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Biosorption of nickel(II) and copper(II) ions from aqueous solution by Streptomyces coelicolor A3(2)
Colloids and Surfaces B: Biointerfaces 34 (2004) 105–111
Biosorption of nickel(II) and copper(II) ions from aqueous solution by Streptomyces coelicolor A3(2) Ayten Öztürk a,∗ , Tuba Artan a , Ahmet Ayar b a b
Department of Biology, Faculty of Sciences and Arts, Nigde University, Nigde 51200, Turkey Department of Chemistry, Faculty of Sciences and Arts, Nigde University, Nigde 51200, Turkey Accepted 24 November 2003
Abstract The biosorption of nickel(II) and copper(II) ions from aqueous solution by dried Streptomyces coelicolor A3(2) was studied as a function of concentration, pH and temperature. The optimum pH range for nickel and copper uptake was 8.0 and 5.0, respectively. At the optimal conditions, metal ion uptake was increased as the initial metal ion concentration increased up to 250 mg l−1 . At 250 mg l−1 copper(II) ion uptake was 21.8% whereas nickel(II) ion uptake was found to be as high as 7.3% compared to those reported earlier in the literature. Metal ion uptake experiments were carried out at different temperatures where the best ion uptake was found to be at 25 ◦ C. The characteristics of the adsorption process were investigated using Scatchard analysis at 25 ◦ C. Scatchard analysis of the equilibrium binding data for metal ions on S. coelicolor A3(2) gave rise to a linear plot, indicating that the Langmuir model could be applied. However, for nickel(II) ion, divergence from the Scatchard plot was evident, consistent with the participation of secondary equilibrium effects in the adsorption process. Adsorption behaviour of nickel(II) and copper(II) ions on the S. coelicolor A3(2) can be expressed by both the Langmuir and Freundlich isotherms. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm. However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption only and not for nickel(II) ion. © 2004 Elsevier B.V. All rights reserved. Keywords: Streptomyces coelicolor A3(2); Biosorption; Scatchard analysis; Adsorption isotherms
1. Introduction Heavy metal pollution is spreading throughout the world with the expansion of industrial activities, nickel and copper are known to be commonly used heavy metals [1]. Many industries, especially plating and battery, release heavy metals like nickel and copper in wastewaters. These metals, which find many useful applications in our life, are very harmful if they are discharged into natural water resources and may pose finally a serious health hazard [2–4]. Such environmental constraints have forced especially the metal plating industry to reduce their emissions to water systems, otherwise mass usage of metals could cause severe environmental problems. Consequently, industrial wastewaters contain high levels of heavy metals and in order to avoid water pollution treatment is needed before disposal. Therefore, effective removal of heavy metals from wastewaters and industrial wastes still remains a major topic of present research [5]. ∗
Corresponding author. E-mail address: [email protected] (A. Öztürk).
0927-7765/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2003.11.008
Metal removal treatment systems using micro-organisms is a cheap and practical alternative to conventional processes, since low cost sorbent materials are used. Micro-organisms based technologies must compete with both operational and economical terms in existing metal removal treatment systems. Non-living biomass appears to present specific advantages in comparison to the use of living micro-organisms. For instance, the former may be obtained with much lower (if any) cost (it is considered basically as waste), it is not subjected to metal toxicity, the nutrient supply is not necessary as well as their greater binding capacities for toxic metals. Micro-organism–metal interactions are divided into two processes energy-dependent (bioaccumulation) and energy-independent (biosorption) [6–12]. Both mechanisms may be used to remove metal ions from industrial waste streams [13,14]. These interactions between the metal and other classes of binding sites on the biosorbent during the biosorption process could be either specific or non-specific binding. The characteristics of the adsorption process can be investigated using Scatchard analysis. When the Scatchard plot is a straight line it means that there is no change in the
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affinity of the binding sites for the metal over the range of concentration used. wheareas a curved plot indicates that binding sites are present with a metal affinity dependent on the metal concentration [15]. Metal sorption performance depends on some external factors such as pH, temperature, other metals, organic materials and cell metabolic products in solution [12]. However, biosorption of single-solute of heavy metals using micro-organisms is affected by several factors such as temperature, pH and initial metal concentration. In this work, we aimed to study the removal of toxic metals from solutions by Streptomyces coelicolor A3(2). This strain which produces several antibiotics such as methylenomycin and actinorhodin may be considered as a potential pharmaceutical wastes [16,17]. However, the sorption ability of this strain was not studied before. Our study was performed on free biosorbent using nickel(II) and copper(II) as the metals of interest. The basic objective of the study is to contribute to the understanding and modelling of the equilibria of adsorption processes. For this purpose, various factors affecting the adsorption, such as treatment time, initial pH of the solution and metal ion concentration, were investigated by the batch equilibration technique.
to which different initial metal concentrations was added. Solution concentrations were varied from 25 to 250 mg l−1 and were agitated on a shaker for 8 h which is more than ample time for adsorption equilibrium. Samples were taken at definite intervals for their residual metal ion concentrations in the solution. Solid–liquid separation was performed by centrifugation (13,000 rpm for 5 min) and analysed for the remaining metal ions spectrophotometrically at 460 and 320 nm using sodium diethyl dithiocarbamate as the complexing agent, respectively [18]. For each sample a blank test without micro-organisms was also performed to avoid confusion between biosorption and possible metal precipitation. However, biosorption experiments were carried out as duplicates and values used in calculations were the arithmetic averages of experimental data.
