According to a new study, ultrasound might have the ability to treat a class of dangerous chemicals known as PFAS to remove them from contaminated groundwater.
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Per- and poly-fluoroalkyl substances, sometimes known as “forever chemicals,” were invented about a century ago and were previously widely utilized to make cookware, waterproof clothes, and personal care items.
Scientists now know that PFAS exposure could result in a variety of human health problems, including birth abnormalities and cancer. However, because the bonds within these chemicals are tough to break down, they are notoriously difficult to remove from the environment.
Due to these limitations, researchers at The Ohio State University are investigating how ultrasonic degradation, a process that employs sound to break down compounds by cleaving apart the molecules that make them up, could operate against various types and quantities of these chemicals.
Experiments on lab-made combinations, including three different-sized compounds of fluorotelomer sulfonates—PFAS compounds commonly found in firefighting foams—revealed that the smaller compounds decomposed significantly quicker than the larger ones during a three-hour period. In contrast to many other PFAS treatment approaches, smaller PFAS are more difficult to treat.
We showed that the challenging smaller compounds can be treated, and more effectively than the larger compounds. That is what makes this technology potentially really valuable.
Linda Weavers, Study Co-Author and Professor, Civil, Environmental and Geodetic Engineering, The Ohio State University
The Journal of Physical Chemistry A published the findings.
The study is an extension of previous research by Weavers that found that the same technique can also eliminate pharmaceuticals in municipal tap and wastewater. It is one of the few studies to investigate how ultrasound might be used to purge the surroundings of harmful PFAS chemicals.
Weavers added, “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. So, we really need to be developing an array of technologies to figure out which ones might be useful in different applications.”
Weavers explained that ultrasound helps to clean these contaminants by transmitting sound at a frequency considerably lower than generally employed for medical imaging, as opposed to other conventional destruction techniques that try to break down PFAS by reacting them with oxidizing agents. Cavitation bubbles are formed when the solution is compressed and pulled apart by the low-pitched pressure pulse of ultrasound.
“As the bubbles collapse, they gain so much momentum and energy that it compresses and over-compresses, heating up the bubble,” Weavers stated.
These small bubbles can reach temperatures of up to 10,000 Kelvin, similar to strong combustion chambers. It is this heat that dissolves the PFAS’s stable carbon-fluorine bonds, rendering the byproducts largely harmless.
Weavers noted that despite the fact that this degrading technique can be expensive and energy-consuming, there are not many alternatives; therefore, the public may need to consider investing in it to safeguard groundwater for drinking and other uses.
While the manufacturing sector is beginning to reduce the usage of PFAS, regulatory organizations are attempting to increase public understanding of how to avoid them. The National Primary Drinking Water Regulation (NPDWR), which the US Environmental Protection Agency proposed earlier this year, would force public water systems to monitor for certain PFAS, inform the public of these levels, and take action to reduce them if they exceed a particular limit.
According to the study, because ultrasound is so good at removing PFAS from solutions, researchers and governmental organizations should think about incorporating it into the development of future treatment technologies as well as other combined therapy strategies.
Weavers’ research is not yet ready to be scaled up to support more extensive anti-contamination initiatives. Still, the study did remark that their work could be the first step toward developing portable, high-energy water filtering systems for use by the general population within the house.
Weavers concluded, “Our research revolves around trying to think about how you scale to something bigger and what you need to make it work. These compounds are found everywhere, so as we learn more about them, understanding how they can degrade and break down is important for furthering the science.”
William P. Fagan and Shannon R. Thayer, both from Ohio State, are additional co-authors.
Fagan, W. P., et al. (2023) Kinetics and Mechanism of Ultrasonic Defluorination of Fluorotelomer Sulfonates. The Journal of Physical Chemistry A. doi:10.1021/acs.jpca.3c03011