Quantifying Water Matrix Controls on PFAS Electrooxidation Degradation and Energy Efficiency

Abstract Electrooxidation (EO) has been studied for PFAS treatment, but water matrix effects remain poorly understood. This study investigates how water matrix composition, PFAS concentration, and ionic conductivity govern EO performance and energy efficiency. Using a bench-scale EO reactor, electrochemical impedance spectroscopy, and response surface methodology (RSM), we evaluated PFAS degradation, electrical energy per order (EE/O), and short-chain transformation products. PFOS exhibited faster kinetics than PFOA (2.20 vs 0.25 h–1), achieving 99.5% removal at 1 ppm. Decreasing PFOS concentration to 0.01 ppm increased EE/O from 1.47 to 4.05 kWh m–3 order–1. Decreasing ionic conductivity from 50 to 1 mS cm–1 reduced 1-h PFOS removal from 98.4% to 73.5% and increased EE/O from 1.89 to 5.87 kWh m–3 order–1, consistent with increasing uncompensated resistance. Coexisting anions showed divergent effects: chloride enhanced PFOS degradation, nitrate inhibited it above 10 mM, and sulfate exhibited concentration-dependent behavior. The RSM-predicted optimal anion composition (30 mM SO42–, 0 mM NO3–, 10 mM Cl–) was experimentally validated (38.9% vs 40.8% predicted removal). Natural organic matter was the dominant inhibitor in complex matrices. These results quantify how water matrix composition governs EO performance and energy efficiency in PFAS-laden brines and regenerants.