Effects of ferric oxide on the microbial community and functioning during anaerobic digestion of swine manure

Iron-based materials have been suggested as environmentally-friendly additives that can enhance methane production during anaerobic digestion (AD). In this study, the effects of ferric oxide (Fe 2 O 3 ) addition on methane production were investigated during swine manure AD. In addition, the effects of Fe 2 O 3 addition on the AD ternary pH buffer system and microbial community were evaluated. Fe 2 O 3 could improve the accumulative methane production by maximum 11.06% when adding 75 mmol of Fe 2 O 3 . Higher methane production could be attributed to the enhancement of direct interspecies electron transfer (DIET) and the formation of Fe-S precipitates, but not the addition of Fe 2 O 3 as a nutrient. Furthermore, Fe 2 O 3 addition enhanced methanogenesis rather than acetogenesis, as evinced by analysis of functional genes. Nevertheless, high-throughput sequence analysis of microbial community composition revealed the lack of a significant influence by Fe 2 O 3 addition, and Fe 2 O 3 addition did not significantly affect the ternary pH buffer system.