Mechanistic insight into the generation of reactive oxygen species in sulfite activation with Fe(III) for contaminants degradation

Since the reactive species during the sulfite activation by Fe(III) (Fe(III)/sulfite process) had not been directly determined and the role of in-situ generated Fe(II) was overlooked, this study evaluated the oxidation performance of the Fe(III)/sulfite process, identified the reactive species, and investigated the role of in-situ generated Fe(II) in this process. The results demonstrated that carbamazepine (CBZ) could be degraded at different sulfite concentrations. Compared to the single-dosing mode, sulfite applied with multiple-dosing mode was beneficial to CBZ removal in this process when the same amount of sulfite was dosed. Fe(II) was rapidly generated and then decayed in this process, which were consistent with the trends of CBZ degradation and sulfite consumption. Electron paramagnetic resonance and scavenging experiments showed that SO₄^[rad]− was a major oxidant, while HO^[rad] also played a significant role in CBZ degradation in this process. The tert-butyl alcohol assay indicated that the generation and re-oxidation of Fe(II) was accompanied with the generation of reactive species. Besides sulfite dosage, CBZ degradation was also affected by initial pH, Fe(III) dosage, and CBZ concentration. Cl⁻ showed little inhibition on CBZ degradation while humic acid inhibited CBZ degradation in this process. This study advances the application of this oxidation system.