Microbial perchlorate reduction with elemental sulfur and other inorganic electron donors

Abstract

ClO 4 - 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 H 2 as electron donor. Aerobic activated sludge was evaluated further and it supported perchlorate reduction with Fe 0 and S 0 additions under anaerobic conditions. Heat-killed sludge did not convert ClO 4 - , confirming the reactions were biologically catalyzed. ClO 4 - (3 mM) was almost completely removed by the first sampling time on d 8 with H 2 (⩾0.37 mM d −1), after 22 d with S 0 (0.18 mM d −1) and 84% removed after 37 d with Fe 0 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 S 0 as an electron donor. The enrichment culture also utilized S 2− and S 2 O 3 2 - as electron-donating substrates to support ClO 4 - reduction. The mixed cultures also catalyzed the disproportionation of S 0 to S 2− and SO 4 2 - . Evidence is presented demonstrating that S 0 was directly utilized by microorganisms to support perchlorate-reduction. In all the experiments, ClO 4 - 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.