Selenium Reduction in Batch Bioreactors

Selenium is toxic to aquatic life at very low levels and can also be harmful to human health. Anthropogenic sources of selenium are wide spread including electronic and photography, glass manufacturing, pigments, additives for metal processing, copper refining operations, fossil fuel combustion, petroleum refining, and agricultural drainage waters in the Western United States. This study investigates selenium removal by microbial reduction with a pure culture of selenium-reducing bacterium Escherichia coli strain EWB32213 isolated in our laboratory from a coal slurry pond. Environmental factors evaluated include temperature, pH, and selenium concentration with optimal conditions observed at pH 7 and 30°C. A two-stage reduction process, from selenate to selenite, followed by selenite to elemental selenium and subsequent precipitation was observed in the batch culture. The reduction of selenite to elemental selenium in the second stage was found to be the rate limiting process with reduction rate significantly lower than that in the first-stage.