Due to the fact that the volumes of water consumption are constantly growing, and groundwater sources are limited, the shortage of water is replenished at the expense of surface water bodies.
The quality of drinking water must meet the high requirements of the standard. And the quality of water used for industrial purposes depends on the normal and stable operation of devices and equipment. Therefore, this water must be well purified and meet the standards.

But in most cases, the quality of water is low, and the problem of water purification is of great relevance today.
It is possible to improve the quality of wastewater treatment, which is then planned to be used for drinking and for household purposes, by using special methods for their treatment. For this, complexes of treatment facilities are being built, which are then combined into water treatment plants.

But attention should be paid to the problem of purifying not only the water that will then be eaten. Any wastewater, after passing through certain stages of purification, is discharged into water bodies or onto land. And if they contain harmful impurities, and their concentration is higher than the permissible values, then a serious blow is dealt to the state of the environment. Therefore, all measures for the protection of water bodies, rivers and nature in general begin with improving the quality of wastewater treatment. Special facilities that serve to treat wastewater, in addition to their main function, also make it possible to extract useful impurities from wastewater that can be used in the future, possibly even in other industries.
The degree of wastewater treatment is regulated by legislative acts, namely the Rules for the Protection of Surface Water from Pollution by Wastewater and the Fundamentals of Water Legislation of the Russian Federation.
All complexes of treatment facilities can be divided into water and sewer. Each species can be further divided into subspecies, which differ in structural features, composition, and technological cleaning processes.

Water treatment facilities

The water purification methods used, and, accordingly, the composition of the purification facilities themselves, are determined by the quality of the source water and the requirements for the water to be obtained at the outlet.
The cleaning technology includes the processes of clarification, bleaching and disinfection. This happens through the processes of settling, coagulation, filtration and chlorine treatment. In the event that initially the water is not very polluted, then some technological processes are skipped.

The most common methods of clarification and bleaching of effluents in water treatment plants are coagulation, filtration and settling. Often, water is settled in horizontal settling tanks, and it is filtered using various loads or contact clarifiers.
The practice of building water treatment facilities in our country has shown that the most widely used are those devices that are designed in such a way that horizontal sedimentation tanks and fast filters act as the main treatment elements.

Uniform requirements for purified drinking water predetermine the almost identical composition and structure of facilities. Let's take an example. Without exception, all water treatment plants (regardless of their capacity, performance, type and other features) include the following components:
- reagent devices with a mixer;
- flocculation chambers;
- horizontal (rarely vertical) settling chambers and clarifiers;
- ;
- containers for purified water;
- ;
- utility and auxiliary, administrative and household facilities.

sewerage treatment plant

Wastewater treatment plants have a complex engineering structure, as well as water treatment systems. At such facilities, effluents go through the stages of mechanical, biochemical (it is also called) and chemical treatment.

Mechanical wastewater treatment allows you to separate suspended solids, as well as coarse impurities by filtering, filtering and settling. At some cleaning facilities, mechanical cleaning is the final stage of the process. But often it is only a preparatory stage for biochemical purification.

The mechanical component of the wastewater treatment complex consists of the following elements:
- gratings that trap large impurities of mineral and organic origin;
- sand traps that allow you to separate heavy mechanical impurities (usually sand);
- settling tanks for separation of suspended particles (often of organic origin);
- chlorination devices with contact tanks, where clarified waste water is disinfected under the influence of chlorine.
Such effluent after disinfection can be discharged into a reservoir.

Unlike mechanical cleaning, with a chemical cleaning method, mixers and reagent plants are installed in front of the settling tanks. Thus, after passing through the grate and the sand trap, wastewater enters the mixer, where a special coagulation agent is added to it. And then the mixture is sent to the sump for clarification. After the sump, the water is released either into the reservoir or to the next stage of purification, where additional clarification takes place, and then they are released into the reservoir.

The biochemical method of wastewater treatment is often carried out at such facilities: filtration fields, or in biofilters.
On the filtration fields, the effluents after passing through the purification stage in gratings and sand traps enter the settling tanks for clarification and deworming. Then they go to the fields of irrigation or filtration, and after that they are dumped into the reservoir.
When cleaning in biofilters, effluents go through the stages of mechanical treatment, and then subjected to forced aeration. Further, effluents containing oxygen enter the biofilter facilities, and after it they are sent to the secondary sedimentation tank, where suspended solids and excess taken out of the biofilter are deposited. After that, the treated effluents are disinfected and discharged into the reservoir.
Wastewater treatment in aeration tanks goes through the following stages: gratings, sand traps, forced aeration, settling. Then the pre-treated effluents enter the aerotank, and then to the secondary settling tanks. This cleaning method ends in the same way as the previous one - with a disinfection procedure, after which the effluents can be discharged into a reservoir.

One of the main tasks of the enterprise is the effective purification of water obtained from natural surface sources in order to provide residents with high-quality drinking water. The classical technological scheme used at Moscow water treatment plants makes it possible to accomplish this task. However, the continuing trends in the deterioration of water quality in water sources due to anthropogenic impact and the tightening of drinking water quality standards dictate the need to increase the degree of purification.

