Study On Transformation Mechanism Of Estradiol In Seawater Disinfection And Control Of Disinfection By-product

Residues of environmental estrogen(EEs)not only cause water pollution,but also prevent effluent from reacting with disinfectants to form EEs-based disinfection by-products(DBPs)during chlorination of water bodies,resulting in secondary pollution.The study of EEs as a precursor of Cl-DBPs in drinking water has been reported,but for marine aquaculture water which containing Br-,EEs will produce more toxic Br-DBPs.This research priority will be mainly focused on the kinetics,pathways and the finalproducts especially the Br-DBPs of the reaction between chlorinecontaining disinfectant and E2 in the marine aquaculture water.Otherwise,The QSAR model analysis revealed the biotoxicity of halogenated DBPs with EEs as precursors.The UV-activated persulfate(UV/PS)was used to degrade E2 to control the formation of DBPs.(1)The degradation and transformation products of E2 in sodium hypochlorite(NaCIO)disinfection processes of different water samples were investigated.The reaction kinetics research showed that the degradation rates of E2 were considerably dependent on the initial pH value and the types of watersamples.In fresh water,synthetic marine aquaculture water and seawater,the reaction rate constant was 0.133 min-1,2.067 min-1 and 2.592 min-1,respectively.The reasons for the above phenomena may be due to the different concentrations of bromide ions(Br)in these three water samples which could promote the reaction between NaCIO and E2.Furthermore,Br-could also cause the formation of brominated DBPs(Br-DBPs).The main DBPs,reaction centers and conceivable reaction pathways were explored.Seven halogenated DBPs have been observed including three chlorinated DBPs(Cl-DBPs)and four Br-DBPs.The active sites of E2 were found to be the pentabasic cyclic ring and the ortho position of the phenol moiety as well as C9-C10 position.(2)The QSAR model constructed by using logkow values proves that when the compounds have similar structures in Br-DBPs,the biotoxicity of the compounds increases with the increase of the number of halogen atoms.Using the log BCF value of the compound as a predictor,the biotoxicity of Br-DBPs in the E2 halogenated DBPs obtained from the EPI-suite simulation assay was greater than that of the chlorinated analog.(3)The pH of the reaction system will affect the rate of degradation of E2 by UV/PS.Under neutral conditions,the degradation rate is the fastest.Over-alkali or per-acid will inhibit the reaction;while anions such as Br-and Cl-in water will promote UV/PS degrades the reaction of E2,HCO3-has an inhibitory effect on the reaction,SO42-and cation(Na+,Mg2+,K+)have no effect on the degradation rate;the same intermediate products are detected in brackish water and fresh water,and UV/PS degradation of E2 is also a mineralization process The mineralization rate can reach 90.97%at 8h;in the UV/PS system,E2 is mainly degraded by hydroxylation,deoxygenation and hydrogenation.The E2 reaction site is mainly located in benzene.On the ring,there are mainly carbonylation on the five-membered ring,and the bond cleavage between CIO and C5 leads to the de-benzene ring and the carboxylation of the C2 and C3 sites;in the presence of halogen ions,UV/PS degrades E2.Halogenated DBPs are not produced;E2 present in the UV/PS system can inhibit the formation of bromate,which proves that UV/PS is a safe and reliable method for degrading E2 compared to conventional chlorination.