Microbial reduction of hexavalent chromium

This study evaluated the effects of several environmental factors on Cr(VI) reduction by a group of ATCC cultures. Biological reduction of hexavalent chromium was affected by growth medium, cell concentration, chromium concentration, pH, temperature, and the presence of co-contaminants. Nutrient broth and yeast extract in the growth medium reduced chromium to a significant degree in anaerobic cultures. The rate of chromium reduction increased with increasing cell density but decreased at higher chromium concentrations. The optimum chromium reduction rate was observed at pH 7 and 36°C in E. coli 33456 under anaerobic conditions. Sulfate and nitrate at very high concentrations(4000 -8000 mg/l), did not interfere chromium reduction in this strain. The presence of phenolic compounds (1000 - 7700 mg/l) or heavy metals (100 400 mg/l), however, significantly inhibited chromium reduction.