Insight into the formation of iodinated tr ihalomethanes dur ing chlor ination,monochloramination, and dichloramination of iodide-containing water

摘要

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 p H conditions. The results demonstrated that ITHM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral p H. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as p H 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 p H 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/Imolar 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/Imolar 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.