The overall goals of this proof-of-concept project are to improve the understanding of the effects of cosolvents on hydrothermal treatment of per- and polyfluoroalkyl substances (PFAS) and co-occurring organic chemicals, and to apply optimal cosolvent-mediated reaction conditions to treat real-world PFAS-impacted concentrates and residuals. Recently, as part of SERDP project ER18-1501, it was observed that there were very promising results from a preliminary screening test on the effects of adding a cosolvent, methanol, on hydrothermal alkaline treatment (HALT) of perfluorooctanesulfonate (PFOS) and trifluoromethanesulfonate (TFMS). Results of these experiments showed that the addition of methanol to a HALT reaction (300°C, 1 M NaOH, 60 min, 60% v/v methanol:water) increased defluorination of PFOS and TFMS up to seven-fold (75% defluorination compared to 10-14% without methanol addition). The exceptional enhancement observed suggests significant potential of applying cosolvent to enhance hydrothermal treatment of PFAS and co-occurring organic chemicals (e.g., trichloroethene and 1,4-dioxane) at milder reaction conditions (e.g., lower temperatures, alkali concentrations, and shorter reaction time).

Initial experiments will be conducted to screen the effects of cosolvent identity on the hydrothermal reactivity of TFMS (the most recalcitrant PFAS identified to date). A variety of common water-miscible cosolvents and a full set of reaction conditions will be tested. Then, with optimal reaction conditions and cosolvent screened from hydrothermal treatment of TFMS, evaluation of whether cosolvent effects on enhanced TFMS defluorination can be extended to other PFAS and co-occurring chemicals. Moreover, experiments and analyses will be undertaken to identify mechanisms responsible for cosolvent-enhanced PFAS destruction. Finally, the project team will apply optimized cosolvent-enhanced hydrothermal treatment processes to real-world PFAS-impacted concentrates and residuals, including ion exchange resin regeneration solutions, soil wash and fire-fighting truck rinsate, foam fractionate, and spent granular activated carbon. The project team will also evaluate cosolvent reuse and the effects of cosolvent use on reactor corrosion.

Successful completion of this project will provide an improved cost-effective hydrothermal approach for addressing PFAS-impacted materials with co-occurring organic chemicals. The multiple strengths of hydrothermal treatment with a cosolvent include enhanced PFAS and co-occurring chemical destruction, recycling of cosolvents, reduced reactor corrosion, lower energy requirements, and easy translation to on-site remediation. This will be particularly beneficial for treating concentrate samples that often contain complex matrices (e.g., elevated background dissolved organic matter) that are difficult to treat with most available technologies. The investigation of cosolvent-enhanced PFAS destruction will also provide novel defluorination mechanisms that could be applied to design other effective PFAS treatment approaches. Development of new PFAS treatment technologies will result in cost-effective, field-ready solutions that support defending the homeland and ensuring installations remain mission-capable while safeguarding critical defense infrastructure and the workforce. (Anticipated Project Completion – 2027)