Integrating kinetic modeling and experimental insights: PFAS electrochemical degradation in concentrated streams with a focus on organic and inorganic effects

This study investigated the impact of organic and inorganic constituents on electrochemical degradation of per- and poly-fluoroalkyl substances (PFAS) in a sulfate-based brine from regeneration of spent ion exchange (IX) resin. The system's performance was assessed in the presence of natural organic matter (NOM) and common inorganic constituents: chloride, nitrate, and bicarbonate. Results revealed distinct outcomes based on constituent type, concentration, and specific PFAS variant. NOM hindered PFAS decomposition, especially for more hydrophobic compounds. Chloride reduced degradation and defluorination efficiencies through competitive interactions with PFAS for the anode's active sites and scavenging effects on SO₄^•- and ^•OH. Nitrate and bicarbonate minimally impacted degradation but significantly reduced defluorination. Investigating the electrochemical process in real brine solutions showed higher efficiency and lower electrical energy consumption when methanol was distilled, as methanol scavenges reactive radicals and competes for active anode sites. A kinetic model was also developed to determine the direct electron transfer (DET) and mass transfer coefficients for the species present, considering both surface and bulk solution interactions. The model predicted mass transfer (mol m^-2 s^-1) and DET (m² mol^-1 s^-1) coefficients of 6:2 FTCA, PFOA, GenX, and PFBA to be (5.0 ×10^-10, 3.7 ×10¹¹), (1.0 ×10^-9, 8.0 ×10⁸), (6.0 ×10^-8, 7.5 ×10⁸), and (6.2 ×10^-8, 4.2 ×10⁸), respectively.