Removal, Concentration, and Destruction of Per- and Polyfluoroalkyl Substances Using Foam Fractionation Coupled with Enhanced Contact Plasma

Abstract

Per- and polyfluoroalkyl substances (PFAS) can occur in groundwater at elevated concentrations due to use in numerous commercial and industrial applications. Foam fractionation, which utilizes the surfactant properties of air–water interfacial adsorption and foaming to recover surfactants from the aqueous phase, has recently been applied to remove PFAS from impacted waters. When coupled with a PFAS destructive technology such as enhanced contact plasma (ECP), the resulting treatment train may be capable of removing, concentrating, and destroying PFAS in a cost-effective and definitive manner. Because of their site-specific dependencies, a bench-scale treatability study was conducted to assess the feasibility of implementing a combined treatment train consisting of foam fractionation and ECP for cost-effective PFAS removal, concentration, and destruction for both a low- and a high-foaming water. In general, perfluoroalkyl acid (PFAA) removal efficacies via foam fractionation increased with increasing perfluorinated chain length for the high-foaming water. Additionally, perfluorinated sulfonic acids were removed more effectively than the corresponding perfluorinated carboxylic acids (PFCAs). Addition of a cationic surfactant such as cetrimonium bromide (CTAB) marginally improved the removal of short-chain PFCAs, such as PFBA and PFPeA, that are generally difficult to remove via foam fractionation. In addition to improved short-chain removal, CTAB addition also significantly improved the foam quality, thereby increasing the volume reduction potential by approximately 3 to 5 times. Negligible PFAA removal via foam fractionation was observed with the low-foaming groundwater. PFAS removal via aerosolization was demonstrated to be effective in achieving multilog PFAS reduction, particularly for long-chain PFAAs, and corresponded generally with their air–water interfacial adsorption coefficients. Overall, the bench-scale ECP system demonstrated successful removal of PFAS in the foam fractionate. Concentrations of 17 of the 19 detected PFAA precursors and short- and long-chain PFAS present in the generated foam fractionate were reduced to below detection limits during the 765-min ECP treatment period. This finding supports the premise of a treatment train (concentration via foam fractionation or aerosolization followed by destruction) approach for the treatment of PFAS-impacted water sources.