Critical role of oxygen for rapid degradation of organic contaminants in permanganate/bisulfite process

Organic contaminants can be oxidized rapidly in permanganate/bisulfite (PM/BS) process due to generation of Mn(III)_aq. However, the influence of O₂ and its role in contaminants degradation in PM/BS process are poorly understood. Thus, the influence of O₂ concentration on phenol removal was quantified and isotopic oxygen tracers (¹⁸O-labeled water and ¹⁸O₂) were employed to further unravel the mechanisms of PM/BS process. The introduction of O₂ to PM/BS process appreciably improved phenol oxidation. Under oxic conditions the oxidation products of bisulfite included SO₄²⁻ and HSO₅⁻ while SO₄²⁻ was the single stable oxidation product under anaerobic conditions. The oxygen isotope labeling experiments confirmed that HSO₅⁻ originated from the oxidation of SO₃^[rad]− by O₂ to SO₅^[rad]− and the following reduction of SO₅^[rad]− by HSO₃⁻. Incorporation of oxygen isotope from H₂¹⁸O to MnO₂ due to the disproportionation of Mn(III)_aq was observed, which verified the generation of Mn(III)_aq in PM/BS process. The critical influence of O₂ on PM/BS process was mainly associated with rapid oxidation of SO₃^[rad]− by O₂ to SO₅^[rad]−, which otherwise competed with target contaminants for Mn(III)_aq. Oxygen from H₂O and/or O₂ can also be incorporated in the degradation products of organics in PM/BS process.