Per- and polyfluoroalkyl substances (PFAS) are used throughout industry, from fluoropolymer coatings and firefighting foams to semiconductor and fluorochemical manufacturing. The strength of the C–F bond gives them their value and makes them the so-called “forever chemicals”; as a result, they resist degradation, migrate through water and soil, and accumulate in humans. PFAS exposure is associated with liver and thyroid disorders, immune suppression, and cancer. Drinking-water limits are now set at tens of ng/L or below. Destructive treatment that defluorinates PFAS, rather than moving them to another medium, is therefore a critical field of study. Short-chain PFAS (≤C8) are the hard case: they pass through the foam-separation and activated-carbon trains that retain long-chain species. Non-thermal plasma in contact with water has been shown to destroy PFAS effectively, yielding fluoride and shorter-chain products [1,2]. However, when the discharge acts on the bulk liquid, most of its energy goes into the water rather than the solute.
     This study uses a self-concentrating rotating-disk reactor. A polymer disk rotates through the wastewater, and PFAS adsorb onto its surface. The loaded surface is then removed from the liquid and exposed to a pulsed surface discharge, so the plasma acts only on the adsorbed layer. To simulate this condition, a high-density polyethylene (HDPE) disc was pretreated with pulsed plasma in Ar/H₂O (5 µs pulses at 1 kHz and 8 kV) to hydrophilize the surface and increase PFAS adsorption. After soaking in PFAS-containing liquid (50 µg/L PFOA), the plate underwent the same plasma treatment for decomposition. Preliminary results show the loaded PFAS decomposed in place, but fluoride alone did not close the fluorine balance.
     Fluorine is quantified by combustion ion chromatography (CIC; AQF-5000H, Nittoseiko Analytech) directly on the plate, and by ion chromatography and LC-MS (LCMS-2020, Shimadzu) in the liquids. Organic and inorganic fluorine are split using a carbon adsorption unit (TXA-04, Nittoseiko Analytech). A sealed modular chamber designed for the plate enables a full fluorine mass balance across the plate, wash liquid, and exhaust gas; thus, decomposition can be reported as a mineralization ratio.
This research is based on results obtained from a project, JPNP14004, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

1. Singh, R. K.; Fernando, S.; Baygi, S. F.; Multari, N.; Mededovic Thagard, S.; Holsen, T. M., Environ. Sci. Technol. 2019, 53 (5), 2731–2738.
2. Ganzallo; Babalola; Holsen, T. M.; Mededovic Thagard, S., Chem. Eng. J. 2026, 531, 174175.

PFAS; pulsed surface discharge; plasma-treated HDPE; fluorine mass balance