Electrodialysis (ED) in its "conventional" form is a separation technique that extracts ions through selective ion exchange membranes under the influence of an applied electric field. Two types of membranes are used: cation-exchange membranes only allow cations to transport, and anion-exchange membranes only allow anions through. These membranes are impermeable to liquids. A large number of alternating cation and anion-exchange membranes are assembled to form diluate and concentrate compartments in what is known as an electrodialysis stack.
Bipolar membrane electrodialysis (EDBM) takes advantage of the specific property of a bipolar membrane to effectively divide water into H+ and OH- under the influence of an applied electric field (a process known as “water splitting”). A bipolar membrane electrodialysis stack is formed by assembling a large number of bipolar and monopolar (cation/anion-exchange) membranes to convert saline (mineral or organic) solutions into acids and bases.
High-temperature electrodialysis is a variant of conventional and bipolar membrane electrodialysis and can be used to process solutions at temperatures of up to 65°C. Depending on the application, temperatures at this level can be used to reduce the viscosity of the solutions being treated, reduce energy consumption, and/or reduce the growth of most of the micro-organisms that can compromise the operation of stacks.