Aqueous film forming foams (AFFFs) are a major source of per- and poly-fluoroalkyl substance (PFAS) contamination to the environment. In this study, electrochemical oxidation of PFAS in a diluted AFFF solution was performed using a tubular TiO2 Magneli phase reactive electrochemical membrane (REM) in flow through mode. Experiments were conducted at a flux of 610 L m-2 h-1 and 40 mA cm-2 current density, and results from target analyses showed efficient removal of long chain (C7 to C9) perfluorinated carboxylates and perfluorinated sulfonates. In general, the short chain (C4 to C6) PFAS showed increases in concentration until ~4 h of electrolysis and net removal thereafter. The suspect analyses data primarily showed removal of perfluoroakane sulfonamide precursors and the formation of perfluorosulfonamides (FASA). During the electrochemical oxidation of precursors, the N-methyl perfluoroalkyl sulfonamido acetic acid (MeFASA) compounds were removed after 4 h of electrolysis. It was concluded that the degradation of PFAS was a result of a combination of hydroxyl radical and direct electron transfer reactions. Ion chromatography data showed formation of fluoride and sulfate ions for up to 2 h of treatment. The decrease in fluoride concentration after 2 h was due to adsorption of fluoride on the REM under acidic conditions. The detected fluoride concentration at 2 h accounted for ~84% of the total fluoride in the AFFF solution, where the balance of fluoride was present in short chain PFAS. The energy consumption for 90% defluorination was 27.3 W h L-1. The energy consumption for REM was significantly lower compared to that reported in literature for 90% defluorination using state-of-the-art boron-doped diamond (BDD) electrode, which was 430 W h L-1. The REM proves to be a promising technology for treatment of AFFF because of its ability to electrochemically degrade PFAS effectively.

Destruction of perfluoroalkyl substances in aqueous film forming foams by electrochemical oxidation using TiO2 magneli phase electrochemical membranes

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