3. Results and discussion The results are given as a unit of adsorbed and unadsorbed metal ion concentration per gram of dried biosorbent in solution at equilibrium. Adsorption yield (Ad%) is defined as the ratio of adsorbed quantity of metal ion per gram of bacterium at equilibrium to the initial amount of metal ions and is calculated from Eqs. (1) and (2).
2. Material and method Ad% = 2.1. Culture and growth conditions S. coelicolor A3(2) strain was grown and maintained on GYM Streptomyces medium, which contained 4 g glucose, 4 g yeast extract and 10 g malt extract per liter. The pH was adjusted to 7.2 with dilute potassium hydroxide. Streptomyces strain was cultivated in 500 ml Erlenmayer flasks containing 200 ml of medium and were shaken in an orbital rotary shaker at 100 rpm, for 15 days at 28 ◦ C. Cultures were harvested by means of centrifugation at 13,000 rpm for 5 min and were washed three times with distilled water. The pellet was soaked in petri dishes and dried at 70 ◦ C for 24 h. 2.2. Preparation of metal solutions Test solutions containing single nickel(II) and copper(II) ions were prepared from analytical grade chemicals (nickel nitrate and copper sulphate). The concentrations of both metal ions prepared from stock solutions ranged from 25 to 250 mg l−1 . Before mixing the micro-organisms, the pH of each test solution was adjusted to the required value by using 1 M NaOH and HNO3 or H2 SO4 . 2.3. Biosorption experiments The biosorption experiments were carried out using the batch equilibrium technique at different pH and temperature values. Equilibrium biosorption was determined by using 1 g l−1 of the dried and ground bacterium suspension sample
q =
qeq X C0
Ceq C0 X
(1) (2)
where X is the bacterium concentration (g l−1 ), qeq is the adsorbed metal ion quantity per gram of micro-organism at equilibrium (mg g−1 ), C0 is the initial metal ion concentration at equilibrium (mg l−1 ) and Ceq is the residual metal ion concentration at equilibrium (mg l−1 ). 3.1. Effect of pH on nickel(II) and copper(II) biosorption Earlier studies on heavy metal biosorption have shown that pH was the single most important parameter affecting the biosorption process [6,19]. Fig. 1 shows the uptake of nickel(II) and copper(II) ions at different initial pH values using S. coelicolor A3(2). The maximum uptake of nickel(II) ion was obtained at an initial pH 8.0, while the maximum uptake of copper(II) ion was at 5.0. The nickel speciation was not studied about pH 8.0 because of the precipitation of Ni(OH)2 . This was clearly evident from the high uptake value of 99.4% at pH 11.0. However, it is believed that different pH binding profiles for nickel(II) and copper(II) ions are due to the nature of the chemical interactions of each metal with the bacterial cells. The metal-binding properties of Gram-positive bacteria, such as actinomycetes (i.e. Streptomyces), are largely due to the existence of specific anionic polymers in the cell wall structure, consisting mainly of peptidoglycan, teichoic or teichuronic acids.
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Fig. 1. The effect of initial pH on equilibrium adsorption of metal ions (C0 : 150 mg l−1 , X: 1.0 g l−1 , temperature: 25 ◦ C).
Fig. 2. Time variations of adsorption of metal ions (C0 : 150 mg l−1 each initial metal ion concentration, X: 1.0 g l−1 , temperature: 25 ◦ C).
Due to this high fixed anionic content of S. coelicolor, they may exhibit large sorption capacities, which could be of an important aspect for its industrial application as biosorbent specially the nickel ions, since they belongs to the transition metal ions that have high affinity not only to surface ligands, such as phosphoryl, SO3 2− RNH2 and R2 NH, but also to carbonyl (COO− ) groups too [11].
is the initial concentration of the metal ion, the larger is the amount of metal ion taken up. When the initial copper(II) concentration was increased from 25 to 250 mg l−1 , the loading capacity has increased from 16.4 to 48.4 mg g−1 . The maximum nickel(II) loading capacity at 250 mg l−1 of the biosorbent was found to be 18.8 mg g−1 . The increase of loading capacities of biosorbents with the increase of metal ion concentration could be attributed to higher probability of interaction between metal ions and biosorbents. Adsorption yields determined at different initial metal ion concentrations are given in Table 1. As is seen from this table high adsorption yields were observed at lower concentrations of metal ions, accordingly the uptake percentage of nickel was minimum (7.3%, mg l−1 ) when the concentration was maximum 7.5%. Similarly the uptake of copper(II) ion minimum was at 21.8%, mg l−1 when the maximum was 50.9%.
