Study on Efficient Operating Conditions for Bipolar Membrane Electrodialysis Using Different Ion Species and Anion-Exchange Membranes

To investigate efficient operating conditions for bipolar membrane electrodialysis (BMED), a comparison of current efficiency (<i>CE</i>) and power intensity (<i>PI</i>) was conducted using different anion-exchange membranes (AEMs) and salt solutions (NaCl and Na₂SO₄) as feed solutions in BMED. The results indicated that <i>CE</i> was higher and <i>PI</i> was lower for a commercial proton-blocking AEM (ACM) than for a standard AEM (ASE) when NaCl was used. This is because ASE has a higher water content than ACM, leading to greater H⁺ permeability, which reduces <i>CE</i>. Conversely, when Na₂SO₄ was used, ASE exhibited higher <i>CE</i> and lower cell voltage (<i>CV</i>) than ACM, resulting in lower <i>PI</i> for ASE. This is attributable to the fact that, with Na₂SO₄, the effect of <i>CV</i> was more significant than H⁺ permeability. These findings suggest that efficient operation can be achieved by selecting the appropriate combination of AEMs and salt solutions.