Health Risk Assessment Of Sodium Hypochlorite Drinking Water Disinfection And Disinfection By-products

[Objective]1.Select the sodium hypochlorite disinfectant produced by the sodium hypochlorite generator produced by a domestic enterprise,and observe that different effective chlorine concentrations and disinfection time reduce the amount of surviving E.coli bacteria to 0 CFU/100mL,so that the water sample reaches the effective dose of the national drinking water standard.At the same time,study the influence of bacteria concentration,water temperature,organic matter and pH value on the sterilization effect of sodium hypochlorite,and provide a reference for the scientific use of the disinfectant generated by the sodium hypochlorite generator as a disinfection product for drinking water.2.Research and analyze 6 water plants with the same water source and water purification process at the same time.After the original liquid chlorine disinfection is converted to the sodium hypochlorite disinfection method,the changes in the water quality of the factory water are observed,in order to establish and optimize the drinking water sanitation monitoring system of the sodium hypochlorite disinfection method.The production process provides basic data.3.Understand the distribution levels of trihalomethanes and haloacetic acids in the factory water of the six water plants using the same water source from 2016 to 2020,and evaluate the health risks of the six water plants' chlorination disinfection by-products,and compare different waters Plants,different chlorination disinfection methods,dry and high water periods,and gender have carcinogenic and non-carcinogenic risks of oral exposure to trihalomethanes and haloacetic acids in factory water,providing technical support for exploring scientific drinking water disinfection methods and ensuring drinking water safety.[Methods]1.The study adopts quantitative test methods,passes the neutralizer identification test,bactericidal effect test,and bactericidal effect influencing factor test under laboratory conditions.Escherichia coli is used as the indicator microorganism,and the microporous membrane suction method is used to count the viable bacteria.Observe the sterilization effect of different disinfectant concentrations on Escherichia coli in the water and the effect of bacterial liquid concentration,water temperature,organic matter concentration and pH value on the sterilization effect.2.Collect 22 samples of factory water before and after the change from liquid chlorine to sodium hypochlorite disinfection from 6 water plants in Jiangsu Province from 2018 to 2019,describe the basic situation of the water plants before and after the disinfection method,and measure the effective chlorine content in the factory water for one month.,Comparative analysis of the effects of two disinfectants on the sensory,chemistry,microorganisms and 13 disinfection by-product indicators of factory water,and comparative analysis of the influence of different free residual chlorine concentrations in factory water on the 13 disinfection by-product indicators.3.Select 6 municipal water plants in Jiangsu Province that use the same water source.From 2016 to 2020,a total of 49 samples of factory water were collected during the dry season(January to March)and the wet season(July to September),and the factory water was tested.Concentration levels of trihalomethanes and haloacetic acids,using the health risk assessment model recommended by USEPA to assess the lifetime carcinogenic and non-carcinogenic risks of trihalomethanes and haloacetic acids in the factory water through oral exposure.[Results]1.Under the test temperature of 20?±2?,the sodium hypochlorite disinfectant with an effective chlorine concentration of 0.8 mg/L can completely kill E.coli in the water for 6 minutes;as the effective chlorine concentration increases,the action time prolongs,disinfection The effect gradually improved(P<0.01).Under the condition of an effective chlorine concentration of 0.2 mg/L,with the decrease of the concentration of the bacterial suspension and the extension of the action time,the disinfection effect of sodium hypochlorite gradually increases(P<0.01);at a water temperature of 5?±2? and an organic matter of 10??Sodium hypochlorite disinfectant cannot completely kill E.coli in the water at 15 degrees;the pH range of 6.5 to 8.5 has no effect on the sterilization effect.2.The sensory,chemical,microbiological,and 13 disinfection by-product indicators of the two disinfection methods in the factory water all meet the national drinking water standards,and the pass rate is 100%;after 6 water plants converted to sodium hypochlorite disinfection in 2019,13 The concentrations of trihalomethane,trichloromethane,dichloromonobromomethane,chloroacetaldehyde,dichloromethane,tribromomethane and monochlorodibromomethane in the disinfection by-products were all lower than those of liquid chlorine disinfection methods,and the difference was statistically significant(P<0.05);when the free residual chlorine concentration level of the factory water is<1 mg/L,the 13 kinds of disinfection by-product indicators include trihalomethane,trichloromethane,dichloromonobromomethane,trichloroacetaldehyde,tribromomethane and monochlorodichloride The concentration of methyl bromide was lower than that when the free residual chlorine concentration level was greater than or equal to 1 mg/L,and the difference was statistically significant(P<0.05);the sodium hypochlorite disinfectant with 10%effective chlorine content was measured continuously for one month,stored at 32? The available chlorine content is 67.40%of the original content,and the available chlorine content is 89.51%of the original content under the storage condition of 4?.3.The detection