3.2. Effect of contact time and concentration on uptake of nickel(II) and copper(II) ions Fig. 2 shows the effect of treatment time on the adsorption of nickel(II) and copper(II) ions onto biosorbent from aqueous solutions. Time of contact of adsorbate and adsorbent is of great importance in adsorption since contact time depends on the nature of the system used. Microbial metal uptake by non-living cells, which is metabolism-independent passive binding process to cell walls (adsorption), and to other external surfaces, it is generally considered as a rapid process, taking place within a few minutes [20]. Therefore, for nickel or copper-bacterium system the adsorption was achieved within 5 min as is shown in Fig. 2. The initial metal ion concentration remarkably influenced the equilibrium metal uptake and adsorption yield as shown in Table 1. The higher
3.3. Effect of temperature on biosorption of metal ions The effect of temperature on the equilibrium metal uptake was less significant than pH. In general, maximum initial adsorption yields were found at temperatures between 20 and 30 ◦ C. Adsorption is an exothermic reaction and therefore uptake of pollutants by adsorption process
Table 1 Equilibrium adsorbed quantities and adsorption yields of each metal ion obtained at different initial metal ion concentrationsa Nickel(II) C0
(mg l−1 )
35.6 53.3 114.1 147.5 194.5 255.6 a b
Copper(II) qeq
(mg g−1 )b
2.70 (±0.005) 4.11 (±0.004) 8.71 (±0.004) 11.1 (±0.04) 14.5 (±0.02) 18.8 (±0.005)
Ad%
C0 (mg l−1 )
qeq (mg g−1 )
Ad%
7.5 7.7 7.6 7.5 7.4 7.3
32.2 54.9 97.0 144.9 208 221
16.4 26.6 37.2 42.0 47.0 48.4
50.9 48.5 38.3 28.9 22.5 21.8
X: 1.0 g l−1 , temperature: 25 ◦ C, agitation rate: 100 rpm, pH is equal to optimum value for each metal ion. Each value is an arithmetical average of a duplicate experimental data.
(±0.04) (±0.03) (±0.03) (±0.05) (±0.01) (±0.03)
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Table 2 Comparison between the results of this work and others found in the literature Metal
Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel
Biosorbenta
Streptomyces noursei (1) Pseudomonas syringae (1) Cladosporium resinae (2) Aureobasid pullulans (2) Aspergillus niger (2) Ganoderma lucidum (2) Penicillum digitatum (2) Saccharomyces cerevisiae (3) Arthrobacter sp. (1) Chlorella vulgaris (4) Chlorella fusca (4) Chlorella vulgaris (4) Spirulina platensis (4) Chlorella vulgaris (4) Scenedemus quadricauda (4) Chlorella vulgaris (4) Scenedemus obliquus (4) Synechocystis sp. (4) Streptomyces coelicolor Streptomyces coelicolor Chlorella vulgaris (4) Scenedemus obliquus (4) Synechocystis sp. (4) Pseudomonas syringae (1) Streptomyces noursei (1) Rhizopus arrhizus (2) Ascophyllum nodosum (4) Fucus vesiculosus (4) Arthrobacter sp. (1)
Operating conditions (◦ C)
pH
T
5.5 n.a.d 5.5 5.5 5 5 5.5 4 3.5–6 4 6 6 6 5 4 4.5 4.5 4.5 5 8 5 5 5 n.a. 5.9 6–7 6 3.5 5–5.5
30 22 25 25 n.a. n.a. 25 25 30 25 20 25 25 25 25 25 25 25 25 25 25 25 25 22 30 n.a. 25 25 30
Cb
(mg l−1 )
0.6–65 (i) 0–13 (i) 1–320 (i) 1–320 (i) 100 (e) 5–50 (e) 10–50 (e) 3.2 (i) 180 (e) 100 (i) 6.3 (i) 20 (i) 20 (i) 5 (i) 5 (i) 100 (i) 100 (i) 100 (i) 150 (i) 150 (i) 100 (i) 100 (i) 100 (i) 0–12 (i) 0.6–60 (i) 10–600 (i) 200 (e) 200 (e) 150 (e)
X
qH c (mg g−1 )
References
9 25.4 16 6 4 24 3 0.8 148 37.6 3.2 7.5 10.0 1.8 2.8 40.0 20.0 23.4 42 11.1 42.3 18.7 15.8 6 0.8 18.7 70 17 13
[23] [24] [20] [20] [25] [25] [26] [27] [28] [29] [30] [31] [31] [32] [32] [19] [19] [19] This work This work
(g l−1 )
3.5 0.28 1 1 n.a. n.a. 6.5 2 0.4 0.75 n.a. 1 1 1 1 1 1 1 1 1 1 1 1 0.28 3.5 3 n.a. n.a. 1.4
[24] [23] [33] [34] [34] [28]
a
1: Bacterium; 2: fungus; 3: yeast; 4: alga. i: Initial metal concentration; e: metal equilibrium concentration. c q highest value experimentally observed of the specific uptake. H d n.a.: Not available. b
decreases as reaction temperature increases. However, in our work the maximum adsorption (qeq ) for both nickel(II) and copper(II) ions were found to be at 25 ◦ C as is indicated in Fig. 3. When our results (Table 2) are compared with
those reported in the literatures, the values of nickel(II) and copper(II) specific uptake is found to be significantly higher than those given elsewhere. 3.4. Adsorption isotherms
Fig. 3. The effect of temperature on the 150 mg l−1 each initial metal ion concentration (X: 1.0 g l−1 ).
