PFAS: Forever Chemicals, Real Problems

Understand the sources, risks, and evolving technologies in the fight against forever chemicals in water treatment

by Melissa John, Research Scientist

PFAS, better known colloquially as “forever chemicals” or “persistent organic pollutants” (POPs), stands for per- and polyfluoroalkyl substance(s). These chemicals contain multiple carbon-fluorine bonds, which are extremely strong and stable, allowing them to resist degradation both in the environment and within the human body. PFAS are a family of approximately 5,000 human-made chemicals that are resistant to water, oil, and heat. Due to their stability, they were widely used in a variety of consumer products, including surface protection products, industrial surfactants, non-stick cookware, and more.

The two most studied PFAS are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These chemicals were produced in the largest quantities in the United States and are now widely found across all trophic levels-air, soil, and water-throughout the country. While PFOA and PFOS are no longer produced in the US due to their health and environmental impacts, short-chain PFAS still are.

How to determine if PFAs are there?

The method produced by the EPA for measuring 24 PFAS in wastewater samples uses liquid chromatography/ tandem mass spectrometry (LC-MS/MS). This analytical equipment works by separating the complex mixtures of compounds using liquid chromatography (LC), followed by two stages of mass spectrometry (MS) to identify and quantify compounds based on the mass-to-charge ratio. The first MS filters ions, and the second fragments to provide structural information for accurate analysis.

What methods are in place to limit PFAS?

Since PFAS resist degradation, standard activated sludge treatment does not effectively remove these chemicals. Therefore, removal technologies are needed to effectively remove PFAS from water. The most effective removal technologies are ion exchange resins, granular activated carbon, and high-pressure membranes.

Ion exchange resins are made from hydrocarbons, which are a polymeric material with a high porosity making it insoluble in water, acids, and bases. The ion exchange resins are in two categories: cationic and anionic. For PFAS, which are negatively charged, anion exchange resins (AER) are particularly effective, as the positively charged anion resin captures the contaminated material passing through water, allowing for the capture of many PFAS compounds.

Another method, which is also the most studied and less expensive than AER, is granular activated carbon (GAC), which is made from organic materials with high carbon contents, such as wood. GAC adsorbs many compounds in water systems, including organics, odor, and synthetic organic chemicals. Its high porosity and large surface area make it an effective adsorber. Adsorption, the process by which contaminants are captured, accumulates substances like PFAS at the surface interface between the water and the GAC. This method has proven effective in removing long-chain PFAS, such as PFOA and PFOS, but is less effective for short-chain PFAS. Effective removal depends on variables such as type of carbon, depth of carbon bed, flow rate, species of PFAS, temperature, and the presence of other contaminants. In drinking water applications, GAC has shown effectiveness when used in flow-through filters after the removal of particulates.

Alternatively, powdered activated carbon (PAC) has been shown to remove PFAS from water, albeit not as efficiently or effectively as GAC. PAC, like GAC, is made of activated carbon with the main difference being size, as PAC is a smaller particle size. Because of this, PAC needs to be added directly to the water and removed with other particulates in clarification, making it less economical than GAC.

Lastly, high-pressure membranes, such as those used in reverse osmosis (RO) or nanofiltration (NF), can effectively remove PFAS. These systems work by filtering feedwater through a membrane, producing treated water while rejecting waste. Both RO and NF use thin synthetic polymer membranes that are spiral wound, but RO has a tighter membrane than NF. Since these are spiral wound membranes, they cannot be backwashed, so suspended solids must be removed from the feed beforehand. While both treatments take pressurized source water and separate out monovalent ions and organic molecules, RO utilizes the natural osmosis process, in which liquid passes through a semi-permeable membrane from low to high concentration- or, in the case of reverse osmosis, the opposite direction, as the name suggests. According to the EPA, these membranes are more than 90% effective at removing PFAS, including short-chain PFAS. However, the main disadvantage is that 20% of the water is rejected as high-strength waste, making this option better suited for small volumes due to disposal challenges.