A treatment train approach incorporating an upfront destruction technology will be utilized to destroy per- and polyfluoroalkyl substances (PFAS) in aqueous film-forming foam (AFFF) concentrate. While destructive PFAS technologies are typically most cost-effective treating low-volume, highly concentrated waste from a PFAS-concentrating technology, AFFF concentrate is already concentrated and thus a destructive technology that can treat larger volumes is desired for this application. A commercial-sized electrochemical oxidation (EO) system will serve as the destruction element followed by effluent polishing using surface active foam fractionation (SAFF) and adsorbent media (EO-SAFF treatment train). The concentrated waste produced by the SAFF system (referred to as foamate) will be fed back into the EO system for PFAS destruction. Because AFFF concentrate may contain total PFAS concentrations in the thousands of parts per million, polishing following EO can achieve low part per trillion discharge criteria. Specific technical objectives of this project include the following: Develop a technically and commercially viable EO-SAFF treatment train to treat AFFF concentrate. Optimize treatment train design and operation based on waste-specific characteristics. Quantify PFAS treatment effectiveness utilizing a fluorine mass balance, destruction efficiency based on mass removal, costs, and operational metrics.

EO has recently been demonstrated with Magnéli-phase Ti₄O₇ anodes as an efficient and reliable treatment technology for PFAS destruction in two ongoing SERDP projects (ER-2717 and ER18-1320). EO with Ti₄O₇ anodes degrades PFAS via direct electron transfer at the anode surface in concert with indirect oxidation by hydroxyl radicals and other reactive species produced on the anode. EO offers advantages over other technologies such as: scalability, flexibility to variations in waste composition and flow rate, no chemical addition, modular reactor design, and compatibility with other treatment technologies. Furthermore, the porous ceramic materials, Ti₄O₇, enables a reactive electrochemical membrane (REM) reactor configuration, in which the anode can also serve as a membrane providing a larger reactive surface area.

The commercial-scale EO system proposed for this project uses REM reactors. EO effluent will be treated further with SAFF to remove and concentrate PFAS. During foam fractionation, gas (ambient air) bubbles through an aqueous solution of amphiphiles (PFAS) that adsorb to the surface of rising bubbles. These bubbles form a froth/foam layer that is removed and collapsed to form a “foamate” liquid enriched in PFAS and leave behind residual liquid depleted of PFAS. A SAFF®05 unit is proposed for this demonstration and comprises two foam fractionation stages in series operating in a semi-batch mode. The first stage (primary fractionator) ‘strips’ PFAS from impacted feed and produces a PFAS-depleted rejectate that is then pumped from the bottom of the aeration vessel and sent to the ‘clean’ water discharge. The primary PFAS enriched foamate is fed into the second stage (secondary fractionation), which further concentrates PFAS to a factor of over 2,000:1. The concentrated foamate is fed back to the DE-FLUORO® system for PFAS destruction.

The described treatment train offers an effective approach for treating AFFF concentrate, integrating both PFAS destruction and waste minimization. It ensures PFAS levels in AFFF concentrate are reduced to low parts per trillion levels. The closed-loop system between SAFF and EO technologies minimizes waste, with the only PFAS waste being a small volume of adsorbent media. Leveraging over five years of EO technology development, the EO-SAFF treatment train provides a robust PFAS destruction system. AECOM and partners will continue to optimize, scale, and commercialize this technology, offering a solution for redundant AFFF stockpiles. Such advancements in large-scale PFAS remediation and destruction will contribute to sustainment of force readiness and the operational capacity of the defense industrial base, preventing disruptions to production and supply chains. (Anticipated Project Completion - 2027)