Open Journal of Applied Sciences, 2012, 2, 146-152
doi:10.4236/ojapps.2012.23021 Published Online September 2012 (http :/ /www.SciRP.org/journal/ojapps)
A Comparative Study on Biosorption of Cr(VI) by
Fusarium solani under Different Growth Conditions
Mousumi Sen
Department of Applied Chemistry, Amity School of Engineering & Technology, New Delhi, India
Received May 24, 2012; revised June 25, 2012; accepted July 4, 2012
ABSTRACT
Biosorption of Cr(VI) from aqueous solution was studied in a batch bioreactor using the resting cells of Fusarium so-
lani isolated from soil. The specific Cr(VI) removal decreased with increase in pH from 2.0 to 6.0 and increased with
increase in initial Cr(VI) concentration, upto 500 mg·l–1. By increasing biomass concentration from 2.0 - 5.0 g·l–1, the
specific metal removal remained almost constant. The maximum specific Cr(VI) removal was 60 mg·g–1 achieved at
500 mg·l–1 initial Cr(VI) concentration and by using resting cells (36 h old). The Langmuir adsorption isotherm con-
stants, Qo and b were observed to be 57.1 mg·g–1 and 0.06 l·mg–1 respectively. These results were compared with the
Cr(VI) removal obtained in earlier studies conducted by the present authors using non living and growing cells of F.
solani.
Keywords: Biosorption; Cr(VI); Fusarium solan i; Resting Cells
1. Introduction
Chromium(VI) is one of the toxic heavy metals that are
present as chromate

2
4
CrO hromate

and dic


2
27
Cr O

waste water [1] of many industries such as
dye, electroplating, metal cleaning, leather, tanneries
metal plating, metal cleaning and processing, manufac-
ture of anticorrosive agents, wood preservation, wood
processing, alloy preparation, pigment manufacture, lea-
ther tanning, manufacturing of dyes, printing, etc. [2-4].
The persistant nature of Cr(VI) makes it accumulate in
the food chain which with time reach harmful levels in
living beings resulting in serious health hazards. There-
fore, removal of Cr(VI) from waste water prior to its
discharge into natural water systems, adjoining land-
masses, sewer systems, etc. requires serious and immedi-
ate attention. The conventional treatment techniques used
for removal of Cr(VI) from wastewaters are expensive,
result in the production of harmful by-products and are
not efficient when initial Cr(VI) concentration is in the
range of 10 - 100 mg Cr(VI) l–1 [5]. Bioremediation in-
volves potential application of microorganisms in re-
moval of heavy metals and has been recognized as a po-
tential alternative to the conventional methods for treat-
ment of contaminated wastewaters [6]. Several research-
ers reported removal of Cr(VI) from aqueous solution
using growing, resting and non-living cells of different
microorganisms [7-19].
in aqueous
However, most of the work to remove Cr(VI) have
been carried out using non-living fungal cells which have
advantages over growing and resting cells due to the ab-
sence of both toxicity limitations and requirements for
growth media and nutrients. The metal ion uptake by the
growing as well as the resting cells, though is a function
of cell age, composition of growth media and pH of the
solution, the cells can be maintained biologically active
to remove Cr(VI) from aqueous solution by maintaining
the suitable cell energetic biochemical reaction condi-
tions, whereas biochemical reactions are no longer con-
tinued in case of non-living biomass as the cells are dried.
Further, resting cells have the advantage over growing
cells in that the former require very low maintenance
energy to remain biologically active. The earlier studies
were conducted by the present authors on biosorption of
Cr(VI) by using F. solani isolated from soil under dif-
ferent growth conditions i.e., resting cells [20] growing
cells [21,22] as well as non living biomass [23]. Signifi-
cant Cr(VI) removal was observed using growing cells in
batch and continuous modes of operations and using non
living biomass in batch bioreactor.
The present study has been conducted to evaluate the
potential of the resting cells of the F. solani for Cr(VI)
removal from aqueous solution with an aim to develop
suitable operational strategy for treatment of Cr(VI) con-
taminated wastewaters. The effects of pH, initial Cr(VI)
concentration, biomass concentration and age of the cul-
ture on Cr(VI) removal from aqueous a solutions were
studied using synthetic Cr(VI) solution in batch bioreac-

