PFAS and water decontamination: current avenues for treating these "eternal pollutants".
PFAS, the per- and polyfluoroalkylated substances often dubbed the "eternal pollutants", represent a major environmental challenge due to their persistence and toxicity.
Today, in addition to better regulating their use, we need better ways of treating these pollutants, i.e. first extracting them from the environment, then destroying them. A real challenge, since these molecules are both highly varied and highly resistant - which is what makes them so successful.
Julie Mendret, University of Montpellier and Mathieu Gautier, INSA Lyon - University of Lyon
Measures to control and ban PFAS emissions, which are essential to limit their release into the environment, are already underway. According to a law passed in February 2025, France must aim for a total halt to industrial PFAS emissions within five years.
A recent survey by Le Monde and 29 partner media revealed that decontaminating soil and water contaminated by these substances could cost between €95 billion and €2,000 billion over a twenty-year period.
As with other organic contaminants, there are two main families of treatment processes.
Some technologies involve separating and sometimes concentrating PFAS from the polluted environment to enable the discharge of a treated effluent, but this generates by-products to be managed which still contain the pollutants. Other technologies involve degrading PFAS. These processes involve the destruction of the C-F (carbon-fluorine) bond, which is very stable, often with high associated energy requirements.
In this article, we list some of the many processes currently being tested at different scales (laboratory, pilot, even full-scale), from innovative materials, which can sometimes simultaneously separate and destroy PFAS, to the use of living organisms, such as fungi or microbes.
Processes for separating and concentrating PFAS in water
At present, the techniques used to remove PFAS from water are essentially separation processes designed to extract PFAS from water without decomposing it, requiring subsequent management of PFAS-saturated solids or liquid concentrates (PFAS-concentrated waste).
The most commonly used technique is "adsorption", which relies on the affinity between the solid and the PFAS molecules that bind to the porous surface. Adsorption is an effective separation technique for many contaminants, including PFAS. It is widely used in water treatment, not least because of its affordability and ease of use. Adsorbent selection is determined by its adsorption capacity with respect to the targeted pollutant. A wide range of adsorbent materials can be used (activated carbon, ion exchange resin, minerals, organic residues, etc.).
Among them, adsorption on activated carbon is very effective for long-chain PFASs, but not very effective for medium- and short-chain PFASs. After PFAS adsorption, activated carbon can be reactivated by high-temperature thermal processes, which entails a high energy cost and a transfer of PFAS to the gas phase to be managed.
The first mobile activated carbon PFAS treatment unit has recently been deployed at Corbas, in the Rhône region, and is capable of treating 50 cubic meters of drinking water per hour.
Another adsorption process involves ion exchange resins, which consist of positively (anion) or negatively (cation) charged beads. PFAS, which are often negatively charged due to their carboxylic or sulfonic functional groups, are attracted and can bind to positively charged anion exchange resins. Differences in efficiency have also been observed according to PFAS chain length. Once saturated, ion exchange resins can be regenerated by chemical processes, producing PFAS-concentrated waste streams that need to be treated. It should be noted that ion exchange resins are not approved in France for use in the production of drinking water.
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Today's most effective technique for removing a wide range of PFAS - both short- and long-chain - from water is filtration by nanofiltration or reverse osmosis membranes. Unfortunately, this technique is energy-intensive and generates separation by-products known as "concentrates". These contain high concentrations of PFAS, which can be difficult to manage (concentrates are sometimes discharged into the environment when they would otherwise require further treatment).
Finally, foam fractionation flotation exploits the properties of PFASs (hydrophilic head and hydrophobic tail) , which settle at the air/liquid interface in foam bubbles and are recovered at the surface. Extraction rates of 99% are thus obtained for long-chain PFAS. As with previous techniques, this produces a concentrate which must be disposed of at a later stage.
