PFAS removal process aims to stamp out pollution ahead of semiconductor industry growth

A previous U. of I. study showed that short- and long-chain PFAS can be removed from water using electrochemically driven adsorption, referred to as electrosorption, but this method is ineffective for ultra-short-chain molecules because of their small size and different chemical properties. The new study, led by Illinois chemical and biomolecular engineering professor Xiao Su, combines a desalination filtration technology, called redox electrodialysis, with electrosorption in a single device to address the problems associated with capturing the complete PFAS size spectrum.

The study findings are published in the journal Nature Communications.

"We decided upon redox electrodialysis because the very short-chain PFAS behave a lot like salt ions in water," Su said. "The challenge was to produce an efficient, effective electrodialysis system to capture the ultra-short-chain PFAS, have it work in tandem with the electrosorption process for the longer-chain PFAS, destroy them with electrochemical oxidation, and make it happen within a single device."

Su's team has previously demonstrated highly efficient electrodialysis devices that remove various non-PFAS contaminants. However, the process requires ion-exchange membranes, which are expensive and quickly fouled by PFAS molecules.

To clear the membrane hurdle, Su's team introduced an inexpensive nanofiltration membrane that enables the electric-field-driven removal of PFAS without becoming fouled. This technology is based on prior advances made by their group in combining redox polymers with these nanofiltration membranes to enable energy-efficient desalination.

For PFAS removal, having the right material for the job is one thing, but finding the most effective configuration is a significant challenge on its own.

"After experimenting with a variety of device configurations, we finally settled on a system that desalinates the PFAS-contaminated water to remove the ultra-short-chain molecules, then at the same time, carbon electrodes remove the remaining short- and long-chain molecules," Su said. "This process also concentrates all the PFAS, making them easier to destroy once captured."

Finally, the electrochemical oxidation process inherent to redox electrodialysis destroys the captured PFAS by converting them to fluoride ions, a key step towards eliminating these persistent contaminants from the environment.

Su said that the team is excited about the prospect of scaling up the process so they can take it out of the lab and into the field not only to address wastewater applications but also to incorporate the system on-site into industrial wastewater streams.

"This work is very timely due to interest from the U.S. government, wastewater treatment facilities and the semiconductor industry," Su said. "Semiconductor production is expected to rise over the coming years, and PFAS abatement for sustainable production will become a major issue moving forward."

Illinois researchers Nayeong Kim, Johannes Elbert and Ekaterina Shchukina contributed to this study. The National Science Foundation ERASE-PFAS program supported this research. Su also is affiliated with civil and environmental engineering, chemistry and the Beckman Institute for Advanced Science and Technology at the U. of I.