| Summary: | The indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant in Brits (North West Province, South Africa) biocatalytically reduced Cr6+ in the presence of As3+. Treatment of these elements before disposal of wastewater is critical since they are both known to be carcinogenic and mutagenic at very low concentrations. Both compounds are known to be acutely toxic under high exposure conditions (Cr6+>50 mg/L, As3+>20 mg/L). In this study, experiments were conducted to evaluate the rate of Cr6+ reduction under anaerobic conditions in the presence of As3+. Near complete Cr6+ reduction wasachieved under initial Cr+6 concentrations up to 70 mg/L under an As3+ concentration of 20 mg/L. However, after increasing Cr6+ concentrations to 100 mg/L, an inhibitory effect was observed. Further experiments conducted at Cr6+ concentration of 70 mg/L and varying As3+ concentration from 5-70 mg/L showed that Cr6+ reduction rate increased with increasing As3+ concentration from 5-40 mg/L. However, 20 % drop in Cr6+ reduction efficiency was observed. These results suggest that the rate of Cr6+ reduction was hindered by the dual toxicity of the Cr6+ and As3+ in the system. The observed inhibitory effect was attributed to thetoxicity effect of Cr6+ and As3+. Initial evaluation of the bacteria using DNA finger printing showed that cells in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus sp., Enterobacter sp., and Bacillus sp.
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