With the beginning of the new millennium in Moscow, for the first time in Russia, in addition to the classical scheme, highly efficient innovative technologies for preparing drinking water of a new generation are used. The projects of the 21st century are modern treatment facilities, where the classical technology is supplemented by the processes of ozonation and sorption on activated carbon. Thanks to ozone sorption, water is better cleaned of chemical contaminants, unpleasant odors and tastes are eliminated, and additional disinfection occurs.

The use of innovative technologies eliminates the impact of seasonal changes in the quality of natural water, ensures reliable deodorization of drinking water, its guaranteed epidemic safety even in cases of emergency contamination of the water supply source. In total, about 50% of all treated water is prepared using new technologies.

Along with the introduction of new methods of water purification, disinfection processes are being improved. In order to improve the reliability and safety of drinking water production by eliminating liquid chlorine from circulation, in 2012 all water treatment plants were transferred to a new reagent - sodium hypochlorite which, according to the average data for 2018, the concentration of chloroform in Moscow tap water did not exceed 5–13 µg/l, while the standard was 60 µg/l.

Technological schemes for artesian water purification are individual for each facility, taking into account the characteristics of the water quality of exploited aquifers and contain the following steps: iron removal; softening; water conditioning on coal sorption filters; removal of heavy metal impurities; disinfection with sodium hypochlorite or using ultraviolet lamps.

To date, in the territory of the Troitsky and Novomoskovsky administrative districts of the city of Moscow, about half of the water intake units supply water that has undergone technological processing.

The phased introduction of new technologies is carried out in accordance with the General Scheme for the Development of the Water Supply System, which provides that the complete reconstruction of all water treatment facilities will allow supplying water of the highest quality to all residents of the Moscow metropolis.

The third belt covers the area surrounding the source, which affects the formation of water quality in it. The boundaries of the territory of the third belt are determined based on the possibility of contamination of the source with chemicals.

1.8. Water treatment facilities

Water quality indicators. The main source of prices

The trawled domestic and drinking water supply in most regions of the Russian Federation is the surface water of rivers, reservoirs and lakes. The amount of pollution entering surface water sources is varied and depends on the profile and volume of industrial and agricultural enterprises located in the catchment area.

The quality of groundwater is quite diverse and depends on the conditions of groundwater recharge, the depth of the aquifer, the composition of the water-bearing rocks, etc.

Water quality indicators are divided into physical, chemical, biological and bacterial. To determine the quality of natural waters, appropriate analyzes are carried out in the most characteristic periods of the year for a given source.

to physical indicators include temperature, transparency (or turbidity), color, smell, taste.

The water temperature of underground sources is characterized by constancy and is in the range of 8 ... be within t = 7…10 o C, at t< 7 о C вода плохо очищается, при t >10 o C, bacteria multiply in it.

Transparency (or turbidity) is characterized by the presence of suspended solids (particles of sand, clay, silt) in the water. The concentration of suspended solids is determined by weight.

The maximum permissible content of suspended solids in drinking water should not exceed 1.5 mg/l.

The color of the water is due to the presence of humic substances in the water. The color of water is measured in degrees of the platinum-cobalt scale. For drinking water, a color of no more than 20 ° is allowed.

Tastes and smells of natural waters can be of natural and artificial origin. There are three main tastes of natural water: salty, bitter, sour. Shades of taste sensations, composed of the main ones, are called flavors.

To odors of natural origin include earthy, fishy, ​​putrid, marsh, etc. Odors of artificial origin include chlorine, phenolic, oil products, etc.

The intensity and nature of smells and tastes of natural water is determined organoleptically, with the help of human senses on a five-point scale. Drinking water may have an odor and taste with an intensity of no more than 2 points.

To chemical indicators include: ionic composition, hardness, alkalinity, oxidizability, active concentration of hydrogen ions (pH), dry residue (total salt content), as well as the content of dissolved oxygen, sulfates and chlorides, nitrogen-containing compounds, fluorine and iron in water.

Ionic composition, (mg-eq/l) - natural waters contain various dissolved salts, represented by cations Ca + 2 , Mg + 2 , Na + , K + and anions HCO3 - , SO4 -2 , Cl- . Analysis of the ionic composition allows you to identify other chemical indicators.

Water hardness, (mg-eq / l) - due to the presence of calcium and magnesium salts in it. Distinguish between carbonate and non-carbonate hard

bone, their sum determines the total hardness of water, Zho \u003d Zhk + Zhnk. Carbonate hardness is due to the content of carbonate in water.

sodium and bicarbonate salts of calcium and magnesium. Non-carbonate hardness is due to calcium and magnesium salts of sulfuric, hydrochloric, silicic and nitric acids.

Water for household and drinking purposes should have a total hardness of not more than 7 mg-eq / l.

Alkalinity of water, (mg-eq/l) - due to the presence of bicarbonates and salts of weak organic acids in natural water.

