STATISTICAL OPTIMIZATION AND

CHARACTERIZATION OF FLUORIDE
BIOSORPTION USING DEAD MICROBIAL
BIOMASS

A PROJECT REPORT

Submitted by

JAYASREE S. (Reg. No. 201807020)

MARY GLADYS V. (Reg. No. 201807029)
RAMAPRIYA G. (Reg. No. 201807040)

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGY
in

BIOTECHNOLOGY

DEPARTMENT OF BIOTECHNOLOGY
MEPCO SCHLENK ENGINEERING COLLEGE, SIVAKASI
(An Autonomous Institution affiliated to Anna University Chennai)

May 2022
 ii

BONAFIDE CERTIFICATE

Certified that this project report titled STATISTICAL OPTIMIZATION AND

CHARACTERIZATION OF FLUORIDE BIOSORPTION USING DEAD

MICROBIAL BIOMASS is the bonafide work of Ms. S. JAYASREE, Ms. V. MARY

GLADYS, Ms. G. RAMAPRIYA, who carried out the research under my supervision.

Certified further, that to the best of my knowledge the work reported herein does not form

part of any other project report or dissertation on the basis of which a degree or award was

conferred on an earlier occasion on this or any other candidate.

Mrs.M.Sivasankari, M.Tech., Dr.M.L. Stephen Raj, M.Tech., Ph.D;

Internal guide Head of the Department

Assistant Professor, Senior Professor,
Department of Biotechnology, Department of Biotechnology,
Mepco Schlenk Engineering College, Mepco Schlenk Engineering College,
Sivakasi. Sivakasi.

Submitted for Viva-Voce Examination held at MEPCO SCHLENK ENGINEERING

COLLEGE, SIVAKASI (AUTONOMOUS) on ……………..............

Internal Examiner External Examiner

 iii

Abstract

Excessive fluoride consumption (> 2.0 ppm) results in a condition called fluorosis resulting
in staining of teeth or weakening of bones. Thus, it is critical to concentrate on
defluoridation of water. Adsorption has been a conventional method of fluoride biosorption
in aqueous solution. Adsorption is advantageous over other conventional methods like
filtration and membrane separation because of its cost effectiveness and low sludge
formation. Biosorbents are cost-effective, easily obtainable, and ecologically sustainable
sources of adsorbents. In this study, aqueous solution containing fluoride is treated with
dead bacterial biomass. Effect of process conditions like initial fluoride concentration,
biomass dosage, pH, temperature, and contact time were studied one factor at a time. The
process conditions were statistically optimized for fluoride biosorption using Central
Composite Design (CCD) with 30 experiments with 6 center points. The maximum
fluoride biosorption of 95% was observed after 8 hours of biosorption with 20 ppm initial
fluoride concentration, 400 mg L -1 of biomass dosage, at temperature 45℃ and at pH 4.
Biosorption kinetic studies revealed that fluoride biosorption followed a pseudo second-
order kinetics and adsorption isotherm was best described by Freundlich isotherm. The
biosorption efficiency of immobilized biosorbent was also studied using column approach
and a maximum fluoride biosorption of 67% was obtained. Biosorbent was characterized
using Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red Spectroscopy
(FTIR), and Energy Dispersive X-Ray spectroscopy (EDX). This study suggests that dead
bacterial biomass could serve as a potential biosorbent for fluoride biosorption.

Keywords: Defluoridation; biosorbent, optimization, adsorption isotherm

 iv

ACKNOWLEDGEMENT

First and foremost, we thank God Almighty for showering his blessing in all our
endeavors. We would like to thank Dr. S. Arivazhagan, Principal, Mepco Schlenk
Engineering College, Sivakasi for granting us with the opportunity to carry out our project
in this esteemed institution.

We are extremely indebted to DR. M. L. Stephen Raj, Senior professor and Head of the
Department, Mepco Schlenk Engineering College, Sivakasi, for his valuable suggestions
and support during the course of our research work.

We are extremely indebted and wish to record our deep sense of gratitude and profound
thanks to our research supervisor Mrs. M. Sivasankari, Assistant professor, Department of
Biotechnology, Mepco Schlenk Engineering College, Sivakasi, for her keen interest, inspir-
ing guidance, constant encouragement with our work during all stages, to bring this thesis
into fruition and also for being a constant pillar of support in number of ways throughout
this period.

We owe our thanks to Mrs. A. Arul Jayanthi, Mr. M. Sankar, Staff members,
Technicians, and all friends, who had supported us throughout our project work.

Finally, we extend our indebtedness towards our beloved parents for their support which
made this project a successful one.

S. JAYASREE

V. MARY GLADYS

G. RAMAPRIYA
 v

TABLE OF CONTENTS

CONTENTS PAGE NO

Bonafide certificate ii

Abstract iii

Acknowledgement iv

List of tables viii

List of figures x

List of equations xii

List of symbols and xiii

abbreviations

CHAPTER 1 INTRODUCTION
1.1 CHEMICAL NATURE OF FLUORINE 1
1.2 FLUORIDE SOURCES
1.2.1 Natural sources 2
1.2.2 Anthropogenic sources 2
1.3 FLUORINE ADSORPTION IN HUMAN BODY 3
1.4 ADVANTAGES OF FLUORINE INTAKE 3
1.5 HEALTH IMPACTS OF CONSUMING 4
FLUORINATED WATER
1.6 REMOVAL OF FLUORIDE IN DRINKING WATER 4

CHAPTER 2 REVIEW OF LITERATURE

2.1 CONVENTIONAL METHODS AVAILABLE FOR 6
DEFLUORIDATION
2.2 ADSORPTION 7
2.2.1 Biosorption 7
2.2.2 Advantages of using biosorption in water treatment 8
 vi

2.3 FLUORIDE REMOVAL BY VARIOUS ADSORBENTS

2.3.1 Activated carbon 8
2.3.2 Biochar and bone char 9
2.3.3 Polymers 9
2.3.4 Clay 10
2.3.5 Biosorbents 10

CHAPTER 3 MATERIALS AND METHODS

3.1 PREPARATION OF BIOSORBENT FOR FLUORIDE 13
ADSORPTION
3.2 FLUORIDE MEASUREMENT IN AQUEOUS 14
SOLUTION
3.3 SELECTION OF BIOSORBENTS BASED ON 14
SORPTION EFFICIENCY
3.4 THE EFFECT OF PROCESS PARAMETERS ON 15
FLUORIDE BIOSORPTION
3.5 COLUMN APPROACH FOR FLUORIDE 16
BIOSORPTION
3.6 OPTIMIZATION OF FLUORIDE BIOSORPTION 17
USING CENTRAL COMPOSITE DESIGN
3.7 CHARACTERIZATION OF BIOSORBENT 18

CHAPTER 4 RESULTS AND DISCUSSION

4.1 SELECTION OF BIOSORBENT FOR FLUORIDE 19
BIOSORPTION
4.2 EFFECTS OF PROCESS PARAMETERS ON
FLUORIDE BIOSORPTION
4.2.1 Effect of initial concentration of fluoride 20
4.2.2 Effect of biosorbent dosage 21
4.2.3 Effect of contact time 23
4.2.4 Effect of pH 24
4.2.5 Effect of temperature 25
4.3 ADSORPTION ISOTHERMS 27
 vii

4.4 ADSORPTION KINETICS 30

4.5 FLUORIDE BIOSORPTION USING COLUMN 33
APPROACH
4.6 STATISTICAL OPTIMIZATION OF FLUORIDE 34
BIOSORPTION USING RESPONSE SURFACE
METHODOLOGY
4.7 CHARACTERIZATION OF BIOSORBENT USING
FTIR, SEM AND EDX ANALYSIS
4.7.1 FTIR analysis of biosorbent 42
4.7.2 SEM and EDX analysis of biosorbents 43

CHAPTER 5 CONCLUSION 46

CHAPTER 6 REFERENCE 47
 viii

LIST OF TABLES

TABLE NAME OF THE TABLE PAGE NO.

NO.

2 Adsorptive capacities and characteristics of various 11

biosorbents in fluoride removal
4.2.1 Adsorption capacity and % fluoride biosorption for effect of 20
initial fluoride concentration
4.2.2 Adsorption capacity and % fluoride biosorption for effect of 22
biosorbent dosage
4.2.3 Adsorption capacity and % fluoride biosorption for effect of 23
contact time
4.2.4 Adsorption capacity and % fluoride biosorption for effect of 25
pH
4.2.5 Adsorption capacity and % fluoride biosorption for effect of 26
temperature
4.3.1 Langmuir parameters for fluoride biosorption 28
4.3.2 Freundlich parameters for fluoride biosorption 29
4.3.3 Isothermal model fitting parameters for fluoride adsorption 30
on biosorbent
4.4.1 Pseudo first order kinetic parameters for fluoride biosorption 31
4.4.2 Pseudo second order kinetic parameters for fluoride 32
biosorption
4.4.3 Kinetic model fitting parameters for fluoride adsorption on 33
biosorbent
4.5 % Fluoride biosorption for packed bed column 33
4.6.1 Fit Summary for fluoride biosorption 35
4.6.2 Fit Statistics for fluoride biosorption 36
4.6.3 ANOVA for Quadratic model for fluoride biosorption 36
 ix

4.6.4 The actual and predicted values of RSM model for fluoride 37
biosorption
 x

LIST OF FIGURES

TABLE NAME OF THE FIGURES PAGE NO.

NO.

2 Conventional methods for defluoridation 7

3.1 Biosorbent prepared from the bacterial culture 14
3.5 Column mode of fluoride biosorption 17
4.1 % Fluoride biosorption of biosorbents 19
4.2.1 Effect of initial concentration of fluoride on fluoride 21
biosorption
4.2.2 Effect of biosorbent dosage on fluoride biosorption 22
4.2.3 Effect of contact time on fluoride biosorption 24
4.2.4 Effect of pH on fluoride biosorption 25
4.2.5 Effect of temperature on fluoride biosorption 27
4.3.1 Langmuir isotherm model for fluoride biosorption 29
4.3.2 Freundlich isotherm model for fluoride biosorption 29
4.4.1 Pseudo first order kinetic model for fluoride biosorption 31
4.4.2 Pseudo first order kinetic model for fluoride biosorption 32
4.5 % Fluoride biosorption for packed bed column 34
4.6.1 Comparison between the actual values and the predicted 37
values of RSM model for fluoride biosorption
4.6.2a The effects of experimental parameters A (Initial fluoride 39
concentration) and B (Biosorbent dosage) on fluoride
biosorption
4.6.2b The effects of experimental parameters A (Initial fluoride 39
concentration) and C (pH) on fluoride biosorption
4.6.2c The effects of experimental parameters A (Initial fluoride 40
concentration) and D (Temperature) on fluoride biosorption
4.6.2d The effects of experimental parameters B (Biosorbent 40
dosage) and C (pH) on fluoride biosorption
4.6.2e The effects of experimental parameters B (Biosorbent 41
 xi

dosage) and D (Temperature) on fluoride biosorption

4.6.2f The effects of experimental parameters C (pH) and D 41
(Temperature) on the fluoride biosorption
4.7.1a FTIR spectrum of biosorbent before adsorption 42
4.7.1a FTIR spectrum of biosorbent before adsorption 43
4.7.2a SEM images of biosorbent before adsorption 44
4.7.2b SEM images biosorbent after adsorption 44
4.7.2c EDX analysis of biosorbent before fluoride adsorption 45
4.7.2d EDX analysis of biosorbent after fluoride adsorption 45
 xii

LIST OF EQUATIONS

TABLE NAME OF THE EQUATION PAGE NO.