Towards technologies that degrade PFAS
Other processes seek to degrade the contaminants present in water to provide a more sustainable solution. There are various technologies for destroying pollutants in water: advanced oxidation processes, sonolysis, plasma technology, etc. These processes can be deployed to complement or replace certain concentration technologies. These processes can be deployed to complement or replace certain concentration technologies.
The destruction of a pollutant is influenced by its biodegradability and oxidation/reduction potential. The natural degradation of PFAS is very difficult due to the stability of the C-F bond, which has a low biodegradation potential (i.e. it is not easily destroyed by processes occurring in nature, e.g. driven by bacteria or enzymes).
Advanced oxidation processes are techniques that use highly reactive and potentially effective free radicals to break C-F bonds. They include ozonation, UV/hydrogen peroxide and electrochemical processes.
Electrochemical treatment of PFAS is an innovative and effective method for degrading these highly persistent compounds. The process relies on the application of an electric current through specific electrodes, generating powerful oxidizing radicals capable of breaking carbon-fluorine bonds, among the most stable in organic chemistry.
For all these advanced oxidation processes, one monitoring point is essential: the production of PFAS with shorter chains than the product initially treated must be avoided.
Recently, a company based at the Swiss Federal Institute of Technology in Zurich (Switzerland) has developed an innovative technology capable of destroying over 99% of PFAS present in industrial water by piezoelectric catalysis. The PFAS are first separated and concentrated by foam fractionation. The concentrated foam is then processed in two reactor modules, where piezoelectric catalysis technology breaks down and mineralizes all short-, medium- and long-chain PFASs.
Sonochemical degradation of PFASs is another avenue currently being explored. When high-frequency ultrasonic waves are applied to a liquid, they create so-called "cavitation" bubbles, inside which chemical reactions take place. These bubbles eventually implode, generating extremely high temperatures and pressures (several thousand degrees and several hundred bars), which create reactive chemical species. The cavitation phenomenon is thus capable of breaking carbon-fluorine bonds, ultimately resulting in less harmful and more easily degradable components. Highly promising in the laboratory, cavitation remains difficult to apply on a large scale, due to its energy cost and complexity.
So, despite these recent advances, several challenges remain for the commercialization of these technologies, notably their high cost, the generation of potential toxic by-products requiring additional management, and the need to determine the optimum operating conditions for large-scale application.
What's the outlook for tomorrow?
Faced with the limitations of current solutions, new avenues are emerging.
The first is to develop hybrid treatments, i.e. combining several technologies. Researchers at the University of Illinois (USA), for example, have developed an innovative system capable of capturing, concentrating and destroying PFAS mixtures, including ultra-short-chain PFAS, in a single process. By coupling electrochemistry and membrane filtration, it is possible to combine the performance of the two processes without the problem of concentrate management.
Innovative materials for PFAS adsorption are also being studied. Researchers are working on stereolithography 3D printing as an integral part of the adsorption materials manufacturing process. A liquid resin containing photosensitive polymers and macrocycles is solidified layer by layer using UV light to form the desired object and optimize the material's properties to improve its adsorption performance. These adsorbent materials can be coupled with electroxidation.
Finally, research is underway on bioremediation to mobilize micro-organisms, notably bacteria and fungi, capable of degrading certain PFAS). The principle is to use PFAS as a carbon source to defluorinate these compounds, but degradation times can be long. This type of promising biological approach could therefore be coupled with other techniques capable of making molecules more "accessible" to micro-organisms, in order to speed up PFAS elimination. For example, a technology developed by researchers in Texas uses a plant-based material that adsorbs PFAS, combined with fungi that degrade these substances.
Nevertheless, despite these technical advances, it remains essential to implement regulations and measures upstream of PFAS pollution, to limit damage to ecosystems and human health.
Julie Mendret, Senior Lecturer, HDR, University of Montpellier and Mathieu Gautier, University Professor, INSA Lyon - University of Lyon
This article is republished from The Conversation under a Creative Commons license. Read theoriginal article.