Redox electrodialysis and electrosorption combined to remove PFAS

This is the claim of a team from the University of Illinois Urbana-Champaign (UIUC) whose study is said to be the first to describe an electrochemical strategy to capture, concentrate and destroy mixtures of PFAS — including ultra-short-chain PFAS — from water in a single process.

PFAS (per- and polyfluoroalkyl substances) are a group of synthetic chemicals that are used in numerous products and are often referred to as ‘forever chemicals’. According to the US Agency for Toxic Substances and Disease Registry, studies have linked exposure to certain PFAS with health effects in humans and animals, including liver damage, immune system damage, low birth weight, and birth defects. 

This new development looks set to address the growing industrial problem of contamination with PFAS, particularly in semiconductor manufacturing.

A previous U. of I. study showed that short- and long-chain PFAS can be removed from water using electrochemically driven adsorption (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 (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 Nature Communications.

“We decided upon redox electrodialysis because the very short-chain PFAS behave a lot like salt ions in water,” Su said in a statement. “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 previously demonstrated highly efficient electrodialysis devices that remove various non-PFAS contaminants. However, the process requires ion-exchange membranes that are expensive and quickly fouled by PFAS molecules.

To overcome this, 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.

According to UIUC, finding the most effective configuration of materials is a significant challenge in PFAS removal.

“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,” said Su. “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.

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 to address wastewater applications and incorporate the system into industrial wastewater streams.

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