bowman, 1994) was responsible for the retention of
anionic species on SMZ.
While the surfactant molecules formed mainly a
monolayer on the zeolite surfaces due to the initial surfactant concentration was less
than the cmc, it resulting in a greatly reduced anion sorption (Li et al., 1998a). The
surfactant bilayer forms an organic-solvent-like coating on the surface into which
non-polar organic solutes can partition into the organic pseudophase created by the
surfactant tail groups (Li and Bowman, 1998). A schematic diagram of sorption
mechanisms for anions, cations, and non-polar organics is presented in Figure 2.6
(Bowman et al. 2000).
Figure 2.6: Schematic diagram of sorption mechanisms for anions, cations, and nonpolar organics on SMZ.
33
2.6.3 Biological Toxicity of Surfactant and SMZ
Quaternary ammonium compounds (QAC) are active biocides applied widely
as disinfectants (Jungermann, 1969; Tadros, 2005).
In fact, QAC, a class of
chemical reagents received a lot of attention as general and medicinal antiseptics and
germicides. This is probably due to the properties inherent in the agents that they
contain no phenol, iodine, active chlorine, mercury, or other heavy metals. Diquat
and paraquat are herbicides in which the ammonium cation is part of a pyridinium
ring structure. The exchange of these cations on mineral surfaces reduces their
availability for plant uptake and biodegradation and attenuates their toxicology
toward plant and animal targets (Nye et al., 1994). QAC are common components of
domestic waste waters as it were used widely in detergents, fabric softeners, and hair
conditioners. U. S. consumption of alkyldimethylbenzylammonium compounds
representing just one type of QAC was estimated to be 20-25 million lb in 1979
(Boething, 1984).
In receiving waters, the toxicity of these compounds toward
bacteria and algae is inversely related to the concentration of suspended particulate
material (Tubbing and Asmiraal, 1991), and microbial adaptation and cation
degradation are commonly observed in environments with a history of exposure
(Ferdele and Ventullo, 1990).
Previous studies revealed that QAC when present in the solution phase are
potent biocides which bind to proteins and nucleic acids, disrupt membrane integrity
and cause leakage of cytoplasmic ions and macromolecules (Nye et al., 1994; Guerin
and Boyd, 1997). Nevertheless, the concentrations at which different organisms are
susceptible vary and plasmid-conferred resistance to these compounds has been
reported for certain bacteria. Besides, organisms able to utilize HDTMA as a sole
carbon and energy source have recently been isolated (Ginkel et al., 1992). Later,
Nye and co-researchers (1994) conducted a detailed investigation on heterotrophic
activity of microorganisms in soils treated with QAC to evaluate the feasibility of
using the HDTMA-saturated soil to enhance the immobilization of organic
contaminants while at the same time, coupling contaminant immobilization with
subsequent bioremediation.
34
In the studies by Nye et al. (1994), aqueous HDTMA-Br added to soils
caused increased lag periods and decreased rates and extents of mineralization
compounds as a result of selective toxicity toward Gram-negative soil
microorganisms. Toxic effects were more pronounced at higher HDTMA treatment
levels. However, once HDTMA become bounded to the cation-exchange sites in
soils or minerals, HDTMA toxicity was largely diminished. Findings by Li et al.
(1998) on the studies of biological toxicity of surfactant modified zeolite were in
good agreement with Nye’s results. Their results of the SMZ toxicity experiments
indicated that the bacteria remained viable in all the microcosms with SMZ. In those
microcosms containing aqueous HDTMA without zeolite, HDTMA inhibited the
growth of the microorganisms. Consequently, the lack of microbial toxicity may
suggest that SMZ could be used as a substrate for enhanced bioremediation.
2.7
Adsorption Theory
Adsorption is defined as the accumulation of atoms, ions, molecules at the
interface between a solid phase and a fluid phase (liquid and gas phase). Jakob
Maarten van Bemmelen (1910) was the founder of the theory of absorption
(adsorption) from solution with his publication entitled Die Absorption. Adsorption
differs from precipitation in some cases for instance metal ions. Instead of forming a
new three-dimensional solid phase, the ions associate with the surfaces of existing
particles (McLean and Bledsoe, 1992).
Adsorption can be classified as physisorption, chemisorption, or electrostatic
adsorption. Physisorption is driven by the weak molecular forces like Van der Waals
or hydrogen bonding force of attraction between the solid sorbents and the adsorbate
molecules (∆Hphysisorption ~ 20 kJ.mol-1), while chemisorption forms a surface
complex or compound through chemical reaction (∆Hchemisorption ~ 200 kJ.mol-1)
(Crittenden and Thomas, 1998). Electrostatic adsorption involves the adsorption of
ions through Coulombic force and is normally referred to as ion exchange. In many
cases, the uptake of adsorbate is confined only to a single layer on the surface of the
35
solid, and even when many layers are involved, an average of ten layers is rarely
exceeded.
Adsorption equilibrium models (Weber et al., 1991) are classified in two
major groups, mechanistic and phenomenological models.
Mechanistic models
include hydrophobic, ion-exchange, and surface complex formation (SCF) models.
In ion-exchange and SCF models the calculations are based on the stability constants
of the adsorbent surface. These constants can be obtained from the potentiometric
titrations and other experiments.
At equilibrium, the relationship between the
concentrations of solute in the liquid or gas phase with that of solid phase at a
constant temperature is expressed by adsorption isotherm equations.
The
phenomenological models are based on these adsorption isotherms. Although these
models were developed for gas phase adsorption, they also have been successfully
applied to dilute liquid phase adsorption. There are many models developed for gas
phase adsorption in single and multicomponent systems and some of them have been
successfully applied to liquid phase adsorption. A summary of these models can be
found in else where. (Kinniburgh et al. 1983; Kinniburgh, 1986; Koopal et al. 1994;
Altin, et al., 1998; Perić et al.). Among them, Langmuir, Freundlich and Temkin
adsorption isotherms are most frequently applied models in the adsorption of gas or
liquid on a solid phase (Kalavathy et al., 2005).
2.7.1 Langmuir Isotherm
The Langmuir equation was first proposed by Irving Langmuir in 1918. The
derivation of this equation was based on the assumption that adsorption is
independent of surface coverage, that there is no interaction between adsorbed ions,
and that only a monolayer of adsorption take place on the surface. The Langmuir
isotherm is expressed as (Langmuir, 1918):
qe =
K L qmCe
1 + K LCe
The linear form of the Langmuir isotherm is given by:
(2.1)
36
Ce Ce
1
=
+
qe qm K L q m
(2.2)
where, qe = amount of adsorbate adsorbed at equilibrium per unit mass sorbent
(mg g-1); Ce = equilibrium concentration of adsorbate in solution (mg L-1); qm = the
maximum monolayer adsorption capacity (mg g-1); KL = Langmuir adsorption
constant (l g-1).
Alternatively,
Donald
Langmuir
has
recommended
the
following
linearization owing to the reason that the above linearized version is incorrect since it
produces an induced correlation with Ce.
1
1
1
=
+
qe K L C e q m q m
(2.3)
Based on the above equation, a plot of 1/qe versus 1/Ce should produce a straight line
of slope 1/KLqm and intercept 1/qm.
The monolayer capacity, qm, determined from the Langmuir isotherm, defines
the total capacity of the adsorbent for a specific adsorbate. Reliable qm values can be
obtained only for systems exhibiting Type-1 isotherms of the Brunauer’s
classification. The monolayer capacity may be used to determine the specific surface
area of the adsorbent by utilizing a solute of known molecular area.
The essential characteristics of Langmuir isotherm have been described by
the dimensionless separation factor or equilibrium constant, RL which is defined as:
RL =
1
(1 + K L C o )
This indicates the nature of adsorption as
RL > 1
unfavorable;
RL = 1
linear;
0 < RL < 1
favorable;
RL = 0
irreversible.
(2.4)
37
2.7.2 Freundlich Isotherm
In contrast with Langmuir model, Freundlich isotherm gives the relationship
between equilibrium liquid and solid phase capacity based on the multilayer
adsorption (heterogeneous surface). The Freundlich isotherm is derived by assuming
a heterogeneous surface with a non-uniform distribution of heat of adsorption over
the surface.
This isotherm assumes that the adsorption sites are distributed
exponentially with respect to the heat of adsorption and is given by:
qe = K F C e1/ n
(2.5)
The linear form of the Freundlich isotherm is given by:
log q e = log K F +
1
log C e
n
(2.6)
where qe and Ce have the same meanings as in equation (2.1). Plotting log Ce
against log qe gives a straight line with a slope 1/n and an intercept log KF. KF (mg/g)
and n relates the multilayer adsorption capacity and intensity of adsorption, n also
known as the heterogeneity factor.
The Freundlich constant KF, unlike the Langmuir constant KL does not predict
the saturation of the solid surface by the monolayer coverage of the adsorbate
(Dinesh and Singh, 2002). But it gives a relative measure in adsorption capacity and
estimates bond strength (Toles and Marshall, 2002). The value of n discloses the
adsorption pattern. The favorable adsorption is understood from the values of 1 < n
< 10 while irreversible adsorption is noticed from n > 10 and unfavorable from n < 1.
2.7.3 Temkin Isotherm
Temkin isotherm, which considers the effects of the heat of adsorption of all
the molecules in the layer decreases linearly with coverage due to adsorbentadsorbate interactions. The adsorption is characterized by a uniform distribution of
the binding energies up to maximum binding energy. The Temkin isotherm equation
is given as (Choy et al., 1999):
38
qe =
RT
ln( K T C e )
b
(2.7)
The linear form of the Temkin isotherm is given by:
qe = B1 ln K T + B1 ln Ce
(2.8)
where B1 = RT/ b and KT are the constants. KT is the equilibrium binding constant (L
g-1) corresponding to the maximum binding energy and constant B1 is related to the
heat of adsorption. A plot of qe against ln Ce enables the determination of the
isotherm constants KT and B1.
2.8
Combination of Adsorption and Biological Treatment
Currently, a combination of adsorption and biodegradation that can be
operated either separately or simultaneously in a unit. It is becoming more popular
and common to remove various contaminants from wastewater, for instance removal
of phenolic compounds (Sutton and Mishra, 1994; Caldeira et al., 1999). Generally,
the presence of both processes in one unit results in a better removal and process
performance. The popularity of this approach can be seen from the synergistic
advantages of the combined process: adsorption could reduce the inhibitory effect of
the compounds for microorganisms while concurrently microbial degradation could
in some extend adsorb (Armenanta et al., 1996) and degrade (Ha and Vinitnantharat,
2000) the substance, to some limits, biodegradation also freeing the adsorption sites
of adsorbents thus extending the life of adsorbents. Adsorbents can also act as a host
or support material for bacteria immobilization, operate as “buffer and depot” or
“sink and source”: protected the immobilized microorganisms by adsorbing toxic
contaminants concentrations and set low quantities of the contaminants for
biodegradation gradually (Ehrhardt and Rehm, 1985, 1989; Oldenburg and Sekoulov,
1995; Wilderer et al., 2000).
By acting as “buffer and depot”, the biocarrier
(adsorbent) greatly reduces the inhibitory effect of the substances for microbial mass.
In some cases, immobilized cell could perform greater for contaminants degradation
than suspended cells (Lee et al., 1994).
39
The simultaneous adsorption and biological treatment is commonly applied in
a conventional activated sludge process added with powder or granular activated
carbon (Metcaff, LaGrega et al., 1994).
The presence of adsorbent shows an
increase in the removal efficiency. The use of biological process is also found in
fluidized, fixed bed reactor, having biofilm on the adsorptive and ion-exchange solid
surface (Durham et al., 1994a, 1994b). In addition, environmental remediation by
reactive barrier is also based on the combination of adsorption and biodegradation
(Scherer et al., 2000; Witthuhn et al., 2005). The barriers consists of adsorptive
zones installed in the contamination plume to prevent further spreading of pollutants
which are distributed over a large area or cannot be localized exactly. Coupled biotic
and or abiotic degradation provide contaminant elimination and sorbent regeneration.
The removal of substances is mechanistically complex in the presence of
microbial film due to the microbial film is essentially always in a dynamic state. The
complex mechanism involving transport of substances from the bulk liquid to the
surface of microbial film; simultaneous mass transfer, adsorption and biochemical
reaction within microbial film; simultaneous mass transfer and adsorption within
adsorbent (Syamsiah and Hadi, 2004).
In the case of an additional adsorbing
material being added to a biological reactor it is essential to determine whether the
adsorbing material retains its adsorption capacity, or if the adsorption process is
limited or reduced by the presence of the microorganisms on its surface.
The
information on this subject is rather limited. Some authors observed that addition of
adsorbent did not improve the contaminant removal; however, they observed better
treatment performance at higher contaminant concentration (Lima et al., 2004).
Biological treatment has been considered in the treatment system using
zeolite and inversely, since microorganisms would probably grow on the surface of
the zeolite immerged in aqueous solution or wastewater. Zeolite covered by biofilm
was named as bio-zeolite, acting as the ion-exchanger and growth media for
microorganisms (Oldenburg and Sekoulov, 1995).
Combination of microbial
degradation with zeolite adsorption were extensively studied since Semmens and coworkers’ pioneering works (Semmens and Goodrich, Jr., 1977a; Semmens et al.,
1977b; Semmens and Porter, 1979), when they were inspired to regenerate the
ammonium-saturated clinoptilolite by using the nitrifying bacteria.
There were
40
several approaches to couple the zeolite and nitrification, such as in a hybrid
biological-ion exchange multireactor system (Semmens et al., 1977a, 1977b, 1979),
two mode process in a single reactor (Green et al., 1996; Lahav and Green, 1998).
Generally, adsorption or colonization of the zeolite by mixed cultures of nitrifying
bacteria could improve the zeolite performance and extended the cycle life of zeolite
(McVeigh, 2000; Park et al., 2002). However, in the study by Wen et al. (2006),
they compared the sorption kinetics of ammonium onto natural zeolite, and natural
zeolite covered by biofilm at two particle size. They found that biofilm covered on
the zeolite with smaller particle size (1.0-3.0 mm) did not affect the ion-exchange but
improved the initial sorption rate due to biosorption.
However, for the bigger
particle size (8-15 mm), the attached biofilm reduced the ion-exchange rate resulting
in a 22 % drop of the total equilibrium capacity.
Besides that, recently a wide variety of applications of zeolite with biological
treatment was undertaken, to mention a few: Jung et al. (1999, 2004) recommended
the modified zeo-SBR (sequencing batch reactor) for a new nitrogen removal process
that has a special function of consistent ammonium exchange and bioregeneration of
zeolite-floc; Son et al. (2000) and Park et al. (2000) used zeolite as biocarriers in
oxic/anoxic process for nitrogen removal; Ahn et al. (2002) used zeolite to remove
ammonia thus improve the lowering of chemical oxygen demand and the solids
separation prior to activated sludge process; Chang et al. (2002) reported the
application of lab and pilot scale downflow biological aerated filter (BAF) for textile
wastewater using natural zeolite as media; Kim et al. (2003) treated the landfill
leachate by white rot fungus in combination of zeolite filters as a sink for
ammoniacal nitrogen; Kargi and Pamukoglu (2004) investigated and compared the
adsorption performance of powdered activated carbon and powdered zeolite in
aerobic biological treatment by fed-batch operation of pretreated landfill leachate;
Aiyuk et al. (2004) applied zeolite to remove ammonium either after CEPT
(chemically enhanced primary treatment ) or preferably after biological treatment in
the UASB (upflow anaerobic sludge blanket) reactor, the ion exchange system is
regenerated by biological nitrification; Fernández et al. (2001) developed two
experiences with anaerobic fluidized bed reactors (AFBR) using both Cuban raw
material, activated carbon and natural zeolite, as support media, with the purpose of
obtaining high organic matter removal rates and keeping sulfide and ammonium
41
concentrations in the permissible ranges for vinasse treatment; Cuban researchers
(Sanchez et al., 1995 ; Milán et al., 2001, 2003; Montalvo et al., 2005) studied
extensively to use zeolite towards enhancement of the anaerobic digestion processes
of piggery waste, zeolite was used to remove ammonium that are present in raw
piggery wastewater and those produced during anaerobic degradation of proteins,
amino acids and urea.
Furthermore, zeolite has been used to immobilize bacteria, Pseudomonas
fluorescens for biodegradation of cyanide compounds (Suh et al., 1994).
The
combination of adsorption and biodegradation can also extend to the surfactantmodified minerals. For instance, Witthuhn et al. (2005) examined the suitability of
surfactant-modified clay (SMC) combined with biodegradation in 2, 4-dichorophenol
remediation techniques and their investigations gave encouraging results. They
proposed a precondition for using SMC coupled with biodegradation that the coating
density of the SMC should be lower than the strong adsorption capacity to avoid free
surfactants which might be harmful to bacteria. Fuierer et al. (2001) studied the
feasibility of using a reactive nutrient –amended microbial support system comprised
of surfactant-modified zeolite (SMZ) to stimulate biodegradation of petroleum
hydrocarbons. Due to the high affinity for hydrocarbon, the microbial community
will be protected from high contaminant concentrations.
In the meanwhile, the
reversible nature of toluene sorption should allow sustained degradation of toluene as
it desorbs from SMZ.
CHAPTER 3
EXPERIMENTAL
3.1
Preparation of the Rice Husk Ash
The rice husk used to produce amorphous silica was obtained from Padiberas
Nasional Berhad (BERNAS). The rice husk ash (RHA) was prepared by physical
combustion of local rice husk at 600 °C for 1 h in a Plug Flow Combustor (PFC),
located at Solid State Laboratory, Ibnu Sina Institute for Fundamental Science
Studies (IIS), MTDC building, UTM. Prior to burning, the rice husk was washed by
immersing them in distilled water to eliminate undesirable materials such as rice,
sand and dust. The rice husk was then placed under sunlight for a period of time until
the entire rice husk was virtually dried.
3.2
Determination of Silica Content in Rice Husk Ash
The water content of rice husk ash was determined by conducting the loss of
ignition (LOI) test followed the standard procedures (SIRIM ISO 3262-1975). One
gram of dried sample was place in a platinum crucible and ignited in the muffle
furnace (Carbolite) at 1000 °C for 30 minutes to achieve constant mass, followed by
cooling in a desiccator. The loss of ignition as a percentage by mass is given by the
formula:
43
% LOI =
m0 − m1
× 100
m0
(3.1)
where m0 is the mass of the sample and m1 is the mass of sample after ignition
The determination of silica was followed based on the standard procedures
(SIRIM ISO 3262-1975). The residue remained from the LOI test was added slowly
with 1 mL of 50 % sulphuric acid (diluted from 95-96 % sulphuric acid, Merck).
The crucible was heated gently until the fuming ceased and the heating was
continued at 900 °C for 30 minutes in the muffle furnace. After heating, the residue
was removed from the furnace, cooled in the desiccator and weighed (m2). The
residue was dissolved in 1:5 mixture of H2SO4 (95-97 %, Merck): HF (49 %, Merck)
solution and evaporated on a hot plate until no further white fumes observed. The
crucible was ignited in the muffle furnace at 90 °C for 30 minutes and then cooled in
the desiccator. The cooled crucible was weighed as m3. The silica content (% Si)
was calculated using the following equation:
% SiO 2 =
3.3
m2 - m3
× 100
m1
(3.2)
Detailed Description of Synthesis of Zeolite Y from Rice Husk Ash
Zeolite Y (Si/Al=3) was synthesized under hydrothermal conditions from
reactive sodium aluminosilicate gels using only inorganic reactants in alkaline media
at a temperature of about 100 ºC. Commercially available sodium aluminate (50-56
% w/w Al2O3, 40-45 % w/w Na2O, Riedel de Haën) and sodium hydroxide (99 %,
Merck) were used as received.
Sodium aluminate was a source of alumina in
producing zeolite while sodium hydroxide supplied the supplementary sodium ion
and prepared the alkaline media. Throughout this study, local rice husk ash was
utilized as the major and the only source of silica in preparing zeolite samples.
Initial aluminosilicate gel (seed gel) slurry was prepared following the molar
composition of 15 Na2O: Al2O3: 15 SiO2: 220 H2O and used as a source of seeds
44
which act as nucleation centres. The respective amounts of constituting materials in
a synthesis of 15 g batch (10 % of Al) seed gel are as follows:
NaOH
:
4.1874 g
NaAlO2
:
0.7291 g
RHA
:
3.5885 g
H2O
:
15 mL
About 4.1874 g of NaOH was dissolved properly in about 15 mL of distilled water.
Then about 5 mL of prepared NaOH solution was added into the 0.7291 g NaAlO2
and gently heated under rigorous stirring until dissolved. About 3.5885 g RHA was
slowly added, a little at a time, into the remaining NaOH solution under rigorous
stirring and gentle heating.
Loss of material while stirring and heating was
minimized by covering the apparatus with a glass plate. After the materials have
been dissolved in NaOH solution, the aluminate and silicate solution were allowed to
cool down under stirring condition. Later the silicate solution was added to the
aluminate solution thus forming a loose gel in the mixture.
The mixture was
thoroughly stirred for 1 hour to homogenize the aluminate-silicate mixture. Then, the
mixture was poured to a propylene beaker and sealed with parafilm.
Concurrently, another feed stock aluminosilicate was prepared with molar
composition of 4 Na2O: Al2O3: 10 SiO2: 180 H2O. The respective amounts of
constituting materials in a synthesis of 135 g batch (90 % of Al) feed stock gel are as
follows:
NaOH
:
9.0261 g
NaAlO2
:
8.0189 g
RHA
:
26.3158 g
H2O
:
135 mL
The preparation of feed stock gel was similar to the seed gel except for the
preparation of silicate solution; the RHA was digested in NaOH solution in a water
bath for 2 hours at 80-90 °C. The feed stock gel was transferred to a Nalgene Teflon
FEP
(fluorinated
ethylene
propylene)
bottle
with
a
Tefzel
ETFE
(ethylenetetrafluroethylene) screw closure and left to age at room temperature for 1
day.
45
After aging period, the seed gel was added slowly to the feed stock gel under
rigorous stirring for 2 hours. The overall mixture with a molar composition of 5.1
Na2O: Al2O3: 10.5 SiO2: 184 H2O was aged at room temperature for 24 hours.
Subsequently, the hydrothermal reaction was carried out by heating the mixture at
100 °C in a drying oven.
After 24 hours reaction, the crystallization was stopped by immersing the
Teflon FEP bottle in water. Then the product was recovered by vacuum filtration
and washed out of the entrained sodium salts with copious quantity of hot distilled
water until the pH of the filtrate is below 10. Then the filtrate was dried in an oven
at 100 °C overnight, ground and sieved to retain the particles of size less than 800
µm.
The products from different batch experiments were mixed thoroughly in a
plastic container and homogenized for 26 h by a roller machine to ensure the
homogeneity for use in subsequent studies.
3.4
Characterization Techniques
The prepared rice husk ash and zeolite samples were characterized by several
techniques such as X-ray Diffraction (XRD), Fourier transform infrared (FTIR)
spectroscopy, thermogravimetry-differential thermal analysis (TG/DTA) depending
on the significances. The collection of information on the structural and chemical
characteristics of zeolites ought to derive relations between their chemical and
physicochemical properties on the one side and the adsorptive properties on the
other.
3.4.1 X-ray Diffraction (XRD)
The crystallinity and the structure of the sample was examined with a powder
X-ray diffractometer (Bruker D8 Advance Diffractometer, Cu Kα radiation with λ =
46
1.5418 Å). The pulverized sample was divided finely to permit packing of sample
into an XRD sample holder as a self-supporting window. The X-ray diffraction
pattern was collected by scanning over the angle range from 5.00 to 50.00 ° 2θ at a
scanning speed of 3°/min.
Prior to the X-ray diffraction analysis for the zeolite, the sample was dried in
a drying oven at 100 °C overnight, and then cooled in the hydrator maintained at
constant humidity by a saturated solution of ammonium chloride for at least 72
hours. These steps of drying followed by rehydration results in filling the zeolite
pores with water of hydration but without an excess of moisture residing on the
surface of the zeolite particles. The application of these steps is important for zeolite
because different degree of hydration on zeolite will provide different value of the
interplanar spacing (d-spacing). The crystalline phase of synthetic zeolite was
matched with good-quality single phase pattern in Powder Data File (PDF, compiled
by International Centre for Diffraction Data) by employing the Diffraction EVA
software.
3.4.2 Fourier Transform Infrared (FTIR) Spectroscopy
Fourier transform infrared (FTIR) spectroscopy was performed to observe the
presence of functional groups in the sample. The potassium bromide (KBr) pellet
method was followed by using a Fourier Transform Infrared Spectrophotometer
Shimadzu 8300. About 1 mg of powder sample was well mixed with about 200 mg
of KBr powder; the mixture was then pressed at 10 tonnes of pressure for 1 minute to
form a transparent pellet. The FTIR spectrum was scanned in a spectral range of
4000 to 400 cm-1.
47
3.4.3 Thermogravimetry-Differential Thermal Analysis (TG-DTA)
Thermal analysis (thermogravimetry TG and differential thermal analysis
DTA) were carried out on a Perkin Elmer Diamond Thermogravimetric/ Differential
Thermal Analyzer (Diamond TG/DTA). The instrument operating conditions were 5
°C/min or 10 °C/min step from room temperature to 900 °C, using an approximately
10 mg of samples in an platinum crucible and an N2 flow of 200 mL/min. The
record of data and thermogram were assisted by the Pyris software provided by the
supplier.
