PFAS Destruction in IX Still Bottoms with Plasma Vortex Technology

Abstract

The present study investigated the feasibility of remediating per- and polyfluoroalkyl substances (PFAS)-contaminated groundwater using a combined regenerable ion exchange (IX) and plasma treatment approach at Joint Base Cape Cod in Massachusetts. Approximately 1,200,000 L of groundwater was treated with regenerable IX, meeting the treatment goal of 20 nanograms per liter sum of perfluorooctanesulfonate, perfluorooctanoate, perfluorohexanesulfonate, perfluorononanoate, perfluorheptanoate, and perfluorodecanoate. After IX media regeneration with a solvent brine solution, 45 L of a distilled PFAS concentrate (“still bottom”) containing approximately 640 mg per liter total PFAS was recovered, representing an overall process concentration factor of approximately 30,000. A novel plasma vortex technology was employed to destroy the PFAS in the still bottom, which destroyed 97% of the PFAS initially present in a 25% diluted still bottoms, with 99% of the destroyed PFAS recovered as inorganic fluoride. The energy consumption of the plasma vortex process treating the dilute still bottoms was 1885 kW h/m³, or 12,140 kW h/kg PFAS destroyed. The treated still bottom was further reduced to nondetectable PFAS levels using reverse osmosis (RO) treatment, with the RO retentate returned to the plasma treatment system, thus creating a completely closed loop for plasma-treated regenerant waste with no liquid discharge.

Plasma vortex treatment, followed by reverse osmosis, resulted in a 99.99% PFAS destruction with no liquid discharge. TOF-8, calculated from the measured concentrations of 8 individual PFAS compounds, and inorganic fluoride ion (F-) as a function of plasma treatment time in a plasma vortex reactor.