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 cult ure was used for a series of batch tests to investigate several enviro nmental factors affecting microbial Cr(VI) reduction. Under carbon-lim iting conditions, the extent of Cr(VI) reduction proportionally depend ed on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon t he initial biomass level and the type of organic compounds. The develo ped model predicted Cr(VI) reduction well at different Cr(VI) concentr ations. Sulfate at 120 mg SO42-/L or nitrate at 150 mg N/L sightly inh ibited Cr(VI) reduction. Reduction of nitrate but not sulfate was obse rved along with Cr(VI) reduction. Cr(VI) was not reduced by the aerobi cally growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature f or Cr(VI) reduction were found to be 7.3 and 32 degrees C, respectivel y. in addition, Cr(VI) reduction was sensitive to the metal ions that may coexist with Cr(VI) in industrial wastes containing Cr(VI).