3.4.4 Field-Emission Scanning Electron Microscopy (FESEM) and Energy
Dispersive X-Ray Analysis (EDAX)
The surface morphology of zeolite samples was observed from the magnified
images of the crystallites by field-emission scanning electron microscopy (FESEM,
Zeiss Supra 35 VP with GEMINI field emission column). Below are the operating
conditions of the instrument:
•
Electron Sources: Field Emission Gun
•
Imaging Modes: Secondary Electron, Backscattered Electron, VVP
Secondary Electron, In-Lens Secondary Electron
•
Accelerating Voltages: 0.1 - 30.0 kV by 0.1 kV steps
•
Working Distances: 0mm to 49mm
•
Magnifications: 15x - 500,000x
•
5-axis Motorized stage
•
EDAX Genesis Energy Dispersive X-ray microanalysis system
•
HKL ESBD analysis system
Besides microscopy investigation, the instrument also imparts the detection of
scattered X-ray for the characteristic radiation of a specific element in an energy
dispersive system to identify the element semi-quantitatively.
48
3.4.5
Surface and Porosity Analysis with Nitrogen Adsorption
The surface and porous structure of zeolites was analyzed by N2
adsorption-desorption at 77K with an accelerated surface area and porosimeter,
ASAP 2010. The Brunauer, Emmett and Teller (BET) equation and t-plot
method were used to calculate surface area and microporosity. The single point
total pore volume was measured from the amount of nitrogen adsorbed at the
relative pressure of 0.99.
3.5
Determination of Cation Exchange Capacity and External Cation
Exchange Capacity
The cation exchange capacity (CEC) of zeolite is the amount of all
exchangeable cations and it is defined by the number of equivalents of fixed negative
charges per amount of zeolite (Inglezakis, 2005). However, it should be noted that
the CEC does not correspond to the operating exchange capacity which is commonly
lower in practice (Inglezakis, 2005; Du et al., 2005). In this study, the CEC was
measured by ammonium displacement from the sodium-saturated zeolite samples.
This method was applicable to most soil and mineral samples. The procedures were
adopted from the classical “Ammonium Acetate Method at pH 7” with appropriate
modification (Hendershot et al., 1993).
The reagents employed for this method were sodium acetate (NaOAc), 1.0 N,
ammonium acetate (NH4OAc), 1.0 N and isopropyl alcohol supplied by Merck.
Sodium acetate (NaOAc), 1.0 N was prepared by dissolving NaOAc (136 g) in water
and diluted to 1000 ml in a volumetric flask. The pH of this solution was adjusted by
adding a few drops of acetic acid or NaOH to the solution to pH 8.2. The 1.0 N of
ammonium acetate (NH4OAc) was prepared by diluting glacial acetic acid (99.5%,
114 mL) with distilled water to a volume approximately one liter in a 2 L volumetric
flask. The concentrated ammonium hydroxide (NH4OH) (138 mL) was then added
and mixed with water to obtain an amount of about 1980 mL. The pH was adjusted
49
with NH4OH to obtain a pH of 7 and this solution was diluted to the 2 L mark with
distilled water.
Sodium-saturated zeolite was prepared through exhaustive exchange of the
raw zeolite with pH-buffered sodium acetate (1.0 N) for 4 times. Then it was
thoroughly washed with 2-propanol for 3 times to rinse down the excessive sodium
loosely bound onto zeolite.
The total CEC measurement was accomplished by
mixing 1.0 N ammonium acetate solution with sodium-saturated zeolite for 3 times.
Two phases were separated by centrifugation and the washes were mixed together
prior to AAS analyses. Analysis of the sodium in solution yields the total CEC of
zeolite samples. The sodium content in solutions was analysed in air-acetylene flame
using flame atomic adsorption spectrometer of Perkin Elmer, model AAnalyst 400.
On the other hand, external cation exchange capacity (ECEC) was measured
based on the appropriate modification of the Ming and Dixon’s method (1987) as
shown by Haggerty and Bowman (1994). In the modification, HDTMA as HDTMAbromide instead of t-butylammonium was employed for surface exchange with
sodium to measure ECEC.
The experimental procedures were similar to the
determination of CEC except for the last step where the HDTMA solution (1.0 mmol
L-1) was used for surface exchange with sodium rather than ammonium acetate
solution. The ECEC is relevant for surfactant modification of zeolites since large
amines such as HDTMA are excluded from the internal exchange sites.
3.6
Preparation of Surfactant-Modified Zeolites
The mordenite and zeolite Y were treated with a quantity of HDTMA-Br,
(Merck) equal to 50 %, 100 %, 150 % and 200 % of the ECEC to investigate the
optimum ratio of surfactant modification. Typically, 5 g of zeolite and 100-200 mL
of aqueous surfactant solution of the appropriate concentration were placed in a 250
mL conical flask.
The flasks were mechanically shaken for 3 days at room
temperature, a period to allow it to attain HDTMA sorption equilibrium (Li, 1999).
Then the mixtures were filtered by vacuum filtration, rinsed with distilled water
50
several times to remove excess or loosely bound HDTMA before air-drying and
storage. The annotations and the modification conditions of the prepared sorbents
are summarized as Table 3.1.
Table 3.1: The annotations of the prepared surfactant-modified zeolites
Zeolite
Quantity of HDTMA
SMZ
(% of the zeolite ECEC)
Mordenite
Zeolite Y
3.7
50 %
SMM-50
100 %
SMM-100
150 %
SMM-150
200 %
SMM-200
50 %
SMY-50
100 %
SMY-100
150 %
SMY-150
200 %
SMY-200
Adsorption Studies
The performance of the zeolites (mordenite and zeolite Y) and its surfactantmodified forms in removing contaminants from aqueous solutions were
investigated using batch mode adsorption tests. Batch mode adsorption means
adsorption of the known concentration adsorbates by known quantity of sorbent
(zeolite in this work) in a vessel within a prescribed time.
The uptake of
adsorbate by the zeolite samples was obtained from the concentration difference
before and after adsorption. The following equation (3.3) was used to calculate
the adsorbate uptake in mg by a quantified mass of zeolite.
51
q=
(C 0 − C t )V
1000m
(3.6)
where q = adsorbate uptake, mg.g-1-sorbent; C0 = initial concentration, mg.L-1; Ct =
concentration, after a prescribed duration (t), mg.L-1; V= volume of solution, mL; and
m = mass of sorbent used, g. The detailed procedures are described in the following
sections.
Due to the fact that zeolite in its native form possesses great cation exchange
capacity, adsorption of ammonium, NH4+ was carried out and the obtained
equilibrium data were fitted to various equilibrium models.
The ammonium
adsorption studies also include the effect of the initial pH of the species.
On the
other hand, the series of SMZ were evaluated systematically by using the isotherm
equilibrium study to acquire the maximum adsorption of the oxyanions included
nitrate (NO3-), sulfate (SO42-), phosphate (PO43-) and anionic organic dye, Acid
Orange 7 (AO7).
3.7.1 Test and Standard Solutions
The stock solutions of the ions were prepared from analytical grade
ammonium chloride, NH4Cl (GCE), sodium nitrate, NaNO3 (GCE), sodium sulfate,
Na2SO4 (Merck), sodium orthophosphate hydrate, Na3PO4.12H2O (Riedel de Haën),
and Acid Orange 7, AO7 (TCI) in the form of sodium salt. Synthetic acid dye, C. I.
Acid Orange 7 is also known as Orange II and p-(2-hydroxy-1-naphthylazo)
benzenesulfonic acid, the chemical structure of AO7 is shown in Figure 3.1. Stock
solution of concentration of 1000 mg.L-1 of each of the solutes was prepared by
dissolving appropriate amount of the salts, respectively, followed by dilution to 1000
mL using distilled water. Various concentrations of test solutions of single solute
were prepared by subsequent dilution of the respective stock solution using distilled
water.
The initial pH of the solution was measured with a pH meter (Hanna
Instruments). Where appropriate, the solutions were adjusted with hydrochloric acid
or sodium hydroxide to desired pH while monitoring the pH change with a pH meter.
52
O
N
O
Na
S
O
N
OH
Figure 3.1: Structural formula of AO7
3.7.2 Kinetic Studies
Kinetic studies were conducted at room temperature using 400 mL of
adsorbate solution (pH = 7) at certain concentrations and fixed amount adsorbents of
1 g in a 500 mL conical flask. The reaction mixture was stirred by a Teflon-coated
magnetic bar driven by a magnetic stirrer. The samples at different time intervals
were taken. The two phase at the designed time were separated by filtration through
a 0.45 µm membrane filter (for time lesser than 2 h) or centrifugation. The initial and
final ammonium concentrations remaining in supernatant were analyzed. Duplicate
samples were prepared for all initial conditions. Table 3.2 depicts a summary of the
experimental conditions of kinetic studies for different adsorbates.
3.7.3 Adsorption Equilibrium (Isotherm) Studies
All equilibrium studies were carried out in batch system at room temperature.
Accurately known of 0.1 g of zeolite or modified zeolite sample was equilibrated
with fixed volume of adsorbate solutions in a 50 mL polypropylene centrifuge tube.
Shaking was applied by placing the sealed tubes in an orbital shaker with a constant
53
shaking rate of 150 rpm. The shaking time was set at a certain period of time which
was proven through the kinetic studies that the equilibrium of exchange could be
reached prior to the shaking time. At the end of sorption experiments, centrifuge
tubes were removed from the shaker and the solutions were separated from the
adsorbent by centrifugation.
The final adsorbate concentrations remaining in
solutions were determined. The amount of adsorbate sorbed was determined from
the difference in solution concentration before and after equilibration.
The
adsorption equilibrium data were obtained by varying initial adsorbate ion
concentrations while the mass of adsorbent, contact time, shaking rate and initial pH
were kept constant. Duplicate samples were prepared for all initial conditions. The
adsorbents used in the isothermal experiments were similar to the kinetic
experiments (Table 3.2). The experimental conditions of adsorption equilibrium
studies for different adsorbates are summarized in Table 3.3.
54
Table 3.2: Conditions of kinetic studies
Adsorbate
Conc. (mg/L),
Adsorbents
Volume (mL)
NH4
+
50 mg/L, 400 mL
zeolite Y, mordenite (powder)
mordenite (granular)
NO3-
40 mg/L, 400 mL
zeolite Y, mordenite,
SMM-50, SMM-100, SMM-150, SMM-200,
SMY-50, SMY-100, SMY-150, SMY-200
SO42-
25 mg/L, 400 mL
zeolite Y, mordenite,
SMM-50, SMM-100, SMM-150, SMM-200,
SMY-50, SMY-100, SMY-150, SMY-200
PO43-
12.5 mg/L, 400 mL
zeolite Y, mordenite,
SMM-50, SMM-100, SMM-150, SMM-200,
SMY-50, SMY-100, SMY-150, SMY-200
AO7
200 mg/L, 200 mL
zeolite Y, mordenite,
SMM-50, SMM-100, SMM-150,
SMY-50, SMY-100, SMY-150
Table 3.3: Conditions of adsorption equilibrium studies
Adsorbate
Range of
Volume of
Initial Conc. (mg/L)
Adsorbate (mL)
+
10—500
10 mL
NO3-
15—165
20 mL
SO42-
15—110
20 mL
PO43-
2.5—100
10 mL
AO7
10—1200
10 mL
NH4
55
3.7.5 Chemical Analysis
Ammonium concentration in aqueous solutions was determined by the
standard Nesslerization method using the Hach DR 4000 Spectrophotometer (APHA,
1992; Hach, 1997a). Firstly, 25 mL of sample (with appropriate dilution when
necessary) and 25 mL of distilled water (as blank sample) were measured. Then
three drops of mineral stabilizer (Hach) was added to each solution, stopped and
inverted several times to mix, later three drops of polyvinyl alcohol dispersing agent
(Hach) was added to each solution by holding the dropping bottle vertically. It was
inverted several times to induce mixing. Nessler reagent (Hach) was pipetted into
each cylinder and inverted several times to mix. After a one-minute reaction period,
the ammonium concentration was
measured by using Hach DR 4000
Spectrophotometer.
Nitrate concentration in aqueous solutions was determined by the cadmium
reduction method (Hach, 1997b). 10 mL of solution was place in sample cell. Then
Nitra Ver 5 nitrate reagent was added and shaken vigorously for one minute. The
sample was allowed to stand for five minutes to allow reaction period to begin, and
then transferred into the cell holder with a lid. A blank was prepared with distilled
water. The concentration of nitrate in solution compared to that of the blank was
measured by using Hach DR 4000 Spectrophotometer. The sample would turn from
colourless to yellow colour as the intensity indicates the amount of nitrate
concentration.
Sulfate concentration in aqueous solution was measured by standard
turbidimetric method (APHA, 1992; Hach, 1997c) where 10 mL of solution was
filled in a clean sample cell and the content of Sulfa Ver 4 reagent was added and
swirled to mix well. The mixtures were then allowed to react for 5-minute and then
transferred into the cell holder. The second sample cell was filled with 25 mL of
distilled water as a blank. The comparison of sulfate concentration between prepared
sample and blank was measured using Hach DR 4000 Spectrophotometer. The
presence of sulfate would turn the colour from colourless to pink.
56
Phosphate concentration in aqueous solution was analyzed by ascorbic acid
method in accordance to Standard 4500-P-E (APHA, 1992; Hach, 1997d). The
solution (10 mL) was measured in sample cell. Then, Phos Ver 3 Phosphate reagent
was added and the mixture was swirled immediately to mix it well. The prepared
sample was placed into the cell holder after allowing it to stand for 2 minutes.
Another sample cell was filled with distilled water as a blank. The concentration of
phosphate in solution in comparison to blank was measured by using Hach DR 4000
Spectrophotometer. The high concentration of phosphate in sample was indicated by
an intense blue colour.
Concentration of Acid Orange 7 in aqueous solution was determined by a
Cary 100 UV-Vis spectrophotometer at the respective λmax value, which was
determined earlier as 482 nm for AO7. The calibration curve for the dye at the
respective wavelengths was established as a function of dye concentration.
3.8
Aseptic Working Condition
Sterilization is the treatment resulting in death of all living microorganisms
and viruses in a material, equipment or media. Thus all of the apparatus and medium
used in the experiments related to microorganism must be sterilized in order to avoid
contamination. Plasticwares such as rubber tubes can be sterilized by dipping in 70
% alcohol overnight and then exposed under ultraviolet (UV) light at a wavelength of
220 to 300 nm.
This helps eliminate microorganisms by damaging their DNA
(Cappuccino and Sherman, 1996). Glass apparatus and autoclavable plasticwares
were sterilized in an autoclave at 121°C for 15 min. For plastic bottles, caps were
loosened before autoclaving to prevent distortion. All microbiological preparation
and experiments were carried out under aseptic condition throughout this study.
57
3.9
Preparation of Growth Medium
Culture media are media (liquid state or semisolid state) containing all of the
nutrients and necessary physical growth parameters suitable for microbial growth.
The nutrients present in the culture medium provide the microbial cell with the
ingredients required for the cell to produce more cells like itself.
Nutrient broth was prepared by dissolving the nutrient broth (8.00 g, Merck)
in distilled water (1 L). Nutrient broth was autoclaved for 15 minutes at 121 °C,
101.3 kPa. This medium is commonly used for the propagation of large number of
organisms, fermentation studies, and various other tests. Nutrient agar was prepared
by adding nutrient agar powder (20.00 g, Merck) in distilled water (1L) and then
autoclaved (121 °C, 101.3 kPa, 15 minutes). After autoclaving, the agar was poured
into Petri dishes and allowed to solidify. Agar plates should be prepared aseptically
in the laminar flow hood to prevent contamination. These solid media were used for
developing surface colony growth of bacteria and trying to isolate organisms from
mixed cultures.
3.9.1 Nitrate Selective Agar
Nitrate selective agar was used to differentiate microorganisms based on their
ability to reduce nitrate. The colony that grew on the agar was tested with zinc dust,
and if the bacterial culture had reduced the nitrate to nitrite, a pink to red colour
colony will form. The composition of nitrate selective agar is shown in Table 3.4.
The materials were mixed and dissolved in 1 L of distilled water. The pH of the
media was adjusted to about pH 7 before autoclaving at 121 °C, 101.3 kPa for 15
minutes.
58
Table 3.4: Composition of nitrate selective agar
Material
Quantity (g)
Gelatine
5.0
Potassium nitrate
1.0
Beef extract
3.0
Agar
15.0
3.9.2 Sulfate Selective Agar
The composition of sulfate selective agar is shown in Table 3.5.
The
materials were mixed and dissolved in 1 L of distilled water. The pH of the media
was adjusted to about pH 7 before autoclaving at 121 °C, 101.3 kPa for 15 minutes.
The bacterial colony that had the ability to reduce the sulfate would appear as a black
coloured colony or with black dots in the middle of the colony.
Table 3.5: Composition of sulfate selective agar
Material
Quantity (g)
Beef extract
5.0
Protease peptone
5.0
Lactose
10.0
Sodium citrate
9.0
Sodium sulfate
8.4
Ferric chloride
1.0
Cobalt chloride
0.03
Cresol red
0.03
Agar
15.0
59
3.9.3 Phosphate Selective Agar
For the selection of phosphate removal bacteria, a white colony would form
on agar plate which had the ability to reduce the phosphate. The composition of
phosphate selective agar is shown in Table 3.6 The materials were mixed and
dissolved in 1 L of distilled water. The pH of the media was adjusted to about pH 7
before autoclaving at 121 °C, 101.3 kPa for 15 minutes.
Table 3.6: Composition of phosphate selective agar
Material
3.10
Quantity (g)
Gelatine
5.0
Dipotassium Hydrogen Phosphate
1.0
Yeast Extract
1.5
Agar
15.0
Isolation of Bacteria from Wastewater
Wastewater contains mixed population of microorganism.
Therefore
isolation of bacteria was carried out to obtain pure cultures. A certain volume of
wastewater (5 mL) from an oxidation pond at UTM was serially diluted from one to
eight folds. Then 0.1 mL of each dilution was pipetted on a nutrient agar plate and it
was made evenly by a “hockey stick”. Later the plates were incubated at 30 °C
overnight. Pure single colony of bacteria observed forming on the plates was further
isolated on a nutrient agar plate using streak plate method.
3.11
Screening Studies of Bacteria for Contaminants Removal
Preliminarily, pure colonies isolated from wastewater were grown on
selective media for their ability to remove pollutants.
Later detailed nutrient
60
reduction tests were conducted to investigate the ability of the isolated strains to
remove certain nutrients; the procedures of which were adopted from Tan (2004)
with appropriate modification. The medium used in this study was filtered-sterilized
wastewater with addition of the nutrient concentration at certain level.
Typically for the bacterial pellet preparation, a loopful of each bacterium was
inoculated into 200 mL of nutrient broth and incubated for 24 h at 30 °C. After the
incubation period, the optical density of the nutrient broth containing the pure culture
was determined by a Jenway 6300 Spectrophotometer at 600 nm. About 10 mL or
20 mL of the nutrient broth was placed in a 50 mL propylene centrifuge tube and
centrifuged at 5000 rpm for 15 minutes to obtain the bacterial pellet. Nutrient broth
was removed and replaced with 25 mL of sterilized distilled water and vortexed to
wash the bacterial pellet free from the nutrient broth residual.
The washing
procedures were carried out twice.
For aerobic condition, 25 mL of test media were added in the centrifuge tube
with bacterial pellet from 10 mL of nutrient broth, and then it was shaken at 200 rpm
at ambient temperature. On the other hand, for facultative condition, 50 mL of the
test media was added in the centrifuge with bacterial pellet from 20 mL of nutrient
broth, and placed statically without shaking at ambient temperature.
Time course of nutrients reduction was also investigated with total media
volume of 300 mL. For aerobic condition, the bacterial pellet was put on the test
media; it was incubated at 30 °C and shaken at 150 rpm. For facultative condition,
the bacterial pellet was put on the test media, incubated at 30 °C without shaking.
The samples at different time intervals were taken, centrifuged and analyzed. The
period observed was as long as seven days.
3.12
Preparation of Zeolite Particle
The basic constituents of the composite which made up the zeolite particle
were zeolite Y, mordenite, SMY, SMM using calcium hydroxide as the binder.
61
There are four types of zeolite particle prepared in this study; the materials and
mixing ratio used in the preparation are tabulated in Table 3.7. The amount of
materials used was weighed using a top loading balance. The components were
subsequently mixed manually. Water was then slowly poured into a hollow in the
centre of the container and the dry materials were mixed in the water. More water
was added and mixing was done until the mixture was uniform in colour. After the
mixing process, the mixture was made into small spherical beads by hand. After
that, the particles were let to harden and cured in a room. All apparatus were kept
clean during the preparation process.
The prepared zeolite particles were
characterized by several techniques such as X-ray diffraction, cation exchange
capacity and stability in acidic and alkaline solutions.
Table 3.7: The materials and mixing ratio for the preparation of zeolite particle
Sample Code
Materials and Weight Ratio
ZP-1
mordenite: Ca(OH)2: H2O
3: 2: 2
ZP-2
(mordenite, zeolite Y): Ca(OH)2: H2O
(1.5+ 1.5): 2: 2
ZP-3
SMM: Ca(OH)2: H2O
3: 2: 2
ZP-4
(SMM, SMY): Ca(OH)2: H2O
(1.5+ 1.5): 2: 2
Prior to the preparation of zeolite particle, zeolite Y was pre-conditioned in
aluminium chloride hexyhydrate solution (2.5 %) overnight to remove the excess
alkalinity of the synthesized zeolite Y. Typically, 6 g of zeolite Y was mixed into a
200 mL of the aluminium chloride hexyhydrate solution (2.5 %) and shaken for 22 h
on an orbital shaker at 150 rpm. Later the conditioned zeolite Y was recovered by
vacuum filtration and oven-dried.
As the dissolved HDTMA-Br might be harmful to bacteria as mentioned in
the previous chapter (Chapter 2 Literature Review: 2.6.3 Biological Toxicity of
Surfactant and SMZ), a soxhlet extraction was performed to minimize the free
62
amount of HDTMA-Br derived from the weakly bound surfactant. The ground SMZ
was extracted in a soxhlet for 24 h with a mixture of water and n-butanol (20: 80 vol.
%) (Witthuhn et al., 2005) and then air-dried.
3.13
Use of Zeolite Particle for Wastewater Treatment
Two set of experiments were carried out to evaluate the performance of
zeolite particle with or without bacteria on wastewater treatment. Textile wastewater
from Ramatex, Batu Pahat was chosen as samples in this study. Five strains of
bacteria isolated and screened in the previous experiments were used in the form of
mixed culture.
In the first set of experiments, a loopful of each bacterium was cultured in
nutrient broth for 1 day at 30 °C incubator. After that, a volume of the nutrient broth
was transferred into the pre-sterilized wastewater to help the adaptation of the
bacteria in the wastewater environment. After 1 day incubation, bacterial pellet of
each of the five types of bacteria was prepared through centrifugation of 20 mL
bacterial inoculum. It was washed by sterilized distilled water prior to usage. The
five bacterial pellets were transferred into a 1 L pre-sterilized wastewater (10 % of
nutrient broth was added in the wastewater to provide necessary nutrients for bacteria
growth). The wastewater medium with bacteria (1 L) was divided into 4 portions
(250 mL).
50 g of sterilized zeolite particles (ZP-1, ZP-2, ZP-3, ZP-4) were
immersed in an 500 mL conical flasks containing the wastewater medium with
bacteria (250 mL) for 6 days at room temperature to allow bacterial growth leading
to the formation of biofilm on the zeolite particles. Aeration device (air pump) was
used to supply necessary oxygen content continuously for bacterial growth.
After the 6-day period, the zeolite particles with bacteria (noted as Bio-ZP-1,
Bio-ZP-2, Bio-ZP-3, Bio-ZP-4) were transferred into 2 L of sterilized wastewater
(with 0.5 % glycerol as carbon source for bacteria) for wastewater treatment study.
Besides that, the sterilized zeolite particles (ZP-1, ZP-2, ZP-3, ZP-4) were also used
without bacteria. The facultative system was operated continuously for 7 days.
63
Samples were collected from time to time, centrifuged and stored in the fridge for
further analysis. The parameters monitored in this study were pH, COD, ADMI,
ammonium, nitrate, sulfate and phosphate.
In the second set of experiments, the bacterial pellets preparation and
treatment system is similar with the first set of experiments. The bacteria were added
separately or individually in the wastewater treatment system in the form of bacterial
pellets instead biofilm form attached on zeolite particle. There were three set of
experimental systems, first is the zeolite particles without bacteria, second is the
zeolite particles with bacteria while the third is the bacteria without zeolite particles.
The zeolite particles used were ZP-4.
3.14
Laboratory Analysis
Ammonium, nitrate, sulfate and phosphate were analyzed by the procedures
stated in the previous section. (3.7.5 Chemical Analysis).
The chemical oxygen demand (COD) was measured by standard procedure,
5200 D Closed Refluxed, Colorimetric Method (APHA, 1992).
Prior to COD
analysis, a digestion solution and sulfuric acid reagent were prepared.
For the
preparation of digestion solution, 10.216 g potassium dichromate (K2Cr2O7, primary
standard grade, previously dried at 150 °C for 2 h), 167 mL concentrated sulfuric
acid, (97 % H2SO4) and 33.3 g mercuric sulfate, HgSO4 were added to about 500 mL
of distilled water. It was dissolved, cooled to temperature and diluted to 1000 mL.
Sulfuric acid reagent was prepared by adding silver sulfate (Ag2SO4) powder to
concentrated H2SO4 at the rate of 5.5 g Ag2SO4/ kg H2SO4. It was let to stand for 1 to
2 days to dissolve. A sample (2.5 mL) was transferred into a glass vial containing
3.5 mL of sulfuric acid reagent and 1.5 mL of digestion solution. The mixture was
shaken vigorous and refluxed for 2 hours at 150 °C using a COD reactor (Hach
DRB200). The blank sample was prepared by replacing the sample with distilled
water. After that, samples and blank were cooled down to room temperature and the
64
COD value was determined by using a Hach DR 4000 Spectrophotometer (Hach,
1997e).
