What is EDI?
Electrodeionization (EDI) is a continuous water-purification process that combines ion-exchange resin, ion-selective membranes and direct-current (DC) electricity. It is commonly used after reverse osmosis (RO) to further reduce dissolved ions in RO permeate. The electric field helps transfer ions out of the product-water stream while allowing ongoing electrochemical regeneration of the resin inside the module.
Core Components
Ion-exchange resins provide exchange sites and ion-conducting pathways in low-conductivity water. Selective membranes favour the movement of positively or negatively charged ions, separating diluting and concentrating compartments. DC electrodes and power supply drive ion migration, while flow channels collect product and concentrate streams. Sensors and controls monitor operating conditions.
How the Process Works
- Prepare the feedwater: pretreatment and RO remove most of the incoming dissolved load and protect downstream EDI modules.
- Introduce water into the EDI module: dissolved ions interact with resin media packed between selective membranes.
- Apply DC current: an electric field moves ions toward the relevant membranes and from the dilute stream to the concentrate stream.
- Continuously regenerate the resin: electrically generated H⁺ and OH⁻ help restore ion-exchange sites during normal operation, avoiding periodic chemical regeneration of the EDI stage.
- Monitor product quality: conductivity, resistivity, flow and other project-defined operating indicators are checked.
Why Is RO Important Before EDI?
RO permeate normally provides a more suitable low-ionic-load feed for EDI than untreated water. Feedwater hardness, silica, carbon dioxide and other constituents affect EDI performance; pretreatment requirements therefore depend on the specific project.
EDI Compared with Conventional Ion Exchange (IX)
Both technologies use ion-exchange media. Conventional IX systems are serviced by resin replacement or, in regenerable configurations, periodic regeneration. EDI additionally uses selective membranes and a DC electric field to remove ions continuously and regenerate its resin electrically. The best choice depends on throughput, incoming water quality, target specifications and operating requirements.
Advantages and Design Considerations
EDI can support continuous high-purity water production, avoid periodic chemical regeneration of the EDI stage and integrate with industrial RO and monitoring systems. It is not a substitute for all pretreatment or for control of every nonionic contaminant, particle or microorganism. Sensitive uses may require additional UV or final filtration and validated water-quality monitoring.
Maham Industrial and Laboratory Systems
Maham Kimiya Pajouh offers the APEX PURE EDI-E 50 laboratory system with 50 L/h ultrapure-water output and custom-engineered industrial EDI projects. Capacity, module selection and controls are specified after project assessment.