Environmental factors and modeling in microbial chromium (VI) reduction

A Cr(VI)-reducing culture was enriched from an anaerobic chemostat fed with synthetic media containing acetate and Cr(VI). The enriched culture was used for a series of batch tests to investigate several environmental factors affecting microbial Cr(VI) reduction. Under carbon-limiting conditions, the extent of Cr(VI) reduction proportionally depended on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon the initial biomass level and the type of organic compounds. The developed model predicted Cr(VI) reduction well at different Cr(VI) concentrations. Sulfate at 120 mg SO42-/L or nitrate at 150 mg N/L sightly inhibited Cr(VI) reduction. Reduction of nitrate but not sulfate was observed along with Cr(VI) reduction. Cr(VI) was not reduced by the aerobically growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature for Cr(VI) reduction were found to be 7.3 and 32 degrees C, respectively. in addition, Cr(VI) reduction was sensitive to the metal ions that may coexist with Cr(VI) in industrial wastes containing Cr(VI).