Three properties were described color, namely hue, chroma and value. Hue is
“color”, whether it is blue, red, green, yellow, etc. Chroma is color intensity (bright
or dull). Value is the amount of color (light or dark). The ADMI Weighted Ordinate
Method (Hach, 1997f) used in this study to determine the color concentration
measures only the amount of color, or color value in a sample. It is independent of
the hue and chroma. Transmittance is measured from 400 to 700 nm and converted
to a set of abstract numbers. These numbers describe the color as seen by an average
human eye. They are converted to a single number that indicates the color value.
This number is expressed on a scale used by the American Dye Manufacturers
Institute to measure color value.
The ADMI has adopted the Platinum-Cobalt
standard of the American Public Health Association (APHA) as the standard for
color value. Although this standard is yellow, the ADMI method works for all hues.
Prior to analysis, all samples were pre-treated consistently by centrifugation. About
10 mL of distilled water (blank) and sample solution were place in a sample cell
respectively. The ADMI value in solution compare to blank was measured by using
Hach DR 4000 Spectrophotometer.
CHAPTER 4
RESULT AND DISCUSSION PART I:
SYNTHESIS, CHARACTERIZATION AND AMMONIUM REMOVAL
STUDIES OF ZEOLITES
4.1
Characterization of Rice Husk Ash (RHA)
Prior to their utilization in zeolite synthesis, RHA was characterized by XRD,
FTIR and chemical analysis to ensure their applicability in producing zeolite and to
determine the silica content in RHA for initial reactant calculation.
Judging from the XRD pattern (Figure 4.1), the rice husk ash was in
completely amorphous form without the presence of crystalline phase as indicated by
the featureless diffractogram. It shows that the combustion of the rice husks under
controlled temperature at 600 °C can yield highly reactive amorphous silica for the
zeolite synthesis. The featureless diffractogram and the appearance of a diffuse
maximum at 23° 2θ is characteristics for amorphous silica (Real et al., 1996;
Hamdan et al., 1997).
From the IR spectrum (Figure 4.2), the sample exhibited very strong bands at
wave numbers 1105.1 cm-1, 800.4 cm-1 and 466.7 cm-1. The strong, intense and broad
peak at 1105.1 cm-1 corresponds to asymmetric stretching of tetrahedral SiO4, and
due to the greater ionic character of the Si-O group, this band is much more intense
than the corresponding C-O band for ether (Socrates, 1994). The bands at 800.4 cm-1
66
and 466.7 cm-1 correspond to symmetric stretching of tetrahedral SiO4 and O-T-O
bending band vibrations respectively.
RHA-Pilot Plant
100
90
80
Lin (Counts)
70
60
50
40
30
20
10
0
5
10
20
30
40
50
2-Theta - Scale
RHA-Pilot Plant - File: RHA-Pilot Plant.RAW - Type: 2Th/Th locked - Start: 5.000 ° - End: 50.000 ° - Step: 0.050 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 5.000 ° Operations: Import
Figure 4.1: XRD pattern of RHA
100.0
RHA-PilotPlant
%T
800.4
80.0
466.7
60.0
1639.4
40.0
1105.1
2287.4
20.0
3490.9
0.0
2000.0
1500.0
1000.0
500.0
1/cm
Figure 4.2: FT-IR spectrum of RHA
The rice husk ash obtained from pilot-plant combustor appeared to be a
white-brownish powder. This appearance indicates that there might be a presence of
minor amount of carbon. By applying conventional chemical analysis on the RHA,
67
the results show that RHA samples contained 96.61 % of SiO2 while the value of loss
of ignition (LOI, at 1000 °C) is 4.18 %. Table 4.1 presents the value of silica content
and loss of ignition of the RHA.
Table 4.1: Silica content and LOI in RHA
4.2
Sample
% LOI
% SiO2
1
3.98
96.74
2
4.38
96.47
Average
4.18
96.61
Synthesis of Zeolite Y
In the preliminary attempts of direct synthesis of zeolite Y from RHA without
seeding, some forms of zeolite has been produced. However, the products were
generally consisting of a mixture of zeolite Y and zeolite P. These results are in
complete agreement with previous reports (Ramli et al.; 1996; Zhao et al., 1997)
since zeolite Y is thermodynamically metastable, some of the crystallites will
transform to zeolite P or sometimes even zeolite P appears as the first and dominant
crystalline phase in the products. Figure 4.3 presents the typical X-ray diffractogram
for a mixture of zeolite Y and zeolite P directly synthesized from rice husk ash.
Identification and purity of types of zeolite crystals products were determined by
matching the diffractogram of the prepared samples with the diffractogram of goodquality single-phase patterns of Powder Data File (PDF, compiled by the
International Centre for Diffraction Data, ICDD) using the Diffraction EVA software.
In Figure 4.3, the blue peaks indicate the PDF 40-1464 of zeolite P whereas the red
peaks indicate the PDF 43-0168 of zeolite Y.
In order to obtain a pure zeolite Y crystalline phase, aging and seeding are of
two important techniques employed in the zeolite synthesis. High purity zeolite Y
was obtained from aluminosilicate gel of 10 % seed gel with 15 Na2O: Al2O3: 15
SiO2: 220 H2O and 90 % feed stock gel with 4 Na2O: Al2O3: 10 SiO2: 180 H2O. The
68
obtained zeolite Y is considered pure and highly crystalline as proven by the highly
intense and narrow peaks without elevated baseline and extra peaks. The XRD peaks
of the synthetic zeolite Y are well matched with the PDF 43-0168 (sodium
aluminium silicate hydrate zeolite Y, (Na)—Na2Al2Si4.5O13.xH2O) as shown in
Figure 4.4. However, the crystallinity of the synthetic zeolite is considerably lower
than the commercial zeolite Y as indicated by the intensity of the peaks from the Xray diffractograms as shown in Figure 4.5.
Intensity (counts)
2-Theta (°)
Figure 4.3: X-ray diffractogram for mixture of zeolite Y and zeolite P
69
Intensity (counts)
2-Theta (°)
Figure 4.4: X-ray diffractogram of synthetic zeolite Y
Intensity (counts)
2-Theta (°)
Figure 4.5: X-ray diffractogram of synthesized zeolite Y and commercial zeolite Y
The X-ray diffraction data of as-synthesize zeolite Y, commercial zeolite Y
and PDF 43-0168 are shown in Table 4.2 for clarity.
70
Table 4.2: X-ray diffraction data of as-synthesize zeolite Y, commercial zeolite Y
and PDF 43-0168
Zeolite Y (this study)
Commercial Zeolite Y
PDF 43-0168
d (Ǻ)
I / Io
d (Ǻ)
I / Io
d (Ǻ)
I / Io
14.3626
100
14.2692
100
14.1730
100
8.7491
15.8
8.7182
20.2
8.6964
16.7
7.4724
10.4
7.4342
12.2
7.4338
13.5
5.6846
24.9
5.6455
33
5.6575
28.3
5.0346
4.3
5.0070
2
5.0135
0.1
4.7640
8.3
4.7441
15.5
4.7517
11.1
4.3696
16.4
4.3500
20.5
4.3575
14.3
4.1053
5.9
4.1567
2.5
4.1711
0.5
3.9133
5.7
3.8947
7.4
3.9047
4.3
3.7785
26.2
3.7559
33.4
3.7613
16
3.5786
3.1
3.5509
2.9
3.5617
2.3
3.4711
4.6
3.4499
5.7
3.4536
1.2
3.3103
16.7
3.2925
24.5
3.2953
8
3.2179
5.2
3.2080
5.3
3.2151
1.7
3.0236
9.1
3.0104
9.3
3.0140
6.7
2.9155
12.3
2.9059
12.6
2.9070
3.1
2.8589
24.6
2.8457
27.8
2.8484
8.1
2.7678
11.0
2.7550
10.1
2.7583
2.9
2.6916
5.7
2.7043
3.8
2.7072
1.8
2.6389
8.7
2.6275
8.4
2.6307
3.1
2.5950
5.4
2.5847
4.4
2.5875
1.3
2.5267
3.4
2.5164
2
2.5191
1
2.4307
2.7
2.4203
1.8
2.4194
0.6
2.3837
6.3
2.3751
5.8
2.3745
3.4
2.2340
2.7
2.2235
1.9
2.2249
0.4
2.1618
3.8
2.1519
2.7
2.1569
3.1
2.0997
4.0
2.0894
3.4
2.0919
0.9
2.0635
3.1
2.0551
3
2.0573
0
1.9095
2.8
1.9032
2.3
1.9042
0.7
71
4.3
Characterization of Zeolite Y
In characterizing synthesized zeolites, besides the X-ray powder diffraction
pattern obtained for mineralogical–crystallographical identification, FTIR adsorption
spectrum, TG-DTA curves, FESEM-EDAX and nitrogen adsorption analyses were
also obtained to investigate the structural features of zeolite frameworks and thermal
behaviors respectively.
4.3.1 Fourier Transform Infrared (FT-IR) Spectroscopy
FT-IR adsorption spectrum obtained from the synthetic zeolite is shown in
Figure 4.6 while the significant value of absorption bands found here is compiled in
Table 4.3. The infrared spectrum in the region of 200 to 1300 cm-1 is a sensitive tool
indicating structural features of zeolite frameworks. According to Flanigen et al.
(1971), the region at 1250-950 cm-1 is attributed to the inner bonds of tetrahedral
asymmetric stretching zone and the asymmetric stretching of external bonds between
tetrahedral zones. The main band is located at 1009.7 cm-1; it is asymmetric due to
the overlapping on another peak at 1092.6 cm-1. The obtained data are consistent
with those known for zeolite Y (Flanigen et al., 1971; SiO2/Al2O3 = 3.42) with
reported values of 985 cm-1 for the main band and 1135 cm-1 for the secondary one.
Besides, the data are also consistent with those known for commercial zeolite Y as
shown in Table 4.3.
There is no evidence of IR absorption in the range of 820-750 cm-1; it is
generally assigned to the stretching vibrations of external bonds between tetrahedra.
In the spectral zone 820-650 cm-1 there are two poorly defined bands at 773.4 and
693.4 cm-1. They are in good agreement with the values for zeolite Y and
commercial zeolite according to Flanigen et al. (Table 4.3).
72
60.0
Zeo-Y5B-S2
%T
2338.5
50.0
40.0
1650.0
693.4
773.4 569.9
493.7
30.0
20.0
1092.6
3452.3
461.9
1009.7
10.0
0.0
2000.0
1500.0
1000.0
Figure 4.6:
IR spectrum of the synthesized zeolite Y
Table 4.3:
Infrared adsorption bands for zeolite Y
Zeolite
Asymmetric
Symmetric
Double
stretch
stretch
Rings
1092.6 (msh)
773.4(m)
569.9 (m)
1009.7 (s)
693.4 (m)
NaY (*)
1135 (msh)
760 (m)
(SiO2/Al2O3 = 3.42)
985 (s)
686 (m)
NaY (*)
1130 (msh)
784 (m)
(SiO2/Al2O3 = 4.87)
1005 (s)
714 (m), 635
NaY (this study)
500.0
1/cm
T-O bends
493.7 (wsh)
461.9 (ms)
564 (m)
508 (wsh)
460 (ms)
575 (m)
500 (wsh)
455 (ms)
(vw)
NaY (C)
1141.8 (msh)
792.7 (m)
((SiO2/Al2O3 =5.1)
1022.2 (s)
717.5 (m)
578.6 (m)
(*) Flaningen et al. (1971)
(C) Commercial zeolite Y (CBV100, Zeolyst International)
s = strong; ms = medium strong; m = medium; sh = shoulder
505.3 (wsh)
462.9 (ms)
73
In the spectral region of 650-500 cm-1 relative to the double-ring bond
vibration zone, there is a band at 569.9 cm-1. This is consistent with the known
values of zeolite NaY as proposed by Flanigen et al. and also that of commercial
zeolite.
In the sector 500-420
cm-1 related to the deformation vibrations of
O—T—O bond there is evidence of two bands at 493.7 and 461.9 cm-1 as
characterized by a weak shoulder and a peak of moderate intensity respectively.
These values are also in good accordance to those reported in literature (Flanigen et
al.) and the commercial zeolite.
4.3.2 Thermal Behavior
Zeolite Y having at least five cation sites, the effect of dehydration or partial
dehydration may be clearly noticeable. The water molecules present in clusters seem
to be joined into a continuous intracrystalline phase; the zeolite is referred to as nonstoichiometric hydrate because the water is present as a guest molecule in the host
structure (Breck, 1974).
Figure 4.7 and 4.8 presents the TG and DTA curve of the zeolite Y
synthesized from RHA and of the commercial zeolite Y, CBV100 respectively
during the heating process in nitrogen atmosphere (heating rate, 10 °C/min; flow rate,
20 cm3/min). Thermal behavior of synthesized zeolite Y is similar to that of
commercial zeolite Y. In both cases, the mass loss (from TG curve) is a result of lost
of moisture or water molecules located in the zeolite cavities, or other volatile
species that may be present.
The TG curves reveal a continuous water loss over a broad range
commencing from about 50 °C to 600 °C. The continuous and smooth dehydration
event in zeolite Y can be attributed to the wide pore nature of the three-dimensional
channels framework, in other word, the water molecules are “mobile” in wide pore
and behaving like liquid water. Commercial zeolite Y loses about 24.60 % of water
when heated up to a temperature of 200 °C and 25.54 % of water at a temperature of
350 °C where the sample weight becomes almost constant. On the other hand,
74
synthetic zeolite Y loses 22.00 % and 24.23 % of water respectively. Maximum
amount of water loss in synthetic zeolite amounts to 24.7 % which is slightly lower
than that of commercial zeolite, containing 25.6 % of water (according to Breck,
1974, 26 %).
Accumulated weight loss between 50 °C to 175 °C is related to the loss of
water placed in large supercages of the zeolitic framework while losses at higher
temperature are related to the more tightly bound molecules in the sodalite cage.
Water loss continues at a very slow rate up to 600 °C and achieves almost total
removal of moisture.
a.) Synthetic Zeolite NaY
105
30
TG Curve
100
25
DTA Curve
20
Weight % (%)
15
90
10
5
85
0
80
-5
75
-10
70
0
100
200
300
400
500
600
700
800
900
o
Temperature ( C)
Figure 4.7: TG and DTA curve of the zeolite Y synthesized from RHA
-15
1000
Heat Flow Exo Up (mW)
95
75
b.) Commercial Zeolite NaY
105
25
TG Curve
DTA Curve
100
Weight % (%)
95
DTA Curve
15
90
85
10
Heat Flow Exo Up (mW)
20
80
TG Curve
5
75
70
0
100
200
300
400
500
600
700
800
900
0
1000
o
Temperature ( C)
Figure 4.8: TG and DTA curve of the commercial zeolite Y, CBV100
From the DTA curve, the first endothermic peak appears in the temperature
range of 50 to 330 °C for the synthetic zeolite while the first endothermic peak
appears in the temperature range of 50 to 300 °C for the commercial zeolite. Such
endothermic effect corresponds to water release from the zeolite structure and the
size of its area speaks about the amount of water loss and temperature limits in which
the release takes place. It is well known that the endothermic effect in the heating
process of zeolites is a consequence of the consumption of the heat or energy for
dehydration of the hydrated cations positioned in the zeolite framework and the
release of water molecules from the nanochannels of the zeolite structure (Breck,
1974). According to literature data (1974), the temperature of endothermic minimum,
decrease together with the increase of the effective diameter of the channels and the
heat needed to remove water molecules from zeolites channels decreases with the
increase in the effective diameter of these channels.
At the temperature range of 800—850 °C, for both the synthetic and
commercial zeolite, it seems an exothermal peak corresponding to the break down of
crystal structure which resulted in the formation of amorphous solid or re-
76
crystallization to some non-zeolitic mineral.
However, the DTA thermogram is
unclear to deduce such conclusions.
The clarification of thermal incidence on a possible phase’s evolution has
been completed with XRD study on high-temperature treated zeolite Y at different
temperature up to 1000 °C. Thermal transformations of zeolites into other crystalline
phases may happen directly but are commonly preceded by the formation of
intermediate amorphous phases (Dondur and Dimitrijević, 1982; Norby and Fjellvåg,
1992; Kosanović et al., 1997). As observed in Figure 4.9, when the synthesized
zeolite Y was heated at elevated temperatures of between 600 °C and 700 °C for 4 h
at ambient atmosphere, the crystallinity of the zeolite decreased. After heating at
800 °C, the featureless XRD pattern obtained indicated that the elevated temperature
generates the steam from water, thus breaks the aluminum-oxygen bonds and the
aluminum atom is expelled from the zeolite framework. This process is known as
dealumination. After dealumination, the zeolite structure has collapsed and
amorphous phases formed. Later the amorphous phases were completely converted
into nepheline as indicated by the characteristic peaks which were fitted with PDF
35-0424 (nepheline, NaAlSiO4). On the other hand, commercial zeolite Y (CBV 100)
exhibited greater thermal stability; it remained in the zeolitic structure with
considerable high crystallinity even after heat-treatment at 800 °C (Figure 4.10). It
became an amorphous phase after heating at 900 °C. Contradictory with synthesized
zeolite Y, the commercial zeolite Y did not transformed into nepheline even after
heat-treated at 1000 °C.
77
Intensity (counts)
2-Theta (°)
Figure 4.9: XRD patterns of the heat-treated zeolite Y
Intensity (counts)
2-Theta (°)
* the two XRD patterns at the bottom of figure are denoted to heat-treated samples at 900 °C
and 1000 °C for 4 h, respectively
Figure 4.10: XRD patterns of the heat-treated commercial zeolite Y
78
4.3.3 Textural and Physico-Chemical Characterization
FESEM images provide evidence of the crystalline growth of zeolite Y from
hydrothermal synthesis (Figure 4.11 and Figure 4.12). As presented by the FESEM
images, the microsized zeolite Y has been produced with homogenous cubic crystal
size less than 1 µm.
Figure 4.11: FESEM image of the zeolite Y at magnification of 1000 ×
Figure 4.12: FESEM image of the zeolite Y at magnification of 5000 ×
79
Figure 4.13 shows the typical EDAX spectrum of synthesized zeolite Y while
the elemental composition of zeolite samples calculated from EDAX spectra
(average value from three spectra taken on the different spots of a sample) was
summarized in the Table 4.4. It should be noted that the EDAX analysis is a
qualitative to semi-quantitative composition analysis, it is scanned from a tiny spot
thus is not representative of a sample. Thus the values given below can be taken as a
general reference of chemical composition of zeolite rather than an ultimate
composition means.
Figure 4.13: Typical EDAX spectrum of zeolite Y
Table 4.4: Chemical composition of the zeolite Y from EDAX analysis
Element
Weight %
Na
7.99
Al
23.72
Si
66.84
K
0.25
Ca
1.21
Gas adsorption measurements are widely used for the characterization of a
variety of porous solids such as zeolites (IUPAC, 1994). Of particular importance is
the application of physisorption (physical adsorption) for the determination of the
80
surface area, pore size distribution and pore volume of certain materials. According
to the International Union of Pure and Applied Chemistry (IUPAC, 1985), the
following pore widths or diameters were specified: micropores < 2 nm, mesopores 250 nm, macro pores > 50 nm. Some authors recently use the term ultramicropores to
denote pores of width < 1 nm and refer to the wider micropores as supermicropores
(Sing and Schüth, 2002). In this study, nitrogen was used as probe molecules to
assess the surface area, the total pore volume and the distribution between macro-,
meso- and micro-pores. However, with this method it is impossible to accurately
differentiate between the sizes of the micropores (Jentys and Lercher, 2001).
Figure 4.14 presents the nitrogen gas adsorption-desorption isotherm of
zeolite Y. Since the isotherm is of type-I and type-IV (IUPAC, 1985), it reveals the
presence of microporosity while an upward deviation and the presence of a hysteresis
loop at high relative pressure (> 0.9) discloses the coexistence of narrow mesopores.
The single point surface area and BET surface area are 387.61 m2g-1 and 373.90 m2g1
respectively.
180
Volume Adsorbed cm
3
/g STP
160
140
120
100
80
60
40
Adsorption
20
Desorption
0
0
0.2
0.4
0.6
0.8
1
Re lativ e Pre ssure (P/Po)
Figure 4.14: N2 adsorption-desorption isotherms of zeolite Y synthesized from RHA
81
4.3.4 Cation Exchange Capacity
The cation exchange capacity (CEC) and external cation exchange capacity
(ECEC) from triplicate analysis were measured as 3.1519 ± 0.1246 meq/g and
1.2672 ± 0.0656 meq/g respectively (Table 4.6).
Table 4.5: CEC and ECEC data of synthesized zeolite Y
4.4
Sample/ Replicate
CEC (meq/g)
ECEC (meq/g)
1.
Zeolite Y-1
3.2144
1.2381
2.
Zeolite Y-2
3.0085
1.2211
3.
Zeolite Y-2
3.2329
1.3423
Average value
3.1519 ± 0.1246 1.2672 ± 0.0656
Characterization of Mordenite
In characterizing synthesized zeolites, besides the X-ray powder diffraction
pattern obtained for mineralogical–crystallographical identification, FTIR adsorption
spectrum, TG-DTA curves, FESEM-EDAX and nitrogen adsorption analysis were
also obtained to investigate the mineralogical–crystallographical and physicochemical properties of natural mordenite used.
4.4.1 Mineralogical Characterization
The mineralogical phase of natural mordenite in powdered form as well as
granular form was confirmed by matching the powder XRD patterns of the samples
with the appropriate diffractograms of single-phase patterns from Powder Data File
(PDF, compiled by the International Centre for Diffraction Data, ICDD). The XRD
patterns of the samples were presented in the Figure 4.15 and Figure 4.16 (with PDF).
The XRD of the samples matched well with the single phase pattern of mordenite,
82
PDF PDF 29-1257, (Na2, Ca, K2)Al2Si10O24. The elevated background pattern may
be attributed to the amorphous materials present in the sample. The mordenite used
was mined from local deposit; it is well known that zeolites are rarely found in nature
in their pure form but contain impurities such as other types of zeolite, other minerals
or amorphous materials.
In this case, the quartz impurities were also found in
mordenite as indicated by PDF 46-1045 (quartz, SiO2). The X-ray diffraction data of
mordenite and its PDF 29-1257 are shown in Table 4.7 while the characteristic peaks
of quartz present in the samples are shown in Table 4.8 for clarity.
Figure 4.15: X-ray diffractograms of powdered mordenite (upper pattern) and
granular mordenite (lower pattern)
83
Figure 4.16: X-ray diffractograms of powdered mordenite with PDF 29-1257,
mordenite and PDF 46-1045, quartz (peaks with black dot)
84
Table 4.6: X-ray diffraction data of powdered mordenite, granular mordenite and
PDF 29-1257, (Na2, Ca, K2)Al2Si10O24
Powdered mordenite
Granular mordenite
PDF 29-1257
d (Ǻ)
I / Io
d (Ǻ)
I / Io
d (Ǻ)
I / Io
13.5085
29.0
13.4281
29.5
13.6080
79.1
10.2056
6.3
10.3335
7.5
10.2915
27.5
9.0328
65.4
8.9740
56.7
9.0620
81.7
6.5724
35.8
6.5564
42.7
6.5852
54.2
6.0417
8.7
5.9999
10.9
6.0682
30.1
5.7876
18.0
5.7873
12.2
5.8017
26.8
4.8486
6.8
4.8514
6.3
4.8820
10.5
4.5038
38.4
4.5015
27.7
4.5310
51.0
4.1336
8.2
4.1326
7.9
4.1500
26.1
4.0190
31.5
4.0302
39.8
4.0000
67.3
3.8231
9.7
3.8302
5.9
3.8388
24.8
3.7642
16.5
3.7579
16.3
3.7716
37.3
3.6106
9.0
3.6305
5.6
3.6312
15.7
3.5326
7.7
3.5312
6.6
3.5310
34.6
3.4632
90.7
3.4609
100.0
3.4800
77.1
3.3784
39.5
3.3857
29.1
3.3907
63.4
3.3419
100.0
3.3300
27.9
3.2900
40.5
3.2128
55.0
3.2080
57.0
3.2201
100.0
3.1157
28.7
3.1109
5.5
3.1007
21.6
3.0563
8.3
3.0305
3.3
3.0296
22.9
2.9322
15.3
2.9020
14.9
2.9425
25.5
2.8875
25.4
2.8877
21.1
2.8947
41.8
2.7559
7.0
2.7526
3.7
2.7416
15.7
2.7323
5.4
2.6955
6.8
2.7144
16.3
2.6487
1.9
2.6498
11.9
2.6324
11.1
2.5973
8.8
2.5707
10.9
2.5875
31.4
2.5737
12.5
2.5674
10.9
2.5648
35.3
2.5146
14.6
2.5114
8.6
2.5206
32.7
2.4537
9.8
2.4536
4.9
2.4586
29.4
85
Table 4.7: X-ray diffraction data of powdered mordenite, granular mordenite and
PDF 46-1045 (quartz, SiO2)
Powdered mordenite
Granular mordenite
PDF 46-1045
d (Ǻ)
I / Io
d (Ǻ)
I / Io
d (Ǻ)
I / Io
4.2383
12.9
4.2352
11.5
4.2534
21.2
3.3419
90.7
3.3361
30.3
3.3437
100
2.4537
9.8
2.4536
4.9
2.4571
4.3
2.2823
8.3
2.2823
5.5
2.2819
9.1
2.1227
4.8
2.1276
3.2
2.1278
5.2
1.9794
4.4
1.9431
6.9
1.9798
2.7
4.4.2 Fourier Transform Infrared (FT-IR) Spectroscopy
FT-IR adsorption spectra obtained from the mordenite samples are shown in
Figure 4.17 and Figure 4.18 while the significant value of absorption bands found
here is compiled in Table 4.9. The region at 1250-950 cm-1 is attributed to the inner
bonds of tetrahedral asymmetric stretching zone and the asymmetric stretching of
external bonds between tetrahedral zones. The main band is located at 1041.5 cm-1
and 1047.3 cm-1 for powdered mordenite and granular mordenite. The obtained data
are consistent with those known for Zeolon which was synthetic analogous of
mordenite (Flanigen et al., 1971) with reported values of 1046 cm-1 for the main band.
