Study On The Generation Rules And Removal Technique Of Disinfection By-products In Typical Water Treatment Process

Chlorine disinfection is the main disinfection method for the water purification process in China.During the chlorination,the reaction between natural organic matter in water and chlorine will form disinfection by-products.These disinfection by-products are often toxic and harmful to human health.With the background of Suzhou water project which topic is“Technology Integration and Comprehensive Application of Drinking Water Safety Techniques in Suzhou City”,this paper analyzed the generation law of disinfection by-products in the typical water plant of Taihu Lake Basin through on-site monitoring,from 2018 to 2019.The removal of organic matter and disinfection by-product precursors during water treatment process were analyzed.Furthermore,the disinfection by-product removal technique was explored through experiments.The research work and main conclusions:?1?The formation law of disinfection by-products in typical water plants was studied.The total amount and seasonal variation of disinfection by-products of THMs,HAAs and HANs,and bromate in the water plant were analyzed during the year.The results showed that in 2018-2019,the average pollution levels of the four disinfection by-products,inculding THMs,HAAs,HANs and bromate in the chlorine disinfected factory water,did not exceed the national limit,and all reached the drinking water sanitation standards.?2?The removal efficiency of organic matter and disinfection by-product precursors by typical water treatment process was studied.Taking pre-ozone—coagulation sedimentation—sand filtration—ozone activated carbon—chlorination disinfection process as the research object,the removal efficiency of organic matter(UV₂₅₄,COD_Mn,DOC)and disinfection by-product precursors?expressed in terms of generated potential,THMFP?HAAFP?HANFP?were analyzed.The results showed that the removal efficiency of UV₂₅₄,COD_Mn,DOC in the coagulation sedimentation and ozone activated carbon stage was obvious.The average removal rate in the coagulation and sedimentation stage reached 23.3%?22.1%?and 17.6%,respectively.The average removal rate in the ozone activated carbon stage was 36.6%?19.4%?13.3%.The three disinfection by-product precursors of THMs,HAAs and HANs were most effective in the ozone-activated carbon phase.The average removal rate of THMFP in the ozone-activated carbon phase was 33.8%;the removal effect of HAAFP was greatly increased compared with THMFP,the average removal rate was 39.8%;the average removal rate of HANFP was 29.3%.The hydrophilicity and small molecule organic matter cannot be effectively removed in the conventional treatment stage,and the removal effect of the disinfection by-product precursor was not good,but the removal of organic matter in the water was advantageous;The advanced treatment stage?ozone-activated carbon?had better effects on removing organic matter and disinfection by-product precursors,and can effectively reduce the effluent disinfection by-products before entering the pipe network,which was beneficial to the effluent biological stability and water quality safety protection.?3?The degradation efficiency of chloroacetonitrile?CANs?by UV/Persulfate?UV/PS?advanced oxidation system was studied.Taking two kinds of chloroacetonitriles?dichloroacetonitrile and trichloroacetonitrile?which were ubiquitous in drinking water and highly toxic as earch object,the effects of PMS concentration,Cl^-concentration,initial pH and water matrix on the degradation of CANs in UV/PS system and reaction mechanism were investigated troungh single factor control experiments.Research indicated:UV/PS advanced oxidation system can effectively degrade CANs,and its degradation process accorded with pseudo first-order kinetic model?R²?0.91?,SO₄·-and·OH were active free radicals involved in the reaction,of which SO₄·-dominated;the degradation efficiency increased with the initial concentration of PS,and the first-order reaction rate constant k increased with the PS dosage;compared with neutral conditions?pH=7?and strong acid conditions?pH=4?,partial acidity?pH=6?was more favorable for the degradation of CANs;the effect of chloride ion?Cl^-?on the degradation efficiency in the system was negligible;the temperature had little effect on the degradation of CANs in the system,but the increase of TCAN was greater than that of DCAN;the heavy carbonate?HCO₃^-?and natural organic matter?HA?were the determinants of the system's degradation ability in actual water bodies.?4?Technical feasibility of the chloroacetonitrile?CANs?removal by ultraviolet/persulfate?UV/PS?advanced oxidation system was analyzed.The removal efficiency of CANs by UV/PS advanced oxidation system in actual water body and ultrapure water were studied respectively.The results showed that the degradation rate of CANs in ultrapure water was significantly higher than that of actual water bodies.So,in practical applications,to increase degradation rate of CANs,the relevant measures such as properly pretreatment or advanced treatment and appropriately increasing of oxidant PS were necessary.