Biosorption of Lead by Aspergillus niger: Equilibrium, Kinetics and Process Mechanism

BIOSORPTION OF LEAD BY ASPERGILLUS NIGER: EQUILIBRIUM, KINETICS AND

PROCESS MECHANISM

P. B. KODOLIKAR1, S. P. KODOLIKAR

2, D. S. BHATKHANDE

3 & S. S. GORE

4

1AS, Honeywell Automation India Ltd., Pune, Maharashtra, India

2Department of Chemical Engineering, Sinhgad College of Engineering, Pune, Maharashtra, India

3Department of Chemical Engineering, Vishwakarma Institutes, Pune, Maharashtra, India

4Department of Microbiology, Fergusson College, Pune, Maharashtra, India

ABSTRACT

This paper describes the equilibrium, kinetics and process mechanism studies on biosorption of lead ions from

aqueous solution using ‘Aspergillus niger’ in a batch process. The results indicate that biosorption of lead is influenced by

various experimental parameters such as initial concentration of lead, amount of biomass used, variation in pH of solution

and agitation speed. The lead uptake by biomass was quantitatively evaluated using sorption isotherms like Freundlich and

Langmuir isotherm. The results indicate that Langmuir isotherm model describes the present data very well indicating

favorable biosorption. Since the process follows pseudo second order kinetics, the mechanism of biosorption of lead by

Aspergillus niger can be explained by shrinking core model.

KEYWORDS: Biosorption, Lead Removal, Aspergillus niger

INTRODUCTION

The presence of heavy metals like lead, zinc, nickel, mercury, cadmium etc. in aquatic environment has been of

great concern because of an increase in discharge, their toxic effects and other adverse effects on receiving water. To solve

the water pollution problem by toxic heavy metal contamination resulting from human technological activities has for long

presented a challenge. With well defined point sources of lead contamination, the major spread of lead in environment has

been curbed by introduction of leaded gasoline, mining operations, refining ores, sludge disposal, automobiles and battery

manufacturing, electronics and electrical equipments, e-wastes, mobiles, car batteries, television sets etc.[4,8,18,20]

Biosorption is defined as the ability of biological materials to accumulate heavy metals from waste water through

metabolically mediated or physico-chemical pathways of uptake [18].

The uptake of heavy metals by biomass can reach up

to 50% of biomass dry weight. New biosorbents can be manipulated for better efficiency and multiple reuses to increase

their economic attractiveness [2, 4]

. The biomass used for this purpose must come from nature or even has to be a waste

material like sea weeds, moulds, yeasts, bacteria, crab shells etc. The mechanism involved due to interaction between a

metal ions and biomass are complex in nature. The complex structure of microorganisms implies that there are many ways

for the metal to be taken up by the microbial cell. It has been postulated that the different metal binding mechanisms active

in biosorption are chemisorptions, physical adsorption, and micro precipitation.

MATERIALS AND METHODS

Preparation of Biomass

Aspergillus niger of NICM grade From National Chemical Laboratory, Pune was used for the experimentation.

Aspergillus niger was obtained on slants, which was cultivated in liquid medium using shake flask method. Spores and

International Journal of Bio-Technology

and Research (IJBTR)

ISSN 2249-6858

Vol. 3, Issue 4, Oct 2013, 77-90

© TJPRC Pvt. Ltd.

78 P. B. Kodolikar, S. P. Kodolikar, D. S. Bhatkhande & S. S. Gore

mycelium from these slants were transferred to 250 ml Erlenmeyer flasks containing 100 ml of growth medium.

Growth medium of following composition for 1 lt of medium was used; (all weights in g) Bacto Dextrose 20;

Peptone 10; NaCl 0.2; CaCl2HO 01; KCl 0.1; KHPO 0.5; NaHCO 0.05; MgSo 0.25; Fe(SO)HO 0.005. The second type of

medium that was prepared was called Sabouraud Broth. It was of the following composition for 1 lt of medium; (all

weights in g) Dextrose 40; Peptone 10. Both the mediums were prepared in distilled water and were autoclaved adjusting

the pH value to 5.0 using 1N HCl. Flasks containing the growth medium were kept in autoclave. Then the pressure in the

autoclave was maintained at 15 kg/cm2 for 15 minutes. The biomass was inoculated in this sterilized growth medium.

