Bioreduction of nitrate in high-sulfate water using a hydrogen-based membrane biofilm reactor equipped with a separate carbon dioxide module

Abstract

A hydrogen-based membrane biofilm reactor (MBfR) equipped with separate hydrogen (H2) and carbon dioxide (CO2) adjustable gas-transfer modules was used to explore denitrification in a water containing a high concentration of sulfate (SO42−) (500 mg S/L). CO2 was used for pH control and as the sole carbon source for long-term operation of the MBfR, during which >90% denitrification was achieved. Short-term experiments demonstrated that increasing the SO42− loading had negligible effect on nitrate (NO3−) reduction, but SO42− reduction was strongly suppressed by high NO3− loading regardless of H2 availability. Sulfide oxidation accompanied with SO42− reduction occurred in the biofilm, and the intermediate element sulfur was further oxidized to SO42−. Results of high-throughput sequencing suggest that sulfide oxidation was carried out by the known sulfide-oxidizing bacteria: Starkeya and Xanthobacter. And sulfide oxidation coupled to denitrification was a primary reason for minimal net SO42− reduction when the NO3− loading was high enough. This study demonstrates the promise of effective denitrification without net SO42− reduction in MBfR systems and documents the important sulfur-conversion processes.