The WPT Electrodeionization Solution
Electrodeionization (EDI) offers users a non-hazardous, reverse-osmosis (RO) post-treatment solution that eliminates costs and hazards of chemical-based, resin-regeneration systems.
EDI offers a continuously-regenerating resin that eliminates operating expenses and labor associated with daily, chemical-based resin regeneration. Although RO technology is a cost effective roughing treatment for most ion removal and feed water with contaminants, it does not produce water pure enough for many applications. EDI is a cost-effective way to polish RO water to meet high-purity-water standards, because the system:
- Produces consistently high purity water, comparable to mixed bed DI water.
- Eliminates operating expenses and labor associated with a daily, chemical-based resin regeneration system.
- Mitigates environmental compliance risks associated with the disposal of regeneration chemicals.
- Minimize operational downtime and thus the need for redundant systems, which would be necessary with chemically regenerated systems.
- Removes contaminants, such as silica and total organic carbon (TOC), at rejection rates >90 percent.
- Has a smaller footprint than mixed-bed systems.
- Can be configured horizontally or vertically.
- Reduces onsite system monitoring costs through WPT's automated-control system.
A Custom Solution for an Off-the-Shelf Price
EDI utilizes both resin and membrane technologies. While cations and anions in the feed water are exchanged for hydrogen ions just as in normal resin exchange systems, the EDI resin is regenerated continuously. With conventional ion exchange, chemical regeneration is performed intermittently with resulting downtime, labor and chemical costs. By contrast, the resin in an EDI system is continuously regenerated by an electric current, thus reducing downtime, labor and chemical costs.
Because EDI is used as a polishing system, the water must be of high enough quality to not foul the EDI cells.
Below illustrates the EDI process in an annotated schematic diagram.
- Feed water enters the EDI stack and flows into a series of cells.
- The system applies DC voltage across each cell. Positively-charged ions like sodium (Na+), migrate towards the negative electric current discharged by the cathode. Negatively-charged ions, like chloride (Cl-), migrate towards the positive electric current discharged by the anode.
- Contaminant ions attach to their respective ion exchange resins and are attracted through their respective membranes into the concentrate "C" chambers where the ions are carried away by the concentrate flow.
- Deionized water in the dilute "D" chambers flows out of the stack.
- Concentrate water either recirculates back through the stack's, fed back into the system ahead of the RO, or is discharged to drain.
- The electrolyte to waste stream carries away any gases formed from the water splitting reaction.
- The resin bed continuously regenerates as voltage discharges, splitting water molecules into hydrogen ions. Like contaminant ions, hydrogen ions migrate through their respective membranes into the "C" chambers.
- The EDI control system operates and monitors the water treatment system onsite or remotely via modem or LAN. The PLC supports three operating modes for ultimate flexibility: Automatic, Semi-Automatic, and Manual.
The Electrodeionization Process. Using this process, WPT develops a solution tailored for each project's water quality and application.
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