Per- and poly-fluoroalkyl substances (PFAS) are a group of anthropogenic chemicals that are of global concern due to their ubiquitous detection, potential toxicity, and impact on human health. Electrochemical processes have shown promising potential for PFAS degradation given their high treatment efficacy and lower cost compared to other treatment methods. Electrochemical processes degrade organic pollutants through direct electron transfer on the anode surface and indirect oxidation by generated oxidants such as ●OH or SO4●-). Given the unique structure of PFAS, the mechanism of PFAS electrochemical oxidation is not fully established and is the subject of much research. In this study, we investigated the electrochemical decomposition of PFOA, as a model PFAS, using a bench-scale electrochemical reactor, equipped with boron-doped diamond as the anode and stainless steel as the cathode. The effects of operating parameters such as current density (2-10 mA/cm2), electrode gap (1-2 cm), and stirring speed (400-700 rpm) were investigated through a design of experiment methodology. Upon the identification of optimum operating conditions, further experiments were performed with PFOA in different solution media representing different water bodies (e.g., natural waters, wastewater, or regenerant brine solutions), pH, dissolved oxygen (DO), PFOA concentration, and electrolyte (Na2SO4) concentration. Acidic pH favored the decomposition of PFOA, while DO showed a negligible role in the degradation efficiency. 100% and 67% degradation efficiencies were observed in 0.2 ppm and 20 ppm PFOA within 1 h, showing the adverse effect of high initial concentration of PFOA. Effect of electrolyte (Na2SO4) concentration was investigated in low and high concentrations of PFOA to examine the possible interaction of PFOA and sulfate dosage. Results showed that the effect of sulfate concentration on PFOA decomposition depends on PFOA initial concentration. In this presentation, we will present the details of the experimental methods, along with a detailed discussion of the results that shows the impact of each of the tested parameters. Further, using inert electrolytes and an appropriate scavenger showed the negligible and important roles of ●OH and SO4●-, respectively, on PFOA decomposition. We also proposed a mechanism for the degradation and defluorination of PFOA in different conditions by analyzing the fluorine recovery, defluorination efficiency, and generated intermediates.

Electrochemical degradation of PFOA: Effects of main electrochemical and solution parameters, roles of ●OH or SO4●-, and decomposition pathway

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ACS Fall 2022

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