Nanyang Yang, Yunqiao Guan, Shasha Yang, Qingquan Ma, Caitlyn Olive, Sujan Fernando, Wen Zhang, Thomas M. Holsen, Yang Yang
5 min
Aqueous film-forming foams (AFFF) are a major source of environmental PFAS contamination. Existing disposal methods, such as incineration, face regulatory hurdles, while nonthermal technologies often struggle with the high concentrations and complex organic matrices of undiluted AFFF. This study investigates a novel piezoelectric ball milling (BN-BM) approach, using boron nitride as a piezoelectric material to generate high-potential energy during mechanical collisions to destroy PFAS molecules.
The researchers successfully treated undiluted AFFF, which contained a total organic fluorine (TOF) concentration of 9080 mg/L and a total organic carbon (TOC) of 234 g/L. By comilling the AFFF with boron nitride, the team achieved 99.7% defluorination, effectively converting organofluorine into fluoride ions. The study identified that the thickness of the liquid film (Z) at the collision interface is a critical descriptor of performance; effective defluorination occurs only when this film is thinner than 2.3 μm. To maintain this threshold, the researchers validated the use of SiO2 as a dispersant and pre-evaporation techniques to reduce the liquid volume, thereby enhancing the treatment capacity.
The study suggests that the piezoelectric effect is the primary driver of PFAS destruction. Upon collision, boron nitride generates kilovolt-level potentials that facilitate the oxidative cleavage of carbon-fluorine and carbon-sulfur bonds. The reaction pathway involves the participation of water molecules, which act as electron donors and acceptors to produce hydroxyl (•OH) and hydrogen (•H) radicals. These radicals further degrade PFAS intermediates into shorter-chain perfluoroalkyl carboxylic acids (PFCAs) and eventually into mineralized fluoride.
This research provides a scalable, nonthermal, and chemical-free pathway for the direct destruction of concentrated AFFF stockpiles. By avoiding the need for high-temperature incineration or large-scale dilution, this method offers a more sustainable and efficient solution for managing legacy PFAS waste, potentially meeting the goal of zero PFAS pollution.
The nonthermal destruction of aqueous film-forming foam (AFFF) stockpiles, one of the major culprits responsible for water and soil contamination by per- and polyfluoroalkyl substances (PFAS), is extremely challenging because of the coexistence of mixed recalcitrant PFAS and complicated organic matrices at extremely high concentrations. To date, the complete defluorination of undiluted AFFF at ambient conditions has not been demonstrated. This study reports a novel piezoelectric ball milling approach for treating AFFF with a total organic fluorine concentration of 9080 mg/L and total organic carbon of 234 g/L. Near-complete defluorination (>95% conversion of organofluorine to fluoride) of undiluted AFFF was achieved by comilling with boron nitride. By carefully examining the experimental data, we identified AFFF liquid film thickness ( Z ) at the collision interface as a descriptor of treatment performance. We further validated that effective defluorination proceeded when Z was less than the criteria value of 2.3 μm. In light of this new understanding, the addition of SiO 2 as a dispersant and the pre-evaporation solvents to reduce Z have been validated as effective strategies to promote AFFF treatment capacity.
Alex: So the whole system lives or dies on keeping that liquid layer almost impossibly thin.
Sam: Right. And when they managed that, the results were significant. By ensuring direct contact between the steel balls and the boron nitride, they achieved over 95% conversion of the toxic fluorine compounds into stable, harmless mineral waste—all at ordinary room temperature and pressure. The fluorine atoms, which are the dangerous part, end up locked into inert solids rather than floating free in the environment.
Alex: Are there limitations they're honest about?
Sam: Yes, and the paper is straightforward about this. The method works well at laboratory scale, but moving it up to handle the kinds of volumes you'd find at a military base—potentially thousands of gallons—requires careful engineering. Keeping that liquid film thin enough across a large industrial system is not trivial. The researchers suggest approaches like adding dispersants, which are substances that help spread the liquid into a thinner, more even layer, or partially evaporating the solvent before milling. But these are practical hurdles that still need to be worked out before the method could be deployed widely.
Alex: So the key insight isn't just the material choice—it's understanding and controlling the physical conditions of each collision.
Sam: That's it. The study shows that once you understand why the process works—direct mechanical contact generating a piezoelectric spark—you can engineer around the obstacles. Managing the liquid film is what makes the difference between a process that works in a lab and one that could eventually be used on-site at contaminated facilities. The paper frames this as a meaningful step toward addressing a long-standing environmental problem without the energy costs and logistical complexity of high-temperature incineration.
Alex: It's a good reminder that some of the most persistent environmental problems don't necessarily require the most elaborate solutions—sometimes it's about understanding the physics of a collision well enough to make it work. Thanks for walking me through it, Sam.
Sam: My pleasure. It's a clear example of how understanding a fundamental physical mechanism can open up practical options for problems that have resisted other approaches for a long time. Thanks for listening to ResearchPod.