Removal of arsenic(III) from aqueous solutions using fresh and immobilized plant biomass
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Transcript of Removal of arsenic(III) from aqueous solutions using fresh and immobilized plant biomass
ARTICLE IN PRESS
0043-1354/$ - se
doi:10.1016/j.w
�Correspondfax: +9140 716
E-mail add
(K.C. Sekhar).1Present add
Metallurgical R
500 058, India.
Water Research 39 (2005) 2815–2826
www.elsevier.com/locate/watres
Removal of arsenic(III) from aqueous solutions using freshand immobilized plant biomass
C.T. Kamalaa, K.H. Chub, N.S. Charya, P.K. Pandeyc, S.L. Rameshd,A.R.K. Sastrye, K.Chandra Sekhara,�,1
aAnalytical Chemistry and Environmental Sciences Division, Indian Institute of Chemical Technology, Uppal Road, Habsignda,
Hyderabad 500 007, AP, IndiabDepartment of Chemical and Process Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
cCenter for Environmental Science & Engineering, Department of Engineering Chemistry, Bhilai Institute of Technology, Durg, CG, IndiadGeochemistry Division, National Geophysical Research Institute, Hyderabad 500 007, AP, India
eOrganic Coatings and Polymers Division, Indian Institute of Chemical Technology, Hyderabad 500 007, AP, India
Received 23 June 2004; received in revised form 28 March 2005; accepted 26 April 2005
Available online 5 July 2005
Abstract
The ability of Garcinia cambogia, an indigenous plant found in many parts of India, to remove trivalent arsenic from
solution was assessed. Batch experiments were carried out to characterize the As(III) removal capability of fresh and
immobilized biomass of G. cambogia. It was found that the kinetic property and uptake capacity of fresh biomass were
significantly enhanced by the immobilization procedure. The uptake of As(III) by fresh and immobilized biomass was
not greatly affected by solution pH with optimal biosorption occurring at around pH 6–8. The presence of common
ions such as Ca and Mg at concentrations up to 100mg/l had no effect on As(III) removal. However, the presence of
Fe(III) at 100mg/l caused a noticeable drop in the extent of As(III) removal but the effect was minimal when Fe(III)
was present at 10mg/l. The adsorption isotherms quantitatively predicted the extent of As(III) removal in groundwater
samples collected from an arsenic-contaminated site in India. Immobilized biomass loaded with As(III) was amenable
to efficient regeneration with NaOH solution. Column studies showed that immobilized biomass could be reused over
five cycles of loading and elution. The excellent As(III) sequestering capability of fresh and immobilized G. cambogia
biomass could lead to the development of a viable and cost-effective technology for arsenic removal in groundwater.
r 2005 Elsevier Ltd. All rights reserved.
Keywords: Adsorption; Arsenic; Biosorption; Column; Immobilization; Plant biomass
e front matter r 2005 Elsevier Ltd. All rights reserve
atres.2005.04.059
ing author. Tel.:+91 40 27153884;
0387.
resses: [email protected], [email protected]
ress: Analytical Chemistry Group, Defense
esearch Laboratory, Kanchanbagh, Hyderabad
1. Introduction
Arsenic contamination in drinking water and ground-
water has created serious health problems in countries
like India and Bangladesh and in other parts of the
world (Das et al., 1996; Pandey et al., 2002; Chandra
Sekhar et al., 2003a; Wang and Wai, 2004). As a result,
extensive research has been focused on develop-
ing arsenic removal methods in recent times. The
d.
ARTICLE IN PRESS
Nomenclature
ARE absolute relative error
b Langmuir binding constant (l/mg)
Ce As(III) concentration of solution phase at
equilibrium (mg/l)
Ci initial As(III) concentration of solution
phase (mg/l)
IGCFIX immobilized Garcinia cambogia biomass
PR As(III) percent removal
PRexp experimental As(III) percent removal
PRcal calculated As(III) percent removal
qe As(III) concentration in the adsorbent phase
at equilibrium (mg/g)
qm maximum uptake capacity of the adsorbent
(mg/g)
w adsorbent dosage (g/l)
C.T. Kamala et al. / Water Research 39 (2005) 2815–28262816
conventional arsenic removal method is precipitation–
coagulation with lime and Fe(III) salts followed by
adsorption onto the resulting Fe(III) hydroxide flocs. A
problem with this technique is the separation and
handling of the hazardous sludge. Recently, adsorption
processes have attracted considerable attention owing to
their ability to treat aqueous solutions contaminated
with trace quantities of arsenic. Various adsorbent
materials have been tested for their ability to remove
the two inorganic arsenic species commonly found in
water; arsenite [As(III)] (Singh and Pant, 2004; Thir-
unavukkarasu et al., 2005) and arsenate [As(V)] (Xu et
al., 2002; Dousova et al., 2003; Rau et al., 2003; Zhang
et al., 2003; Genc--Fuhrman et al., 2004a; Vaishya and
Gupta, 2004). Simultaneous removal of both arsenic
species by adsorption has also been reported (Elizalde-
Gonzalez et al., 2001; Chakravarty et al., 2002;
Katsoyiannis and Zouboulis, 2002; DeMarco et al.,
2003; Zeng, 2003; Daus et al., 2004; Genc--Fuhrman et
al., 2004b; Kim et al., 2004). In general, As(III), which
exists predominantly as nonionic H3AsO3 in natural
waters, is more difficult to remove compared to As(V),
which exists predominantly as deprotonated oxyanions
H2AsO�4 or HAsO2�
4
� �(DeMarco et al., 2003). As a
result, some of the proposed arsenic removal methods
require a preoxidation step which oxidizes As(III) to
As(V) (Bissen and Frimmel, 2003). A literature review
on adsorption processes based on inorganic adsorbents
for arsenic removal is available elsewhere (Dambies,
2004).
