title: Photodegradation of iodinated trihalomethanes in aqueous solution by UV 254 irradiation.
abstract: Photodegradation of 6 iodinated trihalomethanes (ITHMs) under UV irradiation at 254 nm was investigated in this study. ITHMs underwent a rapid photodegradation process through cleavage of carbon-halogen bond with first-order rate constants in the range of 0.1-0.6 min(-1). The effects of matrix species including nitrate, humic acid (HA), bicarbonate, sulfate, and chloride were evaluated. The degradation rate increased slightly in the presence of nitrate possibly due to generation of HO at a low quantum yield via direct photolysis of nitrate, while HA lowered the photodegradation rate of ITHMs due to its competitive UV absorption. Moreover, bicarbonate, sulfate, and chloride had no significant effect on photodegradation kinetics, as there is no UV absorption for these 3 species. In the study using surface water, treated water, and secondary effluent from a wastewater treatment plant, high turbidity and natural organic matters present in the water inhibited the photodegradation of ITHMs. The degradation rates of 6 ITHMs in UV/H2O2 system were rather comparable and significantly higher than those achieved in the UV system without H2O2. To develop a quantitative structure-reactivity relationship (QSAR) model, the logarithm of measured first-order rate constants was correlated with a number of molecular descriptors. The best correlation was obtained with a combination of 3 molecular descriptors, namely the bond strength of carbon-halogen to be broken in the rate-determining step, steric and electronic effects of all substituents to the carbon center.
authors.affiliation: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore; Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Rongli
authors.initials: R
authors.lastname: Fan
authors.affiliation: Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Junqi
authors.initials: J
authors.lastname: Yue
authors.affiliation: School of Physical and Mathematic Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Republic of Singapore.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Webster
authors.affiliation: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore; Nanyang Environment and Water Research Institute (NEWRI), Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Republic of Singapore. Electronic address: cttlim@ntu.edu.sg.
authors.forename: Teik-Thye
authors.initials: TT
authors.lastname: Lim
mesh_terms: D054879:Halogenation / Q000528:radiation effects*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D008962:Models, Theoretical; D009566:Nitrates / Q000737:chemistry; D010782:Photolysis / Q000528:radiation effects*; D021281:Quantitative Structure-Activity Relationship; D011789:Quantum Theory; D012996:Solutions; D013997:Time Factors; D022882:Trihalomethanes / Q000737:chemistry*; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000528:radiation effects*
chemical_list: D009566:Nitrates; D012996:Solutions; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical; D014867:Water; D006861:Hydrogen Peroxide
keywords: Direct photolysis; Humic acid; Iodinated disinfection by-product; Nitrate; QSAR model; Quantum yield; Water matrix