By U.S. EPA
Per-and polyfluoroalkyl substances, otherwise known as PFAS, are a large group of human-made organic compounds with properties that make many of them toxic and persistent in the environment. PFAS have been manufactured and used since the 1940s in items such as fire-fighting foams, adhesives, cosmetics, paper products, and stain and water repellants. Until now, researchers have been unable to destroy PFAS in a way that has potential for larger scale use.
PFAS molecules are made up of a chain of linked carbon and fluorine atoms. Thanks to recent trials, EPA researchers may have found an effective method of breaking this chain link of carbon and fluorine to destroy PFAS—called Supercritical Water Oxidation (SCWO).
SCWO is a technology that brings water to a temperature above 705°F and pressure of 221.1 bar, which is considered “supercritical”. Supercritical water has special properties that allow organic compounds to be easily degraded. SCWO has been used since the 1980s to successfully treat a variety of hazardous wastes, such as chemical warfare agents. In this case, the SCWO process super-heats the PFAS-contaminated water in a sealed vessel, which breaks apart the strong fluorine and carbon chains that are the hallmark of PFAS. SCWO essentially acts as a pressure cooker, “cooking” out the chains that form PFAS particles.
Last year, Max Krause and a team of EPA researchers oversaw three different trials to test the efficacy of SCWO technology on PFAS destruction. The researchers used the SCWO treatment on fire-fighting foam, a water-based product with very high levels of PFAS. All three experiments showed a greater than 99 percent reduction of the PFAS identified in a targeted analysis. This is a very important finding as it may mean that there is an effective alternative to traditional PFAS disposal methods. This technology could be used by federal and state governments, the Department of Defense, and operators that treat PFAS waste.
“There are several other factors that we need to evaluate with SCWO systems before we’re certain that it’s actually destroying these compounds and not just moving them around” says EPA Engineer Max Krause. “It’s exciting that three commercial groups independently showed us similar findings. Because SCWO already has shown some commercial utility in other areas, this could be a technology that quickly finds a role for treating PFAS-containing wastewaters and even sludges.”
The next steps will be to trial more types of PFAS-contaminated substances other than fire-fighting foam to show if this method could be used more broadly on waters and wastewaters. Another important next step is to measure if there are any harmful by-products that occur during the SCWO treatment.