2.3. Electrodialysis (ED) Stack

A laboratory‑scale single stage electrodialysis stack (model: 08002-001) was purchased from PCCell/PCA, GmbH (Heusweiler, Germany). The anode was made of titanium metal with platinum/iridium coating, and the cathode was stainless steel. The end-plates, surrounding the electrodes and compressing the stack, were made of polypropylene. The active cross-sectional area of membrane subjected to the applied electric field was 7.84 cm² (2.80 × 2.80 cm). Polyester mesh spacer-gaskets of thickness 0.45 mm physically separated the AEMs and CEMs. In assembling the ED stack, the end-plates compressing the stack were tightened until a given flow rate yielded the same pressure drops (i.e., 3 kPa) through the stack (i.e., from inlet to outlet of diluate and concentrate streams) for each experiment. For a specific combination of membranes, consistency across the replicate tests was confirmed by measuring the distance between the end-plates with a digital caliper.