Activation of Metabisulfite by Dissolved Fe(III) at Environmentally Relevant Concentrations for Organic Contaminants...

Currently, iron-catalyzed low-valent sulfur species processes are regarded as potentially valuable advanced oxidation processes (AOPs) in wastewater treatment. As a commonly used low-valent sulfur species in the food industry, metabisulfite (MBS) can undergo decomposition to bisulfite when dissolved in water. Therefore, the combination of MBS with dissolved Fe(III) at environmentally relevant concentrations is proposed in this study to accelerate organic contaminants degradation while simultaneously minimizing the production of iron sludge. The results show that the Fe(III)/MBS process could degrade various organic contaminants, including acid orange 7 (AO7), and the removal efficiency of AO7 obeyed the pseudo-first-order kinetic. The rate constant values exhibited variations depending on the initial concentrations of Fe(III) and MBS, pH values, as well as the reaction temperature. Moreover, the contribution of HO^• and SO₄^•- to AO7 degradation was estimated as 51.59% and 46.45%, respectively. Furthermore, Cl^- showed a minimal effect while HCO₃^- and humic acid resulted in a significant inhibitory effect on AO7 degradation. The satisfactory degradation of AO7 was achieved in three real water bodies. Ultimately, the results of gas chromatography-mass spectrometry and the theoretical calculations greatly facilitate the proposal of AO7 degradation pathways, including N=N cleavage, hydroxylation, and hydrogen abstraction. The findings of this study indicate that the Fe(III)/MBS process may be a promising AOP for further application in organic contaminants degradation during wastewater treatment.