The biosorption of Pb(II), Zn(II) and Ni(II) from industrial wastewater using Stenotrophomonas maltophilia and Bacillus subtilis was investigated under various experimental conditions regarding pH, metal concentration and contact time. The optimum pH values for the biosorption of the three metals were in the range 5.0-6.0, while the optimal contact time for the two bacterial species was 30 min. Experimental data was analyzed using Langmuir and Freundlich isotherms; the former had a better fi t for the biosorption of Pb(II), Zn(II) and Ni(II). The maximum adsorption uptakes (q max ) of the three metals calculated from the Langmuir biosorption equation for S. maltophilia were 133.3, 47.8 and 54.3 for Pb(II), Zn(II) and Ni(II), respectively, and for B. subtilis were 166.7, 49.7 and 57.8 mg/g, respectively. B. subtilis biomass was more favorable for the biosorption of Pb (II) and Ni (II), while S. maltophilia was more useful for the biosorption of Zn (II).

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The optimum conditions for biosorption of Pb(II) and Ni(II) from aqueous solution were investigated, by using living and nonliving Pseudomonas fluorescens and Bacillus pumilus isolated from wastewater treatment plant. It was found that the optimum pH for Pb(II) removal by living and nonliving cells was 6.0, while 7.0 for Ni(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased. The binding capacity by living cells is significantly higher than that of nonliving cells at tested conditions. The maximum biosorption capacities for lead and nickel by using Ps. fluo-rescens and B. pumilus were 77.6, 91.4 and 65.1, 73.9 mg/g, respectively. The results of bio-sorption time and desorption experiments suggested that Pb(II) and Ni(II) uptake by the living bacterial biomass might be enhanced by intracellular accumulation.

This study examined the biosorption process of Ni(II) and Zn(II) from an aqueous solution by dead biomass of Yarrowia lipolytica. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature. The biosorbent was characterized by FTIR, which indicated the participation of hydroxyl, carboxyl, amide and amine groups in the process of binding the metal ions. The results showed that the biosorption processes of both metal ions closely followed pseudo-second order kinetics. The equilibrium data of Ni(II) and Zn(II) ions at 20, 30 and 40 o C fi tted the Langmuir and Freundlich isotherm models. Langmuir isotherm provided a better fi t to the equilibrium data, with a maximum biosorption capacity of the Y. lipolytica biomass for Ni(II) and Zn(II) of 30.12 and 44.44 mg/g respectively. The calculated thermodynamic parameters demonstrated that the biosorption of Ni(II) and Zn(II) ions onto the Y. lipolytica was feasible, spontaneous and endothermic.

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