The contact time of 15 min and pH values of 8.0 and 5.0 were chosen as the experimental conditions for the determination of adsorption isotherms of nickel(II) and copper(II) ions (Fig. 4). The adsorption isotherms show that the amount of metals adsorbed increases as their equilibrium concentration increases in solution. As evident from these data, the adsorption isotherms of nickel(II) ion were steeper than the corresponding isotherm for copper(II) ion, indicating a greater affinity of nickel on S. coelicolor A3(2). To evaluate and compare the saturation capacities of S. coelicolor A3(2) toward the two heavy metal ions, the adsorption isotherms were analysed and fitted using Scatchard equation (Fig. 5). The Scatchard analysis is used here not only to estimate the adjustable parameters, but also to have a preliminary analysis about the number of site types and their relative affinity for metal ions. The presence of more
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Table 3 Adsorption isotherm parameters for nickel(II) and copper(II) ions on S. coelicolor A3(2) Metal ions
Langmuir isotherm As
Nickel(II) Copper(II)
(mg g−1 )
416.6 66.66
Scatchard analysis Kb
(l mg−1 )
1.85 × 10−4 0.011
Freundlich isotherm (mg g−1 )
r2
Kb
qm
0.80 0.99
1.84 × 10−4 0.0098
418.5 72.24
than one inflection point on a plot based on Scatchard analysis usually indicates the presence of more than one type of binding site. When the Scatchard plot showed a deviation from linearity, greater emphasis was placed on the analysis of the adsorption data in terms of the Freundlich model, in order to construct the adsorption isotherms of the ligands at particular concentrations in solutions. Fig. 4 shows the adsorption isotherms of metals on S. coelicolor A3(2), whilst Fig. 5 presents the adsorption characteristics assessed from the Scatchard plot. Equilibrium binding data for metals gave rise to a linear plot, indicating that the Langmuir model could be applied for adsorption process [21,22]. In the adsorptions of metals, Scatchard analysis of the equilibrium binding data for metal ions on S. coelicolor A3(2) gave rise to a linear plot, indicating that the Langmuir model could be applied. However, for nickel(II) ion, divergence from the Scatchard plot was evident, consistent with the participation of secondary equilibrium effects in the adsorption process. To test the fit of data, the Freundlich and Langmuir isotherm models were applied to this study. The linearised Freundlich isotherm model is
r2
k (mg g−1 )
1/n
r2
0.79 0.94
0.08 2.88
0.98 0.53
0.99 0.95
experimental data. The linearised Langmuir isotherm model is C 1 C = + q K b As As where Kb and As are the adsorption binding constant and saturation capacity, respectively. These constants were evaluated from the intercept and the slope of the linear plot of C/q versus C based on experimental data. Adsorption constants, metal-binding constant and correlation coefficients for the metals were calculated from Langmuir, Freundlich isotherms and Scatchard analysis are given in Table 3. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm (Fig. 6).
ln q = ln k + 1/n ln C where q is the amount of the adsorbed ligands per unit weight of adsorbent at the equilibrium concentration C, k is a Freundlich constant related to the adsorption capacity and 1/n is related to the adsorption intensity of a adsorbent. The values of k and 1/n were evaluated from the intercept and the slope, respectively, of the linear plot of ln q versus ln C based on
Fig. 4. Isotherms for the equilibrium binding of metal ions on S. coelicolor A3(2).
Fig. 5. Scatchard plots for nickel and copper adsorption by S. coelicolor A3(2).
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Fig. 6. Freundlich adsorption isotherms of heavy metals on S. coelicolor A3(2).
A3(2) is good adsorbing media for metal ions and had high adsorption capacity in the treatment of wastewater containing nickel(II) and copper(II) ions. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm. However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption only and not for nickel(II) ion. Based on the above results the following conclusions may be drawn, S. coelicolor A3(2) strain is an excellent adsorbent for wastewater containing nickel(II) and copper(II) and that the uptake of nickel(II) ion is very rapid compared to copper(II) which was found to be rather slow. pH Adjustment could be made in favour of the ions of interest to be removed. Biosorption can be accomplished with high yield by increasing metal ion concentrations from 25 to 250 mg l−1 , Therefore, microbial biosorption can be used successfully with both low and high metal ion concentrations in wastewaters. Increasing the mass of the microbial sample also seems to be the best method to increase the amount of the metals removed in solution. Consequently, microbial biosorption technologies are still being developed and much more work is required. Some practical applications have been achieved, and fundamentals look very promising: low concentrations of micro-organisms have the potential to remove metal ions and accumulate large amounts of specific toxic elements. The process is based upon the natural, very high affinity of micro-organisms for heavy metal ions. Metal ions are adsorbed by the biosorbent, and once saturated with metal ions, metal ions can be stripped from the material in a highly concentrated form. Consequently, S. coelicolor A3(2) offers a lot of promising benefits for heavy metal treatment applications.
Fig. 7. Langmuir adsorption isotherms of heavy metals on S. coelicolor A3(2).
Acknowledgements
However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption but not for nickel, (Fig. 7) moreover, these results have showed reasonable agreement with Scatchard analysis.
4. Conclusions In this study we aimed to determine the biosorption ability of S. coelicolor A3(2) strain in the removal of nickel(II) and copper(II) ions. Adsorption behaviour of S. coelicolor A3(2) toward nickel(II) and copper(II) ions from aqueous solutions was investigated by the batch equilibrium technique under various conditions such as treatment time, initial pH of the solution and metal ion concentration. It was found that maximum of 15 min of adsorption time is sufficient for reaching the adsorption equilibrium, and that the adsorption equilibrium data correlate well with the Langmuir isotherm equation. The obtained results showed that S. coelicolor
We are very grateful to Dr. A. Boybek Grabenwoger for providing us with S. coelicolor A3(2) used in this work.
