Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam

Abstract

The widespread use of aqueous film-forming foam (AFFF) for firefighting activities (e.g., fire training to extinguish fuel-based fires at aircraft facilities) has led to extensive groundwater and soil contamination by per-and polyfluoroalkyl substances (PFASs) that are highly recalcitrant to destruction using conventional treatment technologies. This study reports on the hydrothermal alkaline treatment of diverse PFASs present in AFFFs. Quantitative and semiquantitative high-resolution mass spectrometry analyses of PFASs demonstrate a rapid degradation of all 109 PFASs identified in two AFFFs (sulfonate-and fluorotelomer-based formulations) in water amended with an alkali (e.g., 1−5 M NaOH) at near-critical temperature and pressure (350 °C, 16.5 MPa). This includes per-and polyfluoroalkyl acids and a range of acid precursors. Most PFASs were degraded to nondetectable levels within 15 min, and the most recalcitrant perfluoroalkyl sulfonates were degraded within 30 min when treated with 5 M NaOH. 19 F NMR spectroscopic analysis and fluoride ion analysis confirm the near-complete defluorination of PFASs in both dilute and concentrated AFFF mixtures, and no stable volatile organofluorine species were detected in reactor headspace gases by the gas chromatography−mass spectrometry analysis. These findings indicate a significant potential for application of hydrothermal treatment technologies to manage PFAS waste streams, including on-site treatment of unused AFFF chemical stockpiles, investigation-derived wastes, and concentrated source zone materials.

Aerobic BTEX biodegradation increases yield of perfluoroalkyl carboxylic acids from biotransformation of a polyfluoroalkyl surfactant, 6:2 FtTAoS

“…The closest transformation product reported to date is the eight-carbon perfluorooctanesulfinate in aerobic transformation of N -ethyl perfluorooctanesulfonamido ethanol by activated sludge 24 and abiotic hydrothermal treatment of AFFF. 25…”

Thermal Decomposition of Anionic, Zwitterionic, and Cationic Polyfluoroalkyl Substances in Aqueous Film-Forming Foams

“…The authors observed a substantial PFOS removal of up to >99.9995% from the treated media . Strathmann and co-workers recently developed a hydrothermal treatment , that can effectively decompose a variety of PFASs at near-critical temperature and pressure (350 °C; 16.5 MPa) within 15–30 min …”

Validation of supercritical water oxidation to destroy perfluoroalkyl acids

“…T A B L E 5 Calculated E EM for example PFAS destruction technologies the conditions reported, which is expected given the lower temperature and pressure and enhanced reductive defluorination facilitated under alkaline treatment conditions (Wu et al, 2019) and could be optimized further (Hao et al, 2021).…”

“…Considering the range and average of the E EM of the non‐SCWO destruction technologies (1.9 × 10 1 –1.5 × 10 7 ; μ = 2.0 × 10 6 ; n = 12; σ = 4.0 × 10 6 ), the E EM of this SCWO validation study is less than the average and considerably more PFAAs mass was treated. It is notable that the calculated E EM associated with alkaline hydrothermal treatment (∼350°C and <16.5 MPa) is approximately 94% lower than SCWO for the conditions reported, which is expected given the lower temperature and pressure and enhanced reductive defluorination facilitated under alkaline treatment conditions (Wu et al, 2019) and could be optimized further (Hao et al, 2021).…”

“…Since its introduction in the 1980s from work at the Massachusetts Institute of Technology, SCWO has been thoroughly reviewed throughout the literature for various applications and potential challenges, and various patents have been pursued and awarded (Hong & Spritzer, 2002;Krause et al, 2022;Kritzer & Dinjus, 2001;Marrone, 2012;Pinkard et al, 2021;Tester et al, 1993;Yesodharan, 2002). Recent research on the applicability of highpressure thermal treatment (e.g., SCWO and alkaline hydrothermal treatment) has demonstrated a high degree of certainty for the complete mineralization of perfluorooctane sulfonic acid (PFOS) in water (Krause et al, 2022;Pinkard et al, 2021;Wu et al, 2019), PFAS within wastewater treatment sludge (Yu et al, 2020), and PFAS associated with aqueous film-forming foam (AFFF) (Hao et al, 2021;Pinkard, 2022). The theorized mechanism of SCWO facilitated destruction is thermal oxidation of PFAS, resulting in fully mineralized carbon dioxide and inorganic fluoride, though instantaneous sequential defluorination reactions related to chemical oxidation and/or reduction via manipulated pH may also occur (Wu et al, 2019).…”