Degradation of diclofenac aqueous solutions in a 3D electrolytic reactor using carbon-based materials as pseudo third electrodes in fluidized bed, anodic and cathodic configurations

In this study, the degradation of diclofenac (DCF) in a 3D electrochemical reactor was evaluated. Several parameters were studied including the reactor configuration: fluidized bed (FB), anodic packed bed (APB) and cathodic packed bed (CPB); and the type of pseudo third electrode material: granular activated carbon (GAC) and granular expanded graphite (GEG). The configuration that showed the highest total organic carbon (TOC) removal was the APB, with values up to 85%. In addition, when the substrate saturation of the pseudo third electrode was 20% in the APB, the energy consumption was 2.5 times lower than the conventional 2D reactor. This efficient conversion was the result of improved contacting and reaction between hydroxyl (HO•) and sulfate (SO4•-) radicals electro-generated on the anode surface and DCF adsorbed on the particulate carbon. While the degradation efficiency with the 3D CPB reactor was higher than the FB configuration, it was less effective than the 3D APB reactor because of H2O2 production in the cathode, which decomposed to generate HO•, but only slowly and not sufficiently to oxidize DCF to a significant extent. Furthermore, it was also found that when two 3D APB reactors were connected in series a more significant TOC decrease (98%) and lower energy consumption (4 times) could be achieved than in a single 2D reactor configuration. This result demonstrated that the 3D electrochemical process can be cheaper and faster. All these results highlight the 3D anodic electro-oxidation process as a potential technology to efficiently treat recalcitrant contaminants of emerging concern. [Display omitted] •Packed bed anodic 3D reactor configuration has the highest DCF mineralization.•DCF anodic oxidation promotes indirect degradation by the production of radicals.•Cathodic 3D reactor configuration favors the desorption of the pollutant.•Higher TOC removals were achieved at highest current density for GAC and GEG.•Attrition and long electric current contact tend to damage GAC and GEG.