Effects Of Nano-zerovalent Iron On Antibiotic Resistance Genes During The Anaerobic Digestion Of Livestock Waste

Antibiotics are widely used in feed for livestock and poultry farming,which induce the production of antibiotic resistance genes?ARGs?in animal intestines and poultry feces.ARGs can be spread among different microorganisms through horizontal gene transfer.When a large amount of organic fertilizers carrying antibiotics and ARGs are applied to the farmland,the risk of soil microorganisms acquiring antibiotic resistance will increase,ultimately harming human health.Anaerobic digestion is an important method for the utilization of livestock and poultry manure,but there is a great risk of ARGs transmission in fermentation products.Nano-zerovalent iron?n ZVI?has strong reducibility and high reactivity and superior performance in remedying antibiotic pollution and improving anaerobic digestion efficiency.Therefore,this study adopts nano-zerovalent iron?n ZVI?as an additive to improve the anaerobic digestion process of cattle manure,and explore the effects of different concentrations(0?80 and 160 mg·L^-1)of n ZVI on the anaerobic digestion gas production performance,ARGs,mobile genetic elements?MGEs?and microorganisms.The relationship between ARGs and MGEs,microbial communities,and environmental factors was clarified,and investigate the key factors that drive the fate of ARGs.The main results and conclusions are as follows:?1?The addition of n ZVI effectively enhanced the methane yield,where it significantly increased by 6.56%and 6.43%with 80 mg·L^-1 and 160 mg·L^-1 n ZVI.In the early stage of fermentation,the addition of n ZVI increased the concentration of VFAs and NO₃^--N in the system and improved the peak gas production.?2?sul1,tet M,sul2 and erm F are the most abundant ARGs in the initial anaerobic digestion.Anaerobic digestion effectively controlled 12/14 of the detected ARGs.Compared with CK,the addition of 160 mg·L^-1 n ZVI effectively reduced the absolute abundance of ARGs in fermentation products by 5.5–9.4 logs.160 mg·L^-1 n ZVI had the best reduction effect on MGEs,which mainly reduced the absolute abundance of Tn916/1545.?3?Firmicutes,Bacteroidetes,Actinobacteria and Proteobacteria are the dominant microorganisms at the phylum level.n ZVI mainly improves methane production by modifying the members of the bacterial community related to hydrolysis and acetogenesis.The addition of 160 mg·L^-1 n ZVI effectively facilitated the removal of the major host bacteria?Acinetobacter?in anaerobic digestion product.MGEs are the most important factors that affect the changes of ARGs,int I1 and Tn916/1545 have the greatest impact on ARGs.n ZVI indirectly affected the host bacteria by influencing the environmental variables,thus affecting the fate of ARGs.nZVI can improve the gas production performance of anaerobic digestion,increase the production of methane,maintain the stability of the anaerobic digestion system.MGEs are the main driver for ARGs changes.Adding n ZVI can reduce the abundance and transmission risk of ARGs.The addition of 160 mg/L n ZVI can effectively promote the reduction of ARGs?dominant MGE?Tn916/1545?and main host bacteria?Acinetobacter?in anaerobic digestion products.