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

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 communitys 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/m(2)-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/m(2)-d, probably because of cellular toxicity. Although Archaea were present through all stages, Bacteria dominated the ClO(4)(-)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 O-2 needed as a cosubstrate for the mono-oxygenation of CH4-.