A novel synergistic three-dimensional electrode system for emerging contaminants degradation: Significantly enhanced Mn(III)aq generation by organic pollutants and GAC

Currently, the electro-activated permanganate (PM) process, as one of the reactive manganese species (RMnS)-based advanced oxidation processes, has shown great potential for environmental remediation. However, the activation efficiency of PM in the electro-activated PM (E-PM) process is limited due to the poor mass transfer and electron transfer efficiency in the two-dimensional (2D) process. In this study, to overcome these drawbacks, granular activated carbon (GAC) was introduced as particle electrodes, establishing an efficient three-dimensional (3D) electrode process (E-GAC-PM), which promoted the generation of RMnS. Comparative experiments exhibited the significant synergy between PM and the 3D electrode process, resulting in the highest diclofenac (DCF) removal (90.2 %) with the lowest energy consumption. Electrochemical impedance spectroscopy and Tafel curve showed that the addition of GAC greatly attenuated the electrochemical impedance, facilitating the activation of PM. Further studies revealed that GAC can serve as an electron mediator, transferring electrons from contaminants to PM, thereby generating Mn2+ and promoting Mn(III)aq formation. Meanwhile, in-situ generated Mn2+ can also be oxidized by the anode and particle electrodes into Mn(III)aq. Besides, the in-situ generated MnO2 facilitates the performance via oxidation and catalysis effects. Under the protection of the electric field, GAC showed a relatively stable performance which could be regenerated and maintain active after 10 cycles. All these results demonstrated that the E-GAC-PM process was an efficient, energy-saving, and sustainable method for refractory organic contaminants removal, which showed potential for practical application.