The overall objective of this project is to demonstrate and validate that colloidal gas aphrons (aphrons) provide a solution to the poor removal of short-chain per- and polyfluoroalkyl substances (PFAS) from water by current separation processes. This project will test both 1) a novel aphron separation technology capable of removing short-chain PFAS and precursors from water streams, and 2) a new modified plasma treatment system capable of directly utilizing aphrons in the reactor to improve the removal of short-chained PFAS. The project team envisions that aphron separation can also be coupled with other separation processes (e.g., surface active foam fractionation), with other concentrate destruction technologies (e.g., supercritical water oxidation), or with concentrate disposal in landfills. In addition, this project will test if existing, off-the-shelf aphron generation equipment used for commercial water treatment problems (e.g., removal of suspended solids) can be repurposed to make PFAS treatment via aphrons a simple, turn-key operation.
Aphrons are microstructures comprised of water and air with multiple layers of surfactants that are formed by mixing gases, water, and surfactants in a high-shear environment. Aphrons are are significantly smaller than conventional air bubbles. Obtaining diameters of approximately 10-100 µm, aphrons have ~100x greater contact area as compared to typical air bubble diameters (e.g., diffuser plate pore sizes) of 100–50,000 µm. More importantly, using a cationic surfactant will create aphrons with positive electrostatic surface charges that can be used to adsorb anionic water chemicals such as perfluoroalkyl acids. While more stable than simple gas bubbles, aphrons naturally coalesce back into a liquid phase, resulting in a concentrate comprised of surfactant, water, and the PFAS that were previously adsorbed to the aphrons. Aphrons can be generated using any surfactant depending on the treatment process requirements, including either anionic or cationic surfactants.
Bench-scale laboratory experiments using aphrons performed at Clarkson University showed that removals of ultra-short chain (triflate), and short-chain (perfluorobutanoic acid, perfluorobutanesulfonic acid) PFAS with a treatment time of 10 minutes were as follows: 60-90% (ultra-short chain), and 91-95% (short-chain). In addition, the ability for aphrons to be used in a continuous flow reaction to remove a PFAS surrogate dye (methylene blue which is a proxy for short-chain PFAS), was successfully demonstrated by GSI Environmental Inc. where their 1 gpm aphron separation system removed 91% of the PFAS surrogate dye. The plasma technology that the aphron technology will be coupled with has been demonstrated successfully at several field sites. It uses electricity to convert water into a mixture of highly reactive species (i.e., plasma) that rapidly and non-selectively degrade a broad spectrum of PFAS. Since this process requires the PFAS to be present at the interface adjacent to where the plasma is generated, there is likely significant synergy by combining plasma with aphron technology to destroy PFAS in water.
The key benefit is a new, potentially high efficiency method to remove and destroy short-chain PFAS from water. This project will leverage the existing ESTCP investment in plasma reactors to make a more flexible, cost-effective treatment system capable of separating and destroying the entire range of short- to long-chain PFAS. Additionally, aphron-based separation processes for PFAS could be used to augment/improve other separation processes or as a low-cost separation unit where PFAS concentrate is managed by disposal in landfills or other destructive technologies. If successful, aphron-based separation processes will make treating PFAS-impacted water more robust, reliable, cost effective, and easy to add to existing treatment systems. (Anticipated Project Completion - 2025)