Numerous biological materials have been tested for
removal of toxic ions from aqueous solutions over the
last two decades. However, only a limited number of
studies have investigated the use of adsorbents derived
from biological sources, e.g., chitosan (Mcafee et al.,
2001; Dambies et al., 2002), alginate (Zouboulis and
Katsoyiannis, 2002), orange waste (Ghimire et al., 2002,
2003), fungal biomass (Loukidou et al., 2003; Say et al.,
2003a, b), methylated yeast biomass (Seki et al., 2005),
and chicken feathers (Teixeira and Ciminelli, 2005), to
remove arsenic from aqueous solutions. Biological
materials represent a potential source of abundant,
low-cost adsorbents. This communication investigates
biosorption of As(III) by Garcinia cambogia, a yellowish
pumpkin shaped tropical tree fruit native to India.
Previous studies have demonstrated the effectiveness of
similar plant biomass in removing toxic ions from
aqueous solutions (Chandra Sekhar et al., 2003b, 2004).
Because most biological materials are fragile and have a
tendency to swell when wet, they are not suitable for use
in standard process equipment such as continuous-flow
column contactors which are often operated under high
pressure conditions. However, if the biomass is chemi-
cally reinforced or immobilized on a solid support, the
resulting product becomes useful for applications in
column contactors without causing operational pro-
blems such as clogging and pressure drop fluctuations.
One of the earliest examples of immobilized biomass is
the polymeric beads containing sphagnum peat moss or
algal biomass developed by the US Bureau of Mines.
The immobilized biomass exhibited excellent adsorption
capability for toxic ions including arsenic (Jeffers et al.,
1991). In this study, batch experiments were performed
to evaluate the adsorption characteristics of fresh and
immobilized G. cambogia biomass for As(III) in
synthetic solutions as well as actual groundwater
samples. Previous studies reported that the groundwater
samples examined in the current study contained
relatively high concentrations of As(III) (Pandey et al.,
2002; Chandra Sekhar et al., 2003a). Continuous-flow
experiments were then performed using a column
packed with immobilized biomass to evaluate As(III)
removal and recovery over multiple cycles of operation.
2. Materials and methods
2.1. Preparation of immobilized biomass
Immobilized G. cambogia biomass beads, designated
as IGCFIX, were prepared using a method developed by
Indian Institute of Chemical Technology. The dried fruit
rinds of G. cambogia were used. A wide range of bead
fabrication parameters were tested to identify factors
having the most significant effects on the chemical and
physical characteristics of immobilized biomass beads
(Jeffers et al., 1991). Variables investigated included the
concentration of biomass in bead, the solvent type, the
ARTICLE IN PRESSC.T. Kamala et al. / Water Research 39 (2005) 2815–2826 2817
composition and temperature of the polymerizing
media, and the bead curing time. The amount of raw
biomass in an optimized bead constituted 0.95 g per
gram of total bead weight. The polymerization was
performed at 2972 1C. Water was found to be the best
solvent and the bead curing time was set at 30min which
allowed biomass to become tack free. The average bead
size was about 1mm.
2.2. Batch studies
As(III) stock solutions were prepared by dissolving
NaAsO2 salt in deionized water. A known amount of
fresh biomass or IGCFIX was washed twice with 0.01M
HCl to remove any debris or soluble components that
might interact with As(III). Batch kinetic studies were
first conducted with fresh biomass or IGCFIX to
determine the time needed for the As(III) binding
process to reach the equilibrium state. Based on the
kinetic experiment results, all equilibrium experiments
were conducted for a period of 30min. Flasks contain-
ing fresh biomass or IGCFIX in 100ml As(III) solutions
were agitated in a mechanical shaker (Techno India Ltd)
at 300 rpm and 30 1C. Upon equilibration solution
samples were filtered and analyzed by GF-AAS for
As(III). The effects of process variables such as pH
(2–10), biomass dosage (5–40 g/l), initial As(III) con-
centration (50–2500mg/l), and background ions (Ca,
Mg, and Fe(III)) on As(III) uptake were investigated. In
addition, batch elution experiments were carried out to
desorb bound As(III) from IGCFIX using different
eluting agents such as HCl, HNO3, NaCl, Na2CO3, and
NaOH. Finally, water samples collected from the
groundwater of West Bengal and Chhathisgarh which
is believed to be contaminated with arsenic released by
natural processes and from the groundwater of Patan-
cheru which is believed to be contaminated with arsenic
discharged by industrial sources were treated with fresh
biomass or IGCFIX in batch experiments. The sam-
pling, preservation, and storage of groundwater samples
were carried out in accordance with the prescribed
methods which have been described in detail elsewhere
(Pandey et al., 2004).
