The dominant role of the peroxymonosulfate radical for removing contaminants in a Fenton process with metabisulfite

The accumulation of micropollutants in water effluents is calling for effective remediation methods such as the Fenton reaction catalyzed by the tetra-amido macrocyclic ligand-iron complex, yet the identification of the active species in this reaction is debated due to the presence of several reactants. Here we hypothesized that radical species are the main active species, rather that metal-based species. We studied phenol removal catalyzed by the iron complex with various reactants and quenchers at pH 7 and 10, and actives species were monitored by electron paramagnetic resonance in the presence of spin trappers. Results using the iron complex and metabisulfite show negligible phenol removal in the absence of dioxygen, or in the presence of ascorbic acid or 5,5-dimethyl-1-pyrroline-N-oxide. By contrast, in the presence of dioxygen, we observed a near complete removal and the presence of radical species. These findings reveal the involvement of the peroxymonosulfate radical, which can be easily produced from metabisulfite.