Removal of sulfamethoxazole by Fe(III)-activated peracetic acid combined with ascorbic acid

Ascorbic acid (AA) was used as a reducing agent to improve the Fe(III)-activated peracetic acid (PAA) system for the removal of sulfamethoxazole (SMX) in this work. The efficiency, influencing factors and mechanism of SMX elimination in the AA/Fe(III)/PAA process were studied. The results exhibited that AA facilitated the reduction of Fe(III) to Fe(II) and subsequently improved the activation of PAA and H₂O₂. Various radicals, including organic radicals (e.g. CH₃C(O)O• and CH₃C(O)OO•) and hydroxyl radical (HO•), were rapidly formed from the activated PAA and H₂O₂, resulting in SMX removal. Increasing dosages of PAA and Fe(III) contributed to enhanced SMX degradation, while excessive PAA and Fe(III) did not further promote SMX degradation. Due to the radicals' quenching effect, excess AA hindered SMX elimination in the AA/Fe(III)/PAA process. The presence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>HCO</mml:mi></mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> and Cl^- inhibited SMX removal in this system, whereas <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>SO</mml:mi></mml:mrow><mml:mn>4</mml:mn><mml:mrow><mml:mn>2</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> and natural organic matter had little impact on SMX degradation. The transformation pathways of SMX in the AA/Fe(III)/PAA system included hydroxylation, bond cleavage and amino oxidation. This research provides a strategy to enhance the Fe(III)-activated PAA system for the elimination of refractory organic pollutants.