2.3. Column studies
Experiments using a laboratory-scale column were
conducted to investigate As(III) removal by IGCFIX
under continuous-flow conditions, elution of the bound
As(III), and regeneration of IGCFIX for reuse. IGCFIX
beads were packed into a column having an internal
diameter of 1.6 cm and a column height of 20 cm.The
active height of the packed bed was 7 cm. An aqueous
solution containing 100mg/l As(III) was passed through
the column at a flow rate of 13.3ml/min. The pH of the
feed solution was continuously monitored and main-
tained constant by addition of 0.01M NH4OH or HCl.
Elution of the bound As(III) from IGCFIX was carried
out using an aqueous 0.05M NaOH solution at a flow
rate of 1ml/min. Eluted IGCFIX beads were washed
with deionized water for regeneration. Regenerated
IGCFIX beads were tested for As(III) uptake to
determine their reusability. Five cycles of As(III) loading
and elution were conducted.
2.4. Spectroscopic studies
In order to investigate the main functional groups
responsible for As(III) adsorption and the chemical
nature of the adsorbed arsenic, Fourier transform
infrared (FT-IR) and electron spectroscopy for chemical
analysis (ESCA) spectra of fresh biomass and IGCFIX
samples were obtained. Fresh biomass or IGCFIX was
first loaded with As(III) by contacting 1 g of biomass
with 100ml of a 1000mg/l As(III) solution at pH 6 for
30min. The As(III)-laden biomass was then collected by
filtration, washed with distilled water, and finally dried
in an oven. Additional fresh biomass and IGCFIX
beads were treated the same way except for the absence
of As(III). Infrared spectra of biomass samples were
recorded on a Nexus 670 FT-IR spectrometer (Thermo
Nicolet, USA). Disks of 150mg KBr containing 5mg of
finely ground powder of each sample were prepared for
the FT-IR analysis. ESCA spectra were acquired on a
Kratos/Shimadsu AXIS 165 system (Kratos Analytical,
UK). The X-ray source was Mg Ka radiation
(1253.6 eV) operated at 75W and 5mA. The instrument
was operated with a pass energy of 40 eV for high-
resolution scans.
3. Results and discussion
3.1. Spectroscopic observations
To better understand the involvement of main
functional groups in As(III) binding and the chemical
nature of the adsorbed arsenic, FT-IR and ESCA
spectra of fresh biomass and IGCFIX samples were
obtained. The resulting infrared spectra of fresh biomass
and IGCFIX gave similar results. Thus, only the spectra
of fresh biomass before and after As(III) adsorption are
shown in Fig. 1. The band assignments are given in
Table 1. As seen in Fig. 1, both spectra show the O–H
stretching region from 4000 to 2000 cm�1 and the
fingerprint region from 2000 to 1200 cm�1. For pristine
biomass the band at 1626 cm�1 can be ascribed to the
asymmetrical C¼O stretching of the carboxyl group
while the band at 1737 cm�1 is probably due to the
vibration of C¼O of the ester group. The latter C¼O
band at 1737 cm�1 was invisible on the spectrum of
As(III)-loaded biomass. Another noticeable change is
ARTICLE IN PRESS
Table 1
Assignments of infrared absorption bands for pristine and
As(III)-loaded biomass samples
Wavenumber (cm�1) Assignment
Pristine biomass As(III)-loaded biomass
3427 3417 O–H stretching
1737 – C¼O stretching
1626 1602 C¼O stretching
– 1429 C¼O stretching
Band assignments were made according to Lewis and Neela-
kantan (1965).
3417
.32
2922
.65
1602
.88
1429
.85
1265
.33
1104
.39
803.
90 603.
85
483.
2652
3.91
1066
.32
1212
.20
1626
.85
1737
.88
2925
.69
3427
.48
80
86
92
98
75
85
95
80
90
5001000150020003000
3417
.32
2922
.65
1602
.88
1429
.85
1265
.33
1104
.39
803.
90 603.
85
483.
2652
3.91
1066
.32
1212
.20
1626
.85
1737
.88
2925
.69
3427
.48
% T
rans
mitt
ance
% T
rans
mitt
ance
(a)
(b) Wavenumber (cm-1)
Fig 1. FT-IR spectra of (a) fresh biomass of G. cambogia and (b) As(III)-loaded biomass of G. cambogia.
C.T. Kamala et al. / Water Research 39 (2005) 2815–28262818
that the C¼O vibration band at 1626 cm�1 observed for
the spectrum of pristine biomass shifted to 1602 cm�1
with a different magnitude for As(III)-loaded biomass.
Furthermore, the spectrum of As(III)-loaded biomass
displayed a peak at 1429 cm�1 which can be ascribed to
the symmetrical C¼O stretching of the carboxyl group.
These band changes indicate the carboxyl group
involvement in As(III) adsorption, probably through
chelation/complexation. Carboxyl group is a character-
istic group of hydroxycitric acid which is the principal
organic acid found in G. cambogia (Jena et al., 2002).
