239 Research report
Fluoride 46(4)239–245 October-December 2013
Fluoride biosorption by Aspergillus and its Ca-impregnated biomass Mondal, Kundu, Das, Bhaumik, Datta
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BIOSORPTION OF FLUORIDE FROM AQUEOUS PHASE ONTO ASPERGILLUS AND ITS CALCIUM-IMPREGNATED BIOMASS AND EVALUATION OF ADSORPTION KINETICS Naba Kumar Mondal,a,* Monalisa Kundu,a Kousik Das,a Ria Bhaumik,a Jayanta Kumar Dattaa Burdwan, West Bengal, India
SUMMARY: Adsorption of fluoride (F) by Aspergillus and Ca-pretreated Aspergillus biomass was conducted in an aqueous batch system and the maximum F adsorption capacities were found to be 8.09 mg/g (at pH 10) and 4.80 mg/g (at pH 8) respectively. For both the Aspergillus and Ca-pretreated Aspergillus adsorbents, the equilibrium isotherm fitted with the Freundlich isotherm and the adsorption kinetics obeyed the pseudo-second order equation. Thermodynamic analysis indicated that the adsorption process was exothermic and spontaneous for both adsorbents. Fourier transform infrared analysis of Aspergillus indicated the existence of potential fluoride-capturing functional groups. Keywords: Adsorption; Aspergillus; Defluoridation; Isotherm; Thermodynamics; Calcium-loaded Aspergillus. INTRODUCTION
The presence of fluoride ion (F) in potable water has unique effects on human health1 and there has been a increasing global concern with fluoride due to its toxicity in biological systems.2 According to the World Health Organization (WHO), the tolerance limit of fluoride concentration in drinking water is 1.5 mg/ L3 and it is important to remove of such toxic inorganic constituents from drinking water when they are present at an excessive level. De-fluoridation is normally carried out by membrane filtration,4 precipitation, nanofiltration,5 ion-exchange,6 electro-coagulation7 and adsorption,8 with the latter being the most effective and widely used method. In recent years, considerable attention has been focused on fluoride removal using natural biomass materials such as egg shell and calcareous solutions8,9 but these adsorbents have limitations10 and there is still a need for an effective, low cost adsorbent. The present study focused on F adsorption from an aqueous synthetic solution by Aspergillus and Ca-pretreated Aspergillus biomass with examination of various operating parameters including biomass dosage, solution pH, F concentration, contact time and working temperature. The adsorption capacity, isotherm, kinetics, thermodynamics and adsorption chemistry were also analyzed. MATERIALS AND METHODS
Preparation of Aspergillus biomass: A malt extract medium, 150 mL in volume, was prepared, sterilized in a autoclave, and allowed to cool at room temperature. One loop of a pure culture of Aspergillus sp. was added and, after mixing, the inoculated medium was incubated at 28ºC. After seven days of incubation the biomass of Aspergillus had grown into the medium and after ten days the biomass aDepartment
of Environmental Science, The University of Burdwan. *Corresponding author: Dr Naba Kumar Mondal, Assistant Professor, Department of Environmental Science, The University of Burdwan. E-mail:
[email protected]
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of Aspergillus was harvested by filtration and dried in a incubator at 37ºC. The dried biomass was then ground and kept, in powdered form, in a desiccator for further use. Preparation of Ca-pretreated Aspergillus biomass: Dried biomass, weighing 0.5 g, was suspended in a beaker containing 100 mL of aqueous CaCl2 solution in a concentration of 100 mg/L and mixed well for 30 min on stirring machine. It was then filtered with Whatman-42 filter paper and allowed to dry at room temperature. The dried biomass was then stored for further use in an air-tight container in a desiccator. The physico-chemical analyses of both the adsorbents are shown in Table 1. Table 1. Physica l cha racter istics of Aspergi llus sp. V alues are Mean ± SD P arameters
Aspe rgillus sp .
Calcium pretrea te d Asperg illus sp.
