The Enhanced Removal And Control Mechanism Of Antibiotics And Antibiotic Resistance Genes In Wastewater Treatment System

In recent decades,antibiotics,as antimicrobial agents,have been extensively used in human production and life,but the concentration of antibiotics in the environment has gradually increased owing to improper control.As the gathering places of various wastewater,WWTPs(wastewater treatment plants)are the main treatment sites for antibiotics.However,the removal of antibiotics is limited,which because the traditional wastewater treatment technologies in WWTPs are designed only for conventional pollutants such as nitrogen and phosphorus.Thus,the generation of ARB(antibiotic resistance bacteria)and ARGs(antibiotic resistance genes)are induced and promoted in WWTPs under the long-term antibiotic selection pressure.Moreover,WWTPs even provide a favorable environment for ARB reproduction and ARGs horizontal transfer owing to the high microbial population and rich nutritional conditions.As emerging contaminants,antibiotics and ARGs have posed potential threats to ecological security and human health.Therefore,aiming at the problem of low efficiency of antibiotic removal and serious antibiotic resistance pollution in WWTPs,this dissertation first constructed a nZVI enhanced anaerobic treatment system to explore the fate of ARGs during the improved degradation of antibiotics,and reduce antibiotic selection pressure and ARGs abundance in WWTPs.On this basis,the multifunctional electroactive ultrafiltration membrane systems were developed by combining membrane separation with electrochemical advanced oxidation technology to further deeply treat the low concentration antibiotic,ARB and ARGs in the wastewater effluent,to improve the removal efficiency of antibiotic in wastewater effluent and control the emission of ARGs into receiving water.Finally,the mechanism of ARB inactivation and ARGs degradation by electroactive ultrafiltration membrane through electrodisinfection were clarified,and the subsequent transfer ability of damaged ARGs was also evaluated,which reduces the risk of antibiotic resistance transmission.The enhanced removal of antibiotics and the effective control of antibiotic resistance pollution in wastewater treatment systems were systematically studied from three aspects,namely,process intensification,pipe-end treatment and risk control,to provide a theoretical basis and technical reference for emerging contaminant control,advanced wastewater treatment and regeneration and reuse.The main research contents and conclusions are as follows:1.This chapter explored the changes in system performance and the fate of ARGs during the nZVI-assisted anaerobic system enhanced the removal of antibiotics.The performance enhancement mechanism and ARGs transfer mechanism of the anaerobic system were analyzed by the microbial community structure and correlation analysis of ARGs.The results showed that as nZVI concentrations increased from 0 to 1 g/L,the CAP removal efficiency was appreciably improved from 46.5%to 99.2%,and the CH4 production was enhanced 20.3 times,while the abundance of ARGs in sludge was decreased significantly.According to microbial community analysis,the enhanced CAP removal resulted from the enrichment of dechlorination-related bacteria and other functional bacteria associated with refractory contaminants degradation.The improved CH4 production was ascribed to the increase in fermentative-related bacteria,homoacetogen,and methanogens.Additionally,the increased abundances of anaerobic functional genes further verified the mechanism of CH4 production.The correlation analysis between microbial community and ARGs showed that the attenuation of ARGs was attributed to the decrease of potential hosts of ARGs.This work provides an effective technology for the treatment of high-concentration antibiotic wastewater,which can effectively alleviate the discharge of antibiotics into the receiving water and reduce the propagation and transmission of ARGs in WWTPs.2.In this chapter,a multifunctional electroactive C/PVDF ultrafiltration membrane was prepared by combining membrane separation and electrochemical advanced oxidation technology to solve the problems of low-concentration antibiotic,ARB and ARGs in WWTP effluent.The degradation properties of SMX,ARB and ARGs were investigated under two electrofiltration modes:anode filtration and cathode filtration,and the degradation mechanism of the two electrofiltration modes was also elucidated.The antifouling and regeneration properties of electroactive C/PVDF ultrafiltration membranes were analyzed by several cycles of electrofiltration and backwashing experiments,and their repeatability