Hydroxycitric acid has a chemical structure similar to
that of citric acid. It has been shown that As(III) was
able to reduce citric acid content in citrus fruit although
the exact interaction mechanism has not been elucidated
(Sadka et al., 2000). It is postulated that the carboxyl
group of hydroxycitric acid was involved in As(III)
binding through chelation/complexation. ESCA is a
spectroscopic technique for chemical analysis of surfaces
and can provide information about the oxidation states
of an element. The overall ESCA spectrum for a sample
of As(III)-loaded biomass is shown in Fig. 2a. An
enlargement of the As(3d) binding energy region from
Fig. 2a is shown in Fig. 2b. It is evident that the As(3d)
peak position for the As(III)-loaded biomass sample
strongly correlates with the presence of an As(III)
surface species.
3.2. Batch studies
3.2.1. Kinetics of As(III) removal
Batch kinetic experiments were performed to deter-
mine the time required for the As(III) binding process to
reach equilibrium. Fig. 3 shows time profiles for As(III)
removal by the two types of biomass in batch systems
maintained at pH 6 and containing an aqueous 100mg/l
As(III) solution and 5 g/l biosorbent. It can be seen that
As(III) binding by fresh biomass reached equilibrium
after a contact time of �30min, yielding a maximum
removal of 90%. In contrast, equilibrium was reached
within 5min of contact in the case of IGCFIX. A
removal level of �100% was observed which remained
stable up to a contact time of 60min, after which it
decreased marginally following another 60min of
contact. The rapid binding of As(III) by IGCFIX
suggests that most of the As(III) binding sites of G.
cambogia cell walls are located on the exterior surfaces
of the beads, thereby eliminating intraparticle diffusion
which is a relatively slow rate process. The slower
binding kinetics exhibited by fresh biomass implies that
intracellular diffusion within the cell wall structure could
be a rate limiting step. The cell wall structure was
presumably destroyed by the immobilization procedure,
enabling immobilized biomass to exhibit faster uptake
ARTICLE IN PRESS
Fig. 2. (a) ESCA spectrum of As(III)-loaded biomass of G.
cambogia. (b) An enlargement of the As(3d) binding energy
region.
50
60
70
80
90
100
0 20 40 60 80 100 120 140Time (min)
As(
III)
perc
ent
rem
oval
Fresh biomassImmobilized biomass
Fig. 3. Time profiles for As(III) removal by fresh and
immobilized biomass.
50
60
70
80
90
100
0 42 6 8 10pH
As(
III)
perc
ent r
emov
al
Fresh biomassImmobilized biomass
Fig. 4. Effect of pH on As(III) removal by fresh and
immobilized biomass.
C.T. Kamala et al. / Water Research 39 (2005) 2815–2826 2819
kinetics. Based on the kinetic results presented in Fig. 3,
a contact time of 30min was selected for all subsequent
batch uptake experiments with either fresh biomass or
IGCFIX in order to ensure that equilibrium was
established in each case.
3.2.2. Effect of pH
Experimental results showing As(III) removal at
varying pH (2–10) are presented in Fig. 4. The figure
clearly shows that both types of biomass exhibited
maximum As(III) removal from batch systems contain-
ing an aqueous 100mg/l As(III) solution and 5 g/1
biosorbent within the pH range of 6–8. As(III) removal
was insensitive to pH variations within this range. This
finding indicates that fresh biomass or IGCFIX would
perform optimally in treating As(III)-contaminated
drinking water or groundwater whose pH values
typically fall within the same range. The relative
distribution of dissolved arsenic species (As(III) and
As(V)) is influenced by pH and the redox condition.
Under mildly reducing conditions and at pH below 9,
As(III) exists predominantly as H3AsO3 (DeMarco et
al., 2003). It may be inferred that G. cambogia biomass is
capable of binding nonionic H3AsO3 within the typical
pH range of natural waters (pH 6–8).
3.2.3. Effect of biosorbent dosage
The extent of As(III) removal as a function of fresh
biomass or IGCFIX dosage (5–40 g/l) in batch systems
maintained at pH 6 and containing an aqueous 100mg/l
As(III) solution was studied. The results are presented in
Fig. 5. The percent removal of As(III) increased from 90
to �100% when the dosage of fresh biomass was
increased from 5 to 40 g/l.When the initial As(III)
concentration and the volume of solution are fixed, the
fraction of As(III) removed from a batch contactor will
increase with increasing biosorbent dosage. The trend
displayed by fresh biomass is therefore expected when
the percent removal of As(III) is less than 100%. The
percent removal of a given biosorbent dosage may be
predicted from the adsorption equilibrium isotherm, as
will be discussed later. An increasing trend of percent
removal was not observed in the case of IGCFIX
because the lowest dosage of IGCFIX tested (5 g/l) was
ARTICLE IN PRESS
50
60
70
80
90
100
0 500 1000 1500 2000 2500
As(
III)
perc
ent
rem
oval
.
Fresh biomassImmobilized biomass
Initial As(III) concentration (mg/l)
Fig. 6. Effect of initial concentration on As(III) removal by
fresh and immobilized biomass.
50
60
70
80
90
100
0 10 20 30 40
As(
III)
perc
ent
rem
oval
Fresh biomassImmobilized biomass
Biosorbent dosage (g/l)
Fig. 5. Effect of biosorbent dosage on As(III) removal by fresh
and immobilized biomass.
