Removing harmful chemicals from contaminated water is only one step toward their elimination to prevent contamination from simply moving into another waste stream.
Researchers at the University of Utah's John and Marcia Price College of Engineering have developed a new method to break down "forever chemicals" under relatively mild conditions. These chemicals, formally known as per- and polyfluoroalkyl substances (PFAS), have many beneficial uses, but are difficult to destroy and can persist in the environment.
PFAS are a class of water pollutants of global concern because of their severe and long-lasting effects on ecosystems and public health. Their strong carbon-fluorine bonds make them resistant to natural breakdown.
The industry-funded study was led by Ling Zang, a distinguished professor in the Department of Materials Science & Engineering and associate dean for research at the Price College of Engineering.
"The ultimate goal is to destroy and detoxify PFAS and reduce their hazards, so cleanup does not simply move contamination from water into another waste stream," Zang said. The results appear in the Nature-affiliated journal Communications Chemistry.
Zang's previous research has focused on removing PFAS through filtration and adsorption and on monitoring treatment performance. This new study builds on that work by introducing a potential method for destroying the chemicals after they have been collected.
To break down PFAS, the research team used reactive chemicals called nucleophiles to sever their strong carbon-fluorine bonds. This process, known as defluorination, released nearly all of the fluorine as fluoride from several tested compounds, including PFOA and trifluoroacetic acid (TFA), a particularly stubborn small molecule. Defluorination is central to PFAS destruction and detoxification.
The method also achieved efficient fluorine removal from two fluorinated plastics, PVDF and PCTFE, which are commonly used in batteries, industrial products and munitions.
Most tests were conducted at temperatures of 110 degrees Celsius (230 degrees Fahrenheit) or below, although some materials required temperatures up to 150 degrees Celsius. These temperatures are substantially lower than the 1,000 degrees Celsius or higher often used for PFAS incineration.
Incineration also presents challenges because incomplete breakdown can produce secondary pollutants, including smaller fluorinated compounds. Some of these byproducts are more volatile than the original chemicals and can disperse through the atmosphere, creating additional concerns about environmental contamination.
The reported method works in ordinary air and does not require the specialized conditions or inputs used by some other PFAS destruction methods, including inert gas atmospheres, deep-ultraviolet irradiation, highly reactive alkali metals, heavy-metal catalysts, externally applied high pressure and energy-intensive mechanical processing.
This approach could eventually allow PFAS to be captured from contaminated water, concentrated into a smaller waste stream and destroyed, rather than transferred from water into another material.
The research remains at the laboratory stage; future studies will explore alternative reagents and reaction conditions to improve its effectiveness and reduce its environmental impact. The researchers also plan to evaluate the method using real waste streams, assess treatment costs and determine the safety of the remaining products.