Transformation Of Endocrine Disrupting Chemicals(EDCs)by Chloramines In Water Distribution System

In recent years,with the rapid development of the industry and the continuously raise of life level,the pollution of aquatic environment has been increasingly highlighted and people pay more attention to the safety of drinking water.Meanwhile,more and more endocrine disrupting chemicals(EDCs)were detected in water environment with the development of detection technology.The ubiquitous presence of EDCs in the aquatic environment has been confirmed to cause estrogenic effects.In addition to this,chloramination is a common disinfection used in drinking water,but relatively few studies have been carried out to detect the degradation and transformation of EDCs by chloramination in water distribution system.17β-estradiol(E2),estriol(E3)and bisphenol A(BPA)were selected as target compounds in this study and pilot-scale water distribution system in Yuquan campus of Zhejiang University was choosed as experiment equipment.The degradation,transformation products and estrogenic effects of EDCs by chloramines in pilot-scale water distribution system(WDS)were investigated in this study.The blank experiments of chloramines degradation were carried out to to conform the chlorine to nitrogen ratio(Cl/N)and chloramines concentration used in EDCs degradation experiments.When the Cl/N ratio was between 1 and 14,the formation of free chlorine,monochloramine and total chlorine in different water qualitity was deionized water>bulk water>ductile iron pipe.However,the formation of dichloramine in ductile iron pipe was much higher than that in deionized water.At Cl/N ratio of 10,the percentage of dichloramine was more than 90%of the total chlorine.When the Cl/N ratio changed from 3 to 6,the degradation tendency of virous form of chloramines in ductile iron pipe were the same.The rate constant of monochloramine under different Cl/N ratios follows:6:1>3:1>4:1>5:1.Under different Cl/N ratio,dichloramine increased in the initial hours and then decreased with the increasing time,and this phenomenon has little correlation with Cl/N ratio.When the degradation experiments were taken out in different pipes,the degradation of monochloramine was stainless steel pipe>PE pipe>ductile iron pipe.The concentration of dichloramine increased in the initial hours,and the increased tendency followed the order:stainless steel pipe>PE pipe>ductile iron pipe.The degradation experiments of EDCs were investigated in deionized water and pilot-scale water distribution system.Under different Cl/N ratio,the degradation of EDCs in pilot-scale water distribution has great difference with that in deionized water.When the experiments were carried out 9 h,at Cl/N ratio of 3 or 4,less than 30%of EDCs was removed in deionized water,while more than 70%of EDCs was removed in pilot-scale water distribution system.The main reason for this was the different percentage of NH2Cl and NHCI2 in deionized water and pilot-scale water distribution system.In addition to this,the increase of initial total chloramines concentraton,temperature,pH and velocity can also accelerate the degradation rate of EDCs.When the concentration of briomide iron changed from 0 μg/L to 80 μg/L,it has little influence on EDCs degradation.The overall effect of the pipe material occurs as a result of pipe scale,biofilm,pH,and chloramines concentration.The degradation rate of EDCs in three pipes was ductile iron pipe>PE pipe>stainless steel pipe.The experiments in deionized water,tap water and pilot-scale water distribution were taken out to investigrate the influence of natural organic matter in tap water and pipe wall.The results shown that natural organic matter in tap water and pipe wall themselves have no influence on EDCs degradation.However,when chloramines was added in the system,natural organic matter in tap water and pipe wall would have negative influence on EDCs degradation.The intermediates of EDCs chloramination were detected by gas chromatography-mass spectrometry(GC-MS).Ten specific degradation products of E2 produced by chloramination were identified,and one nitrogenous disinfection byproduct was detected for the first time.The reaction of substitution and elimination and hydrogenation were the main reaction in E2 chloramination,and these reaction occurred on benzene ring,C9 and C17.Nine specific degradation products of E3 produced by chloramination were identified.E2 and 2-chloro-E3 were two main byproducts,indicates that electrophilic substitution reaction was the main reaction in E3 chloramination.Twelve specific degradation products of BPA produced by chloramination were identified,with 2-chloro-BPA as the main byproduct.One nitrogenous byproduct produced by BPA chloramination was detected for the first time.The main reaction occurred during BPA chloramination was electrophilic substitution reaction on ortho-positions of phenolic hydroxyl.No byproducts were detected due to the splitting of benzene ring.The estrogenic activity of the solution during EDCs chloramination were investigated.The results shown that the estrogenic activity of the solution has larger fluctuation in the initial hours.In the early period of the degradation experiment,the estrogenic activity of the solution were higher than that in blank experiment,which means the decrease of EDCs concentration does not means the the decrease of estrogenic activity of the solution,and the estrogenic activity of the intermediates maybe higher than the estrogenic activity of parent molecule.Therefore,the assessment of estrogenic activity during EDCs degradation progress should confirm disinfection time.When the contaminants were removed by disinfection,necessary measure should be taken to reduce the formation of intermediates.