Purification of drinking water

Drinking water treatment - exemption from suspended substances and reduction of its color, in accordance with the hygienic requirements to drinking water quality. The removal of turbidity and reduced color (light) water is achieved by its assertion in special tanks. However, very small particles suspended substances and humic compounds do not fall out of the water, even after prolonged standing. To increase the efficiency clarification of the water is treated in a special chemical reagents - coagulants, often salts trivalent metals. Particles coagulant, interacting with suspended substances and humic compounds that bind them into flakes, quickly settle on the bottom of the pit. Recently to speed up the process of coagulation in water add so-called flocculants. Often as occulant uses high-molecular compounds, such as polyacrylamide. For final clarification of the water is passed through a slow-acting or rapid filters. When slowly filtering through the filter layer of sand, the water flows with the speed of 0.1 - 0.3 m/hour, while in the delay of suspended solids, larvae and eggs of helminths, and a significant amount of bacteria in the upper layer of sand formed the so-called biological film contributing filtration efficiency. Slow filters can work without prior coagulation of water and are used in smaller pipelines, mainly in rural areas. Through rapid filters water is filtered with a speed of 5-8 m/h, in the upper layer of sand also form a skin flakes coagulant that improve filtering.
Are also new designs of filters high performance: a double-layer, in which the filtering layer consists of sand and crushed anthracite, a two-line, in which water is given from above and from below, and is discharged through pipe from thickness of filter layer, as well as the so-called contact clarifiers, in which water and the solution of coagulant and replace strainers and filters. In this type of constructions coagulation and delay flakes coagulant and suspended particles occur in the thickness of the filtering layer.
After coagulation, sedimentation and filtration, the water becomes transparent and colorless, significantly reduced its bacterial contamination. Final disinfection of water - removal from it of pathogens - produced by chlorination, ozonization, ultraviolet germicidal rays, ultrasound , high-intensity ultrashort waves, radioactive radiation through the use of the bactericidal properties of silver, copper, and other Chlorination of drinking water is carried out by use of chlorine gas, chlorine, chloramine, pantied, chlorine dioxide and other Chlorine, penetrating into microorganisms, destroys their enzyme system. In simple clarified water chlorination dose is determined by chloroplast (average of 0.5 - 1 mg/l). For a better effect if the water is very polluted, is a double chlorination - up of water treatment and after it. If in water there are substances that can make it unpleasant smell and taste after chlorination, to water pre add ammonia or ammonium salt. At chlorination of water with high doses of chlorine (5-10 times more, than at usual chlorination) subsequent dechlorination is physical, (activated carbon filters) or chemicals (sodium thiosulfate, dioxide of sulphur, sodium sulphate, etc). Ozonization of water is produced using a special apparatus - ozone generators, of which the air enriched with ozone (03), flows into the water and mixed with her. In water 03 gives an atom of oxygen and creates high oxidation potential. Apply this method in centralized water supply. Disinfection of drinking water with ultraviolet rays, ultrasound, etc. performed by means of special equipment.
If necessary, remove from water excessive amounts of iron will be deferrization by splashing water on special constructions with the purpose of its aeration and oxidation of ferrous iron to ferric iron and then filtering for his delay. Elimination of smells and flavors of water (deodorization) is water filtration through activated carbon treatment with high doses of chlorine, ozonation and other
At high water hardness produce its softening. At home softener is achieved by boiling in water, which precipitate salts of calcium and magnesium.
At the municipal water pipelines is used for softening soda-lime method. The most advanced method of water softening is filtering it through the so-called ion-exchange filters, which filter layer is a material that has the property to exchange contained in them ions on ions of salts dissolved in water.
When sanitary control of water treatment, the sample is collected in the course of technological process: the place of water intake from water source, after settling tanks, filters, and tanks, and pipelines. The samples are taken paramedical personnel in accordance with the existing instructions. Purification of water in the field is mainly for decontamination and disposal. Decontamination of drinking water has to remove from the water toxic substances and poisons or turn them into less toxic compounds. The water to be treated, filtered through activated charcoal special arrangements (carbohydrogen), is made by chlorination of water with high doses of active chlorine (for example, to remove from the water mustard gas). Each S or group S in the water he is neutralized by special technology. Disposal of arsenic compounds is achieved their oxidation and conversion into insoluble compounds.
Sarin, soman neutralized by adding to water in which they are located, 5 mg/l soda ash up to 1 mg/l of these substances in the water. After you add soda ash water for 1 hour, stir, then he is neutralized it. For water treatment in the field used car filtering station, the tissue-carbon filters, multi-functional handheld filters and mobile desalination plant. Cm. also Water.