M. SEN 147
tors. An attempt was made to fit the equilibrium data to
Langmuir and Freundlich adsorption isotherms. The ad-
sorption constants were determined from the adsorption
isotherms. An attempt was also made to compare these
results with those obtained using both growing cells and
non living cells of F. solani obtained earlier.
2. Materials and Methods
2.1. Microorganisms and Inoculums
The fungus F. solani (isolated from soil) used in the pre-
sent study was grown in 250 ml Erlenmeyer flasks in a
shaking incubator at 30˚C and 180 rpm using 100 ml
liquid media of the following composition (g·l–1): Glu-
cose, 10.0; K2HPO4, 0.5; NaCl, 1.0; MgSO4, 0.1; NH4NO3,
0.5 and Yeast extract, 5.0. The pH of the media was 6.0.
An inoculum of 10% (v/v) of a 36 h old culture was used
for the growth of the organism.
2.2. Preparation of Biomass
After 36 h of growth, the fungal cells were centrifuged at
5000 rpm for 5 minutes at 30˚C and then washed thrice
with distilled water. A weighed amount of washed rest-
ing cells (4.5 g·l–1, on dry wt. basis) was used as a bio-
sorbent in all the experiments. Dry cell weight was esti-
mated gravimetrically by taking separately the amount of
washed cells used in the experiment and drying it at 80˚C
for 24 h.
2.3. Preparation of Cr(VI) Solutions
Cr(VI) solutions of different concentrations [100 - 1000
mg·l–1] were prepared by diluting a stock solution [2.82
g·l–1] prepared by dissolving the required quantities of
potassium dichromate in distilled water.
2.4. Batch Studies
A weighed amount of the resting cells (4.5 g·l–1 on dry wt.
basis) was added to the flask containing 100 ml of Cr(VI)
solution of a known concentration. Before mixing the
biomass the pH of the solution containing Cr(VI) was
adjusted to the required value with 1N H2SO4 solution
and a small quantity of glucose (0.05 g·l–1) was added to
the flask which was required only for maintenance of the
cells. The flask was inoculated and incubated in a shaker
at 150 rpm for 24 h at 30˚C. Periodically samples were
withdrawn and centrifuged at 5000 rpm for 5 minutes.
The separated supernatant liquid was analyzed for the
residual Cr(VI) concentration. All the batch experiments
were carried out in a similar manner in triplicates. The
effect of pH (2.0 - 6.0) was studied at initial Cr(VI) con-
centration of 500 mg·l–1. A parallel control run was car-
ried out at the same concentration and at same pH values
to examine the chemical reduction of Cr(VI) to Cr(III) in
the absence of F. solani. The effect of initial Cr(VI) con-
centration [100 - 1000 mg·l–1], biomass concentration
(2.0 - 5.0 g·l–1) and culture age (12 - 48 h) were studies at
pH 4.0. The effluent contained multi metal ions: Cr(VI)
500; zinc 9 and nickel 10 mg·l–1 was procured from an
electroplating industry. The initial pH of the effluent was
2.0. The batch biosorption studies using resting cells
were carried out similarly as described above.
2.5. Assay Techniques
The residual Cr(VI) concentration was determined spec-
trophotometrically (Systronics, UV-VIS Spectrophotome-
ter 117) at 540 nm using di-phenyl carb azide as the com-
plexing agent. The concentration of zinc and nickel pre-
sent in the sample was estimated using atomic absorp-
tion spectrophotometer (Perkin-Elmer Model-Analyst 200
AAS), [24].
3. Results and Discussion
Figure 1(a) shows the effect of pH (2.0 - 6.0) on removal
of Cr(VI) both in the presence and in the absence (con-
trol) of the resting cells ( 36 h) of the F. solani at initial
500 mg·l–1 concentration using the biomass concentration
of 4.5 g·l–1 (dry wt. basis). In the absence of F. solani the
concentration of Cr(VI) removed chemically decreased
from 12.5 to 5 mg·l–1 with an increase in pH from 2 to 3
and no removal was observed beyond pH 3.0. Increased
availability of H+ ions at lower pH (upto 3.0) favours a
chemical redox reaction between the dichromate anioins
and the H+ ions resulting in conversion of Cr(VI) to
Cr(III). In the presence of F. solan i a significant decrease
in the biological removal of Cr(VI) from 287.5 mg·l–1 to
225.5 mg·l–1 was observed with an increase in pH from
2.0 to 6.0. The higher Cr(VI) removal at lower pH is due
to the increased availability of hydrogen ions for the
protonation of the cell wall functional groups, thereby
increasing the interaction between the negatively charged
dichromate anions and the protonated cell functional
groups. The values of specific Cr(VI) removal (mg·g–1)
as shown in Figure 1(b) decrease with increase in pH.
The specific Cr(VI) removal obtained in the present
study using resting cells at different pH values are com-
pared in the Table 1 with the values obtained in earlier
studies conducted by the present authors using the same
fungi (F. solani) under growing condition [2 1,22] and as
adsorbent usi n g no n -living cells [23]
The Table 1 shows no Cr(VI) removal using growing
cells at pH 2.0. This is due to the fact that growth of the
organism was inhibited at pH below 3.5, whereas sig-
nificant specific Cr(VI) removal could be achieved using
the resting and non living cells at the same pH. Again,
higher Cr(VI) removal observed in case of resting cells

