Energy-Efficient Electrochemical Oxidation of Perfluoroalkyl Substances Using a Ti₄O₇ Reactive Electrochemical Membrane Anode

Abstract

An energy-efficient Magnéli phase Ti4O7 reactive electrochemical membrane (REM) was applied for the oxidation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Approximately 5-log removal of these compounds was achieved in a single pass through the REM with residence times of ∼11 s at 3.3 V/SHE for PFOA and 3.6 V/SHE for PFOS. The permeate concentrations of PFOA and PFOS were <86 and 35 ng L–1, from initial concentrations of 4.14 and 5 mg L–1, respectively. The highest removal rates were 3415 ± 203 μmol m–2 h–1 for PFOA and 2436 ± 106 μmol m–2 h–1 for PFOS at a permeate flux of 720 L m–2 h–1 (residence times of ∼3.8 s). The levels of energy consumption (per log removal) to remove PFOA and PFOS to below the detection limits were 5.1 and 6.7 kWh m–3, respectively. These values are the lowest reported for electrochemical oxidation and approximately an order of magnitude lower than those reported for other technologies (i.e., ultrasonication, photocatalysis, vacuum ultraviolet photolysis, and microwave–hydrothermal decomposition), demonstrating the promise of the REM technology for water treatment applications.