CHROMIUM (VI) REDUCTION BY BACTERIA ISOLATED FROM SEWAGE TREATMENT PLANT

Bacterial reduction of chromium (VI) has been seen as one of the biological means of detoxifying toxigenic chromium. This study was carried out to investigate the ability of bacterial isolates from sewage treatment plant to reduce Cr (VI). The bacteria were isolated using standard culture techniques while the amount of Cr (VI) reduced by the isolates was determined using 1, 5-diphenylcarbazide method. The influence of concentration and inoculum size on the reduction of Cr (VI) by the isolates were studied. Chromium (VI) tolerant bacteria identified as Bacillus sp., Pseudomonas sp., Escherichia coli and Staphylococcus sp. were isolated from the sewage treatment plant. The isolates displayed varying degrees of Cr (VI) reduction under different conditions. All the isolates showed the highest reduction rate at 50 mu g/ml concentration with a range of between 89.9% and 99.4% at 72 h and least reduction rate at 500 mu g/ml ranging between 13.3 and 23.85% also at 72 h. The rate of reduction increased with increase in inoculum size with the highest reduction of 98.9% by Pseudomonas sp at an inoculum size of 12 x 10(8) cfu/ml. The results showed significant difference (p <= 0.05) in the amount of chromium (VI) reduced by the isolates at 24 h, 500 mu g/ml and inoculum size of 12 x 10(8) cfu/ml. Statistical analysis of the results showed that Pseudomonas sp. was the best reducer of Cr (VI) followed by Bacillus, Staphylococcus and then E.coli. The results of this study suggest that these bacteria can be useful for chromium (VI) detoxification in contaminated environments.