Approved culture of Aspergillus niger was used for inoculation. Aseptic conditions required for inoculation was

prepared by using two burners at a distance of approximately 6 inches, wherein the inoculation was carried out. Nichrome

wire loop was sterilized by holding it in the blue flame of the burner. With the help of the wire loop small amount of

culture was transferred into the sterilized growth medium, in the aseptic zone between the two burners. Then the flasks

with the culture were kept on the shaker incubator at 25oC and 160 rpm. The culture was incubated for 96 hrs when

sufficient growth was observed. [5]

After 96 hrs the biomass was observed under microscope for its growth. The grown biomass was then killed in the

autoclave. The same procedure as explained above was repeated. The killed biomass was then separated from its growth

medium by centrifuge. Then the biomass was dried at 60oC in the drier for 24 hrs. The dried biomass was then powdered in

mortar and pestle and used for further experimentation. [9, 10]

Lead solutions of desired concentrations were prepared from

PbNO3, by dissolving the exact quantities of Lead salt in deionized water. All Chemical were commercial products used

without purification.

Studies on Equilibrium, Uptake Kinetics and Adsorption of Metal

The initial concentration of the metal concentration was 60 mg/l for all experiments except for that carried out to

examine the effect of the initial concentration of lead. For metal removal kinetics studies, 0.2 g of Aspergillus niger was

contacted with 100 ml of solution with initial metal concentration of 300 mg/l, in an Erlenmeyer flask, in an incubator

shaker. In all cases working pH was that of the solution and was not controlled. At appropriate time intervals, shaking was

briefly interrupted while 1-5 ml volumes of supernatant solutions after decantation was pipetted from the reactor and were

analyzed to determine the residual metal concentration in the solution. [3, 9, 10]

The analysis of the lead was done using

atomic absorption spectrophotometer AAS- Chemito – 201 (Flame Atomic Absorption Spectrophotometer) using air-

acetylene flame.

The adsorption capacity is obtained by using a mass equilibrium equation. The adsorption capacity expressed as

follows:

[1]

Co and C* being the initial and equilibrium concentration respectively. V is the experimental volume expressed in

liters. m is the adsorbent mass expressed in grams. q is amount of metal adsorbed in mg/g of biomass. The equilibrium

isotherms were determined by contacting a constant mass (0.2g) of Aspergillus niger with range of different concentrations

of lead solutions. The biomass and metal solution were agitated in a series of 250ml flasks with equal volumes of solution

(100ml) for a period of 24h at room temperature.

The contact time was determined by kinetic tests using same conditions.

Biosorption of Lead by Aspergillus niger: Equilibrium, Kinetics and Process Mechanism 79

RESULTS AND DISCUSSIONS

All batch sorption experiments reported here were investigated at the initial pH value < 7, because further

biosorption of metal decreases probably because of chemical precipitation, due to the formation of insoluble products of

metal hydroxides. Kinetic experiments were carried out to evaluate the potential of the biomaterial for commercial

applications.

Effect of Contact Time

In comparison to conventional processes biosorption reaction kinetics are fairly rapid, usually in the order of

seconds or minutes. Research has shown that the majority of metal ions are removed within the first 15 min of the reaction.

High, rapid sorption rates are typical for adsorption of dissolved substances on a solid material. [Figure 1] Observed

adsorption patterns are usually biphasic and appear similar, i.e. an initial rapid metabolism-independent stage followed by a

slower second stage with equilibrium usually been attained in a few minutes. The effect of initial metal ion concentration

affects reaction kinetics significantly. High initial concentrations establish stronger driving forces for mass transfer and

result in faster kinetics than do lower metal concentrations.

