Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals used in industry and can be found in numerous household products. Known as “forever chemicals,” PFAS do not easily break down over time due to strong chemical bonds and could build to levels that harm individuals’ health and the environment.
Since many PFAS can dissolve in water, higher levels are often found in water supplies and above Environmental Protection Agency (EPA) limits. According to the Natural Resources Defense Council, approximately half of the U.S. population is drinking water contaminated with PFAS.
To help address the challenges of removing PFAS, Chemical Engineering Professor Zhenmeng Peng is currently part of a National Science Foundation-funded tri-state collaborative.
The four-year project began in early September and is a collaborative effort among Delaware, South Carolina and Alabama, which includes seven universities and 13 faculty members. The overall project is led by the University of Delaware with the University of South Carolina receiving $1.2 million as the lead institution in South Carolina, which also includes Clemson University and Benedict College.
“We designed this as a collaboration because PFAS pollution does not stop at state lines and neither should the solution,” says Professor Dongxia Liu from the University of Delaware and overall project lead. “Our partners contribute complementary strengths in advanced adsorbent materials and destruction technologies, along with real-world test beds spanning diverse source waters.”
The overall goal is to remove and convert PFAS by integrating expertise in a variety of areas, including materials science, electrochemistry and reaction engineering. The project will utilize a multi-scale research framework, integrating experiments and modeling, to incorporate technologies for PFAS separation and conversion.
PFAS are widely used, and their characteristics have many important applications. But they are stable and hard to remove, which poses safety concerns. The PFAS content in drinking water is ultra-low and at the part per trillion (ppt) level, which refers to the concentration of a contaminant in a volume of water. While the EPA limit for PFAS is a few ppt levels, that limit is exceeded in many locations.
“For example, one ppt means there is one gallon of contaminant per trillion gallons of water, which is a small amount. If we want to remove PFAS, we first need to concentrate them, otherwise it’s too dilute in the water,” Peng says. “If we can find an effective and economic way to remove them from the drinking water, we’ll already be making big impact.”
Peng’s research group previously developed redox-mediated electrodialysis method, which removes different types of ions from the water while concentrating them in a different channel. Peng believes this approach can be adapted to help remove PFAS from the water and up-concentrate them for chemical treatment.
Meanwhile, Liu’s group focuses on the research and application of zeolite materials. According to Peng, since these materials have a large surface area that can help absorb PFAS materials from the water, he believes it is possible to integrate both research areas to absorb some of the PFAS from the drinking water.
“When it’s absorbed and saturated, we think our electrochemical device can apply a cell voltage using electricity to drive the migration of the PFAS ions to another channel for continuing to concentrate it,” Peng says.
After gaining a better fundamental understanding of the migration pathway, Peng aims to design improved membranes and optimize the operation conditions for more efficiency.
“This is the first stage and our main research focus,” Peng says. “With the new absorbent material developed by the University of Delaware, we plan to incorporate it into our device to selectively capture PFAS.”
By integrating both methods, Peng believes PFAS levels in water can be significantly reduced, while simultaneously concentrating PFAS to at least the millimolar level or even higher in a separate channel.
“We need to figure out how to upcycle the collected PFAS since the the carbon-fluorine bonding is strong,” Peng says. “One possible approach is to use the electrochemical catalysis method to reduce them into more valuable chemicals.”
Peng also plans to utilize non-thermal plasma chemistry, which applies a high voltage alternating electric field to accelerate free electrons. These energetic electrons can ionize gas molecules, which then help break PFAS into smaller compounds, allowing fluorine atoms to be removed and converted into more valuable products.
“The electrons become energetic, and when they collide with molecules, they can easily be broken down, allowing the chemical reaction to occur under ambient conditions,” Peng says.
The project will also feature a significant education and outreach element. This includes building PFAS expertise, launching sustainable STEM education and training programs across seven partner institutions, and creating long-term collaborations with national labs, industry, and communities.
“About half of the 13 faculty members for this project are junior faculty members,” Peng says. “In addition, nearby Benedict College will recruit undergraduate students to spend some time in my group. We will also organize workshops and other activities.”
As a chemical engineer, Peng feels especially sensitive to the issue of PFAS and is committed to removing them from water and other contaminated sources.
“Not only do we want to remove them from water, but we also want to turn them into valuable chemicals in an economic way,” Peng says. “It will be another major breakthrough since it supports both recycling and the recovery of carbon resources.”