Modeling of ozone decomposition, oxidant exposures, and the abatement of micropollutants during ozonation processes

This study demonstrates new empirical models to predict the decomposition of ozone (O₃) and the exposures of oxidants (i.e., O₃ and hydroxyl radical, [rad]OH) during the ozonation of natural waters. Four models were developed for the instantaneous O₃ demand, first-order rate constant for the secondary O₃ decay, O₃ exposure (∫[O₃]dt), and [rad]OH exposure ((∫[[rad]OH]dt)), as functions of five independent variables, namely the O₃ dose, concentration of dissolved organic carbon (DOC), pH, alkalinity, and temperature. The models were derived by polynomial regression analysis of experimental data obtained by controlling variables in natural water samples from a single source water (Maegok water in Korea), and they exhibited high accuracies for regression (R² = 0.99 for the three O₃ models, and R² = 0.96 for the [rad]OH exposure model). The three O₃ models exhibited excellent internal validity for Maegok water samples of different conditions (that were not used for the model development). They also showed acceptable external validity for seven natural water samples collected from different sources (not Maegok water); the IOD model showed somewhat poor external validity. However, the [rad]OH exposure model showed relatively poor internal and external validity. The models for oxidant exposures were successfully used to predict the abatement of micropollutants by ozonation; the model predictions showed high accuracy for Maegok water, but not for the other natural waters.