Hexavalent chromium sorption by biomass of chromium tolerant Pythium sp.

Journal of Basic Microbiology 2011, 51, 173 – 182

173

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Research Paper

Hexavalent chromium sorption by biomass
of chromium tolerant Pythium sp.

B. Kavita, Jayeshree Limbachia and Haresh Keharia

BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India

The removal of Cr(VI) from aqueous solutions by live and pretreated fungal biomass of Pythium
sp was investigated in a batch mode. The influence of biomass dose, solution pH, initial metal
ion concentration, temperature and pretreatment of biomass on biosorption efficiency was
studied. The acid pretreated biomass adsorbed 1.7 times more hexavalent chromium in com-
parison to untreated biomass. The chromium removal rate increased with decrease in pH and
increase in Cr(VI) concentration, biomass dose and temperature. The adsorption data was
described well by Freundlich isotherm model. Evaluation of biosorption mechanism using in-
frared spectroscopy showed the involvement of positively charged amino groups in Cr(VI) bio-
sorption. The biosorption of Cr(VI) by Pythium sp. followed second order kinetics, the biosorp-
tion process was found to be spontaneous and endothermic with high affinity of biomass for
Cr(VI).

Keywords: Chromium / Bioremediation / Biosorption / Pythium / Thermodynamics

Received: May 22, 2010; accepted: September 12, 2010

DOI 10.1002/jobm.201000191

Introduction

Rapid industrialization and increase in pollution has
lead to many fold increase in the utilization and release
of chemicals including heavy metals in the environ-
ment [1]. Amongst all toxic heavy metals discharged
into the environment through various industrial was-
tes, chromium is one of the most toxic and has become
a serious health concern. Chromium is used extensively
in industries like electroplating, stainless steel produc-
tion, leather industry and wood preservation [2, 3].
Although chromium is an essential trace metal to hu-
mans, its teratogenicity, mutagenicity, carcinogenicity
and toxicity makes it hazardous at very low concentra-
tion and it has been classified as priority pollutant by
United States Environmental Protection Agency [4, 5].
Various methods used for removal of chromium ions
include chemical reduction and precipitation, reverse
osmosis, ion exchange, adsorption on activated carbon

Correspondence: Prof. Dr. Haresh Keharia, BRD School of Bioscien-
ces, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India
E-mail: haresh970@gmail.com
Phone: +91 2692 234413 – ext 214
Fax: +91 2692 226865

etc. But all these methods suffer from serious con-
strains such as incomplete metal removal, high reagent
or energy requirements, generation of toxic sludge or
other waste product that require safe disposal [6, 7].
There is, therefore, a need for some alternative efficient
and cost effective technology for remediation of chro-
mium containing wastewaters. The ability of some
microorganisms to interact with chromium ions makes
them attractive in the context of environmental bio-
technology [8]. The utilization of microbial biomass for
the removal of chromium from industrial waste water
by biosorption has already been recognized [9, 10]. Fun-
gal cell wall contains large quantity of polysaccharides
and proteins [9, 11]. These biopolymers offer many
functional groups such as carboxyl, hydroxyl, sulphate,
phosphate and amino groups which can bind metal
ions through adsorption, ion exchange coordination,
complexation etc. [9, 12].
The aim of the present study is to increase the bio-
sorption efficiency of Pythium sp by various chemical
and physical treatments and to describe the mechanism
of biosorption by chemically treated dead fungal bio-
mass of Pythium sp. using kinetics and thermodynamic
studies.

174 B.

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Materials and methods

Chemicals
All the chemicals used in the present study were of
analytical grade and were prepared in deionized dis-
tilled water. The K

was used as a source of Cr(VI)

in present study.

