Inhibition mitigation and ecological mechanism of mesophilic methanogenesis triggered by supplement of ferroferric oxide in sulfate-containing systems

Methanogenesis can be inhibited by volatile fatty acids (VFAs)accumulation and sulfate during anaerobic wastewater treatment. In this study, effects of ferroferric oxide (Fe₃O₄)on VFAs degradation and methanogenesis in sulfate-containing environment were investigated. Methanogenesis in reactors with or without sulfate were both favored through the addition of Fe₃O₄. In reactors without sulfate, the dosage of Fe₃O₄ increased the maximum methane production rate by 21.7% accompanied with faster acetate and propionate degradation. Metagenomic analysis showed that Fe₃O₄ mainly promoted electron exchange between Mesotoga, Syntrophobacter, Smithella and Methanosaeta without altering the syntrophic patterns. However, in the sulfate-containing reactor with low methanogenic efficiency, syntrophic ethanol users and Methanosaeta were replaced by sulfate-reducing bacteria and Methanosarcina, respectively. The supplement of Fe₃O₄ re-enriched the syntrophic partners inhibited by sulfate and rebuilt a new syntrophic interaction with high efficiency similar to that in sulfate-free environment, leading to better methanogenic performance in sulfate-containing environment.