C.T. Kamala et al. / Water Research 39 (2005) 2815–28262820
able to remove virtually all the As(III) present in the
batch system. It is obvious that further increase in
IGCFIX dosage will have no effect on the percent
removal of As(III). No noticeable As(III) removal
was observed in similar experiments using beads
made from the immobilization material only, indicating
that As(III) uptake can be attributed entirely to G.
cambogia biomass contained within immobilized bio-
mass beads. The practically important conclusion from
Fig. 5 is that immobilized biomass can easily outperform
fresh biomass, requiring a much lower biosorbent
dosage to achieve quantitative removal of As(III). The
immobilization procedure has not resulted in any
adverse effects on the As(III) uptake capability of G.
cambogia biomass. On the contrary, it appears to
enhance As(III) binding, presumably by exposing
previously inaccessible binding sites in fresh biomass
to As(III) or creating new binding sites having an
affinity for As(III).
3.2.4. Effect of initial As(III) concentration
The effect of initial As(III) concentration on the
extent of removal is shown in Fig. 6. The biosorbent
dosage and pH for these batch experiments were fixed at
5 g/l and pH 6. As expected, increasing the initial As(III)
concentration while keeping the other conditions con-
stant in a batch system resulted in decreasing percent
removal. In the experiments with fresh biomass percent
removal dropped rapidly from about 95 to 58% when
the initial As(III) concentration was increased from 50
to 1000mg/l. In contrast, IGCFIX exhibited a relatively
slow reduction in percent removal over a much larger
initial As(III) concentration range; at the maximum
initial As(III) concentration tested (2500mg/l), the
percent removal of As(III) remained at about 92%.
The results in Fig. 6 confirm that the As(III) uptake
capacity of IGCFIX is significantly larger than that of
fresh biomass.
3.2.5. Adsorption isotherms
The observed effects of biosorbent dosage and initial
As(III) concentration described above indicate that
IGCFIX can easily outperform fresh biomass with
regard to As(III) removal. A more systematic and
quantitative way of judging and comparing adsorbent
performance is through adsorption isotherm analysis.
When equilibrium is established in a batch adsorption
system, the adsorbate concentration in the adsorbent
phase is given by the following mass balance equation:
qe ¼ qi þCi � Ceð Þ
w, (1)
where qe (mg/g) and Ce (mg/l) are the adsorbate
concentration in the adsorbent and solution phase at
equilibrium, qi (mg/g) and Ci (mg/l) are the initial
adsorbate concentration in the adsorbent and solution
phase, and w (g/l) is the adsorbent dosage. Experimen-
tally generated qe vs. Ce equilibrium data are used to
construct the adsorption isotherm graphically which can
be modeled in terms of isotherm models such as the
simple Langmuir and Freundlich equations.
For liquid-phase adsorption systems containing a
single adsorbate, the adsorption isotherm is a function
of environmental factors such as pH, ionic strength, and
temperature. Once these factors are fixed, the adsorption
isotherm is, in principle, independent of the experi-
mental conditions employed to measure it. In other
words, a unique isotherm can be generated by using any
convenient measurement method (batch or continuous-
flow) and by varying either w or Ci. Adsorption
isotherms for As (III) on fresh biomass and IGCFIX
may thus be constructed from the equilibrium data
shown in Figs. 5 and 6 which have been generated by
varying w and Ci. In the case of IGCFIX, adsorption
isotherm cannot be constructed from the equilibrium
data of Fig. 5 because the percent removal of As(III)
was �100% in all cases. On the other hand, the
ARTICLE IN PRESSC.T. Kamala et al. / Water Research 39 (2005) 2815–2826 2821
equilibrium data of Fig. 6 indicate that appreciable
amounts of As(III) were still present in solution at
equilibrium (percent removalo100%). For fresh bio-
mass, adsorption isotherm can be constructed from the
equilibrium data of either Fig. 5 or Fig. 6 because the
percent removal of As(III) in most cases was o100%. It
was decided to use the equilibrium data of Fig. 6 to
construct adsorption isotherms for As(III) on the two
types of biomass.
The percent removal of As(III) (PR) is given by
PR ¼ 100Ci � Ce
Ci
� �. (2)
Combining Eqs. (1) and (2) yields
qe ¼Ci
w
PR
100. (3)
Values of qe estimated from the percent removal data of
Fig. 6 using Eq. (3) are plotted against the correspond-
ing Ce values for each type of biomass, as shown in
Fig. 7. It can be seen that the shape of the two
adsorption isotherms is convex. Notice the different
scales on the y-axis of Figs. 7a and b. It is evident that
0
20
40
60
80
100
120
0 100 200 300 400 500
0
100
200
300
400
500
0 50 100 150 200 250 300
Fresh biomass
Immobilized biomass
Ce (mg/l)
Ce (mg/l)
q e (m
g/g)
q e (m
g/g)
(a)
(b)
Fig. 7. Equilibrium data of As(III) uptake by (a) fresh biomass
and (b) immobilized biomass fitted with the Langmuir model.
IGCFIX is superior to fresh biomass in binding As(III)
over the entire range of solution phase equilibrium
concentration tested. For example, at Ce ¼ 10mg/l, the
uptake capacity of IGCFIX is about five times that of
fresh biomass while at Ce ¼ 200mg/l the IGCFIX to
fresh biomass uptake capacity ratio climbs to about 7.
