Ions in Motion
Electrodialysis reverses the natural tendency of dissolved salts to remain dispersed by applying an electric field across a stack of ion-exchange membranes. Cations (Na⁺, Ca²⁺, Mg²⁺) migrate through cation-exchange membranes toward the cathode, while anions (Cl⁻, SO₄²⁻) pass through anion-exchange membranes toward the anode. The alternating membrane arrangement creates channels that are alternately depleted and concentrated in salt.
Stack Architecture
A commercial ED stack contains 200–600 cell pairs, each consisting of a cation membrane, a dilute channel, an anion membrane, and a concentrate channel. The voltage across each cell pair is typically 0.5–1.0 V, so total stack voltage ranges from 10–60 V. Spacers maintain channel width (0.5–2 mm) and promote turbulence to reduce concentration polarization at the membrane surfaces.
Energy Proportional to Salt
Unlike pressure-driven RO where energy scales with water volume regardless of salinity, ED energy consumption is directly proportional to the amount of salt removed. This makes ED exceptionally efficient for low-salinity brackish water and partial desalination tasks. At 3,000 ppm feed, ED consumes 1–2 kWh/m³; at 500 ppm, it can operate below 0.5 kWh/m³ — far less than RO for the same task.
Reversal and Longevity
Electrodialysis reversal (EDR) periodically switches electrode polarity, swapping dilute and concentrate channels. This self-cleaning mechanism dissolves scale deposits and extends membrane life to 7–10 years. EDR is particularly valuable for inland brackish water with high scaling potential. This simulation lets you explore how voltage, stack size, and salinity interact to determine energy consumption and product quality.