Kinetics and pathways of ibuprofen degradation by the UV/chlorine advanced oxidation process

The UV/chlorine advanced oxidation process (AOP), which forms reactive species such as hydroxyl radicals (HO center dot) and reactive chlorine species (RCS) such as chlorine atoms (Cl-center dot) and Cl-2(center dot-), 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 x 10(-3) s(-1) to 5.5 x 10(-4) s(-1) with increasing pH from 6 to 9. Both HO center dot 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 center dot-induced hydroxylation and Cl-center dot-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 mu M after 90% degradation of 50 mu M 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. (C) 2015 Elsevier Ltd. All rights reserved.