The total alkalinity of water is determined by the total content of anions in it: HCO3 -, CO3 -2, OH-.

For drinking water, alkalinity is not limited. The oxidizability of water (mg / l) - due to the presence of or-

organic substances. Oxidability is determined by the amount of oxygen required for the oxidation of organic substances in 1 liter of water. A sharp increase in the oxidizability of water (more than 40 mg/l) indicates its contamination with domestic wastewater.

The active concentration of hydrogen ions in water is an indicator characterizing the degree of its acidity or alkalinity. Quantitatively, it is characterized by the concentration of hydrogen ions. In practice, the active reaction of water is expressed by the pH indicator, which is the negative decimal logarithm of the concentration of hydrogen ions: pH = - lg [Н + ]. The pH value of water is 1…14.

Natural waters are classified by pH value: into acidic pH< 7; нейтральные рН = 7; щелочные рН > 7.

For drinking purposes, water is considered suitable at pH = 6.5 ... 8.5. The salinity of water is estimated by dry residue (mg / l): pre-

sleepy100…1000; salted 3000…10000; heavily salted 10000 ... 50000.

In the water of domestic drinking water supply sources, the dry residue should not exceed 1000 mg/l. With a greater mineralization of water in the human body, salt deposition is observed.

Dissolved oxygen enters water when it comes into contact with air. The oxygen content in water depends on temperature and pressure.

AT dissolved oxygen is not found in artesian waters,

a its concentration in surface waters is significant.

AT In surface waters, the content of dissolved oxygen decreases when there are processes of fermentation or decay of organic residues in the water. A sharp decrease in the content of dissolved oxygen in water indicates its organic pollution. In natural water, the content of dissolved oxygen should not be

less than 4 mg O2 / l.

Sulfates and chlorides - due to their high solubility, they are found in all natural waters, usually in the form of sodium, calcium

calcium and magnesium salts: CaSO4, MgSO4, CaCI2, MgCl2, NaCl.

AT drinking water content of sulfates is recommended not higher than 500 mg/l, chlorides - up to 350 mg/l.

Nitrogen-containing compounds - are present in water in the form of ammonium ions NH4 +, nitrites NO2 - and nitrates NO3 -. Nitrogen-containing pollution indicates the contamination of natural waters with domestic wastewater and effluents from chemical plants. The absence of ammonia in the water and at the same time the presence of nitrites and especially nitrates indicate that the pollution of the reservoir occurred a long time ago, and the water

self-purifying. At high concentrations of dissolved oxygen in water, all nitrogen compounds are oxidized to NO3 - ions.

The presence of nitrates NO3 - in natural water up to 45 mg / l, ammonium nitrogen NH4 + is considered acceptable.

Fluorine - in natural water is contained in an amount of up to 18 ml / l and more. However, the vast majority of surface sources are characterized by the content of fluorine in the water - an ion of up to 0.5 mg / l.

Fluorine is a biologically active trace element, the amount of which in drinking water in order to avoid caries and fluorosis should be in the range of 0.7 ... 1.5 mg / l.

Iron - quite often found in the water of underground sources, mainly in the form of dissolved ferrous bicarbonate Fe (HCO3) 2 . In surface waters, iron is less common and usually in the form of complex complex compounds, colloids, or finely dispersed suspensions. The presence of iron in natural water makes it unsuitable for drinking and industrial purposes.

hydrogen sulfide H2S.

Bacteriological indicators - It is customary to consider the total number of bacteria and the number of E. coli contained in 1 ml of water.

Of particular importance for the sanitary assessment of water is the definition of bacteria of the Escherichia coli group. The presence of E. coli indicates water pollution by fecal effluents and the possibility of pathogenic bacteria, in particular typhoid bacteria, entering the water.

Bacteriological contaminants are pathogenic (pathogenic) bacteria and viruses that live and develop in water, which can cause typhoid fever,

paratyphoid, dysentery, brucellosis, infectious hepatitis, anthrax, cholera, poliomyelitis.

There are two indicators of bacteriological water pollution: coli-titer and coli-index.

Coli-titer - the amount of water in ml per one Escherichia coli.

Coli index - the number of Escherichia coli in 1 liter of water. For drinking water, if the titer should be at least 300 ml, if the index is not more than 3 Escherichia coli. Total number of bacteria

in 1 ml of water, no more than 100 is allowed.

Schematic diagram of water treatment facilities

ny. Treatment facilities are one of the constituent elements of water supply systems and are closely related to its other elements. The location of the treatment plant is assigned when choosing a water supply scheme for the facility. Often, treatment facilities are located near the source of water supply and at a slight distance from the pumping station of the first lift.

Traditional water treatment technologies provide for water treatment according to classical two-stage or one-stage schemes based on the use of microfiltration (in cases where algae are present in the water in an amount of more than 1000 cells / ml), coagulation followed by sedimentation or clarification in a layer of suspended sediment, rapid filtration or contact clarification and disinfection. The most widespread in the practice of water treatment are schemes with gravity flow of water.

