Insight into mechanism of arsanilic acid degradation in permanganate-sulfite system: Role of reactive species

This work investigated the fast degradation of ASA by a novel advanced oxidation process (permanganate (Mn^VII)-sulfite (S^IV)). The results showed that the combination of Mn(VII) (50 μM) and S(IV) (250 μM) at pH 5.0 triggered near-instantaneous decomposition of ∼71% ASA (5 μM) within 15 s. The reaction parameters, which affected the degradation of ASA, such as pH (4.0–9.0), initial concentration of ASA (1–30 μM), and molar ratio of S(IV)/Mn(VII) (1–20), were systematically investigated. Specifically, sulfate radical (SO₄ ^[rad]−), hydroxyl radical (^[rad]OH), and Mn intermediates were considered as the important reactive species in Mn(VII)-S(IV) process. Radical scavenging tests showed that both SO₄ ^[rad]− and ^[rad]OH contributed to the removal of ASA, with SO₄ ^[rad]− playing a dominant role. The contributions of reactive radicals, which were excluded in Mn(VI)-S(IV) system by previous researchers, for the degradation of organic contaminants was clarified for the first time. Therefore, our study can be considered as a necessary complement to previous studies about Mn(VII)-S(IV) system. Halide ions inhibited the removal of ASA following a trend of F⁻ < Cl⁻ < Br⁻ < I⁻ due to their competition for reactive radicals with ASA. The degradation products of ASA were identified, and the plausible reaction pathways were proposed, and their toxicity was assessed using luminescent bacteria Vibrio fischeri. Finally, the satisfying performance of Mn(VII)-S(IV) system in a natural water sample indicated it was a promising method for degrading organic contaminants in real water.