| Global pollution of microplastics（MPs,particle size<5mm）has attracted widespread attention.Despite the high removal rate of MPs by wastewater plants,a large amount of MPs still enter the natural environment with the effluent of wastewater plants,making wastewater plants one of the important pathways for MPs to enter the natural environment.MPs may have complex interactions when they are coexisted with antibiotics and antibiotic resistance genes（ARGs）,which are widely present in wastewater.Ultraviolet（UV）disinfection,one of the most commonly used wastewater disinfection technologies,is widely used to kill antibiotic-resistant bacteria（ARBs）and destroys ARGs in wastewater,which is essential to inhibit the spread of ARGs in the environment.In addition,UV disinfection accelerates the photodegradation of antibiotics,which is important for reducing antibiotic residues in the environment and maintaining ecological balance.However,photo-oxidation by UV radiation can change the surface characteristics of MPs,which in turn potentially affects their interaction with antibiotics and ARGs,interfering with the removal of antibiotics and ARGs and leading to more serious environmental risks.In order to clarify the effect of MPs on the removal and fate of antibiotics and ARGs during UV disinfection of wastewater,this thesis focuses on the complex contamination characteristics and interactions of MPs with antibiotics and ARGs during UV disinfection of wastewater,in order to investigate the effect and mechanisms of MPs and the released organic matter（MP-DOM）on the degradation process of antibiotics during UV disinfection of wastewater and to reveal the effect of MPs on the microbial composition and fugacity characteristics of ARGs and thehorizontal gene transfer behavior of ARGs during UV disinfection.The main results are as follows:（1）The effects of three common MPs,polystyrene（PS）,polypropylene（PP）and polyethylene terephthalate（PET）,and the derived MP-DOM on the photodegradation of sulfadimethylpyrimidine（SMT）were investigated by simulating UV disinfection process of wastewater.The results showed that the presence of the three MPs significantly inhibited the photodegradation of SMT,reducing the degradation rate by more than 50%.MP-DOM significantly promoted the photodegradation process of SMT,increasing the degradation rate by more than 20%.Mechanism analysis showed that the photodegradation of SMT by MP-DOM was mainly caused by the shading effect and photosensitization effect.Among them,the shading effect inhibited the photodegradation of SMT,while the photosensitization effect could generate a large amount of reactive oxygen species（ROS）such as hydroxyl radicals（·OH）and singlet oxygen（1O2）,which promoted the photodegradation of SMT.The role of MP-DOM was related to its type and concentration,and there are differences in the role of MP-DOM with different characteristics.（2）The effects of PS on the distribution characteristics and removal of microbial communities and ARGs in wastewater were investigated by simulating the wastewater UV disinfection process.The results showed that PS interfered with the removal of specific ARGs such as OXA-182 and Erm H during UV disinfection,which may be related to the characteristics of ARBs.PS changed the composition of the microbial community,for example,the content of microorganisms such as Deinococcus-Thermus and Bacteroidetes phylum increased from 21%and 0.4%to 24%and 1.9%,while the content of Actinobacteria phylum decreased from 1.9%to less than 0.5%.Also,the gene expression was altered in the effluent,particularly that the functions related to the processing and metabolism of genetic information were affected.PS also enriched ARBs in the effluent by providing colonization sites,thereby inhibiting the UV killing effect.（3）The effect of different MPs on the horizontal gene transfer of ARGs between cells during simulated UV disinfection was investigated.E.coli DH5a was selected as the donor bacteria（referred to as donor bacteria）and E.coli ETEC as the recipient bacteria（referred to as recipient bacteria）.The conventional material PS and the biodegradable material polylactic acid（PLA）were used as representatives of MPs to illustrate the potential effects of different characterized plastics on the horizontal gene transfer of ARGs between cells.The results showed that the splice transfer frequency increased from 4.9×10-7 to more than 1.8×10-6after 15 min of UV irradiation in the presence of MPs,and the PS concentration reached 6.4×10-4 at 20 mg/L.The promotion of horizontal gene transfer by MPs as well as MP-DOM was related to the generation of ROS,which altered the permeability of the cell membrane.In addiiton,PS can also induce the intracellular production to exacerbate horizontal gene transfer by providing an additional carbon source to promote bacterial growth.In summary,the presence of MPs increases turbidity,generates DOM,forms a large number of ROS,interferes with the removal of antibiotics during UV disinfection of wastewater,reduces the removal efficiency of ARGs and promotes the occurrence of horizontal gene transfer,which increases the environmental risk. |
