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Formation of iodinated trihalomethanes during breakpoint chlorination of iodide-containing water.

Research paper by Zhi Z Liu, Yi-Li YL Lin, Bin B Xu, Chen-Yan CY Hu, An-Qi AQ Wang, Ze-Chen ZC Gao, Sheng-Ji SJ Xia, Nai-Yun NY Gao

Indexed on: 02 May '18Published on: 02 May '18Published in: Journal of Hazardous Materials



Abstract

This study investigated the formation of toxic iodinated trihalomethanes (I-THMs) during breakpoint chlorination of iodide-containing water. Impact factors including I concentration, natural organic matter (NOM) concentration and type, pH as well as Br/I molar ratio were systematically investigated. Moreover, the incorporation of I into I-THM formation was also calculated. The results showed that I-THM formation varied in different zones of the breakpoint curves. I-THMs increased with increasing chlorine dosage to breakpoint value and then dropped significantly beyond it. Iodoform (CHI) and chlorodiiodomethane (CHClI) were the major I-THMs in the pre-breakpoint zone, while dichloroiodomethane (CHClI) was the dominant one in the post-breakpoint zone. The formation of I-THMs increased remarkably with I and dissolved organic carbon (DOC) concentrations. More bromine-containing species were formed as Br/I molar ratio increased from 0.5 to 5. In addition, the major I-THM compound shifted from CHClI to the more toxic CHClBrI. As pH increased from 6.0 to 8.0, I-THM formation kept increasing in the pre-breakpoint zone and the speciation of I-THMs changed alongside the breakpoint curves. The incorporation of I during breakpoint chlorination was highly dependent on chlorine, I, and NOM concentrations, NOM type, solution pH and Br/I molar ratio. Copyright © 2018 Elsevier B.V. All rights reserved.