‘With few other options [it is a method] that the public needs to consider investing in to protect groundwater for drinking and other uses.’
Researchers at The Ohio State University, US, have found that ultrasound may be useful in treating per and poly-fluoroalkyl substances (PFAS) and eliminating them from groundwater.
In a study published in The Journal of Physical Chemistry A, researchers found that in laboratory-derived mixtures comprising different sized compounds of fluorotelomer sulphonates – PFAS compounds typically found in firefighting foams – the smaller sized molecules, which have been found challenging to treat, were degraded more quickly than the larger molecules over a period of three hours using ultrasound. This work is an extension of research using ultrasound to 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 do not 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,’ said Linda Weavers, Professor of Civil, Environmental and Geodetic Engineering at The Ohio State University.
Weavers explains that ultrasound’s low-pitched pressure wave effectively compresses and pulls apart solutions containing PFAS which creates pockets of vapour called cavitation bubbles.
‘As the bubbles collapse, they gain so much momentum and energy that it compresses, heating up the bubble,’ says Weavers. The temperature inside these bubbles can reach up to 10,000°K, and this heat causes the cleavage of the stable carbon-fluorine bonds that make up PFAS leading to harmless by-products.
While the research has found this technique to be effective, it can be costly and energy intensive. ‘With few other options [it is a method] that the public needs to consider investing in to protect groundwater for drinking and other uses,’ Weavers says.
Regulatory bodies around the world are moving to restrict PFAS. In 2021 the US Environmental Protection Agency released a Comprehensive Strategic Roadmap for tackling PFAS contamination. And at the start of 2023, 3M said that it would stop producing PFAS across its production portfolio by the end of 2025. Just last month, the European Chemical Agency said that it had received comments from more than 4,400 organisations, companies and individuals on proposed restriction of PFAS in the European Union.