Complete Perchlorate Reduction Using Methane as the Sole Electron Donor and Carbon Source

Abstract

Using a CH4-based membrane biofilm reactor (MBfR), we studied perchlorate (ClO4–) reduction by a biofilm performing anaerobic methane oxidation coupled to denitrification (ANMO-D). We focused on the effects of nitrate (NO3–) and nitrite (NO2–) surface loadings on ClO4– reduction and on the biofilm community’s mechanism for ClO4– reduction. The ANMO-D biofilm reduced up to 5 mg/L of ClO4– to a nondetectable level using CH4 as the only electron donor and carbon source when CH4 delivery was not limiting; NO3– was completely reduced as well when its surface loading was ≤0.32 g N/m2-d. When CH4 delivery was limiting, NO3– inhibited ClO4– reduction by competing for the scarce electron donor. NO2– inhibited ClO4– reduction when its surface loading was ≥0.10 g N/m2-d, probably because of cellular toxicity. Although Archaea were present through all stages, Bacteria dominated the ClO4–-reducing ANMO-D biofilm, and gene copies of the particulate methane mono-oxygenase (pMMO) correlated to the increase of respiratory gene copies. These pieces of evidence support that ClO4– reduction by the MBfR biofilm involved chlorite (ClO2–) dismutation to generate the O2 needed as a cosubstrate for the mono-oxygenation of CH4.