Bushehr University of Medical Sciences, Bushehr, Iran. Bushehr, Iran. Research Institute, Bushehr University of Medical Sciences, Bushehr, Iran.

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1 ISSN: X CODEN: IJPTFI Available Online through Research Article BIOSORPTION OF COPPER AND COBALT FROM AQUEOUS SOLUTION BY RHIZOPUS ORYZAE FUNGUS: A KINETIC AND EQUILIBRIUM ISOTHERM ANALYSES Akram Kiani Kori 1, Sina Dobaradaran 2,3,4, Mozhgan Keshtkar 3, Behrouz Naeimi 5*, Mahboobe Madani 1, Farzaneh Sadeghzadeh 6, Rauf Foroutan 7 1 Islamic Azad University Falavarjan Branch Faculty of Biology 2 The Persian Gulf Marine Biotechnology Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences, Bushehr, Iran. 3 Department of Environmental Health Engineering, Faculty of Health, Bushehr University of Medical Sciences, Bushehr, Iran. 4 Systems Environmental Health, Oil, Gas and Energy Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences, Bushehr, Iran. 5 Department of Microbiology and Parasitology, School of Medicine, Bushehr University of Medical Sciences, Bushehr, Iran. 6 Department of Medical Laboratory Sciences, Faculty of Paramedical, Bushehr University of Medical Sciences, Bushehr, Iran. 7 Young Researchers and Elite Club, Bushehr Branch, Islamic Azad University, Bushehr, Iran. * Department of Microbiology and Parasitology, Bushehr University of Medical Sciences. b.naeimi1350@gmail.com Received on: Accepted on: Abstract The fungus Rhizopus oryzae (R. oryzae) was used to remove toxic metal ions of copper and cobalt from aqueous solution. The effecting parameters including biosorbent dose (2-7 g/l), initial ion concentrations (10-40 mg/l), contact time (5-150 min), rate of mixing (0-400 rpm), and ph (2-12), were examined. The highest biosorption efficiencies for copper and cobalt ions were 97.65% and 96.37%, respectively at contact time of 150 min, ph value of 8, initial ion level of 40 mg/l, and agitation rate of 250 rpm. The highest biosorption capacities of cobalt and copper by R. oryzae were 15.6 and mg/g, respectively. Keywords: Biosorption, Cobalt, Copper, Rhizopus oryzae Introduction Due to more production and activities, industries release more contaminants including toxic metals to the environment and water resources [1-3]. Industrial and metallurgical processes in areas such as photography, aviation, nuclear energy facilities, and the petrochemical industry discharge toxic metals into water resources [4-6]. These pollutants are also continuously pumped into the environment by textile, electroplating, battery manufacturing, mining, ceramic and glass-making facilities [7]. In addition, the existence of toxic metals in the environment and IJPT June-2017 Vol. 9 Issue No Page 30058

2 seafood [8, 9] and their accumulation in the food chain is very high [10, 11]. So due to toxicity to aquatic organisms, humans, and other living beings the removal of toxic metals from the wastewater is imperative [12]. The adverse effects of toxic metals on humans and other living beings make the removal and recovery of the high levels of toxic metals in the environment a major developmental challenge. Various procedures have been used to recover and/or remove toxic metal ions from wastewater and water solutions, including chemical sequestration, reverse osmosis, electrolysis, ion exchange, extraction by means of solvents, and adsorption [13-19]. Some of these methods have disadvantages which can adversely influence their usefulness. For example, the chemical sequestration, reverse osmosis, and ion exchange methods show unpredictable toxic metal recovery, have rigid requirements for reactants, and produce toxic sludge along with requiring careful disposal of the resulting sludge [20]. Among these strategies, adsorption is one of the most recommended physicochemical treatment processes for removal of inorganic contaminants and especially heavy metals [21-28]. Biosorption methods are more cost effective, easier to implement, and have higher efficiency [29]. They also can be implemented by a variety of methods [30] and materials. Researchers have investigated various materials with different biosorption capacities to find substances with high adsorption rates [31]. Algae, sawdust, agricultural wastes and seafood processing wastes, fungus, and inactive bacteria are examples of biosorbents that have been used for inorganic contaminants and especially toxic metals removal from aqueous solution [32-44]. Other biological materials such as microbial biomass have also been considered for biosorption and they can effectively adsorb toxic metals, even in diluted solutions [45]. The present study used the biomass of the filamentous saprotrophic fungus R. oryzae as a biosorbent to remove toxic metals of copper and cobalt from aqueous solutions. The influence of parameters such as initial ph of solution, biosorbent dose, rate of mixing, and initial metal ions concentration levels of the aqueous solution at different contact times were investigated. In order to study the kinetics of biosorbent behavior as well as isotherms, pseudo-first-order and pseudo-second-order models as well as the Langmuir and Freundlich isotherm models were used. Materials and methods Preparation of fungal biomass The fungus R. oryzae ATCC 9363 was obtained from the Industrial and Infectious Bacteria and Fungi Collection Center of Iran, and cultured in potato dextrose agar (PDA) then stored at -24 C. To prepare the fungal biomass, CFU of R. oryzae was aerobically cultured in a broth medium containing 50 g/l glucose, 5 g/l yeast extract, 5.7 g/l ammonium sulfate, 5.3 g/l potassium hydrogen phosphate, 0.75 g/l MgSO 4.7H 2 O, and 1 g/l CaCl 2.2H 2 O at a IJPT June-2017 Vol. 9 Issue No Page 30059

