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Formation of iodo-trihalomethanes, iodo-acetic acids, and iodo-acetamides during chloramination of iodide-containing waters: Factors influencing formation and reaction pathways.

Research paper by Shaogang S Liu, Zhenlin Z Li, Huiyu H Dong, Bernard A BA Goodman, Zhimin Z Qiang

Indexed on: 09 Sep '16Published on: 09 Sep '16Published in: Journal of Hazardous Materials



Abstract

This study investigated systematically the factors influencing the formation of iodinated disinfection by-products (I-DBPs) during chloramination of I(-)-containing waters, including reaction time, NH2Cl dose, I(-) concentration, pH, natural organic matter (NOM) concentration, Br(-)/I(-) molar ratio, and water matrix. Among the I-DBPs detected, iodoform (CHI3), iodoacetic acid (IAA), diiodoacetic acid (DIAA), triiodoacetic acid (TIAA), and diiodoacetamide (DIAcAm) were the major species produced from reactions between reactive iodine species (HOI/I2) and NOM. A kinetic model involving the reactions of NH2Cl auto-decomposition, iodine species transformation and NOM consumption was developed, which could well describe NH2Cl decay and HOI/I2 evolution. Higher concentrations of CHI3, IAA, DIAA, TIAA, and DIAcAm were observed in chloramination than in chlorination, whereas IO3(-) was only formed significantly in chlorination. Maximum formation of I-DBPs occurred at pH 8.0, but acidic conditions favored the formation of iodinated haloacetic acids and DIAcAm. Increasing Br(-)/I(-) molar ratio from 1 to 10 did not increase the total amount of I-DBPs, but produced more bromine-substituting species. In addition, chloramination of 18 model compounds indicated that low-SUVA254 (specific ultraviolet absorbance at 254nm) NOM generally favored the formation of I-DBPs compared to high-SUVA254 NOM. Finally, potential pathways for I-DBPs formation from chloramination of NOM were proposed.