Enhanced ferrate(VI)) oxidation of sulfamethoxazole in water by CaO2: The role of Fe(IV) and Fe(V)

Abstract

Recently, the enhancing role of hydrogen peroxide (H₂O₂), a self-decay product of ferrate (Fe(VI)), on Fe(VI) reactivity has received increasing attention. In this study, we found that calcium peroxide (CaO₂) as a slow-releasing reagent of H₂O₂ could also enhance the Fe(VI) performance for removing sulfamethoxazole (SMX). Compared with sole Fe(VI), sole CaO₂ and Fe(VI)-H₂O₂ systems, the Fe(VI)-CaO₂ system showed higher reactivity to remove SMX. The radical scavenger and chemical probe test results indicated that the better oxidation performance of Fe(VI)-CaO₂ system than Fe(VI) alone was ascribed to the generation of Fe(Ⅳ) and Fe(Ⅴ) rather than ^•OH. In addition, the performance of Fe(VI)-CaO₂ system for degradation of contaminants was also superior to Fe(VI)-Na₂SO₃, Fe(VI)-NaHSO₃ and Fe(VI)-Na₂S₂O₃ systems under the same experimental conditions. Moreover, the effects of critical operating parameters, inorganic anions, inorganic cations, and humic acid on the degradation of SMX by Fe(VI)-CaO₂ system were revealed. The Fe(VI)-CaO₂ system exhibited good applicability in authentic water. Finally, the underlying degradation intermediates of SMX by Fe(VI)-CaO₂ system and their toxicity were confirmed. In conclusion, this study provides a new strategy for enhancing the oxidation capacity of Fe(VI) and comprehensively reveals the oxidation mechanism.

Keywords: Calcium peroxide; Ferrate; High-valent iron intermediates; Sulfamethoxazole.