Study On The Reductions Of Tetracycline Resistance Genes By Anaerobic Digestion Of Dairy Manure Combined With Ultrasound And Adsorption

In recent years,the expansion of livestockproduction has led to a large number of livestock manure,and the antibiotic resistance genes(ARGs)contained in manure may posed a serious threat to the ecological environment.The biological treatments of livestock manure can realize resource utilization,but their reduction effects on ARGs were limited.The combined physical method is expected to solve this problem and reduce the ecological risk of livestock manure.Therefore,in this study,dairy manure wastewater was used as substrates to carry out anaerobic digestion combined with ultrasound-adsorption test,and the changes and main influencing factors of tetracycline resistance genes(TRGs)during digestion were analyzed.The cell fragmentation and extracellular TRGs abundance changes in biogas slurry under different ultrasound conditions were explored.The dairy manure biochar was further prepared to adsorb biogas slurry in order to reduce TRGs in biogas slurry.The main research results are as follows:(1)The average methane production rate of anaerobic digestion of dairy manure was 100.66 m L/d,and the total methane content was 4529.48 m L.The absolute abundance of tet Q and tet G increased while the absolute abundance of tet C,tet O,tet T and tet X decreased after digestion.Through network analysis and redundancy analysis,it can be seen that the changes of microorganisms is the main factor affecting the changes of TRGs.Unidentified＿Boidales,unidentified＿Sphaerochaetaceae,unidentified＿Pseudomonadaceae and other bacteria related to anaerobic environment are the potential host bacteria of TRGs,and their relative abundances increases with the accumulation of ammonia nitrogen,resulting in a small change in the abundance of TRGs after anaerobic digestion.(2)Ultrasound of biogas slurry showed that the number of colonies and biomass decreased significantly,and the abundances of TRGs decreased significantly,indicating that ultrasound could effectively reduce TRGs in biogas slurry.Under the same ultrasonic density,the longer the ultrasonic time,the lower the abundances of TRGs in biogas slurry.The highest removal rate of TRGs was 83.29%at 1.5w/m L-40 min.(3)Ultrasound broke the cells and some TRGs became extracellular free,and adsorption could effectively reduce extracellular TRGs.Biochar prepared from cow dung at three pyrolysis temperatures(500°C,600°C,700°C)was used to adsorb TRGs from biogas slurry after ultrasonic.The results showed that the adsorption efficiency of TRGs was higher at 600°C,and the removal rate of TRGs reached65.34%,especially the removal rate of extracellular TRGs reached 88.35%.(4)Comprehensive analysis of the changes of TRGs in anaerobic digestion combined with ultrasound-adsorption showed that TRGs were greatly reduced,the total reduction was 3.37×10~9 copies/m L,and the removal rates were 99.32%and93.63%.The maximum reduction of TRGs in biogas slurry by ultrasound and adsorption was 1.69×10~8 copies/m L,and the maximum removal rate was 88.11%,indicating that this process not only realizes the resource utilization of cow dung wastewater,but also effectively reduces TRGs and reduces the pollution and ecological risk of dairy manure wastewater.