Do film reactions affect ozone gas–liquid fast-moderate reaction kinetics in the proximity of gas–water interface?

Abstract

Kinetics of the ozonation of water contaminants is usually based on mol balance equations applied in the water bulk. In these models, direct and free radical reactions are considered, neglecting the contribution of reactions developed in the proximity of the gas–water interface. In this work, a theoretical kinetic model of the ozonation involving direct and free radical reactions in the film and water bulk is carried out. The model is based on film and penetration absorption theories. Time concentration profiles are assessed by coupling the non-stationary penetration theory with bulk mass balances. Studied variables are chosen according to their influence on the numbers of Hatta and instantaneous reaction factor. These parameters are equilibrium ozone and compound concentrations, direct rate constant, and mass transfer coefficient. The effect of pH and hydrogen peroxide are studied. Calculated results reveal that direct reaction contribution in the film has a significant importance, especially in fast-moderate kinetic regimes of ozone absorption. Absence of film free radical reactions leads to compound removal rates slightly lower than the complete mechanism (fast regimes develop). Formation of hydrogen peroxide and its reaction with ozone leads to the formation of free radicals.