Comparative studies on the microbial adsorption of heavy metals

Comparative studies on the microbial adsorption of heavy metals

Advances in Environmental Research 7 (2003) 311–319 Comparative studies on the microbial adsorption of heavy metals N. Goyala, S.C. Jaina, U.C. Baner...

229KB Sizes 15 Downloads 128 Views

Advances in Environmental Research 7 (2003) 311–319

Comparative studies on the microbial adsorption of heavy metals N. Goyala, S.C. Jaina, U.C. Banerjeeb,* a

Department of Chemical Engineering and Technology, Panjab University, Chandigarh 160 014, India b Institute of Microbial Technology, Sector – 39 A, Chandigarh 160 036, India Accepted 5 December 2001

Abstract A process of competitive biosorption of Cr(VI) and Fe(III) ions on Streptococcus equisimilis, Saccharomyces cerevisiae and Aspergillus niger is described and compared to single metal ion adsorption in solution. The ability of these three microorganisms to adsorb metal ions wCr(VI) and Fe(III)x, is shown as a function of metal concentration, pH, temperature, growth medium composition, culture age and contact time with the biosorbents. The effect of addition of an extra energy source in the form of glucose, fructose and sucrose in the adsorption medium is studied for the biosorption of metal ions by microorganisms. Freundlich constants are determined from the Freundlich adsorption isotherms for all the organisms. The adsorbed metals from the sorbents can be regenerated in situ with 0.1 M sodium hydroxide. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biosorption; Streptococcus equisimilis; Saccharomyces cerevisiae; Aspergillus niger; Biosorbents; Freundlich constants; Isotherms

1. Introduction The toxic heavy metals cause serious threat to the environment, animals and humans. Many industries such as mining, iron-sheet cleaning, plating, metal processing, automobile parts manufacturing, dyeing, textile, fertilizer and petroleum industries release heavy metals such as chromium and iron in the environment (Rapoport and Muter, 1995). Like all transition metals, chromium can exist in several oxidation states from Cr(0), the metallic form to the hexavalent form, Cr(VI). However, only the trivalent and hexavalent forms are environmentally important; the latter being of particular concern because of its greater toxicity. Iron present in industrial *Corresponding author. Department of Biotechnology, National Institute of Pharmaceutical Education and Research, Sector 67, S.A.S. Nagar, Mohali 160 062, Punjab, India. Tel.: q91-172-214682–87; fax: q91-172-214692. E-mail address: [email protected] (U.C. Banerjee).

wastes is primarily in the form of the trivalent Fe(III) ion. Chromium and ferric ion concentrations in industrial waste water approach 200–500 and 10–50 mgyl, respectively. According to the US Environmental Protection Agency (EPA) the acceptable value of Cr is 0.05 mgyl and for Fe, it is less than 1 mgyl (Sag et al., 1998). Chemical oxidation–reduction, precipitation, adsorption, solidification, electrolytic recovery and ion exchange are some of the physico-chemical wastewater treatment processes which are being used for metal removal. Application of such processes, however, is sometimes restricted because of technical or economical constraints. Precipitation by alkali addition usually produces large quantities of solid sludge for disposal. Adsorption and ion exchange processes are expensive when the heavy metal concentrations are in the range of 10–100 mgyl (Eccles, 1999). Therefore, there is a need for the development of low cost processes where metal ions can be removed economically. The search

1093-0191/03/$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 0 9 3 - 0 1 9 1 Ž 0 2 . 0 0 0 0 4 - 7

