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Xiao Y.,Nanyang Technological University | Xiao Y.,Water Research Analytical Laboratories | Zhang L.,Water Research Analytical Laboratories | Zhang W.,Water Research Analytical Laboratories | And 4 more authors.
Water Research

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 cm2 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[Formula presented]− generated in the UV/PS process yields a greater mineralization of IAA than [Formula presented] 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, [Formula presented], and SO4[Formula presented]− 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. © 2016 Elsevier Ltd Source

Xiao Y.,Nanyang Technological University | Xiao Y.,Water Research Analytical Laboratories | Fan R.,Water Research Analytical Laboratories | Zhang L.,Water Research Analytical Laboratories | And 4 more authors.
Water Research

Photodegradation of 6 iodinated trihalomethanes (ITHMs) under UV irradiation at 254nm 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 0.1-0.6min-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. © 2013 Elsevier Ltd. Source

Xiao Y.,Nanyang Technological University | Xiao Y.,Water Research Analytical Laboratories | Zhang L.,Water Research Analytical Laboratories | Yue J.,Water Research Analytical Laboratories | And 3 more authors.
Water Research

Photodegradation of I-THMs including CHCl2I and CHI3 by the UV/H2O2 system was investigated in this study. CHCl2I and CHI3 react rapidly with hydroxyl radical (OH) produced by the UV/H2O2 system, with second-order rate constants of 8.0×109 and 8.9×109M-1s-1, respectively. A fraction of CHCl2I could be completely mineralized within 15min and the remaining fraction was mainly converted to formic acid (HCO2H). Cl- and I- were identified as the predominant end-products. No ClO3 - was observed during the photodegradation process, while IO3 - was detected but at less than 2% of the total liberated iodine species at the end of the reaction. The effects of pH, H2O2 dose, and matrix species such as humic acid (HA), HCO3 -, SO4 2-, Cl-, NO3 - on the photodegradation kinetics were evaluated. The steady-state kinetic model has been proven to successfully predict the destruction of CHCl2I and CHI3 by UV/H2O2 in different water matrices. On this basis, the kinetic model combined with electrical energy per order (EE/O) concept was applied to evaluate the efficiency of the photodegradation process and to optimize the H2O2 dose for different scenarios. The optimal H2O2 doses in deionized (DI) water, model natural water, and surface water are estimated at 5, 12, and 16mgL-1, respectively, which correspond to the lowest total energy consumption (EE/Ototal) of 0.2, 0.31, and 0.45kWhm-3order-1. © 2015 Elsevier Ltd. Source

Hu R.,Water Research Analytical Laboratories | Yang Z.,Water Research Analytical Laboratories | Zhang L.,Water Research Analytical Laboratories

Acidic pharmaceutical residues are pollutants of emerging concern and are generally monitored by HPLC-MS/MS. However, due to the limited separation efficiency of HPLC column and lack of suitable mass transition for confirmation analysis, some interference may not be separated completely and differentiated from ibuprofen, which may cause the results with interference, especially in sample with complex matrix. The objective of this study is to develop a sensitive and reliable method for the determination of acidic pharmaceutical residues in water samples by GC-MS with better resolution by using methylation derivatization and isotope dilution techniques. TMSDM, a mild reagent, was used as the derivatization reagent coupling with the isotope dilution technique, for the first time, to improve the precision and accuracy of the analytical method to determine the pharmaceutical residues in water. The MDLs for the five acidic organic compounds: ibuprofen, gemfibrozil, naproxen, ketoprofen and diclofenac were from 0.7 to 1.1 ng/L, with recoveries ranging from 93 to 110%. Alternative to the HPLC-MS/MS method, the developed GC-MS protocols provides an additional option for the analysis of acidic pharmaceutical residues in water, with better separation efficiency in reducing interferences from complicated sample matrix, for determination of ibuprofen residues. © 2011 Elsevier B.V. All rights reserved. Source

Zhang Y.,Nanyang Technological University | Zhang Y.,Nanyang Environment and Water Research Institute | Zhang J.,Nanyang Technological University | Zhang J.,Nanyang Environment and Water Research Institute | And 5 more authors.
Chemical Engineering Journal

This study investigated the removal of azathioprine (AZA), an immunosuppressant xenobiotic found in hospital effluent, using direct UV-254 nm photolysis, UV/H2O2 and UV/persulfate (UV/PS). AZA cannot be effectively degraded by direct UV photolysis, while the photodegradation efficiency of AZA significantly increases with addition of H2O2 or PS, due to the generation of HO[formula presented] and SO4[formula presented]−, respectively. Compared with AZA removal of 10% by direct UV photolysis at UV dose of 510 mJ cm−2, UV/H2O2 and UV/PS can remove 68% and 87% of AZA, respectively, at an oxidant dose of 100 μM. The second-order rate constants of AZA with HO[formula presented] and SO4[formula presented] are 1.86 × 109 M−1 s−1 and 2.16 × 109 M−1 s−1, respectively. There is a proportional increase of AZA degradation efficiency with the increasing oxidant dose in the range of 10–100 μM, beyond which radical scavenging effect can negate the radical generation process. The effects of water quality, including pH, NOM and inorganic anions, were also investigated. The removal efficiency of AZA in the UV/H2O2 and UV/PS processes constantly decreases with the increasing pH. NOM significantly reduces the degradation efficiency of AZA through radical scavenging and UV absorption. The inhibition of AZA photodegradation is also affected by the presence of inorganic anions, following the order of HCO3 − > Cl− > NO3 − ≈ SO4 2−. Real water samples of treated water from a water treatment plant and secondary effluent from a wastewater treatment plant were used for the assessment of the UV treatment performances. Various AZA transformation by-products were identified to investigate the degradation mechanism of AZA in the UV-AOP systems. The addition of 100 μM oxidant significantly decreases the treatment cost from 0.844 (for UV photolysis) to 0.078 (for UV/H2O2) and 0.067 US$ m−3 order−1 (for UV/PS), respectively, indicating that UV/PS is the most cost-effective process for AZA degradation. © 2016 Elsevier B.V. Source

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