Bioreduction of hexavalent chromium by chromium resistant alkalophilic bacteria isolated from tannery effluent

Abstract

Two chromium resistant alkalophilic bacterial strains (CRAB), namely Bacillus cohnii SR2 and Bacillus licheniformis SR3 were isolated and identified from tannery effluent. Bioreduction of chromium (VI) into chromium (III) by CRAB was investigated in the present study. Optimization of process parameters with respect to bioreduction percentage was studied by Response Surface Methodology (RSM) software, v12. Both the strains were found to achieve highest chromium (VI) bioreduction of 94 and 95% in 100 mg/L at the end of 25 h at pH 9.0. At an optimized concentration of 550 mg/L, a maximum bioreduction of 82 and 90% by SR2 and SR3 was noted within 25 h. In addition, both the strains showed tolerance to chromium until 1000 mg/L. Scale-up studies using Air lift bioreactor system by CRAB with real tannery effluent showed 100% bioreduction within 8 h. Therefore, this study signified the astonishing bioreduction capability of CRAB isolates that was quite evident in scale-up studies too. Keywords: Alkalophilic, Bioreduction, Chromium resistant, Response surface methodology, Tannery effluent