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

Abstract

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.