A BIOPROCESSING STRATEGY THAT ALLOWS FOR THE SELECTION OF CR(VI)-REDUCING BACTERIA FROM SOILS

Anaerobic bacteria that reduce hexavalent chromium [Cr(VI)] to trivale nt [Cr(III)] are common in soils and were used to develop a bioprocess employing a selection strategy. Indigenous Cr(VI)-reducers were enric hed from Cr(VI)-contaminated soil under anaerobic conditions. The mixe d culture was then tested for Cr(VI)-reducing activity in a chemostat, followed by transfer to a l-L packed-bed bioreactor operated at 30 de grees C for additional study. The support material used in the reactor consisted of 6-mm porcelain saddles. Cr(VI) concentrations in the liq uid ranged from 140-750 mg L-1. Cr(VI)-reducing bacteria were the domi nant population with Cr(VI)-reduction rates of approximately 0.71 mg g (-1) dry cells h(-1) achieved at Cr(VI) concentrations of 750 mg L-1. These results indicate a potential for selecting and maintaining indig enous Cr(VI)-reducers in a bioreactor for Cr(VI)-remediation of ground water or soil wash effluents.