312

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

for new and innovative treatment technologies has focussed attention on the metal binding capacities of microorganisms such as bacteria, yeast and algae, etc. Bacteria, yeasts and fungi have been used successfully as biosorbents for heavy metals. The metal uptake process, however, is complex and dependent on the chemistry of the metal ions, specific surface properties of the organisms, cell physiology and the physicochemical influence of the environment like pH, temperature and metal concentration. The same metal ions appear to be accumulated by different mechanisms in different microorganisms. The present work is focussed on the use of various microbes i.e. Streptococcus equisimilis (bacteria), Saccharomyces cerevisiae (yeast) and Aspergillus niger (fungus) for the biosorption of the heavy metal ions Cr(VI) and Fe(III). 2. Materials and methods

potassium permanganate solution until the iron solution remained faintly pink. The solution was cooled and diluted to 1 l (Sag and Kutsal, 1996). 2.3. Assay The concentration of unadsorbed Cr(VI) in the biosorption medium was determined spectrophotometrically at 540 nm in a spectrophotometer (Shimadzu, Japan) using diphenyl carbazide as the complexing agent (Snell and Snell, 1959). The presence of Fe(III) in Cr(VI) containing medium did not interfere with Cr(VI) analysis. The concentration of free Fe(II) in the biosorption medium was also determined spectrophotometrically (Sandell, 1961). The colored complex of Fe(III) with sodium salicylate was read at 530 nm. 2.4. pH and temperature studies

2.1. Growth and preparation of cellmass suspension S. equisimilis was grown at 34 8C in a fermenter (Chemap AG. Switzerland) for 12 h. The composition of the medium was (gyl): brain heart infusion 25, peptone 10, dextrose 40, NaH2PO4 6 and Na2CO3 4. The pH of the medium was adjusted to 7.8. S. cerevisiae was grown in a medium containing (gyl): yeast extract 10, peptone 10 and dextrose 20. The pH of the medium was adjusted to 4.8. The cells were grown at 30 8C for 2 days in an incubator shaker (200 rpm). A. niger was grown at 30 8C in the fermenter for 3 days. The medium composition was (gyl): starch 10, glucose 30, KCl 0.5, MgSO4 0.5, FeSO4 0.1 and NH4NO3 5. The pH of the medium was adjusted to 5.5. After the fermentation was over, cells of S. equisimilis, S. cerevisiae and A. niger were collected by centrifuging the individual fermentation broth at 10,000 rpm for 20 min at 4 8C. The cells were thoroughly washed with distilled water and used for bioadsorption studies. 2.2. Preparation of metal solutions The test solutions containing single Cr(VI) or Fe(III) ions were prepared from the analytical grade chemicals. The ranges of concentrations of both metal ions prepared from stock solutions varied between 25 and 250 mgyl. Before mixing the microorganisms, the pH of each test solution was adjusted to the required value with 1 M H2SO4. A stock solution of Cr(VI) was obtained by dissolving 0.283 g of dried potassium dichromate (K2Cr2O7) in 1 l double distilled water. Stock of Fe(III) solution was prepared from ferrous ammonium sulphate as follows: 7.022 g of crystallized ferrous ammonium sulphate was dissolved in 500 ml double distilled water and 50 ml of 1:1 sulfuric acid was added. The solution was warmed and oxidized with approximately 0.1%

To check the effect of pH on biosorption, the cellmass was conditioned to different pH environments (ranging between 2 and 5) with different initial Cr(VI) concentrations. The cellmass of S. equisimilis, S. cerevisiae and A. niger was exposed to metal solution in flasks incubated at different temperatures (ranging between 25 and 40 8C) in an incubator shaker (200 rpm) for 24 h. The metal sorption ability of the cellmass at varying temperatures was determined by estimating residual metal concentration in the solution. 2.5. Effect of cations To study the effect of Fe(III) on Cr(VI) adsorption, the initial Cr(VI) concentration was varied between 25 and 150 mgyl, while the Fe(III) concentration in each biosorption medium was kept constant at 10, 25 and 50 mgyl. To see the effect of Cr(VI) on the adsorption of Fe(III), the initial concentration of Fe(III) was varied between 10 and 50 mgyl, while the Cr(VI) concentration in each biosorption medium was held constant at 25, 50, 75, 100 and 150 mgyl. 2.6. Effect of cellmass concentration The effect of cellmass concentration was checked by exposing the cellmass (5–40 mg dry cellmass) to 20 ml of metal solution at optimum pH and temperature. 2.7. Effect of culture age In order to see the effect of culture age and cellmass composition on the adsorption of metal ions, organisms were grown to different phases of growth and in different media.

