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

Abstract

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 kO3 from < 0.1 to 2.5 × 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 O3 exposure (112 %-120 %) and hydroxyl radical (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, O3-reactive PPCPs (acetaminophen, acyclovir, carbamazepine, gemfibrozil and sulfamethoxazole) and O3-resistant PPCPs (p-CBA) were removed by O3 and OH under all DOM concentration conditions, respectively. While, with increasing DOM concentration, dominant abatement of moderately O3-reactive PPCPs (bezafibrate and benzotriazole) were changed from OH to O3 in conventional ozonation, but were still OH in catalytic ozonation, further verifying the role of MnO2-Co3O4 catalyst on enhancement abatement of moderately O3-reactive PPCPs. By quantitative structure–activity relationship analysis, a positive correlation between hydrophobicity of PPCPs and reaction kinetics of OH was firstly proposed, which revealed the role of hydrophilicity-hydrophobicity of PPCPs on PPCPs abatement in heterogeneous catalytic ozonation.