3 ph level of 5.5 ± 0.1 [46]. Following one week of incubation at 30 C, the fungal culture was filtered and the collected biomass was washed 7 times with double-distilled water. Pretreatment of R. oryzae biomass For chemical modification, the fungal biomass was immersed in a 0.2 M sodium hydroxide solution for 30 min. After recovery from treatment in solution, the biomass was rinsed several times with double-distilled water and its ph level was adjusted to 6-7. After that biomass was autoclaved for 30 min at 121 C and dried for 24 h at 60 C [47]. The dried biomass was then ground, milled, and sieved through a 0.71 mm screen. Preparation of copper and cobalt stock solution Stock solutions (1000 mg/l) of toxic metals were prepared by dissolving a sufficient amount of copper nitrate (Merck, Germany) and cobalt nitrate (Merck, Germany) in one liter of double distilled water. This solution was stored at 4 C for further dilutions and preparation of different concentration levels of Cu and Co ions for experiment. SEM biosorbent analysis Scanning electron microscopy (SEM; Hitachi S4160) was used to study the surface changes of the biosorbent in the raw and processed states as well as before and after cobalt and copper ion biosorption. Images were obtained using an electron microscope of the biosorbent surfaces after they were covered with a thin layer of gold both before and after biosorption the metal ions. Batch biosorption experiments The biosorption experiments were conducted within a 250 ml glass flask containing 100 ml soluble copper and cobalt at different concentration levels of mg/l, ph values of 2-12, different biosorbent doses of 2-7 g/l, and agitation rate of rpm. All experiments were conducted at room temperature. A flame atomic absorption (Varian SpectrAA-10, USA) was used to determine the amount of ions remaining after each experiment. The percentage of ions biosorption (R %) was calculated by using Eq. (1): R% = (1) Where C i and C e (mg/l) are the initial and equilibrium concentration levels of metal ions, respectively. The equilibrium biosorption capacity of R. oryzae at different concentration levels of Cu and Co was calculated by using the following Eq. (2): q e = (2) IJPT June-2017 Vol. 9 Issue No Page 30060

4 Where C i and C e (mg/l) are defined before, V is the volume of the solution (L), and m is the mass of the biosorbent (g). To study the kinetics of the biosorbent, biosorption experiments were performed at different initial concentrations (10-40 mg/l) of metal ions at a biosorbent dose of 6 g/l for different contact times (0-150 min). Pseudo-first-order and pseudo-second-order kinetic models were used to investigate the kinetic behavior of the biosorbents. To evaluate the isothermic behavior of the biosorbent, the equilibrium data achieved at the stage of biosorbent dose optimization and the data were analyzed using the Freundlich and Langmuir isotherm models. Results and Discussion Analysis of biosorbent properties The surface changes in R. oryzae were examined by SEM after covering the hyphae surfaces with a thin layer of gold. Fig. 1 shows the external surfaces of R. oryzae both before and after chemical pretreatment as well as the pretreated fungal surfaces before and after biosorption of metal ions. The SEM micrographs indicated structural changes in the biosorbent. Many cavities were found after chemical pretreatment, but were not observed after biosorption, indicating successful copper and cobalt biosorption onto R. oryzae. Fig. 1. SEM images of the fungus R. oryzae surfaces: (a) prior to chemical treatment, (b) after chemical treatment, (c) after copper biosorption, and (d) after cobalt biosorption. IJPT June-2017 Vol. 9 Issue No Page 30061

