Removal of Copper and Lead Ions from Aqueous Solution Using Brewer Yeast as Biosorbent

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1 Removal of Copper and Lead Ions from Aqueous Solution Using Brewer Yeast as Biosorbent ANDREEA STANILA 1, TANIA MIHAIESCU 2 *, CARMEN SOCACIU 1, ZORITA DIACONEASA 1 1 University of Agricultural Sciences and Veterinary Medicine, Faculty of Food Science and Technology, , 3-5 Manastur St., Cluj-Napoca, Romania 2 University of Agricultural Sciences and Veterinary Medicine, Faculty of Agriculture, , 3-5 Manastur St., Cluj-Napoca, Romania Biosorption is an effective procedure of heavy metal ions removal from wastewater. Brewer yeast, a byproduct of brewing industry could be a low cost and promising adsorbent for copper and lead ions from aqueous solutions. In this work the removal of these ions from water solutions by brewer yeast was performed as function of key parameters such ph, contact time, yeast dose and initial metal ions concentrations. Results demonstrate that the highest equilibrium adsorption capacity was reached at the ph=6 for both metal ions. It was found that the adsorptive capacity q e of both copper and lead ions on brewer yeast increase with the increasing of the contact time until the equilibrium stage was obtained. The biosorption process was rapid in the first 15 min. and the equilibrium was reached after 60 min. Results showed that the percent of metal removal increase as yeast dosage increase up to 1 g/100 ml solution for metal ions. The increase in metal uptake with yeast dosage confirms the increase in binding sites for metal ions. The metal uptake decrease with the increasing of yeast dosage over 1 g/100 ml due to aggregation of the yeast. Biosorption experiment was carried out at different initial concentrations of Cu(II) and Pb(II) ions, ranged between 1 mg L -1 to 10 mg L -1. The removal efficiency increase with the increasing of metal ions concentrations until 7 mg L -1 for Pb(II) ions and 8 mg L -1 for copper ions. The sorption equilibrium data were analyzed using the Langmuir adsorption isotherms. The data obtained represent a favorable adsorption in the case of adsorption of Cu(II) and Pb(II) ions. The maximum loading capacities of beer yeast was obtained as 20.6 mg g -1 for Cu(II) ions and 22.9 mg g -1 for Pb(II) ions, so the ability of lead adsorption is higher than copper ions. Keywords: biosorption, brewer yeast, metal ions removal, Saccharomyces cerevisae Heavy metals are discharged from various industries and pose serious environmental and human health problems. Biosorption represent the removal of metal species compounds from aqueous solution by biological materials such as bacteria, fungi, algae and yeast [1]. Biosorption exploits the ability of microbial biomass to sequester heavy metal ions from aqueous solution by physico-chemical mechanisms [2, 3]. Charged groups such carboxylate, amines and hydroxyl present in the biopolymers of biomass cell walls are believed to be responsible for the sequestration of metal ions [4]. A number of literature data have proved that S. cerevisiae can remove toxic metals, recover precious metals and clean radionuclides from aqueous solutions to various extents [6-12]. The biosorption of heavy metals using microorganisms like S. cerevisae is affected by several factors. These factors include the specific surface properties of the biosorbent and the physico-chemical parameters of the solution such as temperature, ph, initial metal ion concentration and biomass concentration [13]. The pretreatment and killing of biomass either by physical or chemical treatments or crosslinking are known to improve the biosorption capacity of biomass. Carboxylate and amine in yeast play an important role in metal biosorption [14]. Copper and lead ions were chosen for this study with regard to their wide use in industry and due to their potential pollution impact. Copper, which is a very widely used metal, like others heavy metal could be potentially toxic for the living organisms. Lead can contaminate the environment from anthropogenic sources as well as natural geochemical