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  3365  ARTICLE DOI: 10.5504/BBEQ.2012.0091  A&EB BIOTECHNOL. & BIOTECHNOL. EQ. 26/2012/6Biotechnol. & Biotechnol. Eq. 2012, 26 (6), 3365-3370 Keywords:  biosorption, Cu(II), immobilized  Trametes versicolor  , isotherm models, kinetics Introduction Due to the accelerated rates of development of various industries, constantly increasing amounts of pollutants annually discharge into the environment. Environmental pollution by heavy metals in particular, because of metals toxicity and capability of bioaccumulation by food chain, represents one of the major concerns of the modern society. The heavy and toxic metals As, Sb, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Tl, and Zn are included in the EPA list of the 129 priority pollutants of the environment (31). Among them, Cu enters the environment in great quantities, due to the intensive anthropogenic activities such as copper ore mining and processing, metal and electrical manufacturing, agricultural and domestic application of Cu-containing pesticides and fungicides, leather processing, and automotive brake pads production. Though Cu is essential to life, it is toxic at higher concentrations. The excessive intake of Cu(II) by human beings leads to serious health problems such as severe mucosal irritation, capillary, hepatic, renal and central nervous system damages (20). Thus, copper removal from polluted environment is of primary importance.Traditional methods for removing dissolved heavy metal ions from waste waters: chemical precipitation, chemical oxidation or reduction, ltration, ion exchange, and electrochemical treatment, exhibit signicant disadvantages  because of the incomplete metal recovery, especially at low metal concentrations, expensive equipment, and potential risk of generation of hazardous by-products (12, 33). Biosorption provides an opportunity to solve this serious environmental problem by cost-effective and environment- friendly technology. Biosorption can be dened as the  potential of various biomaterials, mainly microbial cells, to  bind and concentrate heavy metals from aqueous solutions in a non-metabolic way onto the cell surface. The biosorption capacities of many types of microbial cells (14, 22, 27, 33) and agricultural waste materials (4, 6, 19) for Cu(II) removal were investigated. Unfortunately, free biosorbents demonstrate some disadvantages such as small size particles and low density, poor mechanical strength, desorption and separation difculties and reduced possibilities for biosorbent regeneration (17). To a great extent immobilized biosorbents overcome these drawbacks. Among the studied immobilized biosorbents for heavy and radioactive metals removal, fungi immobilized in Ca-alginate beads are the dominant (2, 5, 9, 10, 34). Some authors report studies on Cu(II) and Cd(II) biosorption  potential of  Aspergillus niger   immobilized in polyvinyl alcohol (30), Cu(II) and Pb(II) biosorption on Trametes versicolor   immobilized in carboxy methyl cellulose (8), Cu(II), Ni(II), Cd(II) and other divalent metal ions removal by  Phanerochaete chrysosporium  and  Penicillium simplicissimum  immobilized on loofa sponge (16, 23), and Cu(II) adsorption on polyamide covalently immobilized dead yeast cells (13). According to the published results optimal pH values for Cu(II) removal by immobilized fungal biosorbents are in the interval of 4.0–6.0 and equilibriums are reached for about 1 h. Usually Langmuir and Freundlich isotherm equations are used for description of experimental results and rst and second order models are developed to study the biosorption kinetics. BIOSORPTION OF Cu(II) FROM AQUEOUS SOLUTIONS BY IMMOBILIZED MYCELIUM OF TRAMETES VERSICOLOR Velizar Gochev 1 , Zdravka Velkova 2 , Margarita Stoytcheva 3 , Husein Yemendzhiev 4 , Zlatka Aleksieva 4 , Albert Krastanov 51 University of Plovdiv “Paisii Hilendarski”, Department of Biochemistry and Microbiology, Plovdiv, Bulgaria 2 Medical University of Plovdiv, Department of General Chemistry and Biochemistry, Plovdiv, Bulgaria 3 Autonomous University of Baja California, Institute of Engineering, Mexicali, Mexico 4 Bulgarian Academy of Sciences, The Stefan Angeloff Institute of Microbiology, Soa, Bulgaria 5 University of Food Technologies, Department of Biotechnologies, Plovdiv, BulgariaCorrespondence to: Margarita StoytchevaE-mail: ABSTRACT The biosorption potential of heat inactivated mycelium of Trametes versicolor, free and immobilized in Ca-alginate and co-immobilized in Ca-alginate with bentonite and activated carbon, for Cu(II) removal from aqueous solutions was investigated.  