Treatment of iodine-containing water by the UV/NHCl process: Dissolved organic matters transformation, iodinated trihalomethane formation and toxicity variation.

UV/NHCl process is becoming increasingly important for water treatment, while its impact on iodine-containing water remains unknown. In this study, the structure transformation of dissolved organic matters (DOMs), generation of iodinated trihalomethanes (I-THMs), and variation of acute toxicity were evaulated during the UV/NHCl treatment of iodine-containing water. The combination of exciation emission matrix-parallel factor analysis and two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy showed that fulvic-like fraction of DOM was more susceptible to UV/NHCl process and particularly iodo and polysaccharide groups gave the fastest resopnses. Consequently, UV fluence lower than 60 mJ/cm promoted the production of I-THMs, while excessive UV exhausted NHCl and reactive iodine species and subsequently reduced I-THM generation. Moreover, DOM concentration and source, NHCl dosage, and I concentration had significant impacts on I-THM formation in the UV/NHCl process. Additionally, a positive correlation was found between acute toxicity variation and I-THM formation when treating iodine-containing waters with UV/NHCl. These results together provide a comprehensive understanding on UV/NHCl treatment of iodine-containing water.