The UV/chlorine advanced oxidation process (AOP), which forms reactive species such as hydroxyl radicals (HO•) and chlorine atoms (Cl•), is being considered as an alternative to the UV/H₂O₂ AOP for the degradation of emerging contaminants. This study investigated the kinetics, formation of by-products 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 Cl• contributed to t...[ Read more ]

The UV/chlorine advanced oxidation process (AOP), which forms reactive species such as hydroxyl radicals (HO•) and chlorine atoms (Cl•), is being considered as an alternative to the UV/H₂O₂ AOP for the degradation of emerging contaminants. This study investigated the kinetics, formation of by-products 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 Cl• contributed to the degradation, and the contribution of Cl• increased from 22% to 30% with increasing pH from 6 to 9. 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.

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. Four chlorine-containing intermediates/products were newly identified. Significant amounts of chlorinated intermediates/byproducts were formed from the UV/chlorine AOP. 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. Subsequent chlorination followed after the UV/chlorine AOP increased the TOCl formation to 41.06 μM, while 33.88% of which was known DBPs. Compared to the UV/H₂O₂ AOP with subsequent chlorination, the concentrations of TOCl and known DBPs were increased by 13.57 μM and 5.79 μM, respectively, in the UV/chlorine AOP with subsequent chlorination.