Read the full article by Emily Pontecorvo (Grist)
“Christopher Sales is an environmental microbiologist, and until recently, his world was about harnessing the power of microorganisms to break down contaminants in the environment. But a resilient intruder that does not succumb to the same old tricks has shaken up the remediation community and led Sales to look outside of his field for a solution. It’s a chemical that’s been found in water, soil, and food all over the planet: PFAS…
‘PFAS is becoming a big issue,’ Sales told Grist. ‘It’s being found in a lot of different places, and unfortunately we haven’t found a microorganism that can degrade it.’
Sales is a professor at Drexel University, and he has experimented a little bit with biological treatments for PFAS with little success. But while chatting with one of his colleagues at Drexel’s Nyheim Plasma Institute, he learned that plasma was being used to kill bacteria and other contaminants in water, and wondered if it might be effective on PFAS. Plasma is the fourth state of matter after solids, liquids, and gases, and it is created by applying heat or electricity to gas. In September 2017, when the Department of Defense announced new funding for technologies to degrade PFAS, Sales asked the Nyheim researchers if they would be interested in collaborating. They secured a grant and got to work.
In January, Sales published a study detailing the results of that collaboration. After testing a new plasma-based treatment system on water samples contaminated with 12 different types of PFAS, they found that it degraded significant amounts of all of the compounds, and for some types of PFAS, the system degraded more than 90 percent of the contamination.
Degrading PFAS doesn’t necessarily remove their threat, because it can result in new, smaller molecules of PFAS. The real target, and the more challenging one, is to defluorinate them, or break apart their carbon-fluorine bond. In some of the tests at Drexel, the plasma treatment system successfully defluorinated about a quarter of the compounds.
‘In terms of treatment efficiency, plasma technology ranks really high,’ said Jinxia Liu, an environmental engineering professor at McGill University who was not involved in the study. Liu said that plasma treatments for PFAS are promising because they do not require any added chemicals and do not seem to produce harmful byproducts.
There are two ways to remove PFAS from water. Right now, the most widely used approach is to filter them out. But because PFAS don’t break down, filters just transfer the contamination from one medium to another. If the filter ends up in a landfill, PFAS can still seep out into groundwater. The other approach is to try to destroy the compounds altogether. Currently, the only scalable method to destroy PFAS is incineration, but that requires large amounts of heat and is very energy intensive.
Sales’ plasma treatment still requires energy, but much less. In plasma, what were once gas molecules have been broken apart, creating what scientists call a highly reactive environment. The freely floating electrons, ions, and unstable neutral atoms in this environment can be deployed as a sort of arsenal of weapons against other molecules. Depending on what the original gas was, some of these weapons will attack pollutants like PFAS. In their study, the Drexel researchers used regular air, which is cheap and abundant, as the gas…”