This means that a much smaller amount of IGCFIX is
needed compared to fresh biomass to remove a given
amount of As(III).
The experimental adsorption isotherms shown in Fig. 7
can be expressed in terms of mathematical models.
Because the shape of the two isotherms conforms to
the convex type, the simple Langmuir model with two
adjustable parameters is expected to provide a good fit
to the experimental data. The Langmuir model is
qe ¼ qmbCe
1þ bCe, (4)
where qm is the maximum or saturation uptake capacity
of the adsorbent (mg/g) and b (l/mg) is a binding
constant that reflects the slope of the isotherm in the low
solution phase equilibrium concentration range. Eq. (4)
predicts that the equilibrium uptake of an adsorbent
increases with increasing solution phase equilibrium
concentration, finally leveling off at qm as the Ce term in
the denominator becomes dominant. Eq. (4) was fitted
to the isotherm data in Fig. 7 by a nonlinear regression
analysis to obtain the parameters qm and b. The best-fit
values of the parameters together with the R2 values are
listed in Table 2. The isotherm simulations from the
Langmuir equation are shown as lines in Fig. 7. Both the
simulations and R2 values suggest that very good
agreement was obtained with the experimental isotherm
data.
In addition to comparing biosorbent performance,
adsorption isotherms are useful for designing and
analyzing adsorption processes. The design/performance
equation of a batch adsorption system obeying the
Langmuir model can be derived by combining Eqs. (1),
(2), and (4). The resulting equation is given below:
PR ¼ 100 1�� 1
b� Ci þ qmw
� �þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1b� C i þ qmw
� �2þ 4
Cib
q2Ci
0@
1A.
(5)
In this study the criterion for measuring the predictive
capability of Eq. (5) is the absolute relative error (ARE)
Table 2
Estimation of qm and b by nonlinear regression
Qm (mg/l) b (l/mg) R2
Fresh biomass 128.10 0.011 0.971
Immobilized biomass 704.11 0.008 0.965
ARTICLE IN PRESS
Table 3
Absolute relative errors (AREs) in Eq. (5)’s estimates of the
percent removal data of Fig. 5
Experimental conditions ARE (%)
Ci (mg/l) w (g/l)
Fresh biomass 100 5 4.7
100 10 0.1
100 20 1.4
100 40 1.8
Immobilized biomass 100 5 3.5
100 10 1.8
100 20 0.9
100 40 0.4
70
80
90
100
10 25 50 100
As(
III)
perc
ent r
emov
al
Ca Mg Fe(III)
Initial concentration (mg/l)
Fig. 8. Effect of Ca, Mg, and Fe(III) on As(III) removal by
immobilized biomass.
C.T. Kamala et al. / Water Research 39 (2005) 2815–28262822
as defined in the following equation:
ARE ¼ 100PRexp � PRcal
PRexp
��������, (6)
where PRexp and PRcal denote experimental and
calculated percent removal. Table 3 shows AREs in
Eq. (5)’s estimates of the percent removal data of Fig. 5.
The calculations are based on the qm and b estimates
listed in Table 2. Note that the equilibrium data of Fig. 5
were not used to estimate qm and b in the nonlinear
curve-fitting exercise. For both types of biomass, the
predicted values of percent removal are very close to the
experimental values. The small AREs (maximum
AREo5%) are indicative of the good quality of these
predictions.
3.2.6. Effect of background ions
Ionic species such as Ca, Mg, and Fe are usually
present in drinking water and groundwater contami-
nated with arsenic (Smedley and Kinniburgh, 2002).
These ions may interfere in the uptake of arsenic by
adsorbent through competitive binding or complexa-
tion. Batch equilibrium experiments were conducted to
evaluate the influence of Ca, Mg, and Fe(III) on As(III)
removal by IGCFIX. Fig. 8 displays As(III) removal
obtained from experiments with Ci ¼ 10mg/l and
w ¼ 5 g/l at several initial concentrations of Ca, Mg,
and Fe(III). The bars in Fig. 8 denote the extent of
As(III) removal as a percentage of the original removal
when no background ions were present in solutions
containing As(III) (original percent removal ¼ �100%).
Within the initial concentration range of 10–100mg/l,
Ca and Mg had no noticeable effect on As(III) removal
by IGCFIX. On the other hand, when both As(III) and
Fe(III) were present in solution, As(III) removal
decreased with increasing Fe(III) concentration. The
presence of Fe(III) at an initial concentration of 10mg/l
reduced the original percent removal slightly, by about
3%. Increasing the initial Fe(III) concentration to
100mg/l caused the percent removal of As(III) to drop
to about 85%. From a practical standpoint, the
detrimental effect of Fe(III) on As(III) removal would
not pose much of a problem because the iron contents of
natural waters are usually much lower than 100mg/l.