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

Fig. 1. Effect of pH on the adsorption of Cr(VI) ion by S. equisimilis, S. cerevisiae and A. niger (temperature, 25 8C; Cr(VI) ion, 100 mgyl; cellmass, 0.75 gyl; agitation, 200 rpm).

2.8. Effect of carbon source Glucose, fructose and sucrose were added (10 gyl, each) as individual carbon sources in the growth medium. 2.9. Effect of nutrient condition The yeast, S. cerevisiae, was grown in basal medium (standard medium) containing (gyl): glucose 10; (NH4)2SO4 2; (NH4)2HPO4 0.64; KCl 0.29; MgSO4Ø7H2O 0.15; CaCl2Ø2H2O 0.094; CuSO4Ø5H2O 0.00078; ZnSO4Ø7H2O 0.003; MnSO4Ø2H2O 0.0035; FeCl3Ø6H2O 0.0048; biotin 0.00001; m-inositol 0.02; Ca-pantothenate 0.01; Vitamin B1 0.02 and Vitamin B6 0.0005. For studies regarding the influence of additional glucose, phosphate, ammonia and cysteine, the basal medium was supplemented with 5 gyl glucose (final concentration 15 gyl), 0.32 gyl ammonium hydrogen sulphate (final concentration 0.96 gyl), 1 gyl ammonium sulphate (final concentration 3 gyl), 1 gyl ammonium chloride and 1 gyl cysteine.

313

optimum pH of the medium was found to be 2 for Cr(VI) adsorption by S. equisimilis, S. cerevisiae and A. niger. It is evident from Fig. 1 that the adsorption of Cr(VI) increases with decreasing pH of the adsorption medium. It is related to the mechanism of metal adsorption on the surfaces of microorganisms and reflects the nature of the physico-chemical interaction of both the ions in solution and the nature of the cell adsorption sites. When the initial pH of the medium was adjusted to the higher values (pH 7.5), Cr(VI) precipitation was observed because of the existence of OHy ions in the adsorption medium. For S. cerevisiae, biosorption increased at a slower rate as compared to S. equisimilis and A. niger. The Cr(VI) uptake by microorganisms was very sensitive to changes in the pH of the adsorption medium. At pH values above the isoelectric point, there is a net negative charge on the cells and the ionic states of ligands such as carboxyl, phosphate and amino groups become such as to promote reaction with Cr(VI) (Sag et al., 1995). As the pH was lowered to 1.5, the overall surface charge on the cells become positive and reduction of Cr(VI) to Cr(III) took place, which inhibited the chromium adsorption as Cr(III) (data not shown). Cr(III) is not so easily adsorbed as compared to Cr(VI) (Sharma and Forster, 1995). It has been reported (Gadd and White, 1993) that the majority of the metal binding by peptidoglycan arises from the carboxylate residues on the peptide chains. Fig. 2 indicates that the rise in incubation temperature influenced very sharply the biosorption rates of Cr(VI) by S. equisimilis, S. cerevisiae and A. niger. Maximum biosorption of Cr(VI) by S. equisimilis and A. niger was obtained at temperatures in the range of 35–40 and 30–35 8C, respectively. For S. cerevisiae, maximum

2.10. Desorption of Cr(VI) from cellmass A part of the cellmass loaded with Cr(VI) was treated with 0.1 M NaOH at room temperature (25 8C), with constant shaking for 20 min. 3. Results and discussion Fig. 1 shows the effect of pH on the biosorption of Cr(VI) by different organisms. The pH of the media affected the adsorption by the microbial cells. The

Fig. 2. Effect of temperature on the adsorption of Cr(VI) ion by S. equisimilis, S. cerevisiae and A. niger (pH 2; Cr(VI) ion, 100 mgyl; cellmass, 0.75 gyl; agitation, 200 rpm).

314

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

Fig. 3. Effect of Cr(VI) ion concentration on the adsorption of Cr(VI) ion by S. equisimilis, S. cerevisiae and A. niger (temperature, 30 8C; pH 2; cellmass, 0.75 gyl; agitation, 200 rpm).