processes. It can accumulate along the food chain and is not amenable to biological degradation [15]. * tmihaescu@yahoo.com 1276 The aim of this study was to use brewer s yeast as biosorbent for copper and lead ions in aqueous solution. The objective of this work was to study the influence of the uptake of Cu(II) and Pb(II) by brewer s yeast in different adsorptive conditions. Experimental part Biomass and chemicals preparation Saccharomyces cerevisae biomass was supplied as a lyophilized by-product from industrial ethanol production. The waste biomass as washed with deionized water by stirring followed by centrifugation at 3000 rpm for 20 minutes. The supernatant was discarded and the pellet was reslurried in deionized water. The procedure was repeated for three times until the supernatant was clear. The chemicals used for this study were analytical grades of Pb(NO 3 ) 2, CuSO4 5H O, HCl, NaOH, 4-(2-pyridylazo) 2 resorcinol, purchased from Merck (Darmstadt, Germany). Stock solution of 100 mg L -1 Cu(II) and Pb(II) were prepared from the above metal salts dissolved in deionized water. The stock solutions were diluted as required to obtain working solution. The ph of the working solutions was adjusted by addition of HCl 0.1 M or NaOH 0.1 M. Biosorption experiments Metal ion binding experiments were performed by incubation of 250 mg biomass (dry weight) with 50 ml metals ions-containing solution in test tube on an orbital rotary shaker at 120 rpm for a maximum of 120 minutes. Samples were taken at given time intervals and then spin dried at 5500 rpm for 15 minute. The experiment was conducted at different ph values and were established by adjusting it with HCl 0.1 M or NaOH 0.1 M solutions.

2 The data obtained in batch mode studies was used to calculate the equilibrium metal adsorptive quantity. It was calculated for each sample of Cu(II) and Pb(II) by using the following expression: q e = v (c 0 c e ) / m (1) where q e is the amount of metal ions adsorbed onto per unit weight of beer yeast in (µg g -1 ), v is the volume of the solution in (L) and m is the weight of the dry biomass used in (g), c 0 and c e are the initial and metal equilibrium concentration in (µg L -1 ). Effect of contact time on biosorption Batch biosorption tests were done at different contact time at the initial concentration of 963 µg L -1 for Cu(II) and 986 µg L -1 for Pb(II) respectively and brewer yeast dose concentration 5 g L -1 in 50 ml solution. The ph established was 6. Test tubes were agitated on an orbital rotary shaker at 120 rpm, then the samples were collected at different intervals (5, 15, 30, 60, 90 and 120 min.) and were centrifuged. The concentrations of metal ions in the supernatant solution were analyzed using UV-Vis diode array spectrometer (Hewlet-Packard). Each determination was repeated three times and the given results were the average values. The standard deviation is less than 5%. Effect of ph solution on biosorption For metal ions biosorption the ph is one of the most important environmental factor. The effect of ph on the adsorption capacity of brewer yeast was investigated using solutions of 963 µg L -1 for Cu(II) and 986 µg L -1 for Pb(II), and brewer yeast dose concentration 5 g L -1 in 50 ml solution. The ph values ranged from 3.5 to 8 at 293 K. Experiments could not be performed at higher ph value due to the possibility of the lead ions precipitation. Test tubes were agitated on an orbital rotary shaker at 120 rpm for 60 min to ensure that the equilibrium was reached. Then the mixtures were centrifuged and the concentration of metals in the supernatant was measured. C e /q e = 1 / K L x q m + q e /q m (3) where C e (mg L -1 ) is the equilibrium concentration of adsorbate in solution; q e (mg g -1 ) is the adsorption amount of adsorbent at equilibrium, q m (mg g -1 ) is the maximum adsorption amount of metal ions and K L (L mg -1 ) is the equilibrium adsorption constant which is related to the affinity of the binding sites. Metal ions quantification by UV-Vis spectroscopy After the biosorption experiments were completed, metal concentrations were determinated