Isolation and characterization of fungal culture
Soil samples were collected from a landfill site in
Baroda, Gujarat, India, where Cr(VI) containing waste
was being dumped for more than a decade. Soil sample
was diluted in sterile saline (0.85% NaCl) and 0.1 ml
aliquots of diluted soil suspension were spread on Po-
tato Dextrose Agar (PDA) plates amended with Cr(VI).
A fungal culture growing on a PDA plate containing
1000 mg/l of Cr(VI) was isolated and used for further
studies. It was maintained by periodic subculturing on
Potato Dextrose Agar plates and preserved in refrigera-
tor. The Cr(VI) tolerant fungal isolate was identified as
Pythium sp on the basis of microscopic observation by
Fungal culture identification facility at Agharkar Re-
search Institute, Pune, India.

Preparation of biomass
Pythium sp was inoculated to 500 ml Erlenmeyer flasks
filled with 200 ml of culture medium composed of the
following (g/l): Potato infusion forms, 200; Dextrose, 20.
Once inoculated, the flasks were shaken on a rotary
shaker at 150 rpm for five days at 30 °C. Upon incuba-
tion, the biomass produced was separated by filtration
and the resulting biomass was washed thoroughly sev-
eral times with distilled water and then used for ad-
sorption studies.

Various pretreatments to biomass
An amount of live biomass (5 g) was subjected to vari-
ous pretreatments in an effort to study their effect on
Cr(VI) adsorption efficiency of fungal biomass. The live
biosorbent was autoclaved for 15 min at 121 °C (re-
ferred as heat inactivated biomass) or boiled for 15 min
in 500 ml of NaOH (1 N) or treated with o-phosphoric
acid (10%, v/v) or with hydrochloric acid (1 M) or
treated with glutaraldehyde (2%, v/v) or formaldehyde
(15%, v/v). Following the desired pretreatment, biomass
were collected by filtration and washed with deionized
water until the pH of the washing solution was close to
pH 7 ± 0.1. The effect of pretreatments on Cr(VI) bio-
sorption efficiency of biomass was analyzed with refer-
ence to the biosorption efficiency of untreated live
fungal mycelium.

Effect of pH on Cr(VI) biosorption
The fungal biomass (10 mg/ml) was added to 100 mL
Cr(VI) solution (100 mg/l) with varying pH (pH 1.0 to
8.0). The pH of the solution was adjusted using 0.1 N
HCl/0.1 N NaOH. At all pH values, controls without
biomass addition were kept in order to compensate for
effect of pH on Cr(VI). It should be noted that pH of the
solution did not influence the concentration of Cr(VI).
The amount of chromium adsorbed was monitored by
determining residual Cr(VI) in the solution at different
time intervals and subtracting it from the initial chro-
mium. The Cr(III) was not detected experimentally in
the aqueous phase during any of the biosorption ex-
periments performed (data not included).

Effect of biosorbent concentration on Cr(VI)
biosorption
The varying amount of biomass (2–20 mg/ml) was used
in biosorption experiment and residual Cr(VI) was
monitored at regular time intervals.

Effect of initial Cr(VI) concentration on Cr(VI)
biosorption
The fungal biomass (10 mg/ml) was added to 100 ml of
Cr(VI) solution with concentration varying from 100–
500 mg/l, in 250 ml Erlenmeyer flasks and residual
Cr(VI) concentration was determined at regular inter-
vals of time.

Adsorption isotherm
All the data were analyzed using Langmuir and Freund-
lich equilibrium isotherms to determine the feasibility
of adsorption treatment. The Freundlich isotherm
equation is an empirical equation based on the biosorp-
tion on a heterogeneous surface suggesting that the
binding sites are not equivalent or dependent [13].
Langmuir isotherm equation is based on monolayer
sorption onto a surface with finite number of identical
sites, which are homogeneously distributed over the
sorbent surface [14].

Kinetics of Cr(VI) biosorption
Pseudo first order and pseudo second order rate equa-
tion have been used for modeling the kinetics of Cr(VI)
biosorption. Pseudo-first order rate equation [15] is
expressed as follows

log (

) log

2.303

k t

−

(1)

where, q

and q

is sorption capacity at time t and at

equilibrium, respectively and k

is pseudo-first order

rate constant.

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Hexavalent chromium sorption by Pythium sp.

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Similarly, pseudo-second rate equation [16] is expres-
sed as

(

)

k q

(2)

where, K

is pseudo second order rate constant.

