Degradation of organic contaminants through activating bisulfite by cerium(IV): A sulfate radical-predominant oxidation process

In this study, the activation of bisulfite by cerium(IV) (Ce(IV)/HSO₃ ⁻ process) is proposed for the first time to degrade organic contaminants. Experiments show that carbamazepine (CBZ), a representative recalcitrant contaminant of emerging concern, is oxidized by Ce(IV)/HSO₃ ⁻ treatment at pH_ini 3.0–7.0 when O_2(aq) is present to promote HSO₃ ⁻ autoxidation. SO₄ ^[rad]−, HO^[rad], and SO₅ ^[rad]− were identified as active oxidants of CBZ based on the ESR spectra and the results of alcohol quenching experiments. Quantitative analysis indicates that SO₄ ^[rad]− plays a major role, while HO^[rad] and other species play minor roles in the degradation of CBZ in the Ce(IV)/HSO₃ ⁻ process. SO₄ ^[rad]− radicals are derived from the reaction of SO₅ ^[rad]− with HSO₃ ⁻ and the activation of hydrogen peroxomonosulfate (HSO₅ ⁻) by Ce(IV). Five degradation pathways of CBZ are proposed based on transformation products identified by UPLC-QToF-MS/MS, and proposed sites for radical attack are supported by the results of frontier electron density calculations. Elevated concentrations of Cl⁻, Fe(III), and humic acid (HA) inhibit CBZ degradation, while other non-target solutes have minimal effects on CBZ degradation in the Ce(IV)/HSO₃ ⁻ process. Finally, experiments demonstrating degradation of a suite of other organic contaminants suggests that the Ce(IV)/HSO₃ ⁻ system can be applied as a new advanced oxidation process for wastewater treatment.