Fig. 4. Freundlich adsorption isotherms obtained for Cr(VI) ion by different microorganisms: S. equisimilis, S. cerevisiae and A. niger (temperature 30 8C; pH 2; cellmass, 0.75 gyl; agitation, 200 rpm).

biosorption was obtained at a temperature of 45 8C. The increase in metal uptake at increased temperature is due to either higher affinity of sites for metal or an increase in binding sites on the relevant cellmass. At higher temperature the energy of the system facilitates Cr(VI) attachment on the surface and also when the temperature is very high, there is a decrease in metal sorption due to distortion of some sites of the cell surface available for metal biosorption (Puranik and Paknikar, 1999). Next the effect of chromium concentration on its adsorption was studied with the three organisms. The equilibrium biosorption of metal ions by S. equisimilis, S. cerevisiae and A. niger increased with increasing metal ion concentration up to 200, 100 and 250 mgyl, respectively (Fig. 3). The maximum equilibrium biosorption of Cr(VI) by S. equisimilis, S. cerevisiae and A. niger was determined as 56.5, 16.6 and 101 mgyg cellmass at 200, 100 and 250 mgyl of initial Cr(VI) concentration, respectively, at 30 8C (pH 2). The observed enhancement of metal sorption could be due to the increase in electrostatic interactions (relative to covalent interactions), involving sites of progressively lower affinity for metal ions (Puranik and Paknikar, 1999). These concentrations involve the limit concentration of metal ions in wastewater. If the concentration of metal ion in wastewater is higher than the concentration at which maximum biosorption is obtained, the wastewater can be diluted with tap water. From Fig. 3, it can be seen that A. niger was more efficient than S. equisimilis and S. cerevisiae in removing the higher concentration of Cr(VI). For the adsorption of Cr(VI) to the walls of microbial cells, the equilibrium occurred within 30–40 min.

The uptake of metal ions by microorganisms in batch systems has been shown to occur in two stages: an initial rapid stage (passive uptake), followed by a much slower process (active uptake). The first stage is thought to be physical adsorption or ion exchange at the cell surface. The adsorption equilibrium occurs within 30– 40 min at the end of rapid physical adsorption. This equilibrium can be represented by the Freundlich adsorption isotherm equation: 1yn qeqsKfCeq

(1)

where Kf and n are Freundlich constants. Kf and 1yn are indicators of adsorption capacity and adsorption intensity, respectively. Ceq and qeq also show the residual metal concentration and amount of metal adsorbed on cellmass (mgygdw) at equilibrium, respectively. This equilibrium equation is nonlinear and can be linearized in logarithmic form and the Freundlich constants can be determined from the slope and intercept which are equal to 1yn and Kf at Cs1.0, respectively. The Freundlich adsorption isotherms of each microorganism for Cr(VI) adsorption are given in Fig. 4, at the optimum pH and temperature. For each isotherm, the initial Table 1 Kf and n values obtained from Freundlich isotherms for Cr(VI) adsorption by S. equisimilis, S. cerevisiae and A. niger at 30 8C and pH 2 (corresponding to Fig. 4) Microorganism

Kf (lymg)

n

S. equisimilis S. cerevisiae A. niger

14.91 6.08 28.47

1.92 2.0 1.88

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

315

by S. equisimilis, S. cerevisiae and A. niger in the presence of increasing concentration of Cr(VI) ion. The maximum amount of adsorbed Fe(III) ion per unit weight of dried biomass, at 50 mgyl Fe(III), by S. equisimilis, S. cerevisiae and A. niger was measured as 19.73, 16.9 and 22.27 mgyg, respectively. When 50 mgyl Cr(VI) was added to the biosorption media containing 50 mgyl Fe(III), the adsorption of Fe(III) by S. equisimilis, S. cerevisiae and A. niger after 24 h decreased to 15.33, 12.1 and 20 mgyg, respectively. However, higher concentrations of both the metal ions seemed to be better tolerated by the fungus than the bacteria and yeast (Sag and Kutsal, 1998). 3.1. Kinetic studies on metal adsorption by microorganisms in batch reactor

Fig. 5. Effect of Fe(III) ion concentration on the adsorption of Cr(VI) ion by S. equisimilis, S. cerevisiae and A. niger (temperature, 30 8C; pH 2; cellmass, 0.75 gyl; agitation, 200 rpm): S. equisimilis (yؖؖ); S. cerevisiae (——); A. niger (-------).