using UV-Vis spectroscopy. UV-Vis spectra were recorded on an UV-Vis diode array spectrometer (Hewlet-Packard). For copper and lead quantification it was used a method according to Szabo et al. (2011), which consist in the complexation of these metal ions with 4-(2-pyridylazo) resorcinol (PAR) [16]. This ligand is a non-selective azo dye, widely used as colorimetric reagent for metal ions because of forming very stable, water-soluble and highly colored complexes with the majority of transition metals [17]. For the metal complex preparation, copper sulphate and lead nitrate of 10-4 M concentrations were mixed with 10-4 M PAR solution at 1:2 molar ration resulting in Cu(PAR) 2 and Pb(PAR) 2 complexes. According to literature data, PAR forming bidentate complexes with copper and lead at ph above 5 [17]. The atoms involved in the coordination are pyridine nitrogen, the azo nitrogen farthest from the heterocyclic ring and the o-hydroxyl group [17]. The UV-Vis spectroscopy is one of the most used method for the detection and quantification of metallic ions. The UV-Vis spectra of copper and lead ions with PAR show a broad band for metal-ionofor complexes (fig. 1). The PAR molecule present the absorption maximum at 412 nm, while for Cu(II) complex this maximum is located at 505 nm and for Pb(II) at 515 nm. For quantitative determination of Cu(II) and Pb(II) ions in the supernatant after biosorption it was used calibration curves based on the absorbance of these complexes at their maxima (fig. 1). Effect of yeast dose on biosorption Batch sorption test were done at different yeast concentration between 0.1 g/100 ml and 1.5 g/100 ml at ph=6, for a contact time of 60 min. The initial concentration of Cu(II) and Pb(II) were 963 µg L -1 for Cu(II) and 986 µg L -1 for Pb(II). The mixtures were centrifuged and the concentration of metals in the supernatant was measured. Sorption dynamic studies Samples of biomass were placed into a series of 250 ml conical flasks followed by addition of 150 ml copper and lead solution concentration of 1, 25, 50, 75 and 100 mg L -1. The brewer yeast concentration was established at 2 g L -1. The mixture were adjusted at ph=6 using 0.1 M NaOH and 0.1 M HCl solutions. The sorption equilibrium data were analyzed using the Langmuir adsorption isotherms. Langmuir adsorption isotherm is often used to describe maximum adsorption capacity of an adsorbent and it is given as: q e = q m x K L x C e / 1 + K L x C e (2) Fig. 1. The UV-Vis spectra of PAR, Pb(PAR) 2 and Cu-(PAR) 2 complexes In figure 2 it is presented the calibration curve for Cu- (PAR) 2 complex. The squares (R 2 ) of the correlation coefficient of the calibration curves were found to be for copper complex and for lead complex. where q e (mg g -1 ) is the adsorption amount of adsorbent at Results and dicussions equilibrium; q m (mg g -1 ) is the maximum adsorption The effect of contact time amount of metal ions, C e (mg L -1 ) is the equilibrium The effect of contact time on copper and lead ions concentration of adsorbate in solution and K L (L mg -1 ) is biosorption by brewer s yeast was studied and the results the equilibrium adsorption constant which is related to the are presented in the figure 3. It was found that the affinity of the binding sites. The Langmuir constants K L and adsorptive capacity q q m are calculated with the following equation: e of both copper and lead ions on 1277

3 Fig. 2. Calibration curve for Cu-(PAR) 2 complex Fig. 3. The effect on contact time on biosorption brewer yeast increase with the increasing of the contact time until the equilibrium stage was obtained (fig. 3). The biosorption process was rapid in the first 15 min. and the equilibrium was reached after 60 min. with a very slow increase until 90 min. This trend emphasizes that sorption time play an important role on recovery efficiency, which decreases with the increasing of contact time with metal solution. Metal accumulation inside the cells may resulted from bioaccumulation, slow dependent removal mechanism, or by simple metal diffusion [19, 20]. Han et al. (2006) reported that the uptake of