Among the studied biosorbents heat inactivated fungal mycelium co-immobilized in Ca-alginate with activated carbon was  selected as the most successful. The effect of pH, initial metal ion concentration, duration and temperature on the removal efciency of the biosorbent was studied. Maximum Cu(II) removal 66.80% was reached at pH 4.0, 20 °C, and biosorbent dosage of 2.0°g·dm -3 . The Langmuir adsorption model matched very well the adsorption equilibrium data in the studied conditions. The kinetic data were found to follow the pseudo-second order model. The negative values of ΔH° and ΔG° revealed the exothermic nature and the feasibility of adsorption.  3366 BIOTECHNOL. & BIOTECHNOL. EQ. 26/2012/6In this work the biosorption potential of a series of novel  biosorbents including dead mycelium of Trametes versicolor  , free and immobilized in Ca-alginate gel, and co-immobilized with activated carbon and bentonite in Ca-alginate gel was investigated. These biosorbents are supposed to be very efcient because of the high capacity for metal complexation of the multifunctional groups of the dead cells, the enhanced  biomass loading in the presence of activated carbon and zeolite, and the synergetic action of the biosorbent components. The effect of pH, temperature, biosorbent dose, contact time, and initial Cu(II) concentration on the sorption capacity of the sorbents was studied. Optimum conditions for maximum Cu(II) removal were determined. Equilibrium, kinetic and thermodynamics characteristics of the process were identied. Materials and Methods Preparation of heat-inactivated mycelium of Trametes versicolor   used as biosorbent The fungal strain was cultivated as described earlier by Yemendzhiev et al. (35). The mycelium was separated from the culture broth through ltration and dried in an oven at 80 °C. The dried mycelium was ground in the laboratory and sieved until particles of uniform size of 300 µm were obtained. Biosorbent immobilizationImmobilization in Ca-alginate beads Sodium alginate (BDH, Poole, UK) was dissolved in hot distilled H 2 O at a mass concentration of 2 %. Cell suspension of heat inactivated mycelium of Trametes versicolor   was mixed with sodium alginate solution in a ratio of 1:1 on a magnetic stirrer until complete homogenization. Then using the syringe method, the suspension was extruded dropwise to a gelling solution of 0.1 mol·L -1  CaCl 2 , previously cooled to 4 °C. The beads were left to polymerize for 30 min and then were separated from the solution by ltration using a Büchner funnel and washed twice with distilled H 2 O. Ca-alginate beads without cells were also prepared as a control sample. Co-immobilization in Ca-alginate beads with bentonite Bentonite clay at a mass concentration of 6°% was added to sodium alginate solution to reach nal concentration of 3 % (w/v). Then the procedure for immobilization in Ca-alginate  beads described above was followed. Ca-alginate-bentonite  beads without mycelium were also prepared as a control sample. Co-immobilization in Ca-alginate beads with activated carbon Activated carbon was added to sodium alginate solution to reach a nal mass concentration of 3 %. Then the above procedure for immobilization in Ca-alginate beads was followed. Ca-alginate-activated carbon beads without mycelium were also  prepared as a control sample. All types of beads were stored in distilled H 2 O at 4 °C until biosorption experiments. Biosorption studies The stock solution of Cu(II) 1000 mg·dm -3  was prepared by dissolving a weighed quantity of CuSO 4 .5H 2 O (Merck, p.a.) in deionised water. Cu(II) solutions of different concentrations were prepared by adequate dilution of the initial solution. The effect of Cu(II) initial concentrations was studied at 20 mg·dm -3 , 30 mg·dm -3 , 50 mg·dm -3 , 70 mg·dm -3 , 150 mg·dm -3 , 200 mg·dm -3 , and 250 mg·dm -3 . The effect of pH was studied in the range of 2.0–6.0. The effect of biosorbent amount was studied in the range of 0.5 g·dm -3  to 4 g·dm -3 .Batch biosorption experiments