NO.

3.1 % Fluoride biosorption 15

3.2 Adsorption capacity of fluoride 16
3.3 Linear model (RSM) 17
3.4 Quadratic model (RSM) 17
4.1 Langmuir Isotherm 27
4.2 Affinity between the adsorbent and adsorbate 27
4.3 Freundlich isotherm 28
4.4 Pseudo first order kinetics 30
4.5 Pseudo second order kinetics 30
 xiii

LIST OF ABBERRATIONS AND SYMBOLS

FTIR Fourier transform infrared

SEM Scanned electron microscopy
EDX Energy dispersive x-ray
NB Nutrient broth
ANOVA Analysis for variance
HCl Hydrochloric acid
H2SO4 Sulfuric acid
CaCl2 Calcium chloride
OH Hydroxyl group
Ca Calcium
P Phosphorous
Al Aluminum
Zr Zirconium
Ce Cerium
La Lanthanum
Mg Magnesium
% Percentage
g/mol gram per mole
ppm parts per million
mg/g milli gram per gram
min. minutes
Fig. figure
h hour
β beta
W/V weight per volume
mg/L milli gram per litre
m²/g meter square per gram
ml/hour milli litre per hour
A° Armstrong
K Kelvin
 xiv

℃ Degree Celsius
g gram
ml milli litre
nm nano meter
cm centimeter
psi pounds per square inch
rpm rotation per minute
M Molar
kV kilovolt
 1

CHAPTER 1

INTRODUCTION

Fluorine is widely distributed in nature and it is the 13th most abundant element on the
planet (Mason & Moore, 1982). Fluoride is the most electronegative of other chemical
elements. Therefore, it combines with other elements and does not occur in the
elemental state (Ponikvar, 2008). It is the lightest halogen and can exist as a diatomic
gas. Fluorine is distributed universally in soils, plants and animals including humans.
It is an essential element in humans for the formation of tooth enamel but when it
exceeds the permissible limit it is harmful to humans (World Health Organization and
Safety, 1996). Fluorine is considered as one of the significant ground water
contaminants and consuming fluorine contaminated water can cause both long-term
and short-term effects on human health. So, developing a highly efficient and cost-
effective technique for fluorine removal in drinking water is a serious concern in the
society and it has an impact on the overall development in growing nations.

1.1 CHEMICAL NATURE OF FLUORINE

Fluorine is an element of the halogen group which is placed at VIIA in the periodic
table. Fluorine exists as yellow green pungent gas with the atomic number 9 and with
the molecular weight of 18.999 g/mol. It is univalent and the stereochemistry of
fluorine resembles that of OH because of their similarity in ionic radii (O’Donnell,
1975). It is the most electronegative element in the periodic table (Kapp, 2005) and the
inorganic form of fluorine can either exists freely or it is bound to the mineral matrix.
Fluorine has an electronic configuration, 1s2 2s2 2p5. It needs to gain only one electron
 2

in its outer shell to attain the stable electronic configuration. This property of fluorine
makes it a highly electronegative species. The high reactivity of fluorine results from
its high electronegativity, low dissociation energy and greater bond strength of the
compounds it forms. So, fluorine generally exists in combined form with other
elements.

1.2 FLUORINE SOURCES

1.2.1 Natural sources

Fluorine is incredibly reactive, so it exists as fluoride ions in the minerals such as

fluorspar or fluorite, fluorapatite, and cryolite. Fluorite or fluorspar (CaF2 ) is usually
associated with quartz, calcite, dolomite, or barite. The largest amount of fluoride
exists as fluorapatite [Ca5 (OH, F)(PO4 ) 3] (Fuge, 1988). Besides fluorspar (49%),
fluorapatite (4%) and cryolite (54%), several other silicates such as topaz, oxides,
carbonates, sulfates, phosphates, sellaite and sodium fluoride contains minimum
amount of inorganic fluoride (Reimann & Caritat, 2011). Host minerals such as mica
(layer silicates), amphiboles (chain silicates), apatite, tourmaline, and clays, such as
montmorillonite, kaolinite, and bentonite also contain inorganic fluoride. A part of the
fluorine may be present in clay material and limestone (Fuge, 1988).

1.2.2 Anthropogenic sources

In the developing countries the native fluoride content in the soil is widely affected by
the application of fertilizers and from industrial pollutants. The fluorine content in the
soil is enriched from different sources and the main sources include coal burning, oil
refining, steel production, chemical production, clay production, Aluminum smelting,
glass and enamel manufacture, brick and ceramic manufacturing, distribution of
fluoride-containing fertilizers and pesticides, wastes from sewage and sludges,
production of uranium hexafluoride (UF6 ) and uranium trifluoride (UF3 ) from the
nuclear industry. Phosphatic fertilizers are the most important sources of fluoride
contamination to agricultural lands and it may elevate the soil fluoride content by 5-
 3

10 ppm (Fuge & Andrews, 1988) ( Reimann & Caritat, 2011). The main source of
fluorine contamination in water is from the industries and leaching from the minerals.

1.3 FLUORINE ADSORPTION IN HUMAN BODY

In human the main route of fluoride adsorption is via the gastrointestinal tract. Fluoride
ions are released from the soluble compounds such as sodium fluoride, hydrogen
fluoride, fluor silicic acid and sodium mono-fluorophosphate are completely absorbed
by passive diffusion. Fluoride is released into the blood stream by absorption from
both stomach and intestine. It is absorbed in the form of weak acid hydrogen fluoride
(HF), which employs that the fluoride in the acidic environment of the stomach lumen
is readily converted into HF (Whitford & Pashley, 1984). Once, it is adsorbed into the
blood circulation fluorine highly retains in the Ca rich areas like bones and teeth.

1.4 ADVANTAGES OF FLUORINE INTAKE

Studies suggest that the sufficient intake of fluorine can prevent tooth decay and helps
in the strengthening of bones. Fluorine protects the tooth decay by remineralization
and demineralization (World Health Organization and Safety, 1996). Less than 1.5
ppm of fluorine in drinking water has benefits such as

• Prevents dental carries

• Provides resistance to acid attack in teeth

• Rebuilds the weakened tooth enamel

• Slows down the loss of minerals from tooth enamel

• Prevents the growth of harmful oral bacteria

• Supports mineralization of bones

• Improves gum health

 4

1.5 HEALTH IMPACTS OF CONSUMING FLUORINATED WATER

At trace amount, fluoride is beneficial for the maintenance of healthy bones and teeth
in humans (Boldaji et al., 2009). The deficiency of fluoride causes development of
dental carries, lack of enamel formation and bone fragility (Ayenew, 2008). However
excessive intake of fluoride through drinking water influences the metabolism of Ca
and P in human body (Kumar et al., 2008). This results in hyperparathyroidism which
increases the secretion of thyroid hormones. It causes depletion of Ca in bones and
excess concentration of Ca in blood and it leads to health problems such as dental and
skeletal fluorosis, neurological damage, thyroid disorder, Alzheimer’s disease,
infertility as well as liver and kidney damages (Nigri et al., 2017). Dental fluorosis is
characterized by the appearance of yellowish stains on the tooth and this may occur
when a developing tooth is exposed to high concentration of fluoride. Skeletal
fluorosis results in weakening of bones and malformation of skeleton. In this case, the
bones will become hardened and less elastic increasing the risk of bone fracture.

1.6 REMOVAL OF FLUORIDE IN DRINKING WATER

Fluoride is highly reactive and one of the pollutants of groundwater contamination

(Hussain et al., 2010). The World Health Organization (WHO) recommended a
permissible limit of 1.5 ppm of fluoride in drinking water (UNEP, 1984). More than
20 developed and developing countries has been reported for excessive fluoride
concentration such as Mexico, central and western China, South Africa, and India
(Meenakshi & Maheshwari, 2006). Excessive fluoride concentration in water is
consumed by 200 million people, worldwide (He et al., 2014). In India more than 15
states have rich fluoride concentration in groundwater (Gupta et al., 2006) and 25
million people are affected by fluoride contamination (Arlappa et al, 2013).

Fluoride contamination in water mainly happens through industrial effluents with high
fluoride concentration from semiconductors manufacturing, electroplating, glass and
 5

ceramic production, aluminum smelters and coal fired power plants (Bhatnagar et al.,
2011). It is also released into the water naturally by weathering of fluoride containing
rocks (Ma et al., 2017). So, technologies such as nanofiltration (Jadhav et al., 2016),
membrane separation (Ndiaye et al., 2005), electro-coagulation (Sandoval et al.,
2014), reverse osmosis (Colla et al., 2016), adsorption (Ali, 2014), ion exchange
process (Markovski et al., 2017), chemical coagulation and precipitation (He et al.,
2015) etc. have been adapted for defluorination of water. However, there are various
disadvantages such as high cost, energy consumption and production of secondary
contaminants after treatment in these methods (Gentili & Fick, 2017). Among these
techniques, adsorption has many advantages in water treatment because of its cost
effectiveness, regeneration of adsorbents, easy implementation, and maintenance
(Chen et al., 2010).

There is a need for development of potential biosorbents because they are naturally
abundant, and they have less harmful effects on environment. Biosorbents can be
prepared either from plant and animal sources (Das et al., 2014) (Kanaujia et al., 2015)
or microbial sources such as bacteria, fungi, algae (Gupta & Rastogi, 2008)
(Vijayaraghavan & Yun, 2008) (Wang & Chen, 2006). So, in this study bacterial
isolates from fluorine contaminated region are used as the source for preparation of
biosorbents. The present study focusses on optimizing the process parameters such as
initial fluoride concentration, biosorbent dosage, contact time, pH and temperature for
effective fluoride removal. Batch and column mode of study was performed for
fluoride removal. In addition to that adsorption kinetics and isotherms was constructed
for studying the fluoride biosorption. Finally, the biosorbent was characterized using
FTIR, SEM and EDX analysis.
 6

CHAPTER 2

REVIEW OF LITERATURE

2.1 CONVENTIONAL METHODS AVAILABLE FOR DEFLUORIDATION

The conventional methods available for defluoridation are precipitation, membrane

separation, ion exchange process and adsorption. In precipitation, alum salts and lime
were the most used coagulants. One of the most common precipitation techniques is
the Nalgonda technique, in which fluoride removal is dependent on the flocculation,
sedimentation, and filtration of the fluoride from the aqueous solution. It can treat
water in large quantities, and it is cost effective but after treatment there is high sludge
formation. Membrane separation involves a semi-permeable membrane which acts as
a barrier for separation of contaminants. Reverse osmosis, nanofiltration, dialysis, and
electrodialysis are examples of membrane separation. These methods are effective;
however, it is costly. Ion exchange process is a technique which utilizes various
cationic and anionic resins for the purification, but resins are expensive and produces
high fluoride loaded wastes (Khan et al., 2021). Among these techniques adsorption is
cost effective, and adsorbents are readily available (Mohapatra et al., 2009).
 7

• Efficient but • Works at wide pH

expensive but expensive

Ion exchange Membrane

Precipitation Adsorption

• Easy and efficient • Low cost and

but results in sludge effective but only at
formation and other specific conditions
ions precipitation

Figure 2: Conventional methods for defluoridation

2.2 ADSORPTION

Adsorption is a surface phenomenon which causes the transfer of molecules from the
bulk fluid to the solid surface. Compared with other methods, adsorption is a cheap
and reusable method. Generally, there are two types of adsorptions which is physical
adsorption and chemical adsorption. Physical adsorption is caused by intermolecular
forces like van der Waals and the adsorption is weak. Chemical adsorption is caused
by the formation of chemical bonds and it is more stable and firmer than physical
adsorption (Artioli, 2008). Generally, in adsorption chemical adsorption and physical
adsorption takes place simultaneously.

