Insights into the enhanced degradation of flumequine by UV/ClO2 integrated process: Kinetics, mechanisms and DBPs-related toxicity in post-disinfection

The enhanced elimination of flumequine by combined UV/ClO2 advanced oxidation processes (AOPs) and disinfection by-products (DBPs)-related toxicity during post-disinfection were investigated. The efficient removal of flumequine by UV/ClO2 could be depicted with pseudo first order kinetics. The roles of main reactive species were identified by quenching experiments and EPR spectrum. The contributing proportions of UV photolysis, singlet oxygen (1O2), OH and reactive chlorine species (RCS) were calculated to be 11.37%, 14.72%, 19.79% and 54.12%, respectively. Then key influence factors including UV intensity, ClO2 dosages, pH and water matrices (co-present anions and nature organic matter (NOM)) were examined comprehensively. The degradation rate of flumequine (kobs) gradually increased with ClO2 dosage and UV intensity, but decreased obviously as pH ascended. The coexistence of Cl− showed negligible impact on kobs while HCO3− displayed notable inhibitory effect. However, kobs was greatly depressed by the NOM presence and the negative correlations between kobs and organic indexes were verified. Based on FT-ICR-MS analysis, the UV/ClO2 destruction pathways of flumequine were proposed to involve hydroxylation, decarboxylation, demethylation and defluorination. Comparatively, although UV/Cl2 showed better removal efficiency and lower energy requirement than UV/ClO2, the latter process induced much less toxicity connected with DBPs in post-oxidation. The results implied that the oxidation characteristics of 1O2 (non-radical pathway) varied greatly from those of OH and RCS, which may lead to the distinct advantage of UV/ClO2 in DBPs control. Take flumequine as an example, this paper is devoted to better comprehending the UV/ClO2 integrated technique. The findings may also shed light on the feasibility of UV/ClO2 and UV/Cl2 AOPs systems in tradeoffs among factors including removal effectiveness, operational cost and toxicity concerns of the treated waters containing emerging contaminants.