were carried out in Erlenmeyer asks at 20 °C on a shaker for 180 min. The effect of temperature on the biosorption capacity of the biosorbent was studied in the range from 20 °C to 40 °C. The concentration of Cu(II) in the solution before and after  biosorption was measured using Spectroquant ®  Cooper Test (Merck, Darmstadt, Germany) following the manufacturer’s instructions.The Cu(II) uptake was calculated by the simple difference method (32): W V C C q  f  i  − =  (Eq. 1)where q  is the Cu(II) uptake, mg·g -1 ; V   is the volume of the solution in the ask, dm 3 ; C  i  and C  f   are the initial and nal concentrations of Cu(II) in the solution, mg dm -3  and C  i - C  f = C  t ; W   is the mass of biosorbent, g. The the efciency of Cu(II) removal was calculated as: ( ) %  ,.C C C  R i f  i 100 − =  (Eq. 2) Equilibrium isotherm studies Langmuir and Freundlich models were used to determine the sorption equilibrium between the biosorbent and Cu(II) ions (25).The Langmuir model is described by the following equation: e Le Lme C  K C  K qq += 1  (Eq. 3)where C  e   is the metal concentration in the solution at equilibrium, mg·dm -3 ; q m  is the maximum amount of metal adsorbed per unit of biomass, mg·g -1 ;  K   L   is the binding stability constant, dm 3 ·mg -1 .Freundlich adsorption isotherm is given by: (Eq. 4)where:  K   and 1/n  are Freundlich adsorbent constant and exponent characterizing the system.The isotherm constants for the two models can be obtained  by their linearized forms (7): me Lme  qC  K qq 1111 +=  (Eq. 5) (Eq. 6)  3367 BIOTECHNOL. & BIOTECHNOL. EQ. 26/2012/6 Kinetics studies Two types of kinetic models including pseudo-rst-order and  pseudo-second-order equations were used to investigate the mechanism of biosorption (25). The pseudo-rst-order equation is given as:  (Eq. 7)where q e  and q t , mg·g -1  are the amounts of adsorbed copper ions on the biosorbent at equilibrium and at time t  , respectively, and k  1 , min -1  is the pseudo-rst-order biosorption rate constant. The second-order equation is given as: t qqk qt  eet  11 22 +=  (Eq. 8)where k  2 , g·mg -1 ·min -1  is the second-order biosorption rate constant, and q e , mg·g -1  is the biosorption capacity calculated  by the pseudo-second-order kinetic model. Biosorption thermodynamics The thermodynamic parameters for the biosorption process in solution were calculated using the following standard thermodynamic relations: (Eq. 9)and 000 S T  H  G  ∆−∆ = ∆  (Eq. 10)where  ΔG o   is the standard free energy change, J·mol -1 , T is the temperature, °K,  R is the universal constant (8.314   J·mol -1 ·K  -1 ),  ΔH  o   is   the enthalpy change, J·mol -1  and  ΔS  o   is   the entropy change, J·mol -1 . The sorption distribution coefcient  K  0  for the sorption reaction was determined from the slope of the plot ln( q e / C  e ) against C  e  at different temperatures and extrapolating to zero C  e  (4, 36). Results and Discussion Screening for suitable matrix for immobilization. Effect of biosorbent dose To select the most appropriate immobilized biosorbent for Cu(II) removal from aqueous solutions, the biosorption of Cu(II) ions with heat inactivated mycelium of Trametes versicolor   immobilized on different carriers was studied and the results are listed in Table 1 .Biosorption was carried out with initial Cu(II) concentration of 50.00 mg·dm -3 , biomass concentration of 2 g·dm -3  (dry weight), pH 5 and contact time 180 min at a temperature of 20 °C. The highest metal uptake (62.43 mg·g -1 )was reached with heat inactivated mycelium of Trametes versicolor   co-immobilized in Ca-alginate with activated carbon. Immobilized biosorbents in Ca-alginate and co-immobilized in Ca-alginate with bentonite demonstrated lower Cu(II) uptake: 56.15 mg·g -1  and 58.25 mg·g -1  respectively, followed by free heat inactivated fungal mycelium. Control Ca-alginate beads without fungal mycelium demonstrated the lowest Cu(II) uptake. The highest Cu(II) uptake of heat inactivated mycelium of Trametes versicolor   co-immobilized in Ca-alginate with activated carbon is obviously due to the accumulation of biosorption potential of microbial cells and activated carbon, which is well known as a prospective sorbent. On the basis of the results obtained biosorbent of heat inactivated mycelium of Trametes versicolor   co-immobilized