Prediction of metal-adsorption behaviour in the remediation of water contamination using indigenous microorganisms

摘要

Minerals Processing and Technology Research Centre, Department of Metallurgy, Faculty of Engineering and the Built Environment, University of Johannesburg, PO Box 526, Wits 2050, Johannesburg, South Africa ;Minerals Processing and Technology Research Centre, Department of Metallurgy, Faculty of Engineering and the Built Environment, University of Johannesburg, PO Box 526, Wits 2050, Johannesburg, South Africa ;Department of Chemical Technology, Faculty of Science, University of Johannesburg, PO Box 17011, Doomfontein, Johannesburg, South Africa ;Water and Health Research Centre, Faculty of Health Sciences, University of Johannesburg, PO Box 17011, Doomfontein 2028, Johannesburg, South Africa;%In recent years, the adsorption of heavy metal cations onto bacterial surfaces has been studied extensively. This paper reports the findings of a study conducted on the heavy metal ions found in mine effluents from a mining plant where Co~(2+) and Ni~(2+) bearing minerals are processed. Heavy metal ions are reported to be occasionally present in these mine effluents, and the proposed microbial sorption technique offers an acceptable solution for the removal of these heavy metals. The sorption affinity of microorganisms for metal ions can be used to select a suitable microbial sorbent for any particular bioremediation process. Interactions of heavy metal ions (Co~(2+) and Ni~(2+)) and light metal ions (Mg~(2+) and Ca~(2+)) with indigenous microbial cells (Brevundimonas spp., Bacillaceae bacteria and Pseudomonas aent-ginosa) were investigated using the Langmuir adsorption isotherm, pseudo second-order reaction kinetics model and a binary-metal system. Equilibrium constants and adsorption capacities derived from these models allowed delineation of the effect of binding affinity and metal concentration ratios on the overall adsorption behaviour of microbial sorbents, as well as prediction of performance in bioremediation systems. Although microbial sorbents used in this study preferentially bind to heavy metal ions, it was observed that higher concentrations (>90 mg/8) of light metal ions in multi-metal solutions inhibit the adsorption of heavy metal ions to the bacterial cell wall. However, the microbial sorbents reduced Ni~(2+) levels in the mine-water used (93-100% Ni~(2+) removal) to below the maximum acceptable limit of 350 ng/C, established by the South African Bureau of Standards. Competition among metal ions for binding sites on the biomaterial surface can occur during the bioremediation process, but microbial sorption affinity for heavy metal ions can enhance their remediation in dilute (<5 mg/C heavy metal) wastewaters.