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...