title: Kinetics and pathways of ibuprofen degradation by the UV/chlorine advanced oxidation process.
abstract: The UV/chlorine advanced oxidation process (AOP), which forms reactive species such as hydroxyl radicals (HO) and reactive chlorine species (RCS) such as chlorine atoms (Cl) and Cl2(-), is being considered as an alternative to the UV/H2O2 AOP for the degradation of emerging contaminants. This study investigated the kinetics and pathways of the degradation of a recalcitrant pharmaceutical and personal care product (PPCP)-ibuprofen (IBP)-by the UV/chlorine AOP. The degradation of IBP followed the pseudo first-order kinetics. The first-order rate constant was 3.3 times higher in the UV/chlorine AOP than in the UV/H2O2 AOP for a given chemical molar dosage at pH 6. The first-order rate constant decreased from 3.1 × 10(-3) s(-1) to 5.5 × 10(-4) s(-1) with increasing pH from 6 to 9. Both HO and RCS contributed to the degradation, and the contribution of RCS increased from 22% to 30% with increasing pH from 6 to 9. The degradation was initiated by HO-induced hydroxylation and Cl-induced chlorine substitution, and sustained through decarboxylation, demethylation, chlorination and ring cleavage to form more stable products. Significant amounts of chlorinated intermediates/byproducts were formed from the UV/chlorine AOP, and four chlorinated products were newly identified. The yield of total organic chlorine (TOCl) was 31.6 μM after 90% degradation of 50 μM IBP under the experimental conditions. The known disinfection by-products (DBPs) comprised 17.4% of the TOCl. The effects of water matrix in filtered drinking water on the degradation were not significant, demonstrating the practicality of the UV/chlorine AOP for the control of some refractory PPCPs. However, the toxicity of the chlorinated products should be further assessed.
authors.affiliation: SYSU-HKUST Research Center for Innovative Environmental Technology (SHRCIET), School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-Sen University), Guangzhou 510275, PR China; Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Yingying
authors.initials: Y
authors.lastname: Xiang
authors.affiliation: SYSU-HKUST Research Center for Innovative Environmental Technology (SHRCIET), School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-Sen University), Guangzhou 510275, PR China. Electronic address: fangjy3@mail.sysu.edu.cn.
authors.forename: Jingyun
authors.initials: J
authors.lastname: Fang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong; Hong Kong Branch of Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, Hong Kong. Electronic address: cechii@ust.hk.
authors.forename: Chii
authors.initials: C
authors.lastname: Shang
mesh_terms: D002713:Chlorine / Q000032:analysis / Q000737:chemistry; D004203:Disinfection; D060766:Drinking Water / Q000032:analysis*; D054879:Halogenation; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical; D007052:Ibuprofen / Q000032:analysis*; D007700:Kinetics; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry; D013696:Temperature; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification / Q000379:methods*
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; D002713:Chlorine; D006861:Hydrogen Peroxide; D010100:Oxygen; D007052:Ibuprofen
keywords: Chlorine atoms; Hydroxyl radicals; Ibuprofen; Pharmaceutical and personal care products (PPCPs); UV/chlorine advanced oxidation process; Water treatment