New method to degrade PFAS found effective in the lab

UNSW Sydney has announced that its scientists are developing catalysts able to break down PFAS chemicals that contaminate water.

Per- and poly-fluoroalkyl substances (PFAS) are known as ‘forever chemicals’ because they are notoriously resistant to degradation. Due to their stable chemical structure, PFAS — which are found in thousands of variants — are used in oil- and grease-resistant food packaging, non-stick cookware, cosmetics, clothing and firefighting foams.

The chemicals are so widespread that they have infiltrated water sources and soil. Recent reports have found that much of our global water resources exceed the drinking limits of PFAS and concerns over their environmental and health impacts have steadily escalated.

Despite ongoing efforts to develop ways of degrading PFAS, current methods are limited by a lack of efficient, scalable and environmentally friendly processes.

Now, a team of scientists from UNSW’s School of Chemistry have designed a catalyst system that can activate a reaction to break down common types of branched PFAS. The new method, developed by Dr Jun Sun and Professor Naresh Kumar and recently published in the journal Water Research, holds promise for more efficient and sustainable PFAS remediation in the future.

Working alongside Prof Denis O’Carroll, Prof Michael Manefield and Dr Matthew Lee from the UNSW School of Civil and Environmental Engineering, and funded by a $3 million grant from the Australian Research Council in 2019, the team have designed a catalyst system that could play a key role in solving the problem of PFAS.

“Owing to its robust nature, simple application and cost-effectiveness, the new system we have developed shows successful PFAS remediation in the lab, which we hope to eventually test at a larger scale,” Sun said.

Since the 1940s, PFAS chemicals have been produced on an industrial scale, with their unique structure used in various commercial and industrial applications, most notably firefighting foam. But the chemical is so resistant to degradation that people in Australia — and all over the world — are likely to have low levels of PFAS in their bodies.

“In the time that PFAS was being produced globally, it wasn’t realised that this chemical is essentially non-destructible,” Kumar said. “PFAS is such a robust chemical that it cannot be degraded within the human body, and that has become a concern.”

Some scientific research suggests that exposure to certain PFAS may lead to adverse health outcomes, but more evidence is needed to reveal how different levels of exposure to PFAS can lead to various health effects.

“The pressing need for effective PFAS remediation has driven the investigation into a wide array of treatment methods, spanning from physical separation processes to advanced destruction techniques, all which have their limitations,” Sun said.

PFAS is a fluorinated chemical bound by strong carbon-fluoride (C-F) bonds, which are famously hard to break. An existing method to remove PFAS from water and soil works by absorbing PFAS onto carbon material. “So if you’ve got a pad of activated carbon, and you pass water through it, you can absorb PFAS onto the activated carbon, but you then have to burn it to destroy the PFAS, or safely store it,” Kumar said.

“There is an ongoing need to come up with an energy-efficient and environmentally friendly way to remove PFAS from water,” Sun said. “The method we have developed is a type of reductive defluorination, which decreases the toxicity of PFAS by breaking the strong C-F bonds of branched PFAS.”

Nano zero-valent metals (nZVMs) are a type of eco-friendly chemical reducing agent that scientists have used extensively for decades in the treatment of groundwater and soil contaminated with chlorinated compounds, using a dechlorination process. Previous studies indicate that PFAS can be degraded using nano zero-valent zinc and the naturally occurring catalyst vitamin B12, a water-soluble vitamin present in our daily diet. But again, the process has been found to be slow and inefficient.

“Inspired by the fact that B12 has the potential to catalyse this reaction, we wanted to synthesise a catalyst that mirrors the unique ring shape of B12, which we did using a structure known as a porphyrin ring,” Sun said.

Testing their method out on two common types of PFAS — branched PFOS and PFOA — Kumar and Sun mixed the PFAS chemicals with nZVMs and measured the amount of fluoride ion that is produced by the reaction.

The results from this latest study revealed that within five hours, approximately 75% of the fluoride had been released from branched PFOS and PFOA, significantly reducing the amount of PFAS within the solution. Meanwhile, the B12-based catalyst system only showed less than 8% defluorination within five hours.

“The next step for us is to really try this on a pilot scale to see if this can be done out of the laboratory on a real sample,” Kumar said. “Then we’d like to try it out in a real water purification system or sites which are contaminated with PFAS.”

The team are also considering ways to scale up the process in an environmentally friendly way, by incorporating the catalyst into an electrode. “These findings would allow us to set up the catalytic system in an electrochemical cell, where applied voltage can replace the nano zero-valent zinc so that the PFAS can be degraded within the cell,” Kumar said.

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