After the GAC: Removing PFAS From Water Is Only Half the Job
By Noelle DeStefano, National PFAS Sector Lead
PFAS treatment discussions usually focus on the front end: how to get these compounds out of finished water, which treatment technology makes sense, and how to meet performance targets. That is understandable, because removal is the immediate objective and the most visible part of the job.
But once PFAS is captured on GAC (granular activated carbon) the problem has not been solved so much as... moved. The compounds are no longer in the treated water, which is obviously the point, but they are now concentrated on a managed solid media. That shift matters more than many people realize, because it is where some of the hardest practical questions begin.
This was the focus of my recent presentation at the VA AWWA Annual Drinking Water Quality & Research Seminar. The basic message was straightforward: GAC is a separation technology at the plant, not a destruction technology at the plant. It does important work and remains one of the most practical and widely used PFAS treatment options for drinking water. But once the carbon is spent, utilities are left with a new responsibility that gets much less attention than treatment performance itself: understanding what happens next.
From PFAS Removal to PFAS Responsibility
That is where the conversation tends to get murkier. Where does the spent carbon go? Is the PFAS actually destroyed, or is it being transferred into a different management system? Who handles it after it leaves the site? What records come back? And if leadership, regulators, or the public ask those questions later, will the utility be in a position to answer them clearly?
In practice, there are only a few real downstream pathways, and they are not all equal.
Reactivation is often the most practical and most established route. The carbon is treated off site and restored for reuse, with virgin makeup added to replace losses. Under controlled reactivation conditions, much of the targeted PFAS may be substantially reduced or destroyed, but that outcome depends on the treatment conditions, downstream controls, and what was actually measured and verified. “Reactivated” is not a magic word, and it should not be treated like one. The meaningful questions are still about operating conditions, emissions controls, residuals, and documentation.
Thermal destruction sounds more final, which is part of why it gets so much attention. But it also requires the most discipline in how it is discussed. Low target PFAS in one output stream may be encouraging, but that is not the same as proving complete destruction across gases, liquids, solids, and possible byproducts. The stronger the claim, the stronger the supporting evidence needs to be.
Disposal is usually the simplest answer operationally and the weakest answer conceptually. It tells you where the media went, but not whether the PFAS problem is over. In a landfill setting, PFAS is being managed in a containment system, not destroyed, and that means long-term questions can remain about leachate and downstream residual handling. Containment is not destruction, and that distinction matters both technically and publicly.
Emerging destruction technologies should not be dismissed, and some have shown strong performance, especially on more concentrated waste streams. But that is not the same as saying they are the routine default for drinking water utilities managing spent GAC today. The real question is not whether destruction can work in some context. It is where it fits right now, for which waste streams, and how confidently the outcome can be verified and documented.
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Asking Better Questions Downstream
This is why the issue is not only technical. It is also operational, contractual, and communicative. Utilities may not operate the downstream facility, but they are increasingly expected to understand the path and explain it. That means knowing whether the spent carbon was reactivated, destroyed, or disposed. It means understanding whether the downstream path can change, whether the carbon is pooled, and what paperwork actually comes back. It also means recognizing that treatment expectations are becoming clearer while downstream residuals management is still much less cleanly defined.
To me, that is the real takeaway. Utilities do not need to become experts in every destruction technology on the market, and they do not need to overpromise certainty they do not have. They do need to ask better questions. Where is the spent carbon going? What exactly is being done with it? What documentation will be returned? If the answer changes later, how will they know?
For most utilities, the smartest move today is not to promise that PFAS has been “taken care of” once it leaves the finished water. It is to understand the downstream pathway, ask the right questions before the truck shows up, and keep records strong enough to answer those questions later.
Because the treatment story does not end at the GAC vessel. It just becomes a different kind of story.
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