Studies on biosorption of zinc(II) and copper(II) on Desulfovibrio desulfuricans

The objectives of these studies are to determine the equilibrium concentration and kinetics of metal sorption on sulfate-reducing bacteria (SRB) isolates. Adsorption establishes the net reversible cellular metal uptake and is related to SRB metal toxicity and the effects of environmental factors. Results from biosorption equilibria and kinetics of copper(II) and zinc(II) ions on Desulfovibrio desulfuricans and the effects of adsorption of these metals on SRB are discussed. Adsorption studies were conducted using stationary phase cells with equilibrium uptake at 24 h and pHs in the range of 4-7. Equilibrium adsorption in milligram of metal/g dry cell for copper(II) of 2.03 (pH 4.0) and 16.7 (pH 5.0) and zinc(II) of 6.40 (pH 5.5), 13.8 (pH 6.0), 39.2 (pH 6.2) and 49.6 (pH 6.6) was measured experimentally. Negligible biosorption of copper and zinc was found below pH 4.0, with metal sorption increasing within a limited range of pH mainly due to the neutral and/or deprotonated state of binding ligands on cell walls. Competition of metal ions during biosorption was investigated by conducting sorption experiments with Zn(II) using potassium phosphate buffer (KP) and deionized/distilled water. Zn(II) sorption capacity was lower in KP buffer than deionized water due to competition from potassium ions. Scanning Electron Microscope micrographs indicated that metal biosorption on SRB may be related to the production of extracellular polymeric substance (e.g., polysaccharide). Published by Elsevier Science Ltd.