GAC Adsorption Treatment for Perfluorinated Compound Removal
Last Modified: Aug 10, 2018
- David Briley - Hazen and Sawyer
The U.S. Environmental Protection Agency issued health advisory levels (HALs) for PFOA and PFOS at a level of 70 ppt. The Gadsden Water and Sewer Board (Gadsden, Alabama) relies on the Coosa River for its water supply and levels of PFOA and PFOA in the source water have raised concerns about consistently maintaining finished water quality below the HAL. The C.B. Collier WTP is a conventional treatment facility, and a MIEX system was added in recent years for disinfection byproduct precursor removal. Monitoring data has shown that MIEX does not provide sufficient removal of perfluorinated compounds (PFCs) in order to maintain finished water below the HALs.
Gadsden decided to proceed with expedited implementation of Granular Activated Carbon (GAC) adsorption to ensure the finished water is within the EPA HALs. Whereas the short-term goal was control of PFOA and PFOS, removal efficiencies for short chain PFCs was also a consideration. The initial capacity of the GAC Facility is less than the full WTP capacity and will rely on blending of GAC treated water with filtered water from the WTP to meet the HALs. The initial capacity of the Phase 1 GAC Facility is 6 mgd with planning for future expansion of the GAC Facility up to the full WTP capacity of 24 mgd.
The GAC Facility will consist of pressure vessel type GAC contactors designed for an empty bed contact time (EBCT) of 20 minutes. The objective is the expedited implementation of the GAC Facility to provide an additional tool for control of PFOA and PFOS below the HALs. This presentation will provide a case study for utilities facing EPA Health Advisory Levels, which are implemented on fast track and vary significantly from standard rulemaking process.
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