Selenate and Nitrate Bioreductions Using Methane as the Electron Donor in a Membrane Biofilm Reactor

摘要

Selenate (SeO_4~(2-)) bioreduction is possible with oxidation of a range of organic or inorganic electron donors, but it never has been reported with methane gas (CH_4) as the electron donor. In this study, we achieved complete SeO_4~(2-) bioreduction in a membrane biofilm reactor (MBfR) using CH_4 as the sole added electron donor. The introduction of nitrate (NO_3~-) slightly inhibited SeO_4~(2-) reduction, but the two oxyanions were simultaneously reduced, even when the supply rate of CH_4 was limited. The main SeO_4~(2-)-reduction product was nanospherical Se~0, which was identified by scanning electron microscopy coupled to energy dispersive X-ray analysis (SEM-EDS). Community analysis provided evidence for two mechanisms for SeO_4~(2-) bioreduction in the CH_4-based MBfR: a single methanotrophic genus, such as Methylomonas, performed CH_4 oxidation directly coupled to SeO_4~(2-) reduction, and a methanotroph oxidized CH_4 to form organic metabolites that were electron donors for a synergistic SeO_4~(2-)-reducing bacterium.