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[21] M. Uçan, A. Ayar, Colloids Surf. A 207 (2002) 41. [22] A. Ayar, A.I. Pekacar, B. Mercimek, Colloids Surf. A 212 (2003) 51. [23] B. Mattuscka, B.G. Straube, J. Chem. Tech. Biotechnol. 58 (1993) 57. [24] J.P.S. Cabral, Microbios 71 (1992) 47. [25] C. Venkobachar, Water Sci. Technol. 22 (1990) 319. [26] M. Galun, E. Galun, B.Z. Siegel, P. Keller, H. Lehr, S.M. Siegel, Water, Air Soil Pollut. 33 (1987) 359. [27] C.P. Huang, A.L. Morehart, Water Res. 24 (1990) 433. [28] F. Vegliò, F. Beolchini, A. Gasbarro, Process Biochem. 32 (2) (1997) 99. [29] Z. Aksu, T. Kutsal, Environ. Technol. 11 (1990) 979. [30] B. Wehrheim, M. Wettern, Appl. Microbiol. Biotechnol. 41 (1994) 725. [31] E. Sandau, P. Sandau, O. Pulz, Acta Biotechnol. 16 (1996) 227. [32] P.O. Harris, G.J. Ramelow, Environ. Sci. Technol. 24 (1990) 220. [33] E. Fourest, J.C. Roux, Appl. Microbiol. Biotechnol. 37 (1992) 399. [34] Z.R. Holan, B. Volesky, Biotechnol. Bioeng. 43 (1994) 1001.
Biosorption of nickel(II) and copper(II) ions from aqueous solution by Streptomyces coelicolor A3(2) Ayten Öztürk a,∗ , Tuba Artan a , Ahmet Ayar b a b
Department of Biology, Faculty of Sciences and Arts, Nigde University, Nigde 51200, Turkey Department of Chemistry, Faculty of Sciences and Arts, Nigde University, Nigde 51200, Turkey Accepted 24 November 2003
Abstract The biosorption of nickel(II) and copper(II) ions from aqueous solution by dried Streptomyces coelicolor A3(2) was studied as a function of concentration, pH and temperature. The optimum pH range for nickel and copper uptake was 8.0 and 5.0, respectively. At the optimal conditions, metal ion uptake was increased as the initial metal ion concentration increased up to 250 mg l−1 . At 250 mg l−1 copper(II) ion uptake was 21.8% whereas nickel(II) ion uptake was found to be as high as 7.3% compared to those reported earlier in the literature. Metal ion uptake experiments were carried out at different temperatures where the best ion uptake was found to be at 25 ◦ C. The characteristics of the adsorption process were investigated using Scatchard analysis at 25 ◦ C. Scatchard analysis of the equilibrium binding data for metal ions on S. coelicolor A3(2) gave rise to a linear plot, indicating that the Langmuir model could be applied. However, for nickel(II) ion, divergence from the Scatchard plot was evident, consistent with the participation of secondary equilibrium effects in the adsorption process. Adsorption behaviour of nickel(II) and copper(II) ions on the S. coelicolor A3(2) can be expressed by both the Langmuir and Freundlich isotherms. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm. However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption only and not for nickel(II) ion. © 2004 Elsevier B.V. All rights reserved. Keywords: Streptomyces coelicolor A3(2); Biosorption; Scatchard analysis; Adsorption isotherms
1. Introduction Heavy metal pollution is spreading throughout the world with the expansion of industrial activities, nickel and copper are known to be commonly used heavy metals [1]. Many industries, especially plating and battery, release heavy metals like nickel and copper in wastewaters. These metals, which find many useful applications in our life, are very harmful if they are discharged into natural water resources and may pose finally a serious health hazard [2–4]. Such environmental constraints have forced especially the metal plating industry to reduce their emissions to water systems, otherwise mass usage of metals could cause severe environmental problems. Consequently, industrial wastewaters contain high levels of heavy metals and in order to avoid water pollution treatment is needed before disposal. Therefore, effective removal of heavy metals from wastewaters and industrial wastes still remains a major topic of present research [5]. ∗
Corresponding author. E-mail address: [email protected] (A. Öztürk).
0927-7765/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2003.11.008
Metal removal treatment systems using micro-organisms is a cheap and practical alternative to conventional processes, since low cost sorbent materials are used. Micro-organisms based technologies must compete with both operational and economical terms in existing metal removal treatment systems. Non-living biomass appears to present specific advantages in comparison to the use of living micro-organisms. For instance, the former may be obtained with much lower (if any) cost (it is considered basically as waste), it is not subjected to metal toxicity, the nutrient supply is not necessary as well as their greater binding capacities for toxic metals. Micro-organism–metal interactions are divided into two processes energy-dependent (bioaccumulation) and energy-independent (biosorption) [6–12]. Both mechanisms may be used to remove metal ions from industrial waste streams [13,14]. These interactions between the metal and other classes of binding sites on the biosorbent during the biosorption process could be either specific or non-specific binding. The characteristics of the adsorption process can be investigated using Scatchard analysis. When the Scatchard plot is a straight line it means that there is no change in the
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affinity of the binding sites for the metal over the range of concentration used. wheareas a curved plot indicates that binding sites are present with a metal affinity dependent on the metal concentration [15]. Metal sorption performance depends on some external factors such as pH, temperature, other metals, organic materials and cell metabolic products in solution [12]. However, biosorption of single-solute of heavy metals using micro-organisms is affected by several factors such as temperature, pH and initial metal concentration. In this work, we aimed to study the removal of toxic metals from solutions by Streptomyces coelicolor A3(2). This strain which produces several antibiotics such as methylenomycin and actinorhodin may be considered as a potential pharmaceutical wastes [16,17]. However, the sorption ability of this strain was not studied before. Our study was performed on free biosorbent using nickel(II) and copper(II) as the metals of interest. The basic objective of the study is to contribute to the understanding and modelling of the equilibria of adsorption processes. For this purpose, various factors affecting the adsorption, such as treatment time, initial pH of the solution and metal ion concentration, were investigated by the batch equilibration technique.
to which different initial metal concentrations was added. Solution concentrations were varied from 25 to 250 mg l−1 and were agitated on a shaker for 8 h which is more than ample time for adsorption equilibrium. Samples were taken at definite intervals for their residual metal ion concentrations in the solution. Solid–liquid separation was performed by centrifugation (13,000 rpm for 5 min) and analysed for the remaining metal ions spectrophotometrically at 460 and 320 nm using sodium diethyl dithiocarbamate as the complexing agent, respectively [18]. For each sample a blank test without micro-organisms was also performed to avoid confusion between biosorption and possible metal precipitation. However, biosorption experiments were carried out as duplicates and values used in calculations were the arithmetic averages of experimental data.
