Research On The Inactivation Mechanism Of Typical Pathogenic Microorganisms By Ultraviolet In Water

Contaminated drinking water contributes to the occurrence of waterborne diseases such as cholera,diarrhoea and typhoid fever.An increasing world population and global connectivity increase the risk of waterborne diseases,so effective water disinfection processes are essential to protect public health.Ultraviolet disinfection technology has been widely concerned in the field of drinking water disinfection because of its superior bactericidal performance and no disinfection by-products.In recent years,UV-LED light emitting diodes,222 nm excimer lamps and other new UV disinfection technologies with variable wavelength and harmless to human body have been developed rapidly.However,the inactivation effect of different UV light sources on bacteria,viruses and other typical pathogenic microorganisms in water is still not clear,and its disinfection mechanism needs to be further discussed.In this study,staphylococcus aureus,Escherichia coli and phage Phi6 were selected to represent gram-positive bacteria,gram-negative bacteria and coronavirus respectively.The inactivation effects of different ultraviolet light sources on bacteria and viruses were compared,and the inactivation mechanism of ultraviolet light on bacteria and viruses was revealed.(1)The inactivation rate of 222 nm excimeric lamps,LPUV,265 nm,275 nm,285 nm UV-LED to bacteria reached 99.99%within 15 m J/cm~2.Compared with bacteria,viruses have stronger tolerance to ultraviolet radiation,and the inactivation of viruses by different UV light sources varies greatly.Among them,222 nm excimer lamp can effectively inhibit viral infectivity and achieve 99.99%inactivation rate within 24.55 m J/cm~2.(2)The inactivation effect of different UV wavelengths on bacteria and viruses is as follows in descending order:Staphylococcus aureus:265nm>LPUV>275 nm>285 nm>222 nm>300 nm;Escherichia coli:265nm>222 nm>LPUV>275 nm>285 nm>300 nm;Phage Phi6:222 nm>265nm>LPUV>275 nm>285 nm>300 nm.Among them,265 nm UV-LED has the best inactivation effect on bacteria,222 nm excimer lamp has the best inactivation effect on virus,and 300 nm UV-LED has the worst inactivation effect on bacteria and virus.(3)Fluorescence quantitative PCR,scanning electron microscopy(SEM)and flow cytometry(FCM)detection showed that after 265 nm and 285 nm UV-LED irradiation,the concentration of bacterial target gene gradually decreased with the increase of UV dose,no ROS was generated in cells,the integrity of cell membrane was not damaged,and its permeability did not change.Therefore,265 nm and 285 nm UV-LED inactivate bacteria mainly by destroying cell DNA.(4)Through q PCR,SEM and FCM detection,it was found that after irradiation with 222 nm excimer lamp,the concentration of bacterial target gene was significantly reduced,a large number of ROS were generated in cells,and the cell membrane was rough and wrinkled with a lot of granular materials,and its permeability was significantly changed.Therefore,222 nm excimer lamps inactivate bacteria by irreversibly damaging bacterial DNA and producing ROS in cells to destroy the integrity of cell membrane structure and function.(5)The infectivity of the virus was lost mainly through the damage of the viral genomic RNA caused by ultraviolet radiation,but the lipid envelope structure of the virus was not damaged.The 222 nm excimer lamp had the greatest damage to the viral RNA.