The Removal Performance Of Antibiotic Resistance Genes In Leachate By Landfill Bioreactor And Different Treatment Processes

Recently,with the widespread use of antibiotics in animal husbandry and health care,the increased antibiotics residuals in the environments accelerated the spread of antibiotic resistance genes(ARGs),and the resulting proliferation of ARGs has become a potential risk to public safety and ecology health.As the primary disposal site of municipal solid waste,the landfill contains a large number of expired antibiotics and resistant gene,which will turn into the landfill leachate with the treatment of solid waste.Once the landfill leachate can not be effectively treated,the ARGs will enter the environment with the leachate discharge,and then will result in potential environmental risk.Therefore,it is necessary to investigate the behavior of ARGs in leachate under different conditions.In this study,the lab-scale landfill bioreactors were constructed by using aged refuse from Shanghai Laogang Landfill as the filler.To study the variation ARGs removal rate under different operating conditions,we designed three aerobic reactors with three different hydraulic loadings(25 L/m3·d,50 L/m3·d,100 L/m3·d)and another anaerobic reactor with 50 L/m3·d hydraulic loading.In addition,the removal rate of ARGs in leachate under three different treatment processes was studied,and the effects of different processes on the removal of ARGs were discussed.Main conclusions of this study were as follows:1.The removal efficiency of nutrient elements,heavy metals and ARGs in landfill bioreactor under different hydraulic loading and aerobic conditions was studied,and the correlation between resistance gene removal rate and environmental factors was obtained by correlation analysis.(1)The performance of bioreactors which operated for 81 days under different hydraulic loads were studied.Comparing the removal rate of total nitrogen,ammonia nitrogen and COD in the reactors with 25,50,and 100 L/m3 d of hydraulic loading,it could be found that the higher ammonia nitrogen and total nitrogen removal rate was observed at lower operating load.However,COD removal rate shows a tendency to increase firstly and then decrease with increasing hydraulic loading.In addition,the effects of aerobic and anaerobic conditions on the reactor operation were compared.The results showed that the aerobic conditions are beneficial to the removal of ammonia nitrogen and COD and the anaerobic condition is favorable for the removal of total nitrogen.The reason is that the organic aerobic respiration and nitrification processes are carried out under aerobic conditions,while the anaerobic conditions had a stimulative effect on denitrification.The removal rate of total heavy metals in the reactor under the hydraulic load of 25 L/m3·d was higher than 50 L/m3 ·d and 100 L/m3·d,which indicated that the low hydraulic loading was more favorable for heavy metals removal.By comparing the aerobic and anaerobic conditions of the system operation,it was found that aerobic conditions were more favorable for the removal of heavy metals.(2)The result of resistance gene removal experiment showed that the removal efficiencies of sul1,strB,aadA1 and intll under the hydraulic loading of 25 L/m3·d were higher than the data collected in 50 L/m3 ·d and 100 L/m3·d,which indicated that the low hydraulic loading was more favorable for ARGs removal.By comparing the operating effect of the reactor under different aerobic conditions,it was found that the removal rates of sull,sul2,strB,aadAl and intll in aerobic conditions were significantly higher than those of anaerobic,indicating that the aerobic condition was more favorable for the removal of ARGs.(3)The correlation analysis showed that heavy metals and water quality had a significant correlation with ARGs.There were significant positive correlations between As,Pb,NO3--N and logARGs removal rates,and significant negative correlation between other environmental factors and logARGs removal rates.It showed that water quality and heavy metals had an important impact on the removal of ARGs in this study.2.The effects of different treatment processes on the removal of ARGs were analyzed.The effects of water quality parameters and heavy metal to ARGs removal rate were analyzed.(1)Three treatment processes,including MBR,three-stages A/O and two-stages A/O all had high removal rate of nitrogenous compound and COD(>90%).The removal rate of NO3--N had no significant difference among three treatment processes,while the different removal efficiencies of NH4+-N,NO2--N TN and COD were caused by three treatment processes.The removal rate of TN and COD was the highest in two-stages A/O process,while the removal rate of NH4+-N was the highest in MBR.Then,it could be found that the removal rate of Cu,Ni had no significant difference in three treatment process.The two-stages A/O process increased the concentration of Cd and Zn in the effluent,but had a better effect than other heavy metals compared with MBR and there-stages A/O.It indicated that the removal performance of heavy metal in two-stages A/O process was better than in MBR process and in three-stages A/O process.(2)The result of ARGs in the three processes showed that the MBR process had the highest log-removal efficiency(1.76～3.07 orders of magnitude)for the tetracycline gene and macrolide gene.The two-stages A/O process was more effective for sulfonamides,aminoglycosides,β-lactam and multiple ARGs and integrase gene.The abundance of sull,sul2,aadA1,mexF,intll genes in the there-stages A/O process 03 effluent increased.It indicated that the two-stages A/O process had a higher removal rate for most target genes,MBR process was more suitable for tetracycline and macrolide gene removal.