With the latest technology it is now possible to achieve deionised water without the use of cation and anion resins regenerated with acid and caustic solutions; this technology is known as continuous electro-deionisation or CEDi.
The CEDi cell is constructed from alternating layers of cation and anion permeable membranes; these ion selective membranes prevent the passage of ions, allowing only water to pass through. Cathode and anode electrodes are placed on the outer sides of the stack.
Feedwater flows into the stack and is split, with 90% passing into the Feed/Dilution chamber, 5-10% into the Concentration chamber and <5% into the Electrolyte compartment.
The unwanted ions in the feedwater are exchanged onto the ion exchange resin and the applied DC potential draws the ions towards their respective electrodes. As cations move towards the cathode they pass through the cation permeable membrane and into one of the Concentration compartments. Further movement towards the cathode is halted by anion permeable membranes; the cations are neutralised by anions rejected from the other corresponding chambers. The rejected ions are flushed from the system in the concentrate stream.
How it works