DI, Mixed Bed, EDI Purified water treatment

DI, Mixed Bed, EDI purified water treatment system brings high efficiency, can remove all Ions for highest water quality demands in some special industries

Please refer to the article “RO Water System”.

DI (De-Ionized Water) is also known as deionized water – water in which ions (negative, positive) have been removed by some separate or combined treatment method..

DI water is more qualitative than quantitative, so the quality level should be given in units of measurement such as MegaOhm or µS/cm.

It is also important to distinguish deionized water and pure water, which is deionized water that no longer contains any ions but still contains impurities that are not ionic, while pure water only has water molecules, in addition to water molecules, there are no other ions or compounds.

Currently, many people still think that water filtered from RO system or distillation equipment (1st, 2nd pass ) are DI water, but in fact, these systems have not completely removed ions, so they need to be combined with other treatment. For example the following combinations to get deionized water:

3Resin-H + Ca²⁺+ Na⁺ -> 2Resin-Ca + Resin-Na + 3H⁺

After cationic resin tower, negative ions in water will be continued through anionic resin tower where exchange with the OH^– of resin and are caught here

3Resin-OH + SO4^2- + Cl^– -> 2Resin-SO₄ + Resin-Cl + 3OH^–

OH^– that has just released will immediately combines with the H⁺ from the earlier tower, become H₂O

H⁺ + OH⁺ -> H₂O

Over time, both cationic and anionic resins will saturated, and the effectiveness will be decreased until no capacity of Ion exchanged. The regeneration will follow the original service cycle design and based on actual saturation in operation.

The saturated cationic resin will be regenerated with H from diluted HCl and the saturated anionic resin will be regenerated with OH from the diluted NaOH. When regenerated, all cationic ions, anionic ions, chemical, and water are discharged totally into the waste line.

2Resin-Ca + Resin-Na + 3HCl -> 3Resin-H + [Ca²⁺ + Na⁺ + 3Cl^– (to waste)]

2Resin-SO4 + Resin-Cl + 3NaOH -> 3Resin-OH + [SO₄^2- + Cl^– + 3Na⁺ (to waste )]

Two discharge lines from 2 columns of resin tower need to be put into 1 tank to neutralize pH, a chemical treatment system for further treatment before discharging into the environment (please contact us for help about this regenerated wastewater treatment)

In fact, to bring higher efficiency and durability to equipment, a de-gases tower unit is required after the Cationic resin tower to remove dissolved gases including CO2, H₂S…

Theoretically, all ions are removed after going through 2 resin towers, but in practice it is still not thorough, so a further treatment, called Post -treatment is required to polishing to achieve 10 – 18.2 MegaOhm for Ultrapure water

To visualize the whole, there are 3 processing parts, for example:

Mentioning DI water system, most understanding that have 2 independent Cationic – Anionic towers. Its advantage is that it is very easy to regenerate when the two acid and baz have opposite properties, however, the highest level of deionization has not been achieved, but must be further treatment with mixed resin, called Mixed Bed.

What is Mixed Bed? Mixed Bed is often used after the Cation – Anion resin tower or after the RO membrane for the highest demineralization water quality, the disadvantage is that it is quite time consuming because it is necessary to separate the mixed resin before regeneration and mix it again after regeneration. This can be regenerated in tower ( called Mixed Bed) or take out external regeneration (called Polisher Tower).

The continuously regenerated EDI without chemical, will replace Mixed Bed in some cases or some industries, but at cost is quite high if high capacity installed

To achieve the same demineralization quality, one of the following combination can be a selection

• RO 2 passes -> EDI.
• RO 1, 2 passes -> Mixed Bed.
• Cation -> Degas -> Anion -> Mixed Bed.

DI Mixed Bed water treatment system works as above principle, however, depending on the water source quality and capacity, treated quality to choose the appropriate demineralization system for the lowest investment and operating costs.

– Online flow meter with totalizer

– Conductivity and Resistivity, pH, TOC for feed water and treated water, and periodically microbiology testing

– pH of wastewater.

– Design and install DI Mixed Bed, RO, EDI water treatment system.

– Periodic inspection, system maintenance, transducer cleaning and calibration.

– Supply of consumables.

– Check resin, regenerate, clean RO membrane and resin.

Contact us for support