Study On The Dissemination Of Antibiotic Resistance Genes In A Municipal Solid Waste Landfill System And Its Control

China generates tens of million tons of municipal solid waste（MSW）every year and around 180 million of MSW were estimated to be landfilled annually.However,considerable amount of antibotics,metals and other biotoxical emerging contaminants could be possibly disposed of in MSW landiflls because of inefficient solid waste management.It is becoming increasingly appearent that MSW landfill transferred into a hotspot harboring antibiotic resistant genes（ARGs）.But,the dissemination mechanism of ARGs during the long-term landfilling process has yet to be systematically studied,particularly in different stages and environmental phases.In addition,leachate treatment capacities regarding the removal and containment of ARGs’spread in natural environments have rarely known.Therefore,this study focused on the AMR contamination in Laogang MSW landfills in Shanghai,China.In combination with lab-scale landfill reactors,we exptraploated ARGs’dissemination and major pathwy via the qPCR,16S sequencing and modern bioinformatics.Furthermore,the removal efficiencies of ARGs and containment capacity in leachate-receiving water were studied by sampling and lab-simulation.The major conclusions are listed below:1.There were 12 ARG subtypes,6 mobile genetic elements（MGEs）,11 kinds of antibiotics and bacterial community were tested,and meanwhile variations of common heavy metals and environmental physchemical indice were detected in all samples.Generrally,in refuse,total contents of antibiotics decrased significantly from fresh to mature stages（313.5±212.7μg/kg vs.138.3±117.2μg/kg）.However,the abundance of target ARGs kept around 6.5 log₁₀（copies/ngDNA）.By contrast,even though total concentration of antibiotics deceased by half rom from 1484.5±179.9ng/L to 922.8±180.3 ng/L in leachate samples,target ARGs were enriched during 30years landfill process(6.0 vs.7.2 log₁₀（copies/ngDNA）).Heavy metals in refuse（3500-500 mg/kg）and leachate（8-15 mg/L）exhibited ascending and descending trends across the whole landfilling period,respectively.Regarding bacterial community compositions,refuse and leachates were different and more pronounced differences across different stages were observed in leachate samples;however,the Proteobacteria、Firmicutes、Bacteroidetes（>40%）phylum were dominant,the same to their affiliated genus and genus.Based on a holistic assessment including ARGs,bacterial communnity and environmental contaminants,we found two ARG dissemination pathways.In leachates,ARGs were strongly associated with MGEs in their abundances,which mean that ARGs could be propagated via horizontal transfer across bacteria.In refuse,the effects of MGEs became less important,but it appeared that ARGs were structured more closely with bacterial community2.Pilot-scale vessels were constructed to simulate landfilling process,where 6of 25L reactors were designed into air sealed（anaerobic）and air exposure（aerobic）groups and then were subcategorized into control,antibiotics addition（PenG and SMZ）,and heavy metal addition（K₂CrO₄ and ZnSO₄）vessel.Here,we found that additions of antibiotics and metals slightly increased the content of total sulR target ARGs whereas decreased blaR subtypes’,and the effects of antibiotics were more sunstaintial.However,ambient air exposure was beneficial to the increase of target ARGs during the simulated landfilling process.This study also constructed regression models to simulate the discharge pattern of target ARGs.Here,the sulR were found to be linearly associated with MGEs（intl）,which was further validated by leachates sampled from real landfill sites.But,for the blaR genes,their developments were negatively correlated with MGEs（intl）and may be structured by bacterial community rather than the HGT.3.We quantified target ARGs in the effluents from a combined leachate treatment process,including biological treatment（MBR）,physical separation（UF）,ultraviolet（UV）disinfection and advanced oxidation process（AOP）.The contents of ARGs were enriched in the MBR(8.9±0.04 log₁₀（copies/ngDNA）)effluent,which were then significantly removed in the tertiary treatment process.The UF decreased total ARGs by 1.5 orders of magnitude,and lab-scale UV and AOP finally reduced the ARGs’level to around 6.5 log₁₀（copies/ngDNA）.In the effluent-receiving water,total contents of MGEs and ARGs generally increased by 1-2 and 2-3 orders of magnitude,respectively.Correlations analyses revealed that target ARGs became more closely associated with MGEs in effluent-receiving samples.This may imply that these treatment technologies could be efficiently facilitate the spread of ARGs.In conclusion,this current study systematically explained the dissemination mechanisms of ARGs in landfills spanning 30 years,which was validated by pilot sacle landfilling data.Also,our study also showed that conventional wastewater treatment technologies are inable to remove nor feasible in countering ARGs in effluent-receiving water.The obtained results are expected to provide insights to and theoretical bases for studies of ARGs dissemination mechanisms,AMR risk prediction,and risk control.