Kinetic Study of Hydroxyl and Sulfate Radical-Mediated Oxidation of Pharmaceuticals in Wastewater Effluents

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO^•)- and sulfate radical (SO₄^•-)-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO^•- and SO₄^•--mediated oxidation. In the UV/H₂O₂ process, a simplified kinetic model involving only steady state concentrations of HO^• and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO^• in the removal of PPCPs. In the UV/K₂S₂O₈ process, the calculated steady state concentrations of CO₃^•- and bromine radicals (Br^•, Br₂^•- and BrCl^•-) were 600-fold and 1-2 orders of magnitude higher than the concentrations of SO₄^•-, respectively. The kinetic model, involving both SO₄^•- and CO₃^•- as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO₄^•- could lead to overestimations of the removal efficiencies of the SO₄^•--mediated oxidation of nitroimidazoles in wastewater effluents.