Effect of temperature on Cr(VI) biosorption
The Cr(VI) biosorption efficiency of fungal biomass was
investigated at 30, 35, and 40 °C, at an initial Cr(VI)
concentration of 100 mg/l. The results were analyzed to
determine the rate of biosorption at different tempera-
tures and subsequently used to determine the activa-
tion energy employing Arrhenius equation as follows

ln k = −Ea/RT + ln Ao (3)

where Ea is activation energy and Ao is constant called
the Frequency factor. Value of Ea can be determined
from the Slope (–Ea/R) of ln k versus 1/T plot.

Characterization of Cr(VI) biosorption
The chemical characterization of the untreated, acid
treated and chromium laden acid treated biomass was
done using FTIR analysis. The spectra were collected
by a Perkin Elmer Spectrum GX in the range of 500–
4000 cm

–1

. Specimen of various biosorbent were first

mixed with KBr with an approximate ratio of 1:100 and
then ground in an agate mortar and pressed at 10 tons
for 5 min in order to form pellets.
The presence of Cr(VI) in the unloaded and chro-
mium laden biosorbent was analyzed by scanning elec-
tron microscopy (Philips XL30 ESEM) coupled with en-
ergy dispersive X-ray analysis (EDAX).

Estimation of Cr(VI) concentration
The concentration of the Cr(VI) ions was determined
spectrophotometrically after complexation of the Cr(VI)
ion with 1, 5-diphenylcarbazide [17]. The absorbance was
recorded at 540 nm and concentration was determined
from the standard calibration curve.
All the experiments were performed in triplicates
and the mean values of the results obtained from three
independent experiments were used for interpretation.

Results and discussion

Effect of pretreatment on Cr(VI) adsorption
by fungus
Table 1 shows that biomass pretreated with hydro-
chloric acid (HCl) and high temperature exhibited 1.7
and 1.4-fold higher Cr(VI) biosorption (2.9 mg/g and
2.5 mg/g), respectively in comparison to untreated bio-
mass (1.6 mg/g). On the other hand when biomass was
pretreated with HCl plus heat, not much difference in
the chromium biosorption was observed in comparison
to biomass pretreated only with HCl. Treatment of
biomass with 1.0 N NaOH resulted in reduced Cr(VI)
biosorption efficiency (0.8 mg/g). Alkali pretreatment is
known to cause hydrolysis and deacetylation of protein
constituents. It also causes drastic effects like swelling
of biomass, probably due to polymer chain breakage,
thereby reducing biosorption potential [18, 19]. Form-
aldehyde and glutaraldehyde pretreated biomass too
exhibited lower efficiency of Cr(VI) biosorption. Both
formaldehyde and glutaraldehyde act as a fixative there
by causing cross linking of hydroxyl group of glucose in
the cell wall, hence reducing the accessibility of specific
binding sites for Cr(VI) ions [19]. The increase in adsorp-
tion capacity after acid treatment could be attributed to
the fact that acid hydrolysis results exposure of more
amino sugar moieties on the biomass surface, which
gets more easily protonated at adsorption pH, thereby
enhancing the binding of Cr(VI) through electrostatic
charge attraction [20, 21].

FTIR and EDAX analysis
In order to elucidate the mechanism of Cr(VI) biosorp-
tion by Pythium sp, FTIR analysis of untreated, acid
treated and chromium laden acid treated biomass was
carried out (Fig. 1). The intense broad absorption bands
at frequency level of 3200–3400 cm

–1

represents –OH

groups of glucose and the –NH stretching of proteins
and acetamide groups of chitin. The strong peaks at
1626–1650 cm

–1

can be attributed to the amide bonds

in chitin or protein. The absorption band around
1741 cm

–1

represents C=O stretch of acetamide group.

The moderately strong absorption band around
1032 cm

–1

and 1154 cm

–1

can be assigned to –CN stretch-

Table 1. Effect of pretreatment on biosorption efficiency (

μg/g) of Pythium sp biomass for Cr(VI).

