Environmental Factors Affecting Selenite Reduction by a Mixed Culture

This study presents the results of batch experiments investigating selenite reduction by an enriched anaerobic mixed culture as a function of several environmental factors, including pH, temperature, different electron donors and acceptors, as well as initial selenite concentrations. The initial selenite reduction was a zero-order reaction and was inhibited at higher selenite concentrations (>33 mg Se/L). The optimal temperature/pH for microbial reduction occurred at 30°C and pH 7.2. Selenite reduction was affected in the presence of high concentrations of sulfate [45 times the Se(IV) molar concentration], significantly affected by nitrate [105 times the Se(IV) molar concentration], and completely inhibited by chromate and oxygen. Ethanol was the preferred carbon source for selenite removal, followed by acetate, citrate, lactate, and glucose. The selenite-acclimated culture also reduces selenate without any lag period.