Defected in the spectral zone 820-650 cm-1 at are two poorly defined bands at
788.8 and 702.0 cm-1 for powdered mordenite, and 792.7 and 709.8 cm-1 for granular
mordenite. They are generally assigned to the stretching vibrations of external bonds
between tetrahedra and are in well agreement with the values for Zeolon according to
Flanigen et al. (Table 4.3).
In the spectral region of 650-500 cm-1 relative to the double-ring bond’s
vibration zone, there are two bands at 623.0 cm-1 and 520.7 cm-1 found for powdered
mordenite, and 617.2 cm-1 and 574.7 cm-1 for granular mordenite. These are
86
consistent with the known values of Zeolon as proposed by Flanigen et al.. In the
sector 500-420 cm-1 related to the deformation vibrations of O—T—O bond there is
evidence of a band at 462.9 cm-1 characterized by a medium strong peak for both
mordenites.
These values are also in good accordance to those reported in the
literature (Flanigen et al., 1971).
50.0
Powdered Mordernite
%T
45.0
788.8
623.0
702.0
520.7
40.0
439.7
462.9
35.0
3465.8
3500.0
1041.5
2000.0
1500.0
1000.0
500.0
1/cm
Figure 4.17: IR spectrum of the powdered mordenite
Granular Mordernite
50.0
617.2
%T
709.8
792.7
574.7
45.0
1649.0
516.9
40.0
462.9
3458.1
35.0
1047.3
30.0
3500.0
2000.0
1500.0
1000.0
Figure 4.18: IR spectrum of the granular mordenite
500.0
1/cm
87
Table 4.8: Infrared adsorption bands for mordenite
Zeolite
Mordenite
Asymmetric
Symmetric
Double
stretch
stretch
Rings
1041.5 (s)
788.8 (wb)
623.0 (w)
702.0 (wb)
520.7 (w)
792.7 (wb)
617.2 (w)
709.8 (wb)
574.7 (w)
795 (wb)
621 (w)
715 (wb)
571 (w)
(powder)
Mordenite
1047.3 (s)
(granular)
Zeolon (*)
1046 (s)
T-O bends
462.9 (ms)
462.9 (ms)
448 (ms)
(*) Commercial zeolite product of synthetic analogues of mordenite, Flaningen et al.
(1971)
s = strong; ms = medium strong; m = medium; w= weak; sh = shoulder; b = broad
4.4.3 Textural and Physico-Chemical Characterization
The granular and powdered mordenite showed similar results in the FESEM
analysis (Figure 4.19 and 4.20). In comparison to synthetic zeolite Y with a regular
shape and size, mordenite exhibited the irregular and inhomogeneous crystallites.
The modernite used was mined from local deposits and contained other mineral
impurities such as quartz and amorphous materials as indicated by the XRD patterns
(Figure 4.15 and 4.16).
Figures 4.21 and 4.22 show the typical EDAX spectrum of mordenite while
the elemental composition of the zeolite samples calculated from EDAX spectra
(average value from three spectra taken on the different spots of a sample) was
summarized in Table 4.10. The values given below are as a general reference of
chemical composition of zeolite rather than an ultimate composition means.
88
(a)
(b)
Figure 4.19: Typical topographic images for the granular modernite by FESEM at
magnification of 1000 × (a) and 5000 × (b).
89
(a)
(b)
Figure 4.20: Typical topographic images for the powdered modernite by FESEM at
magnification of 1000 × (a) and 5000 × (b).
90
Figure 4.21: Typical EDAX spectrum of powdered mordenite
Figure 4.22: Typical EDAX spectrum of granular mordenite
91
Table 4.9: Chemical composition of the modernite samples from EDAX analysis
Powdered Modernite
Granular Modernite
Weight %
Weight %
Na
0.82
2.58
Mg
1.06
0.73
Al
14.41
15.61
Si
89.98
87.74
K
1.43
0.32
Ca
1.73
2.94
Fe
1.93
2.00
Element
Figure 4.23 presents the nitrogen gas adsorption-desorption isotherm of
mordenite (powder).
The single point surface area and BET surface area of
mordenite are 13.01 m2g-1 and 13.74 m2g-1 respectively. This material does not
contain micropores but only mesopores structures. Since the isotherm is of type-IV
(IUPAC, 1985) that typical for mesoporous adsorbents, the presence of a hysteresis
discloses the existence of mesopores.
35
Volume Adsorbed cm
3
/g STP
Adsorption
30
Desorption
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
Re lativ e Pre ssure (P/Po)
Figure 4.23: N2 adsorption-desorption isotherms of mordenite (powder)
92
4.4.4 Cation Exchange Capacity
The cation exchange capacity (CEC) and external cation exchange capacity
(ECEC) from triplicate analysis of powdered mordenite were measured as 1.4630 ±
0.1007 meq/g and 0.3238 ± 0.0783 meq/g respectively, while for granular mordenite
were measured as 1.3423 ± 0.0664 meq/g and 0.2608 ± 0.0677 meq/g respectively
(Table 4.12). The results show that the CEC and ECEC for the different particle size
of mordenite do not vary significantly.
Table 4.10: CEC and ECEC data of mordenite samples
4.5
Sample/ Replicate
CEC (meq/g)
ECEC (meq/g)
1.
Powdered mordenite-1
1.3669
0.2496
2.
Powdered mordenite-2
1.5677
0.4057
3.
Powdered mordenite-3
1.4545
0.3162
Average value
1.4630 ± 0.1007 0.3238 ± 0.0783
1.
Granular mordenite-1
1.2812
0.2327
2.
Granular mordenite-2
1.3328
0.2118
3.
Granular mordenite-3
1.4129
0.3381
Average value
1.3423 ± 0.0664 0.2608 ± 0.0677
Ammonium Removal Studies
Natural zeolites such as clinoptilolite, mordenite, phillipsite from different
deposits have been widely reported as an ion exchanger in wastewater ammonium
removal installations owing to ammonium ion selectivity and low cost (Klieve and
Semmens, 1980; Hlavay et al., 1982; Ciambelli et al., 1985). However, the ammonium
removal capacity of a zeolite varies with the source of the zeolite, the location within
a particular deposit and the capacity measurement technique employed (Klieve and
Semmens, 1980).
93
Increased awareness and understanding of the deleterious effects of
ammonium, released from wastewater treatment facilities into natural water systems
has resulted in stringent laws restricting ammonium discharge. The Interim National
Water Quality Standard for Malaysia has set a guide level of 0.1 mg/L of
ammoniacal nitrogen for class I water, 0.3 mg/L of ammoniacal nitrogen for class II
water while 0.9 mg/L of ammoniacal nitrogen for class III water (Ministry of Natural
Resources and Environment, 2000).
4.5.1 Kinetic Studies
Prior to the commencement of batch adsorption equilibrium studies, it was
necessary to determine the equilibrium contact time required for the ammonium ions.
The kinetics of adsorption is important from the point of process efficiency and
required for selecting optimum operating conditions for the full-scale batch process
(Ahmaruzzaman and Sharma, 2005; Kalavathy et al., 2005). Various kinetic models
have been used where the adsorption has been treated as a pseudo first-order, pseudo
second-order, intra-particle diffusion model etc. Different systems conform to
different models.
As illustrated in the plot of ammonium uptake capacity against time (Figure
4.24), the initial uptake of ammonium occurred very fast for zeolite Y (Y) and
powdered mordenite (P-M) and reached equilibrium in a time of less than half and
hour, and two hours respectively. Inversely, granular mordenite (G-M) possessed
slower ammonium uptake and reached equilibrium after about 24 h. The fast rate of
ammonium removal at the initial period of time might be due to the fact that initially,
all adsorbent sites were vacant and the solute concentration gradient was high (Du,
2005). Later the ammonium uptake rate by the zeolites decreased significantly due to
decrease in adsorption sites.
94
Njoroge and Mwamachi (2004) carried out the kinetic experiments of
ammonium uptake for the four particle size ranges of natural zeolite. They found
that the equilibrium time increased with increasing sorbent particle size and ranged
from 15 to 150 min. The variation of equilibrium time with the sorbent particle size
can be explained in terms of the surface area and the time taken for the ammonium
ions to diffuse to sorption sites within the sorbent particles (Njoroge and Mwamachi,
2004). The smaller the particle size, the shorter the routes taken by the sorbate
particle to reach the effective sorption sites of zeolite.
16
14
Q (meq/g)
12
10
8
6
4
2
0
0
10
20
P-M
Time (h)
G-M
30
40
50
Y
Figure 4.24: Kinetic profile of ammonium uptake by zeolites
In order to describe and investigate the adsorption kinetics, pseudo first-order
and pseudo second-order were applied. The pseudo first-order kinetic is given as
dqt
= k1 (qe − qt )
dt
(4.1)
where qt is the amount of adsorbate adsorbed at time t (mg g-1) qe the adsorption
capacity at equilibrium (mg g-1), k1 the pseudo first-order rate constant (min-1) and t
is the contact time (min). The integration of Eq. (1) with the initial condition, qt = 0
at t = 0 leads to:
log(qe − qt ) = log qe −
k1
t
2.303
(4.2)
95
The pseudo second-order model can be represented in the following form:
dqt
2
= k 2 (qe − qt )
dt
(4.3)
where k2 is the pseudo second-order rate constant (g mg-1 min-1). Integrating Eq. (3)
and noting that qt = 0 at t = 0, the following equation is obtained:
t
1
1
=
+ t
2
qt k 2 qe
qe
(4.4)
The initial sorption rate, h (g mg-1 min-1) at t0 is defined as
h = k 2 qe
2
(4.5)
Figures 4.25 and 4.26 illustrate the plots of pseudo first-order kinetic model
for NH4+ sorption onto powdered modernite and granular mordenite. For zeolite Y,
the pseudo first-order kinetic model was not applied due to the unfitness of the model.
The values of adsorption rate constant (k1) for ammonium uptake on zeolites were
determined from the plots of log (qe-qt) against t. The values (k1 = 0.0194 min-1 for
P-M and 1.6121 min-1 for G-M) (Table 4.12) indicate that the rate of ammonium
removal is faster on P-M compared with G-M.
Figures 4.27 to 4.29 show the plots of t/qt (pseudo second-order kinetic
model). The equilibrium adsorption capacity, qe is obtained from the slope of the plot
and the initial sorption rate h is obtained from the intercept. Since qe is known from
the slope, the pseudo second-order constant k2 can be determined from the value of
the initial sorption rate.
The qe,exp and the qe,calc values along with the linear
correlation coefficient for the pseudo first-order model and pseudo second-order
model are shown in Table 4.12.
The qe,exp and the qe,calc values from the pseudo second-order kinetic model
are very close to each other meanwhile the correlation coefficients, R2 are also closer
to unity for pseudo second-order kinetics than that for the pseudo first-order kinetic
model. Consequently, the sorption process can be approximated more accurately by
the pseudo second-order kinetic model than the pseudo first-order kinetic model for
all the adsorbents. The k2 and h values as calculated from Figure 4.27 to 4.29 are
listed in Table 4.13. It is clearly seen that both of the k2 and h values for ammonium
96
removal on zeolite Y is the highest followed by powdered mordenite and granular
mordenite.
1.2
y = -0.0084x + 0.7833
2
R = 0.9015
0.8
Log (qe-qt)
0.4
0.0
0
50
100
150
200
-0.4
-0.8
-1.2
Time (min)
Figure 4.25: Plot of pseudo first-order kinetic model for NH4+ sorption into P-M
1.2
y = -0.0008x + 0.7
2
R = 0.963
Log (qe-qt)
0.8
0.4
0.0
0
200
400
600
800
1000
1200
1400
1600
-0.4
-0.8
Time (min)
Figure 4.26: Plot of pseudo first-order kinetic model for NH4+ sorption into G-M
97
Table 4.11: Kinetic parameters for the removal of ammonium by different
adsorbents
Adsorbent
qe,exp (mg g-1)
qe,calc (mg g-1)
k1 (min-1)
R2
Pseudo first-order
P-M
8.1114
6.0716
0.0194
0.9015
G-M
7.9583
5.0119
1.6121
0.9630
Adsorbent
qe,calc (mg g-1)
h (mg g-1 min-1)
k2 (g mg-1 min-1)
R2
Pseudo second-order
P-M
10.3413
0.21756
0.00331
0.9451
G-M
8.1833
0.07531
0.00119
0.9984
Y*
14.3472
7.33676
0.03642
0.9989
* qe,exp of Y is 14.1940 mg g-1
25
y = 0.0967x + 4.5964
R2 = 0.9451
-1
t/q (min/mg g )
20
15
10
5
0
0
50
100
150
200
Time (min)
Figure 4.27: Pseudo second-order kinetic plot for the ammonium removal by P-M
98
400
y = 0.1222x + 13.278
R2 = 0.9984
t/q (min/mg g-1)
300
200
100
0
0
500
1000
1500
2000
2500
3000
Time (min)
Figure 4.28: Pseudo second-order kinetic plot for the ammonium removal by G-M
8
y = 0.0697x + 0.1363
R2 = 0.9989
-1
t/q (min/mg g )
6
4
2
0
0
20
40
60
80
100
Time (min)
Figure 4.29: Pseudo second-order kinetic plot for the ammonium removal by Y
99
4.5.2 Batch Equilibrium Studies
The salient features of adsorption isotherms are necessary to optimize the
design of an adsorption system for the adsorption of adsorbate.
The dynamic
adsorptive separation of solute from solution onto an adsorbent depends upon a good
description of the equilibrium separation between the two phases. Various models
have been proposed and applied to explain the equilibrium characteristics of
adsorption. However the most important factor is to have applicability over the
entire range of process conditions. The most widely used isotherm models for solidliquid adsorption are the Langmuir, Freundlich, Temkin, Redlich-Peterson isotherms
and so on.
Figure 4.30 shows the plots of Ce/qe against Ce for the construction of the
Langmuir isotherm. The Langmuir constants were calculated from the plots and
summarized in Table 3. The maximum monolayer adsorption capacity obtained
from the Langmuir plots for Y, P-M, and G-M were 42.37, 15.13, 14.56 mg/g,
respectively. These values are closed to the experimental data.
The essential characteristics of Langmuir isotherm have been described by
the dimensionless separation factor or equilibrium constant, RL. The values of RL in
the present investigation have been found to be below 1.0 for the whole
concentration range of ammonium confirming that the adsorption of ammonium is
very favourable. For instance, the values of RL for Y, P-M and G-M are 0.2288,
0.1883, and 0.2342, respectively for Co = 100 mg L-1.
Freundlich isothermal plots are presented in Figure 4.31 while the
coefficients are shown in Table 4.13. The values of 1/n were also found to be less
than 1 for all the zeolites, signifying again that adsorption is favourable.
The Temkin isotherm, which considers the effects of the heat of adsorption of
all the molecules in the layer decreases linearly with coverage due to adsorbentadsorbate interactions. A plot of qe against ln Ce enables the determination of the
isotherm constants KT and B1 (Figure 4.32). Values of KT and B1 as obtained are
shown in Table 3 along with the correlation coefficient value.
100
40
35
30
Ce/qe
25
20
15
10
5
0
0
100
200
300
400
500
Ce (mg/L)
P-M
G-M
Y
Linear (P-M)
Linear (G-M)
Linear (Y)
Figure 4.30: Langmuir isotherm plots for removal of NH4+ by various sorbents (pH
= 7, temperature = room temperature, Co = 10 to 500 mg/L, zeolite dosage = 2.5 g/L)
2.0
1.8
1.6
Log qe
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Log Ce
P-M
G-M
Y
Linear (Y)
Linear (P-M)
Linear (G-M)
Figure 4.31: Freundlich isotherm plots for removal of NH4+ by various sorbents (pH
= 7, temperature = room temperature, Co = 10 to 500 mg/L, zeolite dosage = 2.5 g/L)
101
45
40
35
qe
30
25
20
15
10
5
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Log Ce
P-M
G-M
Y
Linear (Y)
Linear (P-M)
Linear (G-M)
Figure 4.32: Temkin isotherm plots for removal of NH4+ by various sorbents (pH =
7, temperature = room temperature, Co = 10 to 500 mg/L, zeolite dosage = 2.5 g/L)
The experimental adsorption capacity and the predicted adsorption capacity
by the isotherms and the corresponding isotherm parameters, along with the
regression coefficients are listed and compared (Table 4.14). The better regression
coefficients of the Langmuir model compared to Freundlich model proposed that the
adsorption process was monolayer and adsorption of each molecule has equal
activation energy. Langmuir values of RL below 1.0 and Freundlich values of 1/n
between 0.2385 and 0.4667 (0 < 1/n < 1) indicated the favourability of adsorption of
NH4+ onto zeolite Y and mordenite. The high regression coefficient of the Temkin
isotherm may be due to the linear dependence of heat of adsorption at low or medium
coverage. The linearity may be due to the repulsion between adsorbate species or to
intrinsic surface heterogeneity.
The equilibrium studies revealed that the zeolite Y exhibited much higher
overall uptake concentration at equilibrium compared with mordenite. The
adsorption capacity of zeolite Y is nearly three times higher than mordenite. In the
case of mordenite particle size, although powdered mordenite exhibited much faster
rate of ammonium uptake in the kinetic studies, the particle size used did not have
102
any affect on the amount of ammonium adsorbed in the zeolite at equilibrium as
indicated in the values of total CEC (Section 4.5.1) and batch equilibrium studies
(Bernal and Lopez-Real, 1993). This is logical according to Flaningen and Mumpton
(1981), the external surface of the particle accounts for only about 1 % of the total
surface area of the zeolite.
Table 4.12: Isotherm parameters for ammonium removal by zeolites
qm,calc (qm,exp), mg/g
KL (L/mg)
R2
42.3729
(41.1429)
15.1286
(17.2286)
14.5560
(13.7571)
0.0337
0.9963
0.0431
0.9826
0.0327
0.9113
KF (mg/g)
1/n
R2
Y
3.1521
0.4667
0.9087
P-M
3.5383
0.2385
0.9631
G-M
3.0620
0.2522
0.8733
Adsorbent
KT (L/mg)
B1
R2
Y
0.4430
18.5260
0.9814
P-M
2.6856
4.6100
0.9391
G-M
3.9292
3.6799
0.9317
Adsorbent
Langmuir constants
Y
P-M
G-M
Adsorbent
Freundlich constants
Temkin constants
CHAPTER 5
RESULTS AND DISCUSSION PART II:
SURFACE MODIFICATION OF ZEOLITES AND ANIONIC
CONTAMINANTS REMOVAL STUDIES
5.1
Oxyanions Removal Studies
Some studies were conducted to develop and evaluate the zeolite sorbents
towards the removal of non-metal oxyanions such as nitrate, phosphate and sulfate.
Nitrate is the common form of inorganic nitrogen found dissolved in water. In
agricultural regions, ground water can have significant concentrations of nitrate from
unused fertilizer leaching into the underlying aquifers (Hammer, 1986). The health
hazard of ingesting excessive nitrate in water is infant methemoglobinemia (Hammer,
1986). This is due to the conversion of nitrate to nitrite by nitrate-reducing bacteria
in the gastrointestinal tract.
Common forms of phosphorus in wastewater are
orthophosphates, PO43- (50-70 % of phosphorus), polyphosphates and phosphorus
tied to organic compounds.
Since phosphorus is mainly responsible for
eutrophication of surface water, it must be removed by wastewater treatment
processes before discharging of the effluents into surface waters. The sulfate ion is
one of the major anions occurring in natural waters. It is of importance in public
water supplies because of its cathartic effect upon humans when it is present in
excessive amounts. Sulfate is of considerable concern because they are indirectly
responsible for two serious problems often associated with the handling and
treatment of wastewaters. These are odor and sewer-corrosion problems resulting
from the reduction of sulfate to hydrogen sulfide under anaerobic conditions.
104
5.1.1 Nitrate Removal
The uptake values of nitrate from the aqueous solution as a function of
contact time are presented in Figures 5.1 and 5.2 for surfactant-modified mordenite
(SMM) and surfactant-modified zeolite Y (SMY). As illustrated in the figures, the
nitrate removal increases with time and attains equilibrium in about 4 hours for both
modified zeolites at the initial nitrate concentration studied. The plots exhibit the
fast sorption rates where high percentage of nitrate removal is achieved during the
first two hours. At the initial period, the adsorbent sites were vacant and it is easily
occupied by the adsorbate at high solute concentration gradient. Zeolites which are
modified at different HDTMA loadings do have the effect on the total amount of
nitrate removed but the sorption kinetics do not show significant differences from the
kinetic plots.
10
Q (mg/g)
8
6
4
2
0
0
100
200
300
400
500
Time (min)
SMM-50
SMM-100
SMM-150
SMM-200
Figure 5.1: Kinetic profile of nitrate removal by SMM
105
10
Q (mg/g)
8
6
4
2
0
0
100
200
300
400
500
Time (min)
SMY-50
SMY-100
SMY-150
SMY-200
Figure 5.2: Kinetic profile of nitrate removal by SMY
The kinetics of sorption describing the solute uptake rate which in turn
governs the residence time of sorption reaction is one of the important characteristics
defining the efficiency of sorption. The kinetics of nitrate uptake by both modified
zeolites followed the pseudo second order kinetic model (Chapter 4.5.1) since the
plotting of the graphs fitted well with this model as presented in Figures 5.3 and 5.4.
120
100
t/Q
80
60
40
20
0
0
100
200
300
400
500
Time (min)
SMM-50
SMM-100
SMM-150
SMM-200
Linear (SMM-50)
Linear (SMM-100)
Linear (SMM-150)
Linear (SMM-200)
Figure 5.3: Plot of pseudo second order kinetic for NO3- sorption into SMM
106
80
t/Q
60
40
20
0
0
100
200
300
400
500
Time (min)
SMY-50
SMY-100
SMY-150
SMY-200
Linear (SMY-50)
Linear (SMY-100)
Linear (SMY-150)
Linear (SMY-200)
Figure 5.4: Plot of pseudo second order kinetic for NO3- sorption into SMY
The values of these kinetic parameters together with the correlation
coefficients for the adsorption of nitrate on surfactant-modified zeolites (SMZ) are
listed in Table 5.1. The results from Table 5.1 prove that the uptake of nitrate by the
SMZ fitted well with the pseudo second order model since the correlation coefficient
(r2) was higher than 0.99. Besides, the calculated qe values agree very well with the
experimental qe values (Table 5.1). Generally the uptake of nitrate by SMY at
equilibrium is higher than the SMM which may be due to the presence of more active
sites for oxyanions as indicated by the external cation exchange capacity shown in
the previous section (Chapter 4.4.3), thus more surfactant are attached on the zeolite
surface and can take part on the anion sorption.
107
Table 5.1: Kinetic parameters for the removal of nitrate by different adsorbents
k2
qe (mg/g)
qe (mg/g)
h (k2qe2)
(g.mg-1min-1)
experimental
calculated
(mg.g-1min-1)
SMM-50
0.0110
4.4000
4.4803
0.2216
0.9954
SMM-100
0.0062
8.0000
8.1633
0.4131
0.9959
SMM-150
0.0237
6.4000
6.5104
1.0041
0.9996
SMM-200
0.0098
4.9200
5.1440
0.2580
0.9984
SMY-50
0.0127
9.0400
9.1996
1.0711
0.9999
SMY-100
0.0218
8.3200
8.4459
1.5555
0.9999
SMY-150
0.0154
7.5200
7.5758
0.8859
0.9992
SMY-200
0.0138
7.0400
7.1174
0.7012
0.9992
Adsorbent
R2
The adsorption capacity of the SMZ and the unmodified zeolites for the
nitrate removal was determined through the adsorption isotherm studies. The
isotherms for the adsorption of nitrate by SMZ are given in Figures 5.5 and 5.6,
respectively.
10
-
Q (mg NO 3 /g zeolite)
8
6
4
2
0
0
20
40
60
80
100
120
140
160
180
-2
Ce (mg/L)
SMM-50
SMM-200
Linear (SMM-200)
SMM-100
UM
Linear (SMM-50)
SMM-150
Linear (SMM-150)
Linear (SMM-100)
Figure 5.5: The adsorption isotherm of NO3- sorption on unmodified mordenite (UM)
and SMM
108
10
Q (m g N O
3
-
/g ze o lite)
8
6
4
2
0
0
20
40
60
80
100
120
140
160
180
-2
Ce (mg/L)
SMY-50
SMY-200
Linear (SMY-100)
SMY-100
UY
Linear (SMY-150)
SMY-150
Linear (SMY-50)
Linear (SMY-200)
Figure 5.6: The adsorption isotherm of NO3- sorption on unmodified zeolite Y (UY)
and SMY
As shown in Figures 5.5 and 5.6, both untreated mordenite and zeolite Y have
no affinity for nitrate while in contrast SMM and SMZ possess significant adsorption
capacity towards nitrate. The nitrate isotherms for adsorption on both SMM and
SMY are of C-type in the investigated concentration range of 15 to 165 mg/L. The
linear C-type isotherms point to the continuous bonding of nitrate with HDTMA. As
1/ n
discussed in the Chapter 2, the Freundlich equation has the form qe = K F C e where
KF and n are adjustable positive valued parameters. For n = 1 the linear C-type
isotherm would be produced (Bradl, 2004). Thus the trendlines were plotted at the yintercept equal to zero to get the KF for the adsorbents and the values were shown in
Table 5.2. In the adsorption study of hydrogenchromate and dihydrogenphosphate
anions by surfactant-modified clinoptilolite carried out by Vujaković et al. (2000),
they obtain the similar linear C-type isotherm for their study. As shown in the
Figures 5.5 and 5.6, the nitrate uptake by the sorbents increases with increasing
nitrate concentration.