Co nductivity (mS/cm)
12 ± 0.709
1 5 ± 0.43 2
Specific g ravity
0.296 ± 0.006
0 .28 8 ± 0 .05
Bulk density (g/cc)
0.278 ± 0.014
0 .29 3 ± 0 .11 8
Particle density (g/cc)
0.549 ± 0.004
0 .51 1 ± 0 .03 3
Poro sity (% )
36.08 ± 0.145
3 7.2 1 ± 0 .16 4
Mo istur e con ten t (%)
2.69 ± 0.036
3 .10 ± 0.023
pH zpc
8.2
8 .5
The influence of the aqueous phase pH on the F adsorptive uptake was studied by adjusting the reaction mixture to different initial pH values from 2.0 to 10.0 and analyzing for residual F after equilibrium contact time. The F content of the supernatants was determined colorimnetrically using the SPANDS method (APHA, 1998).11 RESULTS AND DISCUSSIONS
Effect of pH: The effect of pH on the removal efficiency of F by Aspergillus and Ca-pretreated Aspergillus was studied at different pHs ranging from 2.0 to 10.0. The maximum removal of F was occurred at pH 10 for Aspergillus biomass (65.06%) and at pH 8 for Ca-pretreated Aspergillus (91.96%). Effect of adsorbent dose (g/100mL): Various concentrations of adsorbent (Aspergillus sp.), in the range of 0.03 g to 0.11 g/100 mL, to used to determine the sorption capacity for the adsorbent for a given initial concentration of the adsorbate in the operating conditions. The minimum percentage of removal was 81.54%. The F removal efficiency for Aspergillus did not change with an increase in the adsorbent dose but for Ca-pretreated Aspergillus the percentage of F removal increased with increasing the adsorbent dose.12 The equilibrium adsorption capacity for Ca-pretreated Aspergillus remained the same with increasing amounts of adsorbent.
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Fluoride 46(4)239–245 October-December 2013
Fluoride biosorption by Aspergillus and its Ca-impregnated biomass Mondal, Kundu, Das, Bhaumik, Datta
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Effect of stirring rate (rpm): The removal of F decreased with increasing the stirring rate from 150 to 250 rpm for Aspergillus at the optimum pH of 10 but increased for Ca-pretreated Aspergillus at the optimum pH of 8. Effect of contact time (min): The adsorption of F by Aspergillus increased with increasing contact time up to 40 min but attained equilibrium and then had the same removal percentage until 60 min. For Ca-preteated Aspergillus, removal of F increased with increasing contact time, and equilibrium was attained at 120 min. Merugu et al.13 also reported time dependent F removal by Aspergillus niger. Effect of initial concentration (mg/L): The percentage removal of F increased with increasing the initial F concentration and showed equilibrium after reaching the maximum concentrations of 35 mg/L for Aspergillus and 5 mg/L for Capreteated Aspergillus. The Ca-pretreated Aspergillus showed a higher percentage of removal with increasing the adsorbent dose compared to Aspergillus. Similar high levels of F adsorption by Aspergillus penicilloides were found by Prajapat et al.12 Bhatnagar et al.14 reported that Ca-treated biomasses of Anabaena fertilissima (2.8 mg Ca2+/g dry wt) and Chlorococcum humicola (4.4 mg Ca2+/g dry wt) accumulated, respectively, 7 mg F/g dry wt from an aqueous solution of 10 mg F/L and 4.5 mg F/g dry wt from 15 mg F/L. Effect of Temperature (ºC): The percentage of F removal increased with increasing temperature for Aspergillus but decreased with increasing temperature for Ca-pretreated Aspergillus. This indicates that F adsorption by Aspergillus and Ca-pretreated Aspergillus are endothermic and exothermic respectively. However, Merugu et al.13 reported the opposite trend for F adsorption by Aspergillus niger. Adsorption isotherm study: The experimental data for the Aspergillus biomass showed an excellent fit, with high correlation coefficients, at all temperatures, to the Freundlich, Dubinin-Radushkevich (D-R), and Tempkin adsorption isotherms, but not to the Langmuir isotherm in which the values of KL and qm decreased with temperature indicating that maximum adsorption occurred at lower temperatures (Tables 2–4). The experimental equilibrium data showed a good fit to the empirical Freundlich model at almost all temperatures except 333K where the R2 value was maximal (R2=0.959). The adsorption capacity KF drastically decreased from 313K to 333K which implies that the sorption process is exothermic in nature (Table 3). High n values were found at all the temperatures studied except for 333K, indicating favourable adsorption. On the other hand, the correlation coefficients for Ca-pretreated Aspergillus showed higher values in the Freundlich and Langmuir isotherms at 333K while the D-R and Tempkin isotherms showed good agreement at all the temperatures studied (Tables 2–4). The constant gives an idea about the mean free energy E (kJ/mole) of adsorption per mole of the adsorbate when it is transferred to the surface of the solute from infinity in the solution and can be calculated using the relationship. The magnitude of E was less than 8 kJ/mole for both the absorbents at all the temperatures studied indicating adsorption mechanism of F on Aspergillus and Ca-pretreated Aspergillus is physiorbtion in nature.
