Investigation of the Deionization Rate of Asymmetric Capacitive Deionization Technology for the Treatment of Short-Chain Perfluoroalkyl Substances (PFAS)

Abstract

Objectives This study aims to introduce and evaluate the effectiveness of asymmetric membrane capacitive deionization (ACDI) in removing short-chain perfluoroalkyl substances (PFAS), specifically perfluorobutane sulfonic acid (PFBS), from aqueous solutions. This study offers important insights for the advancement of CDI technology in the sustainable treatment of industrial wastewater containing PFAS. Methods ACDI was employed by removing the anion exchange membrane from conventional membrane capacitive deionization system. The effect of key operational parameters such as voltage (0.5~1.2 V), initial concentration (50~500 mg/L), and flow rate (1~5 ml/min) on PFBS removal efficiency was systematically investigated. Additionally, PFBS removal performance in the presence of chloride ions was also investigated to determine competing ion effects. Results and Discussion The ACDI system significantly outperformed both CDI and MCDI, achieving a maximum deionization rate of 0.032 mg/g/s, compared to 0.012 mg/g/s for CDI and 0.01 mg/g/s for MCDI. Increasing the applied voltage from 0.5 V to 1.2 V enhanced the deionization rate, with the highest rate observed at 1.2 V. Higher initial PFBS concentrations also improved the deionization rate, increasing from 0.0009 mg/g/s at 50 mg/L to 0.032 mg/g/s at 500 mg/L. The optimal flow rate was found to be 2 ml/min, balancing ion contact time and throughput, resulting in the highest deionization rate. The presence of competing ions, such as chloride, reduced PFBS removal efficiency, as shown by the decrease in deionization rate when NaCl was added to the feed solution. Conclusion Overall, the ACDI system demonstrated superior deionization capacity and energy efficiency for PFBS removal, highlighting its potential as a sustainable and efficient technology for treating water contaminated with short-chain PFAS. Future research should address the challenges posed by competing ions in real-world wastewater to further optimize the ACDI system’s performance.

Keywords

• perfluoroalkyl substances (pfas)
• capacitive deionization
• ion exchange membrane
• asymmetric membrane capacitive deionization