|What is Deionization?|
(DI) is the removal of all ionized minerals and salts (both organic and
inorganic) from a solution through the process of ion exchange. Because
most non-particulate water impurities are dissolved salts, deionization
produces a high purity water that is generally similar to distilled
water. Compared to distillation, deionization is faster, less energy-intensive,
and more cost-effective. In addition, it is an on-demand process that
supplies highly purified water as needed — an important feature because
water at extreme levels of purity degrades quickly.
Deionization filters operate by
exchanging positive hydrogen and negative hydroxyl molecules for the
positive and negative contaminant molecules in the water. Positive
chemicals like sodium, calcium, iron, and copper change places with the
hydrogen molecules, and negative chemicals like iodine, chloride and
sulfate change places with the hydroxyl molecules.
This process is typically done by two ionized resin beds that are opposite in charges: cationic (negative) resin and anionic (positive) resin. Positively charged ions are removed from the solution by the cation resin in exchange for a chemically equivalent amount of hydrogen ions. Negatively charged ions are removed by the anion resin in exchange for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form pure water molecules.
With Service Deionization (SDI)
, Evoqua regenerates ion exchange resin as a service at one of our conveniently-located North American resin regeneration plants, saving customers the cost of investing in on-site equipment .
Where is DI water used?
Deionized (Dl) water is an essential ingredient in hundreds of applications, including medical, laboratory processes, pharmaceuticals, cosmetics, electronics manufacturing, food processing, plating, countless industrial processes, and even the spot-free rinse water at the local car wash. Typically, it serves as an ultra-pure ingredient, a "perfect" cleaning solvent, or as the foundation of a process water recovery/reuse strategy.
Deionized water meeting Water For Injection (WFI) standards of purity is used as the basis for saline and other solutions to be injected into the body during medical procedures. Its bacteria-free and mineral-free purity assures the quality and stability of the solution as other ingredients are added to it. DI laboratory water is also used to clean instruments and lab equipment and to perform tissue cell culture, blood fractionation, and other lab procedures.
Pharmaceutical Water/Neutraceutical Water
Deionized water in the pharmaceutical industry is used for preparing culture media, for making up aqueous solutions, and for washing containers and apparatus. It is also used as a raw material, ingredient, and solvent in the processing, formulation, and manufacture of pharmaceutical and neutraceutical products, active pharmaceutical ingredients (APIs) and intermediates, compendial articles, and analytical reagents.
In semiconductor manufacturing, deionized water's properties for absorbing minerals, enhancing detergents and residue-free drying make it useful for rinsing and cleaning semiconductor wafers. It is also used in wet etching, bacterial testing and many other processes throughout the fabrication facility.
Deionized water is commonly used to top up lead-acid batteries, cooling systems and for other applications.
Deionized water is often used as an ingredient to add purity, stability and performance in many hair care, skin care, body care, baby care, sun care and makeup products, where it is sometimes referred to as "aqua" on product ingredient labels.
Because of its high relative dielectric constant, deionized water is used as a high voltage dielectric in many pulsed power applications for energy research, such as the Sandia National Laboratories Z Pulsed Power Facility.
When used as a rinse after washing cars, windows, and similar applications, deionized spot-free rinse water dries without leaving spots caused by dissolved solutes, eliminating post-wash wipedowns.
Food and Beverage Processing
Deionized water is used as both an ingredient and a process element in food and beverage processing. As an ingredient, it offers stability, purity and sanitation. As a process element, it is used for effective sanitation.
In industrial plants, DI water facilitates water and wastewater recycling; adds efficiency and life extension to boiler and steam processes, and is a key element in industrial commercial water softening.
Boiler Water Treatment Equipment
Deionized water is used to pretreat boiler feed water to reduce scaling and energy use and to control deposition, carryover and corrosion in the boiler system. As such, DI water is an essential element in boiler water recycling.
Deionized water can pretreat cooling tower make-up water to reduce scaling and energy use in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semiconductor plants, and other industrial facilities.
How does ion exchange resin work?
Cationic resin is typically made from styrene containing negatively charged sulfonic acid groups, pre-charged with hydrogen ions. This resin attracts the positively charged ions in the water (Ca++, Mg++, Na+, etc.) and releases an equivalent amount of hydrogen (H+) ions.
Anionic resin is also made from styrene and contains positively charged quaternary ammonium groups. It is pre-charged with hydroxide ions. This resin attracts negatively charged ions (HCO3-, Cl-, SO4--, etc.) and releases an equivalent amount of hydroxide (OH-). The hydrogen and hydroxide ions then combine to form water. (H+ + OH- = HOH or H2O.)
The two resins can be ionized at weak or strong levels. Weaker ionization exchanges only the weak ions, providing for greater capacity and longer filter life; while stronger ionization provides a higher degree of ion exchange at the cost of reduced capacity and shorter filter life.
How long does ion exchange resin last?
Over time, positive and negative contaminants in the water displace all the active hydrogen and hydroxyl molecules on the ion exchange resin and the filter loses its ability to remove contaminants. The lifecycle of a DI filter can vary greatly with the quality of the feed water, the type of resins used, and the filtration system configuration.
When resin is exhausted, it must be removed from the filtration system and regenerated. Equipment and chemicals for regeneration can represent a significant capital investment, in addition to your investment in the filtration system itself. Service DI from Evoqua provides regeneration off-site as a service, eliminating the need for this capital expense.
Are there are other DI processes besides ion exchange resin?
In addition to ion exchange resin technology, DI can be done through a technology that uses electricity, ion exchange membranes, and resin. In electrodeionization (EDI), electric current is used to continuously regenerate the ion exchange resin, reducing the consumption of fuel and chemicals used in the regeneration process. Evoqua's IonRight® systems combine reverse osmosis (RO) with EDI to provide continuous, consistent, high-purity water in a compact, plug-and-play package.
Does DI alone remove all impurities from water?
No. While it is extremely effective at removing minerals and salts, deionization does not remove dissolved organic chemicals, viruses, bacteria and particulates. For that reason, DI systems are typically configured with carbon filtration, ultraviolet (UV) purification, and reverse osmosis (RO) to remove these additional contaminants.
What industry standards apply to DI water?
Technical standards on water quality have been established by a number of professional organizations, including the American Chemical Society (ACS), ASTM International, the U.S. National Committee for Clinical Laboratory Standards (NCCLS), which is now CLSI, and the U.S. Pharmacopeia (USP). These standards apply to DI water as well as to water purified through other processes. The ASTM, NCCLS and ISO 3696 classify purified water into Grade 1-3 or Types I-IV depending upon the level of purity. These organizations have similar, although not identical, parameters for highly purified water. Many laboratory, pharmaceutical, medical, research and dialysis applications require ultra-pure water to meet one of these standards.