Bioreduction of hexavalent chromium by Bacillus cereus isolated from chromite mine overburden soil

The presence of soluble Cr(VI) particularly in the overburden soil samples of the chromite mines area is about 300-500mg Cr(VI)/kg. The level of Cr(VI) in final effluents needs to be reduced to the permissible limit <0.05mg/L (USEPA) using appropriate technology before it is discharged into the soil. Out of 12 bacterial isolates from the mine samples, CSB-9 was proven effective in reducing hexavalent chromium to its trivalent form with its inherent ability to survive proficiently in 200ppm Cr(VI). The isolate, confirmed to be Bacillus cereus, was characterised as gram-positive and capsule forming with the optimum growth at pH 7.0 and 35oC. The process of bioreduction of Cr(VI) using B. cereus was optimized with various parameters, viz., pH, initial concentration, dosage of adsorbent, temperature. The bacterium gave 90% reduction from 100ppm Cr(VI) aqueous feed in 120h at pH 7.0, 35ºC using 1% (v/v) cells/mL.