A two-stage scheme for preparing water for domestic and drinking purposes is shown in fig. 1.8.1.

The water supplied by the pumping station of the first lift enters the mixer, where the coagulant solution is introduced and where it is mixed with water. From the mixer, water enters the flocculation chamber and sequentially passes through a horizontal sump and a quick filter. The clarified water enters the clean water tank. Chlorine from the chlorinator is introduced into the pipe supplying water to the tank. The contact with chlorine necessary for disinfection is provided in a clean water tank. In some cases, chlorine is added to the water twice: before the mixer (primary chlorination) and after the filters (secondary chlorination). In case of insufficient alkalinity of the source water into the mixer simultaneously with the coagulant

lime solution is supplied. To intensify the coagulation processes, a flocculant is introduced in front of the flocculation chamber or filters.

If the source water has a taste and smell, activated carbon is introduced through a dispenser before settling tanks or filters.

Reagents are prepared in special apparatus located in the premises of the reagent facilities.

From the pumps of the first

To pumps

Rice. 1.8.1. Scheme of treatment facilities for water purification for household and drinking purposes: 1 - mixer; 2 - reagent facilities; 3 - flocculation chamber; 4 - sump; 5 - filters; 6 − clean water tank; 7 - chlorination

With a single-stage water purification scheme, its clarification is carried out on filters or in contact clarifiers. When treating low-turbid colored waters, a single-stage scheme is used.

Let us consider in more detail the essence of the main processes of water purification. Coagulation of impurities is the process of enlargement of the smallest colloidal particles occurring as a result of their mutual adhesion under the influence of molecular attraction.

Colloidal particles contained in water have negative charges and are in mutual repulsion, so they do not settle. The added coagulant forms positively charged ions, which contributes to the mutual attraction of oppositely charged colloids and leads to the formation of coarse particles (flakes) in the flocculation chambers.

Aluminum sulfate, ferrous sulfate, aluminum polyoxychloride are used as coagulants.

The coagulation process is described by the following chemical reactions

Al2 (SO4 )3 → 2Al3+ + 3SO4 2– .

After the introduction of a coagulant into the water, aluminum cations interact with it

Al3+ + 3H2 O =Al(OH)3 ↓+ 3H+ .

Hydrogen cations are bound by bicarbonates present in water:

H+ + HCO3 – → CO2 + H2O.

soda is added to the water:

2H+ + CO3 –2 → H2O + CO2 .

The clarification process can be intensified with the help of high-molecular flocculants (praestol, VPK - 402), which are introduced into the water after the mixer.

Thorough mixing of treated water with reagents is carried out in mixers of various designs. The mixing of reagents with water should be fast and carried out within 1–2 min. The following types of mixers are used: perforated (Fig. 1.8.2), cloisonne (Fig. 1.8.3) and vertical (vortex) mixers.

+β h1

2bl

Rice. 1.8.2. perforated mixer

Rice. 1.8.3. Partition mixer

The perforated type mixer is used in water treatment plants with a capacity of up to 1000 m3 / h. It is made in the form of a reinforced concrete tray with vertical partitions installed perpendicular to the movement of water and equipped with holes arranged in several rows.

The partition wall mixer is used at water treatment plants with a capacity of not more than 500–600 m3 / h. The mixer consists of a tray with three transverse vertical partitions. In the first and third partitions, water passages are arranged, located in the central part of the partitions. In the middle partition there are two side passages for water adjacent to

tray walls. Due to this design of the mixer, turbulence of the moving water flow occurs, which ensures complete mixing of the reagent with water.

At stations where water is treated with lime milk, the use of perforated and partition mixers is not recommended, since the speed of water movement in these mixers does not ensure that lime particles are kept in suspension, which leads to

	dit to their deposition in front of partitions.
	At water treatment plants, most
	found more use vertically
	mixers (Fig. 1.8.4). Mixer
	this type can be square or
	round section in plan, with pyramids -
	far or conical bottom.
	In partition chambers, flakes
	formations arrange a series of partitions
	dock that make the water change							Reagents
	direction of movement or
	vertical or horizontal
	plane, which provides the necessary
	dimmable mixing of water.		Rice. 1.8.4. Vertical
	For mixing water and providing
			roar) mixer: 1 - feed
		more complete agglomeration	source water; 2 - water outlet
	small flakes of coagulant into large				from mixer
	serve as flocculation chambers. Them

installation is necessary in front of horizontal and vertical sedimentation tanks. With horizontal settling tanks, the following types of flocculation chambers should be arranged: partitioned, vortex, built-in with a layer of suspended sediment and paddle; with vertical sedimentation tanks - whirlpool.

Removal of suspended solids from water (clarification) is carried out by settling it in settling tanks. In the direction of water movement, sedimentation tanks are horizontal, radial and vertical.

