Electrodeionization (EDI) is used with reverse osmosis (RO) to replace typical ion exchange resin mixed beds (DI), which require onsite or offsite chemical regeneration. EDI offers improved performance at a reduced cost over DI. Furthermore, EDI does not use chemicals nor does it generate hazardous waste.
EDI systems are widely used in the Semiconductor, Pharmaceutical, Laboratory and Power industries where Ultrapure and High Purity water is required. The EDI system provides a final polishing step to remove ions remaining in the RO permeate to the desired target of ultrapure or high purity standard.
The EDI Skid is comprised of these primary components:
- EDI stack(s)
- VDC power supply.
The RO permeate fed to the EDI module is split into three separate streams:
- Product stream
- Concentrate stream
- Electrode stream
An EDI stack consists of alternating layers of anion- and cation-selective membranes filled with mixed ion-exchange resins. This stack of cell-pairs is positioned between an anode and cathode which supply the DC potential to the module. The membranes allow the ions to pass through with anion-selective membranes permeable only to anions and cation-selective membranes permeable only to cations. The membranes are impermeable to water.
Screens placed between the alternating layers of anion- and cation-selective membranes create parallel channels for the permeate and concentrate to flow. By applying an electrical voltage potential difference between two electrodes, ions are removed from the feed water into the concentrate stream.
The voltage potential created by the electric current splits water into H+ and OH- ions on the surface of the resin which continuously regenerates the resin eliminating the need for intermittent regeneration.
If dissolved carbon dioxide or oxygen is present in the water, a membrane contactor is often used for degasification between the RO and the EDI (or DI) to reduce the load on the EDI (or DI)
Aqua Clear designs and builds packaged EDI systems for commercial and industrial clients mounted on a rigid frame completely pre-plumbed and prewired. Aqua Clear also manufactures integrated RO / EDI skids. The option for heat sanitization is available for pharmaceutical clients.
For more information on how we may be able to assist you contact an Aqua Clear Water Treatment Specialist today. Our staff can help identify and troubleshoot any inefficiencies that are occurring in your water treatment system to help you save on capital and operating costs.
