Given the increasing regulation of "forever chemicals" by the U.S. Environmental Protection Agency (EPA), military and commercial aviation officials are seeking ways to clean up the pollution caused by decades of using firefighting foams at military bases and commercial airports.

Firefighting foams contain hundreds of harmful forever chemicals, known as PFAS or per- and polyfluoroalkyl substances. These compounds have extremely strong bonds between fluorine and carbon, allowing them to persist indefinitely in the environment. PFAS compounds are also found in many other products and now contaminate underground water sources used by many municipal water supplies across the country.

Given the association with higher risks of certain cancers and other diseases, the EPA issued a new regulation last month requiring water supply companies to reduce contamination if levels of certain PFAS compounds exceed 4 parts per trillion.

Fortunately, a joint discovery by scientists at the University of California, Riverside, and Clarkson University in Potsdam, N.Y., provides a new strategy for cleaning up these pollutants.

The method is detailed this month in the journal Nature Water. It involves treating heavily contaminated water with ultraviolet (UV) light, sulfite, and a process called electrochemical oxidation, explained UCR associate professor Jinyong Liu.

"This work continues our research on UV-based treatment, but this time we collaborated with an expert in electrochemical oxidation at Clarkson University," said Liu, who has published nearly 20 papers on treating PFAS contamination in polluted water. "We combined these two methods and achieved nearly complete destruction of PFAS in various water samples contaminated with foams."

Liu noted that collaboration with the team led by assistant professor Yang Yang at Clarkson solved major technical problems. Specifically, foams contain various other concentrated organic compounds that make it difficult to break the strong bonds between fluorine and carbon in PFAS compounds.

However, Liu and Yang discovered that electrochemical oxidation also breaks down these organic compounds. Their process allows these reactions to occur at room temperature without the need for additional heat or high pressure to stimulate the reaction.

"In the real world, contaminated water can be very complex," said Liu. "It contains many things that could potentially slow down the reaction."

PFAS compounds are used in thousands of products, from chip bags to non-stick cookware, but firefighting foams are the primary source of PFAS groundwater contamination because they have been used for decades to extinguish aircraft fuel fires at hundreds of military sites and commercial airports. These foams have also been routinely used for smaller fuel spills as a preventative measure to prevent fires.

Invented by the U.S. Navy in the 1960s, the foams form a water film around burning gasoline and other flammable liquids, quickly depriving the fire of oxygen and extinguishing it.

Due to widespread use, the U.S. Department of Defense has ordered an assessment of 715 military sites across the country for PFAS releases and by the end of last year found that 574 of those sites require further investigation or cleanup under federal law.

PFAS cleanups became more urgent last month when the EPA introduced a new regulation requiring water utilities to reduce contamination if levels of certain PFAS compounds exceed 4 parts per trillion.

Liu said the method he developed with Yang is well suited for cleaning heavily contaminated water used to flush tanks, hoses, and other firefighting equipment. The method can also be used to treat leftover foam tanks containing PFAS.

Their method can also help water supply companies address groundwater contamination. Contaminated groundwater is often treated with ion exchange technologies where PFAS molecules bind to resin beads in large treatment tanks. The UV light and electrochemical oxidation method developed by Liu and Yang can also help regenerate the beads so they can be reused, Liu said.

"We want to have sustainable resin management," said Liu. "We want to reuse it."

The title of the study is "Near-Complete Destruction of PFAS in Aqueous Film-Forming Foam Using Integrated Photo-Electrochemical Processes." Besides Liu and Yang, the study authors are Yunqiao Guan, Zekun Liu, Nanyang Yang, Shasha Yang, and Luz Estefanny Quispe-Cardenas, who are current or former students at UCR and Clarkson.

This research was funded by the U.S. Department of Defense Strategic Environmental Research and Development Program.

Source: University of California