Per- and polyfluoroalkyl substances (PFAS) have become a growing concern in water treatment due to their widespread use and persistence in the environment. These "forever chemicals" are commonly found in products like coatings, fire retardants, and semiconductor manufacturing. The complex structure of PFAS, ranging from ultra-short- to long-chain molecules, has made their removal challenging. Traditional methods often require multiple stages of filtration, significantly increasing costs and complexity.
A new study from the University of Illinois Urbana-Champaign, led by chemical and biomolecular engineering professor Xiao Su, presents a groundbreaking solution. The team developed an innovative electrochemical system that integrates redox electrodialysis with electrosorption to remove the full spectrum of PFAS contaminants in a single process. This novel approach also enables the complete destruction of PFAS via electrochemical oxidation, offering a comprehensive and efficient solution for water treatment.
Conventional methods like activated carbon filtration and ion exchange primarily target long-chain PFAS, leaving ultra-short-chain variants untreated. These smaller molecules behave like salt ions in water, making them difficult to capture and remove. As semiconductor production and other industrial applications continue to grow, the prevalence of PFAS contamination is expected to rise, creating an urgent need for effective removal technologies.
The main hurdle in existing electrochemical systems has been the use of costly ion-exchange membranes, which are prone to fouling by PFAS molecules. This issue significantly reduces the efficiency and increases the operational costs of traditional PFAS treatment systems.
To address these challenges, Su's team developed a redox-polymer electrodialysis system that combines affordable nanofiltration (NF) membranes with a water-soluble redox polymer. This design allows for the efficient capture of both ultra-short-chain and longer-chain PFAS, while also performing desalination. The use of NF membranes avoids the fouling issues seen with traditional ion-exchange membranes, making the process more cost-effective and reliable.
“We decided upon redox electrodialysis because the very short-chain PFAS behave a lot like salt ions in water,” said Su. “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.”
The integrated system uses two distinct mechanisms for PFAS removal:
Once captured, the PFAS are concentrated for easier destruction. The final step involves electrochemical oxidation, converting the PFAS into harmless fluoride ions, effectively eliminating these persistent contaminants from the environment.
The redox-polymer electrodialysis system has shown promising results in lab-scale tests, successfully removing PFAS from both synthetic and real wastewater samples. The technology achieved over 90% removal efficiency for a wide range of PFAS, including the highly challenging ultra-short-chain variants like trifluoroacetic acid (TFA). Additionally, the process demonstrated effective desalination, reducing salt concentrations to potable water levels.
The research team is optimistic about scaling up the system for industrial applications, particularly in semiconductor manufacturing, where PFAS use is prevalent. The simplified, single-step approach not only reduces energy consumption but also offers a practical solution for wastewater treatment facilities.
Su noted that development is timely, given the growing interest from the U.S. government and industry stakeholders. With the expected rise in semiconductor production, sustainable PFAS management will become a critical issue.
