Granular Activated Carbon Regeneration
Granular activated carbon (GAC) groundwater and drinking water treatment systems are the most widely accepted and commonly used treatment technologies for per- and polyfluoroalkyl substances (PFAS)-contaminated groundwater that is used for drinking water.
The groundwater is extracted, filtered and passed through tanks filled with GAC. This GAC sorbs the PFAS compounds, removing them from the groundwater.
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Once breakthrough of PFAS compounds is observed at the outlet of the GAC tanks, the GAC is considered spent and must be removed. However, there is currently no efficient regeneration options for spent GAC.
There are GAC systems at many installations and drinking water treatment facilities across the U.S. that are being used to remove PFAS from drinking water. The spent GAC may need to be replaced every one to two years. Currently this spent GAC is shipped back to the vendor and reactivated by heating to 1,300 °F in an oxygen-free environment. This is expensive and very energy intensive.
On-site GAC regeneration would reduce operation and maintenance cost, as well as lengthen the life of the system.
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Battelle has demonstrated that a regenerant solution is capable of removing PFAS from spent GAC and is working to scale up this technology for on-site GAC regeneration and reuse. The regeneration solution can then be recycled on-site and stored for future regeneration cycles. The concentrated regenerant solution containing residual PFAS (removed from the spent GAC) would be thermally treated on-site or shipped off-site for disposal.
Through laboratory studies, Battelle has selected the optimal regenerant solution to regenerate GAC that has been exposed to PFAS contamination. Following regeneration, the GAC has been shown to sorb PFOS and PFOA as well as virgin GAC.
How It Works
The on-site GAC regeneration system is expected to include at least two tanks of GAC. One tank will be taken offline while the second tank will allow GAC treatment to continue uninhibited during regeneration. The regenerant solutions will be stored on-site and will be cycled through the tank for the number of bed volumes (determined during laboratory column studies) that will best regenerate the GAC. The spent regenerant solution will be distilled for recycling.
After the regenerant solution has regenerated the initial tank containing the spent GAC with the bed volumes required to remove the PFAS from the GAC, potable water will be passed through that tank to rinse the GAC before putting it back on-line. While the regenerated GAC is back on-line, the influent and effluent will be monitored to determine when breakthrough of the regenerated GAC occurs.