Untreated

NaOH

-phosphoric acid

HCl

HCHO

Glutaraldehyde

Before autoclave

1680

795

2845

2885

1433.12

1459.5

After autoclave

2515

587

2740

2845

728.1

1586.8

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Figure 1. FTIR spectra of untreated (A), acid treated unloaded biomass (B) and acid treated Cr(VI) loaded biomass (C) of Pythium sp.

ing vibration of chitin, chitosan and protein compo-
nents of fungal cell wall. A short absorption band
at 1456 cm

–1

seems to be due to asymmetric bending

of acetyl moiety. The peaks at 2925, 1549, 1377 and
1032 cm

–1

represents C–H stretching, vibrations, N–H

bending (scissoring), –CH

wagging and C–OH stretch-

ing vibrations, respectively and are due to several func-
tional groups present in fungal cell wall components.
The FTIR spectrum of acid treated biomass shows a
significant difference in absorption bands in the fre-
quency range of 1659 to 1032 cm

–1

, thus indicating the

chemical alterations in the cell wall of acid treated
biomass [20]. The FTIR spectrum of acid treated biomass
loaded with chromium reveals a shift in broad absorp-
tion bands from 3323 to 3303 cm

–1

and decrease in

intensities of peaks associated with –NH bonds. It
should be noted that Cr(VI) behaves as an oxy-anions
(CrO

–2

, or Cr

–2

) in aqueous medium, according to

aqueous solution chemistry of chromium. Therefore, it

may not bind to negatively charged functional groups
on the biomass surface such as carboxylate, phosphate
and sulphate, because of the respective charge repul-
sion. Thus, it can be suggested that the amino groups
of the major cell wall components (i.e. chitin, chitosan
and proteins) gets protonated at low pH (i.e. pH 2.0)
due to acid pretreatment of the biomass and there-
after, negatively charged chromate ions become elec-
trostatically attracted towards the positively charged
amino groups of the fungal cell wall. Similar observa-
tions have been reported by other researchers [21–23].
  Fig. 2 shows the EDAX spectra obtained before and
after Cr(VI) biosorption onto HCl treated fungal bio-
mass, respectively. These spectra clearly indicated the
presence of Cr(VI) ions over the surface of metal loaded
HCl treated fungal biomass whereas Cr(VI) was not
detected in the acid treated biomass (control). This
observation was similar to that reported by Tunali et al.
for adsorption of Cr(VI) by Neurospora crassa [23].

Figure 2. EDAX spectra of acid treated biomass (A); acid treated Cr(VI) loaded biomass (B) of Pythium sp.

Journal of Basic Microbiology 2011, 51, 173 – 182

Hexavalent chromium sorption by Pythium sp.

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Figure 3. Effect of acid treated biosorbent dose on Cr(VI) removal
(mg/l) by fungal biomass. Initial Cr(VI) concentration: 100 mg/l, con-
tact time: 6 h.

Effect of biosorbent dose on Cr(VI) biosorption.
The increase in biosorbent dose from 2–10 mg/ml re-
sulted in rapid increase in the Cr(VI) removal by fungal
biomass (Fig. 3). Further increase of the biomass dose
didn’t affected the Cr(VI) removal. Thus, fungal bio-
mass at a concentration of 10 mg/ml was used for rest
of the experimental studies. The increase in Cr(VI) re-
moval with increasing dose of biomass may be attrib-
uted to increase in the number of adsorption sites.

Effect of pH of solution on Cr (VI) biosorption
Fig. 4 shows that the extent of Cr(VI) biosorption by the
acid treated biosorbent increased with decrease in pH
with highest biosorption at the lowest pH tested i.e. pH
1.0. The Cr VI) biosorption capacity was maximum at
pH 1.0 (12.5 mg/g biomass) and markedly decreased at
pH 2.0 (10.15 mg/g biomass), Cr(VI) biosorption re-
mained constant then after till pH 6.0 and then de-
creased gradually with further increase in pH. This
increase in adsorption with decrease in pH may be due
to protonation of functional groups involved in bio-
sorption of negatively charged chromate ions. At alka-
line pH the overall charge on the biosorbent surface
would become negative and consequently due to re-
spective charge repulsion of negatively charged Cr ions
like HCrO

