Per- and polyfluoroalkyl substance (PFAS) impact to groundwater is widespread, potentially impacting the drinking water of up to 110 million Americans. A major source is aqueous film forming foam (AFFF), which was used for decades for firefighting and is still in use today. The Department of Defense (DoD) has identified at least 425 military sites where water has been impacted by PFAS and a full DoD clean-up effort is expected to surpass $2 billion. Currently, options to destroy PFAS are limited and expensive. The dominant method for removing aqueous PFAS is sorption using granular activated carbon (GAC) or ion exchange resins. This method results in contaminated GAC or resin, which must be incinerated at high temperature (>1100°C) to destroy the PFAS. This incineration step is energy-intensive and may produce undesirable byproducts, necessitating improved technologies for PFAS destruction. The objective of this limited scope project is to explore hydrodynamic cavitation (HC) as a novel and potentially less expensive alternative technology for thermal destruction of PFAS in water, and will research to investigate its feasibility and scalability.

PFAS are exceptionally stable, so destroying them requires extreme reaction conditions. This project's hypothesis is that HC can generate the high temperatures and oxidation conditions needed to destroy PFAS in a process that is scalable and does not produce toxic byproducts. This project builds on prior literature showing PFAS destruction by ultrasonic cavitation. Researchers have shown how the high temperatures and pressures in the collapsing cavitation bubbles enable complete breakdown of PFAS into non-toxic byproducts via pyrolytic removal of the ionic head group, pyrolytic breakage of the carbon chain and oxidative breakage of the C-F bonds. The project team hypothesizes that the same mechanisms for PFAS destruction will occur in cavitation produced by HC. In this limited-scope project, the project team will conduct an experimental study to investigate the effects of HC reactor parameters on PFAS destruction. The project team will also conduct laboratory testing of the byproducts produced, and will conduct analysis to determine how the experimental results from the laboratory-scale testing would scale up to use in the field.

This project seeks to demonstrate that HC is a feasible technology for thermal destruction of PFAS and will deepen the understanding of the important reactor parameters. Such a technology would support cost-effective and efficient DoD and municipal remediation of PFAS-impacted sites. (Anticipated Project Completion - 2023)