3. Results and discussion The results are given as a unit of adsorbed and unadsorbed metal ion concentration per gram of dried biosorbent in solution at equilibrium. Adsorption yield (Ad%) is defined as the ratio of adsorbed quantity of metal ion per gram of bacterium at equilibrium to the initial amount of metal ions and is calculated from Eqs. (1) and (2).
2. Material and method Ad% = 2.1. Culture and growth conditions S. coelicolor A3(2) strain was grown and maintained on GYM Streptomyces medium, which contained 4 g glucose, 4 g yeast extract and 10 g malt extract per liter. The pH was adjusted to 7.2 with dilute potassium hydroxide. Streptomyces strain was cultivated in 500 ml Erlenmayer flasks containing 200 ml of medium and were shaken in an orbital rotary shaker at 100 rpm, for 15 days at 28 ◦ C. Cultures were harvested by means of centrifugation at 13,000 rpm for 5 min and were washed three times with distilled water. The pellet was soaked in petri dishes and dried at 70 ◦ C for 24 h. 2.2. Preparation of metal solutions Test solutions containing single nickel(II) and copper(II) ions were prepared from analytical grade chemicals (nickel nitrate and copper sulphate). The concentrations of both metal ions prepared from stock solutions ranged from 25 to 250 mg l−1 . Before mixing the micro-organisms, the pH of each test solution was adjusted to the required value by using 1 M NaOH and HNO3 or H2 SO4 . 2.3. Biosorption experiments The biosorption experiments were carried out using the batch equilibrium technique at different pH and temperature values. Equilibrium biosorption was determined by using 1 g l−1 of the dried and ground bacterium suspension sample
q =
qeq X C0
Ceq C0 X
(1) (2)
where X is the bacterium concentration (g l−1 ), qeq is the adsorbed metal ion quantity per gram of micro-organism at equilibrium (mg g−1 ), C0 is the initial metal ion concentration at equilibrium (mg l−1 ) and Ceq is the residual metal ion concentration at equilibrium (mg l−1 ). 3.1. Effect of pH on nickel(II) and copper(II) biosorption Earlier studies on heavy metal biosorption have shown that pH was the single most important parameter affecting the biosorption process [6,19]. Fig. 1 shows the uptake of nickel(II) and copper(II) ions at different initial pH values using S. coelicolor A3(2). The maximum uptake of nickel(II) ion was obtained at an initial pH 8.0, while the maximum uptake of copper(II) ion was at 5.0. The nickel speciation was not studied about pH 8.0 because of the precipitation of Ni(OH)2 . This was clearly evident from the high uptake value of 99.4% at pH 11.0. However, it is believed that different pH binding profiles for nickel(II) and copper(II) ions are due to the nature of the chemical interactions of each metal with the bacterial cells. The metal-binding properties of Gram-positive bacteria, such as actinomycetes (i.e. Streptomyces), are largely due to the existence of specific anionic polymers in the cell wall structure, consisting mainly of peptidoglycan, teichoic or teichuronic acids.
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Fig. 1. The effect of initial pH on equilibrium adsorption of metal ions (C0 : 150 mg l−1 , X: 1.0 g l−1 , temperature: 25 ◦ C).
Fig. 2. Time variations of adsorption of metal ions (C0 : 150 mg l−1 each initial metal ion concentration, X: 1.0 g l−1 , temperature: 25 ◦ C).
Due to this high fixed anionic content of S. coelicolor, they may exhibit large sorption capacities, which could be of an important aspect for its industrial application as biosorbent specially the nickel ions, since they belongs to the transition metal ions that have high affinity not only to surface ligands, such as phosphoryl, SO3 2− RNH2 and R2 NH, but also to carbonyl (COO− ) groups too [11].
is the initial concentration of the metal ion, the larger is the amount of metal ion taken up. When the initial copper(II) concentration was increased from 25 to 250 mg l−1 , the loading capacity has increased from 16.4 to 48.4 mg g−1 . The maximum nickel(II) loading capacity at 250 mg l−1 of the biosorbent was found to be 18.8 mg g−1 . The increase of loading capacities of biosorbents with the increase of metal ion concentration could be attributed to higher probability of interaction between metal ions and biosorbents. Adsorption yields determined at different initial metal ion concentrations are given in Table 1. As is seen from this table high adsorption yields were observed at lower concentrations of metal ions, accordingly the uptake percentage of nickel was minimum (7.3%, mg l−1 ) when the concentration was maximum 7.5%. Similarly the uptake of copper(II) ion minimum was at 21.8%, mg l−1 when the maximum was 50.9%.