M. SEN 148
0
100
200
300
400
23456
pH
C r (V I ) r e move d (mg l -1)
Total Biological Control
(mg·l
–1
)
(a)
40
50
60
70
23456
p
H
Specific Cr(VI) remova
l
(mg g-1 )
(mg·l
–1
)
(b)
Figure 1. (a) Effect of pH on removal of Cr(VI) at 500
mg·l–1 concentration; (b) Effect of pH on specific Cr(VI)
removal (mg·g–1 ) at 500 mg·l–1 concen tr a ti on.
Table 1. Comparison of maximum specific Cr(VI) removal
(a) during growth; (b) resting condition and (c) as adsorb-
ent at initial 500 mg Cr(VI) l–1 conce ntration.
Specific Cr(VI) removal (mg·g–1)
pH Resting
cells Cells during growth [21,22] Non living cells [23]
2.0 63.9 No growth 47.5
3.0 61.1 No growth 18.9
4.0 60.0 57 8.0
5.0 53.4 71 3.1
6.0 50.1 69 No removal
as compared to non-living cells of F. solani could be due
to the metabolism independent extracellular as well as
intracellular accumulation of Cr(VI). An intracellular
accumulation of Cr(VI) by the resting cells is mediated
via cell activity induced by the membrane redox enzymes
produced while growing F. solani (separately for resting
cell production) in the absence of Cr(VI) in a growth
media and maintaining the cells under resting condition
using only a small quantity of glucose as maintenance
energy source. The lower Cr(VI) removal by the non
living cells is only due to the extracellular accumulation.
At higher pH value (5.0), the specific Cr(VI) removal
by F. solani during its growth was found to be maximum
(71 mg·g–1) when glucose was completely utilised. At the
same pH a significantly lower (53.4 mg·g–1) Cr(VI) re-
moval was observed using the resting cells and a very
poor removal of 3.1 mg·g–1 was obtained using the non
living cells. In case of resting cells and non living cells
the pronated cell functional groups are assumed to be
responsible for higher Cr(VI) removal at lower pH,
availability of which decreases with increase in pH re-
sulting in decreased Cr(VI) removal. On the other hand,
growth associated enzymatic activity at higher pH value
might have played a key role in higher Cr(VI) removal
by growing cells of F. solani. Although at higher pH
availability of pronated cell functional groups is de-
creased, enzymatic activity is responsible for significant
removal of Cr(VI) by the resting cells. The absence of
enzymatic activity and also decreased pronated cell func-
tional groups at pH 5.0 resulted in poor Cr(VI) removal
when non living cells of F. solani were used as adsorbent.
As the cells were dried for Cr(VI) adsorption, enzymatic
activity was no longer perused. However, the highest
Cr(VI) removal was observed with F. solani at pH 5.0
when the cells were growing and removing Cr(VI) from
the broth. A complex mechanism of intracellular/ex-
tracellular accumulation or intracellular/extracellular re-
duction can be expected by the F. solani during its
growth. The above results strongly indicate that different
mechanisms are involved in Cr(VI) removal by F. solani
under different growth conditions (non living, resting and
growing cells). The mechanism of Cr(VI) removal ap-
pears to be highly dependent on pH conditions. While a
simple mechanism of physical adsorption is involved in
case of non living cells and a combination of extracellu-
lar and intra cellular accumulation is suggested using the
cells under resting conditions, a complex mechanism of
growth associated intracellular/extracellular reduction
along with intracellular/extracellular accumulation is
expected by the F. solani during its growth. However,
more in-depth studies are needed to elucidate the exact
mechanism of Cr(VI) removal.
In the present study, as it was observed from the con-
trol experiment that no chemical reduction of Cr(VI)
took place at pH beyond 3.0 and as the natural pH of
dichromate solution was also found to be 4 at which a
significant Cr(VI) removal (60 mg·g–1) could be obtained
using the cells under resting conditions, the further stud-
ies using resting cells were carried out at pH 4.0.
Figure 2 shows the specific Cr(VI) removal (mg·g–1)
at different initial Cr(VI) concentrations ranging from
100 - 1000 mg·l–1 and at pH 4.0 [25]. As complete Cr(VI)

