Can activated carbon be used for the removal of PFAS and is there such a thing as ‘PFAS carbon’?

PFAS (per- and polyfluoroalkyl substances) constitute a complex group of thousands of man-made chemical compounds. Because of their grease- and water-repellent properties, PFAS are used in numerous industrial products and everyday consumer goods, ranging from water-repellent coatings and cosmetics to firefighting foams and food packagings.

The typical carbon-fluorine bond makes PFAS very persistent, so that they barely or do not break down in the environment or the human body (‘forever chemicals’). This is one of the reasons why they can be harmful to humans and the environment.

PFAS consist of a fluorine-carbon chain with a functional group at one end, i.e. a carboxyl group or sulfonic group. The combination of the hydrophobic carbon-fluorine tail and the hydrophilic functional group creates unique interactions with activated carbon. Among the various adsorption mechanisms, hydrophobic and electrostatic interactions are the most decisive.

Compared to other organic molecules, the binding of PFAS to activated carbon will be far more difficult due to the presence of fluorine atoms. One of the most important parameters influencing the adsorption of PFAS onto activated carbon is the length of the hydrophobic carbon-fluorine chain. It has an impact on the binding energy with the internal surface of the activated carbon. Scientific studies and practical experience show that:

• Longer chains (such as PFOS and PFOA, with 8 carbon atoms) have a stronger hydrophobic interaction with the surface of activated carbon.
• Shorter chains (such as PFBA, with 4 carbon atoms) adsorb much less efficiently, due to weaker interactions and higher mobility in water.

The binding energy thus increases with chain length, meaning that the binding of longer PFAS to the carbon surface is stronger and more stable. Moreover, PFAS molecules with a sulfonic group are adsorbed up to 4 times better on activated carbon than their counterparts with the same number of carbon atoms but with a carboxyl group instead of a sulfonic group.

In general, it can be stated that PFAS adhere to activated carbon less easily than, for example, BTEX, AOX or COD. At Cargen, we know that PFAS removal requires careful monitoring, as well as an in-depth study of the conditions of the purification process.

No. Every type of activated carbon from Cargen’s range, suitable for water purification, will also adsorb PFAS from the water to be purified. Of course, high-quality carbon will adsorb relatively more PFAS than lower-quality carbon.

However, not every application requires the highest quality (and therefore the most expensive) activated carbon. It is essential to correctly combine project data (influent composition, mutual ratio of PFAS molecules, flow rate and contact time, project duration, discharge standards, etc.) with the properties of the carbon (pore structure, surface chemistry, etc.) and practical data to select the best activated carbon in terms of both efficiency and cost.

This way we offer a solution that not only works in the laboratory, but also in practice, without charging customers unnecessary costs.

Removing PFAS via activated carbon is entirely possible. The removal efficiency is, however, strongly dependent on the chain length of the PFAS compounds and the project parameters. A targeted selection of activated carbon based on the type of PFAS present and the application conditions is essential for an effective and (cost-)efficient solution in practice.