Nitrate does not readily adsorb on soils and other minerals due to the lack of
significant positive charges in most soils and minerals. Nevertheless, sorption of
109
nitrate on several soils mostly acidic soils has been reported (Cahn et al., 1992; Eick
et al., 1999). Compared to those soils the nitrate sorption capacity on SMZ was
greater by two to four magnitudes. Although nitrate sorption on SMZ and acidic
soils is due to anion exchange, the creation of sorption sites was different. Sorption
of nitrate on acidic soils was attributed to broken bands created on edges (Cahn et al.,
1992), while the sorption of nitrate on SMZ is due to the HDTMA bilayer formation
(Li and Bowman, 1997).
Table 5.2: Freundlich isotherm parameters for NO3- removal by SMZ
Adsorbent
KF
R2
Adsorbent
KF
R2
SMM-50
0.0429
0.8867
SMY-50
0.0808
0.9518
SMM-100
0.0818
0.8068
SMY-100
0.0712
0.9414
SMM-150
0.0506
0.8998
SMY-150
0.0647
0.9150
SMM-200
0.0492
0.9074
SMY-200
0.0578
0.8937
The maximum adsorption capacity from the adsorption isotherms are
tabulated in Figure 5.7. By carrying the nitrate adsorption by surfactant-modified
clinoptilolite with initial concentration range of up to 200 mmol/L (1364 mg/L), Li
(2003) obtained the adsorption isotherm that fitted well to the Langmuir isotherm
with the maximum adsorption capacity of up to 4.96 mg/g. Generally the prepared
SMY possess higher adsorption capacity than SMM but the effect of HDTMA
loading onto both zeolites is different. At low HDTMA surface coverage, the sorbed
HDTMA molecules predominately exist in a monolayer and the outermost surface is
the hydrocarbon tail group which lacks the positive charges for oxyanion sorption.
While at sufficient surface coverage, the surface became progressively positively
charged with the increase in surfactant loading as shown by electrophoretic mobility
measurement studies, however at excess loadings, excess HDTMA was readily
washed off by water (Li et al., 1998a; Bowman et al., 2000).
Earlier reports
indicated that sorption of oxyanion was due to surface anion exchange (Li and
Bowman, 1997). Thus the nitrate exchange reaction can be written as
HDTMA-Br + NO3- = HDTMA- NO3- + Br-
(5.1)
110
Optimum adsorption of nitrate by SMM occurs on the SMM-100 while for SMZ, it
happens on the SMY-50. It is possibly due to the lower stability of surfactant
attachment on the zeolite Y; this means that although zeolite Y possesses greater
external cation exchange capacity for surfactant attachment, the attachment is
however not strong enough and can be easily washed out in the aqueous solution.
Removal of nitrate from aqueous solution was significantly reduced for the SMM
treated with HDTMA at amounts equal to 50%, 150% and 200% of the ECEC. As
discussed above, the SMM treated at excess level of HDTMA actually retains
slightly HDTMA more than HDTMA than needed to satisfy the ECEC. Furthermore,
the reduced sorption observed at the higher HDTMA level may have been due to the
release of excess, loosely bound HDTMA from admicelles on the SMZ into aqueous
solution (Haggerty and Bowman, 1994). This may have resulted in competition for
the oxyanions by HDTMA in solution and by HDTMA on the surface of the zeolite.
10
9
8
Q (mg/g)
7
6
5
4
3
2
1
0
SMM-50
SMM-100 SMM-150 SMM-200
SMY-50
SMY-100
SMY-150
SMY-200
Sorbents
Figure 5.7: The maximum adsorption capacity of nitrate by the various sorbents
111
5.1.2 Sulfate Removal
The kinetic data of sulfate removal by SMM and SMZ were shown in the
Figures 5.8 and 5.9. It is seen from the figures that the sulfate adsorption approached
equilibrium within 2 hours.
The adsorption kinetics were explained by the pseudo second order model as
presented in Figures 5.10 and 5.11.
The equilibrium adsorption capacity, qe is
obtained from the slope of the plot of t/Q versus t and the initial sorption rate h is
obtained from the intercept. Since qe is known from the slope, the pseudo second
order constant, k2 can be determined from the value of the initial sorption rate. The
experimental qe and calculated qe along with the correlation coefficients for the
model are shown in Table 5.3. The experimental qe and calculated qe values from the
pseudo second order kinetic model are very close to each other while the correlation
coefficients are also closer to unity for pseudo second order kinetics. Therefore, the
sorption can be approximated appropriately by the pseudo second order kinetics for
all the prepared adsorbents.
4.0
3.5
3.0
Q (mg/g)
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
120
140
Time (min)
SMM-50
SMM-100
SMM-150
SMM-200
Figure 5.8: Kinetic profile of sulfate removal by SMM
112
5.0
4.5
4.0
3.5
Q (mg/g)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
120
140
Time (min)
SMY-50
SMY-100
SMY-150
SMY-200
Figure 5.9: Kinetic profile of sulfate removal by SMY
60
50
t/Q
40
30
20
10
0
0
20
40
60
80
100
120
140
T ime (min)
SMM -50
SM M-100
SM M-150
SMM -200
Linear (SM M -50)
Linear (SMM -100)
Linear (SM M-150)
Linear (SM M-200)
Figure 5.10: Pseudo-second order kinetic model for the removal of sulfate by SMM
113
45
40
35
t/Q
30
25
20
15
10
5
0
0
20
40
60
80
100
120
140
Time (min)
SM Y-50
S MY -100
S MY-150
SM Y-200
Linear (SMY -50)
Linear (S MY -100)
Linear (SM Y-150)
Linear (SMY -200)
Figure 5.11: Pseudo-second order kinetic model for the removal of sulfate by SMY
Table 5.3: Kinetic parameters for the removal of sulfate by different adsorbents
k2
qe (mg/g)
qe (mg/g)
h (k2qe2)
(g.mg-1min-1)
experimental
calculated
(mg.g-1min-1)
SMM-50
0.0587
2.2000
2.3207
0.3160
0.9987
SMM-100
0.1107
3.4000
3.4855
1.3450
0.9996
SMM-150
0.0231
3.2000
3.4892
0.2817
0.9953
SMM-200
0.0429
2.9200
3.0111
0.3892
0.9860
SMY-50
0.0501
4.5600
4.7059
1.1096
0.9996
SMY-100
0.2123
3.7200
3.7665
3.0120
0.9999
SMY-150
0.1062
3.2400
3.3190
1.1704
0.9998
SMY-200
0.0519
3.1600
3.2237
0.5396
0.9883
Adsorbent
R2
Figure 5.12 and 5.13 show the adsorption isotherm of sulfate by various SMZ.
The raw form of zeolites without surface modification had little affinity for sulfate
but HDTMA-treated zeolites effectively adsorbed the sulfate from aqueous solution.
114
Batch sorption experiments using sulfate solution were conducted with SMM and
SMZ treated at 50%, 100%, 150% and 200% of ECEC of the HDTMA amount to
determine an HDTMA: zeolite ratio that optimized sulfate sorption. At initial stage,
the experimental isotherms seem to fit in with linear Langmuir and Freundlich
adsorption isotherms but only the Langmuir isotherm was chosen in preference to the
Freundlich isotherm. The linear Langmuir isotherms are depicted in Figures 5.14
and 5.15 followed by tabulation the corresponding parameters in Table 5.4.
3.5
2.5
2.0
Q (mg SO
24 /
g SMM)
3.0
1.5
1.0
0.5
0.0
0
10
20
30
40
50
60
70
80
90
Ce (mg/L)
UM
SMM-50
SMM-100
SMM-150
SMM-200
Log. (UM)
Figure 5.12: Adsorption isotherm of SO42- removal by SMM
100
115
4.5
4.0
Q (mg SO 42-/ g SMY)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
Ce (mg/L)
UY
SMY-50
SMY-100
SMY-150
SMY-200
Log. (UY)
Figure 5.13: Adsorption isotherm of SO42- removal by SMY
60
50
C e /Q
40
30
20
10
0
0
20
40
60
80
100
Ce (mg/L)
SMM-50
SMM-100
SMM-150
SMM-200
Linear (SMM-200)
Linear (SMM-150)
Linear (SMM-100)
Linear (SMM-50)
Figure 5.14: Langmuir isotherm for SO42- removal by SMM
120
116
40
35
30
C e/Q
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
100
Ce (mg/L)
SMY-50
SMY-100
SMM-150
SMM-200
Linear (SMM-200)
Linear (SMM-150)
Linear (SMY-100)
Linear (SMY-50)
Figure 5.15: Langmuir isotherm for SO42- removal by SMY
Table 5.4: Isotherm parameters for SO42- removal by SMZ
Adsorbent
Langmuir parameters
qm,calc (qm,exp) mg/g
KL (L/mg)
R2
SMM-50
2.1295 (1.9200)
0.0522
0.8902
SMM-100
3.1328 (3.2800)
0.1300
0.9554
SMM-150
3.0497 (2.9400)
0.0969
0.8923
SMM-200
2.7770 (2.5600)
0.1868
0.9493
SMY-50
4.4405 (3.8800)
0.0567
0.9332
SMY-100
3.6179 (3.2800)
0.0844
0.9658
SMY-150
3.1526 (2.9400)
0.1217
0.9842
SMY-200
3.0157 (2.8440)
0.1471
0.9842
The qm values clearly show that mordenite treated with HDTMA at amounts
equal to 100 % of the ECEC and zeolite Y treated with HDTMA at amounts equal to
50 % of the ECEC resulted in the highest sorption capacity for sulfate. For SMM
treated up to 100 % of the ECEC, there was a corresponding increase in sulfate
117
sorption with higher HDTMA coverage. Above this, sulfate sorption leveled off and
even decreased slightly. As discussed before, the decrease in sorption for SMM
treated above the ECEC may be due to the release of loosely bound amine from
admicelles and subsequent competition for the anion between HDTMA bound to the
surface and in the HDTMA in solution. On the other hand, the optimum HDTMA
loading for the SMY is 50 % of the ECEC, this may indicate the lower stability of
amines attachment onto zeolite Y. Another possible reason may be due to the overestimation of the ECEC value of zeolite Y. However, further studies on the
mechanism of surfactant sorption onto zeolite were needed to clarify the
phenomenon. For the optimum sorbents, the SMM-100 shows qm value of 3.13 mg/g
while the SMY-150 shows qm value of 4.44 mg/g. According to surface anion
exchange mechanism (Li and Bowman, 1997), the sulfate exchange reaction can be
written as:
HDTMA-Br + SO42- = HDTMA- SO42 + Br-
(5.2)
The values of correlation coefficients (R2) from the Langmuir isotherm in the
range of 0.89 to 0.97 indicate that this model fits all the experimental data very well
under the experimental conditions of the study. Besides, the experimental qm values
were closed to calculated qm values further confirm the suitability of Langmuir model.
As overall, the SMY series performed better than the SMM series.
5.1.3 Phosphate Removal
A series of contact time experiments for phosphate removal has been carried
out with a constant initial phosphate concentration of 12.5 mg/L, SMZ dosage 1g/
400 mL. Figures 5.16 and 5.17 show the effect of agitation time on the removal of
phosphate ions by SMM and SMY prepared at different HDTMA loading. The
results show the obvious rapid sorption rates that happened to achieve equilibrium
within 2 hours.
118
3.5
3.0
Q (mg/g)
2.5
2.0
1.5
1.0
0.5
0.0
0
50
100
150
200
250
300
350
400
450
500
Time (min)
SMM-50
SMM-100
SMM-150
SMM-200
Figure 5.16: Kinetic profile of PO43- removal by SMM
4.0
3.5
Q (mg/g)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
100
200
300
400
500
Time (min)
SMY-50
SMY-100
SMY-150
SMY-200
Figure 5.17: Kinetic profile of PO43- removal by SMY
The phosphate sorption kinetics can be described by the pseudo second order
kinetic model (Figures 5.18 and 5.19). The good agreement between sets of data
reflects the extremely high coefficients of determination obtained are shown in Table
5.5. The results also show the sorption rate constant, k2, initial sorption rate, h and
equilibrium sorption capacity, qe.
119
600
500
t/Q
400
300
200
100
0
0
50
100
150
200
250
300
350
400
450
500
Time (min)
SMM-50
SMM-100
SMM-150
SMM-200
Linear (SMM-50)
Linear (SMM-200)
Linear (SMM-100)
Linear (SMM-150)
Figure 5.18: Pseudo-second order kinetic model for the removal of PO43- by SMM
250
200
t/Q
150
100
50
0
0
50
100
150
200
250
300
350
400
450
500
Time (min)
SMY-50
SMY-100
SMY-150
SMY-200
Linear (SMY-50)
Linear (SMY-200)
Linear (SMY-100)
Linear (SMY-150)
Figure 5.19: Pseudo-second order kinetic model for the removal of PO43- by SMY
120
Table 5.5: Kinetic parameters for the removal of phosphate by different adsorbents
k2
qe (mg/g)
qe (mg/g)
h (k2qe2)
(g.mg-1min-1)
experimental
calculated
(mg.g-1min-1)
SMM-50
-1.0178
0.9720
0.9689
-0.9555
0.9999
SMM-100
0.4177
2.8000
2.8241
3.3311
0.9995
SMM-150
0.0948
3.1640
3.1686
0.9515
0.9998
SMM-200
-0.1789
1.8680
1.8612
-0.6196
0.9996
SMY-50
0.0186
3.4600
3.5039
0.2281
0.9967
SMY-100
0.0330
3.0400
3.0694
0.3105
0.9988
SMY-150
0.0558
2.5960
2.6261
0.3845
0.9997
SMY-200
0.0564
2.4360
2.4722
0.3344
0.9997
Adsorbent
R2
The adsorption isotherms for the removal of phosphate from the aqueous
solutions on to SMM samples and SMY samples were exhibited in Figures 5.20 and
5.21 respectively.
The adsorption isotherm of phosphate removal was regular,
positive and concave to the concentration axis. As the monolayer was formed, it
became increasingly difficult for the sorbate to find available vacant active sites of
adsorption as more sites in the adsorbent are filled.
3.0
Q (mg PO
4
3-
/ g SMM)
2.5
2.0
1.5
1.0
0.5
0.0
0
10
20
30
40
50
60
70
80
90
Ce (mg/L)
UM
SMM-50
SMM-100
SMM-150
SMM-200
Log. (SMM-150)
Log. (SMM-100)
Log. (SMM-50)
Log. (SMM-200)
Log. (UM)
Figure 5.20: Adsorption isotherm of PO43- removal by SMM
100
121
3.5
2.5
2.0
Q (mg PO
4
3-
/ g SMM)
3.0
1.5
1.0
0.5
0.0
0
10
20
30
40
50
60
70
80
90
Ce (mg/L)
UY
SMY-50
SMY-100
SMY-150
SMY-200
Log. (UY)
Log. (SMY-50)
Log. (SMY-100)
Log. (SMY-150)
Log. (SMY-200)
Figure 5.21: Adsorption isotherm of PO43- removal by SMY
The isotherm parameters were evaluated using Langmuir and Freundlich
models. Through the plots in Figures 5.22, 5.23, 5.24 and 5.25, the constants from
the two equations, together with the correlation coefficient are summarized in Table
5.6.
The straight lines obtained in the figures accompanying the high values of
correlation coefficients (Table 5.6) indicated that the adsorption of phosphate by
SMZ fitted well with the two investigated isotherm models. Note that most of the R2
values are >0.99 with the Langmuir model. The finding indicated that monolayer
adsorption occurred at the range of solution concentration studied. Basically the
prepared SMZ possess higher adsorption capacity than SMM but the effect of
HDTMA loading onto both zeolites is different. Earlier work indicated that sorption
of oxyanion was due to surface anion exchange (Li and Bowman, 1997). Thus the
phosphate exchange reaction can be written as
HDTMA-Br + PO43- = HDTMA-PO43 + Br-
(5.3)
Optimum adsorption of nitrate by SMM happens on the SMM-150 while for SMZ, it
happens on the SMY-50. In contrast with nitrate and sulfate sorption studies as
discussed before, the SMM-150 performed better than SMM-100. However, the
difference in the maximum adsorption capacity between these two sorbents is not
122
significant; the SMM-150 performed less than 5 % better than SMM-100 in terms of
maximum adsorption. For the SMY series, similar trends of nitrate and sulfate
adsorption occurred on phosphate. Thus the same explanations for the nitrate and
sulfate adsorption can be extended to phosphate adsorption.
Either Langmuir or Freundlich model showed that SMZ has high affinity
towards phosphate in the solution. Meanwhile, SMY exhibited greater capacity than
SMM. Although the Langmuir and Freundlich constants qm and KF have different
interpretation, in which qm is the maximum monolayer adsorption capacity of the
zeolite and KF gives a relative measure in adsorption capacity, they led to the same
conclusion about the correlation of the experimental data with the sorption model.
The Freundlich adsorption isotherm is an indication of surface heterogeneity of the
adsorbent while the Langmuir adsorption isotherm shifts towards surface
homogeneity of the adsorbent. From the qm value of the Langmuir equation, it was
found that sample SMY-50 possessed the best capability in the removal of phosphate,
which was 3.2165 mg PO43-/g zeolite.
80
70
60
C e /Q
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
Ce (mg/L)
SMM-50
SMM-100
SMM-150
SMM-200
Linear (SMM-200)
Linear (SMM-150)
Linear (SMM-100)
Linear (SMM-50)
Figure 5.22: Langmuir isotherm for PO43- removal by SMM
90
123
40
35
30
C e /Q
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
Ce (m g/L)
SMY-50
SMY-100
SMY-150
SMY-200
Linear (SMY-200)
Linear (SMY-150)
Linear (SMY-100)
Linear (SMY-50)
Figure 5.23: Langmuir isotherm for PO43- removal by SMY
1
1
0
Log Q
0
0
-0.5
0.0
0.5
1.0
1.5
0
0
-1
-1
-1
Log Ce
SMM-50
SMM-100
SMM-150
SMM-200
Linear (SMM-200)
Linear (SMM-150)
Linear (SMM-100)
Linear (SMM-50)
Figure 5.24: Freundlich Isotherm for PO43- Removal by SMM
2.0
124
1
0
Log Q
0
0
-0.5
0.0
0.5
1.0
1.5
2.0
0
0
-1
Log Ce
SMY-50
SMY-100
SMY-150
SMY-200
Linear (SMY-200)
Linear (SMY-150)
Linear (SMY-100)
Linear (SMY-50)
Figure 5.25: Freundlich Isotherm for PO43- Removal by SMY
Table 5.6: Isotherm parameters for PO43- removal by SMM
Adsorbent
Langmuir parameters
qm,calc (qm,exp) mg/g
Freundlich parameters
R2
1/n
R2
0.9953
KF
(mg/g)
0.4013
0.3231
0.9002
SMM-50
1.3512 (1.3815)
KL
(L/mg)
0.3711
SMM-100
2.5510 (2.4250)
0.2494
0.9979
0.8602
0.2716
0.9501
SMM-150
2.6731 (2.5350)
0.2284
0.9979
0.8634
0.2801
0.9568
SMM-200
1.2858 (1.2765)
0.4730
0.9908
0.8712
0.2543
0.9884
SMY-50
3.2165 (3.1100)
0.2617
0.9915
0.9750
0.3015
0.9544
SMY-100
2.8662 (2.7100)
0.2159
0.9983
0.6679
0.3833
0.8865
SMY-150
2.3602 (2.2100)
0.2066
0.9978
0.5162
0.4023
0.8633
SMY-200
2.2331 (2.1000)
0.2369
0.9978
0.5105
0.3973
0.8358
125
5.2
Acid Dye Removal
As illustrated in Figures 5.26 and 5.27, the initial uptake of Acid Orange 7
(AO7) occurred very fast for both SMM and SMY; it reached equilibrium in 1 hour.
The fast rate of AO7 removal at the initial period of time might be due to the fact that
initially, all adsorbent sites were vacant and the solute concentration gradient was
high.
Subsequently, the AO7 uptake rate by the SMM and SMY decreased
significantly due to the decrease in adsorption sites.
50
Q (mg AO7/g zeo)
40
30
20
10
SMM-50
SMM-100
SMM-150
0
0
1
2
3
4
5
Time (h)
Figure 5.26: Kinetic profile of AO7 uptake by SMM
50
Q (mg AO7/g zeo)
40
30
20
10
SMY-50
SMY-100
SMY-150
0
0
1
2
3
4
Time (h)
Figure 5.27: Kinetic profile of AO7 uptake by SMY
5
126
In order to describe the adsorption kinetics, pseudo first-order and pseudo
second-order were applied. The kinetics of AO7 uptake by both modified zeolites
followed the pseudo second order kinetic model since the plotting of the graphs fitted
well with this model. Figures 5.28 and 5.29 show the plot of t/qt against t (pseudo
second-order kinetic model). The equilibrium adsorption capacity, qe is obtained
from the slope of the plot and the initial sorption rate h is obtained from the intercept.
Since qe is known from the slope, the pseudo second-order constant k2 can be
determined from the value of the initial sorption rate. The qe,exp and the qe,calc values
along with linear correlation coefficients for the pseudo first-order model and pseudo
second-order model are shown in Table 5.7.
The qe,calc and qe,exp values from the pseudo second-order kinetic model are
very closed to each other meanwhile the correlation coefficients, R2 are also closer to
unity for pseudo second-order kinetic model. Consequently, the sorption process can
be approximated accurately by the pseudo second-order kinetic model. For the SMZ
with different HDTMA loading, it is noted that SMM-100, SMM-150, SMY-50 and
SMY-100 were capable to remove all the acid dye which are equivalent to 40 mg
AO7 per g SMZ used. However, the differences in adsorption capacity between the
aforementioned sorbents were unclear due to the rather low concentration of sorbate
solution applied.
0.16
0.14
0.12
t/q
0.1
0.08
0.06
SMM-50
SMM-100
SMM-150
0.04
0.02
0
0.00
1.00
2.00
3.00
4.00
5.00
Time (h)
Figure 5.28: Pseudo second order kinetic plot for the AO7 removal by SMM
127
0.14
0.12
0.1
t/q
0.08
0.06
SMY-50
SMY-100
SMY-150
0.04
0.02
0
0.00
1.00
2.00
3.00
Time (h)
4.00
5.00
Figure 5.29: Pseudo second order kinetic plot for the AO7 removal by SMY
Table 5.7: Kinetic parameters for the removal of ammonium by different adsorbents
Adsorbent
R2
qe,calc
qe,exp
h
k2
(mg g-1)
(mg g-1)
(mg g-1 min-1)
(g mg-1 min-1)
SMM-50
28.74
28.50
526.32
0.6372
0.9999
SMM-100
40.16
40.00
3333.33
2.0668
1.0000
SMM-150
40.16
40.00
5000.00
3.1001
1.0000
SMY-50
40.32
40.00
1666.67
1.0252
0.9999
SMY-100
40.49
40.00
1111.11
0.6777
0.9999
SMY-150
34.97
34.89
500.00
0.4089
0.9990
Figures 5.30 and 5.31 present the plots of Ce/qe against Ce for the construction
of the Langmuir isotherm. The Langmuir constants were calculated from the plots
and summarized in Table 5.8. The maximum monolayer adsorption capacity
obtained from the Langmuir plots for SMM-50, SMM-100, and SMM-150 were
40.00, 51.55, 67.57 mg/g, respectively. For the SMY-50, SMY-100 and SMY-150,
128
the maximum monolayer adsorption capacity is 81.26, 74.63, 72.04 mg/g
respectively. These values are closed to the experimental data.
Generally SMY at different HDTMA loadings showed better adsorption
capacity than SMM due to the greater amount of HDTMA attached on the surface.
However for the reduced sorption observed at the higher HDTMA level may be due
to the release of excess, loosely bound HDTMA from the admicelles on the SMZ
into the aqueous solution. This may result in competition for the dyes by HDTMA in
solution and HDTMA on the surface of the zeolite. The essential characteristics of
Langmuir isotherm have been described by the dimensionless separation factor or
equilibrium constant, RL. The values of RL in the present investigation have been
found to be below 1.0 for the whole concentration range of ammonium confirming
that the adsorption of AO7 is very favourable. For instance, the values of RL for
SMM-50, SMM-100 and SMM-150 are 6.69 × 10-3, 3.40 × 10-3, and 4.32 × 10-3,
respectively for Co concentration of 1000 mg L-1.
20
16
Ce/Qe
12
8
4
0
0
100
200
300
400
500
600
700
800
Ce (mg/L)
SMM-50
SMM-100
SMM-150
Linear (SMM-50)
Linear (SMM-100)
Linear (SMM-150)
Figure 5.30: Langmuir isotherm plots for removal of AO7 by SMM
129
8
7
6
Ce/Qe
5
4
3
2
1
0
0
50
100
150
200
250
300
350
400
450
500
Ce (mg/L)
SMY-50
SMY-100
SMY-150
Linear (SMY-50)
Linear (SMY-100)
Linear (SMY-150)
Figure 5.31: Langmuir isotherm plots for removal of AO7 by SMY
Freundlich isothermal plots are presented in Figure 5.32 and 5.33 while the
coefficients are shown in Table 5.8. The values of 1/n were also found to be less than
Log Qe
1 for all the sorbents, signifying again that adsorption is favourable.