Water treatment (drinking) - improvement of the structure and properties of natural water with the aim of bringing it into line with the requirements of the state standard (GOST) on the quality of drinking water.
Purification of water from surface sources is carried out at water treatment plants: the settling tanks, filters; they are water clarification often in combination of discoloration or deodorization.
Water clarification is exempt from suspended solids of varying degrees of dispersion. Removing large particles is achieved by advocating in the settling tanks in which the water is moving at a low speed. In the direction of water movement distinguish between horizontal and vertical tanks. The water from the tanks sent to the filters loaded small river sand. Lighten water passes through a sand and disposed through at the bottom of the filter drainage tanks of clean water.
Thanks formed on the surface of the sand film of mineral and colloidal suspensions, filters detain the smallest turbidity, eggs of helminths, and up to 99% of bacteria. The process outlined simple clarification requires 8 to 24 hours sludge and very low filtration rate to 0.1 m/hour, which severely limits the productivity of the plants. Installation of this type are used only in small rural water supply.
On major pipelines to correct the color of the surface waters, usually called colloidal humic substances used Dodge preliminary coagulation scheme: coagulating → defending > filtering. Coagulants (aluminum sulfate, iron sulfate, and others)that are added to the water in certain doses, form it hydroxide flakes that are relatively then deposited in the pits, carrying away of fine suspended matter and humic substances. However, a sufficient degree of clarification and decolouration of water is achieved after its filtration in rapid filters. These filters are more grain size of the sand, much greater speed filtering - 5 m/hour and more. This method of water purification degree and reliability delay bacteria smaller (not more than 90%); therefore clarified so the water requires disinfection (see Disinfection of drinking water).

diagram Dodge
Fig. 1. Diagram Dodge: 1 - clarified water; 2 - Luggage reaction vortex-type; 3 - zone of suspended sediment; 4 - contaminated water inflow; 5 edition of sediment; 6 - chemoprotectant.

In recent years instead of the usual vertical tanks are used clarifiers with suspended solid, especially the accumulated on the bottom of a settling tank with a layer of 2-2,5 meters of Water flowing into the tank pass through this layer, which plays the role of a filter intercepting mist, thus enabling larger water contact with the surface flakes coagulant. As a result, the effect of clarification and decolouration of water increases (Fig. 1).
Instead of the usual rapid filters are often used filters Academy of municipal economy named. K. D. Pamfilova (Akha), in which water is given from above and from below, and drainage pipes for drainage of filtered water are located in the thickness of the sand on the border between upper and middle third of the filtering layer. Filtering simultaneously from above downward and from below upward through a layer larger gravel and sand increases purification filter more than in 2 times, can increase the speed of filtering up to 12 m/hour.
For relatively little contaminated surface water is often used scheme of water clarification with no advocate: coagulating > filtering. The process of coagulation reaction of education of cereals and their delay together with sorbed water suspensions is happening in the thickness of the filter faster due to better conditions of contact. These filters have received the title of contact clarifiers (Fig. 2); they are economical in construction, but require a skillful and careful operation.

scheme of contact clarifier
Fig. 2. Scheme of contact clarifiers: 1 - submission of wash water; 2 - supply of river water; 3 - grained download; 4 - bend, clarified water; 5 - precast pocket; 6 - bend wash water; 7 - drain.

Frequent use of reservoirs as water sources causes the need to resort to eliminate the smell of water, which is formed as a result of hydrobiological processes, especially through pollution of water bodies with waste waters. The most effective deodorization of water is achieved by oxidation smelling: substances in the process of water disinfection (ozone, chlorine dioxide). Almost most accessible is the sorption process deodorization by plavanie, i.e. in water specific doses of powdered activated carbon.
Water purification of underground water sources, as a rule, has as its goal the improvement of their organoleptic properties (transparency, taste), reduction of water hardness or elimination of water from harmful substances. This is achieved by water deironing (aeration with the subsequent removal of iron hydroxide flakes sedimentation and filtration, desalination, or softening, water, i.e. reduction of the salt content or only hardness salts (see Desalination Vedas) or defluoridation by processing water aluminum sulfate or filtration through ion-exchange materials - anion exchangers.
The choice of concepts, methods and the most efficient types of facilities and equipment for water treatment at water pipes should be made based on the quality of water supply, hygienic requirements for the quality of drinking water provided by the standard, as well as simplicity and reliability in operation. Cm. also, Water, Water.