Microbial perchlorate reduction with elemental sulfur and other inorganic electron donors

ClO4- has recently been recognized as a widespread contaminant of surface and ground water. This research investigated chemolithotrophic perchlorate reduction by bacteria in soils and sludges utilizing inorganic electron-donating substrates such as hydrogen, elemental iron, and elemental sulfur. The bioassays were performed in anaerobic serum bottles with various inocula from anaerobic or aerobic environments. All the tested sludge inocula were capable of reducing perchlorate with H2 as electron donor. Aerobic activated sludge was evaluated further and it supported perchlorate reduction with Fe0 and S0 additions under anaerobic conditions. Heat-killed sludge did not convert ClO4-, confirming the reactions were biologically catalyzed. ClO4- (3 mM) was almost completely removed by the first sampling time on d 8 with H2 (⩾0.37 mM d−1), after 22 d with S0 (0.18 mM d−1) and 84% removed after 37 d with Fe0 additions (0.085 mM d−1). Perchlorate-reduction occurred at a much faster rate (1.12 mM d−1), when using an enrichment culture developed from the activated sludge with S0 as an electron donor. The enrichment culture also utilized S2− and S2O32- as electron-donating substrates to support ClO4- reduction. The mixed cultures also catalyzed the disproportionation of S0 to S2− and SO42-. Evidence is presented demonstrating that S0 was directly utilized by microorganisms to support perchlorate-reduction. In all the experiments, ClO4- was stoichiometrically converted to chloride. The study demonstrates that microorganisms present in wastewater sludges can readily use a variety of inorganic compounds to support perchlorate reduction.