3.2. Effect of contact time and concentration on uptake of nickel(II) and copper(II) ions Fig. 2 shows the effect of treatment time on the adsorption of nickel(II) and copper(II) ions onto biosorbent from aqueous solutions. Time of contact of adsorbate and adsorbent is of great importance in adsorption since contact time depends on the nature of the system used. Microbial metal uptake by non-living cells, which is metabolism-independent passive binding process to cell walls (adsorption), and to other external surfaces, it is generally considered as a rapid process, taking place within a few minutes [20]. Therefore, for nickel or copper-bacterium system the adsorption was achieved within 5 min as is shown in Fig. 2. The initial metal ion concentration remarkably influenced the equilibrium metal uptake and adsorption yield as shown in Table 1. The higher
3.3. Effect of temperature on biosorption of metal ions The effect of temperature on the equilibrium metal uptake was less significant than pH. In general, maximum initial adsorption yields were found at temperatures between 20 and 30 ◦ C. Adsorption is an exothermic reaction and therefore uptake of pollutants by adsorption process
Table 1 Equilibrium adsorbed quantities and adsorption yields of each metal ion obtained at different initial metal ion concentrationsa Nickel(II) C0
(mg l−1 )
35.6 53.3 114.1 147.5 194.5 255.6 a b
Copper(II) qeq
(mg g−1 )b
2.70 (±0.005) 4.11 (±0.004) 8.71 (±0.004) 11.1 (±0.04) 14.5 (±0.02) 18.8 (±0.005)
Ad%
C0 (mg l−1 )
qeq (mg g−1 )
Ad%
7.5 7.7 7.6 7.5 7.4 7.3
32.2 54.9 97.0 144.9 208 221
16.4 26.6 37.2 42.0 47.0 48.4
50.9 48.5 38.3 28.9 22.5 21.8
X: 1.0 g l−1 , temperature: 25 ◦ C, agitation rate: 100 rpm, pH is equal to optimum value for each metal ion. Each value is an arithmetical average of a duplicate experimental data.
(±0.04) (±0.03) (±0.03) (±0.05) (±0.01) (±0.03)
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Table 2 Comparison between the results of this work and others found in the literature Metal
Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel Nickel
Biosorbenta
Streptomyces noursei (1) Pseudomonas syringae (1) Cladosporium resinae (2) Aureobasid pullulans (2) Aspergillus niger (2) Ganoderma lucidum (2) Penicillum digitatum (2) Saccharomyces cerevisiae (3) Arthrobacter sp. (1) Chlorella vulgaris (4) Chlorella fusca (4) Chlorella vulgaris (4) Spirulina platensis (4) Chlorella vulgaris (4) Scenedemus quadricauda (4) Chlorella vulgaris (4) Scenedemus obliquus (4) Synechocystis sp. (4) Streptomyces coelicolor Streptomyces coelicolor Chlorella vulgaris (4) Scenedemus obliquus (4) Synechocystis sp. (4) Pseudomonas syringae (1) Streptomyces noursei (1) Rhizopus arrhizus (2) Ascophyllum nodosum (4) Fucus vesiculosus (4) Arthrobacter sp. (1)
Operating conditions (◦ C)
pH
T
5.5 n.a.d 5.5 5.5 5 5 5.5 4 3.5–6 4 6 6 6 5 4 4.5 4.5 4.5 5 8 5 5 5 n.a. 5.9 6–7 6 3.5 5–5.5
30 22 25 25 n.a. n.a. 25 25 30 25 20 25 25 25 25 25 25 25 25 25 25 25 25 22 30 n.a. 25 25 30
Cb
(mg l−1 )
0.6–65 (i) 0–13 (i) 1–320 (i) 1–320 (i) 100 (e) 5–50 (e) 10–50 (e) 3.2 (i) 180 (e) 100 (i) 6.3 (i) 20 (i) 20 (i) 5 (i) 5 (i) 100 (i) 100 (i) 100 (i) 150 (i) 150 (i) 100 (i) 100 (i) 100 (i) 0–12 (i) 0.6–60 (i) 10–600 (i) 200 (e) 200 (e) 150 (e)
X
qH c (mg g−1 )
References
9 25.4 16 6 4 24 3 0.8 148 37.6 3.2 7.5 10.0 1.8 2.8 40.0 20.0 23.4 42 11.1 42.3 18.7 15.8 6 0.8 18.7 70 17 13
[23] [24] [20] [20] [25] [25] [26] [27] [28] [29] [30] [31] [31] [32] [32] [19] [19] [19] This work This work
(g l−1 )
3.5 0.28 1 1 n.a. n.a. 6.5 2 0.4 0.75 n.a. 1 1 1 1 1 1 1 1 1 1 1 1 0.28 3.5 3 n.a. n.a. 1.4
[24] [23] [33] [34] [34] [28]
a
1: Bacterium; 2: fungus; 3: yeast; 4: alga. i: Initial metal concentration; e: metal equilibrium concentration. c q highest value experimentally observed of the specific uptake. H d n.a.: Not available. b
decreases as reaction temperature increases. However, in our work the maximum adsorption (qeq ) for both nickel(II) and copper(II) ions were found to be at 25 ◦ C as is indicated in Fig. 3. When our results (Table 2) are compared with
those reported in the literatures, the values of nickel(II) and copper(II) specific uptake is found to be significantly higher than those given elsewhere. 3.4. Adsorption isotherms
Fig. 3. The effect of temperature on the 150 mg l−1 each initial metal ion concentration (X: 1.0 g l−1 ).
