Overlooked role of CO· reactivity with different dissociation forms of organic micropollutants in degradation kinetics modeling: A case study of fluoxetine degradation in a UV/peroxymonosulfate system.

Selective oxidizing agent carbonate radical (CO) is an important secondary radical in radical-based advanced oxidation technology for wastewater treatment. However, the role of CO in removing ionizable organic micropollutants (OMs) under environmentally relevant conditions remains unclear. Herein we investigated CO effect on degradation kinetics of fluoxetine in UV/peroxymonosulfate (PMS) system based on a built radical model considering CO reactivity differences with its different dissociation forms. Results revealed that the model, which incorporated CO selective reactivity (with determined second-order rate constants, k, of 7.33 ×10 and 2.56 ×10 Ms for cationic and neutral fluoxetine, respectively) provided significantly more accurate predictions of fluoxetine degradation rates (k). A good linear correlation was observed between k from experiments and literatures for 24 ionizable OMs and their molecular orbital energy gaps and oxidation potentials, suggesting the possible electron transfer reaction mechanism. Cl slightly reduced the degradation rates of fluoxetine owing to rapid transformation of Cl with HCO into CO, which partially compensated for the quenching effects of Cl on HO and SO. Dissolved organic matter significantly quenched reactive radicals. The constructed kinetic model successfully predicted fluoxetine degradation rates in real waters, with CO being the dominant contributor (∼90 %) to this degradation process.