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 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.