Design and Validation of a Novel Electrochemical Flow Cell for Per- and Polyfluoroalkyl Substances (PFAS) Degradation Using Boron-Doped Diamond Anodes

Abstract

Per- and polyfluoroalkyl substances (PFAS) are widely used in products such as non-stick coatings, waterproof fabrics, and firefighting foams due to their exceptional durability and chemical stability. However, their persistence in the environment and associated toxicity have raised increasing concerns about potential health risks, necessitating effective remediation strategies. Various physical, chemical, and biological PFAS remediation methods are available. However, many are limited to removal rather than complete degradation, and/or they are highly energy intensive. A promising method for degrading PFAS is electrochemical oxidation using boron-doped diamond electrodes. This process can be carried out in an electrochemical flow cell, where optimized flow dynamics can significantly enhance degradation efficiency.

This study focused on the rapid prototyping and optimization of a miniature electrochemical flow cell using 3D printing. By integrating computational fluid dynamics models, flow profiles were analyzed and refined to improve pollutant degradation performance. To evaluate the degradation efficiency of different cell configurations, rhodamine B (RhB) was employed as a model contaminant. The study compared two electrode geometries, E21 (21-hole disk) and E41 (41-hole disk), across volumetric flow rates of 25, 50, 75, 100, and 125 mL/min. Despite E41 having approximately 20% lower current densities, its decolorization rates were comparable to E21 across all tested flow rates, suggesting improved mass transfer due to favorable flow dynamics. CFD modeling showed at a volumetric flow rate of 125 mL/min, E41 exhibited 60% lower vorticity magnitude and 30% lower turbulent kinetic energy (TKE) compared to E21. It also demonstrated 18% more uniform vorticity magnitude and 28% more uniform TKE. The E21 configuration achieved a decolorization efficiency of 98.1%, while E41 slightly outperformed it with 98.4%. The corresponding energy consumption was calculated at 156.1 kWh/m³ for E21 and 166.6 kWh/m³ for E41.

The research also explored the impact of gas bubble formation and initial RhB concentrations on system performance. Raman spectroscopy and scanning electron microscopy analyses were conducted to characterize electrode surfaces before and after use, providing insights into material durability and potential fouling behavior.

This research demonstrated that the flexibility of 3D printing enabled rapid prototyping and iterative testing, facilitating the exploration of various flow modifications. Future research will focus on evaluating the electrochemical flow cell’s effectiveness in degrading PFAS, with the expectation that optimized flow dynamics and electrode geometries will enhance the degradation rates of these persistent contaminants. Incorporating additional design modifications, such as flow-directing pillars, can be explored to promote more uniform flow profiles and potentially further enhance degradation efficiency. Such optimizations, developed on a miniature scale, lay the groundwork for future upscaling, with the potential to significantly impact real-world water treatment systems.