5 Removal efficiency % Effect of ph The ph value of the aqueous solution is an important variable in the sorption of metal ions [48]. To examine the effect of ph on biosorption efficiency of copper and cobalt ion, experiments were carried out at room temperature, for a contact time of 60 min, initial concentration level of 20 mg/l of metal ions, a biosorbent dose of 3 g/l, an agitation speed of 200 rpm, and ph range of Fig. 2 shows that the biosorption efficiencies of Cu and Co ions increased as the ph increased from 2 to 8 and the removal rates of these ions were less at lower ph values. This occurred because more H + was present in the solution at lower ph values and competed with the metal ions and occupied the active sites of the biosorbent. By increasing the ph values, the biosorption efficiencies of the toxic metals increased and at ph value of 8, and the removal efficiencies of Cu and Co reached to 78% and 74%, respectively. As the ph rose to above 8, the biosorption efficiencies of the metal ions declined due to the presence of a high amount of OH -, which led to complex formation. In accordance with our study, Tounsadi et al. reported that the Co biosorption capacity by using Diplotaxis harra and Glebionis coronaria L. increased from 0 to 15 % and 5 to 20 %, respectively, as the ph value increased from 3 to 8 [49]. Monier et al. examined Cu (II) and Co (II) removal by using modified magnetic chitosan at ph values of 1 to 7 and reported that the highest Cu (II) and Co (II) removal efficiencies occurred at ph value of 6.0 [50]. Akbari et al. examined Cu (II) and Co (II) removal using the brown algae C. indica. The initial ph values of the solution in their study ranged from 2 to 6. They reported the highest biosorption efficiency at ph value of 6.0 [51] Cu Co ph Fig. 2. The effect of initial ph on the biosorption efficiency of Cu and Co ions (agitation speed: 200 rpm; time: 60 min; temperature: room temperature; biosorbent dose: 3g/L; initial concentration levels of Cu and Co: 20 mg/l). IJPT June-2017 Vol. 9 Issue No Page 30062

6 Effect of agitation rate The rate of solution agitation during biosorption is an important factor due to effect on the chance of contact between the biosorbent and the ions. To investigate the effect of agitation speed on the removal efficiencies of Cu and Co ions, different agitation rates were evaluated from rpm. As seen in Fig. 3, the removal efficiencies of Cu and Co increased as the initial agitation speed increased to 250 rpm. Increasing the speed of mixing above 250 rpm caused the removal efficiencies of ions by R. oryzae biomass declined slowly. The initial increase in agitation speed reduced the stability of the liquid film around the biosorbent and slowly changed its structure and led to increase the biosorption efficiencies [52]. At a high mixing speed (>250 rpm), the efficiencies of metal biosorption declined because the energy necessary for breaking links between the metal ions and the biosorbent is provided by the high mixing speeds. The highest biosorption efficiencies of Cu and Co ions were at agitation rate of 250 rpm with80% and 77%, respectively. Fig. 3. The effect of agitation on the removal efficiency of metal ions (ph: 8; time: 60 min; temperture: room temperature; biosorbent dose: 3g/L; initial concentration levels of Cu and Co: 20 mg/l). Effect of biosorbent dose The effect of biosorbent dose on the removal efficiencies of Cu and Co ions is shown in Fig. 4. As seen, with increasing biosorbent dose from 2 to 6 g/l, the biosorption efficiencies of Cu and Co ions increased from 78.3% to 93% and from 65.75% to 90%, respectively. But by increasing biosorbent dose from 6 to 7 g/l, the biosorption efficiencies of ions almost remained constant. By increasing biosorbent in the solution, the number of active sites and amount of surface area available for biosorption of metal ions increased, which increased the efficiency of biosorption. Similar results have been reported by Sowmya et al. for the removal of Co from aqueous solutions by using Chrysanthemum indicum in its raw (CIF-R) and biochar (CIF-BC) forms. They found that Co removal rate IJPT June-2017 Vol. 9 Issue No Page 30063

