title: Comparative evaluation of iodoacids removal by UV/persulfate and UV/H2O2 processes.
abstract: To develop a cost-effective method for post-formation mitigation of iodinated disinfection by-products, degradation of iodoacids by UV, UV/PS (persulfate), and UV/H2O2 was extensively investigated in this study. UV direct photolysis of 4 iodoacids followed first-order kinetics with rate constants in the range of 2.43 × 10(-4)-3.02 × 10(-3) cm(2) kJ(-1). The derived quantum yields (Ф254) of the 4 iodoacids range from 0.13 to 0.34, respectively. A quantitative structure-activity relationship (QSAR) model was subsequently established and applied to predict the direct photolysis rates of 6 other structurally similar iodoacids whose standards are commercially unavailable. At a UV dose of 140 mJ cm(-2) which is typically applied for disinfection of drinking water, the removal percentages of 4 iodoacids were only between 3.35% and 34.7%. Thus, ICH2CO2H (IAA), the most photo-recalcitrant species, was selected as the target compound for removal in the UV/PS and UV/H2O2 processes. The IAA degradation rates decreased with increasing pH from 3 to 11 in both processes. Humic acid (HA) and HCO3(-) had inhibitory effects on IAA degradation in both processes. Cl(-) adversely affected the IAA degradation in the UV/PS process but had no effect in the UV/H2O2 process. Generally, in the deionized (DI) water, surface water, treated drinking water, and secondary effluent, UV/PS process is more effective than UV/H2O2 process for IAA removal, based on the same molar ratio of oxidant: IAA. SO4(-) generated in the UV/PS process yields a greater mineralization of IAA than HO in the UV/H2O2 process. IO3(-) was the predominant end-product in the UV/PS process, while I(-) was the major end-product in the UV/H2O2 process. The respective contributions of UV, HO, and SO4(-) for IAA removal in the UV/PS process were 7.8%, 14.7%, and 77.5%, respectively, at a specific condition (1.5 μM IAA, 60 μM oxidant, and pH 7). Compared to UV/H2O2 process, UV/PS was also observed as more cost-effective process based on the electrical energy per order (EE/O) and chemical cost.
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: 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: Wei
authors.initials: W
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: Kok-Yong
authors.initials: KY
authors.lastname: Lim
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: D006861:Hydrogen Peroxide / Q000737:chemistry*; D010782:Photolysis; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification
chemical_list: D014874:Water Pollutants, Chemical; D006861:Hydrogen Peroxide
keywords: Hydroxyl radical; Iodinated disinfection by-product; QSAR model; Sulfate radical; UV/H(2)O(2); UV/PS