Biosorption of cadmium and lead using suspended and immobilized Enterobacter cloacae at different pH

Abstract

The aim of this work was to determine the best conditions for biomass production of the bacterium Enterobacter cloacae and for Cd and Pb retention by adsorption on the cell walls or by absorption and accumulation in the bacterial biomass. Suspended and immobilized cultures of this bacterium, acclimated to both metals, were grown for 24 h at pH 6, 7 and 9, in trypticase soy (TS) medium added with 2.73 mg/L of Cd or 16.8 mg/L of Pb. Immobilized cultures at pH 7 and 9 had the highest biomass production. Percentages of Cd retention by adsorption and absorption increased with increasing pH, but adsorption was higher in suspended while absorption was higher in immobilized cultures. Possibly because of different affinity of bacterial cells for these metals, the percentages of Pb retention were higher than those of Cd. In percentage, the highest Pb adsorption on cell walls was at pH 9, while retention by biomass decreased with increasing pH. The amount of metal retained by one g of bacterial biomass, efficiency was higher at pH 6, possibly because of the presence of dead or dying bacterial cells.