in Ca-alginate with activated carbon was selected as the most  promising and all of the following experiments were carried out with it, by varying the biosorbent loading from 0.5 g·dm -3  to 4 g·dm -3 . The percentage removal and adsorption capacity of Cu(II) at different biosorbent concentrations are presented in Table 1 . As demonstrated, the percentage removal increased with the increase of biosorbent dose up to 2.0 g·dm -3  and it is due to the increased surface area of the biosorbent, which in turn increases the number of bindings (11). Nevertheless the increase of the biosorbent dose could produce an opposite effect on the beads wall, protecting the binding sites, thus resulting in lower copper ions sorption per unit (24, 26). Effects of initial pH, initial Cu(II) concentration and temperature The effect of pH in the solutions on the efciency of Cu(II) removal was studied at different pH ranging from 2.0 to 6.0. The results are shown in Table 2 . pH plays an important role in the adsorption process by affecting the surface charge of the adsorbent, as well as the degree of ionization and speciation of the adsorbate. It was observed that the removal efciency of   T. versicolor   co-immobilized in Ca-alginate beads and activated carbon increases from 15.23 % to 66.80 % when the pH values of the solutions changed from 2.0 to 4.0. At pH 5.0 a slight decrease in the removal efciency was observed (62.43 %) and at pH > 6.0 copper precipitation takes place. pH 4.0 was selected as optimum pH for Cu(II) adsorption. The initial Cu(II) concentration was 50.00 mg·dm -3 . The low removal efciency at low pH is apparently due to the presence of higher concentration of hydrogen ions in the solution which compete with the Cu(II) ions for the adsorption sites of the biosorbent. These results were similar to those obtained in different studies related to biosorption onto  biosorbents of a different type (1, 28). Fig. 1a  illustrates the effect of the initial concentration of Cu(II) ions on the biosorption capacity of the biomass at various temperatures. The biosorption capacity increased linearly with increasing the initial concentration from 20 mg·dm -3  to 100 mg·dm -3 at all temperatures studied, indicating that the sorption process was affected to a greater extent by the initial Cu(II) concentration than by temperature. At 20 °C, 30 °C and 40 °C the equilibrium values 42.68 mg·g -1 , 41.50 mg·g -1 and 33.50 mg·g -1  were reached when the initial Cu(II) concentration was 250 mg·dm -3 . This may be due to saturation of the sorption sites and increase in the number of copper ions competing for the available binding sites in the biomass. When the initial metal ion concentration varied from 20 mg·dm -3 to 250 mg·dm -3 , the percentage removal of ions decreased, but  3368 BIOTECHNOL. & BIOTECHNOL. EQ. 26/2012/6 TABLE 1 Biosorption of Cu(II) onto Trametes versicolor immobilized on different carriers and various biosorbent dose MatrixpH 5pH 5pH 5pH 4pH 4pH 4 W  , g·dm -3 q t , mg·g -1  R , % W  , g·dm -3 q t , mg·g -1  R , %Heat inactivated mycelium of T. versicolor  2.013.5654.25 T. versicolor  /Ca-alginate beads2.014.0456.15 T. versicolor  /Ca-alginate beads + bentonite2.014.5658.25 T. versicolor  /Ca-alginate beads + activated carbon0.550.2550.25 T. versicolor  /Ca-alginate beads + activated carbon1.018.5862.83 T. versicolor  /Ca-alginate beads + activated carbon2.015.6162.432.016.7066.80 T. versicolor  /Ca-alginate beads + activated carbon3.010.6964.18 T. versicolor  /Ca-alginate beads + activated carbon4.07.0456.33Ca-alginate beads - control-5.5522.20 Initial Cu(II) concentration 50.00 mg·dm -3 , V = 0.1·dm 3 , t   = 180 min, pH 4.0 and pH 5, 20 °C. TABLE 2 Removal efciency of Cu(II) ions onto Trametes versicolor   immobilized in Ca-alginate beads with activated carbon pH  C  t , mg·dm -3 q t , mg·g -1  R , % 2.042.383.8015.233.030.579.7238.864.016.6016.7066.805.018.7815.6162.436.028.2410.8843.52 V   = 0.1 dm 3 , W = 0.2 g, t   = 180 min, 20 °C, and initial Cu(II) concentration 50.00 mg·dm -3 . TABLE 3 Biosorption equilibrium constants obtained from Langmuir and Freundlich isotherms by using the linear method Langmuir isotherm T = 20 °C T = 30 °C T = 40 °C q m , mg·g -1 47.5045.9939.14  K  L , L·mg -1 0.0310.0280.026  R 2 0.9980.9940.996 Freundlich isotherm T = 20 o C T = 30 °C T = 40 °C  K  3.272.692.571/ n 0.5290.5540.518  R 2 0.9780.9820.970 TABLE 4 Rate constants, q e  estimated, and coefcient of correlation associated to the Lagergren pseudo-rst- and second-order kinetics models; 20 °C C  o ,mg·dm -3 q exp ,mg·g -1 LagergrenPseudo-second-order model  K  1, min -1 q e  ,mg·g -1  R 2  K  2  , g·mg -1 ·min -1 h 0  , mg·g -1 ·min -1 q e  , mg·g -1  R 2 5016.702.53×10 -2 14.790.9841.45×10 -3 0.6320.530.99610027.083.45×10 -2 21.870.9861.60×10 -3 1.6832.580.99515034.502.54×10 -2 27.850.9941.19×10 -3 1.7638.460.995  3369 BIOTECHNOL. & BIOTECHNOL. EQ. 26/2012/6the uptake increased. The maximum percentage removal (72 %) was observed when the initial Cu(II) concentration was 20.00 mg·dm -3 at 20 °C. Effect of contact time Contact time is very important in biosorption dynamics. The effect of contact time on the adsorption of Cu(II) ions onto co-immobilized  T. versicolor   in Ca-alginate beads with activated carbon is shown in Fig. 1b . Batch sorption studies using three concentrations: 50 mg·dm -3 , 100 mg·dm -3  and 150 mg·dm -3 of Cu(II) solutions were carried out at 20 °C as a function of time. The biosorption of Cu(II) ions increases with time and attains equilibrium after 60 min (50 mg·dm -3  and 100 mg·dm -3 initial Cu(II) concentrations) and 120 min (150 mg·dm -3 initial Cu(II) concentration). One hundred and eighty minutes was xed as the minimum contact time for maximum Cu(II) uptake up to 250 mg·dm -3 initial concentration (results not shown). 010203040500 50 100 150 200 250 300 Initial Cu(II) concentration, mg dm -3   q   e  ,  m  g  g   -   1 20 o C30 o C40 o C a 010203040050100150200 Time, min   q    t  ,  m  g  g   -   1 50 mg dm -3  Cu(II) b 100 mg dm -3 Cu(II)150 mg dm -3  Cu(II) Fig. 1. Effect of temperature and initial Cu(II) concentration on equilibrium  biosorption capacity ( A ) at t   = 180 min, pH 4.0, V   = 0.1 dm -3  and W   = 2 g·dm -3 . Effect of contact time on Cu(II) biosorption ( B ) at 20 °C, pH°4.0, V  °=°0.1°dm -3  and W  °=°2°g·dm -3 . Adsorption isotherms The adsorption isotherm shows the distribution of the adsorbed molecules between the liquid phase and the solid phase at equilibrium. Isotherm data are tted to different isotherm models as an important step in nding a suitable model for use for design purposes. The experimental data obtained at 20 °C, 30 °C, and 40 °C were analyzed using the Langmuir and Freundlich isotherms. The isotherm constants and correlation coefcients  R 2  are given in Table 3 .From the Langmuir model the biosorption was found to decrease with increase in temperature and the sorption capacity ( q m ) was also found to decrease (21, 29). The maximum uptake for Cu(II) was obtained at 20 °C. The Freundlich isotherm equation is an empirical equation  based on the sorption on a heterogeneous surface suggesting that binding sites are not equivalent and independent (18). The values of 1/ n  < 1 stand for favorable adsorption. Based on the correlation coefcient  R 2 , the Langmuir isotherm model was the best model to describe the experimental data. Adsorption kinetics The analysis of biosorption kinetics involves the search for a model that best represents the experimental data. Several kinetic models describe the behavior of the biosorbent. The  pseudo-rst-order and pseudo-second-order models were used to test biosorption kinetics data to investigate the mechanism of sorption (3, 15). The plots of pseudo-rst-order and  pseudo-second-order models linear forms at different initial concentrations of Cu(II) at 20 °C are presented in Fig. 2 . Time, min    l   o   g   (   q    e   -   q    t    ) 50100150 a mg dm -3  Cu(II)mg dm -3  Cu(II)mg dm -3  Cu(II) 012345020406080 Time, min    t   /   q    t 50 mg100 mg150 mgdm -3  Cu(II)dm -3  Cu(II)dm -3  Cu(II) b Fig. 2.  First-order ( A ) and second-order ( B ) kinetics modeling of Cu(II)  biosorption. Table 4  lists the results of rate constant studies for different initial Cu(II) concentrations by the pseudo-rst order and pseudo-second order models. The value of correlation coefcient  R 2  for the pseudo-second order adsorption model is relatively high (>0.994), and the adsorption capacities calculated by the model are also likewise those determined  by experiments. It has been concluded that the pseudo-second
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