Modeling of Atmospheric Pressure Plasma Treatment of PFAS-Containing Water

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are organic molecules and water contaminants that are not easily degraded due to the strength of the C-F bond. However, plasma treatments have been shown to effectively decompose some PFAS in water. Since some PFAS molecules behave as surfactants (due to their hydrophilic acid headgroups and hydrophobic fluorinated tails) the breakdown of PFAS may be accomplished not only by solvated reactive species but also by reactive species in the gas phase, such as by electron-impact processes on the surface of the water. The remediation of PFAS molecules in water by an atmospheric pressure plasma producing a surface ionization wave (SIW) on the water was investigated using the 2D plasma hydrodynamics model nonPDPSIM. The model was modified to include reactions between gas phase species (radicals, electrons, ions) in the SIW and surfactants. The reactor consists of a high-voltage pin electrode above a water surface operated in Ar. Electron-impact dissociation cross-sections were calculated for four PFAS molecules (PFBA, PFBS, PFOA, and PFOS). The plasma-surface interactions between the SIW on the water and these surfactant molecules was investigated. The resulting rates of dissociation and products will be discussed.