Laboratory water purification system is one of the commonest equipment for scientific researchers, mainly used to produce ultrapure water for experiments. The great importance of ultrapure water is obvious in that water is an essential and numerously used reagent in the experiment process.

As a kind of deionized water equipment, the laboratory ultrapure water machine primarily adopts solutions such as reverse osmosis(RO), electrodialysis, ion exchange, and EDI. Among them, electrodeionization (EDI), is a new type of pure water and ultrapure water treatment technology gradually developed in the history of pure water production technology. The emergence of EDI is revolutionary progress, marking that the water treatment industry has finally entered the league of the green industry.

The advanced technology is rapidly gaining acceptance by virtue of good environmental protection and accessible operation, which has come into wide application in pharmaceuticals, electronics, electric power and chemical industry, etc.

What is EDI?

A continuous deionization technique

EDI units are also referred to as continuous electrodeionization (CEDI) since the electric current regenerates the resin mass continuously. CEDI technique can achieve very high purity, with conductivity below 0.1 μS/cm.

Electrodeionization, abbreviated as EDI, scientifically integrates electrodialysis and ion exchange technology into one to remove ionized species from water.  This process combines ion-exchange resins and ion-selective membranes, which are used to move ionic impurities into a waste or concentrate water stream, leaving purified product. As impurities leave via the concentrate water stream, their buildup does not exhaust the resin, and it prolongs the resin lifespan. Water resistivity of >15 MΩ-cm may be achieved by using this process.

How does EDI work in the water purification system?

Electrodeionization——Water Purification
Process of Electrodeionization

Several layers of ion-selective membranes are positioned between an anode and a cathode. Layered ion exchange resin beds and concentrate chambers are alternately positioned between them.

The Succession of Alternated Membrane in Electric Field
Ion Transfer through Membranes

On applying an electric voltage, water (H20) is split into H + and OH– in the cell. The H + and Na + cations can migrate through the cation permeable membranes, anions through the anion permeable membranes.

The ions migrate in the direction of the applied voltage, i.e. anions to the positive pole (anode), cations to the negative pole (cathode). The water ions H+ and OH– that migrate through an ion exchange chamber displace salt ions retained by the ion exchange resins and so continually regenerate the resins. The salt ions migrate through the appropriate ion-selective membranes into the concentrate chambers and are flushed out of them by water. As all concentration chambers are flushed through one after the other, excess H+ and OH– ions can again combine to form H20.

Why advocate EDI unit? Low maintenance!

Normally, we first perform reverse osmosis and then remove the remaining impurities by ion exchange resin on raw water when using a laboratory water purification system. Therefore, for any industry laboratory, reverse osmosis membrane and ion exchange resin are both consumables. When the ion exchange resins are about to be depleted, they begin to release weakly ionized substances including some phosphates, silicates and nitrates. And if the colour of the resins has changed, we recommend immediate replacement because the resins, in this case, have lost their ion exchange function.

The above chart depicts the tendency of water resistivity value to change over time in the case of deionization. When the water resistivity drops to the lowest point, it means that the water quality has also become pretty awful. That is, we need to replace the resin directly. Besides, we can also see that the frequency of resin replacement is fairly high.

While in EDI water purification equipment, under the action of a direct-current electric field, water is ionized into H+ and OH- ions to continuously regenerate the resin filled in the bottom layer, so the water quality is properly guaranteed to be constant. As a result, the longer the resin replacement cycle, the lower its frequency. It is the non-complicated water purification process that greatly simplified the labour intensity, easy training within the trainee to accept.

Advantages of EDI unit:

No regeneration chemicals

There is no need to collect, store and dispose of hazardous chemical wastewater. As a result, the new EDI process greatly simplifies the system compared to conventional processes.

Stable water quality

Ion exchange and regeneration are synchronized with the EDI water system so that the water quality is very stable. Unlike mixed beds, the effluent quality is affected by ion leakage at the beginning and end of each regeneration cycle.


The production of electric desalination is continuous, eliminating the need for complex regeneration operations during the mixing process and reducing many spare types of equipment. There is no need to set up operators and operating procedures related to the recycling work.

Low operating cost and maintenance

EDI equipment requires only electricity to operate, while mixed bed technology requires extra acid and alkali. Therefore, ultra-pure water equipment reduces operating costs by saving acid and alkali. No exchange of spent resins or cartridges saves cost.

Water Purification Solution(with EDI Unit) by Heal Force

Contact our team for details about Water Purification System.

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