Dielectric barrier discharge plasma activation and plasma bubble regeneration of biosorbents for perfluorooctanoic acid removal from water

Authors: S. Giannoulia, M.K. Daletou, S. Meropoulis, C.A. Aggelopoulos.

Abstract: The persistent nature of perfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA), poses serious environmental and health concerns due to their resistance to conventional treatment methods. In this study, a sustainable cold plasma approach was developed for the activation and regeneration of PFOA-loaded adsorbents. Among walnut shell (WS) biosorbent, halloysite nanoclay, and Ketjen black, WS showed the lowest adsorption capacity but the highest potential for plasma activation. Air-plasma treatment of WS in a nanosecond-pulsed dielectric barrier discharge (DBD) reactor induced significant surface and chemical modifications, as confirmed by SEM, BET, XPS, and point of zero charge analyses. Plasma activation slightly increased the specific surface area and introduced oxygen-containing functional groups, such as hydroxyl, carbonyl, and carboxyl moieties, enhancing PFOA removal to 88.8 % compared to 43 % for raw WS. Adsorption followed the Freundlich isotherm and pseudo-second-order kinetics, indicating multilayer interactions on a heterogeneous surface. Saturated WS were regenerated using argon-plasma bubbles, which removed surface‑bound PFOA and restored adsorption capacity. Regenerated WS maintained or improved adsorption capacity over multiple cycles, consistent with the presence of residual organic fluorine that enhances fluorophilic interactions. Activation and regeneration required low specific energy (2500 and 148 g-WS/kWh, respectively). This sequential air-plasma activation and argon-plasma bubble regeneration approach offers a green, cost-effective strategy for PFAS‑polluted biosorbent treatment.

Keywords: Perfluorooctanoic acid (PFOA), Cold plasma, Walnut shell biosorbent, Plasma activation and regeneration, Plasma bubbles, PFAS water remediation