Figure 1: Plot of Metal Uptake (q) against Time

Effect of Initial Metal Concentration

Experiments were undertaken to study the effect of initial concentration on the Lead removal kinetics from the

solution. The results obtained are shown in Figures 2 and 3, which indicate that the obtained curves have the same shape.

The necessary time to reach equilibrium is variable according to the initial concentration of Lead: About 6 hrs (Co

= 40 and 60 mg/l), 8 hrs (Co = 80 and 100 mg/l). The maximum quantity of Lead removed was observed at initial

concentration of 60 mg/l, which was used for further experimentation.

Figure 2: Metal Uptake (q) against Time for Various Initial Metal Concentrations


Effect of Dosage of Biomass Aspergillus niger

Figure 3: % Metal Removal against Concentration

To determine the necessary biomass quantity for maximum removal of Lead, the effect of biomass on the kinetics

of lead removal was studied. Figures 3 and 4 shows that the capacity of Lead sorption at equilibrium by biomass increases

with the quantity of the biomass introduced (1 to 5 g/l), this can be explained by the fact that more the biomass increases,

more the surface of contact offered to the sorption of Lead becomes important. The maximum quantity at the equilibrium

of Lead removal by biomass is about 23.5mg/g for 2g/l of biomass. This optimum amount (2g/l) was used for further

experimentation.

Figure 4: Metal Uptake (q) against Time for Varying Dosage of Biomass

Figure 5: % Metal Removal against Dosage of Biomass


Effect of pH

The pH of the medium affects the solubility of metal ions and the concentration of the counter ions on the

functional groups of the biomass cell walls. Sorption of heavy metals from aqueous solution depends on properties of

adsorbent and molecules of adsorbate transfer from the solution to the solid phase. Biosorption capacity of heavy metal

increase as the pH of the solution increases. It was found that the fungal biomass possessed maximum sorption capacity for

the cationic metal ions at pH = 6.0 (refer figures 6 and 7). Further, biosorption of metal decreases, probably because of

chemical precipitation and may be due to the formation of insoluble products of metal hydroxides. Thus, turbidity was

observed when the pH of the solution was 8.0. Optimum value of pH = 6.0 was used for further experimentation.

Figure 6: Metal Uptake (q) against Time for Varying pH

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9

% rem

oval

pH

Figure 7: % Metal Removal against pH

Effect of Agitation Speed

In the goal to determine the optimal speed of agitation, the kinetics of Lead removal by biomass was studied using

agitation speeds ranging from 40 rpm to 200 rpm. Figures (8 and 9) show that the high capacity of Lead removed at

equilibrium, which is about 25.35mg/g of biomass, is obtained with agitation speed of 200 rpm. Figures show that the

drastic increase in metal binding is observed from 40 rpm to 120 rpm. Thereafter, the shaking speed does not show

proportional increase in adsorption (metal binding).


Figure 8: Metal Uptake (q) against Time for Varying Agitation Speeds

67

68

69

70

71

72

73

74

75

0 50 100 150 200 250

% rem

oval

shaking speed (rpm)

Figure 9: % Metal Removal against Shaking Speed

ANALYSIS OF RESULTS OBTAINEDS

Equilibrium Modeling

Modeling the equilibrium data is fundamental for the industrial application of biosorption since it gives

information for comparison among different bio-materials under different operational conditions, designing and optimizing

operating procedures. To examine the relationship between sorbed concentrations (q*) and aqueous concentrations (C*) at

equilibrium, sorption isotherm models are widely employed for fitting the data, of which the Langmuir and Freundlich

equations (effect of initial metal concentration) are most widely used. (Refer figures 10 and 11)

The Langmuir isotherm model assumes the form:

[2]

where Qo (mg/g) is the maximum amount of ion per unit mass of fungi to form a complete monolayer on the

surface and KL is the equilibrium adsorption constant which is related to the affinity of the binding sites. Qo represents a

practical limiting adsorption capacity when the surface is fully covered with metal ions and allows the comparison of

adsorption performance, particularly in the cases where the sorbent did not reach its full saturation in experiments. The

Langmuir parameters can be determined from a linearized form of equation, represented by:


[3]

Therefore, plot of versus C*, gives a straight line of slope 1/Qo and intercept 1/ (QoKL).

y = 0.046x + 0.135R² = 0.966

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70 80

C*/

q*

C*

Figure 10: Langmuir Adsorption Isotherm

y = 0.736x + 0.904R² = 0.126

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

ln C

*

ln(Co-C*)

Figure 11: Freundlich Adsorption Isotherm

On the other hand, Freundlich equation is given by:


[4]

where KF and n are the Freundlich constants, characteristics of the system, indicating the adsorption capacity

and the adsorption intensity, respectively. To simplify the derivation of KF and 1/n the above equation can be linearized in

logarithmic form: [6]

[5]

Kinetic Modeling

The fast biosorption kinetics observed is typical for biosorption of metals involving no energy-mediated reactions,

where metal removal from solution is due to purely physio-chemical interactions between biomass and metal solution. Two

different kinetic models were used to adjust the experimental data of Pb biosorption on Aspergillus niger. The pseudo first

order Lagergren model is generally expressed as

[6]

Integrating between limits, t = 0 to t = t and q = 0 to q = q*

[7]

Linear plots of log (q*- q) versus t indicate the applicability of this kinetic model. (Figure 12) However to adjust

equation to the experimental data, the value of q* must be pre-estimated by extrapolating the experimental data.

Figure 12: 1st Order Lagergren Model (Effect of Initial Metal Concentration)

The pseudo-second order model is based on the assumption that biosorption follows a second order mechanism. So the

rate of occupation of adsorption sites is proportional to the square of the number of unoccupied sites.

[8]


Integrating for the boundary conditions t=0 to t=t and q=q*, and then linearizing it determines an equation

such as:

[9]

q* and k2ads can be calculated from the slope and the intercept of the plot t/q versus t.(Figure 13) It is important

to notice that it is not necessary to estimate the experimental value of q* for the application of such a model. [6]

Figure 13: Pseudo 2nd

Order Lagergren Model (Effect of Metal Concentration)

Effect of Concentration on Adsorption Kinetics

According to Figure 1, the kinetics of Lead removal by Aspergillus niger presents a shape characterized by a

strong increase of the capacity of Lead removal by Aspergillus niger during the first few hours of contact between the

solution and Aspergillus niger; follow up of a slow increase until a state of equilibrium is reached. As an approximation,

the removal of lead ions can be said to take place in two distinct steps: a relatively fast one, followed by a slower one. The

necessary time to reach this equilibrium is about 8 to 10 hours and an increase of removal time to 24 hours did not show

noticeable effects.

Kinetics of Lead removal was studied using first order Lagergren model and pseudo second order Lagergren

model, whereas equilibrium modeling was studied using Freundlich and Langmuir adsorption isotherms. Plots of (ln C* vs.

ln Co-C*) for Freundlich isotherm and (C* vs. C*/q*) for Langmuir adsorption isotherm were plotted. Linear plots of [log

(q*-q) vs. time] and (time/q vs. time) for first order Lagergren model and pseudo second order Lagergren model

respectively, were plotted. Values of high correlation coefficient at different concentration values and for different models

can be tabulated as follows:

Table 1: Comparison of Kinetic Models

Concentration

(mg/l)

First Order

Lagergren (R2)

Pseudo Second Order

Lagergren (R2)

114 0.2223 0.9963

92 0.8022 0.9862

68 0.9050 0.9948

45 0.9549 0.9928


High correlation coefficients for Freundlich and Langmuir adsorption isotherms are as follows: Freundlich

(R2) = 0.1584, Langmuir (R

2) = 0.9664

The order of the models can be explained as follows: Pseudo Second order Lagergren (R2 = 0.9948) >

Langmuir (R2 = 0.9664) > First order Lagergren (R

2 = 0.9050) > Freundlich (R

2 = 0.1584)

Effect of Amount of Biomass on Adsorption Kinetics

The data obtained was fitted for all the above models. It was found that when fitted to the pseudo second order

rate equation (figure 14) straight lines were obtained indicating that the process follows pseudo second order kinetics, with

high correlation coefficient; R2 = 0.9975.