metal ions by microorganisms in batch system has been shown to occur in two stages: an initial rapid stage (passive stage), followed by a slower process (active stage) [15]. The first stage represent a physical adsorption or ion-exchange at the surface of the biomass, which is biosorption. The biosorption equilibrium occurs at the end of the physical adsorption stage. The effect of ph The charge of the adsorbent and the adsorbate depends on the ph of the solution, thus the adsorption of copper and lead ions as a function of ph was measured, and the results are presented in the figure 4. The ph values chosen for experiments were 3.5, 5, 6, 7 and 8. There was an increase in biosorption capacity of biomass with the increasing of the ph until ph=6 for both metals. The highest metal uptake values obtained for copper and lead ions were 69.1 µg g -1 and 78.8 µg g -1 respectively. The low level of Pb(II) and Cu(II) uptake at lower ph values could be attributed to the increased concentration of hydrogen and hydronium ions competing for metal ions binding sites on the biomass. Fig. 5. Effect of yeast dosage on biosorption of Cu(II) and Pb(II) ions The increase in the Pb(II) and Cu(II) biosorption capacity at the higher ph values (between 5 and 7) may be explained by the ionization of functional groups on the cell surface which serve as binding sites related to the isoelectric point of the cells. The decreasing in the biosorption capacity at higher ph (>7) is due to the formation of soluble hydroxylated complexes of the metal ions, especially for Pb(II) ions, and their competition with the active sites, and as a consequence, the retention would decrease again. At ph values above the isoelectric point, there is a net negative charge on the cell wall components and the ionic state of ligands such as carboxyl, amino, phosphate groups could promote reactions with metal cations. Effect of yeast dosage The effect of yeast concentration on removal efficiency is presented in the figure 5. Metal removal percentage (R%) was calculated by equation: R (%) = (C 0 -C t ) x 100 / C 0 (4) where (R%) is the ratio of difference in metal concentration before and after adsorption; C o is the initial concentration of metal (µg L -1 ); C t is the residual concentration of metal after adsorption had taken place over a period of time t (µg L -1 ). Results showed that the percent of metal removal increase as yeast dosage increase up to 1 g/100 ml solution for metal ions. The increase in metal uptake with yeast dosage confirms the increase in binding sites for metal ions. In both experiments it was observed that the metal uptake decrease with the increasing of yeast dosage over 1 g/100 ml due to aggregation of the yeast [21]. The higher uptake at lower biomass concentration could be due to metal ions and biosorbent ratio, which decrease upon an increase in biomass dosage. This fact could be attributed to the formation of aggregates of biomass and may cause interferences between binding sites at higher concentration or insufficiently of metal ions in the solution with respect to available binding sites. It is likely that protons will then combine with metal ions for the ligands and thereby decrease the interaction of metal ions with the cell components Fig. 4. The ph effect on Cu(II) and Pb(II) ions biosorption by brewer s yeast Adsorption equilibrium Adsorption isotherms show the distribution of solute between the liquid and solid phases equilibrium conditions. Langmuir model is probably the most popular isotherm model due to its simplicity and its good agreement with experimental data. Langmuir adsorption isotherm model represents one of the first theoretical treatments of non-linear sorption and suggests that the uptake occurs on a homogenous surface by monolayer sorption without interaction between adsorbed molecules. Although the

