Photodegradation pathway of iodate and formation of I-THMs during subsequent chloramination in iodate-iodide-containing water. (1st April 2021)

• Record Type: Journal Article
• Authors: Tang, Li-Zhen; Lin, Yi-Li; Xu, Bin; Xia, Ying; Zhang, Tian-Yang; Hu, Chen-Yan; Tang, Yu-Lin; Cao, Tong-Cheng; Xian, Qi-Ming; Gao, Nai-Yun
• Is Part Of: Water research. Volume 193(2021)
• Publication Date: 2021-04-01
• Subjects: Iodate (IO3−) -- Iodide (I−) -- Iodinated trihalomethanes (I-THMs) -- UV irradiation -- Chloramination; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.116851
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: IO3 − can be reduced by eaq − in mixed IO3 − /I − system under UV irradiation. Acid pHs and high I − concentration promoted the IO3 − transformation to RIS. Mixed IO3 − /I − system enhanced I-THM formation in UV/post-chloramination. Humic substances promoted I-THM formation in a mixed IO3 − /I − system. Abstract: This study investigated the mechanisms of mixed IO3 − /I − system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO3 − /I − system to that of single I − and IO3 − systems during subsequent chloramination. The effects of initial I − /IO3 − molar ratio, pH, and UV intensity on a mixed IO3 − /I − system were studied. The introduction of I − enhanced the conversion rate of IO3 − to reactive iodine species (RIS). Besides, IO3 − degradation rate increased with the increase of initial I − concentration and UV intensity and the decrease of pH value. In a mixed IO3 − /I − system, IO3 − could undergo direct photolysis and photoreduction by hydrated electron (eaq − ). Moreover, the enhancement of I-THM formation in a mixed IO3 − /I − system during subsequent chloramination was observed. The I-THM yields in a mixed IO3 − /I − system were higher than the sum of I-THMs produced in a single IO3 − and I − systems at all the evaluated initial I − concentrations and pH values. The difference between I-THM formation in a mixed IO3 − /I − system and the sum of I-THMs in a single IO3 − and I − systems increased with the increase of initial I − concentration. As the initial pH decreased from 9 to 5, the difference of I-THM yields enhanced, while the total I-THM yield of a mixed IO3 − /I − system and single I − and IO3 − systems decreased slightly. Besides, IO3 − -I − -containing water with DOC concentration of 2.5-4.5 mg-C/L, which mainly contained humic-acid substances, had a higher risk in I-THMs formation than individual I − -containing and IO3 − -containing water. Graphical abstract: Image, graphical abstract