1.10.5 Special methods or water quality improving

Depending on properties of water-supply sources or consumers’ requirements to the water quality it may needed its treatment: softening, iron removing, stabilization, deodezoridation, demineralization, certain elements deleting or entering, cooling, etc.

Water softening is used to decrease its rigidity through removing or decreasing of calcium and magnesia salts, mainly during water preparation for boiler devices and technological needs of separate enterprises. For example, for separate workshops of textile of chemical industry water for boiler providing of average and high pressure should have rigidity not more than 0.3 мгЧекв/л. Methods of reagent and cation water softening are differed. During underground water softening, as a rule, cation methods are used, for superficial – reagent methods, that are performed together with clearing up.

From methods of the reagent softening the most spread is lime-sodium during which lime is added to the water to remove the temporal (carbonate) rigidity and calcinated sodium to remove contemporal (non carbonate) rigidity. During entering of named reagents to the water insoluble solutions are created, that fall out in sediment, or solutions that are kept in the water, but haven’t properties of salt rigidity. As a rule devices for reagent water softening include reagent economy, mixer, clearing up devices with hanged up sediment, filters.

During lime-sodium method of softening water alkality takes 0.8-1.2 мгЧекв/л, and surplus rigidity 0.5-1 мгЧекв/л. By water heating, it can be achieved the water softening to 0.2-0.4 мгЧекв/л.

Method of cation water softening means the ability of some materials (cations) to exchange cations of natrium or hydrogen by cations of rigidity salts, that are in water. In the role of cations sulphurcoal (grounded up stone coal, treated by concentrated sulphuric acid) or synthetic resins are mostly used.

For softening, water is filtrated through cationite loading, that is loaded mostly in pressure filters. As a result of filtration through cationite, water rigidity decrease till 0.03-0.05 мгЧекв/л. In process of filtration of rigid water cationite layer gradually looses ability to soften water. For filters’ regeneration through cationite layer the solution of sulphuric or salt acid (H-cationite filters) or solution of kitchen salt is passed.

Removing of iron from water. If there is considerable content of iron, water during the contact with oxygen obtains brown color, unpleasant metallic taste. Flakes of oxide hydrate of iron fall out in sediment and can cause overgrowing of pipes. Water with grate content of iron isn’t suitable for some enterprises, because it can cause spoilage of products through changing of its color (fabric production of fabric, artificial fiber, paper, film, photographic paper, etc.). Iron content in drinking water shouldn’t exceed 0/3 mg/l, and in technical water – according to the technologists requirements.

During removing of iron from the underground water the methods without reagents are usually used, for superficial water – reagent methods, as at the same time the task of water clearing up is solved. During methods without reagents, firstly, water is aerated, and than it’s filtrated on contact and sand filters. In the role of reagents for disinfection sulphate of aluminum, lime or reagent-oxidants are used.

Method of iron removing, calculation parameters and reagent dozes are better to be determined on the base of results of technological tests, which act near water-supply sources.

Water stabilization consists in giving to it the properties, during which it looses ability to cause corrosion or to put aside salts. Water stabilization is conducted mostly in industrial systems.

For removing of water corrosion properties on metal is used alkalization or phosphation of water. During adding of alkaline the lime or calcite sodium is moved in water. For preventing of pipe overgrowing by carbonate of calcium it’s used the acidifying the water with sulphuric (salt) acid or water decarbonisation is performed by blowing out of smoke gases through water.

For fight with biological overgrowing of pipes and equipment periodically are used adding of cuprum and chlorination of water.

Removing of salt from water consists in deleting from it of soluble salts. Total salt removing is needed for separate technological processes, in particular, during water preparation of high pressure boilers. Partial removing of soluble salts is named desaltation.

Desaltation of water with salts content up to 2-3g/l is conducted by ion exchange, with salt concentration 3-15g/l – by method of hyperfiltration or by electrolyze, and for water with salts content more than 10 g/l – by freezing, distillation or hyperfiltrattion.

Water deodorization. To decrease intensity of tastes and smells it is used the oxidization with the next persorption of substances, for what water is filtrated through granular absorbent carbone with periodical regeneration or replacement. It is also allowed to enter carbon in state of powder before settling structures or filters. During not considerable intensity of tastes and smells it can be used only oxidation which is conducted with clearing up and discoloring at the same time. Chlorine, ozone, permanganate of potassium can be oxidants. Type of oxidant and its dose is set on the base of technological tests.

For removing from water of chloric and phenic smells water ammonization is successfully used – moving of ammonia into water or solution of its salts (for example, sulfate to the ammonium). Ammonia is taken into water with help of ammoniators, which are similar to chlorine metering devices by their construction.

Water airing can promote decreasing of water smells and tastes before moving of chlorine or other oxidants in the water.

Water degassing consists in deleting of insoluble gases in it. Natural water usually contains the next soluble gases: oxygen, carbonic acid, nitrogen and rarer - sulphured hydrogen and methane.

Chemical and physical methods are used for water degassing. Chemical methods are based on reagent usage, which connect dissolved in water gases. In such way, iron shaving, sulfate of sodium, hydrazones, sulphuric gas are used for oxygen removing from water. Water is processed by chlorine during removing of sulphured hydrogen from it, and sulphur is picked up thread to the crystalline, and falls out in sediment. For connection of free carbonic acid to water is added lime or caustic natrium, replacing it on carbonate-ions.

Physical methods of water degassing are based on creation of conditions, during which solubility of gases becomes close to zero (heating or creation of vacuum).

Fluoridation or removing of fluorine from the water. The total absence of fluorine in drinking water and its increased concentration is harmful for human organism. Optimal fluorine content has to be in range 0.8-1.2mg/l. When concentration is decreased than in water the reagents are poured, which contain fluorine (silicic fluorine sodium or ammonium), when concentration is 1.5mg/l and more removing of fluorine from the water is conducted. Fluorine from water is deleted by its presorption by sediment of hydroxide of magnesium, alluminium or phosphate of calcium or by water filtration through sorbent, which detains fluorine.

Water cooling. Ponds, pools, water-cooling towers are used in systems of industrial water-supply for water cooling. Heated water is thrown out at ponds at one end and cooled water – at another. Heated water in pools is splashed on the water surface with help of attachments, and cooled one is taken away at some depth.

Water-cooling towers are the most spreaded. In them the heated water is served to the top part of the tower and distributed by sprinklers on whole surface. The water is splashed and flows down. Cool air goes to lower part of water-cooling towers and by moving up it cool the water. Height of water-cooling towers is taken 20-80m. Water-cooling towers with forced ventilation are also used. Water-cooling towers are made of wood or reinforced concrete.