Enhanced 2,4,6-Tribromophenol Degradation via Slow-Release S(IV) in Fe(II)-Activated CaSO3 Advanced Oxidation Process

In this study, insoluble CaSO3 was applied to replace soluble sulfite/bisulfite salt in the Fe(II)-activated sulfite/bisulfite [S(IV)] process for the efficient 2,4,6-tribromophenol (TBP) degradation. CaSO3 serves as a low-cost and slow-release source of S(IV), significantly improving S(IV) utilization compared to conventional soluble Na2SO3. The Fe(II)/CaSO3 system generated SO4•− and HO• through Fe(II)/Fe(III) redox cycling. Mechanistic studies confirmed SO4•− as the dominant reactive species, selectively attacking C-Br bonds and hydroxyl groups in TBP. Process optimization revealed effective performance under acidic conditions (pH 3.5–4.0) with minimal inhibition by common anions (Cl−, HCO3−). The reactive sites of TBP were identified through Fukui function calculations, and the degradation pathway was elucidated based on LC-MS analysis. Toxicity evaluation indicated reduced ecological risk of degradation intermediates due to debromination and benzene ring cleavage. This work provides a sustainable strategy for efficient TBP removal and detoxification in wastewater treatment with benefiting S(IV) utilization.