–

, Cr

2–

, CrO

2–

, result in lower adsorption

efficiency [24]. Hence, electrostatic attraction probably
plays an important role in biosorption of negatively
charged chromium ions at low pH. Additionally, the
dominant form of Cr(VI) at pH 1.0 is the acid chromate
ion species (HCrO

–

) and increasing pH shifts the con-

centration of HCrO

–

to other forms, CrO

2–

and Cr

2–

Since there is an increase in sorption of Cr(VI) as pH

Figure 4. Effect of pH on biosorption of Cr(VI) by fungal biomass.
Biomass dose: 10 mg/ml, initial Cr(VI) concentration: 100 mg/l, bio-
mass dose: 10 mg/ml, contact time: 6 h.

decreases to 1.0, it may be suggested that HCrO

–

is the

active form of Cr(VI) which is being absorbed by the
acid treated fungal biomass. Part et al. have demon-
strated the adsorption-coupled reduction of Cr(VI) to
Cr(III) on the surface of dead biomass of Aspergillus niger
[11]. In their experiments, they found that upon incu-
bation of Cr (VI) with dead biomass of Aspergillus niger,
Cr(VI) was completely removed from aqueous solution,
however it was accompanied with appearance of cor-
responding amount of Cr(III) in solution as well as pH
of the solution increased from 2.00 to 2.13. In present
study, we did not find the appearance of Cr(III) in aque-
ous solution concomitant with removal of Cr(VI) (data
not shown) by biomass of Pythium sp. Also, we moni-
tored the pH of solution during the course of all bio-
sorption experiments and no significant change in pH
was observed. Thus, in present study, Cr(VI) removal
from aqueous solution by Pythium biomass seems to
follow anionic adsorption mechanism.

Effect of initial Cr(VI) concentration on Cr(VI)
biosorption by untreated and acid treated biomass
of Pythium sp.
The initial concentration of Cr(VI) in the solution re-
markably influenced the equilibrium uptake of Cr(VI)
for both untreated as well as acid treated biomass
(Fig. 5). The biosorption capacity for Cr(VI) increased
from 2.76 to 7.8 mg Cr(VI)/g of untreated biosorbent on
increasing Cr(VI) concentration from 100 to 500 mg/l.
The biosorption capacity of acid treated biomass was
found to be higher than untreated biomass and it in-
creased from 12.0 to 50.6 mg Cr(VI)/g of treated biosor-

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Figure 5. Effect of initial Cr(VI) concentration on biosorption efficiency of untreated fungal biomass (A) and acid treated fungal biomass (B).
Biomass dose: 10 mg/ml, contact time: 24 h.

bent with increasing Cr(VI) concentration from 100 to
500 mg/l. Increasing metal ion concentration would
increase the number of collision between metal ions
and sorbent thereby enhancing the sorption efficiency
[23].
Evaluation of data showed that the biosorption of
Cr(VI) followed second order rate kinetics over a con-
centration range of 100 to 500 mg Cr(VI)/l (Fig. 6). Ta-
ble 2 shows that values of equilibrium uptake capacity,
q

increases from 2.86 to 8.1 mg Cr(VI)/g of untreated

biosorbent and from 12.5 to 50.5 mg Cr(VI)/g of acid

treated biosorbent. The second order rate constant K

was found to decrease with increasing concentration of
Cr(VI) from 100 to 500 mg/l. This shows that the chro-
mium sorption kinetics is strongly dependent on mass
transfer phenomenon [25].

Effect of temperature on Cr(VI) biosorption
Fig. 7 shows that the biosorption of Cr(VI) by the bio-
sorbent appears to be temperature dependent over the
temperature range of 30 to 40 °C. This 10 degree in-
crease in temperature increased Cr(VI) biosorption ca

Table 2. Second order kinetic parameters for biosorption of Cr(VI) by untreated and treated biomass of Pythium sp at varying initial
Cr(VI) concentration.