2.2.1 Biosorption

Biosorption process is known as an attractive biotechnological process which employs

naturally abundant or waste biomass for removing contaminants from aqueous
solutions (Zaharia, 2015). Biosorption is an emerging tool for wastewater treatment
 8

that has gained attention in the scientific community over the past three decades.
Biosorption is the property of certain biomaterials to bind and concentrate selected
ions or other molecules from aqueous solutions on its surface. Plant, animal and
microbial biomass can be used for biosorbent preparation.

2.2.2 Advantages of using biosorption in water treatment

The overall incentives of biosorption for wastewater treatment (Torres, 2020) are:

• Low cost of biosorbents.

• Great selectivity and efficiency for metal removal at low concentration.
• Potential for biosorbent regeneration
• High velocity of sorption and desorption
• Limited generation of secondary residues
• More environment friendly life cycle of the material.

So far, an industrially relevant method for removal of toxic metals has not been
achieved yet. Biosorbents with different degrees of metal adsorption capacities,
availability, and selectivity have been shown to be promising for water treatment.

2.3 FLUORIDE REMOVAL BY VARIOUS ADSORBENTS

2.3.1 Activated Carbon

Activated charcoal has a good adsorption property because of its high porosity, surface
area and catalytic activity. However activated charcoal has low affinity and adsorption
capacity for inorganic pollutants like Fluoride. So, to overcome this problem activated
charcoal was modified with different chemical species. Vences et al., (2015) used
granular activated carbon (GAC) anchored with lanthanum oxyhydroxides to remove
fluoride from solution. The adsorption capacity of GAC-La was 5 times higher than
commercially available activated carbon. The adsorption process followed Langmuir
 9

isotherm and pseudo second order kinetics with an adsorption capacity of 9.98 mg/g.
In addition to that, a removal efficiency of 92.6 % was obtained in the first hour. Roy
et al., (2017) used calcium-impregnated activated charcoal for fluoride removal and a
removal efficiency of 99.68 % was obtained with a contact time of 40 min. The
adsorption process followed Langmuir isotherm and best fitted with pseudo second
order kinetics with adsorption capacity of 46.32 mg/g.

2.3.2 Biochar and Bone Char

Biochar is a carbon rich material which is produced by the pyrolysis of biomass with
the absence of oxygen. Biochar for fluoride removal is a widely used method because
of its availability, low cost, and easy production. Li et al., (2016) used poly pyrrole-
grafted peanut shell biological carbon for fluoride removal and a fluoride removal
efficiency of 91.2 % was obtained. The maximum adsorption capacity of 17.15 mg/g
was obtained and best fitted with Langmuir isotherm and pseudo second order kinetics.
Wang et al., (2018) studied fluoride removal by lanthanum-loaded pomelo peel
biochar (PPBC-La). After 9 h of treatment 82% of fluoride removal was obtained. The
adsorption was well described by pseudo second order kinetics and Freundlich
isotherm models.

2.3.3 Polymers

Surface properties of polymers are modified to improve the adsorption affinity of

fluoride because of its changeable surface properties, high surface activity, relatively
low cost, and useful properties for adsorbent synthesis. Valdez-Alegria et al., (2020)
synthesized four biopolymers based on chitosan-polyvinyl alcohol (Ch-PVA) cross-
linked with, ethylene glycol diglycidyl ether (EGDE) for fluoride removal from water.
The adsorption equilibrium data followed Freundlich adsorption isotherm, showing a
maximum fluoride adsorption capacity of 12.64 mg/g.
 10

2.3.4 Clay

Defluoridation by adsorption onto cost-effective natural materials like clay was the
most utilized method. Ben et al., (2018) used raw Tunisian clays in the defluoridation
of natural water. The percentage of fluoride removal was 73% for kaolinite and 46%
for smectite was obtained. Mobarak et al., (2018) used modified natural clay which is
modified with decyltrimethylammonium bromide and a combination of hydrogen
peroxide with decyltrimethylammonium bromide. The experimental data were fitted
well with Langmuir model and pseudo-second-order model with a maximum
adsorption capacity of 53.66 mg/g.

2.3.5 Biosorbents

Biosorbents are materials of natural origin like agricultural wastes and microbial
biomasses such as algal, bacterial, fungi and yeast. The advantage of using biosorbents
is that it is readily available, cost effective and no harmful effects on ecosystem. These
biosorbents are effective in treating water because of the availability of surface
functional groups like carboxyl, hydroxyl, sulfuryl groups etc. on their surfaces.
Various chemical and physical treatment like acid and alkali treatment, carbonization,
pyrolysis, or grounding is performed to increase its adsorptive capacity (Torres, 2020).
The adsorptive capacities and characteristics of various biosorbents are given in the
Table 2 below.
 11

Table 2: Adsorptive capacities and characteristics of various biosorbents in

fluoride removal

S.No Biosorbent Adsorption Isotherm Kinetic References

capacity
(mg/g)
1 Aluminum 9 Freundlich Pseudo 2nd (Ganvir &
hydroxide order Das, 2011)
coated rice
husk ash
2 Magnetic corn 6.42 Redlich- Pseudo 1st (Mohan et al.,
stover biochar Peterson order 2014)
3 Tamarind 22.33 Langmuir Pseudo 1st (Sivasankar
(Tamarindus order, et al., 2012)
indica) fruit pseudo 2nd
shell carbon order, intra-
particle
diffusion &
Elovich
4 Bael (Aegle 2.4 Redlich– Pseudo 2nd (Singh et al.,
marmelos) Peterson, order 2016)
shell activated Langmuir,
carbon Radke-
Prausnitz,
Toth, Temkin
& Freundlich
5 Surface 0.3173 Freundlich Pseudo 2nd (Mihayo et
modified order al., 2021)
Adansonia
digitata fruit
pericarps
6 Ash biomass 1 140 Temkin Pseudo 2nd (Zdunek et
order al., 2019)
7 Tinospora 25 Langmuir & - (Pandey et
cordifolia Freundlich al., 2012)
biomass
8 Chemically 1.1441 Langmuir, Pseudo 2nd (Dan &
modified Freundlich & order Chattree,
Moringa Temkin 2018)
oleifera leaves
9 Spirogyra sp. 1.272 Langmuir Pseudo 1st (Mohan et al.,
IO1 order 2007)

10 Blue-green - Freundlich Pseudo 1st (Mittal et al.,

algae order 2020)
Phormidium
sp.
 12

11 White—rot 66.6 Langmuir Pseudo 2nd (Amin et al.,

fungus order 2015)
Pleurotus
eryngii ATCC
90888
12 Banana peel 1.212 Dubinin- Bahangam (Mondal,
(Musa Radushkevich & Pseudo 2017)
acuminate) 2nd order
13 Natural apple 1.38 Langmuir Pseudo 2nd (Zarrabi et
pulp order al., 2014)
14 Staphylococcus 5.198 Freundlich Pseudo 2nd (Mukherjee et
lentus order al., 2018)
(KX941098)
15 Egg shell 1.09 Langmuir Pseudo 2nd (Bhaumik et
powder order al., 2012)
 13

CHAPTER 3

MATERIALS AND METHODS

3.1 PREPARATION OF BIOSORBENT FOR FLUORIDE ADSORPTION

Water samples collected from the villages of Virudhunagar district were serially
diluted and spread in nutrient agar plates. Isolated colonies were grown in NB medium
and glycerol stocks were maintained in -80℃ for future use. Overnight cultures of 4
bacterial isolates were prepared from the stock cultures and biomasses obtained from
the overnight cultures (NB medium) were used in the preparation of biosorbents. The
overnight cultures were centrifuged at 10,000 rpm for 10 minutes and the pellet was
collected and rinsed with sterile double distilled water. The biomasses were autoclaved
at 121°C, 15 psi for 20 minutes and used as biosorbent for fluoride removal.
 14

Figure 3.1: Biosorbent prepared from the bacterial culture

3.2 FLUORIDE MEASUREMENT IN AQUEOUS SOLUTION

Fluoride in the aqueous solution was estimated by using zirconium-alizarin reagent

method. About 0.03 g of Zirconium oxychloride and 0.035 g of alizarin red were
dissolved in 25 ml of double distilled followed by the addition of 2 ml of concentrated
H2 SO4 and 6 ml of concentrated HCl. It was then made up to 50 ml by double distilled
water. Standard fluoride solutions were prepared in the range of 2 to 10 ppm from
standard stock solution of 100 ppm prepared with NaF (221 mg NaF in 1 L of dd H2 O).
5ml of sample from each standard was taken and 0.5 ml of alizarin red reagent was
added and incubated in dark for about 5 minutes and absorbance was measured at 525
nm using spectrophotometer. A graph was constructed with fluoride concentration
versus absorbance and used for the determination of unknown concentration of
fluoride in the aqueous solution (Bumsted & Wells, 1952).

3.3 SELECTION OF BIOSORBENTS BASED ON SORPTION EFFICIENCY

The biosorbent was chosen based on its % removal of fluoride from the aqueous
solution. From the prepared biosorbents, 100 mg L−1 of each were taken and added to
separate flasks containing 5 ppm of fluoride (F − ) solution. This reaction mixture was
agitated in shaker at 160 rpm for about 24 hours. The solutions were then centrifuged
 15

at 10,000 rpm for 10 minutes, and the supernatants were taken as sample. To 5 ml of
samples, 0.5 ml of prepared reagent was added and incubated for 5 minutes in dark.
Then, their absorbance was measured at 525 nm. The % fluoride biosorption is
calculated by the eqn. 3.1.

(Ci − Cf )
% Removal = x 100 (Eq. 3.1)
Ci

Where, Ci is the initial fluoride concentration in the solution (mg L−1) and Cf is the
final fluoride concentration (mg L−1).

