| In recent years,antibiotics have been detected in different environmental media due to their intensive use,which promotes the prevalence of antibiotic resistance.Antibiotic resistance is considered as an emerging pollutant threatening human health and ecosystem,and is recognized as one of the three threats to public health.In wastewater treatment plants(WWTPs),general pollutants,such as organic pollutants,nitrogen,and phosphorus,can be removed with the traditional treatment technologies.However,it is difficult to remove antibiotics,antibiotic resistant bacteria(ARB),and antibiotic resistance genes(ARGs)from waste water.Hence,an efficient technology for the elimination of antibiotics and antibiotic resistance was urgently necessary.The main results are concluded as follows:(1)Taking three WWTPs with different treatment processes in Changchun as the target WWTPs,the distributions of antibiotics,ARB,and ARGs in each main treatment unit were investigated.In detail,6 classes(12 kinds)of antibiotics,which were frequently detected in the environment,were selected as the target antibiotics.The distribution of the residual antibiotics in each main treatment unit was analyzed using solid-phase extraction(SPE)and high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).Among the target antibiotics,the detection frequency of chloramphenicols(chloramphenicol and thiamphenicol)was the lowest.Besides,tetracyclines(tetracycline and oxytetracycline),β-lactam(ampicillin and amoxicillin),roxithromycin,and ciprofloxacin were detected in all sample units with the concentration ranging from41.13 to 638.27 ng/L,and the concentration in the effluent was still 41.63-488.95ng/L.Based on the detection results of antibiotics,the distribution and elimination of ARB(including ARBTCH and ARBAMP)were evaluated using the selective culture.The results showed that the concentration of ARB decreased with the processing of wastewater treatment.Nevertheless,the concentrations of ARBTCH and ARBAMP in the effluent were still 0-2.62 log CFU/m L and 0-2.86 log CFU/m L,respectively.Besides,the abundance of 50 target ARGs in the WWTPs was determined using high-throughput sequencing with 16S r RNA as the reference genes.The results showed that the abundance of some ARGs decreased with the treatment process.However,the abundance of the target ARGs was still 5-6 log copies/m L in the effluent.Collectively,an abundance of residual antibiotics,ARB,and ARGs existed in the WWTPs effluent,which confirmed that traditional wastewater treatment processes were ineffective to remove antibiotics and antibiotic resistance from aqueous media completely.(2)In this study,carbon nanotubes(CNTs)and agarose(AG)were used as the precursors and Ti mesh as the substrate,CNTs/AG/Ti electrode was prepared by the sol-gel method and characterized using scanning electron microscope(SEM),energy-dispersive X-ray spectroscopy(EDS),transmission electron microscopy(TEM),infrared radiation(IR),X-Ray diffraction(XRD),and Raman.The results showed that CNTs were dispersed inside or inset the AG membrane.The CNTs/AG/Ti electrode was constituted with the elements of C,O,and Ti.The functional groups changed slightly after the electrocatalytic reaction,which revealed that the CNTs/AG/Ti electrode has good stability.(3)Based on the detection results of antibiotics in the WWTPs,tetracycline(TCH)and ampicillin(AMP)were selected as the target antibiotics.The influence of different parameters on the electrocatalytic degradation was investigated and the optimal electrocatalytic conditions were achieved.In addition,the electrocatalytic degradation mechanisms and the toxicity in the reaction system were assessed.Under the optimal conditions(4 V,p H=7,5 wt%,and 10 mg/L),the electrocatalytic degradation efficiency for TCH reached up to 97.9%within 30 min.Besides,the degradation efficiency achieved 94.0%after 60 min treatment under the optimal conditions(8 V,p H=8,7 wt%,and 5 mg/L).The radical capture experiments showed that·O2~-played important roles in the electrocatalytic degradation of TCH and AMP.The electrocatalytic degradation pathways and mechanisms for TCH and AMP were explored by HPLC-MS/MS analysis.Based on the QSAR model and inhabitation for E.coli ATCC25922,the toxicity of the parent compounds(TCH and AMP)and corresponding intermediates were assessed.The results showed that intermediates with higher toxicity compared with the corresponding parent compounds were generated during the electrocatalytic degradation.Nevertheless,the toxicity of the electrocatalytic reaction system decreased with the prolonging of the electrocatalytic treatment.(4)The electrocatalytic inactivation capacity and mechanism were explored with ARBTCH and ARBAMP as the model ARB.Under the optimal conditions,the electrocatalytic inactivation efficiency achieved 7.82 log within 10 min and no AR E.coli was available after 30 min treatment.The wrinkles and sinking envelop were observed accompanying the treatment of electrocatalytic inactivation,indicating that the integrality of the cell membrane was destroyed.The concentration of extracellular K~+in the solution increased with the treatment,revealing that the permeability of the cell membrane changed and the internal cytoplasm component was leaked.The results of FDA/PI(fluorescein diacetate/propidium iodide)fluorescence staining showed that the number of living cells decreased and that of dead cells increased gradually with the electrocatalytic treatment.The internal reactive oxygen species(ROS)level was determined using DCFH-DA(2’,7’-dichlorodihydrofluorescein diacetate)as the fluorescence probe,which showed that the concentration of internal ROS increased with the electrocatalytic treatment.Combing with DNA extraction and q PCR(real-time quantitative polymerase chain reaction)analysis,the concentration of internal and total ARGs decreased obviously in the initial 10 min of electrocatalytic inactivation,and the external ARGs were electrocatalytic degraded rapidly.(5)The electrocatalytic degradation efficiency and mechanism were investigated using p BR322 as the model ARGs,which containing tetracycline-resistance genes(tet A)and ampicillin-resistance genes(bla TEM-1).When the initial concentration of p BR322 was 1.0 ng/μL and the applied potential was 3 V,the degradation efficiencies of tet A and bla TEM-1 in dd H2O within 240 min could achieve 7.45 and 8.47 log,respectively.In PBS,the degradation efficiencies of tet A and bla TEM-1 could reach up to 7.58 and 8.42 log after 30 min electrocatalytic treatment.No single bases were determined using HPLC in the electrocatalytic degradation of p BR322.The degradation efficiencies with long amplicon were faster than that of the short ones,and an abundance of short DNA fragments was generated in the process of electrocatalytic degradation.Besides,the degradation efficiency of bla TEM-1 was faster than that of tet A.In the electrocatalytic degradation of p BR322,there was no detection of SNP(single nucleotide polymorphism)or In Del(insertion-deletion)in the re-sequence analysis.Besides,the transformation ability of antibiotic resistance for tet A and bla TEM-1 was eliminated after electrocatalytic treatment.In the mixed electrocatalytic system(antibiotics,corresponding AR E.coli and ARGs),the target antibiotic and AR E.coli could be electrocatalytic removed completely within 240min,and the degradation efficiency of ARGs reached up to 5.61-5.98 log after 12 h electrocatalytic treatment.In summary,the concentration and distribution of the typical antibiotics and antibiotic resistance in the WWTPs were investigated.The electrocatalytic degradation system with high efficiency under mild conditions was established.The effects of different parameters on the degradation efficiency for antibiotics,ARB,and ARGs were evaluated,and the optimal conditions were achieved.Besides,the electrocatalytic degradation pathways and mechanisms were also assayed.This study provided a referential method and basic data for the elimination of antibiotics and antibiotic resistance from aqueous media to improve water environmental quality. |
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