New insights into degradation of emerging contaminants by S(IV)/Fe(VI) system in neutral water: Performance enhancement, reaction mechanisms and toxicity assessment

Abstract

This study proposes a novel approach to enhance the degradation of emerging contaminants (ECs) in neutral water using the S(IV)/Fe(VI) system and identifies the significant role of high-valent iron (Fe(V)/Fe(IV)) in selective oxidation. In the complex of bisulfite and sulfite (B1S3)/Fe(VI) system, the degradation rates and pseudo-first-order rate constants of sulfamethoxazole (SMX), carbamazepine (CBZ), 2,4-dihydroxybenzophenone (BP-1) and 4,4′-sulfonyldiphenol (BPS) were higher than those achieved with single S(IV) activation Fe(VI). The results were attributed to the dominance of Fe(V)/Fe(IV) in the selective oxidations which involved the participation of HO• and SO4•−. In addition, the degradation mechanisms of SMX, CBZ, BP-1, and BPS were proposed, and the acute toxicity, chronic toxicity, developmental toxicity, and bioaccumulation factors of the transformation products were assessed. The results showed that the removal of ECs by the B1S3/Fe(VI) system resulted in a reduction in toxicity. The effects of experimental conditions and water matrix on the removal of ECs were evaluated and achieved satisfactory results in three different real water samples. The B1S3/Fe(VI) system was capable of rapid degradation of ECs at relatively low S(IV) and Fe(VI) doses, and the ultimate products (SO42− and Fe(III)) promoted coagulation, indicating multiple application scenarios and tremendous engineering potential.