New Insights on the Efficiency and Mechanism of Dissolved Oxygen Regulating the Redox Removal of Organic Pollutants by S(Iv) System

Abstract

Abstract：Recently, sulfite (S(IV)) has been extensively studied in the field of wastewater treatment. Multiple investigations have indicated that dissolved oxygen (DO) plays a crucial role in the S(IV) system. However, the mechanism of the effect of DO on the S(IV) system further investigation is required. Herein, the oxidative and reductive removal performance and mechanisms are modulated by adjusting the DO concentration in the S(IV) system. Specifically, an increase in DO concentration promotes the formation of HO• and SO4•−, while SO3•− is more prominently enriched at lower DO concentrations. Within a specific range, as the DO concentration increased, the oxidation proportion increased, while the reduction proportion decreased. In addition, under aerobic conditions, oxidation and reduction were synchronized to remove PNP and most of the organic matter oxidized into small molecules by HO• and SO4•−. In the absence of oxygen, only PNP was reduced to p-aminophenol (PAP) by ZVI and SO3•−. Surprisingly, the same phenomenon was observed for chlorinated organic pollutants. A comprehensive understanding of the mechanisms through which DO concentration modulates the specific removal of characteristic organic pollutants by oxidation and reduction is essential for the S(IV) system in water treatment processes.

Keywords: Keywords: S(IV), Zero-valent iron, Dissolved oxygen, Radical chain reaction, Oxidation and reduction mechanism