Roles of Fe3O4 nanoparticles in enhancing anaerobic digestion of synthetic wastewater with high chemical oxygen demand

Wastewater with a high concentration of chemical oxygen demand is a potential feedstock for biomethane production via anaerobic digestion (AD). However, the accumulation of volatile fatty acids often poses a significant bottleneck, inhibiting biomethane production efficiency. This study investigated the effects of Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) and hydrophobic carbon cloth on AD performance. The addition of Fe 3 O 4 NPs increased the maximum methane production rate (MPR) by 19.6% compared to the control group without conductive materials supplementation (CK). Notably, Fe 3 O 4 NPs were first founded to significantly alleviate the inhibitory effect of hydrophobic carbon cloth on AD; on day 9, the MPR increased to 1.8-fold in the Fe 3 O 4 NPs group and to 1.3-fold in the co-addition group (Fe 3 O 4 NPs and carbon cloth), compared to the carbon cloth group alone. Additionally, Fe 3 O 4 NPs decreased cytochrome c concentration by 40.2% and increased the relative abundance of Clostridium_sensu_stricto_1 in the suspended sludge to 1.3 times compared with the CK. In the carbon cloth biofilm, Fe 3 O 4 NPs enriched the populations of Anaerolineales (2.1-fold increase) and Methanosaeta (1.1-fold increase), and stimulated bacterial metabolic pathways such as membrane transport and carbohydrate metabolism compared to the carbon cloth group. This study helps to elucidate the mechanisms by which Fe 3 O 4 NPs supplementation accelerates the AD process.