The horizontal settling tank (Fig. 1.8.5) is a reinforced concrete tank rectangular in plan. In its lower part there is a volume for the accumulation of sediment, which is removed through the channel. For more efficient removal of sediment, the bottom of the sump is made with a slope. The treated water enters through the distribution

flume (or flooded weir). After passing through the sump, the water is collected by a tray or a perforated (perforated) pipe. Recently, settling tanks with a dispersed collection of clarified water have been used, arranging special gutters or perforated pipes in their upper part, which makes it possible to increase the performance of settling tanks. Horizontal settling tanks are used at treatment plants with a capacity of more than 30,000 m3 / day.

A variation of horizontal settling tanks are radial settling tanks with a mechanism for raking sediment into a pit located in the center of the structure. The sludge is pumped out of the pit. The design of radial sedimentation tanks is more complicated than horizontal ones. They are used to clarify waters with a high content of suspended solids (more than 2 g/l) and in circulating water supply systems.

Vertical settling tanks (Fig. 1.8.6) are round or square in plan and have a conical or pyramidal bottom for sediment accumulation. These settling tanks are used under the condition of preliminary coagulation of water. The flocculation chamber, mostly whirlpool, is located in the center of the structure. Clarification of water occurs with its upward movement. Clarified water is collected in circular and radial trays. Sludge from vertical settling tanks is discharged under hydrostatic water pressure without shutting down the facility from operation. Vertical settling tanks are mainly used at a flow rate of 3000 m3 / day.

Clarifiers with suspended sludge bed are designed for pre-clarification of water before filtration and only in case of pre-coagulation.

Sludge suspended bed clarifiers can be of various types. One of the most common is the in-line clarifier (Fig. 1.8.7), which is a rectangular tank divided into three sections. The two extreme sections are clarifier working chambers, and the middle section serves as a sediment thickener. The clarified water is supplied at the bottom of the clarifier through perforated pipes and is evenly distributed over the area of ​​the clarifier. Then it passes through the suspended sediment layer, is clarified and is discharged to the filters through a perforated tray or pipe located at some distance above the surface of the suspended layer.

For deep clarification of water, filters are used that are able to capture almost all suspensions from it. There are so

the same filters for partial water purification. Depending on the nature and type of filter material, the following types of filters are distinguished: granular (filter layer - quartz sand, anthracite, expanded clay, burnt rocks, granodiarite, expanded polystyrene, etc.); mesh (filter layer - mesh with a mesh size of 20-60 microns); fabric (filter layer - cotton, linen, cloth, glass or nylon fabrics); pre-washed (filter layer - wood flour, diatomite, asbestos chips and other materials, washed in the form of a thin layer on a frame made of porous ceramics, metal mesh or synthetic fabric).

Rice. 1.8.5. Horizontal sump: 1 - source water supply; 2 - removal of purified water; 3 - sediment removal; 4 - distribution pockets; 5 - distribution grids; 6 – sediment accumulation zone;

7 - settling zone

Rice. 1.8.6. Vertical settler: 1 – flocculation chamber; 2 - Rochelle wheel with nozzles; 3 - absorber; 4 - supply of initial water (from the mixer); 5 - prefabricated chute of the vertical sump; 6 - a pipe for removing sediment from a vertical sump; 7 - branch

water from the sump

Granular filters are used to purify domestic and industrial water from fine suspensions and colloids; mesh - to retain coarse suspended and floating particles; fabric - for the treatment of low-turbidity waters at stations of small productivity.

Grain filters are used to purify water in municipal water supply. The most important characteristic of the filters operation is the filtration speed, depending on which the filters are divided into slow (0.1–0.2), fast (5.5–12) and superfast filters.

Rice. 1.8.7. Corridor clarifier with suspended sludge with a vertical sludge thickener: 1 - clarifier corridors; 2 – sediment thickener; 3 - supply of initial water; 4 - prefabricated pockets for the removal of clarified water; 5 – sludge removal from the sludge thickener; 6 - removal of clarified water from the sediment thickener; 7 - sedimentation

windows with canopies

The most widespread are fast filters, on which pre-coagulated water is clarified (Fig. 1.8.8).

The water entering the rapid filters after the sump or clarifier should not contain suspended solids more than 12-25 mg/l, and after filtering the water turbidity should not exceed 1.5 mg/l

Contact clarifiers are similar in design to quick filters and are a variation of them. Clarification of water, based on the phenomenon of contact coagulation, occurs when it moves from bottom to top. The coagulant is introduced into the treated water immediately before it is filtered through the sand bed. In the short time before the start of filtration, only the smallest flakes of suspension are formed. The further process of coagulation takes place on the grains of the load, to which the smallest flakes previously formed adhere. This process, called contact coagulation, is faster than conventional bulk coagulation and requires less coagulant. Contact clarifiers are washed with

Water disinfection. In modern treatment facilities, water disinfection is carried out in all cases when the source of water supply is unreliable from a sanitary point of view. Disinfection can be carried out by chlorination, ozonation and bactericidal irradiation.

Water chlorination. The method of chlorination is the most common method of water disinfection. Usually, liquid or gaseous chlorine is used for chlorination. Chlorine has a high disinfecting ability, is relatively stable and remains active for a long time. It is easy to dose and control. Chlorine acts on organic substances, oxidizing them, and on bacteria, which die as a result of oxidation of substances that make up the protoplasm of cells. The disadvantage of water disinfection with chlorine is the formation of toxic volatile organohalogen compounds.

