Per and polyfluoroalkyl substances (PFAS) have become one of the most difficult compounds to remove from wastewater because of the tight and stable bond that it forms making it resistant to conventional treatment methods. PFAS is commonly found in everything from food to household chemicals and its presence can still be detected in drinking water. This is why PFAS has taken on a more notorious name: “forever chemicals.”
There are a few ways to remove the toxic chemical but destroying the chemical bonds is the most effective way to permanently eliminate it from returning to the environment. It would normally take very high temperatures to break the bonds, but the energy requirement makes it prohibitive to apply on a larger scale.
A group from Drexel University in the U.S. has developed a novel way of effectively removing the toxic chemical from wastewater without consuming a large amount of energy.
Christopher Sales, PhD, an associate professor of environmental engineering at Drexel, is part of a team composed of researchers from Drexel’s College of Engineering and the C. & J. Nyheim Plasma Institute. They are investigating the destabilisation of PFAS by blasting it with a charged gas called cold plasma and presenting their findings in the journal Environmental Science: Water Research & Technology.
“This has become an urgent issue because we are seeing PFAS turn up everywhere, not just in the water and soil near airports that used it in fire-fighting foam, but also in many consumer goods like stain-resistant fabrics and food packaging designed to repel liquids and grease. Because these chemicals do not readily biodegrade, PFAS is leaching into ground and surface water from products that have been sitting in landfills for decades,” Sales said.
It is estimated that up to 98 percent of the U.S. population have been directly exposed to PFAS contamination from their drinking water. They can have profound effects on human health if left unabated.
Sales states that the current standard for PFAS elimination is through activated carbon filtration, but since the compound is simply removed and not destroyed, the filters can potentially return the PFAS to the environment through landfills unless it is incinerated at high temperatures.
Aside from breaking the bonds between the carbon and flouride atoms in PFAS, the other challenge is how to remove the flouride atoms from the compound in a process known as deflourination.
Breaking up the exceptionally stable bond between carbon and fluoride in PFAS requires temperatures of the compounds to be increased to at least 1,000 Celsius — 10x the temperature of boiling water. This is obviously not practical for water treatment operations due to the huge amount of energy it would consume.
Cold plasma offers the benefit of producing high levels of heat without raising the temperature significantly. The process involves a device called a gliding arc plasmatron which creates an electromagnetic field to excite electrons but keeps the gas at room temperature. This process is similar to how fluorescent lights work.
The process is so efficient that the energy needed to run the plasmatron is equivalent to running a tea kettle to boiling. It can eliminate as much as 90 percent of the PFAS and deflourinate a quarter of the compound.
The research team is confident that their project can be scaled because of its low energy requirements and effectivity in eliminating PFAS but further testing is still needed to perfect it.
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