A Comparative Study on Biosorption of Cr (VI) by <i>Fusarium solani</i> under Different Growth Conditions

doi:10.4236/ojapps.2012.23021

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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

Email: mousum[email protected]

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



CrO hromate



and dic





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

100

200

300

400

23456

C r (V I ) r e move d (mg l -1)

Total Biological Control

(mg·l

–1

)

(a)

23456

Specific Cr(VI) remova

(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

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-

12,

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

Specific Cr(VI) remova

(mg g -1 )

Growing Resting Non living

(mg·g

–1

)

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 )

Specific Cr(VI) remova

(mg g -1 )

Cr( VI ) removal

Spec ific Cr(VI) remova l

(mg·g

–1

)

(mg·l

)

Biomass concentration

·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

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

QbC

qbC

 (1)

qQbC





(1a)

CbC C

qQbQbQ





(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

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

eFe

qKC (2)

log loglog

e

C (2a)

where KF and n are the Freundlich constants and are re-

lls of the

not fit the Freundlich isotherm

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

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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