Cr(VI) concentration was varied while the cellmass concentration in each sample was kept constant. Values of Kf and n obtained from the isotherms are compared in Table 1. The magnitude of Kf and n illustrate the separation of metal ions from wastewater and the high adsorption capacity of fungus, yeast and bacteria. The effect of Cr(VI) concentration on its adsorption by S. equisimilis, S. cerevisiae and A. niger in the presence of Fe (III) is given in Fig. 5. To determine adsorption characteristics of Cr(VI) in the binary metal mixtures, the concentration of Cr(VI) was varied between 25 and 150 mgyl, while the Fe(III) concentration in each biosorption medium was held constant at 10, 25 and 50 mgyl. The amount of adsorbed Cr(VI) ion per unit weight of dried S. cerevisiae at the end of 24 h was significantly reduced by lower concentration of Fe(III), whereas this concentration of Fe(III) did not appreciably affect the ultimate uptake of Cr(VI) by S. equisimilis and A. niger. The maximum adsorption of Cr(VI) at a concentration of 150 mgyl was measured as 80.13, 100.3 and 34.5 mgyg cellmass for S. equimillis, A. niger and S. cerevisiae, respectively, at 30 8C (pH 2). When 50 mgy l Fe(III) was added to biosorption media containing 150 mgyl Cr(VI), the equilibrium adsorption of Cr(VI) by S. equisimilis, A. niger and S. cerevisiae decreased to 66.2, 87.9 and 27.5 mgyg, respectively. The effect of Fe(III) concentration on its adsorption by S. equisimilis, S. cerevisiae and A. niger in the presence of Cr(VI), is depicted in Fig. 6. There appeared to be a significant inhibition in the adsorption of Fe(III)

The adsorption in a batch reactor can be considered as a single-stage equilibrium operation and it depends on two basic constraints, that of equilibrium (shown in Eq. (1)) and that of a mass balance (Aksu and Kutsal, 1991). The mass balance for the metal ion is given by VCiqXoqisVCeqqXoqeq

(2)

V(CiyCeq)sXo(qeqyqi)

(3)

yVyXo(CeqyCi)s(qeqyqi)

(4)

where Ci: Ceq: qi: qeq:

initial (or feed) metal ion concentration (mgy l) metal ion concentration (residual) at equilibrium (mgyl) the amount of metal adsorbed per unit weight of cellmass at the beginning (mgyg) the amount of metal adsorbed per unit weight of cellmass at equilibrium (mgyg)

Fig. 6. Effect of Cr(VI) ion concentration on the adsorption of Fe(III) ion by S. equisimilis, S. cerevisiae and A. niger (temperature, 30 8C; pH 2; cellmass, 0.75 gyl; agitation, 200 rpm) S. equisimilis (yؖؖ); S. cerevisiae (——); A. niger (-------).

316

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

Fig. 7. The equilibrium curve and operation line with VyX0: y 1.33 slope for Cr(VI) ion adsorption in the single-staged reactor (temperature, 30 8C; pH 2; Cr(VI) ion, 100 mgyl; cellmass, 0.75 gyl; agitation, 200 rpm).