As has been discussed earlier, based on the evidence
from the FT-IR analysis it is postulated that As(III)
removal is due to chelation/complexation by the
carboxyl groups of G. cambogia biomass. A previous
study has shown that carboxyl groups present in a
seaweed biosorbent participated in the uptake of Fe(III)
ions by chelation (Figueira et al., 1999). Furthermore,
citrate readily forms complexes with Fe(III) (Hug et al.,
1997). As pointed out earlier, hydroxycitric acid, which
has a chemical structure similar to that of citric acid, is
the major organic acid found in G. cambogia. Reduction
of As(III) removal in the presence of Fe(III) may thus be
attributed to competition between As(III) and Fe(III)
for the same carboxyl sites on hydroxycitric acid. Since
Ca and Mg are able to bind to carboxyl sites through ion
exchange, they can in principle compete with As(III) for
the same carboxyl sites on G. cambogia biomass.
However, the results in Fig. 8 suggest that Ca and Mg
compete weakly with As(III) which interacts with
carboxyl sites through chelation/complexation.
3.2.7. Removal of arsenic in groundwater samples
Batch equilibrium experiments were conducted to
assess the ability of fresh biomass and IGCFIX to
remove As(III) in groundwater samples collected from
three arsenic-contaminated sites in India. A biosorbent
dosage of 5 g/l was used in all batch tests. A series of
groundwater samples collected from the West Bengal
area (Das et al., 1996), the industrial region of
Patancheru near Hyderabad (Chandra Sekhar et al.,
2003a), and the state of Chhathisgarh (Pandey et al.,
2002) were analyzed for their As(III), As(V), and iron
contents. The results are tabulated in Table 4. It can be
seen that As(III) concentration ranges from a minimum
ARTICLE IN PRESSC.T. Kamala et al. / Water Research 39 (2005) 2815–2826 2823
of 1.1mg/l to a maximum of 7.9mg/l. Table 5 compares
measured and predicted values of As(III) percent
removal for the two types of biomass. The predicted
values were calculated using the qm and b estimates listed
in Table 2. Under the experimental conditions em-
ployed, almost quantitative removal of As(III) by
IGCFIX was observed in all cases. The predicted
percent removal values are in good agreement with the
measured values. In the case of fresh biomass, the extent
of As(III) removal is about 75% for the five ground-
water samples collected from the West Bengal and
Patancheru areas. The fresh biomass performed better in
removing As(III) in the four groundwater samples
collected from the Chhathisgarh region, yielding
87–90% removal. Interestingly, the predicted values of
percent removal are very close to the measured values
for the Chhathisgarh samples ðARE ¼ 0:422:6%Þ but
are noticeably higher than the measured values for the
Table 4
Arsenic and iron contents of groundwater samples collected
from three regions in India known to suffer from arsenic
contamination
Sampling site Sample
number
As(III)
(mg/l)
As(V)
(mg/l)
Fe
(mg/l)
West bengal W1 7.9 17.4 3.8
W2 6.2 19.8 6.2
Patancheru P1 3.3 4.0 0.3
P2 1.1 2.1 1.8
P3 1.9 2.1 4.1
Chhathisgarh C1 1.9 7.2 2.6
C2 1.1 4.2 2.9
C3 3.4 11.1 3.2
C4 2.0 6.0 4.1
Table 5
Measured and predicted values of As(III) percent removal for ground
Sample number Ci (mg/l) Fresh biomass
Percent removal
Measured Predicted
W1 7.9 73.6 87.5
W2 6.2 75.1 87.5
P1 3.3 73.9 87.5
P2 1.1 74.3 87.6
P3 1.9 75.7 87.5
C1 1.9 89.9 87.5
C2 1.1 88.5 87.6
C3 3.4 87.2 87.5
C4 2.0 89.0 87.5
samples collected from the other two areas
ðARE ¼ 15:6218:8%Þ.
The excellent agreement between the measured and
predicted values of As(III) removal suggests that As(III)
removal in groundwater of Chhathisgarh under field
conditions can be predicted with confidence using the
best-fit qm and b values for the two types of biomass
estimated under laboratory conditions. The deviations
between model predictions and measured values of
percent removal for the groundwater samples of West
Bengal and Patancheru are open to two interpretations.
First, the presence of As(V) species or iron in the
samples may have suppressed As(III) removal, and
second, the lower than expected As(III) removal may be
due to interfering effects of some unidentified chemical
species. The former is not likely to be the main reason
because similar levels of As(V) were also present in the
Chhathisgarh samples and the concentration range of
iron, as shown in Table 4 (0.3–6.2mg/l), was too low to
exert any significant effect on As(III) removal. It is
therefore plausible that the lower than expected As(III)
removal by fresh biomass may be due to the presence of
some chemical species that can either compete with
As(III) for carboxyl sites or impede As(III) uptake. Such
negative effects are much less pronounced or nondetect-
able in the case of IGCFIX owing to its significantly
larger As(III) uptake capacity compared with fresh
biomass. Work is currently underway to identify the
various chemical species present in the groundwater
samples examined in this study and to assess the ability
of fresh biomass and IGCFIX to remove As(V) species.
These results will be reported in future communications.
3.2.8. Elution tests
One of the objectives of biomass immobilization is to
enhance the reusability of the resulting immobilized
water samples treated with fresh biomass and IGCFIX
Immobilized biomass
ARE (%) Percent removal ARE (%)
Measured Predicted
18.8 �100 96.6 3.4
16.5 �100 96.6 3.4
18.4 �100 96.6 3.4
17.8 �100 96.6 3.4
15.6 �100 96.6 3.4
2.6 �100 96.6 3.4
1.1 �100 96.6 3.4
0.4 �100 96.6 3.4
1.6 �100 96.6 3.4
ARTICLE IN PRESS
40
60
80
100
0.025 0.05 0.1 0.2
As(
III)
perc
ent e
lute
d
HCl
HNO3
NaCl
Na2CO3
NaOH
Concentration (M)
0.15
Fig. 9. Elution of bound As(III) from immobilized biomass
using various eluting agents.