0
-1
0
1
2
3
4
Log Ce
SMM-50
Linear (SMM-50)
SMM-100
Linear (SMM-100)
SMM-150
Linear (SMM-150)
Figure 5.32: Freundlich isotherm plots for removal of AO7 by SMM
130
3
Log Qe
2
1
0
-1
0
1
2
3
4
Log Ce
SMY-50
Linear (SMY-50)
SMY-100
Linear (SMY-100)
SMY-150
Linear (SMY-150)
Figure 5.33: Freundlich isotherm plots for removal of AO7 by SMY
131
Table 5.8: Isotherm parameters for AO7 removal by SMZ
Adsorbent
Slope
Intercept-Y
R2
qm,calc (qm,exp),
KL
(mg/g)
(L/mg)
Langmuir
SMM-50
0.0250
0.1688
0.9949
40.00 (41.58)
0.1481
SMM-100
0.0194
0.0662
0.9977
51.55 (51.94)
0.2931
SMM-150
0.0148
0.0642
0.9986
67.57 (68.14)
0.2305
SMY-50
0.0123
0.0497
0.9972
81.26 (81.45)
0.2475
SMY-100
0.0134
0.0688
0.9964
74.63 (74.80)
0.1948
SMY-150
0.0139
0.0725
0.9985
72.04 (72.58)
0.1917
Adsorbent
Slope
Intercept-Y
R2
KF (mg/g)
1/n
SMM-50
0.1418
1.2292
0.8723
3.4185
0.1418
SMM-100
0.1411
1.3741
0.5846
3.9515
0.1411
SMM-150
0.1921
1.3722
0.6991
3.9440
0.1921
SMY-50
0.3417
1.1201
0.8517
1.4073
0.3417
SMY-100
0.3445
1.0789
0.9189
2.9414
0.3445
SMY-150
0.2865
1.1887
0.8820
3.2828
0.2865
Freundlich
CHAPTER 6
RESULTS AND DISCUSSION PART III:
DEVELOPMENT OF ZEOLITE PARTICLE AND COMBINATION WITH
BACTERIA FOR WASTEWATER TREATMENT
6.1
Isolation and Screening of Bacteria from Wastewater
Wastewater samples were collected from oxidation ponds in UTM at several
sampling points. Based on the serial dilution and streak plate techniques (Benson,
1998), 10 different types of pure bacterial colonies were successfully isolated from
the wastewater. Following this, these bacterial colonies were selected for further
analysis of screening studies and nutrient reduction tests.
At the preliminary screening stage, the isolated bacteria colonies were
screened by growing the bacteria on selective agar plate including nitrate selective
agar, sulfate selective agar, and phosphate selective agar. The results in Table 6.1
show that most of the bacterial colonies were able to grow in three types of selective
media. From these preliminary findings, all the indigenous bacteria were subjected
to further analyses for the nutrient reduction test.
133
Table 6.1: Screening of bacteria in selective media
NO3- selective
Notation Code
PO43- selective
SO42- selective
1.
A1-1-1
-
+
-
2.
A1-1-2
-
+
-
3.
A1-1-3
-
+
+
4.
A2-1-2
+
+
+
5.
A3-1-1
-
-
+
6.
A4-1-1
+
+
+
7.
A4-2-1
+
+
+
8.
A4-2-2
+
+
-
9.
A4-2-3
+
+
+
10.
A4-7-1
+
-
+
Figure 6.1 shows the nitrate degradation ability of bacterial colonies obtained
from the previous experiments. After 1-day period, the results show that bacterial
colony 4 (A2-1-2), 9 (A4-2-3) and 10 (A4-7-1) presented better potential to degrade
the nitrate. Some of experiments exhibited negative results and this might be due to
the release of the nitrate from the bacterial pellets into the solution as the bacterial
pellets were prepared from the nutrient broth.
100%
Aerobic
Facultative
Percentage of Reduction
50%
0%
1
2
3
4
5
6
7
8
9
10
11
-50%
-100%
-150%
Sample
Figure 6.1: Nitrate reduction test (initial NO3- concentration = 15.6 mg/L)
134
Figure 6.2 shows the sulfate degradation ability of the bacterial colonies. At
the end of degradation period, the results revealed that bacterial colony 3 (A1-1-3), 9
(A4-2-3) and 10 (A4-7-1) show better potential to degrade the sulfate. Some of the
experiments exhibited negative results and this might be due to the release of the
sulfate from the bacterial pellets as the bacterial pellets were prepared from the
nutrient broth which is rich in sulfate.
15%
Aerobic
Facultative
Percentage of Reduction
10%
5%
0%
1
2
3
4
5
6
7
8
9
10
11
-5%
-10%
Sample
Figure 6.2: Sulfate reduction test (initial SO42 concentration = 153 mg/L)
Figure 6.3 shows the phosphate degradation ability of bacterial colonies. The
results after 1-day degradation show that the bacterial colonies 7 (A4-2-1), 8 (A4-22) and 2 (A1-1-2) presented better potential to degrade the phosphate. According to
Figure 6.3, some experiments show the increment of phosphate values that
represented by the negative removal values. As we know, the nutrient broth used to
prepare the bacterial pellets is rich in phosphate, the negatives values might be due to
the release of phosphate from the bacterial pellet.
From the nutrients reduction test, three potential nutrients degraders for each
nutrient were selected for further evaluation to check the effectiveness of nutrient
removal among selected cultures under aerobic and facultative conditions so as to
choose the best bacterial colonies for nutrients removal.
135
50%
0%
Percentage of Reduction
1
2
3
4
5
6
7
8
9
10
11
-50%
-100%
-150%
-200%
-250%
Aerobic
Facultative
-300%
Sample
Figure 6.3: Phosphate reduction test (initial PO43- concentration = 5.72 mg/L)
6.1.1 Nitrate Removal Test
Results of the nitrate removal of the three selected bacterial cultures under
aerobic conditions were presented in Figure 6.4 while the nitrate removal of the three
selected bacterial cultures under facultative condition was presented in Figure 6.5. It
was found that bacteria A2-1-2 possessed the highest removal of nitrate under
aerobic conditions with the removal percentage of 31.58 % after 7 days, followed by
A4-7-1 with 14.47 % removal and A4-2-3 with 13.16 % removal. On the other hand,
under facultative conditions, A4-2-3 had successfully removed the nitrate with 93.42
% removal while A2-1-2 presented 75 % of nitrate removal.
136
50%
A2-1-2
A4-7-1
A4-2-3
Percentage of nitrate removal
40%
30%
20%
10%
0%
0
1
2
3
4
5
6
7
-10%
Time (d)
Figure 6.4: Time course of NO3- removal (aerobic, initial concentration = 15.2
mg/L)
100%
A2-1-2
A4-7-1
A4-2-3
Percentage of nitrate removal
80%
60%
40%
20%
0%
0
1
2
3
4
5
6
7
-20%
Time (d)
Figure 6.5: Time course of NO3- removal (facultative, initial concentration = 15.2
mg/L)
Figures 6.6 to 6.8 show the comparison of the nitrate removal by each
bacterial colony under aerobic and facultative conditions. Generally, the performance
of the bacteria colonies is better under facultative conditions. For instance, bacteria
137
A4-2-3 removed 93.42 % of nitrate under facultative conditions while it only
removed 13.16 % of nitrate under aerobic conditions.
80%
A2-1-2 (aerobic)
A2-1-2 (facultative)
70%
Percentage of removal
60%
50%
40%
30%
20%
10%
0%
0
1
2
3
4
5
6
7
-10%
-20%
Time (day)
Figure 6.6: Nitrate removal by bacteria A2-1-2 (comparison between aerobic and
facultative condition)
30%
Percentage of removal
25%
20%
15%
10%
5%
A4-7-1 (aerobic)
A4-7-1 (facultative)
0%
0
1
2
3
4
5
6
7
Time (day)
Figure 6.7: Nitrate removal by bacteria A4-7-1 (comparison between aerobic and
facultative condition)
138
100%
Percentage of removal
80%
60%
A4-2-3 (aerobic)
A4-2-3 (facultative)
40%
20%
0%
0
1
2
3
4
5
6
7
-20%
Time (day)
Figure 6.8: Nitrate removal by bacteria A4-2-3 (comparison between aerobic and
facultative condition)
6.1.2 Sulfate Removal Test
Results of the sulfate reduction test of the three selected bacterial cultures
under aerobic conditions were presented in Figure 6.9 while the sulfate reduction of
the three selected bacterial cultures under facultative condition was presented in
Figure 6.10. From the sulfate reduction test, the results show that the bacteria do not
possess good capability in sulfate removal. The best performed bacterium in sulfate
removal was bacteria A1-1-3 under facultative condition and it removed 29 % of the
sulfate. It is known that sulfate reducing bacteria (SRB) ideally present in anaerobic
environment, thus the bacteria should be perform in removing sulfate under
facultative condition than aerobic condition as indicated in Figure 6.11.
139
20%
A1-1-3
A4-7-1
A4-2-3
10%
Percentage of removal
0%
0
1
2
3
4
5
6
7
-10%
-20%
-30%
-40%
-50%
-60%
Time (day)
Figure 6.9: Percentage of SO42- removal (aerobic, initial concentration = 60 mg/L)
60%
A1-1-3
A4-7-1
A4-2-3
40%
Percentage of removal
20%
0%
0
1
2
3
4
5
6
7
-20%
-40%
-60%
-80%
Time (day)
Figure 6.10: Percentage of SO42- Removal (facultative, initial concentration = 60
mg/L)
140
60%
A1-1-3 (aerobic)
A1-1-3 (facultative)
Percentage of Removal
40%
20%
0%
0
1
2
3
4
5
6
7
-20%
-40%
-60%
-80%
Time (day)
Figure 6.11: Sulfate removal by bacteria A1-1-3 (comparison between aerobic and
facultative condition)
6.1.3 Phosphate Removal Test
From the phosphate removal test under aerobic conditions (Figure 6.12), all
three bacteria presented little phosphate removal capability of less than 10 %. On the
other hand, bacteria A1-1-2 possessed greater removal capability under facultative
condition (Figures 6.13 and 6.14). However, bacteria A1-1-2 did not reduce the
phosphate level under aerobic condition but under facultative condition, bacteria A11-2 removed 37 % of the total phosphate.
141
20%
Percentage of phosphate removal
10%
0%
0
1
2
3
4
5
6
7
-10%
-20%
-30%
-40%
-50%
-60%
A4-2-1
A4-2-2
A1-1-2
-70%
-80%
Time (d)
Figure 6.12: Percentage of PO43- Removal (aerobic, initial concentration = 6 mg/L)
50%
A4-2-1
A4-2-2
A1-1-2
Percentage of phosphate removal
40%
30%
20%
10%
0%
0
1
2
3
4
5
6
7
-10%
-20%
Time (d)
Figure 6.13: Percentage of PO43- Removal (facultative, initial concentration = 6
mg/L)
142
0.6
0.4
Percentage of removal
0.2
0
0
1
2
3
4
5
6
7
-0.2
-0.4
-0.6
A1-1-2 (aerobic)
A1-1-2 (facultative)
-0.8
Time (day)
Figure 6.14: PO43- removal by bacteria A1-1-2 (comparison between aerobic and
facultative condition)
6.2
Use of Zeolite Particle for Textile Wastewater Treatment (I)
In the first application of zeolite particle attempt was made to combine the
adsorption and biodegradation processes simultaneously in a unit.
Prior to the
treatment, the zeolite particles were immersed into the growth medium previously
inoculated with mixed bacterial cultures.
Five bacterial strains were chosen to
prepare the mixed bacterial cultures; they were coded as A2-1-2 and A4-2-3 from the
nitrate removal test, bacteria A1-1-3 from the sulfate removal test, bacteria A1-1-2
from the phosphate removal test and bacteria J obtained from laboratory cultures in
which it was proven as capable to remove colors from textile wastewater. The 6-day
period of the immersing step allowed microorganisms to grow and to produce
extracellular polymers that will help adhere and immobilize bacteria to the surface of
zeolite particles contributing to the formation of biofilm. This biologically active
layer of cells known as biofilm plays a key role in the treatment of wastewater
(Bitton, 2005).
particles.
The zeolite particles with bacteria were denoted as bio-zeolite
143
The efficiency of the bio-zeolite particles and zeolite particles in wastewater
treatment was determined from the water quality parameters. Four types of biozeolite particles and four types of zeolite particles were used in the wastewater
treatment as shown in Table 6.2.
Table 6.2: Systems used in the wastewater treatment
Sample
Annotation
Description
1. ZP-1
M
without bacteria
2. ZP-2
Y
without bacteria
3. ZP-3
SMM
without bacteria
4. ZP-4
SMY
without bacteria
5. Bio-ZP-1
Bio-M
ZP-1 with bacteria
6. Bio-ZP-2
Bio-Y
ZP-2 with bacteria
7. Bio-ZP-3
Bio-SMM
ZP-3 with bacteria
8. Bio-ZP-4
Bio-SMY
ZP-4 with bacteria
6.2.1 pH Change
During the 7-day wastewater treatment, the pH values increased slowly from
time to time for all the systems (Figure 6.15). The alkaline conditions were due to the
alkaline nature of the zeolite particles. As mentioned in the previous section, the
zeolite particles were prepared by using calcium hydroxide as binder, thus the
calcium hydroxide of the zeolite particles changed the pH value to alkaline condition.
Comparison between the zeolite particles series and bio-zeolite particles series show
that the systems involved bio-zeolite particle series presented lower solution pH than
the systems involved zeolite particle series. This phenomenon occurred because the
bio-zeolite particles have been immersed in wastewater for a certain period prior to
the wastewater treatment. During the bioaugmentation process, excess alkalinity of
the zeolite particle may be reduced.
144
11.00
10.00
pH
9.00
8.00
7.00
6.00
5.00
0
1
2
3
4
5
6
7
8
Time (d)
Bio-M
Bio-Y
Bio-SMM
Bio-SMY
M
Y
SMM
SMY
Figure 6.15: pH change during 7-day treatment
6.2.2 Color Removal
The removal of color in the ADMI unit in the batch systems are shown in
Figure 6.16. Theoretically, systems inoculated with selected consortium of bacteria
(Bio-ZP series) should perform better than systems without bacteria (ZP series) but,
on contrary, in this study, the ZP series performed better than Bio-ZP series in
general. This phenomenon might due to the fact that during the 6 days immersion of
zeolite particles for bacteria growth, the adsorption sites of the zeolite particles were
occupied or even saturated by the dyes and other contaminants present in the
wastewater. This explanation was affirmed by the observation that after the 6-day
immersion period in the wastewater growth medium, the surface of the zeolite
particle appeared colored. Besides that, the presence of the microorganisms on the
adsorbing material might reduce or limit the adsorption capacity of the zeolite
particles.
145
700
Bio-zeolite particle
Zeolite Particle
Removal of ADMI (mg/L)
600
500
400
300
200
100
0
M
Y
SMM
SMY
Type of ZP or Bio-ZP
Figure 6.16: Comparison of color removal by zeolite particle (ZP) and bio-zeolite
particle (Bio-ZP)
In the study by Wen et al. (2006), they compared the sorption kinetics of
ammonium onto zeolite and zeolite covered by biofilm on two particle size. They
found that biofilm covered on the zeolite with smaller particle size (1.0-3.0 mm) did
not affect the ion-exchange performance but improved the initial sorption rate due to
biosorption. However, for the bigger particle size (8-15 mm), the attached biofilm
reduced the ion-exchange rate resulting in a 22 % drop of the total equilibrium
capacity. In this study, the zeolite particles applied were about 15 mm in diameter,
thus similar findings with Wen’s findings were obtained.
Consequently, the removal of color by the Bio-ZP series can be regarded as
the effect of biodegradation and biosorption rather than the sum up of adsorption and
biodegradation and biosorption.
It should be noted that besides adsorption and
biodegradation, some of the color was removed via agglomeration into agglomerates.
The presence of zeolite particle had accelerated the agglomeration process. On the
other hand, the agglomeration did not occur without the presence of zeolite particle.
However, further investigation of the effect of the zeolite particle on the
agglomeration is needed to reveal the real mechanism.
146
Figure 6.17 shows the time course of color removal by ZP-2 (SMY) and BioZP-2 (Bio-SMY). ZP-2 was prepared from the mixing of mordenite, zeolite Y and
calcium hydroxide. As discussed before, the ZP-2 performed better than Bio-ZP-2,
the removal of color by ZP-2 was 580 mg/L ADMI while the Bio-ZP-2 only
removed color as much as 285 mg/L ADMI. These two systems were among the
optimum systems within the series of ZP and Bio-ZP. For the ZP-2, it removed the
most color within the first two days that accounted 85 % color of its total removal.
800
700
Bio-SMY
SMY
ADMI (mg/L)
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
T ime (d)
Figure 6.17: Comparison of color removal by Bio-SMY and SMY
It is surprisingly to find that the ZP-2 (Y) and ZP-1 (M) possessed the
capability to remove color. These two zeolite particles were prepared from raw
zeolites without surfactant modification and possess no affinity towards the dye
constituents. However, both of the particles removed the color mostly through
agglomeration. It was observed that the surface of these two particles was not
colored while the particles prepared from surfactant-modified zeolites turn colored
after the treatment period. Figure 6.18 shows the comparison of the removal of color
by ZP-2 (Y) and ZP-4 (SMY). The only difference between these two particles was,
ZP-2 was prepared from raw zeolites while ZP-4 was prepared from surfactantmodified zeolites. Through this comparison, we can notice the effect of the surface
modification of zeolite on the color removal from textile wastewater.
After
147
surfactant modification, the sorbents possess higher affinity towards organic and
anionic molecules and thus increased the adsorption towards dye molecules.
800
700
Y
SMY
ADMI (mg/L)
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
T ime (d)
Figure 6.18: Comparison of color removal by Y and SMY
6.2.3 Nitrate Removal
As discussed in the previous section, the ZP series performed better than the
Bio-ZP series in color removal. We proposed that the adsorption sites of the zeolite
particles were occupied or even saturated by the contaminants present in the
wastewater and the presence of the microorganisms on the adsorbing material might
reduce or limit the adsorption capacity. Similar results were obtained for the nitrate
removal. ZP-4 (SMY) removed 18.8 mg/L from the wastewater followed by ZP-3
(SMM) with 14.8 mg/L removal, ZP-2 (Y) with 9.6 mg/L and ZP-1 with 9.4 mg/L
(Figure 6.19). Again, the results show that the surfactant-modified zeolites performed
better affinity towards oxyanions. On the other hand, the removal of nitrate by BioZP series also shows positive results in the removal of nitrate in the range of between
2.8 to 6.8 mg/L (Figure 6.19). The rather lower nitrate removal might be due to the
high volume of wastewater used as compared to the biomass that attached on the
surface of bio-zeolite particles.
148
The two most important mechanisms of biological reduction of nitrate are
assimilatory and dissimilatory nitrate reduction. By assimilatory nitrate reduction,
nitrate was taken up and converted to nitrite.
Denitrification process was an
anaerobic respiration by which NO3- serves as an electron acceptor. Most aerobic
bacteria are facultative anaerobes which can only reduce nitrate in the absence of
oxygen via a process known as nitrate reduction or denitrification. Nitrate was
reduced to nitrous oxide (N2O) and nitrogen gas (N2) while organic matter was
simultaneously oxidized. The microorganisms involved in denitrification are mostly
aerobic autotrophic or heterotrophic microorganisms that can switch to anaerobic
growth when the nitrate is used as the electron acceptor (Hammer, 1986).
20
18
Bio-ZP
ZP
16
Removal (mg/L)
14
12
10
8
6
4
2
0
M
Y
SMM
SMY
Type of Bio-ZP
Figure 6.19: Removal of NO3- by ZP and Bio-ZP
6.2.4 Sulfate Removal
According to Figure 6.20, it is found that as high as 120 mg/L sulfate was
removed by ZP-4 (SMY), followed by 75 mg/L removal by ZP-3 (SMM). For the
Bio-ZP series, the systems removed between 14 to 27 mg/L of sulfate. Similar to
color and nitrate removal, among the Bio-ZP series, Bio-ZP-4 (Bio-SMY) presented
149
the best performance in the removal of sulfate. In the dissimilatory sulfate reduction,
sulfate was the most important source of H2S in wastewater produced by sulfate
reducing bacteria. In the absence of oxygen and nitrate, these anaerobic bacteria use
sulfate as the terminal acceptor.
140
Bio-ZP
ZP
120
Removal (mg/L)
100
80
60
40
20
0
M
Y
SMM
SMY
Type of Bio-ZP
Figure 6.20: Removal of SO42- by ZP and Bio-ZP
6.2.5 Phosphate Removal
Experimental results from Figure 6.21 show the reduction of phosphate by
the eight systems of experiment. Consistent to previous results of color, nitrate and
sulfate removal, the ZP series performed better than Bio-ZP series. Again, ZP-4
(SMY) and ZP-3 (SMM) which were prepared from surfactant modified zeolites,
possess the highest removal of phosphate. The results had shown that phosphate was
removed by ZP-4 (SMY) and ZP-3 (SMM) as high as 21 mg/L and 20 mg/L,
respectively. On the other hand, the Bio-ZP-4 (Bio-SMY) removed only 8.3 mg/L of
phosphate, followed by Bio-ZP-3 (Bio-SMM), 7.4 mg/L.
150
25
Bio-ZP
ZP
Removal (mg/L)
20
15
10
5
0
M
Y
SMM
SMY
Type of Bio-ZP
Figure 6.21: Removal of PO43- by ZP and Bio-ZP
6.2.6 Ammonium Removal
In contrast to previous results of color and various oxyanions removal, the
results of ammonium removal presented some variations. Obviously, from Figure
6.22, ZP-2 (Y) and ZP-1 (M) possess the best removal capacity for ammonium. ZP2 (Y) and ZP-1 (M) were prepared from original zeolites which are aluminosilicates
with high cation exchange capacities, and zeolites have a strong affinity towards
cation such ammonium in this case. In this study, ZP-2 (Y) removed 4.9 mg/L and
ZP-1 (M) removed 3.3 mg/L. Conversely, ZP-3 (SMM) and ZP-4 (SMY) possessed
lower rate of removal.
This can be understood by recalling that during modification, HDTMA
occupy the zeolite’s external cation exchange sites and block some of the internal
sites by the relatively large surfactant, thus lowering the cation exchange capacities
(Bowman et al., 1995). Bowman et al. (2000) however compared the uptake of
strontium on untreated clinoptilolite and on surfactant-modified clinoptilolite (SMC).
They found that the Sr2+ was strongly retained by the untreated clinoptilolite but
most of the retention capacity was lost after surfactant treatment. They explained
151
that the HDTMA occupied all of the external exchange sites and prevented surface
exchange of Sr2+ by the SMC, or the HDTMA blocking access to the internal
channels.
On the other hand, although there were no specific nitrifying bacteria isolated
from wastewater, the Bio-ZP series exhibited some removal of ammonium as well in
the range of 0.7 to 1.5 mg/L. This shows that the biomass attached on the surface of
Bio-ZP biosorbed or consumed the ammonium ions.
6
Bio-ZP
ZP
Removal (mg/L)
5
4
3
2
1
0
M
Y
SMM
SMY
Type of Bio-ZP
Figure 6.22: Removal of NH4+ by ZP and Bio-ZP
6.3
Use of Zeolite Particle for Textile Wastewater Treatment (II)
In previous attempts to apply the zeolite particles for textile wastewater
treatment, the results show that after the immersion of zeolite particles in wastewater
growth medium, the adsorption sites of the zeolite particles were occupied or
saturated by the various contaminants in wastewater, or the attached biomass had
limited or reduced the adsorption process. Previous study by Lahav and Green
(2000) shows that compared to the raw zeolite, the ion-exchange rate in the biozeolite (zeolite covered by biofilm, acting as the ion-exchanger and growth media for
152
microorganisms) was reduced by about 25-30 %, and the rate-controlling step for ion
exchange had shifted from pore diffusion in the virgin zeolite to film diffusion in the
bio-zeolite. In addition, Wen et al. (2006) found that for the bigger particle size (815 mm), the attached biofilm reduced the ion-exchange rate resulting in a 22 % drop
of the total equilibrium capacity.
As a consequence, another attempt to apply the zeolite particles for
wastewater treatment was done. In difference with the first attempt, in the second
attempt, the bacteria were added individually in the wastewater treatment system in
the form of bacterial pellets instead of in the form of biofilm attached on the zeolite
particle. There are three types of experimental systems, namely bacteria only (A),
zeolite particles without bacteria (B) and zeolite particles with bacteria (C). In the
system C, the zeolite particles ZP4 were chosen based on the better overall
performance in removing various contaminants in the previous experiment
6.3.1 pH Change
Results taken during the 7-day wastewater treatment are presented in Figure
6.23 and it shows that the pH values increased slowly from time to time for system B
and system C. On the other hand, conditions in system A did not turn the wastewater
to alkaline condition but slightly decreased the pH. Thus it is clearly seen that the
alkaline conditions in systems B and C were due to the alkaline nature of the zeolite
particles. The zeolite particles were prepared by using calcium hydroxide as binder,
thus the calcium hydroxide of the zeolite particles turned the pH value to alkaline
condition. In comparison between system B and C, it was found that system C
presented the final pH which was lower than that of system B. It can be explained
that the biomass presented in system C had contributed some buffering role in
decreasing the alkalinity of zeolite particles.
