Application of permanganate in the oxidation of micropollutants: A mini review

As a green oxidant, permanganate has received considerable attention for the removal of micropollutants in drinking water treatment. To provide a better understanding of the oxidation of organic micropollutants with permanganate, the oxidation kinetics of 32 micropollutants were compiled. The pollutants include algal toxins, endocrine disrupting chemicals (EDCs), and pharmaceuticals. The oxidation kinetics of micropollutants by permanganate were found to be first order with respect to both contaminant and permanganate concentrations from which second-order rate constants (k″) were obtained. Permanganate oxidized the heterocyclic aromatics with vinyl moiety (i.e., microcystins, carbamazepine, and dichlorvos) by the addition of double bonds. For the polycyclic aromatic hydrocarbons (PAHs) with alkyl groups, permanganate attacked the benzylic C-H through abstraction of hydrogen. The mechanism for the oxidation of phenolic EDCs by permanganate was a single electron transfer and aromatic ring cleavage. The presence of background matrices could enhance the oxidation of some phenolic EDCs by permanganate, including phenol, chlorinated phenols, bisphenol A, and trichlosan. The toxicity of dichlorvos solution increased after permanganate oxidation, and the estrogenic activity of bisphnol A/estrone increased significantly at the beginning of permanganate oxidation. Therefore, the toxicity of degradation products or intermediates should be determined in the permanganate oxidation processes to better evaluate the applicability of permanganate. The influence of background ions on the permanganate oxidation process is far from clear and should be elucidated in the future studies to better predict the performance of permanganate oxidation of micropollutants. Moreover, methods should be employed to catalyze the permanganate oxidation process to achieve better removal of micropollutants.