The contact time of 15 min and pH values of 8.0 and 5.0 were chosen as the experimental conditions for the determination of adsorption isotherms of nickel(II) and copper(II) ions (Fig. 4). The adsorption isotherms show that the amount of metals adsorbed increases as their equilibrium concentration increases in solution. As evident from these data, the adsorption isotherms of nickel(II) ion were steeper than the corresponding isotherm for copper(II) ion, indicating a greater affinity of nickel on S. coelicolor A3(2). To evaluate and compare the saturation capacities of S. coelicolor A3(2) toward the two heavy metal ions, the adsorption isotherms were analysed and fitted using Scatchard equation (Fig. 5). The Scatchard analysis is used here not only to estimate the adjustable parameters, but also to have a preliminary analysis about the number of site types and their relative affinity for metal ions. The presence of more
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109
Table 3 Adsorption isotherm parameters for nickel(II) and copper(II) ions on S. coelicolor A3(2) Metal ions
Langmuir isotherm As
Nickel(II) Copper(II)
(mg g−1 )
416.6 66.66
Scatchard analysis Kb
(l mg−1 )
1.85 × 10−4 0.011
Freundlich isotherm (mg g−1 )
r2
Kb
qm
0.80 0.99
1.84 × 10−4 0.0098
418.5 72.24
than one inflection point on a plot based on Scatchard analysis usually indicates the presence of more than one type of binding site. When the Scatchard plot showed a deviation from linearity, greater emphasis was placed on the analysis of the adsorption data in terms of the Freundlich model, in order to construct the adsorption isotherms of the ligands at particular concentrations in solutions. Fig. 4 shows the adsorption isotherms of metals on S. coelicolor A3(2), whilst Fig. 5 presents the adsorption characteristics assessed from the Scatchard plot. Equilibrium binding data for metals gave rise to a linear plot, indicating that the Langmuir model could be applied for adsorption process [21,22]. In the adsorptions of metals, Scatchard analysis of the equilibrium binding data for metal ions on S. coelicolor A3(2) gave rise to a linear plot, indicating that the Langmuir model could be applied. However, for nickel(II) ion, divergence from the Scatchard plot was evident, consistent with the participation of secondary equilibrium effects in the adsorption process. To test the fit of data, the Freundlich and Langmuir isotherm models were applied to this study. The linearised Freundlich isotherm model is
r2
k (mg g−1 )
1/n
r2
0.79 0.94
0.08 2.88
0.98 0.53
0.99 0.95
experimental data. The linearised Langmuir isotherm model is C 1 C = + q K b As As where Kb and As are the adsorption binding constant and saturation capacity, respectively. These constants were evaluated from the intercept and the slope of the linear plot of C/q versus C based on experimental data. Adsorption constants, metal-binding constant and correlation coefficients for the metals were calculated from Langmuir, Freundlich isotherms and Scatchard analysis are given in Table 3. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm (Fig. 6).
ln q = ln k + 1/n ln C where q is the amount of the adsorbed ligands per unit weight of adsorbent at the equilibrium concentration C, k is a Freundlich constant related to the adsorption capacity and 1/n is related to the adsorption intensity of a adsorbent. The values of k and 1/n were evaluated from the intercept and the slope, respectively, of the linear plot of ln q versus ln C based on
Fig. 4. Isotherms for the equilibrium binding of metal ions on S. coelicolor A3(2).
Fig. 5. Scatchard plots for nickel and copper adsorption by S. coelicolor A3(2).
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Fig. 6. Freundlich adsorption isotherms of heavy metals on S. coelicolor A3(2).
A3(2) is good adsorbing media for metal ions and had high adsorption capacity in the treatment of wastewater containing nickel(II) and copper(II) ions. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm. However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption only and not for nickel(II) ion. Based on the above results the following conclusions may be drawn, S. coelicolor A3(2) strain is an excellent adsorbent for wastewater containing nickel(II) and copper(II) and that the uptake of nickel(II) ion is very rapid compared to copper(II) which was found to be rather slow. pH Adjustment could be made in favour of the ions of interest to be removed. Biosorption can be accomplished with high yield by increasing metal ion concentrations from 25 to 250 mg l−1 , Therefore, microbial biosorption can be used successfully with both low and high metal ion concentrations in wastewaters. Increasing the mass of the microbial sample also seems to be the best method to increase the amount of the metals removed in solution. Consequently, microbial biosorption technologies are still being developed and much more work is required. Some practical applications have been achieved, and fundamentals look very promising: low concentrations of micro-organisms have the potential to remove metal ions and accumulate large amounts of specific toxic elements. The process is based upon the natural, very high affinity of micro-organisms for heavy metal ions. Metal ions are adsorbed by the biosorbent, and once saturated with metal ions, metal ions can be stripped from the material in a highly concentrated form. Consequently, S. coelicolor A3(2) offers a lot of promising benefits for heavy metal treatment applications.
Fig. 7. Langmuir adsorption isotherms of heavy metals on S. coelicolor A3(2).
Acknowledgements
However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption but not for nickel, (Fig. 7) moreover, these results have showed reasonable agreement with Scatchard analysis.
4. Conclusions In this study we aimed to determine the biosorption ability of S. coelicolor A3(2) strain in the removal of nickel(II) and copper(II) ions. Adsorption behaviour of S. coelicolor A3(2) toward nickel(II) and copper(II) ions from aqueous solutions was investigated by the batch equilibrium technique under various conditions such as treatment time, initial pH of the solution and metal ion concentration. It was found that maximum of 15 min of adsorption time is sufficient for reaching the adsorption equilibrium, and that the adsorption equilibrium data correlate well with the Langmuir isotherm equation. The obtained results showed that S. coelicolor
We are very grateful to Dr. A. Boybek Grabenwoger for providing us with S. coelicolor A3(2) used in this work.
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