Towards pilot scale flow-electrode capacitive deionization

Flow-electrode Capacitive Deionization (FCDI) is a viable technology for energy-efficient desalination and salt concentration. Both applications receive growing attention in the context of climate change and the shift towards a circular economy. However, FCDI has yet to reach a technology readiness level (TRL) that would make it suitable for industrial application. This study offers a methodology to bridge the gap from lab-scale systems (TRL 4) documented in literature to a pilot-scale system (TRL 5). Scale-up is achieved by (a) increasing the membrane cross-section and (b) a cell stacking approach similar to electrodialysis. Different module architectures (graphite current collectors and membrane-electrode assemblies) with a membrane cross-section of 320 cm2 were developed and compared in experiments. Additionally, a membrane-electrode assembly (MEA) module with 20 stacking units was built. This corresponds to an increase in membrane area by a factor of 260 from a typical lab-scale system. The module reached a specific salt transfer rate of 1.1 μmol/(min⋅cm2), which is within the range of lab-scale systems described in literature. This system reaches the highest absolute salt treatment capacity documented for FCDI. Based on this design methodology, it will be possible to reasonably compare energy demand and economics of FCDI with established desalination technologies.