The Department of Defense (DoD) has many fire suppression systems impacted by residual entrained per-and polyfluoroalkyl substances (PFAS), as a result of the use of Class B foams such as aqueous film forming foam (AFFF). Amphiphilic PFAS are known to self-assemble in multiple bilayers to coat surfaces at liquid:solid interfaces to form a waterproof coating. Therefore, these layers of PFAS cannot be effectively removed from fire suppression systems by flushing with water. When replacement foam is added to a suppression system, legacy PFAS, such as perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS) and perfluorooctanoic acid (PFOA), can dissolve from the surfaces of the system and contaminate the new foam. An effective method to remove layers of PFAS from fire suppression infrastructure is required.

The objectives of this project are to optimize procedures for effective cleaning of fire suppression infrastructure to remove entrained PFAS firstly at the laboratory scale and then at field scale. The approach employs a field-tested biodegradable cleaning reagent. Specific objectives include:

1. Optimize the formulation of a cleaning reagent for PFAS removal from fire suppression systems,
2. Trial use of the optimized reagent considering soaking times and pressure washing,
3. Demonstrate that PFAS can be removed from the reagent using foam fractionation,
4. Demonstrate successful application of the reagent combined foam fractionation by repeat recirculation through fire suppression infrastructure at laboratory and field scale,
5. Create fire suppression system cleaning protocols, considering reagent composition, soak time and requirement for pressure washing, and
6. Develop a flushing curve for PFAS removal in an aircraft rescue and firefighting (ARFF) vehicle, hangar piping system and hangar AFFF tank, to inform the level of field cleaning efforts required.

The technical approach will optimize and develop an existing Arcadis protocol using a proven cleaning reagent for removal of self-assembled layers of PFAS from fire suppression systems and associated infrastructure. The technology comprises a combination of a cleaning reagent that solubilizes surface self-assembled PFAS and differing approaches for pressure washing tanks and pipework. The cleaning reagents comprise biodegradable, non-toxic aqueous mixture of alcohols, glycols and/or hydrocarbon surfactants, which have significantly higher capacity to dissolve high concentrations of PFAS than water as they can effectively solvate PFAS in aqueous solution. The cleaning protocol involves soaking the surface of fire suppression systems with the reagent for some time as this has advantages, enabling more effective PFAS solvation. Application of the reagent or water at high pressure after soaking also enhances the removal of layers of self-assembled PFAS from surfaces.

An optimized cleaning method to remove residual fluorinated AFFF from fire suppression systems and associated infrastructure will have widespread application and financial benefits to the DoD. The rebound of PFAS, including PFOS and PFOA into firefighting foams from fire suppression infrastructure can significantly contaminate more modern foams. The cost of replacing existing PFAS-impacted AFFF delivery infrastructure across all DoD installations would be prohibitively expensive and result in facility downtime. Treatment and recycling of effective cleaning agents will significantly reduce disposal costs by vastly diminishing waste volumes. Therefore, the development of an effective and standardized method to remove PFAS from existing infrastructure comprises a very important technology for use across DoD. (Anticipated Project Completion - 2023)

Horst, J., J. Quinnan, J. McDonough, J. Lang, P. Storch, J. Burdick, and C. Theriault. 2021. Transitioning Per- and Polyfluoroalkyl Substance Containing Fire Fighting Foams to New Alternatives: Evolving Methods and Best Practices to Protect the Environment. Groundwater Monitoring and Remediation, 41(2):19-26. doi.org/10.1111/gwmr.12444.

Lang, J.R., J. McDonough, T.C. Guillette, P. Storch, J. Anderson, D. Liles, R. Prigge, J.A.L. Miles, and C. Divine. 2022. Characterization of Per- and Polyfluoroalkyl Substances on Fire Suppression System Piping and Optimization of Removal Methods. Chemosphere, 308(2):136254-136363. doi.org/10.1016/j.chemosphere.2022.136254.