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Table 2 . La ngmuir adsorp tio n isother m for Asperg illus sp. and Ca-pretrea te d A spergil lus sp. Temper atu re (k)
Asperg illus sp .
Ca -pretrea ted Asperg illus sp .
q e,e xp (mg/g )
La ngmuir isotherm qm (mg/g)
kL (L/mg)
RL
R2
Equ ati on
3 13
64.27
9 .09
0.45
0 .0 6
0.606
3 33
61.07
6 .17
0.33
0 .0 8
0.89
3 53
56.98
4 .62
0.301
0 .0 8
0.872 3
3 73
50.96
4 .19 6
0.224
0 .1 13
0.768
3 13
34.62
2 .22
2.92
0 .0 09
0.898
3 33
33.32
7 .96
0.835
0 .0 33
0.968 5
3 53
32.48
1 .44
0.934
0 .0 29
0.856
3 73
31.67
1 .56
0.45
0 .0 6
0.943
y = 0.22 5x – 0 .11 0
y = 0.15 4x – 0 .45 0
Ta ble 3. Fr eundl ich ad so rption isoth erm for Aspe rgillus sp . and Ca-p retreated Asperg illus sp.
A sp ergill us sp.
Ca-p retreated A sp ergill us sp.
Temp erature (k)
q e,e xp (mg/g)
313
64.27
333
Freu ndlich isotherm KF (mg
1-(1/n)
1/n
L
-1
g )
2
1/n
R
12 .5 3
1.687
0.885
61.07
2.01
1.83
0.959
353
56.98
3.02 4
1.78
0.917
373
50.96
1.82 4
1.743
0.912
313
34.62
6.19
3.07
0.792
333
33.32
18 .6 6
1.45
0.983
353
32.48
9.83
1.79
0.905
373
31.67
8.05
1.27
0.976
Equ ation
y = 1.687x + 1.09 8
y = 3.071x + 2.79 2
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Table 4. Dubi nin–Rad ushkevich (D-R) adsorption isotherm for Aspergil lus sp. an d Ca -pretreated Aspe rgillu s sp. Temperature (k)
q e,exp (mg/g)
313
64.27
5 5.59
0.307
1.27
0.912
333
61.07
5 5.02
0.497
1.003
0.963 2
353
56.98
5 3.01
0.5489
0.954
0.971 1
373
50.96
4 9.31
0.7935
0.794
0.958
313
34.62
1 75.19
0.164
1.75
0.968 3
333
33.32
2 8.91
0.118
2.05
0.956
353
32.48
2 1.99
0.17
1.71
0.986
373
31.67
2 3.27
0.132
1.95
0.958
Asperg illus sp .
Ca pretreated Asperg illus sp .
Dubin in–Radu sh kevi ch (D-R) isoth erm qm (mg/g)
Β 2 -2 (mmol J )
E (kJ/mole)
R
2
Equa tio n
y= – 0.37 0x + 4.141
y= – 0.16 3x + 5.165
Table 5 . Tempkin adsorptio n isother m for Asperg illus sp. and Ca-pretrea te d A sp ergill us sp.
Asperg illus sp.
Ca -pretrea ted Asperg illus sp.