M. SEN 149
removal could be obtained at concentration lower than
100 mg·l–1, the results have been reported only in the
range 100 - 1000 mg·l–1. The specific Cr(VI) removal
increased with increase in Cr(VI) concen tration upto 500
mg·l–1, then decreased and remained constant upto 1000
mg/l. The maximum specific Cr(VI) removal was found
to be 60 mg·g
–1. The increase in Cr(VI) removal upto
500 mg·l–1 is due to the availability of more and more
Cr(VI) for bioaccumulation by the F. solani. A small
decrease in Cr(VI) removal upto 750 mg·l–1 and no fur-
ther decrease upto 1000 mg·l–1 could be due to the re-
duced accessibility of the binding sites of the F. solani by
Cr(VI) at very high concentrations. The earlier batch
studies conducted by the present authors under similar
conditions showed Cr(VI) removal of 57 mg·g–1 using
growing cells and 8.0 mg·g–1 of dried biomass using the
non living cells of the F. solani.
A similar trend of Cr(VI) removal was observed using
growing cells with a maximum specific Cr(VI) removal
(71 mg/g) at pH 5.0 and at 500 mg/l initial Cr(VI) con-
centration [21,22].
At pH 2.0, using non living cells a similar trend was
observed in Cr(VI) removal with maximum specific
Cr(VI) removal of 47.5 mg·g–1 at 500 mg·l–1 initial Cr(VI)
concentration [23]. The above results indicate that the
process of Cr(VI) mg·l–1 initial Cr(VI) concentration [23].
The above results indicate that the process of Cr(VI) re-
moval using growing cells can be operated at higher pH
nearer to the natural pH (6.0) of the media, whereas us-
ing nonliving cells the process can be operated at lower
pH. However, the resting cells are effective at both
higher and lower pH values. Therefore, both resting and
non living cells have potential in industrial applications
where Cr(VI) contaminated waste waters are highly
acidic in nature. However, for higher Cr(VI) removal
growing cells can be used requiring an additional step of
pH adjustment.
Figure 3 comp ar es max imu m Cr (VI ) re mova l fr om an
0
20
40
60
80
100250500750 1000
initial Cr(V I) concentr ation (mg l -1)
Specific Cr(VI) r emoval (mg g
-
(mg·g
–1
)
(mg·l
–1
)
Figure 2. Specific Cr(VI) removal (mg·g–1) at different ini-
actual industrial effluent (pH 2.0)
tial Cr(VI) concentrations at pH 4.0.
using growing cells
Cr(VI) with respect to biomass con-
ce
12,
24
after adjustment of pH to 5.0 [22] and using non living
[24] and resting cells ( present study) of F. soalni at pH
2.0 at 500 mg·l–1 initial Cr(VI) concentration. The spe-
cific Cr(VI) removal from an actual effluent (Figure 3)
was found to be lower than the values obtained using
synthetic Cr(VI) solution (Table 1). This is due to the
presence of other metals [zinc; 9 mg·l–1 and nickel; 10
mg·l–1] in the effluent, which might have interfered with
the removal of Cr(VI). This was supported by the AAS
analysis indicating complete removal of zinc and nickel
from the effluent.
The removal of
ntrations (2.0 - 5.0 g·l–1) of the resting cells at 500
mg·l–1 initial concentration and at pH 4.0 is shown in
Figure 4. The figure shows that Cr(VI) removal is de-
pendent on biomass concentration of resting cells, al-
though the specific Cr(VI) removal (mg·g–1) remained
nearly the constant at all the biomass concentrations.
The cells harvested from various stages of growth (
, 36 and 48 h) of F. solani in the absence of Cr(VI) were
maintained under resting condition and were used to study
the effect of culture age (physiological state of growth)
on Cr(VI) removal at initial 500 mg·l–1 concentration and
0
20
40
60
80
25
pH
Specific Cr(VI) remova
(mg g -1 )
Growing Resting Non living
(mg·g
–1
)
20
removal
Figure 3. Comparison of maximum specific Cr(VI) removal
from an actual industrial effluent using growing, non living
and resting cells of F. soalni at 500 mg·l–1 initial Cr(VI)
concentration.
100
200
300
400
2345
Biomass concentr ation (g l -1)
Cr(VI) removed (mg l
-1 )
40
50
60
70
Specific Cr(VI) remova
l
(mg g -1 )
Cr( VI ) removal
Spec ific Cr(VI) remova l
(mg·g
–1
)
(mg·l
1
)
Biomass concentration
(g
·l
–1
)
2 3 4 5
removal
Figure 4. Removal of Cr(VI) with respect to biomass con-
centrations at 500 mg·l–1 concentration and pH 4.0.

