Effects of ferroferric oxide on propionate methanogenesis in sequencing batch reactors: Microbial community structure and metagenomic analysis

This study investigated the effects of ferroferric oxide (Fe3O4) on propionate methanogenesis in anaerobic sequencing batch reactor (ASBR). Compared to ASBRC (without Fe3O4 addition), the addition of 10 g/L Fe3O4 (ASBRFe) decreased the maximum methane production rate by 69.6 % when propionate was used as the sole substrate. The addition of Fe3O4 reduced the contents of humic substances, riboflavin and nicotinamide adenine dinucleotide in extracellular polymeric substances. Therefore, Fe3O4 inhibited interspecies electron transfer of microorganisms through electronic mediators. Microbial community analysis revealed that Fe3O4 addition increased the relative abundance of acetate oxidizing bacterium (Mesotoga), but decreased the abundance of hydrogenotrophic methanogen (Methanobacterium). Further metagenomics analysis indicated that Fe3O4 increased the abundance of acetate oxidation genes and decreased that of hydrogenotrophic methanogenesis, quorum sensing and V/A-type ATPase genes. Thus, Fe3O4 reduced propionate methanogenesis during anaerobic digestion. The overall results indicate that Fe3O4 addition inhibits methanogenesis for treatment of propionate-contaminated wastewater in ASBR.