Enhancement of methane production and antibiotic resistance genes reduction by ferrous chloride during anaerobic digestion of swine manure

In this study, effects of ferrous chloride (FeCl2) addition on methane production and antibiotic resistance genes (ARGs) reduction were investigated during anaerobic digestion (AD) of swine manure. FeCl2 could both improve the accumulative methane production and reduce the abundance of total ARGs, i.e., the maximum increase of CH4 production of 21.5% at FC5, and the maximum ARGs reduction of 33.3% at FC25. The reduction of pathogenic bacteria and metal resistance genes (MRGs) was enhanced. Acetate and propionate utilization were intensified by enhancing H-2 utilization and direct interspecies electron transfer (DIET), where DIET was further enhanced by the reaction of the FeCl2 and acetic acid. The bacterial community played important role in the evolution of ARGs (68.26%), which were also affected by MRGs, mobile genetic elements (MGEs), and environmental factors. Therefore, FeCl2-based AD is a feasible and attractive way to improve methane production and ARG reduction.