y = 0.047x + 0.022R² = 0.997

y = 0.040x + 0.034R² = 0.994

y = 0.057x + 0.040R² = 0.996

y = 0.088x + 0.056R² = 0.997

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

t/q

(h

rs.g

/mg

)

time (hrs)

0.1 g

0.2g

0.3g

0.5g

Linear (0.1 g)

Linear (0.2g )

Linear (0.3g)

Linear (0.5g)

Figure 14: Plot for Pseudo 2nd

Order Lagergren Model (Effect Biomass Dosage)

Effect of pH on Adsorption Kinetics



high correlation coefficient; R2 = 0.9998 at various pH values.


y = 0.063x + 0.057R² = 0.995

y = 0.040x + 0.034R² = 0.994

y = 0.039x + 0.032R² = 0.990

y = 0.162x + 0.032R² = 0.999

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 5 10 15 20 25 30

t/q

time(hrs)

pH=4.0

pH=5.0

pH=6.0

pH=8.0

Linear (pH=4.0)

Linear (pH=5.0)

Linear (pH=6.0)

Linear (pH=8.0)


Order Lagergren Model (Effect of pH)

Effect of Shaking Speed on Adsorption Kinetics



high correlation coefficient; R2 = 0.9996 for various shaking speeds.

y = 0.041x + 0.022R² = 0.998

y = 0.039x + 0.017R² = 0.998

y = 0.039x + 0.007R² = 0.999

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30

t/q

time (hrs)

40 rp[m

120rpm

200rpm

Linear (40 rp[m)

Linear (120rpm)

Linear (200rpm)


Order Lagergren Model (Effect of Shaking Speed)

ADSORPTION MECHANISM: SHRINKING CORE MODEL (SCM)

As we have seen that the pseudo second order kinetics model best explains the process, so shrinking core

model or shell progressive model best explains the process mechanism. The SCM can be described by the following

equation, [16, 12]


[10]

On simplification the function can be expressed as

[11]

The plot of f(x) vs. Cdt shows that the shrinking core model or shell progressive model describes the

biosorption of lead metal ions on the biomass Aspergillus niger. (Figure 17)

Table 2: Data for Shrinking Core Model

Concentration(mg/l) Time (mins) C dt f(x)=1-3(1-

x)(2/3)

+2(1-x)

114 0 0 0

97 60 6330 0.075

88 120 8970 0.210

80 240 15160 0.453

77 360 20475 0.693

75 480 25392 1.0

74 600 30150 1.0

y = 3E-05xR² = 0.950

0

0.2

0.4

0.6

0.8

1

1.2

0 5000 10000 15000 20000 25000 30000 35000

f(x)

C dt

Figure 17: Plot for Shrinking Core Model

CONCLUSIONS

Based on the above studies and experimentation of Biosorption, we can conclude the following:

The results obtained confirm that Aspergillus niger in the form of flakes (dried) can remove Lead from aqueous

solution for very low concentration (1-100mg/l).

Sorption of Lead is strongly affected due to the following parameters: Initial concentration of Lead,Initial amount

of Aspergillus niger, Initial pH of solution, Shaking speed of the shaker incubator


The Langmuir adsorption model effectively described the biosorption equilibrium of Lead on Aspergillus niger.

Langmuir model gives better correlation coefficient than Freundlich adsorption isotherm.[regression coefficients

= Freundlich (R2) = 0.1584, Langmuir (R

2) = 0.9664]

The linearity of the plots of [t/q vs t] confirmed that the process follows pseudo second order rate kinetics.

The maximum removal capacity at room temperature of Lead ions is about 24.60 mg/g of Aspergillus niger.

The kinetics of sorption process followed a pseudo second order kinetics and it was apparent that the sorption is

controlled by the diffusion process, as the data fits well into shrinking core model giving straight line passing

through the origin; with high correlation coefficient; R2 = 0.9996 for various shaking speeds.

