Electrodeionization (EDI)

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Dupont

Wisconsin, USA

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Using DC electricity, electrodeionization (EDI) is a continuous, chemical-free method of eliminating ionized and ionizable species from feedwater. When polishing reverse osmosis (RO) permeate, EDI is a clever substitute for traditional mixed bed ion exchange (IX) and can effectively replace it. It is no longer necessary to handle and store dangerous chemicals used for resin regeneration in mixed beds when electrodeionization is applied. Additionally, this permeate polishing technique does not generate a hazardous waste stream because electricity is the sole consumable used in EDI. High-purity water with high contaminate-ion rejection can be produced by our unique, proven EDI modules, which can also optimize performance and sustain ongoing product quality.
What is EDI?
When an electrical current flows through an electrolyte solution, positively and negatively charged materials travel to the negative and positive electrodes, a process known as electrolysis. This mechanism is what propels electrodeionization and efficiently separates water molecules. The hydroxal (OH-) and hydrogen (H+) ions are then separated from the electrolyte solution by electrodialysis, but electrodeionization gets beyond electrodialysis's limitations and permits ion separation without progressively higher voltage.
This is the basic procedure: Consider a basic battery model with two electrodes submerged in a saltwater bath. A reduction reaction involving the water molecules takes place at the cathode when charge is applied to the electrodes; OH-ions are left behind and hydrogen gas is produced. In an oxidation reaction, H+ ions are left behind at the anode while oxygen gas is liberated. By attracting hydrogen ions from the anode and hydroxyl ions from the cathode, the salt in the solution promotes ongoing reactions at the electrodes.
Ions are driven across a semipermeable membrane by electrical current in electrodialysis. In an EDI system, the cathode is placed next to a membrane that permits only cations (OH-ions) to pass through, while the anode is placed next to a membrane that only permits anions (H+ ions) to pass through. The saline solution is now located in a central chamber. The ions will travel over the membranes from the central chamber to their separate electrodes when the system is electrically charged and chemical reactions take place, leaving behind the components of the salt molecules and any additional contaminants.
However, electrodialysis has limitations. Arching may result from the system's increased voltage requirement as the water gets purer, which can reach 600 volts. By adding ion exchange (IX) resins, or ionically conductive medium, to the central chamber, electrodeionization overcomes this difficulty. This eliminates the need for high voltage and makes it simple for the ions to go out of the center, diluted chamber.
How do we handle electrodeionization?
The DuPontTM EDI module is enclosed in a high-strength pressure vessel made of fiberglass reinforced plastic (FRP) and uses a special spiral wound design that contains membrane and ion exchange resins. DuPontTM EDI modules are entirely unique due to the innovative flow method of the concentrate and dilute streams. Up to 18 MΩ-cm of high-purity water with high silica and boron rejection can be produced using DuPontTM EDI modules, which also maximize performance and maintain consistent product quality.

The DuPontTM EDI module has the following benefits, particularly when combined with two-pass reverse osmosis (RO):

No leakage: High-pressure top and bottom end caps firmly seal the DuPontTM EDI module, preventing leaks that are frequently found in plate and frame designs.
Quality control: Before leaving our plant, every DuPontTM EDI module undergoes performance and pressure testing to guarantee trouble-free startup and operation.
Low maintenance: Unlike plate and frame EDI systems, DuPontTM EDI modules don't need to have their nuts and bolts tightened after installation or have them regularly retightened to stop leakage.
Modular, lightweight, and easily accessible designs: The lightweight DuPontTM EDI modules are straightforward to use and don't require any special lifting equipment, resulting in highly modular systems that provide easy access. A separate diluted product water sampling port is included with every module.
Cost-effectiveness: The spiral wound DuPontTM EDI modules allow system integrators to construct systems that have both lower capital and operational costs as compared to plate and frame EDI devices and are really a cost-effective replacement for conventional mixed bed ion exchange.