3.4 THE EFFECT OF PROCESS PARAMETERS ON FLUORIDE

BIOSORPTION

The effect of process conditions on fluoride biosorption were determined one factor at
a time. Fluoride biosorption studies were performed in 100 ml conical flasks with a
working volume of 50 ml NaF solution. The effect of initial fluoride concentration of
0.5, 2.5, 5, 7.5 ppm were determined while keeping other parameters constant
(Biosorbent dosage-100 mgL−1, temperature-37°C, pH-7, contact time-8 hours). The
influence of biosorbent dosage on fluoride removal was studied for 100, 200, 400, 600,
800, 1000 mg L−1 doses by keeping other parameters constant (Initial fluoride
concentration-5 ppm, temperature-37°C; pH-7; contact time-8 hours). The influence
of contact time on fluoride removal was studied by collecting samples at the end of
every hour from the reaction mixture (Biosorbent dosage-100 mg L−1, initial fluoride
concentration-5 ppm, pH-7, temperature-37°C). The effect of pH on fluoride removal
was also studied by varying the pH between the range of pH 2-9 while keeping other
parameters constant (Biosorbent dosage-100 mg L−1, initial fluoride concentration-5
ppm, temperature-37°C, contact time-8 hours). The reaction mixture was maintained
at different temperatures (25, 30, 35, 40, 45, 50°C) for studying its influence on
fluoride removal by keeping other parameters constant (Biosorbent dosage-100
mgL−1, initial fluoride concentration-5 ppm, pH-7, contact time-8 hours). The residual
 16

fluoride concentration in the aqueous solution can be estimated by zirconium

oxychloride method using a spectrophotometer and % fluoride biosorption can be
calculated from the equation (3.1). The adsorption capacity was calculated by using
eqn. (3.2):

(Ce − Ci ) x V
qe = (Eq. 3.2)
w

where, q e is the fluoride adsorbed at equilibrium (mg g −1), Ce is the fluoride

concentration at equilibrium (mg L−1), Ci is the initial concentration of fluoride in the
solution (mg L−1), V is the volume of solution (ml), and w is the weight of the
biosorbent (mg). Adsorption kinetic model and isotherm models were constructed for
studying the adsorption of fluoride to biosorbent.

3.5 COLUMN APPROACH FOR FLUORIDE BIOSORPTION

Initially 2% (w/v) sodium alginate solution was mixed with 0.5% (W/V) of biosorbent
and kept undisturbed for 12 hours. The beads were prepared by dripping the solution
with syringe from a height of 20 cm approximately into 200 ml of 0.2 M CaCl2 solution
(Bouabidi et al., 2018) and the beads prepared were stored for further experiments.
Biosorbent immobilized calcium alginate beads were then packed in a glass column
for fluoride adsorption. 5 ppm of fluoride solution (pH 7 and temperature 37°C) was
topped up to the column at the flow rate of 100 ml h−1 (Simate & Ndlovu, 2015). The
outlets were collected at the end of every hour and the residual fluoride concentration
in the aqueous solution can be estimated by using zirconium oxychloride method with
a spectrophotometer. % Fluoride removal was calculated from the equation (3.1).
 17

Figure 3.5: Column mode of fluoride biosorption

3.6 OPTIMIZATION OF FLUORIDE BIOSORPTION USING CENTRAL

COMPOSITE DESIGN

Response surface methodology (RSM) is used for analyzing the effects of several
independent variables (Mohammad, 2013) on a particular process. It uses quantitative
data obtained from the designed experiments to get the optimum operating conditions
(Tan et al., 2008).

Design expert 13 trial version was used to generate the design for optimization of
fluoride biosorption and statistical analyses. Central composite design was used to
investigate the response function for four independent variables namely initial fluoride
concentration (A; 𝑋1), biosorbent dosage (B; 𝑋2), pH (C; 𝑋3, ), temperature (D; 𝑋4, )
and % fluoride biosorption was taken as the response Y as shown in the Table 4.6.4.
The response of the model can be expressed the following equation (Sahu et al., 2009):

𝑌 = 𝑓 (𝑋1 , 𝑋2, 𝑋3, … … . . 𝑋𝑛 ) ± 𝑒 (Eq. 3.3)

 18

Where, Y is the response, f is the response function, 𝑋𝑖 are the independent variables
and e is the experimental error. RSM approximates f by a suitable polynomial for
independent process variables. The quadratic model for RSM may be expressed as the
following equation (Can et al., 2006):

𝑛 𝑛 𝑛 𝑛
2
𝑌 = 𝛽0 + ∑ 𝛽𝑖 𝑋𝑖 + ∑ 𝛽𝑖𝑖 𝑋𝑖 + ∑ ∑ 𝛽𝑖𝑗 𝑋𝑖 𝑋𝑗 + 𝑒 (Eq. 3.4)
𝑖=1 𝑖=1 𝑖=1 𝑗=1

Where, Y is the predicted response, 𝛽0 is the constant coefficient, 𝛽𝑖 is the linear

coefficient, 𝛽𝑖𝐽 is the quadratic coefficients, 𝑋𝑖 and 𝑋𝑗 are the values of independent
process variables and e is the residual error.

3.7 CHARACTERIZATION OF BIOSORBENT

The biosorbent was analyzed using FTIR to study the functional groups at their
surface. The FTIR spectrum allows us to classify the groups that are present in the
biosorbent which are responsible for binding fluoride from the solution onto
biosorbent. The morphology and porosity of biosorbent before and after adsorption
can be analyzed using Scanning electron microscopy. The surface images of
biosorbent contains information about the surface topography and composition of
biosorbent. Energy Dispersive X-ray Spectrometry was used for elemental analysis of
the biosorbents before and after fluoride adsorption to confirm the fluoride adsorption
(Thakre et al., 2010).
 19

CHAPTER 4

RESULTS AND DISCUSSION

4.1 SELECTION OF BIOSORBENT FOR FLUORIDE BIOSORPTION

Figure 1 shows the highest % fluoride biosorption of the biosorbents prepared using
the isolates obtained from water. Out of the four biosorbents, biosorbent 1 showed
better % fluoride biosorption around 60% which is higher than other biosorbents used
in the experiment and comparable with the defluoridation efficiency of already
reported dead bacterial biomass (Krishna et al., 2018). The bar graph for % fluoride
biosorption of biosorbent was shown in the Fig.4.1.

Figure 4.1: % Fluoride biosorption by biosorbents

 20

4.2. EFFECTS OF PROCESS PARAMETERS ON FLUORIDE BIOSORPTION

4.2.1 Effect of initial concentration of fluoride

Fluoride biosorption with varying initial fluoride concentration (0.5, 2.5, 5, 7.5 ppm)
was studied. Maximum fluoride biosorption of 99.49 % was observed with 0.5 ppm
initial fluoride concentration due to high availability of adsorption sites for adsorption.
In the further steps a drop in % biosorption was observed with increasing initial
fluoride concentration (Figure 4.2.1). The rate of adsorption was reduced because the
availability of adsorption sites was limited in a fixed dose of biosorbent as the fluoride
concentration was increased. On the other hand, an increase in adsorption capacity
with an increase in initial fluoride concentration was observed. Maximum adsorption
capacity (2.4487 mg g −1) was observed at 5 ppm, and it is taken as the optimum initial
concentration for fluoride removal. Similar trend has been reported in previous studies
conducted using Jamun leaf ash (Tirkey et al., 2017), wheat straw, sawdust and
activated bagasse carbon of sugarcane (Yadav et al., 2013).

Table 4.2.1: Adsorption capacity and % fluoride biosorption for effect of initial
fluoride concentration

S.No Initial fluoride 𝐪𝐞 % Fluoride

−𝟏
concentration (mg 𝐠 ) biosorption
(mg 𝐋−𝟏 )
1 0.5 0.49 99.49
2 2.5 1.91 76.67
3 5 2.44 48.97
4 7.5 2.21 29.55
 21

Figure 4.2.1: Effect of initial concentration of fluoride on fluoride biosorption

4.2.2 Effect of biosorbent dosage

The effect of biosorbent dose (200, 400, 600, 800, 1000 mg L−1) on fluoride
biosorption was studied. Initially, there is an increase in fluoride removal with increase
in biosorbent dose because of the availability of adsorption sites (Kebede et al., 2014).
The defluorination efficiency of biosorbent dosage 400 mg L−1 with adsorption
capacity 4.614 mg g −1 , showed the highest fluoride biosorption (90%). Furthe increase
in biosorbent dosage resulted in a decreased fluoride biosorption. At higher biosorbent
dose, aggregation of particles happens, and the adsorption sites are not exposed for
further adsorption of fluoride (Mereta, 2017). So, there is a decrease in fluoride
biosorption at higher biosorbent dose.
 22

Table 4.2.2: Adsorption capacity and % fluoride biosorption for effect of biosorbent
dosage

S.No Biosorbent dosage 𝐪𝐞 % Fluoride

(mg 𝐋−𝟏 ) (mg 𝐠 −𝟏 ) biosorption
1 100 2.40 48.06
2 200 2.40 48.16
3 400 4.61 92.28
4 600 3.50 70.02
5 800 3.39 67.98
6 1000 3.26 65.26

Figure 4.2.2: Effect of biosorbent dosage on fluoride biosorption

 23

4.2.3 Effect of contact time

The effect of contact time on fluoride biosorption was studied at different time
intervals. In this study it was found that the extent of sorption and adsorption capacity
increased with the increase in time up to 8 hours with a maximum fluoride biosorption
of 95%. After this time interval there is no significant increase in the sorption because
of the achievement of sorption equilibrium. At first the increase in sorption was due to
the availability of adsorption sites on the adsorbent surface and after few hours there
was no vacant sites for fluoride adsorption and therefore the sorption was almost
constant (Mondal & Kundu, 2016).

Table 4.2.3: Adsorption capacity and % fluoride biosorption for effect of contact
time

S.No Time 𝐪𝐞 % Fluoride

(hrs.) (mg 𝐠 −𝟏 ) biosorption
1 1 2.5 51.35
2 2 3.23 64.76
3 3 3.47 69.53
4 4 3.71 74.32
5 5 3.90 78.15
6 6 4.16 83.35
7 7 4.52 90.45
8 8 4.76 95.23
9 12 4.81 96.28
10 24 4.83 96.74
 24

Figure 4.2.3: Effect of contact time on fluoride biosorption

4.2.4 Effect of pH

The pH of an aqueous solution is an important parameter that influence biosorption

efficiency because it can affect the surface charges of biosorbents. The biosorbent was
effective in the pH 4 with maximum biosorption of 80%. A significant decrease in
biosorption and adsorption capacity was observed at all other pH ranges. At acidic pH,
the presence of hydroxyl and carboxyl groups impart positive charge on the adsorbent
surface (Mohan & Karthikeyan, 2000). Since, fluoride is highly electronegative there
electrostatic interaction with adsorbent surface favors adsorption (Tuzun et al., 2005).
At alkaline pH, there is an increase in hydroxyl ion concentration which interferes in
fluoride adsorption (Mohan et al., 2004). So, there is a decrease in fluoride removal at
alkaline pH.
 25

Table 4.2.4: Adsorption capacity and % fluoride biosorption for effect of pH

S.No pH 𝐪𝐞 % Fluoride
(𝐦𝐠 𝐠 −𝟏 ) biosorption
1 2 2.18 43.76
2 3 3.48 69.76
3 4 4.28 85.67
4 5 3.28 65.79
5 6 3.00 60.13
6 7 2.39 47.80
7 8 3.23 64.68
8 9 2.86 57.35

Figure 4.2.4: Effect of pH on fluoride biosorption

 26

4.2.5 Effect of temperature

The effect of various temperatures (25, 30, 35, 40, 45, 50°C) on fluoride removal was
studied. The maximum fluoride biosorption (93%) and adsorption capacity of 4.68
(mgg −1 ) was observed at 45°C. Initially, fluoride biosorption increases with the
increase in temperature (until 45°C) because in chemisorption increase in temperature
favors adsorption and increases adsorption capacity (Meena et al., 2005), until it
reaches an equilibrium point. This reaction is endothermic as increasing the
temperature results in favorable adsorption (Lakshmi et al., 2009). There is a decrease
in biosorption at temperatures higher than optimal temperature because of the
structural modification on the biosorbent surface.

