Model prediction and mechanism analysis of PPCPs abatement in secondary effluent by heterogeneous catalytic ozonation: A case study with MnO2-Co3O4 depends on DOM concentration

In this study, the influence of DOM concentration on pharmaceuticals and personal care products (PPCPs) abatement by conventional ozonation and heterogeneous catalytic ozonation with MnO2-Co3O4 catalyst were comparatively investigated. Correspondingly, a kinetic model was proposed to further predict and analyze the abatement of eight PPCPs with k(O3) from < 0.1 to 2.5 x 106 M-1.s(-1). Results showed that increasing DOM concentration in secondary effluent would considerably inhibit PPCPs abatement during conventional ozonation, but only slightly influence PPCPs abatement with MnO2-Co3O4 catalyst. This could be attributed to the promotion of MnO2-Co3O4 catalyst on O-3 exposure (112 %-120 %) and hydroxyl radical (radical center dot OH) exposure (190 %-740 %), which further enhanced Rct-sec values in catalytic ozonation. Furthermore, both PPCPs abatement in conventional and MnO2-Co3O4 catalytic ozonation could be reasonably predicted by kinetic model based on second-order rate constants and reactive oxygen species exposures under various DOM concentration conditions, providing a possibility to predict PPCPs abatement during heterogeneous catalytic ozonation without considering catalyst adsorption. According to the model, independent of conventional and catalytic ozonation, O-3-reactive PPCPs (acetaminophen, acyclovir, carbamazepine, gemfibrozil and sulfamethoxazole) and O-3-resistant PPCPs (p-CBA) were removed by O-3 and radical center dot OH under all DOM concentration conditions, respectively. While, with increasing DOM concentration, dominant abatement of moderately O-3-reactive PPCPs (bezafibrate and benzotriazole) were changed from radical center dot OH to O-3 in conventional ozonation, but were still radical center dot OH in catalytic ozonation, further verifying the role of MnO2-Co3O4 catalyst on enhancement abatement of moderately O-3-reactive PPCPs. By quantitative structure-activity relationship analysis, a positive correlation between hydrophobicity of PPCPs and reaction kinetics of radical center dot OH was firstly proposed, which revealed the role of hydrophilicity-hydrophobicity of PPCPs on PPCPs abatement in heterogeneous catalytic ozonation.