Optimization of nickel and cobalt biosorption by native Serratia marcescens strains isolated from serpentine deposits using response surface methodology.

The treatment of metal-polluted wastes is a challenging issue of environmental concern. Metals can be removed using microbial biomass, and this is an interesting approach towards the design of eco-friendly technologies for liquid waste treatment. The study reported here aimed to optimize nickel and cobalt biosorption from aqueous solutions using three native metal-resistant Serratia marcescens strains. Ni(II) and Co(II) biosorption by S. marcescens strains was found to fit better to Langmuir's model, with maximum uptake capacities of 13.5 mg g for Ni(II) ions and 19.9 mg g for Co(II) ions. Different experimental conditions of initial metal concentration, pH, initial biomass, and temperature were optimized using the Plackett-Burman method, and, finally, biomass and metal concentration were studied using the response surface methodology (RSM) to improve biosorption. The optimum uptake capacities for Co(II) ions by the three biosorbents used were obtained for initial metal concentrations of 35-40 mg L and an initial biomass of 6 mg. For Ni(II) ions, the optimum uptake capacity was achieved with 1 mg of initial biomass for S. marcescens C-1 and C-19, and with 7 mg for S. marcescens C-16, with initial concentrations of 20-50 mg L. The results obtained demonstrate the viability of native S. marcescens strains as biosorbents for Ni(II) and Co(II) removal. This study also contributes to our understanding of the potential uses of serpentine microbial populations for the design of environmental cleanup technologies.