Mechanistic Study on the Formation of Cl-/Br-/I-Trihalomethanes during Chlorination/Chloramination Combined with a Theoretical Cytotoxicity Evaluation.
Chlorination followed by chloramination can be used to mitigate the formation of potentially toxic iodinated disinfection byproducts (I-DBPs) while controlling the formation of regulated chloro-bromo-DBPs (Cl-/Br-DBPs). Water samples containing dissolved organic matter (DOM) isolates were subjected to 3 disinfection scenarios: NH2Cl, prechlorination followed by ammonia addition, and HOCl alone. A theoretical cytotoxicity evaluation was carried out based on the trihalomethanes (THMs) formed. This study demonstrates that the presence of bromide not only enhances the yield and rate of iodate formation, it also increases the formation of brominated I-THM precursors. A shift in the speciation from CHCl2I to the more toxic CHBr2I, as well as increased iodine incorporation in THMs, was observed in the presence of bromide. For low bromide concentrations, a decrease in I-THM formation and theoretical cytotoxicity was achieved only for high prechlorination times, while for high bromide concentrations, a short prechlorination time enabled the full conversion of iodide to iodate. For low DOM concentrations or DOM with low reactivity, Br-/I-THMs were preferentially formed for short prechlorination times, inducing high cytotoxicity. However, for high chlorine exposures, the cytotoxicity induced by the formation of regulated THMs might outweigh the benefit of I-THM mitigation. For high DOM concentrations or DOM with higher reactivity, mixed I-THMs were formed together with high concentrations of regulated THMs. In this case, based on the cytotoxicity of the THMs formed, the use of NH2Cl is recommended.
Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987, Perth Western Australia 6845, Australia.
Sebastien
S
Allard
Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987, Perth Western Australia 6845, Australia.
Jace
J
Tan
Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987, Perth Western Australia 6845, Australia.
Cynthia A
CA
Joll
Eawag, Swiss Federal Institute of Aquatic Science and Technology, ETH Zürich , 8600 Zürich, Switzerland.|School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale Lausanne (EPFL) , 1015 Lausanne, Switzerland.
Urs
U
von Gunten
D001965:Bromides / Q000633:toxicity*; D016923:Cell Death / Q000187:drug effects; D002712:Chlorides / Q000633:toxicity*; D004203:Disinfection; D054879:Halogenation / Q000187:drug effects; D007452:Iodates / Q000633:toxicity; D007454:Iodides / Q000633:toxicity*; D016877:Oxidants / Q000633:toxicity; D013997:Time Factors; D022882:Trihalomethanes / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000032:analysis
D001965:Bromides; D002712:Chlorides; D007452:Iodates; D007454:Iodides; D016877:Oxidants; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical