Application of monovalent selective membranes and bipolar membranes in electrodialysis: A review

This review systematically examines electrodialysis (ED) technologies with an emphasis on advancements in monovalent selective and bipolar membranes. It highlights the fundamental mechanisms of ion transport and membrane selectivity, showing that modifications, such as polyelectrolyte multilayer coatings and the incorporation of nanomaterials into hybrid composite structures, can dramatically enhance permselectivity. For instance, modified monovalent cation exchange membranes have achieved K⁺/Mg²⁺ selectivity factors exceeding 1000, while similar enhancements yield Li⁺/Co²⁺ selectivity over 1000 and Li⁺/La³ ⁺ selectivity above 5000. Enhanced anion exchange membranes have improved Cl⁻/SO₄²⁻ selectivity from 0.66 in pristine membranes to as high as 47.04 after coating. These advanced membranes contribute to significantly improved energy efficiency and operational stability in selective electrodialysis (SED) and bipolar membrane electrodialysis (BMED) systems. In water demineralization applications, especially for agriculture, monovalent selective electrodialysis (MSED) effectively reduces sodium concentrations by 3.6-4.6 times relative to divalent ions, preserving essential nutrients. Data from thermodynamic analyses and integrated renewable energy systems indicate that MSED can achieve recovery rates close to 90 % compared to conventional reverse osmosis while reducing waste production and extending membrane lifetimes. Moreover, selective configurations like anion exchange membrane (AEM)- monovalent selective membrane (MVM)- cation exchange membrane (CEM) stacks demonstrate high current efficiencies for resource recovery from complex mixtures. Looking ahead, the review outlines promising future perspectives that include the integration of renewable energy sources (e.g., photovoltaic, wind, and solar thermal energy) to power ED systems, the advancement of automation and control technologies to optimize process parameters, and continued material innovations to mitigate challenges such as membrane fouling and scaling.