One of the promising methods of water chlorination is the use of sodium hypochlorite(NaClO), obtained by electrolysis of 2-4% sodium chloride solution.

Chlorine dioxide (ClO2 ) helps to reduce the possibility of formation of by-product organochlorine compounds. The bactericidal activity of chlorine dioxide is higher than that of chlorine. Chlorine dioxide is especially effective in disinfecting water with a high content of organic substances and ammonium salts.

The residual concentration of chlorine in drinking water should not exceed 0.3–0.5 mg/l

The interaction of chlorine with water is carried out in contact tanks. The duration of contact of chlorine with water before it reaches consumers should be at least 0.5 hours.

Germicidal irradiation. The bactericidal property of ultraviolet rays (UV) is due to the effect on cell metabolism and especially on the enzyme systems of a bacterial cell, in addition, under the action of UV radiation, photochemical reactions occur in the structure of DNA and RNA molecules, leading to their irreversible damage. UV rays destroy not only vegetative, but also spore bacteria, while chlorine acts only on vegetative ones. The advantages of UV radiation include the absence of any effect on the chemical composition of water.

To disinfect water in this way, it is passed through an installation consisting of a number of special chambers, inside which mercury-quartz lamps are placed, enclosed in quartz casings. Mercury-quartz lamps emit ultraviolet radiation. The productivity of such an installation, depending on the number of chambers, is 30 ... 150 m3 / h.

Operating costs for water disinfection by irradiation and chlorination are approximately the same.

However, it should be noted that with bactericidal irradiation of water, it is difficult to control the disinfection effect, while with chlorination this control is carried out quite simply by the presence of residual chlorine in the water. In addition, this method cannot be used to disinfect water with increased turbidity and color.

Water ozonation. Ozone is used for the purpose of deep water purification and oxidation of specific organic pollution of anthropogenic origin (phenols, petroleum products, synthetic surfactants, amines, etc.). Ozone improves the course of coagulation processes, reduces the dose of chlorine and coagulant, reduces the concentration

ration of LGS, to improve the quality of drinking water in terms of microbiological and organic indicators.

Ozone is most appropriate to use in conjunction with sorption purification on active carbons. Without ozone, in many cases it is impossible to obtain water that complies with SanPiN. As the main products of the reaction of ozone with organic substances, such compounds as formaldehyde and acetaldehyde are called, the content of which is normalized in drinking water at the level of 0.05 and 0.25 mg/l, respectively.

Ozonation is based on the property of ozone to decompose in water with the formation of atomic oxygen, which destroys the enzyme systems of microbial cells and oxidizes some compounds. The amount of ozone required for the disinfection of drinking water depends on the degree of water pollution and is not more than 0.3–0.5 mg/l. Ozone is toxic. The maximum permissible content of this gas in the air of industrial premises is 0.1 g/m3.

Water disinfection by ozonation according to sanitary and technical standards is the best, but relatively expensive. A water ozonation plant is a complex and expensive set of mechanisms and equipment. A significant disadvantage of the ozonator plant is the significant consumption of electricity to obtain purified ozone from the air and supply it to the treated water.

Ozone, being the strongest oxidizing agent, can be used not only to disinfect water, but also to decolorize it, as well as to eliminate tastes and odors.

The dose of ozone required for the disinfection of clean water does not exceed 1 mg/l, for the oxidation of organic substances during water discoloration - 4 mg/l.

The duration of contact of disinfected water with ozone is approximately 5 minutes.

Before entering the city water supply networks and consumer taps, the water undergoes a thorough pre-treatment. To bring it into a state of drinking, water treatment stations are installed that allow you to remove all harmful impurities, garbage, chemical elements that are unsafe for health. However, even the most high-tech installations are not a guarantee of purity, so additional home filters are often used.

Device features and types

Most urban residents are not satisfied with the quality of water supplied through water mains to taps. Moreover, in different regions, the chemical composition of the liquid and the presence of impurities in it differ. Someone notes increased hardness, someone - a white precipitate due to chalk, and sometimes there is a very perceptible smell of mold or other incomprehensible substances. The solution to the problem in most cases is the installation of storage or flow filters.

In fact, before getting to direct consumers, residents of settlements, industrial and other facilities, water undergoes a thorough cleaning. The procedure during which it is brought into line with sanitary standards is called water treatment. Drinking water at the station is supplied from natural reservoirs, storage facilities, canals. The process of its processing depends on the further use: drinking, domestic use, watering or technical needs.

In some settlements or regions, municipal chemical water treatment plants operate. These are large objects of a stationary type or mobile complexes, represented by container, modular and block systems.

