With billions of dollars being spent to clean up contaminated land from PFAS, efforts are underway to find the best method to remove what are being called ‘forever chemicals’ seeping into water supplies.
A new study in the US has shown that rather than filtering out the chemicals using activated carbon or reverse osmosis, in fact, the best way is to destroy them.
Researchers from Drexel University in Pennsylvania have developed what is being called a ‘plasmatron’ technology that they claim breaks down PFAS contaminants, rather than filtering them out.
They said that with current filtration methods, such as carbon filters, PFAS are merely collected, not destroyed, so “unless the filters are incinerated at high temperatures”, the used filters “become a new source of PFAS”.
Known as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), these chemicals are part of a larger group referred to as per-and polyfluoroalkyl substances (PFAS).
With PFAS leaching into ground and surface water from products sitting in landfills for decades, the chemicals do not readily biodegrade. A total of 700 PFAS-contaminated sites were recently identified in the US.
The US Department of Defense is said to be spending “billions of dollars” to clean up contaminated soil water supplies surrounding military bases where PFAS fire-fighting foam has been used.
A study from Duke University and North Carolina State University recently tested point of use/entry systems for their effectiveness in removing PFAS from household water supplies.
Meanwhile, Orange County in the US has started a $1.4 million (S$1.9 million) project with Carollo to explore PFAS removal solutions, including reviewing 10 different carbons and four different resins.
The Drexel team believe that to eliminate these chemicals, you need to split the carbon-fluoride bond. By breaking these chains into smaller pieces, it renders the PFAS inert.
To then remove the fluoride – the temperature of the water needs to be raised to 1,000 Celsius – ten times the temperature of boiling water.
With this “clearly not feasible for water treatment operations” due to the high energy costs, the researchers proposed the use of highly energised gas, or plasma, to activate the PFAS atoms without heating the water.
How does the plasmatron work?
Published in the journal Environmental Science: Water Research & Technology, the study saw the development of a device called a “gliding arc plasmatron”.
Creating a rotating electromagnetic field that splits the chemicals apart in the water, the process was described as the chemical equivalent of “using a blender to make a smoothie”.
Researchers claim the process takes one hour and uses less energy than it takes to boil a kettle while removing more than 90 per cent of PFAS from the water.
The team said previous plasma treatment methods on PFAS did not lend themselves to being easily scaled up for use at large treatment facilities.
Alexander Fridman, PhD and director of the Nyheim Plasma Institute, said the technology could be adjusted to treat contaminated soil, achieving “near-complete defluorination of PFAS compounds”.
What the researchers said
Christopher Sales, PdD, associate professor of environmental engineering at Drexel, said: “The current standard for dealing with PFAS-contaminated water is activated carbon filters. But the problem is that it only collects the PFAS, it doesn’t destroy it.
“So unless the filters are incinerated at high temperatures, the spent filters become a new source of PFAS that can make its way back into the environment through landfill runoff and seepage.”
Fridman added, “Cold plasma has the potential to help us eliminate a variety of chemical toxins that threaten our food and drinking water supplies.”