BIOSORPTION OF CADMIUM (II) IONS FROM SIMULATED WASTEWATERS BY DRIED YEAST BIOMASS

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1 BIOSORPTION OF CADMIUM (II) IONS FROM SIMULATED WASTEWATERS BY DRIED YEAST BIOMASS RALUCA MARIA HLIHOR 1 *, MARIANA DIACONU 1, HUGO FIGUEIREDO 2, TERESA TAVARES 2, MARIA GAVRILESCU 1 * 1 Gheorghe Asachi Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Blvd., , Iasi, Romania, raluca.hlihor@ch.tuiasi.ro, mgav@ch.tuiasi.ro 2 IBB - Instituto de Biotecnologia e Bioengenharia, Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, Braga, Portugal The objective of this study was to obtain the basic information for the design of the process of Cd(II) biosorption on dried baker s yeast. The effect of initial ph (3-7), biosorbent dosage (5-30 g L -1 ), initial Cd(II) concentration ( mg L -1 ) and temperature ( ) on the biosorption potential of Saccharomyces cerevisiae was investigated in batch technique. A maximum uptake of about 12 mg of cadmium per g of dried yeast and 86 % removal of metal solution was observed at 200 mg L -1 cadmium solution and , with an equilibrium time of 24 hours. The equilibrium isotherm data were represented by Freundlich, Temkin and Dubinin Radushkevich isotherms. Thermodynamic parameters such as enthalpy ( H 0 ), entropy ( S 0 ) and Gibbs free energy ( G 0 ) were calculated from the temperature-dependent sorption data. The dried biomass of bakers yeast Saccharomyces cerevisiae shows significant potential for the removal of Cd(II) ions from aqueous solution. Wastewater containing Saccharomyces cerevisiae biomass from certain segments of bakery industry could be redirected in the view of wastewater treatment in cadmium electroplating sectors. Feasibility studies are necessary to determine the difficulty in carrying out this practice, since the real wastewaters are complex and competitive sorption processes could appear. eywords: biosorption, cadmium, yeast. INTRODUCTION One of the most serious environmental issues of the century is represented by the contamination of the aqueous environment by heavy metals due to the discharge of metal containing effluents. Biosorption has emerged in the past few decades as a potential technique for the removal of heavy metals from wastewaters (Gavrilescu, 2004; Vimala and Das, 2009). For the economical reason, researchers have paid much attention to various byproducts from fermentation industry, because they are produced in large quantities. S. cerevisiae yeast is widely used in the food and beverage industry and it is also a kind of solid waste. S. cerevisiae is still a concerned biomaterial in biosorption studies because its unique characteristics in comparison with other microorganisms for metal removal (Hlihor and Gavrilescu, 2009). The aim of the present study is a better understanding of cadmium biosorption on dried yeast biomass (S. cerevisiae) in a batch system by varying ph, biosorbent dosages, heavy metal concentration and temperature. MATERIALS AND METHODS Commercially distributed active wet pressed biomass of Saccharomyces cerevisiae was supplied from a local Romanian brewery store. Biomass was washed in distilled water followed by centrifugation. Yeast biomass was deactivated by heating in an oven 387

2 at 55 o C until a constant weight of dead biomass was achieved. The dried yeast was grounded in a mortar to powder to constant particle size < 0.25 mm. Cadmium stock solution of 1000 mg L -1 was prepared by dissolving 3CdSO. 4 8H 2 O in distilled water. The solution was diluted for different Cd(II) concentration by deionized water as required working solutions. The initial ph of working solutions was adjusted by addition of 0.1M H 2 SO 4 and 0.1M NaOH. Cadmium concentration in samples was determined by spectrophotometric method with xylenol orange at 575 nm (Otomo, 1964) using a T60 UV-Visible Spectrophotometer. For ph measurements a HANNA precision ph meter, model ph 213 was used. The batch experiments were carried out in an orbital