Selenium reduction by a denitrifying consortium

A denitrifying bacterial consortium obtained from the Pullman, Washington w astewater treatment facility was enriched under denitrifying conditions and its ability to reduce selenite and selenate was studied. Replicate experim ents at two different experimental conditions were performed. All experimen ts were performed under electron-acceptor limiting conditions, with acetate as the carbon source and nitrate the electron acceptor. In the first set o f experiments, selenite was present, whereas, in the second set, selenate w as added. A significant lag period of approximately 150 h was necessary bef ore selenite or selenate reduction was observed. During this lag period, ni trate and nitrite use was observed. Once selenite or selenate reduction had started, nitrate and nitrite reduction was concomitant with selenium speci es reduction. Trace amounts of selenite were detected during the selenate r eduction study. Analysis of the data indicates that, once selenium species reduction was induced, the rate of reduction was proportional to the seleni um species concentration and to the biomass concentration. Furthermore, at similar biomass and contaminant concentrations, selenite reduction is appro ximately four times faster than selenate reduction. (C) 1999 John Wiley & S ons, Inc.