REFERENCES

1. Boopathy R., Factors Limiting Bio-remediation Technologies (review paper) Bioresource Technology,(2000),

74,63 to 67.

2. Gavrilescu M., Removal of Heavy Metals from the Environment by BIosorption, Engg life Sci. (2004),4(3), 219-

232.

3. Ramchandra T.V., Kanamadi R.D. and Ahalya N., Biosorption of Heavy metals, Energy, (1. Centre for Ecological

Sciences, Indian Institute of Science, Banglore, India & Department of Zoology, Karnataka University,

Dharwad,India.) review paper

4. Sakal (marathi newspaper) Dt: 22 April 2005,pp 7(main supplement) Article: e- kachara (e-Waste)

5. Kapoor Anoop and T. Viraraghavan, Heavy Metal Biosorption sites in Aspergillus niger, Bioresource

Technology, (1997), 61, 221- 227.

6. Kapoor Anoop, T. Viraraghavan and D. Roy Cullimore, Removal of Heavy Metals using the fungus Aspergillus

niger, Bioresource Technology, (1999), 72, 95- 104.

7. Benguella B., Benaissa H., Cadmium removal from aqueous solutions by Chitin; Kinetic and Equilibrium Studies,

Water Research, (2002), 36, 2463- 2474.

8. Cruz Claudio C.V., Antonio Carlos A. da Costa, Cristiane A.H., Aderval S.L., Kinetic Modeling and Equilibrium

Studies during Cadmium biosorption by dead Sargassum sp. biomass. Bioresource Technology (2004), 91, 249-

251.

9. Preetha .B. and Viruthagiri T. Kinetic Modelling of Biosorption of Hexavalent Chromium, Chemical Engineering

World, (2004), 66- 69.

10. Levenspiel Octave, Chemical Reaction Engineering, Third edition, John Wiley & Sons.

11. Puranik P.R., Paknikar K.M., Influence of co-cations on biosprtion of Lead and Zinc – A comparative evaluation

in binary and multi-metal systems, Bioresource Technology, (1999), 70, 269 - 276.

12. Ramchandra T.V., Kanamadi R.D. and Ahalya N., Biosorption of Heavy metals, Energy, (1. Centre for Ecological

Sciences, Indian Institute of Science, Banglore, India & Department of Zoology, Karnataka University,

Dharwad,India.) review paper

13. Treybel Robert E., Mass Transfer Operations, McGraw Hill, 3rd

edition ,(1981)


14. Volesky Bohumil, Sorption and Biosorption, 1st edition, Cambridge Press, (2003).

15. Volesky Boya, Regine H.S.F Viera, Biosorption: a solution to pollution (review article) International

Microbiology (2000), 3, 17- 24.

16. Zelilea Filiponic Kovacemic, Laszlo sipos and elicita Briski, Biosorption of Chromium, Copper, Nickel and Zinc

ions onto fungun pellets of Aspergillus niger 405 from aqueous solution, Food Technology and Biotechnology,

(2000), 38(3), 211- 216.

17. Zhang Li, Zhas Li, Yaoting Yu and Changzi Chen, Removal of Lead from aqueous solution by non living

Rhizopus nigricans, Water Research, (1998), 32(5), 1437- 1444.

18. Zouboulis Anastasio I, Rouzou E.G., Matis K.A. and Hancock Ian C, Removal of Toxic Metals from aqueous

mixtures; Part I – Biosorption j. Chemical Technology and Biotechnology, (1999), 74, 429 - 436.

19. http://www.mcgill.ca/biosorption/publication/index.htm

20. http://wgbis.ces.iisc.ernet.in/energy/water/paper/researchpaper2.html

21. http://www.osha.gov/SLTC/metalsheavy/index.html

22. http://www.amazon.com/exec/obidos/ASIN/0849349176/002-9325713-0621403

Date post:	09-Jan-2023
Category:	Documents
Upload:	independent
View:	0 times
Download:	0 times

Biosorption of Lead by Aspergillus niger: Equilibrium, Kinetics and Process Mechanism

Documents