V: Xo:

the volume of solution in the reactor (l) the amount of adsorbent (dry weight) in the reactor (g)

Eq. (4) represents a straight line. The line which passes through (Ci, qi) and (Ceq, qeq) with slope (yVy Xo) is termed the operation line of this stage. The relation between qeq and Ceq is given by the Freundlich equation, so the single-stage batch operation can be shown in a figure on the same coordinates by drawing an operation line and equilibrium curve according to Eq. (4) and the Freundlich equation wEq. (1)x, respectively. VyXo for the desired purification or Ceq and qeq values at a given VyXo can be determined from this figure for a given initial (or feed) metal ion concentration. Different VyXo ratios were obtained by increasing the quantity of dry cellmass while the Cr(VI) concentration

Fig. 8. Effect of culture age on the adsorption of Cr(VI) ion by S. cerevisiae grown on different carbon sources (temperature, 30 8C; pH 2; cellmass, 2 gyl; agitation, 200 rpm) w1x: 24 h growth culture; w2x: 48 h growth culture.

and solution volume were kept constant. The change in VyXo with adsorbed Cr(VI) ion concentration (Cx,eq) at different initial Cr(VI) concentration for S. equisimilis, S. cerevisiae and A. niger is given in Table 2. A decrease in VyXo increased the adsorbed Cr(VI) ion concentration because of increasing adsorption surface area. The experimental Cx,eq values showed that increasing cellmass quantity or decreasing VyXo ratios strongly affected the quantities of Cr(VI) removed from aqueous solution. This may be explained by the tendency of the cellmass aggregates to form at higher cellmass concentration resulting in a decrease in active adsorptive area (Aksu and Kutsal, 1991). The equilibrium curves obtained by plotting experimental Ceq and qeq values at 30 8C and pH 2 and the operating line passing through (Cis100 mgyl, qis0) with VyXosy1.33 slope for S. equisimilis, S. cerevisiae and A. niger are given in Fig. 7 for Cr(VI) biosorption in the single-stage batch reactor. Ceq and qeq values obtained from Fig. 7 showed the separation of Cr(VI) from waste water by biosorption at 100 mgyl of initial Cr(VI) concentration in a single batch reactor for the given VyXo ratio (y1.33). The values of Ceq determined for S. equisimilis, S. cerevisiae and A. niger were 62.2, 83 and 40.5 mgyl, respectively (this means for S. equisimilis, S. cerevisiae and A. niger, Cx,eqs37.8, 17 and 59.5 mgyl, respectively, at the same time). The adsorption values of Cr(VI) for the second batch reactor can also be determined from Fig. 7, by taking Ceq as the inlet concentration of Cr(VI) and drawing the straight line with the same slope. For S. equisimilis, S. cerevisiae and A. niger, the values of Ceq were found to be 36.5, 69 and 17 mgyl, respectively. The effect of culture age on Cr(VI) adsorption by S. cerevisiae was studied at different stages of growth and in media containing different carbon sources. As shown in Fig. 8, the amount of Cr(VI) taken up with cultures grown in glucose, fructose and sucrose was about 12.3, 11.8 and 13 mgyg when initial Cr(VI) concentration was 100 mgyl. S. cerevisiae grown in glucose or sucrose generally had a greater uptake than those fed with fructose at higher concentration of Cr(VI). The amount of Cr(VI) adsorbed with cultures grown in glucose, fructose and sucrose with lower concentration of Cr(VI) (50 mgyl) was about 4.3, 5.2 and 3.8 mgyg cellmass. It has been found that cellmass from the logarithmic phase (24 h) is more compact (with lower porosity) as compared to the cellmass from the stationary phase (48 h) (data not shown). The metal sorption after 24 h incubation resulted from enzyme linked, energy dependent transport processes whereas the adsorption obtained after 30 min incubation resulted from surface phenomena. It has been reported (Stoll and Duncan, 1996) that the ability of the yeast to take up metal ions was apparently influenced by the carbon sources.

Xo (g)

VyXo (lyg)

Co (mgyl)

(a) 0.005 0.007 0.01 0.015 0.02 0.04

4 2.86 2 1.33 1 0.5

50 50 50 50 50 50

(b) 0.005 0.007 0.01 0.015 0.02 0.04

4 2.86 2 1.33 1 0.5

(c) 0.005 0.007 0.01 0.015 0.02 0.04

4 2.86 2 1.333 1 0.5

S. equisimilis

S. cerevisiae Cx,eq (mgyl)

qeq (mgygdw)

