EDI (Electro Deionization) System

EDI Reverse Osmosis Plant - Electro Deionization (Edi System)

A water treatment technology that is electrically driven and used, ion exchange membranes, electricity, and resins to purify water by removing ionized species.

Working of EDI Reverse Osmosis

EDI Reverse Osmosis Plant consists of chambers that contain ion exchange resins and are separated by ion-exchange membranes. When water enters the modules, an electrical field at right angles is applied to the flow that forces ions to move through resins and across membranes. The impurities are not bound to a media and are collected in a concentrated stream which is either directed to the drain r recycled.

EDI Reverse Osmosis Plant Advantages

What is pharma grade water?

In pharmaceutical production, the water used in processing, sanitizing and as a feedstock in medicines (IV FLUIDS) must meet the strict criteria on purity standards. That water typically known as pharma grade water, with around 0 to 1 ppm TDS. Different grades of water quality are used which depends upon the end use either water is used as a medium or can be used in the manufacturing process during synthesis, as a cleaning agent or during the production of finished product. As per client’s request, two types of water are used in pharmaceutical production:

Highly Purified
Water for Injection

Major techniques to produce pharma grade water

In pharmaceutical Industries, three types of techniques are used in the form of filtration systems to produce pharma grade water:

ION Exchange Water Filtration Systems: The deplorable water-soluble ions are exchanging with the desirable ones in this system and ionic composition of water is adjust in a desirable direction.

Reverse Osmosis Plant Process: In this technique, the natural osmotic flow of water is disturbed by applying pressure to the concentration solution in an osmosis process. This results in the flow of water from a more concentrated to a less concentrated solution.

Distillation Technique: This is the extensively used technique in pharmaceutical practice. But the most used technique for bigger quantity is RO followed by EDI.

How pharma grade water was being produced through water distillation process?

In order to produce pharma grade water through distillation process, at first 10 to 20 percent of the condensate should be removed since the supply water comprises a large amount of harmful chemicals, later on, the final 20% should be eliminated as well to avoid extra amount of dryness which can result in the contamination of previous distillate by solid impurities. A liquid mixture containing volatile components is boiled by heat and then vapor is recovered with the help of condensation.

How does Electrondeionizaton (EDI) work?

Water contains positively charged cations (plus signs) and negatively charged anions (minus signs).

Cations & anions in feedwater of the EDI

When a pair of electrodes is inserted and an electrical current applied, the electric field drives the cations in the direction of the cathode and at the same time drives the anions in the opposite direction toward the anode.

A pair of electrodes is inserted in the EDI module

When we insert an ion exchange membrane made of cation selectively resins, it will block the flow of anions and water molecules. Only cations will be able to pass through to the other side. When we insert another ion exchange membrane made of anion selectively resins, it will block the flow of cations and water molecules. Only anions will be able to pass through to the other side. This configuration membranes and electrodes forms the framework of an EDI module.

Ion exchange membranes in the EDI allow specified ions pass through

This process is limited however by the slow speed at which ions move through water. In effect, the low conductivity of water impedes ion removal. In other word, as the product compartment water becomes more and more pure, the electrical resistance of this water increases. EDI technology solves this problem by sandwiching a mixture of cation and anion selective resins between the two membranes. The large surface area now offered by the resin beads effectively eliminates the ion diffusion resistance and allows the ions to move freely. Even in ultrapure water solution, the surface of the resin beads acts as a conductive path, effective acting as a bridge for the ions to move quicker toward the membrane surface faster than they were in water alone.

The surface of the resin beads acrs as a conductive path in the EDI

EDI module contains a series of water purification compartments

Take a step back to look how an EDI module is constructed, we can see that if we move the electrodes farther apart and continue to add resin beads sandwiched between the cation and anion selectively membranes, we create a series of water purification compartments alternating with compartments where the ions are concentrated.

As feed water is pumped into the system, it is diverted into separate compartments, namely the concentrating compartment and the purification or dilute compartment. These water streams remain separated throughout the process because only ions can pass through the membranes. Ions migrate and accumulate in the concentrating compartments where they are washed away into the reject stream. The water leaving this compartment contains a concentration of ions approximately 10-20 times higher than the original feedwater. This water may be drained or reclaim for further treatment.

How does Electron deionizaton work?

Three sections in the EDI module

At the top of the purification compartments, the ion concentration is at its highest. Here the surface of the resin beads acts as a conductive path effectively moving the ions to the membrane. At the lower end of the purification compartments, where the ion concentration has been reduced to the ppt level, the electric field becomes concentrated between the resin beads and the surrounding water.

When this localized voltage potential exceeds approximately eight tenths of a volt, an electrochemical reaction occurs and water molecules are split into H+ and OH– ions, which are essentially acid and caustic. The acid and caustic generated in the module regenerate resin beads by replacing other trace ions remaining the attachment of H+ and OH- ions. This is exactly what happens to resin beads when acid and caustic are used for regeneration in conventional deionization systems.

As a result, an EDI system does not need chemicals for regeneration. The electric potential does all the work. You essentially have a worker and a polisher combined into one unit which constantly regenerates.

In sum, an EDI system can consistently and predictably remove dissolved materials such as salts, acids and bases, especially weakly ionized materials such as low molecular organics, carbon dioxide, silica, and boron. The continuous regeneration process also eliminates pH shock and greatly extends the life of the resins.

When this localized voltage potential exceeds approximately eight tenths of a volt, an electrochemical reaction occurs and water molecules are split into H+ and OH– ions, which are essentially acid and caustic. The acid and caustic generated in the module regenerate resin beads by replacing other trace ions remaining the attachment of H+ and OH- ions. This is exactly what happens to resin beads when acid and caustic are used for regeneration in conventional deionization systems.

As a result, an EDI system does not need chemicals for regeneration. The electric potential does all the work. You essentially have a worker and a polisher combined into one unit which constantly regenerates.

Applications

EDI water (Type II water) is often selected for projects requiring ultra-high purity water, typically used in the following fields:

Laboratories
Pharmaceuticals
Power generation

Boiler feed water
Semiconductor production

Electronics & Microelectronics
Food and Beverage

Benefits

Removes dissolved inorganics/low molecular organics effectively

A constant flow of Type II water. Reliable and consistent water quality.
Resistivity: 5-16MΩ • cm @ 25 °C， typically >15MΩ • cm
TOC < 30 ppb

Reliable and consistent water quality

Produce a constant flow of Type II water

Environmentally friendly

No chemical regeneration.
No chemical disposal.
No resin disposal.
Low energy consumption.

Inexpensive Operation Cost:

No need for neutralization units
No need for local permitting
No need for other costs of chemical
Low power consumption

Low Maintenance Needs

Long life-cycle because of continuous regeneration of the ion exchange resins inside the module (little exhaustion)

Safe Operation

No hazardous chemical is required
Less risk to people and accidental discharge
No heating element

Limitations

Feed water limited

Requires good quality water of feed water (hardness < 1; RO water is recommended)