Dielectric barrier discharge plasma combined with peroxydisulfate for efficient regeneration of waste granular activated carbon: Enhancing micropore recovery

In this study, we investigated the synergistic effects of air-purging dielectric barrier discharge (DBD) plasma and peroxydisulfate (PDS) on the regeneration of Volatile Organic Compounds (VOCs)-loaded waste granular activated carbon (wGAC). In a closed-loop circulative mode, the optimized plasma regeneration (1 LPM air flow and 1 h operation) achieved a maximum efficiency of ∼40%, with the addition of PDS to plasma significantly increasing regeneration. An optimal PDS/wGAC ratio of 0.071 mmol g⁻¹ yielded the highest regeneration efficiency of 81% (phenol tracer), exhibiting a two-fold increase compared with plasma alone. Scavenger studies identified ¹O₂ as the primary activator of PDS. Electron spin resonance (ESR) trapping experiments confirmed the generation of SO₄^•− and •OH, and highlighted the synergistic reactive oxygen species (ROS) production in plasma-PDS. Characterization of the regenerated GAC (rGAC) using N₂ adsorption-desorption, FE-SEM, EDS, and XPS confirmed effective VOCs removal and pore structure restoration. Compared with other reported technologies, plasma-PDS demonstrated superior micropore regeneration, which is crucial for VOC removal, with rGAC achieving over 96% micropore volume recovery compared with the new GAC (nGAC). Recycling of the process water for four cycles maintained a stable regeneration efficiency of 74%, demonstrating the economic and sustainability potential of plasma-PDS for wGAC regeneration. Notably, effective wGAC regeneration depends on the different lifetimes of the reactive species. While ¹O₂ and •OH are involved, the much longer-lived SO₄^•− generated from the reaction between ¹O₂ and PDS is the one that allows deep penetration into the GAC pores for efficient pollutant degradation. This synergistic plasma-PDS activation significantly enhanced regeneration, offering a sustainable solution.