38.5 35.3 32.6 31.5 30.2 26.4

11.5 14.7 17.4 18.5 19.8 23.6

46.0 42.0 34.8 24.67 19.8 11.8

46.2 45.0 44.0 43.5 42.9 41.2

3.8 5.0 6.0 6.5 7.1 8.8

15.2 14.28 12.0 8.67 7.1 4.4

38.9 35.5 31.2 29.5 28.0 21.5

11.1 14.5 18.8 20.5 22.0 28.5

44.4 41.42 37.6 27.33 22.0 14.25

100 100 100 100 100 100

79.1 74.5 72.8 71.0 69.3 63.0

20.9 25.5 27.2 29.0 30.7 37.0

83.6 72.85 54.4 38.67 30.7 18.5

91.2 89.5 88.0 87.5 87.0 85.0

8.8 10.5 12.0 12.5 13.0 15.0

35.2 30.0 24.1 16.67 13.0 7.5

68.5 60.2 51.5 50.0 48.3 39.5

31.5 39.8 48.5 50.0 51.7 60.5

126.0 113.71 97.0 66.67 51.7 30.25

150 150 150 150 150 150

125.5 118.8 112.5 110.2 108.5 98.1

24.5 31.2 37.5 39.8 41.5 51.9

98.0 89.14 75.0 53.06 41.5 25.95

142.5 141.0 139 138.4 138.0 136.5

7.5 9.0 11.0 11.6 12.0 13.5

30.0 25.71 22.0 15.46 12.0 6.75

117.5 108.5 93.5 89.0 86.5 76.4

32.5 41.5 56.5 61.0 63.5 73.6

130.0 118.57 113.0 81.33 63.5 36.8

Ceq (mgyl)

Ceq (mgyl)

A. niger Cx,eq (mgyl)

qeq (mgygdw)

Ceq (mgyl)

Cx,eq (mgyl)

qeq (mgygdw)

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

Table 2 Experimental Ceq, Cx,eq and qeq values found at different VyX0 ratios for S. equisimilis, S. cerevisiae and A. niger at equal initial Cr(VI) ion concentration of (a) 50; (b) 100 and (c) 150 mgyl

Temperature, 30 8C; pH 2; agitation, 200 rpm; volume, 20 ml.

317

318

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319

Fig. 9. The effect medium composition on the adsorption of Cr(VI) ion by S. cerevisiae (temperature 30 8C; pH 2; cellmass, 3 gyl; Cr(VI) ion 100 mgyl; agitation, 200 rpm).

Addition of cysteine and glucose in the medium resulted in a higher binding capacity of S. cerevisiae (Fig. 9). In contrast, sorption was comparatively less by the cells grown in ammonium sulphate and phosphate supplements. The best recoveries of Cr(VI) was obtained when the cells were grown in cysteine supplemented medium, followed by glucose, phosphate, ammonium sulphate, and ammonium chloride rich media. Supplement of cysteine, glucose, ammonium sulphate, phosphate and ammonium chloride in fermentation media for the growth of S. cerevisiae clearly led to different functional groups in the corresponding cell surface. Cysteine inserts –S and –N ligands, glucose Cligands, ammonium N-ligands and phosphates P-ligands (Engl and Kunz, 1995). Of all of these, cysteine rich media gave the highest adsorption capacity. Regeneration of Cr(VI) from the cellmass treated with 0.1 M NaOH is shown in Fig. 10. The recovery of Cr(VI) was 42, 38 and 27.5% from S. equisimilis, A. niger and S. cerevisiae, respectively. Recovery in the case of S. equisimilis was more due to its higher surface area per unit weight of cellmass. Treatment of cellmass with NaOH also further enhances the mechanical stability of the pellets for successive operation (Addour et al., 1999). The desorption experiment was carried out at 25 8C. As the biosorption of Cr(VI) is an endothermic reaction, the desorption may be enhanced by further lowering the reaction temperature. 4. Conclusion Three different types of microorganisms (bacteria, yeast and fungi) were used in this study. The behaviour of the organisms differs considerably in metal uptake

Fig. 10. Desorption of Cr(VI) ion from the adsorbed cellmass by NaOH (0.1 M) treatment.