153
12
10
pH value
8
6
4
A
2
B
C
0
0
1
2
3
4
5
6
7
8
Time (d)
Figure 6.23: pH Change during Treatment
6.3.2 Color Removal
Results on removal of color in ADMI unit in the batch systems are shown in
Figure 6.24. System C which comprised the use of zeolite particles and bacteria
achieved the highest level of decolorization which removed 212 mg/L ADMI. It
shows that most of the removal occurred within the first day. On the other hand,
systems B and A removed color of up to 156 mg/L ADMI and 140 mg/L ADMI,
respectively. Although the total color removal by system C may not directly equal to
the sum up of the effect of bacteria degradation and adsorption, the results did
illustrate synergistic output for color removal.
Besides adsorption and
biodegradation, some of the color were removed by agglomeration to particles as can
be seen at the bottom of the experimental vessel.
154
350
300
A
B
C
ADMI (mg/L)
250
200
150
100
50
0
0
1
2
3
4
T ime (d)
5
6
7
8
Figure 6.24: Comparison of ADMI removal by different systems
6.3.3 Ammonium Removal
Figure 6.25 shows the ammonium removal by different systems. The results
show that systems B and C were able to remove ammonium at a rather low capacity;
both only removed 2.2 mg/L of ammonium. On the other hand, system A was not
able to remove any ammonium from the solution.
8
7
+
NH 4 (mg/L)
6
5
4
3
2
1
A
B
1
2
C
0
0
3
4
5
6
7
8
Tim e (d)
Figure 6.25: Comparison of ammonium removal by different systems
155
6.3.4 Nitrate Removal
Results of the nitrate removal by the three systems were illustrated in Figure
6.26. It is found the contaminant reduction trend was similar to the results observed
for color removal.
System C presented the optimum removal of nitrate.
The
removal of nitrate was 8.8 mg/L by system C, and followed by system B at 5.6 mg/L.
Again, the results suggested some synergy between the adsorption of zeolite particle
and bacterial degradation.
In the first 12 h of the experiment, the nitrate
concentration has increased for systems A and C, since system A and C consisted of
bacterial pellet, the increase in nitrate level may be due to the nutrient broth which
was attached to the biomass and released when the pellet was put in the wastewater.
A
B
5
6
C
16
12
8
-
NO 3 Concentration (mg/L)
20
4
0
0
1
2
3
4
7
8
Time (d)
Figure 6.26: Comparison of NO3- Removal by different systems
6.3.5 Sulfate and Phosphate Removal
Figures 6.27 and 6.28 presented the removal of sulfate and phosphate in the
three systems after 7 days of treatment. In consistent to the results of color and
nitrate removal, both of the sulfate and phosphate were removed at the highest value
156
in system C followed by system B. The results show that the addition of zeolite
particle into the biological treatment system helps to increase the efficiency of the
wastewater treatment.
Removal (mg/L)
7
6
5
4
3
2
1
0
A
B
C
Systems
Figure 6.27: Comparison of SO42- Removal by different systems
Removal (mg/L)
140
120
100
80
60
40
20
0
A
B
C
Systems
Figure 6.28: Comparison of PO43- Removal by different systems
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
7.1
Conclusions
From the results of the different analyses, it can be concluded that the
objectives of this study have been achieved. Alike other silica sources such as
colloidal silica, rice husk ash (RHA) which prepared under controlled combustion
provides high purity and high quantity of amorphous silica. The utilization of RHA
as an alternative source of active silica in zeolite synthesis was proven by the success
of the synthesis of high purity zeolite Y in this study. Zeolite Y was successfully
prepared from RHA by employing the aging and seeding methods, it was obtained
from aluminosilicate gel of 10 % seed gel with 15 Na2O: Al2O3: 15 SiO2: 220 H2O
and 90 % of feed stock gel with 4 Na2O: Al2O3: 10 SiO2: 180 H2O. The obtained
zeolite Y is considered pure and highly crystalline as proven by the highly intense
and narrow peaks without elevated baseline and extra peaks in the XRD pattern.
The synthesized zeolite Y and the natural mordenite were characterized using
various techniques such as XRD, FT-IR spectroscopy, FESEM-EDAX, TG-DTA and
nitrogen adsorption analysis. Besides that, total cation exchange capacity (CEC) and
external cation exchange capacity (ECEC) were also determined. These
physicochemical properties were related to the application of the zeolites as
adsorbents for ammonium in water and as basic data for surfactant modification of
zeolites.
158
The as-synthesized zeolite Y and mordenite possessed high capacity to
remove ammonium from the aqueous solutions. The sorption kinetic tests revealed
that the initial uptake of ammonium for both zeolite samples in the powdered form
occurred rapidly and most of them reached 90% of the equilibrium in a time of less
than 2 hours. Inversely, the granular mordenite possessed slower ammonium uptake
and reached equilibrium in about 2 days. Adsorption kinetics can be best represented
by a pseudo second order model with initial sorption rate being highest for
adsorption on zeolite Y. However the particle size of mordenite does not influence
the maximum uptake of ammonium from the aqueous solution.
The maximum
monolayer adsorption capacity obtained from the Langmuir plots for zeolite Y,
powdered mordenite and granular mordenite were 42.37, 15.13 and 14.56 mg
NH4+/g, respectively. Zeolite Y presents as the superior adsorption capacity which is
three times greater than mordenite.
A series of the surfactant-modified zeolite Y (SMY) and surfactant-modified
mordenite (SMM) were prepared by attaching the appropriate amount (50 %, 100 %,
150 % and 200 % of the ECEC) of HDTMA molecule on the zeolite surface. The
SMY and SMM series together with the unmodified zeolites were applied in
removing the oxyanions namely nitrate, phosphate and sulfate from the aqueous
solutions. Both untreated mordenite and zeolite Y have no affinity for oxyanions as
proven from the batch equilibrium tests. The sorption of all oxyanions by the SMM
and SMY were rapid and were based on the pseudo second order kinetic model. The
nitrate isotherms for adsorption on both SMM and SMY are of the C-type isotherm.
Generally the prepared SMY possesses higher adsorption capacity than SMM. For
the optimum loading of HDTMA, SMY-50 removed 9.20 mg/g nitrate while SMM100 removed 8.60 mg/g nitrate. For sulfate adsorption isotherm, SMY-50 removed
4.4405 mg/g sulfate while SMM-100 removed 3.1328 mg/g sulfate as indicated by
the Langmuir parameters. On the other hand, it was found that SMY-50 removed
phosphate at 3.2165 mg/g sorbent while SMM-100 removed phosphate at 2.5510
mg/g sorbent.
In addition to oxyanions, the effectiveness of the prepared surfactantmodified zeolites in removing an azo dye, Acid Orange 7 (AO7) which contains
anionic sulfonate group has also been accessed. Kinetic studies revealed that rapid
159
AO7 removal by SMZ can be best represented by a pseudo second order model. For
equilibrium studies, the Langmuir model provided the best correlation and proposed
that the adsorption process is monolayer and adsorption of each molecule has equal
activation energy. The maximum monolayer adsorption capacity for SMM-150 and
SMY-100 were 67.57 mg/g and 81.26 mg/g, respectively.
Ten bacteria colonies were isolated from the wastewater and further screened
for nitrate, sulfate and phosphate removal under aerobic and facultative conditions.
Finally four bacteria colonies were chosen and used to prepare bacteria mixed
cultures together with another bacterium from laboratory stocks able to decolorize
the wastewater. In the first application of zeolite particle, an attempt was made to
combine the adsorption and biodegradation simultaneously in a unit. However the
results showed that after immersion of zeolite particles in wastewater growth
medium, the adsorption sites of the zeolite particles were occupied or saturated by
the various contaminants in wastewater, or the attached biomass had limited or
reduced the adsorption process. Thus another attempt to apply the zeolite particles
for wastewater treatment was tried. In the second attempt, the bacteria were added
individually in the wastewater treatment system in the form of bacterial pellets
instead of in the form of biofilm attached on the zeolite particle. Finally the results
did illustrate synergistic effect of the combination of zeolite particle and bacteria for
the wastewater treatment. Besides adsorption and biodegradation, some of the color
was removed by agglomeration.
7.2
Contributions
Throughout the whole studies, a zeolite Y was successfully synthesized
through a simple hydrothermal technique by using rice husk ash as silica source via
seeding and aging methods. The applications of the low cost zeolites showed the
ammonium removal at fast rate and high capacity.
Furthermore, the potential
applications of surfactant-modified zeolites to remove various kinds of oxyanions
and anionic organic molecules were also presented. Finally, the fabrication of zeolite
160
particles and presentation of the possible usage together with bacteria degradation
was made.
7.3
Suggestions for Future Studies
In this study, the use of surfactant-modified zeolites to remove acid dye
presents encouraging results. While at the same time, there are only a few references
were found of the investigation of the applicability of surfactant-modified zeolites for
removing dyes (Karcher et al., 2001; Armağan et al., 2003, 2004; Benkli, et al.,
2005). Dyes are one of the major pollutants present in textile wastewater. Synthetic
dyes exhibit considerable structural diversity, the chemical classes of dyes employed
more frequently on industrial scale are the azo, anthraquinone, sulfur, indigo,
triphenylmethyl and phthalocyanine derivatives.
It consists of various chemical
classes such as neutral organics, anionic organics, cationic organics and metal
complex. Zeolites naturally possess a net negative charge thus high affinity towards
cations. After modification by cationic surfactants, the surface chemistry of zeolite
is altered, it happens to neutralize the surface negative charge or further reverse it.
Therefore, SMZ become an efficient sorbents for non-polar organics, oxyanions and
anionic organics. As a result, zeolites and SMZ become attractive sorbents for
various kinds of dyes. Thus, it is suggested that further the study on the usage of
SMZ in removing multiple types of dyes from different chemical classes has to be
done. Since some effective bacterial decolorizers were isolated from textile
wastewater, the bacterial decolorizers can possibly used to regenerate dye-saturated
zeolites or SMZ as well.
Combination of adsorption and biological treatment process is a complex and
complicated subject. In this study, preliminary attempts were made to access the
feasibility of combination of adsorption by zeolite particles and bacterial
degradation. There are still further studies needed to understand the mechanism such
as the identification of the bacteria and analysis of the bacterial community,
interaction between bacteria and zeolite, the formation of biomass on the surface of
zeolite, the roles of biofilm on the adsorption and bio-regeneration, effect of particle
161
size and doses of zeolite addition on biological process, so on and so forth. These
basic understanding can help us on designing the suitable system to provide the best
synergic effects from the combination of zeolite adsorption and bacterial
degradation.
162
REFERENCES
Ahmaruzzaman, M. and Sharma, D. K. (2005). Adsorption of Phenols from
Wastewater. J. Colloid and Interf. Sci. 287: 14-24.
Ahn, D. H., Chung, Y. C. and Chang, W. S. (2002). Use of Coagulant and Zeolite to
Enhance the Biological Treatment Efficiency of High Ammonia Leachate. J.
Environ. Sci. Health A. A37 (2): 163-173.
Aiyuk, S., Amoako, J., Raskin, L., van Haandel, A. and Verstraete, W. (2004).
Removal of Carbon and Nutrients from Domestic Wastewater using a Low
Investment, Integrated Treatment Concept. Wat. Res. 38: 3031-3042.
Altin, O, Önder Özbelge, H., Doğu, T. (1998). Use of General Purpose Adsorption
Isotherms for Heavy Metal-Clay Mineral Interactions. J. Colloid Interface Sci.
198:130-140.
APHA. (1992). Standard Methods for the Examination of Water and Wastewater.
18th ed. Washington, DC : American Public Health Association.
Armagan, B., Turan, M. and Celik, M. S. (2003). The Removal of Reactive Azo
Dyes by Natural and Modified Zeolite. J. Chem. Technol. Biotechnol. 78: 725732.
Armagan, B., Turan, M. and Celik, M. S. (2004). Equilibrium Studies on the
Adsorption of Reactive Azo Dyes into Zeolite. Desalination. 170: 33-39.
Armenante, P. M., Colella, L. S., Kafkewitz, D. and Larkin, M. J. (1996). Effect of a
Biofilm on the Adsorption of 4-Chlorophenol on Activated Carbon. Appl.
Microbiol. Biotechnol. 46: 667-672.
Baerlocher, Ch., Meier, W. M. and Olson, D. H. (2001). Atlas of Zeolite Framework
Types. 5th ed. Amsterdam: Elsevier.
Bajpai, K. P., Rao, M. S. and Gokhale, K. V. G. K. (1981). Synthesis of Mordenite
Type Zeolite Using Silica from Rice Husk Ash. Ind. Eng. Chem. Prod. Res. Dev.
20: 721-726.
163
Barrer, R. M. (1978). Zeolites and Clay Minerals as Sorbents and Molecular Sieves.
London: Academic Press.
Barrer, R. M. (1982). Hydrothermal Chemistry of Zeolites. London:
Academic
Press.
Bemmelen, J. M. Van. (1910). Die Absorption. Gesammelte Abhandlungen über
Kolloide und Absorption. Ostwald, W. ed. Dresden: Verlag von Theodor
Steinkopff.
Benkli, Y. E., Can, M. F., Turan, M. and Celik, M. S. (2005). Modification of
Organo-Zeolite Surface for the Removal of Reactive Azo Dyes in Fixed-Bed
Reactors. 39: 487-493.
Benson, H. J. (1998). Microbiological Applications: Laboratory Manual in General
Microbiology. 7th edition. Boston: McGraw-Hill.
Bernal, M. P. and Lopez-Real, J.M. (1993). Natural Zeolites and Sepiolite as
Ammonium and Ammonia Adsorbent Materials. Bioresource Technol. 43: 27-33.
Bitton, G. (2005). Wastewater Microbiology. 3rd edition. NJ, Wiley-Liss: John Wiley
& Sons.
Boethling, R. S. (1984). Environmental Fate and Toxicity in Wastewater Treatment
of Quaternary Ammonium Surfactants. Water Research. 18 (9): 1061-1076.
Bouffard, S. C. and Duff, S. J. (2000). Uptake of dehydroabietic acid using
organically tailored zeolites.. Water Res. 34: 2469-2476.
Boyd, S. A., Lee, J. F., and Mortland, M. M. (1988a). Attenuating Organic
Contaminant Mobility by Soil Modifications. Nature. 333: 345-347.
Boyd, S. A., Mortland, M. M. and Chiou, C. T. (1988b). Sorption Characteristics of
Organic Compounds on Hexadecyltrimethylammonium-Smectite. Soil Sci. Soc.
Amer. J. 52: 652-657.
Boyd, S. A., Shaobai, S., Lee, J., and Mortland, M. M. (1988c). Pentachlorophenol
Sorption by Organo-Clays. Clays Clay Miner. 125-130.
Bowman, R. S., Haggerty, G. M., Huddleston, R. G., Neel, D. and Flynn, M. M.
(1995). Sorption of Nonpolar Organic Compounds, Inorganic Cations, and
Inorganic Oxyanions by Surfactant-Modified Zeolites. In: Sabatini, D. A., Knox,
R. C., Harwell, J. H., eds. Surfactant-Enhanced Subsurface Remediation. ACS
Symp. Ser. 594: 54-64. Washington, D. C.: American Chemical Society.
Bowman, R. S. Sullivan, E. J. and Li, G. (1996). Surfactant-Modified Zeolites as
Sorbents for Cationic and Anionic Metals. In: Emerging Technologies in
164
Hazardous Waste Management VIII. Industrial & Engineering Chemistry
Division, American Chemical Society National Meeting, 9-12 Sept. 1996,
Birmingham, AL. American Chemical Society, Washington, DC. 702-704.
Bowman, R. S., Sullivan, E. J. and Li, Z. (2000). Uptake of Cations, Anions, and
Nonpolar Organic Molecules by Surfactant-Modified Clinoptilolite-Rich Tuff. In
Colella,
C. and Mumpton, F.A. eds. Natural Zeolites for the Third
Millenium. De Frede Editore, Naples, Italy. 287-297.
Bowman, R. S. (2003). Applications of Surfactant-Modified Zeolites to
Environmental Remediation. Microporous Mesoporous Mat. 61:43-56.
Bradl, H. B. (2004). Adsorption of Heavy Metal Ions on Soils and Soils Constituents.
J. Colloid. Interf. Sci. 277: 1–18
Breck, D. W. (1964a). Crystalline Zeolite Y. (U.S. Patent 3,130,007).
Breck, D. W. (1964b). Crystalline Molecular Sieves. J. Chem. Edu. 41: 678-689.
Breck, D. W. (1967). Synthesis and Properties of Union Carbide Zeolites L, X, Y.
Molecular Sieves. Papers read at the Conference held at the School of Pharmacy
(University of London). April 4-6 . London: Society of Chemical Industry, 47-61.
Breck, D. W. (1974). Zeolite Molecular Sieves, Structure, Chemistry and Use. USA:
Wiley Interscience.
Burt, T.A., Li, Z. and Bowman, R.S. (2005). Evaluation of Granular SurfactantModified Zeolite/ Zero Valent Iron Pellets as a Reactive Material for
Perchloroethylene Reduction. J. Environ. Eng. 131(6):934-942.
Cadena, F. (1989). Use of Tailored Bentonite for Selective Removal of Organic
Pollutants. J. Environ. Eng. 115: 756-767.
Cahn, M. D., Bouldin, D. R. and Crave, M. S. (1992). Sorption in the Profile of an
Acid Soil. Plant Soil. 143: 179-183.
Caldera, M., Heald, S. C., Carvalho, M. F., Vasconcelos, I., Bull, A. T. and Castro,
P. M. L. (1999). 4-Chlorophenol Degradation by a Bacterial Consortium:
Development of a Granular Activated Carbon Biofilm Reactor. Appl. Microbiol.
Biotechnol. 52: 722-729.
Cappuccino, J. G. and Sherman, N. (1996). Microbiology: A Laboratory Manual. 4th
ed. Menlo Park, California: The Benjamin/Cummings.
Chang, W. S., Hong, S. W. and Park, J. (2002). Effect of Zeolite Media for the
Treatment of Textile Wastewater in a Biological Aerated Filter. Process
Biochem. 37: 693-698.
165
Chen, N. Y., Degnan, T. F. Jr. and Smith, C. M. (1994). Molecular Transport and
Reaction in Zeolites: Design and Application of Shape Selective Catalysts. New
York: VCH publisher. 8-47.
Choy, K. K. H., Mckay, G., Porter, J. F. (1999). Sorption of Acid Dyes from
Effluents Using Activated Carbon. Resour. Coserv. Recycl. 27: 57-71.
Ciambelli, P., Corbo, P., Porcelli, C. and Rimoli, A. (1985). Ammonia Removal from
Wastewater by Natural Zeolite. I. Ammonium Ion Exchange Properties of an
Italian Phillipsite Tuff. Zeolites. 5: 184-187.
Cintoli, R., Di Sabatino, B., Galeotti, L. and Bruno, G. (1995). Ammonium Uptake
by Zeolite and Treatment in UASB Reactor of Piggery Wastewater. Water Sci.
Technol. 32: 73–81.
Clark, R. M. and Lykins, B.W. Jr. (1989). Granular Activated Carbon: Design,
Operation and Cost. Michigan: Lewis Publishers.
Cotruvo, J. A., Hanson, H. F., and Thornton, T. P. (1983). Overwiew: Role of
Activated Carbon in EPS’s Regulatory Program. In: McGuire, M. J. and Suffet, I.
H., ed. Treatment of Water by Granular Activated Carbon. Washington, D.C.:
American Chemical Society. 1-6.
Crittenden, B. D. and Thomas, W. J. (1998). Adsorption Technology and Design.
Oxford: Reed Educational and Professional Publishing Ltd.
Cundy, C. S. and Cox, P. A. (2003). The Hydrothermal Synthesis of Zeolites:
History and Development from the Earlist Days to the Present Time. Chem. Rev.
103: 663-701.
Dalal, A. K., Rao, M. S. and Gokhale, K. V. G. K. (1985). Synthesis of NaX Zeolite
Using Silica from Rice Husk Ash. Ind. Eng. Chem. Prod. Res. Dev. 24: 465-468.
Davis, J. A., Coston, J. A., Kent, D. B. and Fuller, C. C. (1998). Application of the
Surface Complexation Concept to Complex Mineral Assemblages. Environ. Sci.
Technol. 32: 2820-2828.
Davis, M. E. and Lobo, R. F. (1992). Zeolite and Molecular Sieve Synthesis. Chem.
Mater. 4: 756-768.
Della, V. P., Kuhn, I. and Hotza. D. (2002). Rice Husk Ash as an Alternate Source
for Active Silica Production. Mater. Lett. 57: 818-821.
Dinesh, M and Singh, K. P. (2002). Single- and Multi-Component Adsorption of
Cadmium and Zinc Using Activated Carbon Derived from Bagasse—An
Agricultural Waste. Water Research 36 (9): 2304-18.
166
Dondur, V. and Dimitrijevi, R. (1986). The Thermal Transformation of Na LiA
Zeolites. A New Polymorph in the System Li2O--Al2O3--SiO2. J. Solid State
Chem. 63 (1): 46-51.
Du, Q., Liu, S., Cao, Z. and Wang, Y. (2005). Ammonia Removal from Aqueous
Solution Using Natural Chinese Clinoptilonite. Sep. Purif. Technol. 44: 229-234.
Durham, D. R., Marshall, L. C., Miller, J. G. and Chmurny, A. B. (1994a).
Characterization of Inorganic Biocarriers That Moderate System Upsets during
Fixed-Film Biotreatment Processes. Appl. Environ. Microbiol. 60 (9): 33293335.
Durham, D. R., Marshall, L. C., Miller, J. G. and Chmurny, A. B. (1994b). New
Composite Biocarriers Engineered to Contain Adsorptive and Ion-Exchange
Properties Improve Immobilized-Cell Bioreactor Process Dependability. Appl.
Environ. Microbiol. 60 (11): 4178-4181.
Ehrhardt, H. M. and Rehm, H. J. (1985). Phenol Degradation by Microorganism
Adsorbed on Activated Carbon. Appl. Microbiol. Biotechnol. 21: 32-36.
Ehrhardt, H. M. and Rehm, H. J. (1989). Semicontinouos and Continuous
Degradation of Phenol by Pseudomonas putida P8 Adsorbed on Activated
Carbon. Appl. Microbiol. Biotechnol. 30: 312-317.
Eick, M. J., Brady, W. D. and Lynch, C. K. (1999). Charge Properties and Nitrate
Adsorption of Some Acid Southeastern Soils. J. Environ. Qual. 28: 138.
Englert, A. H. and Rubio, J. (2005). Characterization and Environmental Application
of a Chilean Natural Zeolite. Int. J. Miner. Process. 75: 21-29.
Ersoy, B. and Çelik, M. S. (2003). Effect of Hydrocarbon Chain Length on
Adsorption of Cationic Surfactants onto Clinoptilolite. Clays Clay Mater. 51 (2):
172-180.
Faghihian, H., Ghannadi Marageh, M. and Kazemian, H. (1999). The Use of
Clinoptilolite and Its Sodium Form for Removal of Radioactive Cesium, and
Strontium from Nuclear Wastewater and Pb2+, Ni2+, Cd2+, Ba2+ from Municipal
Wastewater. Appl. Radia. Isotopes. 1999. 50(4). 655-660.
Federle, T. W. and Ventullo, R. M. (1990). Mineralization of Surfactants by the
Microbiota of Submerged Plant Detritus. Appl. Environ. Microbiol. 56 (2): 333339.
Feijen, E. J. P, Martens, J. A. and Jacobs, P. A. (1994). Zeolites and their Mechanism
of Synthesis. In Weikamp, J., Karge, H. G., Pfeifer, H. and Hölderich, W., eds.
167
Zeolites and Related Microporous Materials: State of the Art 1994. Stud. Surf.
Sci. Catal. 84: 3-22. Amsterdam: Elsevier.
Fernández, N., Fdz-Polanco, F., Montalvo, S. J. and Toledano, D. (2001). Use of
Activated Carbon and Natural Zeolite as Support Materials, in an Anaerobic
Fluidised Bed Reactor, for Vinasse Treatment. Wat. Sci. Techonol. 44 (4): 1–6.
Fischer, V. M. (2001). In Situ Electrochemical Regeneration of Activated Carbon.
Dissertations
of
the
University
of
Groningen.
(http://irs.ub.rug.nl/ppn/228049458)
Flanigen, E. M., Khatami, H. and Szymanski, H. A. (1971). Infrared Structural
Studies of Zeolite Frameworks. In Gould, R. F., ed. Molecular Sieve Zeolites-I.
Advance in Chemistry Series. Washington, D. C.: American Chemical Society.
201-229
Flanigen, E. M. and Mumpton, F. A. (1981). Commercial Properties of Natural
Zeolites. Rev. Mineral. 4: 165-175.
Flanigen, E. M. (1991). Zeolites and Molecular Sieves. An Historical Perspective. In:
Bekkum, H. V. Bekkum, Flanigen, E. M. and Jansen, J. C. (1991). Stud. Surf.
Sci. Catal. 58: 13-34. Amsterdam: Elsevier.
Fuierer, A. M, Bowman, R. S. and Kieft, T. L. (2001). Biodegradation of Toluene
Sorbed to Surfactant-Modified Zeolite. Proc. Sixth International Symp. on In Situ
and On-Site Bioremediation. 4-7 June 2001. San Diego, CA.
Ginter, D. M, Bell, A. T. and Radke, C. J. (1992). The Effect of Gel Aging on the
Synthesis of NaY Zeolite from Colloidal Silica. Zeolites. 12: 742-749.
