DEMINERALIZED WATER

Demineralized water is water low in dissolved solids, and has low electrical conductivity (measured in µS/cm).

ASTM D1193 Specification Standard for Reagent Type Water ( ASTM , American Society for Testing and Materials ),

classifies demineralized water as: “a water containing an electrical conductivity of less than 5 µS/cm.”

Completely the pure water is not a good electrical conductor,

however, In natural waters it contains various dissolved solids that provide ions with positive charges (cations) and negative charges (anions),

these ions present in the water allow the passage of electricity to through it.

The concentration of dissolved solids in water and electrical conductivity are directly proportional,

this means that increasing the concentration of dissolved solids increases conductivity.

The following table shows the most common cations and anions found in water.

What systems do I need to obtain demineralized water?

There are different processes to obtain demineralized water, in the industry the following can be found:

• Ion exchange
• Membrane filtration ( reverse osmosis)
• Distillation
• Electrodialysis
• Electrodeionization (EDI)

Demineralization using ion exchange resins.

The water demineralization process by ion exchange consists of passing it through a bed of cationic resin (loaded with H+ ions) and an anionic resin (loaded with OH- ions), or a single bed with both (mixed resin).

Resins are classified into four main groups,

according to the bound functional groups that are attached to their polymer matrix, they are the following:

• Strong acid cation (SAC)
• Weak acid cation (WAC)
• Strong base anion (SBA)
• weak base anion (WBA)

The design of ion exchange systems will depend on the chemistry of the water (a complete study of anions and cations is recommended),

which determines the most effective combination of resins for a demineralization system.

Demineralization by reverse osmosis (RO).

Reverse osmosis consists of passing water through a semipermeable membrane at a high differential pressure (exceeding the osmotic pressure);

so that the dissolved solids are concentrated on one side of the membrane (rejection) and on the other side water with a low concentration of these (product).

The quality of the product water will depend on the feed and the specification of the percentage of salt rejection of the membrane.

RO systems allow different configurations to be designed, either to obtain better product water quality, to increase production volume or to reduce rejection volume.

Demineralization by distillation.

Demineralization by distillation is the chemical and biological purification of water through thermal vaporization and condensation.

Water distillation systems do not require too many controls on the feed water,

however, special care must be taken with the carryover of impurities and with variations in condensate quality.

Demineralization by electrodialysis.

Electrodialysis is a purification process, in which water is made to flow through cationic and anionic ion-selective membranes,

placed alternately, in a chamber called a battery or accumulator,

which supplies an electrical current for the flow of ions through through the membranes.

Ions are transported from a dilute solution to a concentrated solution.

Demineralization by Electrodeionization (EDI).

Electrodeionization (EDI) systems use a combination of resins,

ion-selective membranes and electrical charges to obtain water with a high degree of purity (up to 18.2 MΩ/cm) and that is also in continuous regeneration.

It consists of passing water through resin chambers delimited by ion-selective membranes.

The resin acts as a conductor allowing the electrical current to displace the anions and cations captured in the resin,

which are concentrated and expelled from the system in the rejection flow.

At the same time, the electric current separates the water into hydrogen (H + ) and hydroxyl (OH – ) ions,

that allow continuous regeneration of the resin without the need to use regenerating chemicals.

What are the benefits of demineralized water for your plant?

Demineralization is usually saved for uses where higher purity levels of water are required,

including process streams used in the manufacturing of electronics,

rinse water for the food and beverage industries, or feed or makeup water for high-pressure boilers.

The list of uses for demineralized water is not exhaustive because there are innumerable applications for it.

Nonetheless, it is an illustration of the most often used applications, separated out by industry:

Strength

Demineralized water is frequently utilized in the power sector for steam production and boiler feed water.

High-pressure boilers and, consequently, more sophisticated feed water treatment systems are needed for boilers

that produce steam to power turbines in order to remove as many contaminants as feasible.

The water particles gather and condense during the production of steam inside the boiler;

they are then recycled and utilized as boiler feed water.

Although the condensate produced by the steam-making process is technically distilled, dissolved gases like carbon dioxide and oxygen can occasionally be found in it.

On boiler pipes and parts, the chemical reactions brought on by the presence of these dissolved gasses can result in severe corrosion.

Usually, chemical scavengers, advanced deaeration equipment, or demineralization are used to eliminate these gasses.

Refinery

High-pressure boilers at refineries are fed with demineralized water, just like in the power industry.

Hardness and dissolved solids can seriously damage a facility’s machinery, and for the majority of high-pressure boilers and process streams, softening is frequently insufficient treatment.

The water treatment train usually includes demineralization by ion exchange or membrane filtration (mostly reverse osmosis or nano filtration),

as many higher-pressure boilers demand a higher quality of water with less pollutants than some lower-pressure boilers.

Chemical and petrochemical

High-purity boiler feed water is also necessary for the chemical and petrochemical sectors. Demineralization serves this purpose.

Cooling tower blowdown is another condition that can be treated with demineralization (which also applies to other industries mentioned).

 In the event that your blowdown system’s water needs to be released, whatever discharge it produces must adhere to all applicable regulations.

Demineralization systems can assist reduce the cost of connecting to water and sewer lines,

which makes them a financially viable choice in locations where water is scarce and hefty sewer connection fees may apply.

If your wastewater is going to be released back into the environment or a publicly owned treatment works (POTW),

then the cooling tower bleed discharge also needs to comply with local municipal discharge requirements.

Food and Drink

Equipment and containers are frequently sanitized using demineralized water.

Although membrane filtration is often the method used to remove organic material, germs, viruses, etc., and it is also utilized in some food processing applications.

Demineralization is frequently a component of the entire water treatment process since the manufacture of food and beverages

must adhere to quality rules requiring ultrapure water at all stages of the manufacturing process.

Medications and Cosmetics

To ensure the quality and safety of their goods,

pharmaceutical and cosmetic manufacturers employ deionized and distilled water in their manufacturing processes.

Reverse osmosis or deionization are two separate processes,

however they produce demineralized water for various applications, cleaning, and rinsing, whereas recipes usually use distilled water.

Other Sectors

In many different industries, such as chemical production, mining, and electrocoating,

where it serves as a carrier for paint solids, demineralized water is employed for both cleaning and rinsing purposes.

It is also utilized in research labs to create a range of solutions.