The use of aqueous film-forming foam (AFFF) for fire training and emergency response has led to per- and polyfluoroalkyl substances (PFAS) impact to soil, groundwater, and surface water. With the Department of Defense’s (DoD's) large number of AFFF-impacted sites requiring investigation, monitoring, and interim remedial activities, a large volume of solid and liquid investigation-derived waste (IDW) has been produced. The treatment and disposal of PFAS-containing IDW presents unique challenges as treatment technologies and best practices for handling and disposition are currently evolving. There is a significant need to treat PFAS-impacted solid IDW that is generated as part of soil removal actions. Few viable technologies are currently available for the treatment of PFAS-impacted solid matrices.

The main objective of this proof-of-concept project is to understand the technical feasibility of the application of supercritical water oxidation (SCWO) technology to destroy PFAS-impacted solid matrices in the form of a soil/sludge slurry. The first objective will involve building and testing the basic functionality of the bench-scale SCWO reactor. The second objective will evaluate PFAS destruction using a bench-scale reactor on spiked soil/sludges and evaluate the mass balance. Further, an assessment of the calcium hydroxide [Ca(OH)₂] addition on PFAS destruction will be performed. The third objective will demonstrate SCWO in treating PFAS-impacted solids collected from an AFFF-impacted DoD site.

This research aims to develop a SCWO destruction technology for the treatment of PFAS-impacted solid matrices to demonstrate PFAS destruction in soil/sludge slurries. The technical approach includes:

• building and testing a SCWO reactor to treat solids,
• investigating PFAS destruction on laboratory-spiked soil/sludges at two concentrations and understanding the mass balance by using different quantitative analytical techniques,
• evaluating the addition of Ca(OH)₂ on the destruction of PFAS,
• demonstrating SCWO on PFAS-impacted soil/sludge collected from a source located at a DoD site, and
• disseminating project findings to the DoD and research community.

This research will address the remediation of PFAS-impacted solid matrices by the development of a treatment technology using SCWO. The key benefits of applying SCWO technology to treat soil/sludges are:

1. SCWO is a scalable technology that destroys total PFAS and results in complete mineralization within short residence times,
2. SCWO is equally effective on short-chain and long-chain perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids,
3. Organic co-occurring chemicals, such as petroleum hydrocarbons and volatile organic compounds, can be destroyed along with PFAS, so no additional treatment is needed for co-occurring chemicals,
4. SCWO generates little or no harmful gas emissions, and
5. SCWO is readily mobilized and scaled for on-site, cost-effective treatment, avoiding the need to ship PFAS-impacted wastes off site.

The results of this proof-of-concept research will demonstrate the functionality of the reactor to treat solids and destroy PFAS.