Electrodialysis

Electrodialysis is a desalination and water treatment technology that uses an electric potential to move ions through selectively permeable ion-exchange membranes, thereby separating and concentrating ionic species from an aqueous feed. A typical system consists of a stack of repeating cells formed by alternating cation-exchange membranes and anion-exchange membranes between two electrodes. When a direct current is applied, cations migrate toward the cathode through the cation membranes and anions migrate toward the anode through the anion membranes. This creates separated streams: a diluate stream that becomes progressively deionized and a concentrate stream in which the removed ions accumulate. Feed water flows through the spaces between membranes, sometimes with spacers to promote mixing and reduce polarization.

Membranes used are selective for either positive or negative ions; in some configurations bipolar membranes are used to generate H+ and OH- ions for in-situ acid and base production, enabling electrodialysis with bipolar membranes (EDBM). The process can be operated at varying recovery rates and is typically powered by a direct-current power source. System design emphasizes minimizing ion transfer losses and fouling, and capitalizes on modular stacks to scale capacity.

Applications include desalination of brackish groundwater or surface water, production of drinking water in remote locations, and demineralization or concentration of process streams in the food and beverage, dairy, pharmaceutical, and electronic industries. Compared with other desalination methods, electrodialysis is often advantageous at lower salinities and for selective demineralization, but becomes less energy-efficient at high total dissolved solids. Brine management remains a consideration in plant design.