7 increased as the biosorbent dose increased from 1 to 4 g/l for CIF-R and 1 to 3 g/l for CIF-BC, after which it remained nearly constant up to 10 g/l [53]. Shakera also examined removal of Co (II), Ni (II), and Cu (II) ions by chitosan-modified poly (methacrylate) nanoparticles at different doses and observed that the rate of biosorption of Co (II), Ni (II), and Cu (II) increased as the biosorbent dose increased from 0.1 to 0.5 g/l; however, there were no significant differences between toxic metal removal at biosorbent doses higher than 0.5 g/l [54]. However, Al- Homaidan et al. reported that increasing the biomass dose of Spirulina platensis from 0.2 to 0.5 g/l increased the biosorption rate from 77% to 78%. But they reported that the removal rate of Cu declined as the biosorbent dose increased from 0. 5 to 15 g/l [55]. Fig. 4. The effect of biosorbent dose on the removal efficiencies of Cu and Co ions (ph: 8; agitation speed: 250 rpm; time: 60 min; temperture: room temperature; initial concentration levels of Cu and Co: 20 mg/l). Effect of initial metal concentration In batch biosorption, the initial concentration level of dissolved metal ions present in the solution play a key role in mass transfer between the solution and the solid phase. So to evaluate the effect of initial concentration levels of Cu and Co on biosorption efficiencies, the experiments were performed at room temperature, ph value of 8, agitation speed of 250 rpm, biosorbent dose of 6 g/l, contact time of min and initial metal concentration levels of mg/l. As shown in Figs. 5 and 6, there are correlations between initial metal concentration levels and biosorption efficiencies. Because increasing concentration levels of Cu and Co ions provided the force necessary for mass transfer between the solid and liquid phases. Also there were positive relationships between contact time and biosorption efficiencies and by increasing contact time, metal ions had sufficient time to reach the active sites and penetrate into the layers of biosorbent. IJPT June-2017 Vol. 9 Issue No Page 30064

8 The highest rate of metal ions biosorption occurred at the beginning of the process, because active and non-saturated sites were available; however, saturation of biosorbent active sites caused the biosorption rate to level off over time. The time to equilibrium for metal ions biosorption was determined to be 60 min, after which biosorption occurred under the influence of penetration, which is a very slow phenomenon. The biosorption efficiencies of Cu and Co ions at equilibrium time (60 min) at a concentration level of 40 mg/l were determined to be 96% and 94%, respectively (Figs. 5 and 6). Similar result have been reported for the removal of Cu and Co from aqueous solution by using chitosan-modified poly (methacrylate) nanoparticles [54]. In contrast, Shengmou and Lin reported that Cu (II) and Hg (II) biosorption by a biomass of dried Sargassum fusiforme decreased as the initial Hg (II) and Cu (II) concentration levels increased [56]. Fig. 5. The effect of initial concentration level of Cu on biosorption efficiency (ph: 8; temperture: room temperature; biosorbent dose: 6 g/l; agitation speed: 250 rpm). Fig. 6. The effect of initial concentration level of Co on biosorption efficiency (ph: 8; temperture: room temperature; biosorbent dose: 6 g/l; agitation speed: 250 rpm) IJPT June-2017 Vol. 9 Issue No Page 30065

9 Biosorption isotherms A variety of isotherm models have been used to describe the laboratory data obtained in biosorption studies. Among these, the Langmuir and Freundlich isotherm models are the most common and were used in this study to investigate the isothermic behavior of biosorbents prepared by using R. oryzae. The linear form of Langmuir isotherm model used in the present study is expressed by the equation (3) [57]: (3) Where C e is the concentration level of metal ions at equilibrium (mg/l), q e is the amount of metal ion biosorbed per gram of biosorbent at equilibrium, and q max and K L are biosorption capacity (mg/g) and biosorption energy (g/l), respectively. These fixed components of the Langmuir model were obtained by measuring the slope and width of linear Langmuir equation as a function of. Another important and effective parameter expressing a main characteristic of the Langmuir equation is R L. This value represents the state of the sorption isotherm model [58]. R L = (4) Where C 0 (mg/l) is initial concentration level of metal ions present in the aqueous solution. The R L values obtained by the Langmuir model for Cu (0.2404) and Co (0.499) ions suggest that the biosorption of these ions by R. oryzae biomass is appropriate. In addition to the Langmuir isotherm model, the Freundlich model was used to describe the equilibrium behavior of the biosorbent for removal of Cu and Co ions. The linear form of this model follows Eq. (5) as [59]: Ln q e = Ln K f + Ln C e (5) Where q e is the equilibrium biosorption capacity (mg/g), C e is the equilibrium concentration of metal ions in solution (mg/l), and K f and n are Freundlich constants that show relationships between biosorption capacity and biosorption intensity, respectively. The Langmuir and Freundlich biosorption isotherms parameters for Cu and Co onto R. oryzae are shown in Table 1. As shown in Fig. 7(a-d), the Langmuir model is a better fit than the Freundlich model. The Langmuir isotherm assumes a homogeneous biosorption surface and the possibility of monolayer biosorption. IJPT June-2017 Vol. 9 Issue No Page 30066

