The synergy of Fe(III) and NO drives the anaerobic oxidation of methane.

The anaerobic oxidation of methane (AOM) driven by NO or Fe(III) alone was limited by slow electron delivery and ineffective enrichment of microbes. The flexible coupling between Fe(III) and NO potentially cooperated to accelerate AOM. One negative control was fed CH and NO, and four treatment reactors were supplemented with CH, NO and ferric citrate (FC)/ferric chloride (FCH)/ chelate iron (FCI)/ferric hydroxide (FH) and were anaerobically operated for 1200 days to verify the synergy and promicrobial roles of Fe(III) and NO in improving AOM. The changes in gas and ion profiles were observed in the reactors, and microbial development was studied using 16S rRNA gene sequencing with the Illumina platform. The results indicated that the combined Fe(III) and NO treatment improved AOM, and their synergy followed the order of FC > FCI > FCH > FH. The biochemical reaction of Fe with NO and its secondary process accelerated electron transfer to microbial cells and subsequently enhanced AOM in the reactors. The total organic carbon (TOC) content, NH content, NO content, and pH value altered the dominant bacteria the most in the FC reactor, FCI, FCH, and FH groups, respectively. Several dominant bacterial species were enriched, whereas only two archaea were highly concentrated in the FC and FCI groups. Only bacteria were detected in the FCH group, and archaea contributed substantially to the FH group. These findings contribute to an improved understanding of the interactions among nitrogen, iron and CH that are paramount to accelerating the process of AOM for engineering applications.