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

The objectives of these studies are to determine the equilibrium concentrat ion and kinetics of metal sorption on sulfate-reducing bacteria (SRB) isola tes. Adsorption establishes the net reversible cellular metal uptake and is related to SRB metal toxicity and the effects of environmental factors. Re sults from biosorption equilibria and kinetics of copper(II) and zinc(II) i ons on Desulfovibrio desulfuricans and the effects of adsorption of these m etals on SRB are discussed. Adsorption studies were conducted using station ary 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 d eprotonated state of binding ligands on cell walls. Competition of metal io ns during biosorption was investigated by conducting sorption experiments w ith Zn(II) using potassium phosphate buffer (KP) and deionized/distilled wa ter. Zn(II) sorption capacity was lower in KP buffer than deionized water d ue to competition from potassium ions. Scanning Electron Microscope microgr aphs indicated that metal biosorption on SRB may be related to the producti on of extracellular polymeric substance (e.g., polysaccharide). Published b y Elsevier Science Ltd.