Real time monitoring of scaling behavior in bipolar membrane electrodialysis

Abstract

In this study, scaling in bipolar membrane electrodialysis (BPMED) was investigated in real time using a custom-made flow cell and Optical Coherence Tomography (OCT). Unlike previous studies that applied OCT in pressure- or thermal-driven membrane processes, this work demonstrates its use in electrodialysis for the first time, enabling in-situ observation and quantification of scaling on the basic side of the bipolar membrane under various operational conditions. The results revealed that higher flow rates and lower applied currents reduced scaling coverage and thickness, attributed to improved hydrodynamics and a lower pH shift. Increasing the system's buffer capacity through higher dissolved inorganic carbon (DIC) concentrations resulted in less scaling, whereas total removal of DIC drastically increased scaling formation due to the loss of buffering capacity, leading to extreme pH shifts. Furthermore, Mg(OH)₂ was identified as the dominant scalant under high-pH conditions, confirming its major role in scaling formation in BPMED. Scaling formation was highly non-uniform, emphasizing the strong influence of hydrodynamic conditions and spacer geometry. These findings can be used in the future to develop and test improved fouling mitigation and cleaning strategies, enhancing BPMED performance and its application in CO₂ capture and related processes.