Common And Iodinated THMs Formation Of Amino Acid Chlorination In Waters

Drinking water safety has been one of the most concerns for human beings and the most basic guarantee for the life quality. Biological safety of drinking water has been always ensured by disinfection and the chlorine as a disinfectant is the most widely used disinfection technology. Unfortunately, some DBPs have been proved to be produced in the process of chlorination disinfection. DBPs have been proved to be carcinogenic, teratogenic and mutagenic to human health. In order to ensure the drinking water safety, it is particularly important to do some researches related to the source of precursors,the occurrence and the control of DBPs. In this paper, two kinds of amino acids-Trp and Asp have been selected as precursors to carry out the chlorination disinfection. And then the formation, impact factors of THMs and I-THMs, formation pathways of DBPs (such as HNMs, haloacetonitriles HANs) were studied.The formation of THMs and I-THMs were 20.94 and 27.21 ?g/L during Trp chlorination, meanwhile, the reaction rate constants were 0.246 and 0.172 h-1,respectively. The formation of THMs and I-THMs were 5.23 and 20.05 ?g/L during Asp chlorination, meanwhile, the reaction rate constants were 0.246 and 0.172 h-1,respectively. Chlorine dosage,temperature,pH and the ratio of bromide and iodide have great influence on the formation of THMs and I-THMs during chlorination.Under the condition of different influence factors, the generate trend of Trp chlorination was the same as Asp chlorination, however, the formation amount was much more than Asp chlorination.The toxicity of water sample of Trp and Asp chlorination was analyzed by toxicity detector and the toxicity of water sample of Trp chlorination was higher than Asp chlorination. According to the chlorination experiments and theoretical analysis for the generation of DBPs with Trp and Asp as the precursors, the reaction mechanism and pathway were as following:(1) THMs, I-THMs, HNMs and HANs were generated during Try chlorination.The pathway of THMs and I-THMs generation was as following: the reaction between Trp with chlorine can open the ring of pyrrole and then further halogenation to form THMs and I-THMs; Ethylamine (EA) was generated during Try chlorination and then formed imine intermediate product after reaction with chlorine, which can further halogenation to THMs. The pathway of HNMs generation was as following:EA reacted with HOCl to form nitroethane. The methyl was eliminated from nitroethane to form HNMs. The pathway of HANs generation was as following: firstly,EA formed acetonitrile by chloro-substituted and elimination, and then acetonitrile can further halogenation to form HANs.(2) THMs, I-THMs,Dichloroacetaldehyde and HANs were generated during Asp chlorination. The pathway of HANs generation was as following: cyanoacetic acid was generated during Asp chlorination and the generated HANs (DCAN, TCAN)by chloro-substituted, decarboxylation. The pathway of Dichloroacetaldehyde generation was as following: the reaction between Asp and chlorine can form imine intermediate product, which can further form Dichloroacetaldehyde and Trichloracetic aldehyde by elimination one CO2 and NH3 molecules. The pathway of THMs and I-THMs generation was as following: TCAN can form THMs and I-THMs by nucleophilic addition and elimination.