10 Fig. 7. Langmuir biosorption isotherm of: (a) Cu and (b) Co by R. oryzae; Freundlich biosorption isotherm of: (c) Cu and (d) Co by R. oryzae. Table 1. Biosorption isotherm parameters for metal ions biosorption onto R. Oryzae. Langmuir Freundlich Metal q max K L R L R 2 n K f R 2 Cu Co Kinetics To examine the mechanism of Cu and Co biosorption prepared by using pretreated R. oryzae biomass, pseudo-firstorder and pseudo-second-order kinetic models were used. The pseudo-first-order kinetic model is expressed as [60]: Ln (q e -q t ) = Lnq e - K 1 t (6) Where q e is the amount of ions biosorbed per gram of biosorbent at equilibrium (mg/g), q t is the amount of ions biosorbed per gram of biosorbent at any time (mg/g), and k 1 is the biosorption constant (1/min). To calculate the constant rate of biosorption (K 1 ), Ln (q e -q t ) is plotted against t. Another kinetic model used in many investigations to describe the mechanism of sorption is the pseudo-second-order kinetic model. The linear form of this model is expressed as [61]: IJPT June-2017 Vol. 9 Issue No Page 30067

11 (7) Where q e is the amount of ions biosorbed per gram of biosorbent at equilibrium (mg/g), q t is the amount of ions biosorbed per gram of biosorbent at time t (mg/g), and K 2 is the equilibrium constant of the second-order kinetic speed (g/mg min). The constants of the pseudo-first-order and pseudo-second-order kinetic models, and all other parameters of these kinetic models are shown in Table 2 and Fig. 8 (a-d). The results demonstrated that both models have the ability to describe the kinetic behavior of the biosorbent; however, based on the value of correlation coefficient R 2 as well as q e, the pseudo-second-order kinetic model is better suited to describe the kinetic behavior of the biosorbent. Fig. 8. The pseudo- first-order kinetic models of: (a) Cu and (b) Co by R. oryzae; the pseudo- second-order kinetic models of: (c) Cu and (d) Co by R. Oryzae. Table 2. Biosorption kinetic parameters of Cu and Co biosorption onto R. Oryzae. Pseudo-first- order Pseudo-second-order Metal C 0 (mg/l) q exp (mg/g) q cal (mg/g) 2 q cal (mg/g) K 2 R 2 Cu IJPT June-2017 Vol. 9 Issue No Page 30068

12 Co Conclusion A biomass of the fungus R. oryzae was chemically modified with sodium hydroxide to remove metal ions of Cu and Co from aqueous solutions. The effect of contact time, biosorbent dose, initial ph value, initial concentration level of dissolved metal ions and agitation speed were examined. The results showed the highest biosorption rates at an initial ph value of 8 at room temperature, an agitation speed of 250 rpm, a contact time of 150 min and a biosorbent dose of 6 g/l and efficiencies were 97.65% and 96.37% for Cu and Co ions, respectively. The kinetic behavior of the biosorbent was examined using the pseudo-first-order and pseudo-second-order kinetic models. Based on the correlation coefficients obtained, the pseudo-second-order kinetic model was better suited to describe the kinetic behavior of the biosorbent. The Langmuir and Freundlich isotherm models were used to describe the equilibrium behavior of the biosorbent during biosorption. According to the determined correlation coefficient, the Langmuir isotherm model is more suited to describe the equilibrium behavior of R. oryzae. Based on the R L values obtained from the Langmuir model, it was appeared that the biosorption of both Cu and Co onto pretreated R. oryzae biomass was appropriate and the biosorption capacities of these ions were in an acceptable range. Our results showed that fungal biosorbent of R. oryzae can be used for the removal of toxic metals such as Cu and Co from aqueous solutions. Acknowledgements The authors are grateful to the Bushehr University of Medical Sciences for their support. Reference 1. A. Netzer, D.E. Hughes, Water Research 18 (1984) S. Dobaradaran, A.H. Mahvi, R. Nabizadeh, A. Mesdaghinia, K. Naddafi, M. Yunesian, N. Rastkari, and S. Nazmara, Bull Environ Contam Toxicol., 85 (2010) 530. IJPT June-2017 Vol. 9 Issue No Page 30069

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