This study shows vanadate (V(V)) reduction in a methane (CH4) based membrane biofilm batch reactor when the concentration of dissolved oxygen (O2) was extremely low. V(IV) was the dominant products formed from V(V) bio-reduction, and majority of produced V(IV) transformed into precipitates with green color. Quantitative polymerase chain reaction and Illumina sequencing analysis showed that archaea methanosarcina were significantly enriched. Metagenomic predictive analysis further showed the enrichment of genes associated with reverse methanogenesis pathway, the key CH4-activating mechanism for anaerobic methane oxidation (AnMO), as well as the enrichment of genes related to acetate synthesis, in archaea. The enrichment of aerobic methanotrophs Methylococcus and Methylomonas implied their role in CH4 activation using trace level of O2, or their participation in V(V) reduction.
Keywords: Hypoxic condition; Membrane biofilm batch reactor; Methane oxidation; Vanadate reduction.