Table 4.2.5: Adsorption capacity and % fluoride biosorption for effect of

temperature

S.No Temperature 𝐪𝐞 % Fluoride

°C (𝐦𝐠 𝐠 −𝟏) biosorption
1 25 2.31 46.39
2 30 2.78 55.76
3 35 3.97 79.46
4 40 4.17 83.46
5 45 4.68 93.78
6 50 4.15 83.05
 27

Figure 4.2.5: Effect of temperature on fluoride biosorption

4.3 ADSORPTION ISOTHERMS

Langmuir and Freundlich isotherm models are the most common models used in
describing the adsorption mechanism. Langmuir isotherm model assumes a monolayer
adsorption with no lateral interaction of adsorbate molecules on adsorbent surface. The
linear form of Langmuir isotherm can be expressed as in equation (4.1):

Ce 1 Ce
= + (Eq. 4.1)
qe qmb qm

Where, Ce is the fluoride concentration at equilibrium (mg L−1), q e is the fluoride

adsorbed at equilibrium (mg g −1 ), q m is the maximum adsorption capacity (mg g −1),
b is the Langmuir constant (L mg −1 ). The coefficient of determination R2 (0.7688)
obtained indicates the unsuitability of Langmuir model for fluoride biosorption. The
 28

affinity between the adsorbent and adsorbate can be calculated by a dimensionless

factor R L , which can be determined from the following equation:

1
RL = (Eq. 4.2)
(1 + bC0 )

where b is the Langmuir constant (L mg −1 ) and C0 is the initial concentration of

fluoride in the solution (mg L−1). The R L value (0.1678) obtained for this reaction is
within the range (0< R L < 1) shows adsorption is favorable.

Freundlich isotherm model is applied on a heterogeneous surface and the linear form
of Freundlich isotherm model is given as (eqn.4.3):

1
ln q e = ln K f + ln Ce (Eq. 4.3)
n

Where, q e is the fluoride adsorbed at equilibrium (mg g −1 ), Ce is the fluoride

concentration at equilibrium (mg L−1), K f is the adsorption capacity (L mg −1) and 1/n
is the adsorption intensity (g mg −1 ). For Freundlich isotherm the regression coefficient
value (R2 -0.9589) and the value of 1/n (0.402; 1/n <0.5) indicated favorable adsorption
(Karthikeyan et al., 2011).

Langmuir and Freundlich isotherm constants for the removal of fluoride from aqueous
solution using biosorbent was calculated and shown in the table 4.3.3.

Table 4.3.1: Langmuir parameters for fluoride biosorption

S.No 𝐂𝐞 𝐂𝐞 /𝐪𝐞
1 0.025798 0.00544
2 0.962661 0.062619
3 2.415479 0.093459
4 3.494908 0.087262
 29

0.10

0.08

0.06

Ce/qe
0.04

0.02

0.00

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Ce

Figure 4.3.1: Langmuir isotherm model for fluoride biosorption

Table 4.3.2: Freundlich parameters for fluoride biosorption

S.No ln 𝐂𝐞 ln 𝐪𝐞
1 -3.65747 1.556464
2 -0.03805 2.732638
3 0.881897 3.252125
4 1.251307 3.690152
 30

ln qe
2

1
-4 -2 0 2
ln Ce

Figure 4.3.2: Freundlich isotherm model for fluoride biosorption

Table 4.3.3: Isothermal model fitting parameters for fluoride adsorption on

biosorbent

Langmuir Freundlich

b qm RL R2 Kf n R2
(Lmg −1) (mgg −1 ) (Lmg −1) (mgg −1 )

0.9912 4.405 0.1678 0.7688 1.9392 2.9649 0.9589

4.4 ADSORPTION KINETICS

Kinetics of fluoride biosorption was studied to determine the rate of biosorption

process. Pseudo first order and pseudo second order models were fitted to elucidate
the adsorption process. The suitability of kinetic models can be determined by the
 31

proximity of R2 value to 1. The equation for pseudo first order kinetics is given in
eqn.4.4 (Ho & McKay, 1998):

ln(q e − q t ) = ln q e − k1 x t (Eq. 4.4)

Where, q e is the fluoride adsorbed at equilibrium (mg g −1 ), q t is the fluoride adsorbed

at the time t, t is the time required for fluoride removal (hrs) and k1 is the equilibrium
rate (hr −1). The pseudo second order equation is given in eqn. 4.5 (Ho & McKay,
1999):

t 1 1
= + ( ) x t (Eq. 4.5)
qt k2 qe2 qe

Where, t is the time required for fluoride removal (hrs.), q e is the fluoride adsorbed at
equilibrium (mg g −1 ), q t is the fluoride adsorbed at the time t and k 2 is the second
order kinetic constant (g mg −1 min−1 ).

The regression coefficient (R2 ) obtained for pseudo first order and pseudo second
order kinetic equation is 0.4448 and 0.9825 respectively. From the closeness
regression coefficient (R2 ) to 1, it was concluded that pseudo second order equation
is more suitable in describing the adsorption kinetics than pseudo first order equation.
From the results obtained it was found that adsorption was dominated by
chemisorption (Duran et al., 2011). Pseudo first and second order kinetic model
parameters was calculated and given in the table 4.5.3.

Table 4.4.1: Pseudo first order kinetic parameters for fluoride biosorption

S.No t ln (𝐪𝒆 -𝐪𝐭 )

1 1 -0.3999
2 2 -1.43297
3 3 -1.42943
4 4 -1.65287
 32

5 5 -1.34725
6 6 -1.03565
7 7 -1.43002
8 8 -2.94798

0.0

-0.5

-1.0
ln(qe-qt)

-1.5

-2.0

-2.5

-3.0

0 1 2 3 4 5 6 7 8 9
t

Figure 4.4.1: Pseudo first order kinetic model for fluoride biosorption

Table 4.4.2: Pseudo second order kinetic parameters for fluoride biosorption

S.No t t/𝐪𝐭
1 1 0.389463
2 2 0.617659
3 3 0.862905
4 4 1.076405
5 5 1.279566
6 6 1.439703
7 7 1.547808
8 8 1.680027
 33

2.0

1.5

t/qt 1.0

0.5

0 2 4 6 8
t

Figure 4.4.2: Pseudo second order kinetic model for fluoride biosorption

Table 4.4.3: Kinetic model fitting parameters for fluoride adsorption on

biosorbent

Pseudo first Pseudo second order kinetic model

order kinetic model

qe k1 R2 qe h k2 R2
−1 −1
(mg g ) (min−1 )
−1
(mg g ) (mg g min ) (g mg min−1 )
−1 −1

1.7939 0.1945 0.4448 5.3792 3.6363 0.1256 0.9825

 34

4.5 FLUORIDE BIOSORPTION USING COLUMN APPROACH

The calcium alginate immobilized biosorbent was packed in the column and aqueous
solution with 5 ppm initial fluoride concentration was fed into the column. Fluoride
removal was estimated in the sample collected at the outlet at the end of each hour.
Maximum fluoride biosorption (68%) was observed at the end of 1 hr. After that there
was a decrease in fluoride biosorption because of the unavailability of adsorption sites
for fluoride in the aqueous solution. The adsorption sites available on the surface of
immobilized biosorbent were readily picking up fluoride ions present in aqueous
solution. As time increases the adsorption sites was preoccupied by fluoride ions in the
solution (Hiremath & Theodore, 2017). So, when time increases there is no availability
of vacant adsorption sites.

Table 4.5: % fluoride biosorption for packed bed column

S.No t % Fluoride biosorption

(hrs.)
1 1 67.29604
2 2 58.32168
3 3 48.06527
4 4 35.71096
5 5 31.51515
6 6 31.01539
7 7 30.25698
8 8 30.07953
 35

Figure 4.5: % Fluoride biosorption for packed bed column

4.6 STATISTICAL OPTIMIZATION OF FLUORIDE BIOSORPTION USING

RESPONSE SURFACE METHODOLOGY

The design includes 30 sets of experimental conditions and their response were
measured in terms of % fluoride biosorption. Run 8 (initial fluoride concentration - 1
ppm, biosorbent dosage – 550 mg L-1 pH – 7, temperature – 45°C) showed maximum
fluoride biosorption efficiency of 96.52%. Run 12 (initial fluoride concentration – 5.5
ppm, biosorbent dosage – 550 mg L-1 pH – 12, temperature – 45°C) showed the lowest
% of fluoride biosorption. The design suggested a quadratic polynomial model for the
responses which was shown in the Table 4.6.1. The model was justified based on the
proximity of R2 value to 1.

The ANOVA results for the responses are given in Table 4.6.3. The model F-value of
12.65 and P-values less than 0.0500 indicate model terms are significant. In this case
A, B, C, D, B², C² are significant model terms (Bhaumik & Mondal, 2016) (Ghosh et
al., 2016). The plot between the actual and predicted values was displayed in the
Fig.4.6.1 and the contour plots describing the nature of interaction between the process
parameters are given in Figure 4.6.2 (a-f). Figure 4.6.2a shows that as the fluoride
 36

concentration and biomass dose increases, % fluoride biosorption also increases until
a state of equilibrium is achieved. Further increase in the above variables results in
decrease in biosorption efficiency. A similar relationship is obtained with initial
fluoride concentration and pH (Figure 4.6.2b). Figure 4.6.2c shows the interaction
between temperature and initial fluoride concentration. As temperature and fluoride
concentration increases, % biosorption also increases. pH and biosorbent dose directly
influence the biosorption upto a certain value after which a decrease in biosorption
efficiency was noticed (figure 4.6.2d). Figure 6e demonstrates the influence of
temperature and biosorbent dose on fluoride biosorption. pH and temperature should
be optimum to support maximum biosorption (Figure 4.6.2f). Based on the
perturbation graph constructed using the design expert software, the robust operating
conditions (initial fluoride concentration - 5.5 ppm, biosorbent dosage - 550 mg/L, pH
- 7, temperature - 45℃) of the process parameters for increased fluoride biosorption
were determined.

