The objective of this Statement of Need (SON) was to develop an improved understanding of the transformation mechanisms, pathways, and kinetics of thermal destruction processes (i.e., thermal desorption, pyrolysis/gasification, incineration, etc.) aimed at treatment of materials laden with per- and polyfluoroalkyl substances (PFAS). Specific research areas of interest included:

• Development of sample collection protocols and analytical methods to identify and quantify specific products (products of incomplete destructions [PIDs], byproducts) generated in thermal processes and support closure of fluorine mass balances. These products are expected to exhibit a wide range of boiling points and polarities, and protocols are needed that effectively capture PIDs over a range of scales (bench-scale experiments to full-scale sampling campaigns). Furthermore, complementary analytical approaches (e.g., gas and liquid chromatography-high resolution mass spectrometry, 19F-nuclear magnetic resonance spectroscopy, Fourier transform infrared (FTIR) spectroscopy] are needed to characterize PFAS degradation pathways.
• Experimental determination of the effects of process-relevant operating conditions such as temperature, residence time, PFAS structure, PFAS concentration, co-occurring chemicals of concern (e.g., chlorinated solvents), and matrix composition (e.g., silicates, calcium) on PFAS destruction mechanisms, mineralization rates, and formation of PIDs and byproducts.
• Combination of experiments with theoretical and kinetic modeling to support mechanistic foundations for optimizing thermal decomposition of PFAS and minimizing PIDs and byproduct formation. Physical simulations or models that can be used to predict thermal-mediated reactions of PFAS occurring in AFFFs are of interest.
• Development of surrogate measurement parameters and analytical approaches (e.g., FTIR) for real-time assessment of PFAS destruction/mineralization efficiencies, as well as stack emission contents.
• Assessment of PFAS destruction efficiencies in thermal processes at multiple scales.
• Evaluation of directly controlled parameters (e.g., temperature, residence times, turbulence, fuel:oxygen:PFAS ratios) as well as indirectly controlled parameters (fluorine versus other radicals, additive/catalytic enhancements, matrix effects) on complete destruction of concentrated PFAS streams.

Proposals addressed one or more of the objectives listed above. Proposers were directed to review the document Summary Report: Strategic Workshop on Management of PFAS in the Environment for additional information on these research objectives. This document provides a summary of the March 2022 strategic workshop on PFAS in which research and demonstration needs were identified so as to improve the management and treatment of PFAS in the environment, ultimately reducing risk and site management costs.

Researchers had to provide the rationale for selected PFAS of study; at a minimum, measurement of the 40 PFAS that can currently be measured by U.S. EPA Method 1633 should be prioritized as possible. Treatment of PFAS at environmentally relevant concentrations is of particular concern, and proposed efforts should have reflected this concern or provide the rationale if different concentrations were proposed.

Research and development activities at laboratory-, bench-, and field-scale were considered. Work did not necessarily have to culminate in a field-scale effort.

Developing destruction technologies for improved management and treatment of PFAS-laden materials will help facilitate the establishment of more cost-effective and efficient remedial action plans that are protective of human health and the environment. The knowledge developed through this SON will improve the reliability and environmental sustainability of thermal treatment processes and expedite the cleanup and closure of PFAS-impacted sites.

PFAS are present in AFFF used by the DoD and other organizations to extinguish hydrocarbon fires. Different AFFF formulations have been used, but all contain a complex mixture of PFAS, including those of greatest regulatory concern - the perfluoroalkyl acids (PFAAs) and potential PFAA precursors. The Environmental Protection Agency (EPA) has recommended a Health Advisory Level for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), and several states have promulgated standards for PFOA, PFOS, and some of the related PFAAs.

It is critical to elucidate the mechanisms and pathways that underlie conventional and innovative thermal technologies for PFAS destruction. Thermal processes are defined as processes in which the temperature of the bulk medium (e.g., water, air, soil) is purposefully raised to a temperature exceeding 100°C. Example technologies include incineration, pyrolysis, supercritical water oxidation, and hydrothermal alkaline treatment. Both experimental and theoretical studies are needed to better understand the mechanisms, rates, and products of the most important pathways by which PFAS transform and mineralize under process-relevant operating conditions (temperature, residence time, reactant concentrations, waste stream composition, gaseous/ condensed phases). Important PFAS thermal decomposition mechanisms include combustion, pyrolysis, oxidations, reactions with radicals such as H abstractions, hydrolysis, elimination, and other reactions. Information on the formation and stability of the PIDs and other byproducts is particularly important to support the design and operation of thermal technologies and ensure that treatment targets are met and undesired product formation is minimized. Understanding PID and byproduct formation may also inform the characterization of source zones at firefighting training sites and inhalation exposure of firefighters using AFFF.

PFAS represent a highly diverse chemical family with a significant range in physiochemical properties and, thus, multiple processes are likely to simultaneously occur across a range of temperatures and other operating conditions. In general, studies have demonstrated that desorption and volatilization of PFAS occurs at relatively lower temperatures (e.g., <700oC), but the possibility exists for some PFAS to transform within the thermal desorption range of others. For a specific suite of conditions, understanding the temperature range where more recalcitrant PFAS become volatile and desorb relative to where other more labile PFAS begin to transform is of critical importance since most AFFF-impacted sites are often characterized by the presence of highly complex mixtures of many PFAS.

The cost and time to meet the requirements of this SON were at the discretion of the proposer. Proposers submitting a Standard Proposal had to provide the rationale for this scale. The two options were as follows:

Standard Proposals: These proposals describe a complete research effort. The proposer should incorporate the appropriate time, schedule, and cost requirements to accomplish the scope of work proposed. SERDP projects normally run from two to five years in length and vary considerably in cost consistent with the scope of the effort. It is expected that most proposals will fall into this category.

Limited Scope Proposals: Proposers with innovative approaches to the SON that entail high technical risk or have minimal supporting data may submit a Limited Scope Proposal for funding up to $250,000 and approximately one year in duration. Such proposals may be eligible for follow-on funding if they result in a successful initial project. The objective of these proposals should be to acquire the data necessary to demonstrate proof-of-concept or reduction of risk that will lead to development of a future Standard Proposal. Proposers should submit Limited Scope Proposals in accordance with the SERDP Core Solicitation instructions and deadlines.