Ultrasound may rid groundwater of toxic 'forever chemicals'

According to recent studies, ultrasonic treatment may be able to remove PFAS (permanently toxic alkaloids) from contaminated groundwater.

Per- and poly-fluoroalkyl compounds, sometimes referred to as "forever chemicals," were developed about a century ago and were formerly widely employed in the production of cookware, waterproof apparel, and personal care products. As of right now, experts know that exposure to PFAS can result in a variety of health problems for people, including cancer and birth abnormalities. However, it is renownedly difficult to remove these compounds from the environment since the connections inside them are tough to break.

Due of these challenges, scientists at The Ohio State University are investigating the potential effects of ultrasonic degradation—a method that breaks down compounds by using sound to split apart their constituent molecules—against various kinds and amounts of these pollutants.

The Journal of Physical Chemistry A published the study.

They observed that, over the course of three hours, the smaller compounds of fluorotelomer sulfonates—PFAS compounds often found in firefighting foams—degraded far more quickly than the bigger ones. These studies were conducted on lab-made mixes comprising three different sized compounds of fluorotelomer sulfonates. In contrast, smaller PFAS are actually harder to treat with many other PFAS treatment techniques.

The Ohio State University professor of civil, environmental, and geodetic engineering Linda Weavers, a co-author of the study, said, "We showed that the challenging smaller compounds can be treated, and more effectively than the larger compounds." "That's what has the potential to make this technology really valuable."

This work, one of the few to investigate the potential applications of ultrasonography to remove harmful per- and polyfluoroalkyl substances (PFAS) from our environment, builds on Weavers's earlier findings that the same technique might break down medications in municipal tap and wastewater.

PFAS chemicals are distinct from other hard-to-remove compounds since many of the destruction methods used in environmental engineering for other compounds don't work for them, according to Weavers. Therefore, in order to determine which technologies could be helpful in various applications, we actually need to be creating a variety of them.

Because ultrasound emits sound at a frequency far lower than that of medical imaging, it purifies PFAS, in contrast to other conventional destruction methods that try to break them down by reacting them with oxidizing chemicals, according to Weavers. Cavitation bubbles are discrete vapor pockets that are produced when the solution is compressed and pulled apart by the low-pitched pressure pulse of ultrasound.

According to Weavers, "the bubbles heat up as they collapse because they gain so much momentum and energy that it compresses and over-compresses."

These small bubbles may reach temperatures of up to 10,000 Kelvin, much like powerful combustion chambers. It is precisely this heat that breaks down the stable carbon-fluorine bonds that make up PFAS and basically renders the byproducts harmless. Weavers stated that although this degrading process can be very expensive and energy-intensive, there may not be many other choices, thus the public may need to consider making an investment in it to safeguard groundwater for drinking and other purposes.

Regulating bodies are trying to raise public knowledge regarding PFAS avoidance while manufacturing sectors are beginning to shift away from using them. The National Primary Drinking Water Regulation (NPDWR), which was proposed earlier this year by the US Environmental Protection Agency, would mandate that public water systems keep an eye out for certain PFAS, alert the public when these levels are exceeded, and take action to lower them.

The study adds that because ultrasound is so good at removing PFAS from solutions, researchers and government organizations ought to think about incorporating it into the development of future treatment technologies, both alone and in conjunction with other combined-treatment strategies.

The study did point out that Weavers's work may be the first step toward developing compact, high-energy water filtration equipment that the general public may utilize inside of homes, even though it is not yet ready to be scaled up to support more extensive anti-contamination initiatives.

Weavers explained, "Our research focuses on attempting to understand how you scale to something bigger and what you need to make it work." Since these substances are ubiquitous, it is critical to advance scientific knowledge of their degradation and breakdown mechanisms as we learn more about them.

William P. Fagan and Shannon R. Thayer, both from Ohio State, are additional co-authors.