Highly Efficient\nDegradation of Emerging Contaminants\nwith Sodium Bicarbonate-Enhanced Mn(II)/Peracetic Acid Process: Formation\nand Contribution of Mn(V)

Organic ligands have been extensively used to enhance\nthe catalytic\nperformance of manganese ion (Mn(II)) for peracetic acid (PAA). In\nthis study, sodium bicarbonate (NaHCO<sub>3</sub>), an economical\nand eco-friendly inorganic ligand, was introduced to enhance the degradation\nof emerging contaminants (ECs) in the Mn(II)/PAA process. NaHCO<sub>3</sub> could significantly improve the oxidizing ability of the\nMn(II)/PAA process over the initial pH range of 3.0–11.0. Mn(V)\nwas identified as the primary reactive species for degrading naproxen\nin the NaHCO<sub>3</sub>/Mn(II)/PAA process. HCO<sub>3</sub><sup>–</sup> could complex with Mn(II) to generate Mn(II)-HCO<sub>3</sub><sup>–</sup>, which has a lower redox potential to enhance the\ncatalytic activity of Mn(II). Mn(II)-HCO<sub>3</sub><sup>–</sup> reacted with PAA to produce Mn(III)-HCO<sub>3</sub><sup>–</sup> and CH<sub>3</sub>C(O)O<sup>•</sup>. Mn(V)-HCO<sub>3</sub><sup>–</sup> was generated via two-electron transfer between\nMn(III)-HCO<sub>3</sub><sup>–</sup> and PAA. Although organic\nradicals were detected in the NaHCO<sub>3</sub>/Mn(II)/PAA process,\nnaproxen was mainly degraded by Mn(V)-HCO<sub>3</sub><sup>–</sup> via one-electron transfer along with the formation of MnO<sub>2</sub>. Notably, the coexisting hydrogen peroxide was vital in the reduction\nof MnO<sub>2</sub> to Mn(II/III), thereby enhancing the continuous\ngeneration of Mn(V)-HCO<sub>3</sub><sup>–</sup>. NaHCO<sub>3</sub>/Mn(II)/PAA process exhibited exceptional oxidation performance\nin actual water samples. This study proposed a strategy utilizing\nan eco-friendly inorganic ligand to address the inherent drawbacks\nof organic ligand-enhanced Mn(II)/PAA processes and highlighted its\npotential applications in the removal of ECs.