Te mperature (k)
qe,exp (mg /g)
313
64 .27
333
Tempkin B1
-1
2
k T (Lg )
R
32.38
1.97
0.905
61 .07
30.46
1.26
0.886
353
56 .98
27.85
1.06
0.944
373
50 .96
21.45
1.16
0.927
313
34 .62
28.582
6.58
0.745
333
33 .32
14.145
4.482
0.885
353
32 .48
12.47
3.59
0.884
373
31 .67
11.75
3.01
0.885
Equa ti on
y = 32.38 x + 2 2.0 3
y = 28.58 x + 5 3.6 2
Adsorption kinetics study: From the kinetic study, we found the pseudo first order model was inappropriate for describing the adsorption kinetics of F on to Aspergillus and Ca-pretreated Aspergillus as the experimental data did not accurately fit the pseudo first order equation for either of the studied adsorbents (Tables 6 and 7). However, the pseudo second order equation showed excellent linearity with high correlation coefficients over the temperature ranges of 313K to 373K (Tables 6 and 7). Thermodynamics study: Effect of temperature (313K to 373K) on F removal indicates that the adsorption rate decreases with increasing temperature for both Aspergillus sp and Ca-pretreated Aspergillus and that both reactions are exothermic in nature. In order to study the feasibility of using the bioadsorbents
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for F removal, the thermodynamic free energy parameter (∆Gº) of the process was calculated. Table 6. Pseu do fir st order mod el i n kine tics study for adsor pti on of fluorid e b y Aspergi llus sp. a nd Ca -pretrea ted A sp ergill us sp. Te mperature (k)
Asperg illus sp.
Ca -pretrea ted Asperg illus sp.
qe,ex p (mg/g)
Pseud o first o rder model qe (mg/g)
-1
K1(mi n )
R
2
Eq uation
313
8 .09
2.593
0.0 09
0.040 8
333
7 .81
1.965
0.0 04
0.016 1
353
7 .12
1.18
0.0 11
0.076 9
373
5 .56
1.16
0.0 02
0.201 4
313
4 .80 2
0.013
0.0 36
0.514 7
333
4 .62 5
0.076
0.0 23
0.397
353
4 .55
0.050
0.0 23
0.258
373
4 .48 5
0.029
0.0 21
0.430
y = 0.00 3x +0.413
y = 0.01 5x – 1.90 3
Table 7 . Pseudo second ord er mo del in ki netics stud y fo r adsorption of fluo ride by A sp ergillu s sp. an d Ca- pretreated Aspe rgillus sp .
Asperg illus sp .
Ca pretreated Asperg illus sp .
Tempe rature (k)
qe,exp (mg/g)
31 3 33 3
P se udo second orde r mo del 2
qe (mg/g )
K2 (g/mg /min)
8 .0 9
8.830
0.024
1.119
0 .9 86
7 .8 1
8.48
0.008
0.575
0 .9 84
35 3
7 .1 2
7.33
0.004
0.215
0 .9 07
37 3
5 .5 6
5.74
0.003
0.009
0 .8 48
31 3
4 .8 02
7.003
0.098
4.806
1 .0 00
33 3
4 .6 25
4.854
0.849
20.003
0 .9 37
35 3
4 .5 5
4.566
0.428
8.923
0 .9 99
37 3
4 .4 85
4.63
0.051
1.09
0 .9 99
h (mg/g/min)
R
Equ ation
y = 0.1 46x – 0.887
y = 0.2 07x + 0 .14 2
The negative value of ∆Gº at all temperatures indicates the feasibility of the process and the spontaneous nature of fluoride adsorption on these bioadsorbents. An increase in the value of ∆Gº with increased temperature suggests that the adsorption is most favourable at lower temperatures. From the negative value of ∆Hº for both adsorbents, it can be suggested that the adsorption phenomenon is exothermic in nature. The negative value of ∆Sº suggests the process is enthalpy driven. This indicate that the spontaneous nature of the adsorption reaction increases with the decreasing T value. The enthalpy change (∆Hº) value was negative for the reaction, indicating the exothermic nature of the reaction. Thus, the adsorption is favoured more with a decreasing T in the reaction in accordance to the La Chattelier principle. The negative value for the entropy change (∆Sº) reflects that the reaction takes place with decreasing entropy.