shaker IA S 4000 ic control. Batch adsorption experiments were conducted at room temperature ( ) to study the effect of ph and biomass dosage with 100 mg. L -1 Cd(II). Equilibrium batch studies were carried out at 125 rpm by mixing the optimum biomass dose with volumes of 25 ml solutions of known initial Cd(II) concentration varying from 25 to 200 mg. L -1 in 100 ml Erlenmeyer flasks at T = After 24 h, when the equilibrium was established, the solutions were centrifuged and the supernatant was analyzed for Cd(II) concentration. All the experimental data were the averages of triplicate experiments. Metal uptake by dried S. cerevisiae was determined according to Eq. (1): C Ce q = V (1) 0 m where q is the amount of metal removed from solution (mg. g -1 ); C 0 and C e are the concentration of metal ions (mg. L -1 ) in the initial solution and at the equilibrium after the experiment; V (L) is the volume of the solution; m (g) is the amount of yeast biomass used in the experiment. Adsorption isotherm is the basic requirement for designing any adsorption system. Freundlich, Temkin and Dubinin Radushkevich isotherms were applied to calculate the relative sorption data of Cd(II) on S. cerevisiae in this paper. Freundlich isotherm model stipulate that the ratio of solute adsorbed to the solute concentration is a function of the solution. This model allows for several kinds of sorption sites on the solid and represents properly the sorption data at low and intermediate concentrations on heterogeneous surfaces (Chen and Gaob, 2009). The model can be expressed in linear form by Eq. (2): 1 log q = log kf + log C e (2) n where k F (mol 1-n g -1 L n ) represents the sorption capacity when metal ion equilibrium concentration equals to 1, and n represents the degree of dependence of sorption with equilibrium concentration. Temkin isotherm is given in the linear form as (Eq. 3): qe = B ln T + B ln C (3) e A plot of q e versus lnc e enables the determination of the isotherm constants B and T from the slope and the intercept, respectively. T is the equilibrium binding constant corresponding to the maximum binding energy and constant B is related to the heat of adsorption (Lawala et al., 2010). The D R isotherm is more general than the Langmuir isotherm, because it does not assume a homogeneous surface or constant sorption potential. It is valid at low concentration ranges and can be used to describe sorption on both homogeneous and 388

3 heterogeneous surfaces. The D R isotherm in the linear form is described by the equation (Şeker et al., 2008): 2 ln q = ln qmax βε (4) where q and q e are defined above, and ε is the Polanyi potential, which is equal to: ε = RT ln( 1+ 1/ C) (5) where R is ideal gas constant ( J mol -1-1 ), and T is the absolute temperature (). The saturation limit q max may represent the total specific micropore volume of the sorbent. The value of β is the activity coefficient related to mean sorption energy (mol 2 kj -2 ). It is related with the adsorption mean free energy, E (kj mol -1 ), defined as the free energy change required to transfer one mole of ions from infinity in solution to the solid surfaces. The relation is as the following (Eq. 6): 1 E = (6) 2β The magnitude of E is useful for estimating the type of sorption reaction. If E is in the range of 8 16 kj mol -1, sorption is governed by chemical ion-exchange. In the case of E < 8 kjmol -1, physical forces may affect the sorption. On the other hand, sorption may be dominated by particle diffusion if E > 16 kj mol -1 (Oczan et al., 2006). Thermodynamic parameters are calculated by using the equation (7): o 0 S H ln d = (7) R RT where H 0, S 0 and T are the enthalpy, entropy, and temperature in elvin, respectively, and R is the gas constant. The values of enthalpy ( H 0 ) and entropy ( S 0 ) are obtained from the slope and intercept of of ln d vs. 1/T plots. The distribution coefficient ( d ) is calculated from the concentration of Cd(II) in suspension (C 0 ) and that of Cd(II) in