Table 4.6.1: Fit Summary for fluoride biosorption

Sequential p- Lack of Fit Predicted

Source Adjusted R²
value p-value R²
Linear 0.0483 0.0013 0.1978 0.0119
2FI 0.9875 0.0005 -0.0087 -0.4738
Quadratic < 0.0001 0.0865 0.8491 0.5616 Suggested
Cubic 0.0865 0.9345 Aliased

Table 4.6.2: Fit Statistics for fluoride biosorption

Std. Dev. 5.34 R² 0.9219

Mean 74.99 Adjusted R² 0.8491
C.V. % 7.12 Predicted R² 0.5616
Adequate
13.7261
Precision
 37

Table 4.6.3: ANOVA for Quadratic model for fluoride biosorption

Sum of Mean
Source df F-value p-value
Squares Square
Model 5050.65 14 360.76 12.65 < 0.0001 Significant
A-Initial
fluoride 569.53 1 569.53 19.98 0.0004
concentration
B-Biosorbent
241.49 1 241.49 8.47 0.0108
dosage
C-pH 610.07 1 610.07 21.40 0.0003
D-
144.64 1 144.64 5.07 0.0397
Temperature
AB 16.98 1 16.98 0.5958 0.4522
AC 0.0931 1 0.0931 0.0033 0.9552
AD 96.31 1 96.31 3.38 0.0860
BC 14.63 1 14.63 0.5132 0.4848
BD 36.42 1 36.42 1.28 0.2761
CD 0.5337 1 0.5337 0.0187 0.8930
A² 10.49 1 10.49 0.3680 0.5531
B² 1287.13 1 1287.13 45.15 < 0.0001
C² 2179.56 1 2179.56 76.45 < 0.0001
D² 44.51 1 44.51 1.56 0.2306
Residual 427.63 15 28.51
not
Lack of Fit 353.44 9 39.27 3.18 0.0865
significant
Pure Error 74.20 6 12.37
Cor Total 5478.29 29
 38

Figure 4.6.1: Comparison between the actual values and the predicted values of
RSM model for fluoride biosorption

Table 4.6.4: The actual and predicted values of RSM model for fluoride
biosorption

A: Initial B: C: D: % Fluoride % Fluoride

fluoride Biosorbe biosorption biosorption
Std concentration nt dosage pH Temperature
(Actual (Predicted
mg L-1 mg L-1 °C Value) values)
1 3.25 325 4.5 35 89.94 91.37

2 7.75 325 4.5 35 83.69 76.60

3 3.25 775 4.5 35 80.26 79.92

4 7.75 775 4.5 35 69.87 64.87

5 3.25 325 9.5 35 78.65 76.68

6 7.75 325 9.5 35 59.23 62.92

7 3.25 775 9.5 35 77.58 72.00

8 7.75 775 9.5 35 55.25 57.17

9 3.25 325 4.5 55 86.52 83.21

10 7.75 325 4.5 55 72.48 78.19

 39

11 3.25 775 4.5 55 80.45 76.89

12 7.75 775 4.5 55 70.25 70.77

13 3.25 325 9.5 55 59.24 65.21

14 7.75 325 9.5 55 62.32 61.21

15 3.25 775 9.5 55 60.03 65.67

16 7.75 775 9.5 55 61.89 60.57

17 1 550 7 45 96.52 96.71

18 10 550 7 45 75.69 76.82

19 5.5 100 7 45 70.36 68.03

20 5.5 1000 7 45 52.27 55.92

21 5.5 550 2 45 60.63 66.2

22 5.5 550 12 45 45.55 41.30

23 5.5 550 7 25 79.22 85.47

24 5.5 550 7 65 85.67 80.47

25 5.5 550 7 45 87.75 89.35

26 5.5 550 7 45 92.14 89.35

27 5.5 550 7 45 85.69 89.35

28 5.5 550 7 45 89.19 89.35

29 5.5 550 7 45 90.45 89.35

30 5.5 550 7 45 90.89 89.35

 40

Figure 4.6.2a: The effects of experimental parameters A (Initial fluoride

concentration) and B (Biosorbent dosage) on the fluoride biosorption

Figure 4.6.2b: The effects of experimental parameters A (Initial fluoride

concentration) and C (pH) on the fluoride biosorption
 41

Figure 4.6.2c: The effects of experimental parameters A (Initial fluoride

concentration) and D (Temperature) on the fluoride biosorption

Figure 4.6.2d: The effects of experimental parameters B (Biosorbent dosage)

and C (pH) on the fluoride biosorption
 42

Figure 4.6.2e: The effects of experimental parameters B (Biosorbent dosage)

and D (Temperature) on the fluoride biosorption

Figure 4.6.2f: The effects of experimental parameters C (pH) and D

(Temperature) on the fluoride biosorption
 43

4.7 CHARACTERIZATION OF BIOSORBENT USING FTIR, SEM AND EDX

ANALYSIS:

4.7.1 FTIR analysis of biosorbent:

FTIR analysis is used for studying the functional groups present on the biosorbent
surface that plays an important role in fluoride adsorption. The FTIR spectrum of
biosorbent before sorption shows distinct peak at 3421.72, 2106.27, 1643.35, 1402.25,
1332.81, 1224.80, 1074.35 and 536.21 cm−1 . The band at 3421.72 cm−1 represents
the presence of O-H stretching vibrations of alcoholic hydroxyl group. The bands at
1643 cm−1 and 1402.25 cm−1 may be attributed to the asymmetric and asymmetric
vibration of carboxyl group respectively (Mustapha et al., 2019). The band at 1074.35
cm−1 was due to the C-O-C vibration. After fluoride biosorption there was a shift in
the bands from 3421.72, 1643.35, 1402.25, 1224.80, 1074.35 and 536.21 cm−1 to
3427.51, 1521.84, 1400.32, 1230.58, 1033.85 and 414.70 cm−1. These shifts in the
bands after sorption indicates their involvement in fluoride adsorption. There is an
appearance of distinct peak at 1116.78 cm−1 after fluoride adsorption because of C-F
interactions which confirms the interaction of fluoride with the functional groups of
biosorbent (Annadurai et al., 2019). The result obtained implies that the fluoride
interacts with functional groups of biosorbent.
 44

Figure 4.7.1a: FTIR spectrum of biosorbent before adsorption

Figure 4.7.1a: FTIR spectrum of biosorbent before adsorption

4.7.2 SEM SS EDX analysis of biosorbents:

The SEM images obtained before and after sorption are shown in figure 4.7.2a and
4.7.2b. Figure 4.7.2a, before fluoride biosorption clearly displays the microporous
structure responsible for biosorption and after fluoride biosorption structural
modification of biosorbent takes place because of the deposition of fluoride on its
surface. On further analysis of biosorbent before and after fluoride sorption using EDX
showed a distinct peak of fluoride after biosorption (Mohan et al., 2012), which are
shown in the Fig. 4.7.2c and 4.7.2d .From this study it is confirmed fluoride is adsorbed
by the biosorbent.
 45

Figure 4.7.2a: SEM images of biosorbent before adsorption

Figure 4.7.2b: SEM images biosorbent after adsorption

 46

Figure 4.7.2c: EDX analysis of biosorbent before fluoride adsorption

Figure 4.7.2d: EDX analysis of biosorbent after fluoride adsorption

 47

CHAPTER 5

CONCLUSION

The biosorbent prepared using isolate1 showed highest fluoride biosorption when
compared to other isolates. The process parameters such as initial fluoride
concentration, biosorbent dosage, contact time, and temperature showed its influence
on fluoride biosorption. Immobilized biosorbent also showed better fluoride
biosorption efficiency. In batch and column studies there is fluoride removal of 95%
and 67% respectively. Fluoride biosorption was optimized using Response surface
methodology (RSM) and maximum fluoride biosorption of 96.52% was obtained at
the optimum condition (initial fluoride concentration - 1 ppm, biosorbent dosage - 550
mg L -1, pH - 7, temperature - 45°C). The biosorbents was characterized before and
after fluoride biosorption using FTIR, SEM and EDX analysis.
 48

CHAPTER 6

REFERENCE

1. Ali, I. (2014). Water Treatment by Adsorption Columns: Evaluation at Ground

Level. Separation & Purification Reviews, 43(3), 175–205.
https://doi.org/10.1080/15422119.2012.748671
2. Amin, F., Talpur, F. N., Balouch, A., Surhio, M. A., & Bhutto, M. A. (2015).
Biosorption of fluoride from aqueous solution by white—Rot fungus Pleurotus
eryngii ATCC 90888. Environmental Nanotechnology, Monitoring &
Management, 3, 30–37.
https://doi.org/10.1016/j.enmm.2014.11.003
3. Annadurai, S. T., Arivalagan, P., Sundaram, R., Mariappan, R., & Munusamy,
A. P. (2019). Batch and column approach on biosorption of fluoride from
aqueous medium using live, dead and various pretreated Aspergillus niger
(FS18) biomass. Surfaces and Interfaces, 15, 60–69.
4. Arlappa, N. (2013). Introduction. International Journal of Research &
Development of Health, 1, 97–102.
5. Artioli, Y. (2008). Adsorption. In S. E. Jørgensen & B. D. Fath (Eds.),
Encyclopedia of Ecology (pp. 60–65). Academic Press.
https://doi.org/10.1016/B978-008045405-4.00252-4
6. Ayenew, T. (2008). The distribution and hydrogeological controls of fluoride
in the groundwater of central Ethiopian rift and adjacent highlands.
Environmental Geology, 54, 1313–1324. https://doi.org/10.1007/s00254-007-
0914-4
7. Ben Amor, T., Kassem, M., Hajjaji, W., Jamoussi, F., Ben Amor, M., &
Hafiane, A. (2018). Study of Defluoridation of Water Using Natural Clay
Minerals. Clays and Clay Minerals, 66(6), 493–499.
https://doi.org/10.1346/CCMN.2018.064117
8. Bhatnagar, A., Kumar, E., & Sillanpää, M. (2011). Fluoride removal from
water by adsorption—A review. Chemical Engineering Journal, 171(3), 811–
840. https://doi.org/10.1016/j.cej.2011.05.028
9. Bhaumik, R., & Mondal, N. K. (2016). Optimizing adsorption of fluoride from
water by modified banana peel dust using response surface modelling
approach. Applied Water Science, 6(2), 115–135.
https://doi.org/10.1007/s13201-014-0211-9
 49

