Ultrasound could get rid of forever chemicals like PFAS

New research suggests that ultrasound may potentially treat a group of harmful chemicals known as PFAS to eliminate them from contaminated groundwater.

New research suggests that ultrasound may potentially treat a group of harmful chemicals known as PFAS to eliminate them from contaminated groundwater.

Per- and poly-fluoroalkyl substances are also known as “forever chemicals.” They were widely used to create products such as cookware, waterproof clothing and personal care items. Today, scientists understand that exposure to PFAS can cause several human health issues, such as congenital disabilities and cancer. But because the bonds inside these chemicals don’t break down quickly, they’re notoriously difficult to remove from the environment.

Such difficulties have led researchers at The Ohio State University to study ultrasonic degradation against these chemicals. It’s a process that uses sound to degrade substances by cleaving apart the molecules that make them up,

The researchers conducted experiments on lab-made mixtures containing three differently-sized compounds of fluorotelomer sulfonates. That’s a set of PFAS compounds typically found in firefighting foams. Their results showed that over three hours, the more minor compounds degraded much faster than the larger ones. This contrasts with many other PFAS treatment methods in which smaller PFAS are more challenging.

“We showed that the challenging smaller compounds can be treated. We also showed that our technique works more effectively than the larger compounds,” said co-author of the study Linda Weavers,civil, environmental and geodetic engineering professor at The Ohio State University. “That’s what makes this technology potentially valuable.”

The research was published in The Journal of Physical Chemistry A.  

How can ultrasound remove PFAS?

This is one of only a few studies to probe into how ultrasound might be used to rid our surroundings of toxic PFAS chemicals. The paper is an extension of Weavers’ previous research. Her research had earlier determined that the same technology could also degrade pharmaceuticals in municipal tap and wastewater.

“PFAS compounds are unique because many of the destruction technologies that we use in environmental engineering for other hard-to-remove compounds don’t work for them,” Weavers said. “So we need to develop an array of technologies to determine which might be useful in different applications.”

Other traditional destruction methods that attempt to break down PFAS by reacting them with oxidizing chemicals. Weavers said that ultrasound purifies these substances by emitting sound at a frequency much lower than typically used for medical imaging. Ultrasound’s low-pitched pressure wave compresses and pulls apart the solution, creating pockets of vapour called cavitation bubbles.

“As the bubbles collapse, they gain so much momentum and energy that it compresses and over-compresses, heating the bubble,” said Weavers.

The temperatures inside these tiny bubbles can reach up to 10,000 Kelvin. It’s this heat that breaks down the stable carbon-fluorine bonds that PFAS are made of and renders the byproducts essentially harmless. Unfortunately, this degradation method can be costly and extremely energy-intensive. It may be something the public needs to consider investing in to protect groundwater for drinking and other uses, said Weavers.

Forever chemicals removal of greater importance

Regulatory agencies are working to heighten public awareness about how to avoid PFAS. At the same time, manufacturing industries are starting to move away from using them. Earlier this year, the U.S. Environmental Protection Agency proposed the National Primary Drinking Water Regulation (NPDWR). It would require public water systems to monitor for certain PFAS, notify the public of these levels and take measures to reduce them if they’re over a specific limit.

The study concludes that scientists and government agencies should consider using ultrasound in future treatment technology development and other combined treatment approaches.

Weavers’ research is not ready to be scaled up to aid in larger anti-contamination efforts. However, the study does note that their work could support creating small, high-energy water filtration devices for public use inside the home.

“Our research revolves around trying to think about how you scale to something bigger. We also need to think about what you need to make it work,” said Weavers. “These compounds are found everywhere. As we learn more about them, understanding how they can degrade and break down is important for furthering the science.”

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