Per- and polyfluoroalkyl substances (PFAS) are a suite of man-made chemicals used for a variety of industrial and consumer applications since the 1950s due to their unique chemical properties. Given the surfactant like properties of many PFAS, they have been used as active ingredients in aqueous film-forming foams (AFFF) used to extinguish hydrocarbon fuel fires. PFAS are of concern due to their persistence in the environment and reported negative health impacts to aquatic organisms and humans. A significant source of PFAS is believed to be the historic use of AFFF used to extinguish chemical fires such as oils, gasoline, or jet fuel. Fluorine-containing AFFF is being phased out, accelerating the need for an effective transition from AFFF to fluorine free foams (F3). The transition from AFFF to F3 may pose a challenge with stockpiles of legacy AFFF and potentially, residual PFAS in fire suppression systems. Given the large number of firetrucks in the U.S. that have been exposed to AFFF and potentially require cleanout, developing an effective approach for firefighting delivery system cleaning prior to foam transition is of interest. In addition, cleanout of firefighting systems is likely to produce a significant amount of PFAS residual waste that requires treatment and/or disposal. Characterization of such rinsate emanating from firefighting system cleanout is also of interest to assess concentrations and types of PFAS and potential treatment options. 

The principal objectives of this research were as follows: 

1. To develop an effective rinsing procedure for removing AFFF components (i.e., PFAS) from AFFF delivery equipment. 
2. To perform a demonstration-scale evaluation of aircraft rescue firefighting (ARFF) cleanout. 
3. To utilize high-pressure membrane treatment to concentrate AFFF rinsing residuals.

This project systematically evaluated the removal of PFAS from fire suppression system components through laboratory- and demonstration-scale investigations. Bench-scale studies were first performed to investigate removal of PFAS from AFFF delivery and storage system piping, evaluate different rinsing agents and cleanout approaches, and develop a propylene glycol-based cleaning agent. In addition, a comprehensive evaluation of the PFAS separation performance of five commercial nanofiltration and reverse osmosis membrane in a closed-circuit desalination (CCD) configuration was evaluated at the pilot scale. After bench- and pilot-scale studies were complete, a demonstration-scale evaluation of ARFF cleanout was conducted to test the outcomes of the bench-scale studies including a rinsing protocol, a developed rinsing agent, and an optimized CCD system for treating and concentrating PFAS-laden rinsing residuals.

Experimental results indicate that the complete removal of PFAS from these systems is difficult as significant masses of PFAS reside on component surfaces that are difficult to remove with only rinsing. Although significant amounts of PFAS can be removed from these systems using various rinsing solvents, the slow desorption of PFAS from surfaces may result in PFAS being released over long periods of time.

Laboratory-scale research indicated that the use of physical scouring methods (e.g., sonication) can improve cleaning effectiveness; however, more research is needed to translate this finding to cleaning of fire suppression systems. Demonstration cleaning of an ARFF vehicle further highlighted the difficulty in near complete cleanout of PFAS residuals emanating from AFFF use. A relatively large amount of PFAS mass was removed from the studied ARFF vehicle through successive rinsing, with PFAS concentrations significantly decreased with each successive rinse. Rebound testing (one-month equilibration with potable water) on the ARFF vehicle, however, resulted in significant desorption of PFAS at concentrations greater than those seen during cleanout activities.

Closed-circuit desalination using nanofiltration or reverse osmosis membranes was determined to be an effective process for separating PFAS from impacted aqueous residuals and reducing the volume requiring disposal. Three membranes were identified during this project that can provide 99% and greater separation of a wide variety of PFAS, and a volume reduction (or product water recovery) of greater than 90% can be achieved using CCD systems. 

In general, the level of PFAS separation is inversely related to membrane permeability (i.e., more permeable membranes allow the partial passage of solutes including PFAS). As opposed to sorption-based technologies (e.g., granular activated carbon, ion-exchange), PFAS separation performance by tight nanofiltration (NF) and reverse osmosis (RO) membranes is similar regardless of chain-length. The use of tight NF or RO in high-recovery membrane systems may improve the prospects of applying PFAS destruction technologies by concentrating PFAS into a smaller volume requiring treatment. The successful completion of this demonstration will ultimately lead to more cost-effective PFAS management, directly benefiting the warfighter and installation communities. (Project Completion - 2024)

Safulko, A., T.Y. Cath, F. Li, B. Tajdini, M. Boyd, R.P. Huehmer, and C. Bellona. 2023. Rejection of Perfluoroalkyl Acids by Nanofiltration and Reverse Osmosis in a High-Recovery Closed-Circuit Membrane Filtration System. Separation and Purification Technology, 326:124867. doi.org/10.1016/j.seppur.2023.124867.