supernatant (C eq ) after centrifugation according to Eq. (8): C Ceq V d = 0 (8) Ceq m where V is the volume of the solution (L) and m is the mass of dried yeast (g) (Chen and Gaob, 2009). The change of Gibbs free energy ( G 0 ) was calculated from the equation (9): G = H T S (9) RESULTS AND DISSCUSSION Effect of ph ph plays an important role both in aquatic environment and adsorption processes. The effect of ph on the biosorption of Cd(II) on dried S. cerevisiae was investigated at ph range of 3-7 and the results are presented in Figure 1. The adsorbent dose and shaking time were kept constant. The working ph range above 7 was avoided due to possibility of cadmium precipitation on biomass surface. The maximum biosorption capacity was found to be 5.2 mg g -1 at ph 6 for 100 mg L -1 Cd(II) and 15 g L -1 biomass dosage. Decrease in biosorption at higher ph (ph>6) is due to the formation of soluble hydroxilated complexes of the metal ions and their competition with the active sites. At ph range from 3 to 5, the biosorption uptake increases from 4.7 to 5.03 mg g -1. At lower ph, the amount adsorbed was found to decrease because the surface area of the 389

4 adsorbent was more protonated and competitive adsorption occurred between H + protons and free metal ions toward the fixation sites (Mouzdahir et al., 2007). Effect of Biomass Dosage Biomass dosage is an important parameter because it determines the capacity of a biosorbent for a given initial concentration. The effect of biomass dosage on the biosorption of Cd(II) ions was studied using different biomass dosages in the range 5-30 g L -1. Results showed that the biosorption efficiency is highly dependent on the increase in biomass dosage in solution (Figure 2). The maximum biosorption of the metal ions was attained at a biomass dosage of 15 g L -1 with a removal efficiency of 85 % and it s almost the same at higher dosages. This trend represents a consequence of a partial aggregation of biomass at higher biomass concentration, which results in a decrease in effective surface area for the biosorption. Therefore, the optimum biomass dosage was selected 15 g L -1 for further experiments q (mg/g) Removal efficiency (%) ph Biomass dosage (g/l) Figure 1. Effect of ph on the removal of Cd(II) ions from aqueous solution using Saccharomyces cerevisiae Figure 2. Effect of dose of S. cerevisiae on its sorption capacity for Cd(II) Effect of Temperature and Thermodynamic Data It is well known that temperature is one of the most important parameters which dominate the physicochemical behavior of metal ions in the environment. The estimated model parameters for linearized Freundlich, Temkin and D-R isotherms of cadmium at different temperatures with correlation coefficients (R 2 ) for the different models are shown in Table 1. The mean free energy of biosorption gives information about biosorption mechanism, physical or chemical. The mean biosorption energy for Cd(II) biosorption on dried yeast was calculated as 7.12 kj/mol for , 7.27 kj/mol for , 6.93 kj/mol for and 7.08 kj/mol for The results indicated that the biosorption processes of Cd(II) on dried yeast biomass may be carried out through physical biosorption. The thermodynamic parameters of Cd(II) biosorption on S. cerevisiae were calculated from the temperature-dependent sorption. The values of enthalpy ( H 0 ) and entropy ( S 0 ) are calculated from the slope and intercept of the plot of ln d vs. 1/T (figure not shown). The thermodynamic data calculated by Eqs. 7-9 are listed in Table

