Kinetic Modeling-Assisted Optimization of the Peroxone (O₃/H₂O₂) Water Treatment Process

In this work, we investigate the influence of H₂O₂ dosage, H₂O₂ dosing method, and electron-rich dissolved organic matter (DOM) on the performance of the peroxone (O₃/H₂O₂) process using oxalate (OA) as the target organic compound. Our results show that the method used for H₂O₂ dosing (i.e., single, multiple, and/or continuous injection(s)) has a significant influence on OA removal after 1 h with nearly 100% of OA oxidized by continuous injection of a total of 1 mM H₂O₂, but only 48 and 80% OA were removed when the same amount of H₂O₂ (1 mM) is applied in single and multiple injection(s), respectively. Inhibition of futile scavenging of ^•OH by H₂O₂ when H₂O₂ is dosed in smaller amounts either frequently or continuously throughout the process results in a higher efficiency of organic oxidation compared to that achieved with a single injection of a high concentration of H₂O₂ at the outset. Our results further show that the presence of high concentrations of humic acids (HA, a representative electron-rich DOM) promotes O₃ decay and concomitant ^•OH generation rates and, as a result, significantly enhances the oxidation rate of OA by ozone alone. As such, any enhancement in ^•OH generation and associated OA oxidation that might be achieved by H₂O₂ addition in the presence of HA will be dependent on the extent of ^•OH generation that results from HA-promoted O₃ decay. Based on our results, we have developed a mathematical model that can be used to predict ^•OH generation and OA oxidation by the peroxone process over a range of conditions. The model provides a good description of the influence of various operating parameters (including ozone dosage, H₂O₂ dosage, H₂O₂ dosing method, and the presence of HA) on OA oxidation and, potentially, can be used to optimize the choice of operating conditions in full-scale peroxone systems.