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

Recently, the enhancing role of hydrogen peroxide (H 2 O 2 ), a self-decay product of ferrate (Fe(VI)), on Fe(VI) reactivity has received increasing attention. In this study, we found that calcium peroxide (CaO 2 ) as a slow-releasing reagent of H 2 O 2 could also enhance the Fe(VI) performance for removing sulfamethoxazole (SMX). Compared with sole Fe(VI), sole CaO 2 and Fe(VI)-H 2 O 2 systems, the Fe(VI)-CaO 2 system showed higher reactivity to remove SMX. The radical scavenger and chemical probe test results indicated that the better oxidation performance of Fe(VI)-CaO 2 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)-CaO 2 system for degradation of contaminants was also superior to Fe(VI)-Na 2 SO 3 , Fe(VI)-NaHSO 3 and Fe(VI)-Na 2 S 2 O 3 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)-CaO 2 system were revealed. The Fe(VI)-CaO 2 system exhibited good applicability in authentic water. Finally, the underlying degradation intermediates of SMX by Fe(VI)-CaO 2 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.