Insight into the formation of iodinated trihalomethanes during chlorination, monochloramination, and dichloramination of iodide-containing water

Bin Xu , Shuang Zhang , Yi-Li Lin , Tian-Yang Zhang , Chen-Yan Hu , Zhi Liu , Zheng-Yu Dong , Meng-Yuan Xu , Carsten Prasse , Xin Yang , Chao Chen , Xing-Fang Li


Received February 28, 2022,Revised , Accepted May 06, 2022, Available online May 20, 2022

Volume 34,2022,Pages 285-294

In this study, the formation of iodinated trihalomethanes (I-THMs) was systematically evaluated and compared for three treatment processes - (i) chlorination, (ii) monochloramine, and (iii) dichloramination - under different pH conditions. The results demonstrated that I-THM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral pH. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as pH increased from 5 to 9 during chlorination and monochloramination processes, while the maximum I-THM formation occurred at pH 7 during dichloramination. The discrepancy could be mainly related to the stability of the three chlor (am) ine disinfectants at different pH conditions. Moreover, in order to gain a thorough insight into the mechanisms of I-THM formation during dichloramination, further investigation was conducted on the influencing factors of DOC concentration and Br/I molar ratio. I-THM formation exhibited an increasing and then decreasing trend as the concentration of DOC increased from 1 to 7 mg-C/L, while the yield of I-THMs increased with increasing Br/I molar ratio from 5:0 to 5:10. During the three processes mentioned above, similar I-THM formation results were also obtained in real water, which indicates that the excessive generation of I-THMs should be paid special attention during the disinfection of iodide-containing water.

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