Experimental Study On Inactivation Of Escherichia Coli In Rural Sewage Tail Water By UV/PMS

As an important basic resource,rural water is related to the problems of agriculture,rural areas and farmers and the realization of the strategic goal of rural revitalization Compared with urban areas,sewage treatment facilities in rural areas are weak,and the collection rate is low.Sewage contains a large number of pollutants and pathogenic microorganisms,which will not only destroy the rural living environment,but also bring great threat to human health.It is difficult for some pathogenic microorganisms to be completely removed after conventional wastewater treatment process.Therefore,it is of great significance to seek a new disinfection technology with high efficiency and environmental protection for the safety of rural living environment and recycling of rural sewage.In this study,the UV activated persulfate sterilization method was used to investigate the bactericidal efficacy of the UV/PMS system on rural sewage,the reaction mechanism of UV/PMS system in killing Escherichia coli was discussed,and the feasibility of practical application was investigated,which provided theoretical reference and application basis for the development of disinfection technology of rural sewage tail water.The main research content is as follows:The bactericidal efficacy of PMS,UV,and UV/PMS methods were compared and analyzed through experiments.The experiment showed that the UV/PMS system had the best bactericidal effect,reaching 5.316 logarithmic orders.The effects of various influencing factors（pH,temperature,oxidant dosage,UV irradiation intensity,coexisting ions,and humic acids）on the bactericidal efficacy of the UV/PMS system were investigated.The results showed that the increase of PMS concentration（0.1～2.0m M）,UV irradiation intensity（0.23～0.56m W/cm²）and temperature（10～40℃）would improve the logarithmic removal rate of Escherichia coli;The logarithmic removal rate of Escherichia coli would decrease with the increase of initial pH（3.0～11.0）;Inorganic anions and humic acids could inhibit the sterilization of UV/PMS systems.Through the contrast test of photoreactivation,it was found that the maximum photoreactivation rate of Escherichia coli after UV/PMS sterilization was only 0.05%,which was far lower than the photoreactivation rate after UV treatment.Within the experimental range,The orthogonal experiments showed that the primary and secondary order of factors affecting the sterilization effect was:irradiation intensity>temperature>PMS concentration>pH.and the optimal experimental condition was determined as PMS dosage=0.5m M,temperature=20℃,pH=7.0,and UV irradiation intensity=0.23m W/cm².According to the free radical quenching test,·SO₄^-plays a major sterilization role in the UV/PMS system,with a contribution rate of free radicals greater than·OH.Through scanning electron microscopy,extracellular protein detection,and SOD enzyme activity detection,it was found that bacteria undergo severe deformation after inactivation,with an increase in extracellular protein content and a first increase followed by a decrease in SOD enzyme activity which proved that highly reactive oxygen species could damage the cell wall of bacteria,release intracellular organic compounds,and then affect the expression of intracellular enzyme activity,leading to bacterial inactivation.The bactericidal feasibility,stability and economy of UV/PMS system in practical application were investigated.The results showed that the presence of COD（0-60mg/L）and total nitrogen（0-20mg/L）would inhibit the bactericidal efficacy of the UV/PMS system,and the bactericidal efficacy decreased by 19.9%and 13.5%with the increase of concentration,The effect of total phosphorus（0-8mg/L）on the bactericidal efficacy of the UV/PMS system was weak,and although it consumed some active free radicals in the system,it still met the emission standard of level A.While meeting the sterilization efficiency,it also has a certain degree of advanced treatment ability,which can optimize the effluent quality,the removal efficiency of COD,total nitrogen,and ammonia nitrogen reached 35.8%,57.4%,and 34.6%,respectively,And it has certain advantages in terms of comprehensive cost and has good application prospects in engineering applications.