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.