Electrodialysis (ED) is used to transport
salt ions from one
solution through
ion-exchange membranes to another solution under the influence of an applied
electric potential difference. This is done in a configuration called an electrodialysis cell. The cell consists of a feed (dilute) compartment and a concentrate (
brine) compartment formed by an
anion exchange membrane and a
cation exchange membrane placed between two
electrodes. In almost all practical electrodialysis processes, multiple electrodialysis cells are arranged into a configuration called an electrodialysis stack, with alternating anion and cation exchange membranes forming the multiple electrodialysis cells. Electrodialysis processes are different than
distillation techniques and other membrane based processes (such as
reverse osmosis (RO)) in that dissolved species are moved away from the feed stream rather than the reverse. Because the quantity of dissolved species in the feed stream is far less than that of the fluid, electrodialysis offers the practical advantage of much higher feed recovery in many applications.
Electrodialysis reversal (EDR) is an advanced electrodialysis process which utilizes a flow and polarity reversal to de-scale membrane surfaces and enable high concentration operation. EDR is used in higher salinity commercial applications where brine volume and scaling is a concern.