Engineering the End of Forever

Beyond Boiling: Obliterating PFAS With a Pressure Cooker on Steroids

Since 2013, Marc Deshusses, professor of civil and environmental engineering at Duke, has been developing what he calls a “pressure cooker on steroids” in a standard 20–foot shipping container behind Hudson Hall. Based on the concept of supercritical water oxidation—or SCWO, pronounced “squow” to those in the business—the technology can turn any organic waste into clean water, carbon dioxide, trace salts and energy in mere seconds.

The project was one of several on Duke’s campus funded by the Bill & Melinda Gates Foundation’s “Reinvent The Toilet” program. Aimed at developing a portfolio of technologies that could help bring improved sanitation to four billion people worldwide, many of the projects emerging from the nearly decade’s worth of funding are finding potential uses in the richer nations of the world as well. 

“A lot of treatment options don’t fully remediate PFAS and end up generating other unwanted byproducts, but our technology is one of the few that can fully destroy all PFAS. And according to the new guidelines, you could contaminate all of the Great Lakes with just a few buckets of PFOA, so we’ve been getting a lot of inquiries.”

According to Ferguson, PFAS is so difficult to destroy because of its extremely tenacious carbon–fluorine bonds. The same chemical factors that make it so useful in industrial applications make it difficult to degrade. No known biological organisms can cleave all those carbon–fluorine bonds, and light can’t degrade them either. Take away the two primary mechanisms to break chemicals down in the environment, and it becomes clear why these chemicals persist in our waters for so long.

When trying to use advanced engineered treatment methods on such strong chemical bonds, researchers have to resort to extreme methods. To turn PFAS into water, carbon dioxide and fluoride—all of which are harmless byproducts—one must break every single carbon–fluorine bond in the molecule. While there are some acids that can manage the trick, the materials involved are also harmful to the environment.

“That’s why SCWO is so promising,” Ferguson said. “It has enough energy and specificity to completely destroy PFAS molecules. It’s one of the very few technologies that is able to do that.”

“The technology is there. The challenge is really in engineering a system that can do it reliably and economically,” Deshusses added. “The potential of SCWO is enormous, because you can build units that are very compact and embed them in communities, or you can build large units that can treat the waste of small cities.”

SCWO works by using high pressure and temperature—over 220 times atmospheric pressure and above 374 degrees Celsius—to break down complex organic compounds into clean water, carbon dioxide, and trace salts and minerals. While the idea has been around for many decades, the technology is only now maturing to the point where large installations capable of treating several tons of waste a day are efficient enough to be economically viable.

Over the course of several years, Deshusses and his research team built out a prototype SCWO unit and used it to refine their designs and operation parameters. The result of these efforts is a spinoff company called 374Water, which was uplisted to the Nasdaq Stock Exchange in June 2022. While Deshusses has been working with his company to produce larger units to deploy in California and Israel to prove their potential, he’s also been working with Ferguson to refine the technology’s operating conditions to more efficiently obliterate PFAS with the help of funding from the Department of Defense.

While it will still be some time before SCWO technology can reach its full potential, it is already well on its way. For starters, 374Water has sold two commercial units and is scaling up their production as well as their designs to treat 30 or, eventually, even 200 tons of waste per day. While that’s a small amount compared to what city-sized treatment facilities require, units of this size could treat dense waste coming directly out of a factory or waste that has been concentrated by separate technologies.

That’s good news, as a 2015 study from Harvard University detected PFAS in the water supplies for six million people across the country, and that number is almost certainly much higher today.