Demineralised process water: Importance and Production

Fully Demineralized Water – The VE Process

In technical jargon, “VE water” is often mentioned, which stands for “fully demineralized water” or demineralized water. The ions and salts found in normal tap water (such as calcium, magnesium, strontium, chloride, sodium, etc.) are not present in VE water. The term “VE process water” essentially encompasses three quality levels of water:

• Conductivity < 50 µS/cm: Low-salt water, produced by single-stage reverse osmosis.
• Conductivity < 1 µS/cm: High-purity water, produced by two-stage reverse osmosis and additional processes like mixed bed resins, depending on the quality of the feed water.
• Conductivity < 0.1 µS/cm: Ultra-pure water, produced by a combination of reverse osmosis, electrodeionization, and mixed bed resins.

To increase the efficiency of reverse osmosis, a softening unit is often pre-installed.

To determine the purity of VE water, electrical conductivity is measured (e.g., with devices like Select, N-LF2000, N-LF420). Conductivity (measured in Siemens S = Ω−1) is determined by alternating current and Ohm’s law (current (I), voltage (U) & electrical conductance (G)) of the analytical solution or its reciprocal.

Conductivity is measured by the voltage difference between the poles. The strength of the electric current or the voltage depends on the medium between the poles.

In short, the fewer salts and ions present in the water, the lower its conductivity. When all ions and salts are removed, the conductivity is very low, which is referred to as autoprotolysis. Although conductivity is measured in µS/cm (microsiemens per centimeter) in technical jargon, the official unit is mS/m (millisiemens per meter).

Depending on the treatment and initial quality, VE water may contain additional impurities. It is also referred to as “distillate-like water” or “demineralized water” and is often marketed as ironing or battery water. Distillate-like water is additionally sterilized to kill any bacteria that may be present.

VE process water is a more aggressive solvent than ordinary water due to the lack of salts and ions. The production of VE water through membrane filtration and possibly ion exchange is significantly more energy and water-efficient than distillation. Therefore, it is often used as an alternative to distilled water in industrial and laboratory environments.

The applications of VE water are diverse, particularly in the technical, chemical, and biological fields, where it is used as a solvent, heat carrier in cooling circuits, or in medical facilities. Treated water also plays an important role in many industrial manufacturing processes.

Process water has higher requirements for quality and properties, so proper water treatment is crucial, especially in the clinical field. Water can contain certain components that are harmful to equipment and processes. The desired quality and allowable residual content of components after treatment depend on the intended use. Improperly treated water can cause significant damage to people and machines and affect production lines.

An example is water with incorrect components, such as a high silicate content, which can damage sterilizers and processed medical instruments. In such cases, proper treatment is only possible through mechanical surface removal or the use of highly aggressive media such as hydrofluoric acid, leading to a drastic reduction in the lifespan of medical products and high reinvestment costs.

When planning water treatment, quality, volume, and legal standards must be considered, which requires expertise. Water treatment must deliver the desired quality and required volume to ensure the process runs smoothly and meets legal requirements.

Typically, water from the municipal supply is used, which is treated according to legal regulations. The chemical composition of drinking water can vary greatly by region, so its treatment must also be considered individually.