Desalination

Desalination of water - reducing the amount of salts contained in natural waters. For drinking water is generally desalinate partially, reducing the salt content up to the value when the water for its taste becomes suitable for drinking (less than 1000 mg/l).
For desalination of water of different methods are used. Chemical method of ion exchange based on filtration of water through special granular materials - exchange resin widely used in practice for desalination of water with a total salt content up to 2 to 3 g/L. the water Desalination-electrodialysis is based on the fact that the electric field cations and anions of water moving towards the submerged the cathode and the anode. The electrodialyzers divided permeable for cations and anions partitions (membranes), and in the Central parts thereof, between the partitions accumulates desalinated water.
When desalination of water by distillation of steam-free salts, if condensation is obtained distilled water.
Desalination of water freezing is based on the fact that during slow cooling water is below 0 degree crystals of freshwater ice that freeze together in units, formed earlier than frozen brine. During the gradual heating frozen between freshwater ice brine go into a liquid state and will drain before you begin to melt crystals of fresh ice. With further melting of fresh water is formed.
Before supply of desalinated water in the water supply it is necessary to disinfect.
Desalination of water through desalination of nuclear installations is made by distilling, electrodialysis and freezing. Preference is given distillation. Discharge of brine to the surface of the earth or in local waterways invalid. Desalinated water is devoid of microelements, tasteless, unsuitable for drinking, cooking drinks and food. Needs enrichment of mineral salts.

Desalination - partial desalination of saline sea water in order to reduce the content of dissolved salts to the degree that makes the water
suitable for household and drinking purposes. Desalination is different from softening, i.e., the partial removal of water cations of calcium and magnesium. In connection with the development of new areas with limited resources of fresh water and with the growing demand in drinking water increasingly require the use of sources of saline waters and marine waters (regions of Kazakhstan, the Caspian sea and others).
Desalination is achieved by changing its aggregate (phase) status (distillation, freezing) and removal of dissolved salts (chemical, electrochemical and ion exchange methods). Distillation method used by approximately 80% of existing installations, O. century is conducted at the temperature of slightly more than 90 degrees, that at the same time contributes to the disinfection of drinking water (see). There are installations operating at low temperatures. The resulting distilled water, devoid of salts, has an unpleasant taste and contains no trace elements; therefore, it automatically adds the source mineralized water, but no more than is allowed by the standard of drinking water quality. In natural conditions the desalination by freezing and solar desalination is possible only in certain climatic zones. In O. C. freezing is not to prevent the pollution of ice, tanks and vehicles.
New perspectives in the field of O. century arose in connection with the production of synthetic ion-exchange materials. These solid insoluble in water granular organic acids and bases have the ability to exchange members ions ions contained in sea water. There are ion-exchange resin as a cation exchange resin, extracts from the water cations (CA+2, Mg+2, Na+, and others), and the anion exchange resin, extracts from the water anions chlorine - ion (Cl-), sulfate-ion (SO-24), and other
Desalination ion-exchange method is filtering through pressure filters (groundwater, not requiring preliminary cleaning and disinfection) and gravity (water surface water is subject to pre-treatment and subsequent disinfection). Ion-exchange resin should not modify the organoleptic properties of water, induce the appearance of substances that may be hazardous to health (formaldehyde, blastomogenic and other unsafe substances used in the production of organic ion exchangers).
Electrochemical method of desalination based on the phenomenon of electrodialysis: practical application it became possible with cheaper electric power and after replacing inert diaphragms initanime (from katiana - and anion-exchange resins), respectively overlooking the cations and anions. Again featured ion-exchange materials is allowed only with the approval of the sanitary authorities.
Desalination nuclear installations. At the Geneva conference on peaceful uses of atomic energy in 1964 was listed on the expediency of construction of combined nuclear desalination plants, designed for simultaneous water desalination and electricity generation. Desalination of sea water at a nuclear facility may be made by the methods of distillation, electrodialysis and freezing. Currently, the preferred distillation. The experimental setup, built in the USA and the USSR, has demonstrated the effectiveness and profitability of dual-purpose stations intended for water desalination and electricity generation. Soviet desalination plant has a capacity of 150 MW of electricity and 120 000 m3 of fresh water a day. Preliminary calculations made in the USA, show that the cost of 1 m3 of desalinated water will not exceed 7 cents in large installations and 14 cents small.
However, desalination and use of desalinated water in national economy - the problem is not only technical, Noah hygiene. Desalinated water is devoid of microelements required for the human body, tasteless, unsuitable for drinking, cooking drinks and food. She needs to enrichment of mineral salts; you must determine which of mineral elements and in what quantities should be added to desalinated water intended for drinking and cooking, how many mineral elements are valid in desalinated water. As is known, in sea water, the concentration of mineral salts is up to 35 000 parts per million (ppm); in brackish water steppes and deserts - from 2,000 to 4,000 ppm; in irrigation drainage water - 4000 ppm and above. The who expert Committee in 1964 were given recommendations on the content of mineral balance in desalinated water: from 500 to 1000 parts per 1 million.
When desalination at nuclear installations discharge of brine remaining after evaporation bitter-salty water on the surface of the earth or diverting it into local waterways invalid. In countries with hot climate for atmospheric evaporation waste water to dry sediment is possible to arrange ponds lined with polyethylene film. At facilities located on the coast, the waste after distillation water is discharged into the sea.