| Anaerobic digestion is widely used in the treatment of livestock and poultry farming manure because it can realize resource utilization.However,antibiotics are commonly added in modern large-scale farming,which not only have certain inhibitory effects on the anaerobic digestion process,but also induce the production of antibiotic resistance genes（ARGs）,which canenter the environment when using the digestate for land application,posing a threat to the ecological environment and human health.Therefore,the effect of antibiotics on the anaerobic digestion of chicken manure and the reduction of antibiotics by anaerobic digestion have received widespreadattention.In this paper,we studied the effects of enrofloxacin（ENR）on anaerobic digestion of chicken manure by batch and continuous experiments.The study aims to understand the effects of different concentrations of ENR on the methane production during anaerobic digestion of chicken manure,as well as the removal efficiency of ENR.The distribution characteristics of ENR in the solid digestate and liquid digestate are also clarified.The study employs metagenomics to analyze changes in microbial population structure and abundance of ARGs,revealing the microbiological mechanism of ENR on anaerobic digestion of chicken manure.The results provide a theoretical basis for the engineering application of anaerobic digestion of ENR-contaminated chicken manure.The main results obtained are as follows:（1）In batch experimental,the inhibition of anaerobic digestion of chicken manure varied among different ENR concentration,including low(5 mg·L-1),medium(30 and 70 mg·L-1)and high(140 and 280 mg·L-1)levels,and the inhibition gradually increased with the increase of ENR concentration level.The inhibition of ENR on anaerobic digestion of chicken manure mainly occurred in the acidification stage.（2）The dominant bacterial groups in anaerobic digestion of chicken manure contaminated with ENR were Bacteroidetes（19.05%～38.66%）and Firmicutes（11.06%～19.83%）,both of these groups can utilize protein;with the increase of ENR addition,the microbial community in the fermentation gradually shifts towards bacterial groups that are related to antibiotics as dominant groups.In addition,the decrease in the abundance of methanogenic bacteria due to ENR addition was the reason for the inhibition of cumulative methane production in anaerobic digestion by ENR.Acetotrophic methanogenesis is the main pathway for methane production in each digestive system,and The key reason for the inhibition of acetoclastic methane producing bacteria Methanothrix by ENR was the weakening of its ACSS,mtr and mcr functional genes.（3）The relative abundance of ARGs in digested sludge increased after ENR addition,and the relative percentages of Mex I and tet W/N/W were absolutely dominant among all ARGs from T2 to T5.The results of the traceability analysis indicated that the host of resistance genes in anaerobic digestion of ENR-contaminated chicken manure was mainly from the Firmicutes phylum.In addition,microorganisms in the digestive system produce resistance through three mechanisms:antibiotic efflux pump（35.82%）,antibiotic inactivation（26.36%）,and antibiotic target site alteration（22.89%）.（4）In continuous experiment,although methanogenic bacteria were quickly inhibited under low concentrations ENR conditions(5 and 30 mg·L-1),microorganisms gradually adapted after running for a period time,and the volumetric gas production rate would eventually restor to a certain extent.And when the ENR concentration reached 70 and 140mg·L-1,the volumetric gas production was significantly reduced and inhibited by 60.6%and91.5%,respectively.（5）ENR inhibits the secretion of EPS by anaerobic microorganisms in the digestive system.However,under higher ENR conditions,anaerobic microorganisms secrete more EPS to protect cells from toxic by adsorbing or preventing the diffusion of foreign pollutants.Compared with phase 1,the EPS protein content decreased by 46.48%～61.08%and EPS polysaccharide content increased by 52.30%～197.10%in phase 2-5,indicating that the decrease in EPS content was mainly manifested by the decrease in EPS protein.（6）The biological removal rate of ENR and its solid and liquid phase residual distribution showed decreasing and increasing trends with increasing ENR concentration,respectively,and the removal rate of ENR ranged from 54.74%to 79.54%under continuous experimental conditions.Therefore,it is recommended that digestate should be subjected to deep processing to control the input of residual ENR in solid and liquid digestate to the environment,which poses a risk to the pollution of farmland and water bodies. |
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