Prediction of micropollutant abatement during homogeneous catalytic ozonation by a chemical kinetic model

Abstract

Prediction of micropollutant abatements by catalytic ozonation is critical for its process design and optimization in water treatment. In this study, a chemical kinetic model based on ozone (O3) and hydroxyl radical (OH) rate constants (kO3 and kOH) and O3 and OH exposures is proposed for the generalized prediction of micropollutant abatement by homogeneous catalytic ozonation. Several micropollutants with kO3 ranging from <0.15 to 1.0 × 106 M−1 s−1 were spiked in water matrices (deionized water and surface water) and then treated by ozonation alone and homogeneous catalytic ozonation with varying transition metals (Ti2+, Co2+, Ni2+, Zn2+, Cu2+, Mn2+, Fe2+, and Fe3+). The addition of the varying catalysts enhanced the kinetics and yield of OH formation from O3 decomposition to different extent. Consequently, for the same applied O3 doses, higher OH exposures can generally be obtained at the expense of lower O3 exposures during catalytic ozonation with the varying catalysts compared to ozonation alone. The changes in O3 and OH exposures did not considerably influence the abatement of micropollutants with high and moderate O3 reactivities (diclofenac, gemfibrozil, and bezafibrate), whose abatement efficiencies were generally >90% during both ozonation alone and catalytic ozonation with the varying catalysts. In contrast, ozone-resistant micropollutants (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) were less effectively abated during ozonation (∼40–60% abatement), and the addition of the varying catalysts could enhance their absolute abatement efficiencies to various extent (∼0–10% in the deionized water and ∼0–22% in the surface water) during catalytic ozonation. Despite the differing catalytic mechanisms of the varying transition metals, the abatement efficiencies of micropollutants by catalytic ozonation could be satisfactorily predicted by the chemical kinetic model using the O3 and OH rate constants of the micropollutants reported in literature and the O3 and OH exposures determined during the treatment processes. These results demonstrate that the chemical kinetic model can provide a useful tool for the generalized prediction of micropollutant abatement by homogeneous catalytic ozonation.