Destruction of PFAS in AFFF-impacted fire training pit water, with a continuous hydrothermal alkaline treatment reactor

Pinkard, Brian R.; Austin, Conrad; Purohit, Anmol L.; Li, Jianna; Novosselov, Igor

doi:10.1016/j.chemosphere.2022.137681

Cited by 12 publications

(11 citation statements)

References 30 publications

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“…This is consistent with findings from an earlier study, in which >99% destruction of most suspect analytes identified in AFFF was achieved within 15 min of the start of treatment with 1 M NaOH at 350 °C . The greater removal of PFCAs compared to PFSAs was consistent with trends observed in other media subjected to HALT, where the latter class requires harsher reaction conditions to accomplish destruction. − ,, This trend was confirmed in an NaOH-free control experiment (Figure S3), where little degradation of the adsorbed PFSAs was measured while complete degradation of the adsorbed PFCAs was observed.…”

Section: Resultssupporting

confidence: 91%

“…22 The greater removal of PFCAs compared to PFSAs was consistent with trends observed in other media subjected to HALT, where the latter class requires harsher reaction conditions to accomplish destruction. [21][22][23]26,30 This trend was confirmed in an NaOH-free control experiment (Figure S3), where little degradation of the adsorbed PFSAs was measured while complete degradation of the adsorbed PFCAs was observed. Effect of HALT on GAC Adsorption Characteristics.…”

Section: ■ Materials and Methodsmentioning

confidence: 82%

“…PFOS is a representative perfluoroalkyl sulfonic acid (PFSA), the class of PFASs that have been shown to be most recalcitrant to destruction during HALT treatment . In comparison to that of other classes of PFASs, effective destruction of PFSAs requires higher temperatures, longer reaction times, and higher NaOH concentrations. − ,, The results of HALT experiments using GAC preloaded with PFOS are presented in Figure a. Decay of PFOS is accompanied by stoichiometric fluoride ion release without a notable lag; LC-QToF-MS targeted and suspect screening analyses did not indicate the formation of stable fluoro-organic intermediates.…”

Section: Resultsmentioning

confidence: 99%

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Application of Hydrothermal Alkaline Treatment to Spent Granular Activated Carbon: Destruction of Adsorbed PFASs and Adsorbent Regeneration

Soker

Hao

Trewyn

et al. 2023

Environ. Sci. Technol. Lett.

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Granular activated carbon (GAC) adsorption is the most common technology applied to treat water contaminated with per- and polyfluoroalkyl substances (PFASs), but rapid exhaustion of the media necessitates frequent replacement and costly off-site thermal regeneration. Here, we extend the application of hydrothermal alkaline treatment (HALT), which uses strong alkali and near-critical temperatures and pressures (e.g., 350 °C, 16.5 MPa, and 1 M NaOH) to degrade and mineralize PFASs, to the regeneration of spent GAC. Mass balance experiments wherein a known mass of perfluorooctanesulfonate (PFOS) was adsorbed onto GAC prior to treatment showed that HALT achieved >99% destruction of PFOS and 96 ± 4% defluorination with no observed fluoro-organic intermediates [167 g L–1 GAC, 350 °C, 1 M NaOH, t rxn = 400 min, and 10–15 mg of PFOS (g of GAC)−1]. Treatment of GAC collected from a field pilot study also showed effective destruction of the range of adsorbed PFASs. Moreover, repeated HALT cycles did not significantly affect the GAC specific surface area, and similar adsorption isotherms for perfluoropentanoic acid and PFOS were recorded for virgin and HALT-treated GAC. These findings suggest a promising strategy for on-site regeneration of PFAS-contaminated GAC and other adsorbent media that may be an alternative to off-site thermal regeneration practices.

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Section: Resultssupporting

confidence: 91%

Section: ■ Materials and Methodsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

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Application of Hydrothermal Alkaline Treatment to Spent Granular Activated Carbon: Destruction of Adsorbed PFASs and Adsorbent Regeneration

Soker

Hao

Trewyn

et al. 2023

Environ. Sci. Technol. Lett.

