Study On Ultraviolet Disinfection For Drinking Water Based On Bacterial Viability And Culturability Assessment

With the development of microbiology,the concepts of bacterial culturability and viability are gradually uncoupled.Ultraviolet disinfection can effectively reduce bacterial culturability by causing DNA damage,but it is generally considered that its direct impact on bacterial viability is limited.In order to evaluate the ultraviolet disinfection technology more comprehensively,this study used Escherichia coli and Staphylococcus aureus as representative strains of Gram-positive bacteria and Gram-negative bacteria respectively.Based on culturability and viability,the influence of ultraviolet radiation on bacteria was studied.An experimental technology system was established to ensure the quality of both the viability experiment and the ultraviolet radiation experiment,and a method to measure the change of the viability index was designed.In order to accurately reflect the effect of ultraviolet disinfection,ATP was selected as an index to evaluate the effect of ultraviolet disinfection on bacterial viability.Based on this choice,a model of the effect of ultraviolet radiation on bacterial viability was constructed,and the mechanism of ultraviolet disinfection was revealed more comprehensively.The results show that ultraviolet radiation can effectively reduce the culturability of bacteria within 40 m J/cm²,but bacteria can regain culturability to a certain extent by using the mechanisms of dark and photo repair.Quantitative polymerase chain reaction?q PCR?can detect DNA damage caused by ultraviolet radiation,but long amplified fragments are needed to detect DNA damage effectively;dark repair of bacteria is relatively inefficient for DNA damage repair,while photo repair can reduce DNA damage effectively.Ultraviolet radiation can cause non-specific damage to RNA;by measuring the RNA content of genes corresponding to bacterial SOS response system and programmed cell death system,the initiation of bacterial repair system and decay system can be detected;bacteria will activate SOS response system to a greater extent after exposure to ultraviolet radiation,but the difference of initiation of programmed cell death system between bacteria exposed to UV and those not was not observed.ATP is suitable for evaluating the bacterial viability of ultraviolet disinfection.The ATP degradation rate of the bacteria exposed by ultraviolet is higher than that of the bacteria not exposed.This accelerated degradation conforms to the exponential decrease in the form of e^{-k T},and the degradation rate coefficient is proportional to the ultraviolet dose.Compared with low-pressure ultraviolet,medium-voltage ultraviolet radiation can accelerate the decline of bacterial viability more efficient,and the acceleration effect starts to saturate after the dose reaches 40 m J/cm².In this study,a new mechanism of ultraviolet disinfection based on viability was revealed:after the bacteria was exposed to UV,in addition to the traditional disinfection mechanism where they will lose culturability and decay at a natural rate due to the DNA damage,they will also initiate the SOS response system,leading to accelerated declince of bacterial viability and relevant indicator.And if their protein is damaged besides DNA damage,the ability of bacteria to repair damage for survival will be further reduced.