values of trihalomethane and haloacetic acid,which are the by-products of chlorinated disinfection in factory water,are lower than the limit of my country's domestic drinking water sanitary standard,and the pass rate is 100%.There is 1 water sample(2.04%)of trichloromethane that exceeds the standard.The risk is level three,three water samples(6.12%)of dichloromonobromomethane have a third-level risk of exceeding the standard,and one water sample(2.04%)of dichlorodibromomethane is a third-level risk of exceeding the standard.The carcinogenic risk of the chlorinated disinfection by-products of the 6 water plants is higher than the EPA recommended carcinogenic risk(<10-6).The cumulative carcinogenic risk(R)of the by-products of the chlorinated disinfection of the factory water is 2.521×10-5.Among them,the carcinogenic risk of men is 2.295×10-5,and the carcinogenic risk of women is 2.748×10-5.6 kinds of chlorinated disinfection by-products have potential carcinogenic risks;the non-carcinogenic risk hazard index(HI)is 0.081,which is acceptable in humans Level.The six water plants chlorinated disinfection by-products all have potential carcinogenic risks.The F water plant has the highest carcinogenic risk(3.783×10-5),followed by the E water plant(3.200×10-5)and the A water plant(3.141×10-5),D water plant(3.037×10-5),C water plant(3.002×10-5),B water plant the lowest(2.704×10-5);the non-carcinogenic risks are all at the human acceptable level(HI<1),F water plant(0.159)is the highest,followed by A water plant(0.151),D water plant(0.149),E water plant(0.149),C water plant(0.147),B water plant(0.142).The carcinogenic risk of by-products of sodium hypochlorite chlorination disinfection is lower than that of liquid chlorine disinfection(P<0.05),and the risk of carcinogenesis is higher in women than in men(P<0.05);the non-carcinogenic risk is lower than that of liquid chlorine disinfection(P<0.05),and the risk of cancer is higher in women Male(P<0.05).The carcinogenic risk of chlorinated disinfection by-products in the dry period is lower than that of the disinfection in the flood period(P<0.05),and the risk of cancer in women is higher than that in men(P<0.05);the non-carcinogenic risk is lower than the disinfection in the flood period(P<0.05),and the risk of cancer in women is Higher than men(P<0.05).[Conclusions]1.The sodium hypochlorite disinfectant produced by the sodium hypochlorite generator has a good killing effect on E.coli in the water.The use of a concentration of less than 1 mg/L can make the microbial indicators in the water reach the national standard in a short time,and kill E.coli in the water.The inactivation effect is greatly related to the effective chlorine concentration of sodium hypochlorite,the disinfection time,the concentration of the bacterial solution,the temperature of the water body,the concentration of organic matter and the pH value.The concentration of microorganisms in the water,the temperature of the water,and the concentration of organic matter in the water have an impact on the disinfection effect.Care should be taken when using it.When the microbial pollution is serious,the water temperature is low,and the organic matter pollution is serious,the effective chlorine concentration should be increased or the disinfection time should be extended to ensure the disinfection effect.2.In this study,six municipal drinking water plants using the same water source and water purification process were converted from liquid chlorine to sodium hypochlorite for disinfection.The sensory,chemical,microbiological,and 13 disinfection by-product indicators in the factory water fully met the drinking water quality standards of my country.The difference in indicators of some disinfection by-products is affected by the type of disinfectant and the free residual chlorine concentration in the factory water.After sodium hypochlorite is used for disinfection,the concentration of some disinfection by-products in the factory water is lower than that of liquid chlorine.The product concentration is lower than the high concentration of free residual chlorine.The effective chlorine content of sodium hypochlorite disinfectant is affected by the storage temperature and time.In order to ensure the disinfection effect,it should be stored as low as possible or used as soon as possible.3.From 2016 to 2020,from 2016 to 2020,a total of 49 water samples from 6 chlorinated disinfection water plants in Jiangsu Province that used the same water source were collected.The detected values of trihalomethane and haloacetic acid in the disinfection by-products met the sanitary standards for drinking water.Limit,the detection value of chlorinated disinfection by-products in some water samples exceeds the risk of level three.The carcinogenic risk of the chlorinated disinfection by-products of the six water plants is higher than the negligible carcinogenic risk recommended by the EPA.The six chlorinated disinfection by-products have potential carcinogenic risks,and the non-carcinogenic risks are acceptable to humans.The byproducts of chlorinated disinfection in the F water plant have the highest carcinogenic risk and non-carcinogenic risk to adults.The carcinogenic risk and non-carcinogenic risk of liquid chlorine disinfection are higher than those of sodium hypochlorite disinfection.The carcinogenic risk and non-carcinogenic risk of water in the wet period are higher than those in the dry period.Men are carcinogenic Both the risk and the non-carcinogenic risk are higher than women.The chlorination disinfection by-products of the 6 water plants have potential carcinogenic risks.It is recommended to strengthen water environmental protection,adopt appropriate disinfection methods,and optimize the production process of the water plants.