Cr (mg/l)

Untreated biomass

Treated biomass

, mg/g

(Expt)

, mg/g

(Cal.)

, mg/g

(Expt)

, mg/g

(Cal.)

100 2.76 2.86 0.0029 0.9903 12.4 12.53

0.00165

0.9998

200 3.5 3.7 0.00193

0.9858 24.25 24.2 0.00125 0.9941

300 4.5 4.6 0.00129

0.973 36.05 30.3 0.0019 0.9996

400 5.77 6.0 0.0010 0.975 42.69 42.7 0.00052 0.9918

500 7.8 8.1 0.00058

0.9575 50.6 50.5

0.00047

0.9919

Figure 6. Linearized second order kinetic plots at varying initial concentrations of Cr(VI) for untreated biomass (A) and acid treated fungal
biomass (B). Biomass dose: 10 mg/ml, contact time: 12 h.

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Hexavalent chromium sorption by Pythium sp.

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Figure 7. Effect of temperature on biosorption of Cr(VI) by untreated fungal biomass(A) and acid treated fungal biomass (B). Initial Cr(VI)
concentration: 100 mg/l, biomass dose: 10 mg/ml, contact time: 6 h.

pacity (mg Cr(VI)/g biosorbent) from 3.84 to 4.5 and
9.04 to 9.38 for untreated and acid treated biomass,
respectively (Fig. 7). The contact time required for com-
plete Cr(VI) removal was found to decrease with in-
crease in temperature. The increase in Cr(VI) biosorp-
tion with increasing temperature may be due to either
higher affinity of sites for chromate ions or an increase
in number of binding sites on biosorbent surfaces as a
result of reorientation of cell wall component of the
fungal mycelium [20, 25]. It has been reported that rise
in sorption capacity with temperature is accompanied
with the rise in the kinetic energy of sorbent particles.
Thus, the collision frequency between sorbent and sor-
bate increases, which results in the enhanced sorption
on the surface of sorbent [20]. Also, at high temperature

Figure 8. Arrhenius plot for Cr(VI) biosorption on untreated and
acid treated biomass of Pythium sp.

due to bond rupture there may be an increase in num-
ber of active sorption sites leading to enhanced sorp-
tion.
The Arrhenius plot was used to determine the activa-
tion energy for the sorption of Cr(VI) by untreated as
well as acid treated biomass (Fig. 8). It was calculated as
44.5 and 50.8 KJ mol

–1

for untreated and HCl treated

biomass, respectively. Values of activation energy sug-
gests that the sorption of Cr(VI) on Pythium sp. biomass
is a chemical process, since activation energy for
chemical adsorption is generally more than 4–6 KJ mol

–1

[26]. Chemical adsorption means that the rate varies
with temperature according to finite activation energy
in the Arrhenius equation. Similar observation has
been reported by Bayramoglu et al. in their studies on
Lentinus sajor-caju for adsorption of Cr(VI) [20].

Thermodynamics studies
Increase in Cr(VI) biosorption with increase in tempera-
ture can be very well correlated with the endothermic
nature of the biosorption process. To further confirm
the temperature dependency of the biosorption process,
thermodynamic parameters were calculated using van’t
Hoff equation, which says [27, 28]:

−

(4)

Here, K

is equilibrium constant calculated as,

(5)

Here, Q

is the amount of Cr(VI) adsorbed per unit bio-

mass (mg/g biomass) and C

is the Cr(VI) concentration

in solution at equilibrium.
Fig. 9 shows the van’t Hoff plot of ln K

vs 1/T (1/K).

Values of enthalpy change (ΔH) and entropy change (ΔS)

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Figure 9. Van’t Hoff plot of ln K

vs 1/T (1/K).

were calculated from the slope and intercept of the plot
(Table 3). Positive value of ΔH (10) shows the Cr(VI)
biosorption process is endothermic. Additionally, ΔS is
also positive (40.7) indicating, high affinity of the Cr(VI)
for sorbent used.
Similarly, Gibb’s free energy (ΔG ) was also calculated
using following equation:

= −

(6)

where, R is the universal gas constant, T is temperature
(K) and K

is equilibrium constant.

