Per- and polyfluoroalkyl substances (PFAS), most commonly known as ‘forever chemicals’, resist water, oil and heat, and are present in everything from pizza boxes to toilet paper, from water to human blood. PFAS are also found in substantial concentrations in aqueous film-forming foam (AFFF), or firefighting foam, which has been applied to land at firefighting-training sites globally for decades. This has led to significant contamination of soil at facilities like refineries, airports, military bases, and potentially many more unknown sites.
A team of scientists from the University of Auckland in New Zealand has now developed a mechanochemical destruction (MCD) method to destroy PFAS from soil contaminated with firefighting foam. The method uses ball milling to grind down the forever chemicals and works similarly to a mortar and pestle but at an extremely high intensity, ‘with the balls moving at incredible speeds to degrade the PFAS at molecular level’, lead researcher Dr Kapish Gobindlal said in a statement.
The team, collaborating with the U.S. Environmental Protection Agency, did laboratory benchtop experiments from 2018 to 2023 to prove the concept, colliding 10 to 30 small metal balls in heavily modified shipping containers.
The method was applied to PFAS in soil from a decommissioned New Zealand Defence Force firefighting training site, AFFF, and in media such as activated carbon, which is used to remove PFAS from water. The only additive employed for MCD treatment was quartz sand, which was used only for the liquid AFFF sample, with no additives required for the destruction of PFASs in the contaminated soil. Destruction efficiencies of target PFAS subgroups reportedly ranged from 99.88% to 100%.
“We’ve established proof-of-concept and believe this method can be scaled up faster and cheaper than alternatives,” said Gobindlal. That the grinding process did not require expensive additives is a promising sign, as additives play a crucial role in ramping up cost and thereby in slowing down economies of scale. “There is a massive need – the U.S. alone has thousands of contaminated sites and regulation is shifting toward mandating remediation of these sites,” Gobindlal continued.
U.S. President Joe Biden said in March that cleaning up PFAS from the environment is a ‘massive task that will require our continuous and dedicated investment in the coming years’. The U.S. Department of Defence estimating in 2021 that its clean-up could cost $31 billion.
The team shared their findings in “Mechanochemical destruction of per- and polyfluoroalkyl substances in aqueous film-forming foams and contaminated soil,” recently published in Environmental Science Advances.