and stability in the preparation and application process were also explored.These results showed that the electroactive C/PVDF membrane had good repeatability and excellent chemical stability.It could degrade the low concentration of SMX in effluent by anode filtration and cathode filtration,and the degradation mechanism was direct oxidation and indirect oxidation.In the anode filtration,the degradation efficiencies of SMX at+2 V and+4 V were 55.7%and 81.5%,respectively.Both electrofiltration processes exhibited significant ARB inactivation,and anode filtration was superior to cathode filtration.Moreover,the two electrofiltration processes could realize ARGs degradation(intracellular ARGs,iARGs;extracellular ARGs,eARGs),the degradation of iARGs located in the genome was more efficient than those located in the plasmid,and these degradation efficiencies at2 V were higher than+2 V.Nevertheless,the degradation efficiencies of eARGs were opposite,and were lower than those of iARGs.Compared with regular filtration,the antifouling ability of the electroactive C/PVDF membrane was improved by 18.0%at-2 V,15.9%at+2 V,and 30.4%at+4 V during wastewater effluent treatment.These results indicate that the electroactive ultrafiltration membrane has good application prospects in enhancing the removal of low concentration antibiotics and controlling the spread and diffusion of antibiotic resistance.3.Aiming at the problem that the removal efficiency of SMX by electroactive C/PVDF membranes in the actual application process needs to be enhanced,a series of organic and inorganic hybrid membranes in this previous chapter were prepared to enhance the electrochemical activity of electroactive C/PVDF membranes by using the excellent conductive property of conductive polymer(PANI)and inorganic nanomaterials(CNT),which were used to futher improve the removal of SMX,ARB and ARGs,thus reducing ecotoxicity and the antibiotic resistance transfer frequency in wastewater effluent,as well as alleviating membrane contamination.The results showed that compared with the pristine electroactive membrane,the PANI/CNT-EMs exhibited enhanced SMX degradation,the degradation efficiencies were more than 97.0%at a voltage of+2 V.And the inactivation ability of ARB and degradation efficiency of iARGs and eARGs were increased by 1-2 order of magnitude by PANI/CNT-EMs at a voltage of+2 V.Meanwhile,compared with pristine electroactive membrane,the anti fouling performance of PANI/CNT-EMs was improved 42.1%under an applied voltage of+2 V during treating wastewater effluent.In addition,the ecotoxicity of degradation products and the frequency of ARGs transfer were significantly reduced,proving that PANI/CNT-EMs was more conductive to reduce ecological risks and ARGs transfer risks.These results indicate that this novel PANI/CNT-EMs further enhances the antibiotic degradation,ARB inactivation and ARGs removal in wastewater effluent,which can more effectively reduce the ecotoxicity of antibiotic in wastewater effluent and the discharge of antibiotic resistance pollution.4.To further analyze the mechanism of ARB inactivation and ARGs degradation by the electroactive membrane,and assess the subsequent transfer ability of damaged ARGs,an electroactive polyaniline hybrid membrane(PANI-EM)was selected to investigate the inactivation and degradation effects of ARB and ARGs through two electrodisinfection methods under different salt concentrations(2,30,50 mM)and electrolytes(Na2SO4 and NaCl).The results showed that the electroactive PANI-EM could effectively inactivate ARB and degrade iARGs and eARGs,and the higher concentrations of Na2SO4 and NaCl contributed to more effective inactivation and degradation ability(50 mM>30 mM>2 mM).Compared with Na2SO4,the inactivation and degration effects were higher under the NaCl condition by PANI-EM.The ARB inactivation and ARGs degradation were attributed to the cell membrane destruction and the DNA chain breakage.It was also found that the degradation efficiency of ARGs was related to the length of the amplicon and the category of ARGs.Furthermore,the conjugative transfer frequencies of ARGs were significantly reduced under different electrodisinfection methods.Compared with Na2SO4,the conjugative transfer frequency under NaCl conditions was lower,indicating that the inhibitory effect of electrochlorine disinfection on conjugative transfer was better than that of direct oxidation.These results indicate that electrochlorine disinfection can reduce the abundance of ARB and ARGs in wastewater effluent and prevent the spread of ARGs in the receiving water to the greatest extent,which plays an important role in reducing the risk of transmission of antibiotic resistance.