Salinity-Dependent PFOA Transport and Membrane Stability in a Hybrid Electrokinetic–Ion Exchange System for Produced Water

Produced water is a challenging industrial wastewater because its high salinity and complex ionic composition can strongly influence electrically driven contaminant transport and membrane stability. This study investigated a two-stage hybrid electrokinetic–ion exchange membrane (EK–IEM) process for PFOA removal from produced water, focusing on the coupled effects of salinity, ionic transport, electrical loading, energy demand, and membrane stability. Experiments were conducted at nominal salinities of 10, 20, and 80 g NaCl/L, with initial PFOA concentrations of 12.32, 14.50, and 17.14 mg/L, respectively. Membrane-free electrokinetic pretreatment substantially reduced oil, chemical oxygen demand, and turbidity before membrane treatment. Subsequent EK–IEM treatment achieved PFOA removals of 99.5%, 96.3%, and 97.5% under low-, medium-, and high-salinity conditions, respectively. Increasing salinity increased electrical current and thermal loading while substantially increasing specific energy consumption. At the highest salinity, physical rupture of the anion exchange membrane was observed under the condition that also exhibited the highest electrical and thermal loading. The results indicate that salinity creates a trade-off between ionic transport, PFOA removal, energy demand, and membrane stability. Rather than removal efficiency alone, these coupled factors should therefore be considered when defining the operating window of EK–IEM treatment for hypersaline PFAS-contaminated wastewater.