HCO3–/CO32– enhanced degradation of diclofenac by Cu(Ⅱ)-activated peracetic acid: Efficiency and mechanism

Diclofenac (DCF), a non-steroidal anti-inflammatory drug, is an emerging and nonbiodegradable contaminant which is detected extensively in aquatic environment. Therefore, low cost and efficient method for DCF degradation has been the aim of many studies. In this study, DCF was efficiently removed by Cu(II)/peracetic acid (PAA) system in the presence of bicarbonate (HCO3–) and carbonate (CO32–). The concentration ratio of HCO3– to CO32– was found to have a significant effect on DCF removal, and the highest removal efficiency of DCF was obtained at [HCO3–]0 : [CO32–]0 = 9:1 due to the formation of CuCO3 and CuCO3(OH)−. According to the results of scavenging experiments and electron paramagnetic resonance (EPR), organic radicals (CH3C(=O)OO• and CH3C(=O)O•) were considered to be mainly responsible for DCF degradation in Cu(Ⅱ)–HCO3–(CO32–)/PAA system. Operational parameters including initial PAA concentration and Cu(Ⅱ) dosage were optimized for DCF removal, and effect of common water matrix (i.e., natural organic matter, SO42−, NO3– and Cl−) on DCF degradation were systematically investigated. Finally, based on the detected degradation products, five probable degradation pathways of DCF were proposed including hydroxylation, decarboxylation, formylation, dehydrogenation and C-N bond cleavage.