rate. Broad screening of microbial cellmass for metal adsorption could serve as a basis for the development of efficient biosorbent materials. Ambient temperature was sufficient to adsorb metal ions from the solution although at a higher temperature the rate of adsorption was higher. A. niger was found to be more efficient than S. equisimilis and S. cerevisiae in removing the higher concentration of chromium ions. The metal uptake by microorganisms occurs in two stages; passive uptake which takes place immediately and active uptake takes place slowly. In the presence of binary metal ions wFe(III) and Cr(VI)x mixture, there was a significant inhibition in the presence of increasing concentration of Cr(VI) ions. Culture age has a direct effect on the adsorption of metal ions by the organisms. Addition of nutrients resulted a higher binding capacity of metal ions by S. cerevisiae. Understanding the effects of nutritional and environmental factors on the quality of microbial cellmass could enable the propagation of desirable types of organisms on cheap nutrients and in a form suitable for direct application. It is evident from the results that regeneration of metal ions by alkali is also possible. The easily cultivable organisms like S. cerevisiae and A. niger may be useful biosorption carriers for large scale operation. The affinity of sites for metal ions binding by the organisms may be enhanced by the application of genetic and protein engineering which could lead to the development of new peptides or biopolymers with increased metal uptake rate and stability. References Addour, L., Belhocine, D., Boudries, N., Comeau, Y., Pauss, A., 1999. Zn uptake by Streptomyces rimosus cellmass using

N. Goyal et al. / Advances in Environmental Research 7 (2003) 311–319 as packed bed column. J. Chem. Technol. Biotechnol. 74, 1089–1095. Aksu, Z., Kutsal, T., 1991. A bioseperation process for removing Pb(II) ions from waste water by using C. vulgaris. J. Chem. Technol. Biotechnol. 52, 109–117. Eccles, H., 1999. Treatment of metal contaminated waste: why select a biological process? TIBTECH 17, 462–465. Engl, A., Kunz, B., 1995. Biosorption of heavy metals by S. cerevisiae: effect of nutrient condition. J. Chem. Technol. Biotechnol. 63, 257–261. Gadd, G.M., White, C., 1993. Microbial treatment of metal pollution a working biotechnology? TIBTECH 11, 353–359. Puranik, P.R., Paknikar, K.M., 1999. Biosorption of lead, cadmium and zinc by Citrobacter strain MCM B-181: characterization studies. Biotechnol. Prog. 15, 228–237. Rapoport, A.I., Muter, O.A., 1995. Bisorption of hexavalent chromium by yeast. Process Biochem. 30, 145–149. Sag, Y., Kutsal, T., 1996. Fully competitive biosorption of Cr(VI) and Fe(III) ions from binary metal mixtures by R. arrhizus: use of competitive langmuir model. Process Biochem. 31, 573–585.

319

Sag, Y., Kutsal, T., 1998. The simultaneous biosorption of Cr(VI), Fe(III) and Cu(II) on R. arrhizus. Process Biochem. 33, 571–579. Sag, Y., Ozer, D., Kutsal, T., 1995. A comparative study of the biosorption of Pb(II) ions to Z. ramigera and R. arrhizus. Process Biochem. 30, 169–174. Sag, Y., Kutsal, T., Acikel, U., Aksu, Z.A., 1998. Comparative study for the simultaneous biosorption of Cr(VI) and Fe(III) on C. vulgaris and R. arrhizus: application of the competitive adsorption models. Process Biochem. 33, 273–281. Sandell, E.B., 1961. Colorimetric determination of traces of metals. third ed.. Interscience Publisher, New York. Sharma, D.C., Forster, C.F., 1995. Continuous adsorption and desorption of chromium ions by sphagnum moss peat from acidic solutions (pH 2). Process Biochem. 30, 293–298. Snell, F.D., Snell, C.T., 1959. Colorimetric method of analysis. third ed.. Vannostrand, New York. Stoll, A., Duncan, J.R., 1996. Enhanced heavy metal removal from waste water by viable glucose pretreated S. cerevisiae cells. Biotechnol. Lett. 18, 1209–1212.