What are the uses of water purification

The production of ultrapure water in detail

One of the most common manufacturing processes for ultrapure water is reverse osmosis. In practice, however, production often takes place in combination with other cleaning processes such as ion exchange, irradiation with UV light or with the help of ultrafiltration.

Reverse osmosis

To put it simply, reverse osmosis is the reverse of natural osmosis and is used to concentrate undesirable components in liquids. A semi-permeable membrane is used for this process. This membrane only allows liquids to pass through, but not the substances dissolved in the liquid. During osmosis, the liquid with the lower concentration of undesirable components reaches the side of the liquid that contains a higher concentration of these substances. This results in an equalization of the concentration of the liquids. With reverse osmosis, this process is reversed.

The liquid is pressed through the membrane in such a way that the water with the higher concentration flows to the side with the lower concentration. The water flow is exactly the opposite of that in osmosis. This ensures that a liquid with a high concentration of foreign substances is present on one side, while very high quality ultrapure water (permeate) is produced on the other side of the membrane.

The ion exchange

In order to allow an ion exchange to take place, what is known as an ion exchanger is required. This is filled with a special material through which the solution to be treated (usually water to be cleaned) flows through it. The ions to be exchanged in this liquid are bound to the material in the ion exchanger, for which purpose an amount of the same charge is released to the liquid.

So-called cation exchangers are used in many areas. These serve to exchange the calcium cations contained in normal tap water for sodium cations, which are in the ion exchanger. The reactions during the ion exchange are reversible, so they can be reversed again. This fact is used by regenerating the ion exchangers.

The ultrafiltration

Ultrafiltration is a special process in which very small particles are filtered out of a liquid and concentrated. As with osmosis or reverse osmosis, semi-permeable membranes are used that can hold back high-molecular substances with an extremely small particle size.

The ultrafiltration takes place with the help of a comparatively low pressure with which the liquids to be cleaned are pressed through the membrane. The type of membrane used depends on the requirements for filtering the water. Particles as small as 0.05 micrometers can be retained. Compared to other filter methods, ultrafiltration offers the advantage that the filtered liquids are sterile, since the membranes in this filter method represent a barrier for bacteria or other microorganisms. In addition, the filter processes can be carried out fully automatically.