Establishment of sulfate radical advanced oxidation process based on Fe²⁺/O₂/dithionite for organic contaminants degradation

The sulfate radical advanced oxidation process is considered as one of the most effective technologies for refractory organic pollutant removal. However, the current sulfate radical generation source is very limited, and so far only peroxydisulfate, peroxymonosulfate and sulfite were reported as the generation sources. In this study, dithionite (DTN) was introduced as sulfate radical generation source for the first time. It was combined with Fe²⁺ and O₂ to form a simple and effective oxidation system: Fe²⁺/O₂/DTN. The established system was used to degrade atrazine (ATZ). The degradation pathways of ATZ and generation mechanism of dominant reactive species in Fe²⁺/O₂/DTN system were investigated. The results showed that ATZ and the total organic carbon (TOC) have been significantly reduced in 20 min with the initial solution pH varying from 5.0 to 7.0 in Fe²⁺/O₂/DTN system. Moreover, the possible degradation pathway of ATZ has been proposed involving dealkylation, dechlorination, carbonylation and hydroxylation. Primary radical identification through quenching experiments, ESR spectra and density functional theory (DFT) revealed the existence of sulfate radical (SO₄^·-) and hydroxyl radical (·OH) in the system. It is suspected that FeSO₃⁺ is the possible precursor of SO₃^·- and SO₄^·-. Therefore, the generation of FeSO₃⁺ and the possible formation pathways of SO₃^·- and SO₄^·- have been predicted based on the results of alternating reaction atmosphere test. The study indicates that Fe²⁺/O₂/DTN system could generate SO₄^·- and has great potential for the remediation of organic micro-pollution water bodies and contaminated soil.