Magnitude

ΔG (KJ mol

–1

) increases with increase in

temperature showing the feasibility of the biosorption
process. The negative values of ΔG (Table 3) confirms
the spontaneity of the Cr(VI) biosorption process.

Table 3. Thermodynamic parameters for the biosorption of
Cr(VI) on acid treated biomass of Pythium sp.

Temperature

(

)

Equilibrium

constant

(

)

Gibb’s

free

energy

(Δ

KJ mol

–1

)

Enthalpy

(Δ

KJ mol

–1

)

Entropy

(Δ

, J mol

–1

)

303 2.51 –2.31

308 2.72 –2.55

10.0

40.7

313 2.85 –2.72

Analysis of adsorption isotherm
Both Langmuir and Freundlich isotherm models were
evaluated to examine biosorption with increasing con-
centration of Cr(VI). Fig. 10 shows typical linearized
plots of Freundlich isotherm models for adsorption of
varying concentration of Cr(VI) by acid treated fungal
biomass of Pythium sp. The values of regression coeffi-
cient (R

) for Freundlich isotherm were found to be

0.8075 and 0.9375 for untreated and acid treated bio-
mass, respectively. The Freundlich isotherm constant K

was calculated as 1.78 and 12.0 for untreated and acid
treated biomass, respectively. Similarly, value of n was
calculated as 2.9, for both untreated and HCl treated
biomass (Table 4).
The high magnitude of K

and n illustrate high ad-

sorption capacity of the biomass. The experimental
value of n is greater than unity which indicates favor-
able adsorption [29].
Freundlich isotherm model fitted the adsorption data,
suggesting that the surface of sorbent is heterogeneous.

Figure 10. Freundlich biosorption isotherm for Cr(VI) sorption by untreated fungal biomass (A), acid treated fungal biomass (B) at varying
initial Cr(VI) concentration (100 to 500 mg/l).

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Hexavalent chromium sorption by Pythium sp.

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Table 4. Isotherm parameters for Cr(VI) biosorption by untreat-
ed and acid treated biomass of Pythium sp. at varying con-
centration of Cr(VI) (100 – 500 mg/l).

Freundlich isotherm constants

n K

Untreated 2.9

1.78

0.8075

Acid treated

2.9

12.0

0.9375

Binding sites are not independent and adsorption en-
ergy of a metal binding site on an adsorbent depends
on whether or not the adjacent sites are already occu-
pied. Thus, the adsorption of Cr(VI) by fungal isolate
seems to be a complex process involving multilayer,
interactive or multiple site type binding [13]. Similar
observations have been made by other workers on
metal biosorption studies using Spirogyra [30], Rhizopus
arrhizus [22].

Concluding remarks
The potential of using pretreated non living biomass of
Pythium sp for removal of Cr(VI) has been demonstrated.
The HCl pretreated fungal biomass exhibited maximum
biosorption efficiency for chromium amongst all pre-
treatment methods. Acid pretreatment of the fungal
biomass helped in increasing the positively charged
amino groups on the surface of biomass (as confirmed
by FTIR analysis). The adsorption of Cr(VI) was very
much affected by changes in pH, temperature and
Cr(VI) concentration of the medium. For both untreated
and acid treated biosorbent, biosorption of Cr(VI) fol-
lowed second order rate kinetics. The Cr(VI) biosorption
by Pythium sp biomass fitted Freundlich isotherm mo-
del. Bioaccumulation of Cr(VI) species extracellularly
on the surface of fungus was confirmed by EDAX analy-
sis. All these studies showed that acid pretreated bio-
mass of Pythium sp. may be used as an inexpensive,
effective and easily cultivable biosorbent for the remo-
val of Cr(VI) species from aqueous solutions.

Acknowledgements

Authors are thankful to Department of Science and
Technology as well as University Grants Commission,
New Delhi, India for financial assistance.

References

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