Modelling of emerging contaminant removal during heterogeneous catalytic ozonation using chemical kinetic approaches

This study evaluated the prediction of emerging contaminant (EC) removal during heterogeneous catalytic ozonation by chemical kinetic models. Six ECs with differing ozone reactivity were spiked in a synthetic water and a groundwater, then treated by conventional ozonation and heterogeneous catalytic ozonation with α- or β-MnO₂ catalysts. Results show that catalysts did not considerably influence the removal of ECs with high and intermediate ozone reactivity (diclofenac, gemfibrozil, and bezafibrate), but enhanced the removal efficiencies of ECs with low ozone reactivity (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) to varied extent (˜10-30%). The removal efficiencies of ECs could be reasonably predicted using chemical kinetic models based on the ozone (O₃) and hydroxyl radical (OH) rate constants of ECs, pseudo-first-order rate constants observed for EC adsorption on the MnO₂ catalysts, and O₃ and OH exposures observed for catalytic ozonation. Furthermore, the model reveals that ECs are removed mainly by O₃ and/or •OH oxidation during heterogeneous catalytic ozonation, while adsorption of ECs on catalysts contributes negligibly. Therefore, the removal efficiencies of ECs could be satisfactorily predicted using a simplified model based only on the O₃ and OH rate constant and the O₃ and OH exposures.