The impact of dissolved oxygen on sulfate radical-induced oxidation of organic micro-pollutants: A theoretical study

Abstract

Sulfate radical (SO4.−)-induced oxidation is an important technology in advanced oxidation processes (AOPs) for the removal of pollutants. To date, few studies have assessed the effects of dissolved oxygen (DO) on the SO4.−-induced oxidation of organic micro-pollutants. In the present work, a quantum chemical calculation was used to investigate the influence of the external oxygen molecule on the Gibbs free energy (Gpollutant) and HOMO-LUMO gap (ΔE) of 15 organic micro-pollutants representing four chemical categories. Several thermodynamic and statistical models were combined with the data from the quantum chemical calculation to illustrate the impact of DO on the oxidation of organic micro-pollutants by SO4.−. Results indicated that the external oxygen molecule increased Gpollutant of all studied chemicals, which implies DO has the potential to decrease the energy barrier of the SO4.−-induced oxidation and shift the chemical equilibrium of the reaction towards the side of products. From the perspective of kinetics, DO can accelerate the oxidation by decreasing ΔE of organic micro-pollutants. In addition, changes of Gpollutant and ΔE of the SO4.−-induced oxidation were both significantly different between open-chain and aromatic chemicals, and these differences were partially attributed to the difference of polarizability of these two types of chemicals. Furthermore, we revealed that all changes of Gpollutant and ΔE induced by DO were dependent on the DO content. Our study emphasizes the significance of DO on the oxidation of organic micro-pollutants by SO4.−, and also provides a theoretical method to study the effect of components in wastewater on removal of organic pollutants in AOPs.