Continuous crystal violet removal in a fluidized-bed three-dimensional electrochemical reactor: Particle-electrode pore accessibility, residual adsorption capacity and electrochemical regeneration

For efficient continuous treatment of refractory organic contaminants in three-dimensional electrode reactors, accessible mass-transfer pathways and regenerable adsorption sites in particle electrodes are both relevant to continuous treatment. Five industrial granular activated carbons (GACs) were evaluated as particle electrodes for crystal violet (CV) removal in a continuous fluidized-bed three-dimensional electrochemical reactor. For four GACs with comparable BET surface areas, removal increased from 74.10% to 91.42% as the t-plot external surface area increased from 25.00 to 235.37 m 2 /g. Across all five GACs, removal was most strongly associated with the capacity-normalized apparent uptake-rate constant. The selected GAC had a BET surface area of 985.60 m 2 /g, an external surface area of 565.67 m 2 /g, and an adsorption capacity of 77.51 mg/g. At the selected high-removal operating point (HRT, 1.0 h), CV, COD, and TOC removals were 97.60 ± 0.13%, 82.63 ± 0.30%, and 83.07 ± 0.11%. During continuous operation, residual adsorption capacity (RAC) stabilized at approximately 54.87 ± 1.75%, consistent with a dynamic adsorption-oxidation-regeneration balance. Across three treatment-regeneration cycles, late-stage CV removal was reproducible at approximately 95.5% during the second and third treatment stages, while RAC before the third regeneration was 52.23%. However, RAC and BET surface area did not fully recover even after subsequent exhaustive ethanol desorption. Therefore, pore-accessibility-related descriptors and RAC serve as complementary structural and operational criteria, respectively, for selecting particle electrodes, evaluating continuous-reactor performance, and designing three-dimensional electrochemical reactors for efficient continuous treatment of organic contaminants.