Effects Of Thermal Hydrolysis Pretreatment On The Changes Of Antibiotic Resistance Genes During Anaerobic Digestion Of Dairy Manure

Antibiotic Resistance Genes（ARGs）exist in livestock manure and enter the environment with manure discharge,which can pose a potential threat to human health and ecological environment.Anaerobic digestion technology is one of the main ways of manure utilization,and it can also simultaneously reduce some ARGs in manure,but its reduction effect needs to be improved.The combination of thermal hydrolysis and anaerobic digestion can effectively improve the anaerobic digestion performance,but its effect on the removal of fecal ARGs and its micro-ecological mechanism is still unknown.Therefore,in this study,tetracycline ARGs in dairy manure were taken as the research object,and the occurrence changes of ARGs in dairy manure after different thermal hydrolysis conditions（T=150,170 and 190 °C,t=30,60 and 120 min）were analyzed to explore the optimal thermal hydrolysis pretreatment conditions.Under the optimal pretreatment conditions,thermohydrolysis and mesophilic anaerobic digestion（T=35°C）were combined to compare and analyze the anaerobic digestion performance,ARGs occurrence,microbial community and dynamic changes of environmental factors,and to explore the removal effect of ARGs combined with the two technologies and reveal their microecological mechanism.The main conclusions are as follows :（1）Thermal hydrolysis experiments showed that extending hydrolysis time combined with higher hydrolysis temperature could improve the reduction effect of ARGs.In the established experimental conditions,when the hydrolysis temperature was T=170 °C and the hydrolysis time was t=120 min,the optimal ARGs and microbial biomass reduction effect（reduction rates were 99.52 % and 99.88 %,respectively）could be obtained.Under this condition,a large number of microbial cells can be broken,thereby reducing the survival rate of microorganisms and effectively reducing the manure ARGs.（2）The combination of thermal hydrolysis and anaerobic digestion technology improved the mesophilic anaerobic digestion performance and the reduction effect of manure ARGs.Compared with the control group,the total methane production of the treatment group increased by 16.45 %;the abundance of 16 S rRNA decreased by 79.03 %;the total abundance of ARGs decreased by 34.04 %;the abundance of tet C decreased by 97.80 %;the abundance of tet G,tet O,tet Q and tet W decreased by 23.33 %-80.85 %,while the abundance of tet X and tet T increased.（3）Microbial ecological mechanism analysis showed that the changes of microbial community structure and physicochemical factors were the driving factors for the changes of fecal ARGs.The analysis of microbial community difference showed that thermal hydrolysis pretreatment could significantly reduce the alpha diversity of microbial community in anaerobic digestion of dairy manure（P < 0.05）and increase the abundance of Firmicutes and Bacteroidetes in the community（7.41% and 16.89%）.The co-occurrence analysis of ARGs and microbial networks showed that the biomarker bacteria such as Syntrophomonas,Sedimentibacter and vadin CA02 were potential hosts of ARGs,and their occurrence changes had a major impact on the reduction effect of ARGs.RDA analysis showed that physical and chemical factors could largely affect the survival of potential host bacteria of ARGs,in which soluble polysaccharides and soluble proteins mainly affected the potential host bacteria of tet X and tet T,while SCOD was related to the changes of potential host bacteria of tet C,tet G,tet Q and tet W.