The design of each installation depends on what it is necessary to purify the water from. According to the filtering method, the following types of stations are distinguished:

• chemical - involve treatment with reagents (chlorine or ozone) to neutralize all inorganic impurities (sulphates, cyanide substances, iron, nitrates, manganese are removed in this way);
• mechanical (physical) - they pass flows through filter systems of a membrane or mesh type to retain and screen out foreign particles (bacteria, suspensions, salts of heavy metals);
• biological - provide for the introduction of special microorganisms into the liquid that destroy harmful and dangerous organic matter (the method is relevant for the disinfection of wastewater);
• physical and chemical - used at industrial facilities and large water treatment plants;
• ultraviolet - designed to destroy pathogenic microflora and bacteria.

All systems are also classified into domestic and industrial, differ in performance and principle of operation. At many urban facilities, several filter systems are installed that perform different functions at the same time.

Operating principle

On the way from the reservoir to the apartment, water flows go through several stages of purification. However, you should not be sure that it becomes perfectly clean and safe. In the summer heat, the number of harmful bacteria and microorganisms increases significantly. It is because of the use of tap water that there is a surge in intestinal diseases and poisoning. In frosty weather, the number of pathogenic microflora is significantly reduced, but the human factor and the negligence of employees of water treatment plants, depreciation of equipment and other problems cannot be written off.

The standard procedure at the water treatment plant takes place in several stages:

• mechanical processing - first, solid, insoluble particles, impurities in the form of silt, sand, grass and algae, as well as debris and human life residues must be removed from the liquid;
• aeration - the process of dissolving contained gases, oxidizing iron (carried out by an aeration column and a special compressor);
• iron removal is the most complex and lengthy stage, where a drainage distribution device with an automatic control unit is used (granular material is poured into the body, on which iron is oxidized first from divalent to trivalent, and then precipitates);
• softening - removal of magnesium and calcium salts from water, which make it hard (regenerating salt solution and ion-exchange resins are used).

The final step is passing through carbon filters. They allow you to improve the color and smell of water, make the taste more pleasant.

A mandatory procedure at any water treatment plant is disinfection - the destruction of bacteriological pollutants . Chlorine is used as a reagent or ultraviolet sterilizing units. However, in the first case, an additional procedure is required to get rid of chlorine residues, which are extremely dangerous to health.

UV rays are considered safer. They are able to penetrate into every cell of microorganisms, destroy them and completely destroy them. Thus, the maximum disinfecting effect is achieved. In most cities, however, preference is given to flushing intracity networks with chlorine. This is evidenced by a periodically appearing characteristic odor for several days with a frequency of 2 times a year.

Technical equipment of urban networks

Stationary stations are huge platforms with numerous nodes and mechanisms. Modern equipment operates fully automatically, so the presence of a person in the work process is minimized. The standard equipment of the devices includes:

• the main reservoir for receiving liquid - here it enters through the utility channels for initial accumulation and rough initial cleaning;
• pumps - units that ensure the further movement of water to working substations;
• mixers - vortex units integrated into the system, which are responsible for the uniform distribution of the added coagulants throughout the mass (velocity within 1.2 m / s);
• filters - special devices in the form of sorption membranes;
• disinfecting unit - modern systems that change the qualitative composition by 95%.

There are several types of stations. The most primitive are block-type structures with closed systems that operate on the principle of pumping equipment.

The most modern installations are complex, modular, multi-stage structures, which include disinfection, filtration, and other stages, and are equipped with distribution channels and outlets. An important feature of such systems is the possibility of their integration into large industrial facilities, as well as changing the set of modules and components.

Another variety is specialized, narrowly focused stations that only destroy bacteria, fungi, and algae.

When choosing equipment needs to be based on different criteria.. For example, at home, installations with a throughput of 2-3 m3/h are sufficient. For industrial facilities, this indicator should be calculated from the daily requirement and be up to 1 thousand m3/hour. The optimal pressure range is considered to be from 6 to 10 bar for large hydrological units, for domestic needs - it is determined individually.

The need for application

After using tap water that has been treated in urban stationary facilities, plaque is often observed, for example, in a kettle, on sinks or in a washing machine. This is a light limescale buildup that needs to be cleaned regularly to keep it from turning into limestone. Drinking water of this quality is dangerous for health, as sooner or later it leads to the formation of kidney stones. Suffer from this composition of the liquid and household appliances. Washing machines and dishwashers quickly break down when scale builds up on the heating elements on a regular basis.

These are far from all the problems that arise as a result of the use of poor quality water in domestic conditions. Therefore, there are additional costs associated with the installation of cleaning mini-stations in your house or apartment.

One of the areas of application of water treatment plants is beer production enterprises. Here, very strict requirements are imposed on the liquid, it is the main raw material. To obtain 1 liter of intoxicating drink, 20 liters of water are required. The taste of the finished product, its durability, softness, as well as the fermentation process depend on its quality.

The main methods for improving the quality of natural water and the composition of structures depend on the quality of the water in the source, on the purpose of the water supply. The main methods of water purification include:

1. clarification, which is achieved by settling water in a sump or clarifiers to settle suspended particles in water, and filtering water through a filter material;

2. disinfection(disinfection) to destroy pathogenic bacteria;

3. softening– reduction of calcium and magnesium salts in water;

4. special water treatment- desalination (desalination), iron removal, stabilization - are used mainly for production purposes.

