Granular activated carbon (GAC)

GAC is carbon made into grains with a huge surface area. Water flows through a bed of it, and contaminants stick to the surface in a process called adsorption. EPA calls activated carbon the most studied treatment for PFAS removal.

EPA says GAC has been shown to effectively remove PFAS from drinking water when it is used in a flow-through filter after particulates have been removed. It works well on longer-chain PFAS such as PFOA and PFOS. Shorter-chain PFAS do not adsorb as well.

GAC also wears out. The carbon fills up, and the bed must be replaced or regenerated. Performance depends on the carbon type, bed depth, flow rate and the other organic matter in the water.

That means a pilot test and a replacement plan matter. Ask any vendor how often the media changes and what happens to the used carbon.

GAC is one of several options. A common alternative is ion exchange. The right choice depends on your water and your target.