H2O Talk: State-of-the-Practice on Addressing PFC (Perfluoroalkyl Compounds) Impacts
Perfluoroalkyl compounds (PFCs), including perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), were released to the environment at many federal and commercial facilities in the United States and elsewhere as a result of historical uses of aqueous film-forming foams (AFFF) to extinguish fuel-based fires. PFOS was one of the main PFCs in AFFF formulations manufactured by 3M. AFFF provided by other suppliers contained other PFCs that could be converted to PFOS and PFOA in the environment. Due to the strength of their carbon-fluorine bonds, PFCs are persistent in the environment and difficult to remediate.
The most common approach for groundwater remediation impacted by PFCs involves groundwater extraction followed by granular activated carbon (GAC) adsorption. Following PFC breakthrough, GAC is typically incinerated. PFOS is stable at temperatures below 1,100°C, making it impractical to thermally regenerate GAC. PFCs have unique surface-active properties and a relatively high affinity for surfaces. This makes soil and sediment remediation more difficult. There are currently few practical solutions beyond capping or excavation followed by off-site disposal. In response to these challenges, researchers across the globe are currently developing several technologies for PFC treatment including sonolysis, electrochemical treatment, treatment with enzyme extracts and photocatalysis. Although these techniques may eventually yield an alternative ex situ treatment option, it is unlikely that they will ever provide significant savings relative to GAC adsorption followed by incineration of spent carbon. Attempts to employ these technologies in situ face significant technical and financial challenges related to high costs for reagents and equipment, and high maintenance requirements for system operation. Furthermore, any technology in which PFCs must flow into a reactive zone will require continuous operation for decades to fully achieve treatment of impacted subsurface media. Most in situ approaches, including chemical oxidation and bioremediation, are ineffective, and only partially degrade PFCs. To date, bioremediation of PFCs has yielded no documented successes despite several ongoing research efforts in the United States funded by the Air Force and SERDP/ESTCP. Chemical treatment holds promise for addressing PFCs in situ. However, recent studies have reported limited success in destroying PFOS and other perfluorinated sulfonates. Furthermore, the use of aggressive treatment technologies at PFC-impacted sites poses unique challenges given the lack of understanding of precursor behavior. AFFF compounds can be transformed to PFOS, PFOA and other PFCs through either microbial action or exposure to oxidants. Therefore, the application of in situ technologies prior to fully elucidating reaction mechanisms at the bench scale or the application of poorly designed remedies at the field scale could result in increased concentrations of PFOA, PFOS and other PFCs at AFFF-contaminated sites.
This presentation will provide an overview of PFC sources, occurrence and chemistry. In addition, a summary of the state of knowledge regarding environmental fate and transport of PFCs will be provided, together with an overview of treatment technologies. The presentation will primarily focus on the research that is being conducted around the globe, and will highlight critical advances and promising results from these studies.
Malcolm Pirnie, Inc., Emeryville, CA