| The overuse of antibiotics in veterinary medicine and humans has led to the emergence and widespread transmission of antibiotic-resistant bacteria(ARBs)and antibiotic resistance genes(ARGs)in the environment.Most antibiotics and ARGs are discharged to wastewater treatment plants and eventually settle in excess sludge.Once the sludge is treated and disposed of resourcefully,bacteria carrying ARGs in the sludge can share resistance genetic information through mobile genetic elements(MGEs).Therefore,safe and effective recovery technologies for excess sludge are of great concern.Vermi-wetland is a sustainable and eco-friendly technology for recycling excess sludge.Compared with conventional vermi-filter,vermi-wetland combines the triple ecological factors of earthworms,plants and microorganisms,and provides a more efficient and stable treatment of excess sludge.However,Studies have shown that ARGs often co-migrate with pollutants in the environment,and in particular,the interaction of microplastics(MPs)and ARGs in different environments has received extensive attention.Although it is well established that ARGs are affected by MPs in wastewater treatment,little attention has been paid to the effect of MPs on ARGs in excess sludge.However,MPs can flow into wastewater treatment plants through municipal sewers and surface runoff and eventually be deposited in sludge in large quantities.These MPs cannot be removed or degraded during the subsequent treatment process.It would complicate the process of reducing ARGs in excess sludge by vermi-wetlands.Therefore,in this study,two groups of vermi-wetlands of the same constructive scale were constructed to treat excess sludge through the addition of PMMA MPs to the excess sludge,with no MPs added as a control.The aim was to investigate the effect of MPs on the degradation of organic matter and the reduction of ARGs in excess sludge in the vermi-wetlands,and to reveal the mechanism of the effect of MPs on ARGs in the process of treating excess sludge in the vermi-wetlands.The main research results are as follows:(1)The results showed that the growth rates of plants and earthworms were significantly inhibited in the vermi-wetland with MPs,leading to a decrease in the degradation efficiency of organic matter in the excess sludge,in which the average removal rates of chemical oxygen demand(COD)and total solids(TS)of the excess sludge decreased by 15.36% and 38.00%,respectively.The addition of MPs significantly increased the DOC content in the vermi-wetland and reduced the conversion efficiency of dissolved organic matter in the sludge,resulting in an unstable organic matter structure in the wetland.The abundance of 16 S rDNA and 18 S rDNA within the vermi-wetland with MPs increased by 53.61% and 75%,respectively,compared with the vermi-wetland without MPs,while the diversity of the bacterial community decreased significantly.The MPs significantly inhibited the growth of Proteobacteria,Actinobacteria and Firmicutes bacteria in the wetlands,while positively promoting the growth of Bacteroidota.Further study revealed that the abundance of Paracoccus and Sphingomonas decreased by 72.85% and 38.97%,respectively,while the abundance of IMCC26207,Luteolibacter and OLB8 increased by 5.90%,115.57% and565.82%,respectively,in the vermi-wetland with the addition of MPs.Comparing the analysis of bacterial metabolic pathways within the two groups of vermi-wetlands,the results showed that the metabolic pathways of microorganisms inside the vermi-wetlands were all inhibited by the addition of MPs.The addition of MPs led to a decrease in the efficiency of pyruvate production and ATP production,and a significant decrease in the abundance of genes encoding ammonia monooxygenase(amo A,amo B,amo C),hydroxylamine oxidase gene(hao),and nitrite oxidase gene(nxr A,nxr B)by 15.81%,16.10%,13.81%,18.35%,4.77%,and 4.60%,which significantly inhibited the nitrification of microorganisms.(2)The addition of MPs reduced the removal of int I1 and ARGs in the vermi-wetland compared to the control,and the removal of ARGs was unstable.The median removal rates of tetM,sul1,sul2,ermF,and ermB in vermi-wetlands decreased by 24.50%,29.24%,15.75%,22.05%,and 32.97%,respectively(P<0.05),while the coefficient of variation of ARGs removal increased by 181.02% to 695.10% in comparison to the control.Analysis of the layer structure of the vermi-wetlands revealed that int I1 and tnp A-04 were mainly retained in the vermicompost layer,and the retention of int I1 and tnp A-04 by the vermi-wetlands with the addition of MPs was significantly increased by 38.99% to 68.29% and 9.22% to 81.91%,respectively.The correlation analysis study found that the addition of MPs weakened the correlation between MGEs and effluent ARGs inside the wetland,while increasing the correlation between internal microorganisms and effluent ARGs.(3)In addition,this study was conducted to investigate the effects of MPs in vermi-wetlands on ARGs in excess sludge,and to quantify the removal and retention effects of MPs and MGEs adsorbed on the surface of MPs in vermi-wetlands.The results showed that the removal effect of MPs with larger size was better in the vermi-wetland,especially the removal rate of MPs of 500 μm was up to 100%.The MPs were mainly retained in the vermicompost of the vermi-wetland,which showed the similar pattern as the retention of MGEs.The correlation analysis showed that MPs at 1 μm were highly correlated with the abundance of Int I1(P<0.001),and MPs at 100 μm and 500 μm were highly correlated with the abundance of tnp A-04(P<0.001).In addition,the 1 μm MPs trapped in the vermi-wetland showed a significant positive correlation(P<0.05)with the abundance of Luteolibacter and IMCC26207.Moreover,the abundances of int I1 and tnp A-04 detected on the surface of MPs were 25.62 ng/g and 7.26 ng/g,respectively.It is evident that the adsorption of MPs and the retention of MPs by the vermi-wetland reduced the removal of ARGs by the vermi-wetland and increased the risk of ARGs transmission in the effluent of the vermi-wetland. |
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