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