Pilot scale removal of per- and polyfluoroalkyl substances and precursors from AFFF-impacted groundwater by granular activated carbon†
The US military, municipal fire stations, airports, and the petroleum-processing industry have used aqueous film forming foam (AFFF) to extinguish hydrocarbon-based fires. Repeat uses of AFFF during firefighting activities resulted in per- and polyfluoroalkyl substance (PFAS) contamination of groundwater. Granular activated carbon (GAC) adsorption is a frequently selected technology for remediating water containing organic contaminants, including PFASs. A pilot study conducted over nine months at a military fire-fighting training area employed two GAC vessels in a lead–lag configuration to evaluate PFAS removal. Breakthrough was quantified for branched and/or linear isomers of 15 PFASs identified by liquid chromatography tandem mass spectrometry (LC-MS/MS) including perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, perfluoroalkyl sulfonamides, and fluorotelomer sulfonates. The total oxidizable precursor (TOP) assay was used to provide information on precursors in the influent and to quantify precursor breakthrough. Individual PFASs quantified by LC-MS/MS accounted for 76% of the PFASs in influent as quantified by the TOP assay. The influent PFAS profile was used to infer the nature of the AFFFs used at the site. Breakthrough of shorter-chain PFAS and branched isomers occurred before breakthrough of longer-chain PFAS and linear isomers. For PFAS with equal perfluoroalkyl chain length, adsorbability for different head groups was in the order –COO− < –SO3− < –CH2CH2SO3− < –SO2NH. TOP assay results further showed that precursors of perfluoroalkyl carboxylic acids (PFCAs) broke through GAC in addition to commonly measured PFCAs and perfluoroalkylsulfonic acids. Chromatographic retention times of PFAS obtained from a single analysis of influent groundwater can be used to predict the relative order of breakthrough for other PFASs at the pilot scale on GAC.