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(70-08) Kinetics of metal bio-precipitation during sulphate reduction and methonogenesis. Samaranayake, Rajika1, Singhal, Naresh*,1, Lewis, Gillian2, Hyland, Margaret3, 1 Department of Civil and Environmental Engineering, Auckland, AK, New Zealand2 School of Biological Sciences, Auckland, AK, New Zealand3 Department of Chmical and Materials Engineering, Auckland, AK, New Zealand ABSTRACT- Batch experiments were conducted in the laboratory to study changes in metal speciation due to electron transfer reactions facilitated by bacteria. Kinetics of bio-precipitation of heavy metals by sulphate reducing bacteria and methanogenic bacteria were examined in sequential environments. A mixed culture extracted from leachate-contaminated soil was used under conditions favorable to anaerobic bacterial growth and enhanced redox processes. Experiments were conducted for different COD: SO4 ratios between 2 to 15 by varying the initial sulphate concentration and for different EDTA concentrations. Results show that methonogenesis was suppressed until complete sulphate reduction occurred. Higher concentrations of sulphate were seen to inhibit methonogenesis. Although nutrient limitations controlled bacterial growth, complete metal removal was achieved. Cu, Pb, Cd and Zn precipitate within 8-15 days while Fe and Ni take longer under sulphate reducing conditions. Ca, Mg and Mn remain constant until methonogenesis starts, and then precipitates completely. In the presence of complexing agents, some metals (Ni>Fe>Zn) remains in the dissolved form more than 20 days. Metal-organic complexations were identified as controlling metal precipitation. Mathematical models were developed for the fate of growth substrates, electron acceptors and metals under the sequential sulphate reduction and methonogenic phases. The model was shown to satisfactorily match experimental observations. The rate of metal precipitation was in the order Cd>Cu>Zn>Ni>Fe during the sulphate reducing phase and Ca>Mg>Mn during the methonogenic phase. Key words: heavy metals, bio-precipitation, kinetics, complexation |