10. Bhaumik, R., Mondal, N. K., Das, B., Roy, P., Pal, K. C., Das, C., Baneerjee,
A., & Datta, J. kumar. (2012). Eggshell Powder as an Adsorbent for Removal
of Fluoride from Aqueous Solution: Equilibrium, Kinetic and Thermodynamic
Studies. E-Journal of Chemistry, 9(3), 1457–1480.
https://doi.org/10.1155/2012/790401
11. Boldaji, M. R., Mahvi, A. H., Dobaradaran, S., & Hosseini, S. S. (2009).
Evaluating the effectiveness of a hybrid sorbent resin in removing fluoride
from water. International Journal of Environmental Science & Technology,
6(4), 629–632.
https://doi.org/10.1007/BF03326103
12. Bouabidi, Z., El-Naas, M., & Zhang, Z. (2018). Immobilization of microbial
cells for the biotreatment of wastewater: A review. Environmental Chemistry
Letters, 17.
https://doi.org/10.1007/s10311-018-0795-7
13. Bumsted, H. E., & Wells, J. C. (1952). Spectrophotometric Method for
Determination of Fluoride Ion. Analytical Chemistry, 24(10), 1595–1597.
https://doi.org/10.1021/ac60070a019
14. Can, M. Y., Kaya, Y., & Algur, O. F. (2006). Response surface optimization
of the removal of nickel from aqueous solution by cone biomass of Pinus
sylvestris. Bioresource T*echnology, 97(14), 1761–1765.
https://doi.org/10.1016/j.biortech.2005.07.017
15. Chen, N., Zhang, Z., Feng, C., Li, M., Zhu, D., Chen, R., & Sugiura, N. (2010).
An excellent fluoride sorption behavior of ceramic adsorbent. Journal of
Hazardous Materials, 1–3(183), 460–465.
https://doi.org/10.1016/j.jhazmat.2010.07.046
16. Colla, V., Branca, T. A., Rosito, F., Lucca, C., Vivas, B. P., & Delmiro, V. M.
(2016). Sustainable Reverse Osmosis application for wastewater treatment in
the steel industry. Journal of Cleaner Production, C(130), 103–115.
https://doi.org/10.1016/j.jclepro.2015.09.025
17. Dan, S., & Chattree, A. (2018). Sorption of fluoride using chemically modified
Moringa oleifera leaves. Applied Water Science, 8(2), 76.
https://doi.org/10.1007/s13201-018-0718-6
18. Das, D., Jaya Sre Varshini, C., & Das, N. (2014). Recovery of lanthanum(III)
from aqueous solution using biosorbents of plant and animal origin: Batch and
column studies. Minerals Engineering, 69, 40–56.
https://doi.org/10.1016/j.mineng.2014.06.013
19. Duran, C., Ozdes, D., Gundogdu, A., & Senturk, H. B. (2011). Kinetics and
Isotherm Analysis of Basic Dyes Adsorption onto Almond Shell (Prunus
dulcis) as a Low Cost Adsorbent. Journal of Chemical & Engineering Data,
56(5), 2136–2147.
https://doi.org/10.1021/je101204j
20. Fuge, R. (1988). Sources of halogens in the environment, influences on human
and animal health. Environmental Geochemistry and Health, 10(2), 51–61.
https://doi.org/10.1007/BF01758592
21. Fuge, R., & Andrews, M. J. (1988). Fluorine in the UK environment.
Environmental Geochemistry and Health, 10(3–4), 96–104.
https://doi.org/10.1007/BF01758677
22. Ganvir, V., & Das, K. (2011). Removal of fluoride from drinking water using
 50

aluminum hydroxide coated rice husk ash. Journal of Hazardous Materials,

185(2–3), 1287–1294. https://doi.org/10.1016/j.jhazmat.2010.10.044
23. Gentili, F. G., & Fick, J. (2017). Algal cultivation in urban wastewater: An
efficient way to reduce pharmaceutical pollutants. Journal of Applied
Phycology, 29(1), 255–262.
https://doi.org/10.1007/s10811-016-0950-0
24. Ghosh, S., Bhaumik, R., & Mondal, N. (2016). Optimization study of
adsorption parameters for removal of fluoride using aluminium-impregnated
potato plant ash by response surface methodology. Clean Technologies and
Environmental Policy, 18.
https://doi.org/10.1007/s10098-016-1097-z
25. Gupta, S., Banerjee, S., Saha, R., Datta, J., Mondal, N., Burdwan, & India.
(2006). Fluoride geochemistry of groundwater in Nalhati-1 block of the
Birbhum district, West Bengal, India. Fluoride, 39.
26. Gupta, V. K., & Rastogi, A. (2008). Biosorption of lead(II) from aqueous
solutions by non-living algal biomass Oedogonium sp. And Nostoc sp.—A
comparative study. Colloids and Surfaces. B, Biointerfaces, 64(2), 170–178.
https://doi.org/10.1016/j.colsurfb.2008.01.019
27. He, J., Siah, T.-S., & Paul Chen, J. (2014). Performance of an optimized Zr-
based nanoparticle-embedded PSF blend hollow fiber membrane in treatment
of fluoride contaminated water. Water Research, 56, 88–97.
https://doi.org/10.1016/j.watres.2014.02.030
28. He, Z., Liu, R., Xu, J., Liu, H., & Qu, J. (2015). Defluoridation by Al-based
coagulation and adsorption: Species transformation of aluminum and fluoride.
Separation and Purification Technology, 148, 68–75.
https://doi.org/10.1016/j.seppur.2015.05.005
29. Hiremath, P., & Theodore, T. (2017). Biosorption of Fluoride from Synthetic
and Ground Water Biosorption of Fluoride from Synthetic and Ground Water
Using Chlorella vulgaris Immobilized in Calcium Alginate Beads in an Upflow
Packed Bed Column. Periodica Polytechnica Chemical Engineering, 61.
https://doi.org/10.3311/PPch.10085
30. Ho, Y. S., & McKay, G. (1998). A Comparison of Chemisorption Kinetic
Models Applied to Pollutant Removal on Various Sorbents. Process Safety and
Environmental Protection, 76(4), 332–340.
https://doi.org/10.1205/095758298529696
31. Ho, Y. S., & McKay, G. (1999). Pseudo-second order model for sorption
processes. Process Biochemistry, 34(5), 451–465.
https://doi.org/10.1016/S0032-9592(98)00112-5
32. Hussain, J., Hussain, I., & Sharma, K. C. (2010). Fluoride and health hazards:
Community perception in a fluorotic area of central Rajasthan (India): an arid
environment. Environmental Monitoring and Assessment, 162(1), 1–14.
https://doi.org/10.1007/s10661-009-0771-6
33. Jadhav, S. V., Marathe, K. V., & Rathod, V. K. (2016). A pilot scale concurrent
removal of fluoride, arsenic, sulfate and nitrate by using nanofiltration:
Competing ion interaction and modelling approach. Journal of Water Process
Engineering, C(13), 153–167.
https://doi.org/10.1016/j.jwpe.2016.04.008
34. Kanaujia, S., Singh, B., & Singh, S. (2015). Removal of Fluoride from
 51

Groundwater by Carbonised Punica granatum Carbon (“CPGC”) Bio-

Adsorbent. Journal of Geoscience and Environment Protection, 03, 1–9.
https://doi.org/10.4236/gep.2015.34001
35. Kapp, R. (2005). Fluorine. In P. Wexler (Ed.), Encyclopedia of Toxicology
(Second Edition) (pp. 343–346). Elsevier. https://doi.org/10.1016/B0-12-
369400-0/00420-8
36. Karthikeyan, M., Kumar, K. S., & Elango, K. P. (2011). Batch sorption studies
on the removal of fluoride ions from water using eco-friendly conducting
polymer/bio-polymer composites. Desalination, 267(1), 49–56.
37. Kebede, B., Beyene, A., Fufa, F., Megersa, M., & Behm, M. (2014).
Experimental evaluation of sorptive removal of fluoride from drinking water
using iron ore. Applied Water Science, 6, 57–65.
https://doi.org/10.1007/s13201-014-0210-x
38. Khan, S. U., Pratap, V., Uddin, M. K., & Farooqi, I. H. (2021). Chapter2—An
overview of conventional and advanced water defluoridation techniques. In M.
Hadi Dehghani, R. Karri, & E. Lima (Eds.), Green Technologies for the
Defluoridation of Water (pp. 17–40). Elsevier. https://doi.org/10.1016/B978-
0-323-85768-0.00008-7
39. Krishna, K. S. L. R., Yamuna, G., & Divya, P. (2018). Biosorption of
Fluoride from Aqueous Solutions Using Bacillus subtilis Biomass. Asian
Journal of Chemistry, 30(2), 427–433.
https://doi.org/10.14233/ajchem.2018.21082
40. Kumar, S., Gupta, A., & Yadav, J. P. (2008). Removal of fluoride by thermally
activated carbon prepared from neem (Azadirachta indica) and kikar (Acacia
arabica) leaves. Journal of Environmental Biology, 29(2), 227–232.
41. Lakshmi, U. R., Srivastava, V. C., Mall, I. D., & Lataye, D. H. (2009). Rice
husk ash as an effective adsorbent: Evaluation of adsorptive characteristics for
Indigo Carmine dye. Journal of Environmental Management, 90(2), 710–720.
https://doi.org/10.1016/j.jenvman.2008.01.002
42. Li, C., Chen, N., Zhao, Y., Li, R., & Feng, C. (2016). Polypyrrole-grafted
peanut shell biological carbon as a potential sorbent for fluoride removal:
Sorption capability and mechanism. Chemosphere, 163, 81–89.
https://doi.org/10.1016/j.chemosphere.2016.08.016
43. Ma, L., Wang, X., Tao, J., Feng, X., Liu, X., & Qin, W. (2017). Differential
fluoride tolerance between sulfur- and ferrous iron-grown Acidithiobacillus
ferrooxidans and its mechanism analysis. Biochemical Engineering Journal,
C(119), 59–66.
https://doi.org/10.1016/j.bej.2016.12.013
44. Markovski, J., Garcia, J., Hristovski, K., & Westerhoff, P. (2017). Nano-
enabling of strong-base ion-exchange media via a room-temperature aluminum
hydroxide synthesis method to simultaneously remove nitrate and fluoride.
Science of the Total Environment, 599–600, 1848–1855.
https://doi.org/10.1016/j.scitotenv.2017.05.083
45. Mason, B. H., & Moore, C. B. (1982). Principles of geochemistry. John Wiley
& Sons.
46. Meena, A. K., Mishra, G. K., Rai, P. K., Rajagopal, C., & Nagar, P. N. (2005).
Removal of heavy metal ions from aqueous solutions using carbon aerogel as
an adsorbent. Journal of Hazardous Materials, 122(1–2), 161–170.
 52

