Why GAC Works Best on PFOA and PFOS
Granular activated carbon (GAC) has become the most widely deployed technology for PFAS removal in drinking water systems. However, its effectiveness is not uniform across all PFAS compounds—it is specifically well-suited for long-chain PFAS like PFOA and PFOS, and this distinction has profound implications for water safety.
The Science of Adsorption Chain Length
PFAS adsorption onto activated carbon is governed primarily by hydrophobic interactions and electrostatic forces. Longer carbon chain PFAS compounds (C8 and above, such as PFOA with 8 carbons and PFOS with 8 carbons) have stronger hydrophobic character that drives them to adsorb tightly onto carbon surfaces. The longer the chain, the more tenaciously the compound binds.
PFOA and PFOS: The Well-Studied Benchmark
Decades of research have established removal efficiencies for PFOA and PFOS on GAC. Properly designed GAC systems achieve 95–99% removal for these two compounds under normal operating conditions with adequate empty bed contact time (EBCT). This strong performance is why PFOA and PFOS became the regulatory focus and why GAC became the standard treatment response.
The False Sense of Security
The problem is that PFOA and PFOS represent just two of over 4,700 PFAS compounds in the environment. When water utilities install GAC to meet PFOA/PFOS MCLs, they achieve compliance—but the filter may allow dozens of other PFAS compounds to pass through largely unimpeded. Understanding this gap is essential for anyone evaluating the true protective value of their water treatment system.