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SEM Study: The SEM (Scanning Electron Micrograph) study was done to understand the surface morphology of Aspergillus. From the surface image, it was observed that the surface morphology has an irregular pattern in both Aspergillus and Ca-pretreated Aspergillus. The image did not allow pore size identification or the size distribution of the adsorbents. FTIR Study: The FTIR (Fourier Transform Infra-Red) spectrums for Aspergillus sp. clearly indicate the strong adsorption band at 3410 cm-1 indicates the presence of –OH groups on the adsorbent surface while peaks at 1638, 1408, and 1036 cm-1 are related to the C=C, C-C, and –C-O- stretching respectively. ACKNOWLEDGEMENT
The authors wish to express their gratitude to Dr Jayanta Kumar Datta, Professor, Department of Environmental Science, The University of Burdwan, for his continuous encouragement. REFERENCES 1 Mohan SV, Ramanaiah SV, Rajkumar B, Sarma PN. Biosorption of fluoride from aqueous phase onto algal Spirogyra IO1 and evaluation of adsorption kinetics. Bioresource Technology 2007;98: 1006-11. 2 Susheela AK, Kumar A, Bhatnagar M, Bahadur R. Prevalence of endemic fluorosis with gastrointestinal manifestations in people living in some North-Indian villages. Fluoride 1993;26:97-104. 3 WHO. Guidelines for drinking-water quality. 2nd ed. Geneva: World Health Organisation; 1993. 4 Ndiaye PI, Moulin P, Dominguez L, Millet JC, Charbit F. Removal of fluoride from electronic industrial effluent by RO membrane separation. Desalination 2005;173:25-32. 5 Simons R. Trace-element removal from ash dam waters by nanofiltrationand diffusion dialysis. Desalination 1993;89:325-41. 6 Ruixia L, Jinlong G, Hongxiao T. Adsorption of fluoride, phosphate, and arsenate ions on a new type pf ion exchange fiber. J Colloid Interface Sci 2002;248:268-74. 7 Hu CY, Lo SL, Kuan WH, Lee YD. Removal of fluoride from semiconductor wastewater by electrocoagulation-flotation. Water Res 2005;39:895-901. 8 Bhaumik R, Mondal NK, Das B, Roy P, Pal KC, Das C, et al. Eggshell powder as an adsorbent for removal of fluoride from aqueous solution: equilibrium, kinetic and thermodynamic studies. E-Journal Chem 2012;9:1457-80. 9 Mondal NK, Das B, Bhaumik R, Roy P. Calcareous Soil as a promising adsorbent to remove fluoride from aqueous solution: equilibrium, kinetic and thermodynamic study. Journal of Modern Chemistry & Chemical Technology 2012;3:1-21. 10 Chena N, Zhang Z, Fenga C, Sugiura N, Li M, Chen R. Fluoride removal from water by granular ceramic adsorption. J Colloid Interface Sci 2010;348:579-84. 11 American Public Health Association (APHA). Standard methods for the examination of water and wastewater. 20th ed. Washington, DC: APHA; 1998. 12 Prajapat R, Gaur RK, Raizada R, Gupta VK. In silico analysis of genetic diversity of begomovirus using homology modelling. J Biol Sci 2010;10:217-23. 13 Merugu R, Garimella SS, Kudal KR, Ramesh D, Rudra MPP. Optimizxation studies for defluoridation of water using Aspergillus niger fungal biosorbent. Inter J Chem Tech Res 2012;4:1089-93. 14 Bhatnagar M, Bhatnagar A, Jha S. Interactive biosorption by microalgal biomass as a tool for fluoride removal. Biotechnol Lett 2002;24:1079-81. Copyright © 2013 The International Society for Fluoride Research Inc. www.fluorideresearch.org www.fluorideresearch.com www.fluorideresearch.net Editorial Office: 727 Brighton Road, Ocean View, Dunedin 9035, New Zealand.
