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Consultant recommends granular activated carbon for PFAS treatment after pilot test showed ion-exchange fouling
Summary
Gannet Fleming presented pilot-test results for PFAS treatment at the borough water plant, reporting both granular activated carbon and ion-exchange removed PFAS but that ion-exchange showed irreversible fouling and head-loss in warm, low-flow conditions, leading the firm to recommend GAC for the design.
A Gannet Fleming consultant briefed the Carlisle Borough Council on pilot testing of treatment options for per- and polyfluoroalkyl substances (PFAS), concluding that granular activated carbon (GAC) is the lower-risk option for the borough’s treatment upgrade.
Joe, the Gannet Fleming presenter, summarized the firm’s earlier recommendation to pilot both ion-exchange resin and GAC. He said both technologies “remove PFAS effectively,” but the pilot showed the ion-exchange resin developed progressive head loss that could not be recovered with backwashing under warm, low-flow conditions. “The biggest challenge we saw was with fouling and head loss,” he said, adding that continued head loss on the resin “would eliminate the cost advantages associated with ion exchange.”
Based on the demonstration, the consultant recommended advancing the design using granular activated carbon—two vessels in a lead–lag configuration—with increased allowance for backwashing and a slightly larger media footprint. He noted an operational option to apply low-dose chlorine “less than half a milligram per liter” if fouling becomes a problem; ion-exchange resins are not compatible with chlorine dosing in the same way.
Nut graf: The recommendation reflects a tradeoff between theoretical advantages of ion exchange (smaller footprint, higher capacity) and demonstrated operational risk (irreversible fouling) under the borough’s observed pilot conditions. Staff asked questions about GAC feedstocks (coal, wood, coconut-based carbons), broader contaminant benefits, and performance in drought; the consultant answered that GAC can remove other organic contaminants and disinfection byproduct precursors but may have different PFAS capacity depending on the carbon type.
The presentation noted the pilot test results will be folded into design work already underway; staff said the borough will seek authorization to proceed from roughly 20% to final design when ready. No formal procurement decision was taken at the workshop; the consultant said pilot testing is required to support a construction permit for surface-water treatment.
Ending: Council members thanked the consultant; staff will return with design authorization and next steps for final design and permitting.
