Nonradical Activation of Peroxydisulfate with In Situ Generated Amorphous MnO2 in an Electro-Permanganate Process: Involvement of Singlet Oxygen, Electron Transfer, and Mn(III)aq

ABSTRACT: A novel water treatment process based on a combination of electrolysis (E) with permanganate (PM) and peroxydisulfate (PDS) was systematically investigated. The combination exhibited significant synergy in degrading refractory organics such as diclofenac (DCF), carbamazepine, and nitrobenzene. In comparison to E-PDS (20.45%, 12.448 kWh m-3) and E-PM (36.36%, 5.200 kWh m-3) processes, the E-PM-PDS process could mineralize 70.45% DCF within 180 min with the lowest specific energy consumption (1.007 kWh m-3). The mechanism study revealed that electricity could significantly promote the activation of PDS with the in situ generated amorphous MnO2 via nonradical pathways (1O2 oxidation and electron transfer), and the activated PDS, in turn, facilitated Mn(II)aq to generate reactive Mn(III)aq. In the E-PM-PDS process, DCF degradation was enhanced upon increasing PM dosage, PDS dosage, and current density, and also by decreasing the pH. Cations facilitated the DCF degradation with the order of positive effects as Fe3+ > Zn2+ > Ca2+ > Mg2+. The presence of humic acid (HA) significantly enhanced the DCF degradation, while the addition of HCO3- or HPO42- caused adverse effects. This work may provide a high-efficiency and low-cost technology for water treatment.