M. SEN 150
at pH 4.0. The specific Cr(VI) removal is shown in Fig-
r(VI) adsorbed
by
ure 5, in which an increase in Cr(VI) removal was ob-
served with an increase in cell age from 12 h (beginning
of the exponential phase) to 36 h (beginning of the sta-
tionary phase).The specific Cr(VI) removal remained
constant with further increase in cell age upto 48 h (sta-
tionary phase). These results suggest that Cr(VI) removal
by the resting cells is also dependent on the age of the
culture. The resting cells harvested from the beginning of
stationary phase appear to be most effective in maximum
Cr(VI) removal per gram of dried biomass. Using 36 h
old culture the maximum specific Cr(VI) removal was
found to be 60 mg·g–1 of dried biomass.
The relation between the amount of C
the adsorbent and unadsorbed Cr(VI) in solution at a
constant temperature can be represented by Langmuir
and Freundlich adsorption isotherm, which provide the
equilibrium data required for the designing of the adsorp-
tion system. The Langmuir adsorption isotherm which is
applicable to monolayer sorption onto a surface with a
number of identical sites homogeneously distributed over
the surface sorbent is given by
1
o
QbC
e
ee
qbC  (1)
1 1e
o
e
bC
qQbC


e
(1a)
11
ee
oo
e
CbC C
qQbQbQ


e
o
(1b)
where qe is the amount of Cr(VI) adsorbed per gram of
sotherm is applicable to
dried biomass at equilibrium [mg Cr(VI) g–1 of dried
biomass] and Ce is the residual (equilibrium) Cr(VI)
concentration remaining in the solution after sorption
[mg l–1]. The Langmuir constants, Qo and b, indicate the
maximum amount of metal ion bound per gram of sor-
bent to form a monolayer and the affinity of the binding
sites, respectively [20,24-27].
The Freundlich adsorption i
50
55
60
65
12 24 36 48
Culture age (h)
Specific Cr(VI) removal
(mg g
-1)
(mg·g
–1
)
Figure 5. Effect of culture age on specific Cr(VI) removal
and is ex-
(mg·g–1) at 500 mg·l–1 concentration and pH 4.0.
removal of Cr(VI) on a heterogeneous surface
pressed as
1n
eFe
qKC (2)
or
1
log loglog
eF
qK
n
e C (2a)
where KF and n are the Freundlich constants and are re-
lls of the
sa
not fit the Freundlich isotherm
an
4. Conclusion
removal can be achieved in batch op-
lated to the adsorption capacity and adsorption intensity
of the adsorbent, respectively. Equation (2) can be lin-
earized in logarithmic form and Freunlich constants n
and KF can be determined from the slope and intercept
which are equal to 1/n and KF, respectively [28-31]. Fig-
ure 6 shows the Langmuir adsorption isotherm of Cr(VI)
obtained at 300 by plotting Ce/qe against the residual
concentration, Ce. The maximum amount of Cr(VI) ad-
sorbed per gram of biosorbent to form a monolayer on
the surface (Qo) was 57.1 mg and the adsorption affinity
(b) for binding the metal ions on the adsorbent sites was
0.06 (l·mg–1). The correlation coefficient (R2) obtained
from Langmuir adsorption isotherm was 0.995.
The values of Qo and b using non-living ce
me fungal biomass were found to be 50.3 [mg·g–1 of
dried biomass] and 0.03 (l·mg–1) respectively, [6]. The
higher values of adsorption constants in case of resting
cells indicates higher amount of Cr(VI) bound per gram
of sorbent to form a monolayer and the higher binding
affinity of the cells sites.
However, the data did
d hence are not shown in the present paper.
Significant Cr(VI)
eration using resting cells of F. solani. Cr(VI) removal is
dependent on pH, initial Cr(VI) concentration, biomass
concentration and cu lture age. pH plays an impo rtant role
in Cr(VI) removal under different growth conditions
(growing, resting and non living). Resting and non living
cells are effective at lower pH thus having great potential
in industrial applications where effluents generated are
highly acidic in nature. pH adjustment is required using
y = 0.0175x + 0.26, R2 = 0.9 95
0
2
4
6
8
10
12
14
0200 400 600 800
Ce (mg/l)
Ce/qe (g/l)
Figure 6. The Langmuir adsorption isotherm of Cr(VI).

M. SEN 151
ce -
[1] L. E. Germaiating and Cyanide
atment Technolog
ors
lls under growing condition. The equilibrium adsorp
tion data fitted well with Langmuir adsorption isotherm
indicating the favorab le monolayer adsorption on th e cell
surface. The findings from this comparative study pro-
vide useful basis for development of suitable operational
strategies for treatment of Cr(VI) contaminated waste-
waters.
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