Study On Disinfection Effect And Influencing Factors Of UV Disinfection And Sodium Hypochlorite Disinfection

Disinfection is important processing procedure to inactivate pathogens in domesticsewage and industrial wastewater, which can be generally divided into two categories:physical disinfection and chemical disinfection. Chlorination, as the most widely usedchemical disinfection method, has the following features:(1) lower costs per unitamount of water for large capacity of treated water;(2) a certain amount of residualchlorine can be sustained after chlorination to perform a continuous sterilization ability;(3) Chlorination as a long history and rich experience, is a relatively mature disinfectionmethods. UV disinfection is a physical disinfection method and has been widely used inmany wastewater plants in China. Advantages of UV disinfection are as following: noneed to add any chemicals, and no change for the molecular structure of water, it alsohave a wide range of sterilization with relatively short time, thus has a good sterilizationeffect.Escherichia coli (E.coli) was selected as bacteria tracer to evaluate the disinfectionefficiency by UV and chlorination(sodium hypochlorite as a chemical oxidationdisinfection, and UV as alight specific injury disinfection). As environmental watercomposition is complicated and has many influencing factors, several influencingfactors which may affect disinfection efficiency were selected in this study to analyzethe extent of environmental impact on the specific removal efficiency of disinfection,and thorough research on it was also conducted.Disinfection efficiency of UV and sodium hypochlorite method to E.coli isrepresented by logarithmic inactivation rate. Real-time fluorescent quantitative PCRwere conducted to judge the extent of bacterial inactivation. The influences of theturbidity, Fe3+concentration and organic matter on UV disinfection, as well as pH, ammonia nitrogen concentration on sodium hypochlorite disinfection were alsoinvestigated. The results indicated that: both UV disinfection and sodium hypochloritedisinfection showed good inactivation effect for E.coli. The inactivation rate of4.55-lgcould be achieved with UV dose of15mJ/cm2. E.coli were completely inactivated afterexposed to sodium hypochlorite at2.5mg/L for30minutes. qPCR results showed thatthe disinfection degradation rate of bacterial nucleic acid was lower than the rate ofbacterial inactivation. The nucleic acid degradation rate of3.0-lg could be achieved withultraviolet radiation being400mJ/cm2, and bacteria of nucleic acids were completelydegraded under conditions of sodium hypochlorite being5mg/L. The inactivation rateof UV disinfection might decline with increasing of the turbidity, Fe3+concentration ororganic content; At different doses of UV inactivation, E.coli was presented differentlevels of resurrection after exposing in fluorescent light for four hours. The inactivationrate of sodium hypochlorite could decline as pH or ammonia nitrogen concentrationincreased, and influent inactivation of E.coli.