C.T. Kamala et al. / Water Research 39 (2005) 2815–28262824
biomass. Reusing immobilized biomass requires that the
bound species be eluted from the biomass. Preliminary
elution tests were conducted using the batch technique
to select an eluting agent that could desorb all the bound
As(III) from IGCFIX. Reusability was assessed using a
packed column set-up described below. IGCFIX beads
were first loaded with As(III) in batch uptake experi-
ments. Batch elution experiments were then carried out
to desorb the bound As(III) from IGCFIX using five
different eluting agents, namely, HCl, HNO3, NaCl,
Na2CO3, and NaOH at a range of concentrations. The
batch elution results are shown in Fig. 9. It is evident
that the two mineral acids, HCl and HNO3, performed
poorly over the range of concentration tested. On the
other hand, close to complete elution of the bound
As(III) could be achieved using 0.2M NaCl, 0.1M
Na2CO3 or 0.05M NaOH. Since high concentrations of
eluting agent may have an adverse effect on reusability,
it was decided to employ 0.05M NaOH for further
testing using a column packed with IGCFIX under
continuous-flow conditions.
4. Column studies
Full-scale adsorption processes are often operated
using continuous-flow fixed-bed columns. Adsorbents
possessing strong mechanical strength and durability are
required for column application in order to avoid
operational problems such as clogging and pressure
drop fluctuations. For this reason, fresh G. cambogia
biomass has been immobilized in a solid matrix to
enhance its mechanical strength. To be viable for
practical application, immobilized biomass should retain
its uptake capacity over multiple cycles of use. In this
study five cycles of As(III) loading and elution were
conducted using a laboratory-scale column packed with
IGCFIX beads. Each cycle consisted of loading with an
aqueous As(III) solution (Ci ¼ 100mg/l) and elution of
the bound As(III) with 0.05M NaOH. In each cycle,
loading was terminated before As(III) breakthrough
occurred at the column exit. The amount of As(III)
loaded onto the column was estimated from the known
amount of As(III) solution applied. Similarly, the
amount of As(III) eluted was estimated from the known
amount of NaOH solution used in the elution step.
Comparison of the amount of As(III) loaded and eluted
within each cycle indicates that As(III) could be
recovered quantitatively in each cycle under continu-
ous-flow conditions. These preliminary experiments
demonstrate that IGCFIX was compatible with column
operation.
5. Conclusion
In this study we have demonstrated the ability of G.
cambogia to remove As(III) in synthetic solutions as well
as groundwater samples collected from arsenic-contami-
nated sites in India. The following specific onclusions
were reached:
�
FT-IR results indicated that carboxyl groups werethe main sites responsible for As(III) binding on G.
cambogia biomass. The carboxyl groups would be
mainly those present in hydroxycitric acid which is
the principal organic acid found in G. cambogia.
�
The immobilized form of biomass showed excellentAs(III) sequestering capabilities compared with fresh
biomass. It was demonstrated that the immobiliza-
tion method enhanced the kinetic property as well as
the equilibrium uptake capacity of fresh biomass.
�
The extent of As(III) removal by fresh and immobi-lized biomass was insensitive to the solution pH. The
pH range of 6–8 was found to provide optimum
As(III) removal. The presence of background ions
such as Ca and Mg at concentrations up to 100mg/l
and Fe(III) at 10mg/l had no significant effect on
As(III) removal.
�
The effects of adsorbent dosage and initial As(III)concentration on As(III) uptake by fresh and
immobilized biomass were characterized using the
batch procedure and the resulting equilibrium data
quantified and validated in terms of the Langmuir
isotherm model. Adsorption isotherms derived under
these laboratory conditions were shown to be a useful
tool for predicting the extent of As(III) removal in
groundwater samples collected from a site contami-
nated with arsenic.
�
Batch elution tests revealed that close to completeelution of bound As(III) from immobilized biomass
could be achieved using aqueous solutions of NaCl,
Na2CO3, or NaOH. Of the three eluting agents,
NaOH appeared to be the most desirable, requiring
ARTICLE IN PRESSC.T. Kamala et al. / Water Research 39 (2005) 2815–2826 2825
the lowest solution strength to achieve complete
elution.
�
Fixed-bed column studies demonstrated the robust-ness of immobilized biomass in five cycles of As(III)
loading and elution. It was established that 0.05M
NaOH could be used to elute bound As(III) without
causing any damage to the uptake capacity of
immobilized biomass.
Acknowledgements
Dr. K.V. Raghavan, Director, Indian Institute of
Chemical Technology (IICT), and Dr. V. Balaram,
Head, Geochemistry Department, National Geophysical
Research Institute (NGRI), encouraged and supported
this work. Fellowships provided by the Council of
Scientific and Industrial Research to C.T. Kamala and
N.S. Chary are gratefully acknowledged.
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