Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7c. Ex Situ PFAS Destruction Technologies

Formatted Title:

Foam Fractionation Coupled with Hydrothermal Alkaline Treatment for Remediation of a PFAS-Impacted Fire Training Pond

Background/Objectives:

The use of per- and polyfluoroalkyl substances (PFAS) in manufacturing processes, consumer goods, and firefighting foams has resulted in widespread need to remediate sites with PFAS-contaminated soil and groundwater. PFAS-impacted matrices require sophisticated treatment train approaches to facilitate safe and complete remediation of contaminated media. Neither incineration nor landfilling of PFAS are attractive options, motivating a search for alternative PFAS treatment and destruction technologies.

Foam fractionation (FF) is a process that leverages the partitioning behavior of PFAS molecules to separate PFAS from aqueous matrices. Hydrothermal alkaline treatment (HALT) is an emerging PFAS destruction process for PFAS-rich liquids that takes place in high pH, subcritical water (T~350 C, P~25 MPa). When coupled, FF and HALT promise end-to-end treatment of PFAS-contaminated liquid matrices.

In this demonstration, two PFAS-impacted liquids were treated with ECT2’s Foam-X FF technology, and Aquagga’s HALT technology to facilitate separation and destruction of PFAS. A total of ~20,000 gallons were treated from a PFAS-impacted fire training pit (FTP), and rinse water from aircraft rescue and fire fighting (ARFF) truck cleanouts. The project site was at Fairbanks International Airport (FAI), and treatment operations were conducted in the summer and fall of 2023.

Approach/Activities:

ECT2’s FF system was mobilized to FAI for several weeks of operation, treating water from the FTP and from the prior ARFF cleanouts over two stages of single pass fractionation. Liquids were sampled in several locations to determine treatment performance, including (i) the system influent, (ii) the produced foamate, (iii) the raffinate after one stage of foaming, and (iv) the raffinate after two stages of foaming. Water quality parameters were also analyzed. After the PFAS-rich foam was produced, Aquagga’s HALT system was leveraged to treat the foam. The HALT system was operated in a continuous flow mode at a flow rate of 6 to 8 gallons per hour (gph). Power consumption was measured during operation, and PFAS destruction performance was assessed by measuring liquid samples for target PFAS compounds via a modified 537.1 method, and for free fluoride via ion selective electrode (ISE).

Results/Lessons Learned:

The FF system treated water with variable influent, typically 0.1 to 5 ppm PFOS and 10 to 50 ppb PFOA, the primary treatment targets. PFOS and PFOA were both removed >99.9% via FF and a highly viscous foamate was generated for further treatment by HALT. A media polish was used on the FF-treated water to ensure non-detect levels of PFOS and PFOA prior to discharge. Preliminary results from the HALT treatment of the PFAS rich foam showed >99.9% destruction of PFOS (~6 ppm to ND [<704 ppt]), PFOA (300 ppb to ND [<305 ppt]), PFHxS (5 ppm to 1 ppb), and 6:2 FTS (4 ppm to ND [<629 ppt]), which were the four analytes initially screened to assess treatment efficacy. The HALT system energy consumption was measured at ~1 kWh per gallon (~264 kWh per cubic meter) during steady state operation. Fluoride measurements showed 1.6 to 2.1 ppm of dissolved inorganic fluoride in the treated HALT effluent, suggesting a high degree of mineralization. More HALT data are expected over the next 6 months. Overall, the efficacy of the FF + HALT treatment train was demonstrated.

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Philip True