The objective of this Statement of Need (SON) was to develop an improved understanding of various per- and polyfluoroalkyl substance (PFAS) concentration technologies in both in situ and ex situ applications. Specific objectives of this SON included the following:

• Develop a framework to predict the performance of full-scale sorption processes for PFAS removal from bench-scale data.
• Understand fundamentals of PFAS adsorption-desorption behavior in mixtures for commercially available sorbents.
• Develop and test conventional or novel adsorbents for capture of treatment off-gases containing PFAS and reaction byproducts.
• Develop novel and existing adsorbents to capture PFAS poorly adsorbed by granular activated carbon (GAC) and ion exchange.
• Develop and validate novel soil amendments for larger-area applications in PFAS secondary source areas.

Proposals may address one or more of the objectives listed above. Proposers should 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. Proposals may address one or more of the objectives listed above. Proposers should review the recently published 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 are proposed.

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

Research should lead to improved management of PFAS sites by facilitating the establishment of more cost-effective and efficient remedial action plans that are protective of human health and the environment. The improved remediation approaches that will be developed through this SON will increase the reliability of treatment processes and expedite the cleanup and closure of Department of Defense (DoD) impacted sites.

In recent years, a number of conventional and novel sorbents have been studied at the bench-scale to evaluate their potential to remove PFAS from water. Many of these studies were designed to support the use of the sorbents in ex situ packed-bed sorption processes. However, it is not always clear what data should be collected at the bench-scale to make accurate predictions of sorbent performance during full-scale applications. One common approach is the rapid small-scale column test (RSSCT); the RSSCT approach was developed decades ago and provides scaling equations to enable the design of a small-scale column that simulates the performance (i.e., breakthrough) of a full-scale packed-bed sorption process. The RSSCT scaling equations rely on knowledge of the sorption kinetics and affinity of a sorbent as a function of particle size and the mechanisms that control mass transfer of the sorbate to the binding sites on the sorbent. These scaling equations have previously been developed for activated carbon and for sorbates that exhibit specific mechanisms of mass transfer. It is unclear whether these scaling equations are useful when evaluating other conventional sorbents (i.e., ion exchange resins) or novel sorbents that exhibit unique sorption mechanisms. It is likewise unclear whether one set of scaling equations will adequately simulate the breakthrough of complex mixtures of PFAS that may have variable diffusion coefficients, or the extent to which background water constituents (e.g., natural organic carbon, anions) impact scale-up in the context of PFAS remediation. There is a critical need to evaluate existing experimental frameworks (i.e., RSSCTs) or to develop and validate novel experimental frameworks to simulate the performance of full-scale adsorption processes for PFAS.

The adsorption behavior of PFAS mixtures on commercially available sorbents, such as activated carbons and ion exchange resins, has received only limited attention in the scientific literature. Additionally, the effects of co-constituents (e.g., natural organic matter), solution properties (e.g., pH, dissolved salts), and co-occurring chemicals of concern (e.g., chlorinated organic compounds) on the adsorption characteristics of PFAS mixtures are largely unknown. To accurately predict competitive adsorption of PFAS mixtures, data are needed for a range of concentrations across a range of molar ratios that are representative of surface and groundwater impact encountered at DoD sites. Furthermore, there is a need to understand the effects of experimental parameters on PFAS desorption (release), adsorption and desorption kinetics (mass transfer), and non-ideal behavior (hysteresis). Data collected from these studies will support the development of multi-component mathematical models that accurately describe the adsorption-desorption behavior of PFAS mixtures on commercially available sorbents over a range of relevant concentrations and environmental conditions.

Development of technologies for treatment of vapor phase PFAS is also of interest. A number of in situ and ex situ treatment technologies that have been proposed to treat PFAS-impacted soil and groundwater are likely to generate vapor streams containing volatile PFAS species that will need to be captured to prevent release into the environment. Whereas vapor-phase GAC systems are likely to be used for off-gas treatment, the performance of vapor-phase GAC systems for PFAS is largely unknown. Furthermore, vapor-phase GAC systems may not effectively remove short-chain length PFAS that may be generated during the treatment process (e.g., in situ thermal treatment) nor non-PFAS fluorocarbon products of incomplete destruction. Therefore, there is a need to develop and test conventional or novel adsorbents that provide effective removal of volatile PFAS generated during remediation activities.

In addition to vapor phase PFAS, treatment of short chain or ultrashort chain may be of increasing concern as the regulatory landscape evolves and toxicity data become available for a wider range of PFAS. Further, as PFAS destruction technologies come online, short-chain and ultrashort-chain PFAS may be generated due to incomplete mineralization of target PFAS. To meet this need, existing adsorbents are likely to be modified or refined and novel adsorbents with broader specificity will continue to be developed. To ensure a detailed and unbiased understanding of the adsorptive capacity, efficacy, and performance of novel adsorbents, fundamental research will be critical to the advancement and adoption of new materials for treatment of PFAS-impacted waters.

Various absorptive soil amendments may also play a critical role in mitigating PFAS transport at impacted sites. In particular, secondary sources with lower PFAS soil concentrations that occupy relatively large footprints may be amenable to treatment via these amendments. The goal of any novel amendment would be to reduce PFAS mobility and bioavailability through enhanced stabilization and retention in surface soils.

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 are 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.