Methane oxidation coupled to perchlorate reduction in a membrane biofilm batch reactor.

A specially designed CH-based membrane biofilm batch reactor (MBBR) was applied to investigate anaerobic methane oxidation coupled to perchlorate reduction (AnMO-PR). The 0.21 mM ClO added in the first stage of operation was completely reduced in 28 days, 0.40 mM ClO was reduced within 23 days in stage 2, and 0.56 mM of ClO was reduced within 30 days in stage 3. Although some chlorate (ClO) accumulated, the recovery of Cl was over 92%. Illumina sequencing of the 16S rRNA gene documented that the bacterial community was mainly composed by perchlorate-reducing bacteria (PRB), methanotrophic bacteria, and archaea. Real-time quantitative PCR showed the archaeal 16S rRNA and mcrA genes increased as more ClO was reduced, and the predominant archaea belonged to Methanosarcina mazei, which is related to ANME-3, an archaeon able to perform reverse methanogenesis. Several pieces of evidence support that ClO reduction by the MBBR biofilm occurred via a synergism between Methanosarcina and PRB: Methanosarcina oxidized methane through reverse methanogesis and provided electron donor for PRB to reduce ClO. Because methanotrophs were present, we cannot rule out that they also were involved in AnMO-PR if they received O generated by disproportionation of ClO from the PRB.