What Is Electrodeionization (EDI)? CEDI Modules and RO+EDI
Electrodeionization (EDI) is a purification technology that continuously removes ions from water by combining ion-exchange resin and ion-selective membranes with an electric current. The resin continuously regenerates in place by the electric current, so no chemical regeneration with acid or caustic is required and production is uninterrupted.
In Turkey, Mikron Proses supplies Ionpure CEDI modules and DC power supplies as an OEM partner and system integrator, engineering RO plus EDI lines for laboratories, power plants and pharmaceutical facilities.
How CEDI Works
A CEDI module holds ion-exchange resin beds in compartments separated by anion- and cation-selective membranes. Direct current is applied between an anode and a cathode at opposite ends of the module. The resulting electrical field drives ions captured by the resin through the membranes into a separate concentrate (reject) stream. At the same time, the field splits a portion of the water into H⁺ and OH⁻ ions; these continuously regenerate the resin in place. Because the resin does not exhaust, the process runs without shutdown for chemical regeneration. The electrical field and water splitting also inhibit bacterial growth inside the module.
Ions are removed sequentially. Strong ions such as Na⁺, Cl⁻, Ca²⁺ and SO₄²⁻ are captured in the initial “working bed”. CO₂ is forced into bicarbonate form and removed in the subsequent “polishing bed”. Weakly ionized species such as silica and boron are removed last; therefore keeping RO permeate conductivity and CO₂ low increases the effective bed length available for these species. Only reactive silica is removed in EDI; colloidal silica must be retained upstream by RO.
In plate-and-frame designs, resin may fill only the product compartments (dilute-filled) or all compartments (all-filled). In all-filled designs, the resin acts as a conductive bridge for ions and current, so no separate brine injection or concentrate recirculation is required; the Ionpure MX series uses this design.
EDI vs Mixed-Bed Deionization
| Parameter | Mixed-bed resin (MBDI) | EDI / CEDI |
|---|---|---|
| Operation mode | Batch: exhaustion, regeneration, rinsing | Continuous |
| Resin renewal | Acid and caustic; ion leakage begins as resin depletes | Electric current, in-place and continuous |
| Chemicals | Acid/caustic storage, pumping, neutralization and disposal | No regeneration chemicals; a concentrate stream forms |
| Downtime | Required for regeneration or resin change | None, except for cleaning or sanitization |
| Space and operation | More floor space and operator effort | Smaller footprint and lower operating cost, according to the Ionpure catalog |
| Feed water | Pre-treatment also required | Similar pre-treatment required; fed with RO permeate, sensitive to chlorine, hardness, iron, manganese and organics |
| Product water | Varies with regeneration cycle | 15–18 MΩ·cm at nominal flow (Ionpure catalog) |
The comparison is compiled from the Ionpure general catalog and training materials. For deionized water applications, see DI water systems.
EDI After RO: Feed Limits and Pre-Treatment
An EDI module is fed with reverse osmosis (RO) permeate. In purified water lines, the typical chain is RO + EDI + UV + UF. EDI is sensitive to hard water, chlorine, iron, manganese and organic matter, so RO permeate must meet conductivity equivalent, hardness, chlorine and silica limits.
- Chlorine and oxidizers: Oxidants degrade resin and irreversibly increase pressure drop. The ideal oxidant concentration is zero; the total chlorine limit is 0.02 ppm for Ionpure LX-X, LX-HI and VNX (0.05 ppm for LX-Z).
- Hardness: Hardness precipitates on high-pH membrane surfaces in concentrate compartments and raises electrical resistance. The Ionpure feed limit is maximum 1 ppm as CaCO₃ (0.1 ppm for VNX55-E, VNX55-EX and VNX-Ultra).
- CO₂ and conductivity equivalent: CO₂ constitutes an ionic load for EDI; high CO₂ harms product quality and silica removal. The feed conductivity equivalent limit is 40 µS/cm, including CO₂ and silica.
- Iron, manganese, TOC and particles: These adhere to resin and membranes, increasing resistance and pressure drop. If the EDI is fed from a tank instead of directly from the RO, the LX manual suggests 5 µm prefiltration directly upstream of the module.
- Power interlock: The module requires a DC power supply interlocked with the feed pump.
EDI does not generate acid or caustic regeneration waste. It does produce a concentrate (reject) stream that carries ions away. According to the Ionpure LX guide, at 90 % recovery the concentrate flow is approximately 11 % of the product water flow.
For feed-water calculations and module sizing, see EDI system selection. For pre-treatment design, see reverse osmosis (RO) systems and the EDI systems overview.
