Developing a new way to capture PFAS using electrochemistry

BY ANTHONY KING

A new way to capture and concentrate per- and polyfluoroalkyl substances (PFAS) has been developed using electrochemistry for the first time. This traps PFAS – dubbed “forever chemicals” – from water in a single process (Nature Communications, DOI: 10.1038/s41467-024-52630-w).

The exceptional stability and thermal resilience of PFAS has made them popular in coatings, semi-conductor manufacturing and fire retardants, as well as household products. Yet there is concern about their persistence in the environment and bioaccumulation in people.

It remains challenging to remove PFAS contamination from water. ‘Wastewater treatment processes are not designed to remove emerging contaminants, such as PFAS,’ notes Lokesh Padhye, an environmental engineer at Stony Brook University, New York.

‘PFAS are particularly challenging because the class includes thousands of compounds with varying chain lengths and functional groups, such as carboxylates, sulfonates.’

A team at the University of Illinois previously reported using an electrode to capture PFAS via electrosorption. This approach does not work well for ultra-short chains.

‘We basically combined an electrosorption process with an electrodialysis process,’ says Xiao Su, who led the new research. The electrodialysis system is similar to a commercial membrane used for removing salts from water, except that PFAS glues to commercial membranes and does not come off easily.

The new system relies on a water-soluble, redox polymer with an inexpensive nanofiltration membrane, capturing various chain-length PFAS without membrane fouling.

An electrochemical redox-reaction assists in the migration of the PFAS through the nanofiltration membrane. The combined approach of electrodialysis and electrosorption eliminated about 90% of ultra-short-, short- and long-chain PFAS, the team reported. Once captured, electrochemical oxidation on a boron-doped diamond electrode can be carried out to defluorinated the PFAS.

‘The system can potentially address the diversity of PFAS structures, a persistent challenge in current remediation technologies,’ says Padhye, who praises it as ‘exciting and innovative.’

‘The use of inexpensive nanofiltration membranes and coupling with desalination makes a compelling case for scalability,’ he adds.

The Illinois group is especially interested in industrial waste streams, such as from semiconductor plants, and scaling up from half a litre, or a litre, to 40 or 50 gallons. ‘We are interested in getting more realistic industrial wastewaters and test this with more complex mixtures of PFAS,’ says Su. They are seeking industrial partners.

‘Mass transfer limitations are a known challenge for electrosorption and electrochemical processes on a large scale, which reduces their efficiency,’ notes Padhye. ‘A techno-economic analysis is necessary.’

‘Technologies that are currently available for PFAS removal from water are limited to physical removal processes, such as ion exchange, adsorption - mostly by activated carbon - and reverse osmosis,’ says Madjid Mohseni, a chemical engineer at the University of British Columbia, Canada.