5 Table 1. Biosorption isotherm model constants for biosorption of Cd(II) on S. cerevisiae at different temperatures Freundlich isotherm Temkin isotherm D-R isotherm Temperature () n F (mg/g(l/mg) 1/n ) R T (L/mg) B R q max (mg/g) β R Table 2. The thermodynamic data of Cd(II) sorption on dried yeast (S. cerevisiae) at different Cd(II) initial solution concentrations C 0 (mol L -1 ) Temperature () H 0 (kj mol -1 ) 2.22 x x x x x x x x S 0 (J (mol ) -1 ) G 0 (kj mol -1 ) As it can be seen from Table 2 the positive enthalpy change ( H 0 ) in the temperature interval means that the process of Cd(II) removal from solution is endothermic as expected. Also the negative enthalpy change ( H 0 ) in the temperature interval means that the process of Cd(II) removal from solution is exothermic at even higher temperatures. This can be explained to a decrease in metal sorption at higher temperature due to distorsion of some sites of the cell surface available for

6 metal biosorption. The Gibbs free energy change ( G 0 ) is negative as expected for a spontaneous process under the condition applied. The values of G 0 become more negative with the increase in temperature in the interval indicating a more efficient sorption at higher temperatures, but at even higher temperature than the uptake is decreasing, indicating a not favorable sorption. The positive values of entropy ( S 0 ) reflects the affinity of S. cerevisiae toward Cd(II) ions in aqueous solution and may suggest some structural changes on the adsorbent (Fan et al., 2009). CONCLUSIONS The removal efficiency of Cd(II) from simulated wastewaters on dried S. cerevisiae was found to be 85 %. The mean free energy values calculated form the D-R model indicated that the biosorption of Cd(II) on dried yeast was taken place by physical nature. The results also revealed an increase in uptake capacity of S. cerevisiae for Cd(II) ions in the temperature interval of and a decrease in uptake capacity in the interval of The thermodynamic calculations showed the endothermic nature at and exothermic nature at , and the feasibility and spontaneous nature of Cd(II) ions on dried S. cerevisiae. It can also be concluded that S. cerevisiae is an effective biomass for Cd(II) removal from aqueous solution because of its reasonable biosorption capacity and its costeffectiveness. Acknowledgement This paper was elaborated with the support of BRAIN project Doctoral scholarships as an investment in intelligence - ID 6681, financed by the European Social Found and Romanian Government and ID_595 Project within the National Program for Research, Development and Innovation, PN-II. REFERENCES Chen, L. and Gaob, X. (2009), Thermodynamic Study of Th(IV) Sorption on Attapulgite, Applied Radiation and Isotopes, 67, 1 6. Fan, Q., Shao, D., Lu, Y., Wu, W., Wang, X. (2009), Effect of ph, Ionic Strength, Temperature and Humic Substances on the Sorption of Ni(II) to Na-Attapulgite, Chemical Engineering Journal, 150, Gavrilescu, M. (2004), Removal of Heavy Metals from the Environment by Biosorption, Engineering in Life Sciences, 4, Hlihor, M.R. and Gavrilescu, M. (2009), Biosorption of Heavy Metals from the Environment Using Yeasts as Biosorbents, Bulletin of the Polytechnic Institute Iasi, Volume LV(LIX), Cluster 1, Lawala, O.S., Sannia, A.R., Ajayib, I.A. and Rabiu, O.O. (2010), Equilibrium, Thermodynamic and inetic Studies for the Biosorption of Aqueous Lead(II) Ions onto the Seed Husk of Calophyllum inophyllum, Journal of Hazardous Materials, 177, Mouzdahir, El Y., Elmchaouri, A., Mahboub, R., ElAnssari, A., Gil, A., orili, S.A., Vicente, M.A. (2007), Interaction of Stevensite with Cd 2+ and Pb 2+ in Aqueous Dispersions, Applied Clay Science, 35, Oczan, A., Oncu, E.M. and Oczan, A.S. (2006), inetics, Isotherm and Thermodynamic Studies of Adsorption of Acid Blue 193 from Aqueous Solutions onto Natural Sepiolite, Colloids and Surfaces, A, 277, Otomo, M. (1964), The Spectrophotometric Determination of Cadmium with Xylenol Orange, Bulletin of the Chemical Society of Japan, 37(4), Şeker, A., Shahwan, T., Eroğlu A.E., Yılmaz, S., Demirel, Z., Dalay, M.C. (2008), Equilibrium, Thermodynamic and inetic Studies for the Biosorption of Aqueous Lead(II), Cadmium(II) and Nickel(II) Ions on Spirulina platensis, Journal of Hazardous Materials, 154, Vimala, R. and Das, N. (2009), Biosorption of Cadmium (II) and Lead (II) from Aqueous Solutions Using Mushrooms: A Comparative Study, Journal of Hazardous Materials, 168,