Ionpure CEDI Module Selection by Flow
| Series | Flow rate | Key feature | Typical application |
|---|---|---|---|
| MX (MX30–MX500) | 30–500 L/h | 75 psi (5 bar), up to 45 °C; 90–95 % recovery; 90–99 % silica removal | Laboratory, small-scale RO systems |
| LX-Z / LX-X | LX-Z 0.22–10 m³/h; LX-X 0.22–7.67 m³/h | Plate-and-frame construction | Power, general electronics, food and beverage, laboratory |
| LX-HI | 0.22–7.67 m³/h | 85 °C hot-water sanitization (1–2 hours); cGMP, USP, Ph.Eur applications | Pharmaceutical, biotechnology, medical |
| VNX (VNX-Max / Mini / Ultra) | up to 22.7 m³/h (single module) | Silica and boron removal: VNX-Max/Mini >95 %, VNX-Ultra ≥99.8 % | Power generation, boiler feed water, microelectronics |
Values are taken from Ionpure datasheets. VNX modules produce product water resistivity typically above 17 MΩ·cm when fed with RO permeate, and above 18 MΩ·cm when fed with DI water. LX-X modules deliver above 15 MΩ·cm at nominal flow. LX-HI product water conductivity is below 0.1 µS/cm.
Power Supplies and Control
Ionpure DC3 is a three-phase DC power supply with 0–600 VDC output and MODBUS TCP-Ethernet. The DCR is a single-phase supply. The G4 is a single-phase controller with electrical resistance logging and a cleaning alarm. Mikron Proses selects the power supply together with the module based on site electrical specifications and control requirements.
How Mikron Proses Helps
Mikron Proses engineers RO plus EDI lines across the module series listed above, from MX to VNX. The company selects the CEDI module, DC power supply and pre-treatment based on RO permeate quality, target water grade and flow rate. For purified-water and WFI applications, Mikron Proses integrates hot-water sanitizable LX-HI modules into validated loops. For module flushing, replacement schedules and sanitization protocols, see EDI module flushing and replacement. To check silica limits before the EDI stage, see silica measurement.
Send RO permeate data and flow requirements via the contact page to select a CEDI module and power supply.
Frequently Asked Questions
Technical answers from Mikron Proses.
What is electrodeionization (EDI)?
Electrodeionization is a continuous purification process that removes ions from water using ion-exchange resin, ion-selective membranes and direct current. The electric current drives ions into a concentrate stream while continuously regenerating the resin with H⁺ and OH⁻ ions produced from water splitting, eliminating the need for acid or caustic regeneration. CEDI (continuous electrodeionization) is the same technology.
How does CEDI work?
Inside the module, resin beds are separated by anion and cation membranes. When direct current is applied, captured ions migrate through the membranes into a reject stream, and water splitting generates H⁺ and OH⁻ ions that regenerate the resin in place. Strong ions are removed in the working bed, CO₂ as bicarbonate in the polishing bed, and weak species such as silica at the end.
What is the difference between EDI and mixed-bed deionization?
Mixed-bed systems operate in batch cycles of exhaustion, regeneration and rinsing with acid and caustic, causing downtime and chemical waste. EDI regenerates the resin continuously with electricity, producing a steady stream of deionized water with no chemical storage or neutralization. According to the Ionpure catalog, EDI also requires less floor space and lower operating cost than mixed-bed systems.
Can EDI produce ultra-pure water after RO?
Yes. In typical purified-water chains, RO permeate is polished by EDI followed by UV and UF. Ionpure VNX modules fed with RO permeate typically produce water above 17 MΩ·cm, while LX-HI achieves product water conductivity below 0.1 µS/cm for pharmaceutical and biotechnology applications.
What are the feed-water limits for an EDI module?
EDI modules require RO permeate with very low oxidants, hardness and organics. Key limits include total chlorine maximum 0.02 ppm for Ionpure LX-X, LX-HI and VNX (0.05 ppm for LX-Z), hardness maximum 1 ppm as CaCO₃ (0.1 ppm for VNX55-E, VNX55-EX and VNX-Ultra), and feed conductivity equivalent maximum 40 µS/cm including CO₂ and silica. A 5 µm prefilter is suggested when the EDI is tank-fed, and the feed pump must be interlocked with the DC power supply.
Which Ionpure module is suitable for high-flow industrial plants?
For high-volume lines, the VNX series covers up to 22.7 m³/h per single module and offers silica and boron removal above 95 % for VNX-Max/Mini and ≥99.8 % for VNX-Ultra. For hot-water sanitizable pharmaceutical loops, the LX-HI series operates at flows of 0.22–7.67 m³/h with 85 °C sanitization. Smaller flows are covered by the MX series at 30–500 L/h and the LX-Z/LX-X series at 0.22–10 m³/h.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.