Known as “forever chemicals,” Per- and polyfluoroalkyl substances (PFAS), anthropogenic hydrocarbons, are found in everything from food packaging to firefighting foam. These substances, chemically stable, can accumulate in ecosystems. The detection of PFAS in natural waters is a major environmental problem and the exposure to these substances can lead to adverse human health effects. Electrochemical anodic oxidation (EO) was classified as a promising remediation technique for water contaminated with PFAS. Previous studies using Boron-doped diamond (BDD) electrodes has successfully degraded highly concentrated PFAS (hundreds of mg/L in most cases) tested individually in solution. Knowledge on the behavior of PFAS mixtures at lower concentrations is much needed. This study assessed 9 perfluoroalkyls acids either individually or in a mixture (1 µg/L and 200 µg/L of each PFAS), using electrochemical oxidation (BDD and Titanium oxide (Ti₄O₇) electrooxidation cells, 2 electrodes of 12.5 cm² separated by 2 mm) in continuous recycling solutions in the presence of 10 mM Na₂SO₄. Results showed that the degradation of some PFAS tested individually was higher than those tested in a mixture since long-chain’s PFAS were found to produce short-chain’s PFAS as by-products. Long chain’s PFAS were found to be better degraded individually than the short ones. C4 PFAS seemed to be relatively stable under these experimental conditions. EO using BDD electrodes clearly showed a better efficiency than the one using Ti₄O₇ electrodes under similar experimental conditions. The presence of dissolved organic matter (DOM, 5 mg/L of humic substances isolated from surface water) did not have significant impact on PFAS degradation, EO efficiency was higher with an initial PFAS concentration of 200 µg/L than with a lower concentration of 1 µg/L. This implies the importance of a treatment combining a concentration phase followed by anodic electro-oxidation mineralization. Factors such as current density, inorganic (Cl^-, NO₃^-, alkalinity) and organic matrix (DOM character), PFAS initial concentration and type of the electrolyte (sodium sulfate, persulfate, with or without ferrous ions at low pH, etc.) are being varied and studied in order to obtain the optimized operation conditions for the elimination of PFAS.

Lama SALEH

PhD Student, University of Poitiers

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