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“…Continuous flow HALT (CF-HALT) was demonstrated to treat PFAS-impacted fire training pit water. 42 However, outside of this case study, the rates and kinetic pathways in the CF-HALT process have not been presented in the literature. Continuous flow hydrothermal systems are advantageous in practical applications and enable real-time process monitoring and control.…”

Section: Introductionmentioning

confidence: 99%

“…Continuous flow HALT (CF-HALT) was demonstrated to treat PFAS-impacted fire training pit water . However, outside of this case study, the rates and kinetic pathways in the CF-HALT process have not been presented in the literature.…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal Destruction and Defluorination of Trifluoroacetic Acid (TFA)

Austin,

Purohit,

Thomsen

et al. 2024

Environ. Sci. Technol.

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Per-and polyfluoroalkyl substances (PFAS) have received increased attention due to their environmental prevalence and threat to public health. Trifluoroacetic acid (TFA) is an ultrashortchain PFAS and the simplest perfluorocarboxylic acid (PFCA). While the US EPA does not currently regulate TFA, its chemical similarity to other PFCAs and its simple molecular structure make it a suitable model compound for studying the transformation of PFAS. We show that hydrothermal processing in compressed liquid water transforms TFA at relatively mild conditions (T = 150−250 °C, P < 30 MPa), initially yielding gaseous products, such as CHF 3 and CO 2 , that naturally aspirate from the solution. Alkali amendment (e.g., NaOH) promotes the mineralization of CHF 3 , yielding dissolved fluoride, formate, and carbonate species as final products. Fluorine and carbon balances are closed using Raman spectroscopy and fluoride ion selective electrode measurements for experiments performed at alkaline conditions, where gas yields are negligible. Qualitative FTIR gas analysis allows for establishing the transformation pathways; however, the F-balance could not be quantitatively closed for experiments without NaOH amendment. The kinetics of TFA transformation under hydrothermal conditions are measured, showing little to no dependency on NaOH concentration, indicating that the thermal decarboxylation is a rate-limiting step. A proposed TFA transformation mechanism motivates additional work to generalize the hydrothermal reaction pathways to other PFCAs.

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Available and emerging liquid treatment technologies for PFASs

DiGuiseppi,

Newell,

Carey

et al. 2024

Remediation Journal

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Per‐ and polyfluoroalkyl substances (PFASs) are present at a wide range of private sector facilities and United States (US) government installations, including those operated by the Department of Defense, the Department of Energy, the National Aeronauts and Space Administration, and other entities, as well as additional sites worldwide. Impacts have been identified in a range of environmental media including drinking water, groundwater, surface water, leachate, wastewater, soil, sediment, and soil gas. Treatment technologies to remove or destroy PFASs cost effectively have proven to be elusive to the industry. However, recent developments are bringing that goal close to reality for some media. This article has been prepared to address only liquid treatment technologies. Soil treatment technologies are presently a lower priority and may be addressed in future articles. The challenge of identifying and evaluating available and emerging liquid treatment technologies was put to the PFAS Experts Symposium in Houston, Texas, on June 7–8, 2023, which was attended by PFAS professionals and subject matter experts with a broad range of backgrounds. The discussions covered a variety of technical approaches and led to the preparation of this manuscript. This article strives to concisely summarize modern technical approaches that are potentially applicable to managing liquid media at PFAS‐impacted sites. Currently, ex situ sorbent technologies using granular activated carbon (GAC) and ion exchange (IX) resin are commercially available and most widely used. Other liquid technologies are summarized and current applications are presented to allow the reader to evaluate each technology for their particular use. This article is not intended to provide guidance on site‐specific design of treatment systems, but instead to serve as an update to earlier articles from this group and others addressing PFAS treatment technologies and related PFAS topics.

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Destruction of PFAS in AFFF-impacted fire training pit water, with a continuous hydrothermal alkaline treatment reactor

Cited by 12 publications

References 30 publications

Application of Hydrothermal Alkaline Treatment to Spent Granular Activated Carbon: Destruction of Adsorbed PFASs and Adsorbent Regeneration

Application of Hydrothermal Alkaline Treatment to Spent Granular Activated Carbon: Destruction of Adsorbed PFASs and Adsorbent Regeneration

Hydrothermal Destruction and Defluorination of Trifluoroacetic Acid (TFA)

Available and emerging liquid treatment technologies for PFASs

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