4 Table 2 CORRESPONDENCE BETWEEN SEPARATION FACTOR R L VALUES AND LANGMUIR ISOTHERM TYPE Fig. 6. Langmuir adsorption model of Pb(II) biosorption on brewer yeast biomass Fig. 7. Langmuir adsorption model of Cu(II) biosorption on brewer yeast biomass Langmuir constant q max is dependent on experimental conditions such as ph solution and temperature, it is a good measure for comparing different sorbents for the same metal sorbate. The mono-component Langmuir constant q max, represents the monolayer saturation at equilibrium or the total capacity of beer yeast for copper and lead ions. The adsorption isotherms of Cu(II) and Pb(II) biosorption on brewer yeast at ph=6 were shown in the figures 6 and 7, and the isotherms parameters are presented in table 1. The Langmuir isotherm in terms of a dimensionless constant separation factor R L is defined by: R L = 1 / 1 + K L C 0 (5) where K L is the Langmuir constant and C 0 is the initial metal ions concentration. The R L values between 0 and 1 indicate favorable adsorption. The shape of isotherm is given by the value of R L as given in table 2. The data obtained represent a favorable adsorption in the case of adsorption of Cu (II) and Pb(II) ions. K L (L mg -1 ) and q max (mg g -1 ) were determinated from the slope and intercept of the Langmuir isotherm plots (fig. 6,7). The maximum loading capacities of beer yeast was obtained as 20.6 mg g -1 for Cu(II) ions and 22.9 mg g -1 for Pb(II) ions, so the ability of lead adsorption is higher than copper ions (table 1), which is in accordance with Han et. al [15]. Table 1 LANGMUIR ISOTHERMS PARAMETERS FOR Cu(II) AND Pb(II) BIOSORPTION ON BREWER YEAST BIOMASS Lower binding capacity of copper ions over lead ions on the biomass could be explained by comparing the covalent index of Pb(II) ion (11.1) with Cu(II) ion (5.67). The high value of the covalent index shows the high degree of binding capacity of the metal ions to the biological ligands. Also, Pb(II) ion is classified as a class b ion, while Cu(II) is classified as borderline ion, so the behavior of adsorption is not full the same and the binding capacity is different. Conclusions The results of our experiments concluded that the lowcost biomaterial, such brewer s yeast, has the ability to adsorb Cu(II) and Pb(II) ions from aqueous solutions. The process of biosorption has reached equilibrium after 60 minutes and the optimum ph for both metals is 6. Results showed that the percent of metal removal increase as yeast dosage increase up to 1 g/100 ml solution for both metal ions. Based on the correlation coefficients, it could be concluded that Langmuir isotherm is suitable to describe equilibrium data of Cu(II) and Pb(II) ions biosorption on brewer yeast. The maximum loading capacities of beer yeast was obtained as 20.6 mg g -1 for Cu(II) ions and 22.9 mg g -1 for Pb(II) ions. Acknowledgements: This work was supported by a grant of the Romanian Ministry of Education, CNCSIS UEFISCDI, PN-II-RU-PD , no. 47/ References 1. GADD, G. M., Interaction of fungi with toxic metals, New Phytol., 124, 1993, p VEGLIO, F., BEOLCHINI, F., Removal of metals by biosorption: a review, Hydrometallurgy, 44, 1997, p GHORBANI, F., YOUNESI, H., GHASEMPOURI, S. M., ZINATIZADEH, A. A., AMINI, M., DANESHI, A., Application of response surface methodology for optimization of cadmium biosorption in an aqueous solution by Saccharomyces cerevisiae, Chem. Eng. J., 145, nr. 2, 2008, COCHRANE, E. I., LU, S., GIBB, S. W., VILLAESCUSA, I. A., A comparision of low cost biosorbents and commercial sorbents for the removal of copper from aqueous media, J. Hazard. Mater., 137, nr. 1, 2006, p WANG, J. L., CHEN, C., Biosorption of heavy metal by Sacharomices cerevisae: a review, Biotechnol. Adv., 24, nr. 5, 2006, p PODGORSKII, V. S., KASATKINA, T. P., LOZOVAIA, O. G., Yeasts biosorbents of heavy metals, Mikrobiol. Zh. (Kiev, Ukraine: 1993), 66, nr. 1, 2004, p VOLESKY, B., Biosorption and metals, Wat. Res., 41, nr. 18, 2007, p DAS, N., VIMALA, R., KARTHIKA, P., Biosorption of heavy metals-an overview, Indian J. Biotechnol., 7, 2008, p MAHMOOD, T., MALIK, S. A., HUSSAIN, S. T., Biosorption of Metals, BioResources, 5, nr. 2, 2010, p ZAN, F., HUO, S., XI, B., ZHAO, X., Biosorption of Cd 2+ and Cu 2+ on immobilized Saccharomices cerevisae, Front. Environ. Sci. Eng., 6, nr. 1, 2012, p

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