An Ozone Consumption Model with Two Second-Order Reactions: Extending the Initial Ozone Demand/Pseudo-First-Order Model

In the study and management of ozonation, a model that describes ozone concentration dynamics is a fundamental framework. However, the conventional initial ozone demand/pseudo-first-order model (IPM) is strongly dependent on the ozone dose and consequently constrains both basic and applied research. Therefore, we propose a new model that expands IPM by representing ozone consumption with two distinct second-order reactions. Using this model, ozone exposure was successfully predicted with a median absolute relative error (MdARE) of 4.8% for various combinations of water temperature and ozone dose within the calibrated range. Even when only one ozone dose dataset is available, the new model was able to reproduce ozone consumption at other ozone doses more accurately than IPM in 79% of cases. Coupling our model with an existing hydroxyl radical (•OH) model accurately reproduced the decay of p-chlorobenzoic acid (a •OH probe compound) with a MdARE of 3.2%. Simulations using the new model revealed that (i) the ozone dose required for the removal of Cryptosporidium parvum oocysts is governed by water temperature rather than dissolved substances, (ii) the O₃/•OH contribution ratio to cis-1,2-dichloroethene oxidation is practically independent of ozone dose, and (iii) the removal efficiency of p-chlorobenzoic acid can be estimated with a MdARE of 14% through real-time monitoring of the ozone consumption rate. This study provides a versatile kinetic framework for mechanistic studies and practical applications in treatment operations.