Factors affecting the formation of iodo-trihalomethanes during oxidation with chlorine dioxide

摘要

Effects of water characteristics, reaction time, temperature, bromide and iodide ion concentrations, oxidant doses, and pH on formation of iodinated trihalomethanes (I-THM) during oxidation of iodide-containing water with chlorine dioxide (ClO_2) were investigated. Among the water samples collected from ten water sources, iodoform (CHI_3) was the predominant I-THM and trace amount of chlorodi-iodomethane (CHClI_2) was occasionally found. CHI_3 yields correlated moderately with specific UV absorbance (SUVA) (R~2 = 0.79), indicating that hydrophobic aromatic content were important precursors. Longer reaction time led to continued formation of CHI_3. I-THM containing bromide was also found in waters containing both bromide and iodide, but CHI_3 was dominant. The formation of CHI_3 was higher at 25 ℃ than 5 ℃ and 35 ℃. CHI_3 formation showed an increase followed by a decrease trend with increasing ClO_2 doses and iodide concentrations and the highest yields occurred at iodide to ClO_2 molar ratios of 1-2. pH 8 resulted in the highest CHI_3 formation. It should be noted that a high iodide concentration was spiked to waters before adding ClO_2 and the results may not reflect the formation yields of iodinated THMs in real conditions, but they provide information about formation trend of I-THM during oxidation of ClO_2.