https://doi.org/10.1016/j.jhazmat.2005.03.024
47. Meenakshi, S., & Maheshwari, R. C. (2006). Fluoride in drinking water and its
removal. Journal of Hazardous Materials, 137(1), 456–463.
https://doi.org/10.1016/j.jhazmat.2006.02.024
48. Mereta, S. T. (2017). Biosorption of fluoride ion from water using the seeds of
the cabbage tree (Moringa stenopetala). African Journal of Environmental
Science and Technology, 11(1), 1–10. https://doi.org/10.4314/ajest.v11i1
49. Mihayo, D., Vegi, M. R., & Vuai, S. A. H. (2021). Defluoridation of aqueous
solution using raw and surface modified biosorbents prepared from adansonia
digitata fruit pericarp. Journal of Dispersion Science and Technology, 0(0), 1–
13.
https://doi.org/10.1080/01932691.2021.1880925
50. Mittal, Y., Srivastava, P., Kumar, N., & Yadav, A. K. (2020). Remediation of
fluoride contaminated water using encapsulated active growing blue-green
algae, Phormidium sp. Environmental Technology & Innovation, 19, 100855.
https://doi.org/10.1016/j.eti.2020.100855
51. Mobarak, M., Selim, A. Q., Mohamed, E. A., & Seliem, M. K. (2018).
Modification of organic matter-rich clay by a solution of cationic
surfactant/H2O2: A new product for fluoride adsorption from solutions.
Journal of Cleaner Production, 192, 712–721.
52. Mohammad, A. S., Azim, A., Mona, S., Bahman, M. S., Gigloo, S. H., Nemati,
H., & Dariush, N. (2013). Optimization of Penicillin G Acylase Immobilization
Process by Surface Response Methodology Using Central Composite Design.
Applied Mathematics, 04(01), 64–69. https://doi.org/10.4236/am.2013.41012
53. Mohan, D., Kumar, S., & Srivastava, A. (2014). Fluoride removal from ground
water using magnetic and nonmagnetic corn stover biochars. Ecological
Engineering, 73, 798–808. https://doi.org/10.1016/j.ecoleng.2014.08.017
54. Mohan, D., Sharma, R., Singh, V. K., Steele, P., & Pittman, C. U. (2012).
Fluoride Removal from Water using Bio-Char, a Green Waste, Low-Cost
Adsorbent: Equilibrium Uptake and Sorption Dynamics Modeling. Industrial
& Engineering Chemistry Research, 51(2), 900–914.
https://doi.org/10.1021/ie202189v
55. Mohan, S. V., & Karthikeyan, J. (2000). Removal of Diazo dye from aqueous
phase by algae Spirogyra species. Toxicological & Environmental Chemistry,
74(3–4), 147–154. https://doi.org/10.1080/02772240009358877
56. Mohan, S. V., Bhaskar, Y. v., & Karthikeyan, J. (2004). Biological
decolourisation of simulated azo dye in aqueous phase by algae Spirogyra
species. International Journal of Environment and Pollution, 21(3), 211–222.
https://doi.org/10.1504/IJEP.2004.004190
57. Mohan, S. V., Ramanaiah, S. V., Rajkumar, B., & Sarma, P. (2007).
Biosorption of Fluoride from Aqueous Phase onto Algal Spirogyra IO1 and
Evaluation of Adsorption Kinetics. Bioresource Technology, 98, 1006–1011.
https://doi.org/10.1016/j.biortech.2006.04.009
58. Mohapatra, M., Anand, S., Mishra, B. K., Giles, D. E., & Singh, P. (2009).
Review of fluoride removal from drinking water. Journal of Environmental
Management, 91(1), 67–77. https://doi.org/10.1016/j.jenvman.2009.08.015
59. Mondal, N. K. (2017). Natural Banana (Musa acuminate) Peel: An
Unconventional Adsorbent for Removal of Fluoride from Aqueous Solution
 53

through Batch Study. Water Conservation Science and Engineering, 1(4), 223–
232.
https://doi.org/10.1007/s41101-016-0015-x
60. Mondal, N., & Kundu, M. (2016). Biosorption of Fluoride from Aqueous
Solution Using Lichen and Its Ca-Pretreated Biomass. Water Conservation
Science and Engineering, 1. https://doi.org/10.1007/s41101-016-0009-8
61. Mukherjee, S., Sahu, P., & Halder, G. (2018). Comparative assessment of the
fluoride removal capability of immobilized and dead cells of Staphylococcus
lentus (KX941098) isolated from contaminated groundwater. Environmental
Progress & Sustainable Energy, 37(5), 1573–1586.
https://doi.org/10.1002/ep.12853
62. Mustapha, S., Shuaib, D. T., Ndamitso, M. M., Etsuyankpa, M. B., Sumaila,
A., Mohammed, U. M., & Nasirudeen, M. B. (2019). Adsorption isotherm,
kinetic and thermodynamic studies for the removal of Pb(II), Cd(II), Zn(II) and
Cu(II) ions from aqueous solutions using Albizia lebbeck pods. Applied Water
Science, 9(6), 142. https://doi.org/10.1007/s13201-019-1021-x
63. Ndiaye, P. I., Moulin, P., Dominguez, L., Millet, J. C., & Charbit, F. (2005).
Removal of fluoride from electronic industrial effluent by RO membrane
separation. Desalination, 173(1), 25–32.
https://doi.org/10.1016/j.desal.2004.07.042
64. Nigri, E. M., Bhatnagar, A., & Rocha, S. D. F. (2017). Thermal regeneration
process of bone char used in the fluoride removal from aqueous solution.
Journal of Cleaner Production, 142(Part 4), 3558–3570.
65. O’Donnell, T. A. (1975). The chemistry of fluorine. Pergamon Press.
66. Pandey, P., Pandey, M., & Sharma, R. (2012). Defluoridation of Water by a
Biomass: Tinospora cordifolia. Journal of Environmental Protection, 03, 610–
616.
https://doi.org/10.4236/jep.2012.37074
67. Ponikvar, M. (2008). Chapter 12—Exposure of Humans to Fluorine and Its
Assessment. In A. Tressaud (Ed.), Fluorine and Health (pp. 487–549).
Elsevier.
https://doi.org/10.1016/B978-0-444-53086-8.00012-6
68. Reimann, C., & Caritat, P. de. (2011). Chemical Elements in the Environment:
Factsheets for the Geochemist and Environmental Scientist. Springer.
69. Roy, S., Das, P., Sengupta, S., & Manna, S. (2017). Calcium impregnated
activated charcoal: Optimization and efficiency for the treatment of fluoride
containing solution in batch and fixed bed reactor. Process Safety and
Environmental Protection, 109, 18–29.
https://doi.org/10.1016/j.psep.2017.03.026
70. Sahu, J. N., Acharya, J., & Meikap, B. C. (2009). Response surface modeling
and optimization of chromium(VI) removal from aqueous solution using
Tamarind wood activated carbon in batch process. Journal of Hazardous
Materials, 172(2–3), 818–825. https://doi.org/10.1016/j.jhazmat.2009.07.075
71. Sandoval, M. A., Fuentes, R., Nava, J. L., & Rodríguez, I. (2014). Fluoride
removal from drinking water by electrocoagulation in a continuous filter press
reactor coupled to a flocculator and clarifier. Separation and Purification
Technology, Complete (134), 163–170.
https://doi.org/10.1016/j.seppur.2014.07.034
 54

72. Simate, G. S., & Ndlovu, S. (2015). The removal of heavy metals in a packed
bed column using immobilized cassava peel waste biomass. Journal of
Industrial and Engineering Chemistry, 21, 635–643.
https://doi.org/10.1016/j.jiec.2014.03.031
73. Singh, K., Lataye, D., & Wasewar, K. (2016). Removal of Fluoride from
Aqueous Solution by using Bael (Aegle Marmelos) Shell Activated Carbon:
Kinetic, Equilibrium and Thermodynamic study. Journal of Fluorine
Chemistry, 194.
https://doi.org/10.1016/j.jfluchem.2016.12.009
74. Sivasankar, V., Rajkumar, S., Murugesh, S., & Darchen, A. (2012). Tamarind
(Tamarindus indica) fruit shell carbon: A calcium-rich promising adsorbent for
fluoride removal from groundwater. Journal of Hazardous Materials, 225–
226, 164–172. https://doi.org/10.1016/j.jhazmat.2012.05.015
75. Tan, I. a. W., Ahmad, A. L., & Hameed, B. H. (2008). Adsorption of basic dye
on high-surface-area activated carbon prepared from coconut husk:
Equilibrium, kinetic and thermodynamic studies. Journal of Hazardous
Materials, 154(1–3), 337–346. https://doi.org/10.1016/j.jhazmat.2007.10.031
76. Thakre, D., Rayalu, S., Kawade, R., Meshram, S., Subrt, J., & Labhsetwar, N.
(2010). Magnesium incorporated bentonite clay for defluoridation of drinking
water. Journal of Hazardous Materials, 180(1–3), 122–130.
https://doi.org/10.1016/j.jhazmat.2010.04.001
77. Tirkey, P., Bhattacharya, T., & Chakraborty, S. (2017). Optimization of
fluoride removal from aqueous solution using Jamun (Syzygium cumini) leaf
ash.
https://doi.org/10.1016/J.PSEP.2017.10.022
78. Torres, E. (2020). Biosorption: A Review of the Latest Advances. Processes,
8(12), 1584. https://doi.org/10.3390/pr8121584
79. Tuzun, I., Bayramoglu, G., Yalcin, E., Başaran, G., Celik, G., & Arica, M. Y.
(2005). Equilibrium and kinetic studies on biosorption of Hg(II), Cd(II) and
Pb(II) ions onto microalgae Chlamydomonas reinhardtii. Journal of
Environmental Management, 77(2), 85–92.
https://doi.org/10.1016/j.jenvman.2005.01.028
80. UNEP (Ed.). (1984). Fluorine and fluorides. World Health Organization.
81. Valdez-Alegria, C. J., Fuentes-Rivas, R. M., Garcia-Rivas, J. L., Zavala Arce,
R. E., Jimenez Nunez, M. de la L., & Garcia-Gaitan, B. (2020). Synthesis of
Chitosan-Polyvinyl Alcohol Biopolymers to Eliminate Fluorides from Water.
Biomolecules, 10(1), E156. https://doi.org/10.3390/biom10010156
82. Vences-Alvarez, E., Velazquez-Jimenez, L. H., Chazaro-Ruiz, L. F., Diaz-
Flores, P. E., & Rangel-Mendez, J. R. (2015). Fluoride removal in water by a
hybrid adsorbent lanthanum-carbon. Journal of Colloid and Interface Science,
455, 194–202. https://doi.org/10.1016/j.jcis.2015.05.048
83. Vijayaraghavan, K., & Yun, Y.-S. (2008). Bacterial biosorbents and
biosorption. Biotechnology Advances, 26(3), 266–291.
https://doi.org/10.1016/j.biotechadv.2008.02.002
84. Wang, J., & Chen, C. (2006). Biosorption of heavy metals by Saccharomyces
cerevisiae: A review. Biotechnology Advances, 24(5), 427–451.
https://doi.org/10.1016/j.biotechadv.2006.03.001
85. Wang, J., Chen, N., Feng, C., & Li, M. (2018). Performance and mechanism
 55

of fluoride adsorption from groundwater by lanthanum-modified pomelo peel

biochar. Environmental Science and Pollution Research International, 25(16),
15326–15335. https://doi.org/10.1007/s11356-018-1727-6
86. Whitford, G. M., & Pashley, D. H. (1984). Fluoride absorption: The influence
of gastric acidity. Calcified Tissue International, 36(3), 302–307.
https://doi.org/10.1007/BF02405334
87. World Health Organization, & Safety I. P. on C. (1996). Guidelines for
drinking-water quality. Vol. 2, Health criteria and other supporting
information. World Health Organization.
https://apps.who.int/iris/handle/10665/38551
88. Yadav, A. K., Abbassi, R., Gupta, A., & Dadashzadeh, M. (2013). Removal of
fluoride from aqueous solution and groundwater by wheat straw, sawdust and
activated bagasse carbon of sugarcane. Ecological Engineering, 52, 211–218.
https://doi.org/10.1016/j.ecoleng.2012.12.069
89. Zaharia, C. (2015). Application of Waste Materials as ‘Low Cost’ Sorbents for
Industrial Effluent Treatment. A Comparative Overview. International Journal
of Materials and Product Technology, 50, 196–220.
https://doi.org/10.1504/IJMPT.2015.068524
90. Zarrabi, M., Noori sepehr, M., Amrollahi, M., & Taghavi, M. (2014).
Biosorption of fluoride by apple pulp from aqueous solution. Koomesh, 16,
213–219.
91. Zdunek, A., Kołodyńska, D., Borowik, K., & Rusek, P. (2019). The removal
of fluoride from aqueous solutions using biomass ash derived from power
industry. Desalination and Water Treastment, 159, 93–109.
https://doi.org/10.5004/dwt.2019.24429