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 (FeCl 2 ) addition on methane production and antibiotic resistance genes (ARGs) reduction were investigated during anaerobic digestion (AD) of swine manure. FeCl 2 could both improve the accumulative methane production and reduce the abundance of total ARGs, i.e., the maximum increase of CH 4 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 FeCl 2 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, FeCl 2 -based AD is a feasible and attractive way to improve methane production and ARG reduction.