Green, M., Mels, A., Lahav, O. and Tarre, S. (1996). Biological-Ion Exchange
Process for Ammonium Removal from Secondary Effluent. Wat. Sci. Technol. 34
(1-2): 449-458.
Guerin, W. F. and Boyd, S. A. (1997). Bioavailability of Naphthalene Associated
with Natural and Synthetic Sorbents. Water Research. 31: 1504-1512.
Hach. (1997a). DR/4000 Spectrophotometer Procedures Manual. Method 8038.
Hach. (1997b). DR/4000 Spectrophotometer Procedures Manual. Method 8039.
Hach. (1997c). DR/4000 Spectrophotometer Procedures Manual. Method 8051.
Hach. (1997d). DR/4000 Spectrophotometer Procedures Manual. Method 8048.
Hach. (1997e). DR/4000 Spectrophotometer Procedures Manual. Method 8000.
Hach. (1997f). DR/4000 Spectrophotometer Procedures Manual. Method 8360.
168
Ha, S. R. and Vinitnantharat, S. (2000). Competitive Removal of Phenol and 2,4Dichlorophenol in Biological Activated Carbon System. Environ. Technol.
21 (4): 387-396.
Haggerty, G. M. and Bowman, R. S. (1994). Sorption of Chromate and Other
Inorganic Anions by Organo Zeolite. Environ. Sci. Technol. 28 (3): 452-458.
Hamdan, H., Muhid, M. N. M., Endud, S., Endang, L. and Ramli, Z. (1997).
29
Si
MAS NMR, XRD and FESEM Studies of Rice Husk Silica for the Synthesis of
Zeolites. J. Non-Crystalline Solids. 211: 126-131.
Hammaini, A. et al. (1999). Activated Sludge as Biosorbent of Heavy Metals.
International Biohydrometallurgy Symposium IBS’99. June 20-23, 1999.
England: Elsevier. 185-192.
Hammer, M. J. (1986). Water and Wastewater Technology. England: John Wiley and
Sons.
Hayakawa, K., Mouri, Y., Maeda, T., Satake, I. and Sato, M. (2000). Surfactant
Modified Zeolites as a Drug Carrier and the Release of Chloroquin. Colloid
Polym. Sci. 278: 553-558.
Hay, R. L. (1986). Geological Occurrence of Zeolites and Some Associated
Minerals. Pure Appl. Chem. 58 (10): 1339-1442.
Hendershot, W. H., Lalande, H. and Dupuette, M. (1993). Ion Exchange and
Exchangeable Cations. In Carter, M. R. (ed.). Soil Sampling and Methods of
Analysis. United State of America: Lewis Publishers. 167-176.
Hlavay, J., Vigh, G., Olaszi, V. and Inczedy, J. (1982). Investigation on Natural
Hungarian Zeolite for Ammonia Removal. Wat. Res. 16: 417-420.
Holmberg, K., Jonsson, B., Kronberg, B. and Lindman, B. (2001). Surfactant and
Polymers in Aqueous Solution. 2nd Edtion. West Sussex: John Wiley and Sons.
Inglezakis, V. J. (2005). The Concept of “Capacity” in Zeolite Ion-Exchange
Systems. J. Colliod Interf. Sci. 281: 68-79.
IUPAC, Physical Chemistry Division, Commission on Colloid and Surface
Chemistry Including Catalysis (1985). Reporting Physisorption Data for
Gas/Solid Systems with Special Reference to the Determination of Surface Area
and Porosity (Recommendations 1984). Pure Appl. Chem. 57 (4): 603-619.
IUPAC, Physical Chemistry Division, Commission on Colloid and Surface
Chemistry,
Subcommittee
on
Characterization
of
Porous
Solids.
169
Recommendations for the Characterization of Porous Solids. Pure Appl. Chem.
66 (8): 1769-1758.
James, J. and Rao, M. S. (1986). Characterization of Silica in Rice Husk Ash. Am
Cerem. New Bull. 65(8): 1177-1180.
Jansen, J. C. (1991). The Preparation of Molecular Sieves: A. Synthesis of Zeolites.
In: Bekkum, H. V. Bekkum, Flanigen, E. M. and Jansen, J. C. (1991). Stud. Surf.
Sci. Catal. 58: 77-136. Amsterdam: Elsevier.
Jentys, A. and Lercher, J. A. (2001). Techniques of Zeolite Charaterization. In van
Bekkum, H., Jacobs, P. A. and Jansen, J. C. (eds.). Introduction to Zeolite
Science and Practice. Amsterdam: Elsevier. 345-386.
Jung, J. Y., Pak, D., Shin, H. S. Chung, Y. C. and Lee, S. M. (2004). Ammonium
Exchange and Bioregeneration of Bio-flocculated Zeolite in a Sequencing Batch
Reactor. Biotechnol. Lett. 21: 289-292.
Jung, J. Y., Chung, Y. C., Shin, H. S. and Son, D. H. (2004). Enhanced Ammonia
Nitrogen Removal Using Consistent Biological Regeneration and Ammonium
Exchange of Zeolite in Modified SBR Process. Wat. Res. 38: 347-354.
Jungermann, E. ed. (1969). Cationic Surfactants. New York: Marcel Dekker.
Kaduk, J. A. and Faber, J. (1995). Crystal Structure of Zeolite Y as a Function of Ion
Exchange. The Rigaku Journal. 12(2): 14-34.
Kalavathy, M. H., Karthikeyem, T., Rajgopal, S. and Miranda, L. R. (2005). Kinetic
and Isotherm Studies of Cu(II) Adsorption onto H3PO4-Activated Rubber Wood
Sawdust. J. Colloid Interface Sci. 292 (2): 354-362.
Karapanagioti, H. K., Sabatini, D.A. and Bowman, R. S. (2005). Partitioning of
Hydrophobic Organic Chemicals (HOC) into Anionic and Cationic SurfactantModified Sorbents. Water Res. 39 (4): 699-709.
Karcher, S., Kornmüller, A. and Jekel, M. (2001). Screening of Commercial Sorbents
for the Removal of Reactive Dyes. Dyes Pigments. 51: 111-125.
Kargi, F. and Pamukoglu, M. Y. (2004). Adsorbent Supplemented Biological
Treatment of Pre-treated Landfill Leachate by Fed-Batch Operation. Bioresource
Technol. 94: 285-291.
Kasahara, S., Itabashi, K. and Igawa, K. (1986). Clear Aqueous Nuclei Solution for
Faujasite Synthesis. In Murakami, Y., Iijima, A and Ward, J. W., eds. New
Developments in Zeolite Science and Technology. Stud. Surf. Sci. Catal. 28: 185192. Amsterdam: Elsevier.
170
Kim, Y. K., Park, S. K. and Kim, S. D. (2003). Treatment of Landfill Leachate by
White Rot Fungus in Combination with Zeolite Filters. J. Enviro. Sci. Heal. A.
A38 (4): 671-683.
Kinniburgh, D. G., Barker, J. A. and Whitfield M. (1983). A Comparison of Some
Simple Adsorption Isotherms for Describing Divalent Cation Adsorption by
Ferrihydrite. J. Colloid Interface Sci. 95 (2): 370-384.
Kinniburgh, D. G. (1986). General Purpose Adsorption Isotherms. Environ. Sci.
Technol. 20 (9): 895-904.
Klieve, J. R. and Semmens, M. J. (1980). An Evaluation of Pretreated Natural
Zeolites for Ammonium Removal, Wat. Res. 14: 161-168.
Komarneni, S and Roy, Rustum (1981). Zeolites for Fixation of Cesium and
Strontium from Radwastes by Thermal and Hydrothermal Treatments. Nucl.
Chem. Waste Manage. 2(4). 259-264.
Koningsveld, H. V. (1991). Structural Subunits in Silicate and Phosphate Structures.
In Bekkum, H. V., Flanigen, E. M. and Jansen, J. C, eds. Introduction to Zeolite
Science and Practice. Stud. Surf. Sci. Catal. 58: 35-76. Amsterdam: Elsevier.
Koon, J. H., and Kaufman, W. J. (1975). Ammonia Removal form Municipal
Wastewaters by Ion-Exchange. J. Water Pollut. Control Fed. 47: 448-465.
Koopal, L. K., Van Riemsdijk, W. H., De Wit, J. C. and Benedetti, M. F. (1994).
Analytical Isotherm Equations for Multicomponent Adsorption to Heterogeneous
Surfaces. J. Colloid Interface Sci. 166: 51-60.
Kosanović, C., Subotić, B., Šmit, I., Čižmek, A., Stubičar, M. and Tonejc, A. (1997).
Study of Structural Transformations in Potassium-Exchanged Zeolite A Induced
by Thermal and Mechanochemical Treatments. J. Mater. Sci. 32:73-78.
LaGrega, M. D., Buckingham, P. L. and Evans, J. C. (2001). Hazardous Waste
Management. 2nd edition. Boston: McGraw-Hill.
Lahav, O. and Green, M. (1998). Ammonium Removal Using Ion Exchange and
Biological Regeneration. Water Res. 32 (7): 2019-2028.
Lahav, O. and Green, M. (2000). Bioregenerated Ion-Exchange Process: the Effect of
the Biofilm on Ion-Exchange Capacity and Kinetics. Water SA. 26: 51-57.
Langmuir, D. (1997). Aqueous Environmental Geochemistry. New Jersey: PrenticeHall Inc.
Langmuir, I. (1918). The Adsorption of Gases on Plane Surfaces of Glass, Mica and
Platinum. J. Am. Chem. Soc. 40 (9): 1361-1403.
171
Lee, J. F., R. C., James and Boyd, S. A. (1989). Enhanced retention of organic
contaminants by soils exchanged with organic cations. Environ. Sci. Technol.
23(11): 1365-1372.
Lee, C. M., Lu, C. J. and Chuang, M. S. (1994). Effects of Immobilized Cells on the
Biodegradation of Chlorinated Phenols. Wat. Sci. Technol. 30 (9): 87-90.
Lee, S. and Speight, J. G. (2000). Environmental Technology Handbook. 2nd edition.
New York: Taylor & Francis.
Lima, S. A. C., Raposo, M. F. J., Castro, P. M. L. and Morais, R. M. (2004).
Biodegradation of p-chlorophenol by a microalgae consortium. Water Research.
38: 97-102.
Li, Z. and Bowman, R. S. (1997). Counterion Effects on the Sorption of Cationic
Surfactant and Chromate on Natural Clinoptilonite. Environ. Sci. Techno. 31:
2407-2412.
Li. Z. and Bowman, R. S. (1998). Density-Controlled Partitioning Mechanism for
Sorption of Perchloroethylene by Surfactant-Modified Zeolite. Environ. Sci.
Technol. 32: 2278-2282.
Li, Z., Anghel, I. and Bowman, R. S. (1998a). Sorption of Oxyanions by SurfactantModified Zeolite. J. Dispersion Sci. Technology. 19: 843-857.
Li, Z., Roy, S. J., Zou and Y, Bowman, R. S. (1998b). Long-Term Chemical and
Biological Stability of Surfactant-Modified Zeolite. Environ. Sci. Technol. 32:
2628-2632.
Li, Z. (1999). Sorption Kinetics of Hexadecyltrimethylammonium on Natural
Clinoptilonite. Langmuir. 15: 6438-6445.
Li, Z., and Bowman, R.S. (2001). Regeneration of Surfactant-Modified Zeolite After
Saturation with Chromate and Perchloroethylene. Water Res. 35:322-326.
Li, Z., Willms, C., Roy, S., and Bowman, R. S. (2003). Desorption of
Hexadecyltrimethylammonium from Charged Mineral Surfaces. Environ. Geosci.
10 (1): 37-45.
Li, Z. (2003). Use of Surfactant-Modified Zeolite as Fertilizer Carriers to Control
Nitrate Release. Microporous Mesoporous Mater. 61: 181-188.
Li, Z. (2004). Influence of Solution pH and Ionic Strength on Chromate Uptake by
Surfactant-Modified Zeolite. J. Environ. Eng. 130 (2): 205-208.
McLean, J. E. and Bledsoe, B. E. (1992). Behavior of Metals in Soils. Ground Water
Issue. 1992. Washington: Environmental Protection Agency (EPA). 1-25
172
McVeigh, R. J. (2000). Biological Enhanced Ion-Exchange Removal of Ammonium
Ion Using Clinoptilonite. PhD Thesis. Queen’s University Belfast.
Meier, W. M. and Olson, D. H. (1987). Atlas of Zeolite Structure Types. London:
Butterworth.
Metcalf and Eddy. (2003). Wastewater Engineering: Treatment, Disposal and Reuse.
4th edition. Revised by Tchobanoglous, G, Burton, F. L. and Stensel, H. D.
Boston: McGraw-Hill.
Milán, Z, Sánchez, E., Weiland, P., Borja, R., Martín, A. and Ilangovan, K. (2001).
Influence of Different Natural Zeolite Concentrations on the Anaerobic Digestion
of Piggery Waste. Bioresource Technol. 80: 37–43.
Milán, Z, Villa, P, Sánchez, E, Montalvo, S., Borja, R., Ilangovan K. and Briones,
R.. (2003). Effect of Natural and Modified Zeolite Addition on Anaerobic
Digestion of Piggery Waste. Water Sci. Technol. 48: 263–269.
Milton, R. M. (1959a). Crystalline Zeolite A. (U. S. Patent 2,882,243).
Milton, R. M. (1959b). Crystalline Zeolite X. (U. S. Patent 2,882,244).
Milton, R. M. (1989). Molecular Sieves Science and Technology: A Historical
Perspectives. In: Occelli, M. L. and Robson, H. E., eds. Zeolite Synthesis. ACS
Symp. Ser. 398: 1-10. Washington, D. C.: American Chemical Society.
Ministry of Natural Resources and Environment, Department of Environment.
(2000). Interim National Water Quality Standards for Malaysia.
Ming, D. W. and Dixon, J. B. (1987). Quantitative Determination of Clinoptilolite in
Soils by a Cation-Exchange Capacity Method. Clays Clay Miner. 35: 463-468.
Montalvoa, S., Díaza, F., Guerrerob, L., Sánchezc, E. and Borjac, R. (2005). Effect
of Particle Size and Doses of Zeolite Addition on Anaerobic Digestion Processes
of Synthetic and Piggery Wastes. Process Biochem. 40: 1475–1481.
Mumpton, F. A. (1999). La Roca Magica: Uses of Natural Zeolites in Agriculture
and Industry. Proc. Natl. Acad. Sci. 96: 3463-3470.
Nishi, K. and Thompson, R. W. (2002). Crystalline Microporous Solids: Synthesis of
Classical Zeolites. In: Schüth, F., Sing, K. S. W. and Weitkamp J., eds.
Handbook of Porous Solids. Weinheim: Wiley-VCH. 736-814.
Njoroge, B. N. K. and Mwaamchi, S. G. (2004). Ammonia Removal from an
Aqueous Solution by the Use of a Natural Zeolite. J. Environ. Eng. Sci. 3: 7-154.
173
Norby, P. and Fjellvåg, H. (1992). Preparation Structural and Thermal Properties of
MAlSiO4 (M = Li, Na, K, Rb, Cs, Tl, Ag) of ABW-Type. Zeolites. 12 (8): 898908.
Nye, J. V., Guerin, W. F. and Boyd, S. A. (1994). Heterotrophic Activity of
Microorganisms in Soils Treated with Quartenary Ammonium Compunds.
Environ. Sci. Technol. 28: 944-951.
Oldenburg, M. and Sekoulov, I. (1995). Multipurpose Filters with Ion-Exchanger for
the Equalization of Ammonia Peaks. Water Sci. Technol. 32: 199-206.
Park, S. J., Lee, H. S. and Yoon, T. I. (2002). The Evaluation of Enhanced
Nitrification by Immobilized Biofilm on a Clinoptilolite Carrier. Bioresource
Technol. 82: 183-189.
Park, S. J., Lee, T. W., and Yoon, T. I. (2004). Production of Extracellular Polymeric
Substances in Anoxic/Oxic Process with Zeolite Carriers for Nitrogen Removal.
Biotechnol. Lett. 26: 1653-1657.
Payá, J., Monzó, J., Borrachero, M. V., Mellado, A. and Ordoňez, L. M. (2001).
Determination of Amorphous Silica in Rice Husk Ash by a Rapid Analytical
Method. Cement and Concrete Research. 31: 227-231.
Ramli, Z., Listiorini, E. and Hamdan, H. (1996). Optimization and Reactivity Study
of Silica in the Synthesis of Zeolites from Rice Husk. Jurnal Teknologi. 25: 2735.
Ranck, J. M., Bowman, R. S., Weeber, J. L., Katz, L. E. and Sullivan, E. J. (2005).
BTEX Removal from Produced Water Using Surfactant-Modified Zeolite. J.
Environ. Eng. 131 (3): 434-442.
Real, C., Alcalá, M. D. and Criado, J. M. (1996). Preparation of Silica form Rice
Husks. J. Am. Ceram. Soc. 79(8): 2012-2016.
Robson, H. (Ed.) and Lillerud, K. P. (2001). Verified Synthesis of Zeolitic Materials.
2nd Edition. Amsterdam: Elsevier.
Sánchez, E., Milán, Z., Borja, R., Weiland, P. and Rodríguez, X. (1995). Piggery
Waste Treatment by Anaerobic Digestion and Nutrient Removal by Ionic
Exchange. Resour. Cons. Recycl. 15: 235–244.
Sarioglu, M. (2005). Removal of Ammonium from Municipal Wastewater Using
Natural Turkish (Dogantape) Zeolite. Sep. Purif. Technol. 41: 1-11.
174
Scherer, M. M., Richter, S., Valentine, R. L., Alvarez, P. J. J. (2000). Chemistry and
Microbiology of Permeable Reactive Barriers for In Situ Groundwater Clean-Up.
Crit. Rev. Environ. Sci. Technol. 30: 363-411.
Schulze-Makuch, D., Pillai, D. S., Guan, H., Bowman, R., Couroux, E., Hielscher,
F., Totten, J., Espinosa, I. Y., Kretzschmar, T. (2002). Surfactant-Modified
Zeolite Can Protect Drinking Water Wells from Viruses and Bacteria. EOS.,
Transactions American Geophysical Union. 83: 193-201.
Schulze-Makuch, D., Bowman, R. S., Pillai, S. D. and Guan, S. D. (2003). Field
Evaluation of the Effectiveness of Surfactant Modified Zeolite and Iron-OxideCoated Sand for Removing Viruses and Bacteria from Ground Water. Ground
Water Monitoring and Remediation. 23 (4): 68-74.
Schulze-Makuch, D., Bowman, R. S. and Pillai, S. (2004). Removal of Biological
Pathogens Using Surfactant-Modified Zeolite. (U.S. Patent 2004/0108274 A1).
Sing, K. S. W. and Schüth, F. (2002). Definitions, Terminology, and Classification of
Pore Structures. In: Schüth, F., Sing, K. S. W. and Weitkamp J., eds. Handbook
of Porous Solids. Weinheim: Wiley-VCH. 736-814.
Semmens, M. J. and Goodrich, Jr., R. R. (1977a). Biological Regeneration of
Ammonium-Saturated Clinoptilolite. I. Initial Observations. Environ. Sci.
Technol. 11 (3): 255-257.
Semmens, M. J., Wang, J. T. and Booth, A. C. (1977b). Biological Regeneration of
Ammonium-Saturated Clinoptilolite. II. Mechanism of Regeneration and
Influence of Salt Concentration. Environ. Sci. Technol. 11 (3): 255-257.
Semmens, M. J. and Porter, P. S. (1979). Ammonium Removal by Ion-Exchange:
Using Biologically Restored Regenerant. J. Water Pollut. Cont. Fed. 51 (12):
2928-2940.
Sherman, J. D. (1999). Synthetic Zeolites and Other Microporous Oxide Molecular
Sieves. Proc. Natl. Acad. Sci. 96: 3471-3478.
Smith, J.V. (1984). Definition of a Zeolite. Zeolites. 4: 389-390.
Socrates, G. (1994). Infrared Characteristics Group Frequencies: Tables and
Charts. England. John Wiley & Sons.
Son, D. H., Kim, D. W. and Chung, Y. C. (2000). Biological Nitrogen Removal
using a Modified Oxic/Anoxic Reactor with Zeolite Circulation. Biotechnol. Lett.
22: 35-38.
175
Stapleton, M. G., Sparks, D. L. and Dentel, S. K. (1994). Sorption of
Pentachlorophenol to HDTMA-Clay as a Function of Ionic Strength and pH.
Environ. Sci. Technol. 28: 2330-2335.
Suh, Y. J., Park, J. M. and Yang, J. W. (1994). Biodegradation of Cyanide
Compounds by Pseudomonas fluorescens Immobilized on Zeolite. Enzyme
Microb. Technol. 16: 529-533.
Sullivan, E. J., Hunter, D. B., Bowman, R. S. (1998a). Fourier-Transform Raman
Spectroscopy of Sorbed HDTMA and the Mechanism of Chromate Sorption to
Surfactant-Modified Clinoptilonite. Environ. Sci. Technol. 32: 1948-1955.
Sullivan, E. J., Carey, J. W., Bowman, R. S. (1998b). Thermodynamics of Cationic
Surfactant Sorption onto Natural Clinoptilolite. J. Colloid Interf. Sci. 206: 369380.
Sun, L. and Gong K. (2001). Silicon-Based Materials from Rice Husks and Their
Applications. Ind. Eng. Chem. Res. 40: 5861-5877.
Sutton, P. W. and Mishra, P. N. (1994). Activated Carbon Based Biological
Fluidized Beds for Contaminated Water and Wastewater Treatment: A State-ofthe-Art Review. Water Sci. Technol. 29: 309-317.
Syamsiah, S. and Hadi, I. S. (2004). Adsorption Cycles and Effect of Microbial
Population on Phenol Removal Using Natural Zeolite. Sep. Purif. Technol. 34:
125-133.
Tadros, T. F. (2005). Applied Surfactants: Principles and Applications. Weinheim:
Wiley-VCH.
Tan, M. T. (2004). Development of Microbial Composite (Bioblock) Used for River
Water Treatment. Universiti Teknologi Malaysia: B.Sc. Thesis.
Thompson, R. W. (2001). Nucleation, Growth, and Seeding in Zeolite Synthesis. In:
Robson, H. ed. Verified Synthesis of Zeolitic Materials. 2nd Edition. Amsterdam:
Elsevier. 21-23.
Toles, C. A., and Marshall, W. E. (2002). Copper Ion Removal by Almond Shell
Carbons and Commercial Carbons: Batch and Column Studies. Separ. Sci.
Technol. 37: 2369-2383.
Tomasevic-Canovic, M. R., Dakovic., Rottinghaus, G., Matijasevic, S. and Duricic,
M. (2003). Surfactant Modified Zeolites: New Efficient Adsorbents for
Mycotoxins. Microporous Mesoporous Mater. 61: 173-180.
176
Tubbing, D. M. J. and Asmiraal, W. (1991). Inhibition of Bacterial and
Phytoplanktonic
Metabolic
Activity
in
the
Lower
River
Rhine
by
Ditallowdimethylammonium Chloride. Appl. Environ. Microbiol. 57 (12): 36163622.
van Ginkel, C. G., van Dijk, J. B. and Kroon, A. G. (1992). Metabolism of
Hexadecyltrimethylammonium Chloride in Pseudomonas Strain B1. Appl.
Environ. Microbiol. 58: 3083-3087.
Vujaković, A. D., Tomašević-Čanović, M. R., Daković, A. S. and Dondur, V. T.
(2000).
The
Adsorption
of
Sulphate,
Hydrogenchromate,
and
Duhydrogenphosphate Anions on Surfactant-Modified Clinoptilolite. Appl. Clay.
Sci. 17: 265-277.
Wang, H. P, Lin, K. S., Huang, Y. J., Li, M. C. and Tsaur, L. K. (1998). Synthesis of
Zeolite ZSM-48 from Rice Husk Ash. J. Hazardous Mater. 58: 147-152.
Weber, W. J. J., McGinley, P. M., and Katz, L. E. (1991). Sorption Phenomena in
Subsurface Systems: Concepts, Models and Effects on Contaminant Fate and
Transport. Water Research. 25(5): 499-528.
Wen, D., Ho, Y-S. and Tang, X. (2006). Comparative Sorption Kinetic Studies of
Ammonium onto Zeolite. J. Hazard. Mater. B133: 252-256.
Wilderer, P. A., Arnz, P. and Arnold, E. (2000). Application of Biofilms and Biofilm
Support Materials as a Temporary Sink and Source. Water Air Soil Poll. 123:
147-158.
Witthuhn, B., Klauth, P., Klumpp, E., Narres, H. D. and Martinius, H. (2005).
Sorption and Biodegradation of 2, 4-Dichlorophenol in the Presence of
Organoclays. Appl. Clay Sci. 28: 55-66.
Xu, S. and Boyd, S. A. (1995). Cationic Surfactant Sorption to a Vermiculitic
Subsoil via Hydrophobic Bonding. Environ. Sci. Technol. 29: 312-320.
Zhang, P., Tao, X., Li, Z. and Bowman, R.S. (2002). Enhanced Perchloroethylene
Reduction in Column Systems using Surfactant-Modified Zeolite/Zero-Valent
Iron Pellets. Environ. Sci. Technol. 36:3597-3603.
Zhang, Z. Z., Sparks, D. L. and Scrivner, N. C. (1993). Sorption and Desorption of
Quaternary Amine Cations on Clays. Environ. Sci. Technol. 27: 1625-1631.
Zhao, X. S., Lu, G. Q. and Zhu, H. Y. (1997). Effects of Ageing and Seeding on the
Formation of Zeolite Y from Coal Fly Ash. J. Porous Mater. 4: 245-251.