The scheme of facilities for the preparation of drinking water using a sump and filter is shown in fig. 1.8.

Purification of natural water for drinking purposes consists of the following activities: coagulation, clarification, filtration, disinfection by chlorination.

coagulation used to accelerate the process of sedimentation of suspended solids. To do this, chemical reagents, the so-called coagulants, are added to the water, which react with the salts in the water, contributing to the precipitation of suspended and colloidal particles. The coagulant solution is prepared and dosed at facilities called reagent facilities. Coagulation is a very complex process. Basically, coagulants coarsen suspended solids by sticking them together. Aluminum or iron salts are introduced into the water as a coagulant. More often aluminum sulphate Al2(SO4)3, ferrous sulfate FeSO4, ferric chloride FeCl3 are used. Their number depends on the pH of the water (the active reaction of water pH is determined by the concentration of hydrogen ions: pH = 7 medium is neutral, pH> 7-acidic, pH<7-щелочная). Доза коагулянта зависит от мутности и цветности воды и определяется согласно СНиП РК 04.01.02.–2001 «Водоснабжение. Наружные сети и сооружения». Для коагулирования используют мокрый способ дозирования реагентов. Коагулянт вводят в воду уже растворенный. Для этого имеется растворный бак, два расходных бака, где готовится раствор определенной концентрации путем добавления воды. Готовый раствор коагулянта подается в дозировочный бачок, имеющий поплавковый клапан, поддерживающий постоянный уровень воды. Затем из него раствор подается в смесители.

Rice. 1.8. Schemes of water treatment stations: with a flocculation chamber, sedimentation tanks and filters (A); with suspended sludge clarifier and filters (B)

1 - first lift pump; 2 - reagent shop; 3 - mixer; 4 – flocculation chamber; 5 - sump; 6 - filter; 7 - pipeline for chlorine inlet; 8 – purified water tank; 9 - second lift pump; 10 - clarifier with suspended sediment

To accelerate the coagulation process, flocculants are introduced: polyacrylamide, silicic acid. The following designs of mixers are most widespread: partition, perforated and vortex. The mixing process should take place before the formation of flakes, so the stay of water in the mixer is no more than 2 minutes. Partition mixer - a tray with partitions at an angle of 45 °. The water changes its direction several times, forming intense swirls, and promotes mixing of the coagulant. Perforated mixers - there are holes in the transverse partitions, water, passing through them, also forms vortices, contributing to the mixing of the coagulant. Vortex mixers are vertical mixers where mixing occurs due to the turbulence of the vertical flow.

From the mixer, water enters the flocculation chamber (reaction chamber). Here it is 10 - 40 minutes to obtain large flakes. The speed of movement in the chamber is such that no flakes fall out and their destruction occurs.

There are flocculation chambers: whirlpool, cloisonné, bladed, vortex, depending on the method of mixing. Partition - a reinforced concrete tank is divided by partitions (longitudinal) into corridors. Water passes through them at a speed of 0.2 - 0.3 m / s. The number of corridors depends on the turbidity of the water. Bladed - with a vertical or horizontal arrangement of the agitator shaft. Vortex - a reservoir in the form of a hydrocyclone (conical, expanding upwards). Water enters from below and moves at a decreasing speed from 0.7 m/s to 4 - 5 mm/s, while the peripheral layers of water are drawn into the main one, a vortex movement is created, which contributes to good mixing and flocculation. From the flocculation chamber, water enters the sump or clarifiers for clarification.

Lightening- this is the process of separating suspended solids from water when it moves at low speeds through special facilities: settling tanks, clarifiers. The sedimentation of particles occurs under the action of gravity, tk. the specific gravity of the particles is greater than the specific gravity of water. Water supply sources have a different content of suspended particles, i.e. have different turbidity, therefore, the duration of clarification will be different.

There are horizontal, vertical and radial sedimentation tanks.

Horizontal settling tanks are used when the plant capacity is more than 30,000 m 3 /day, they are a rectangular tank with a reverse slope of the bottom to remove the accumulated sediment by backwashing. Water supply is carried out from the end. Relatively uniform movement is achieved by the device of perforated partitions, weirs, prefabricated pockets, gutters. The sump can be two-section, with a section width of not more than 6 m. Settling time - 4 hours.

Vertical settling tanks - with a cleaning station capacity of up to 3000 m 3 / day. In the center of the sump there is a pipe where water is supplied. The settling tank is round or square in plan with a conical bottom (a=50-70°). Through the pipe, water descends down the sump, and then rises at low speed to the working part of the sump, where it is collected in a circular tray through the weir. Upflow velocity 0.5 – 0.75 mm/s, i.e. it must be less than the sedimentation rate of suspended particles. In this case, the diameter of the sump is not more than 10 m, the ratio of the sump diameter to the settling height is 1.5. The number of settling tanks is at least 2. Sometimes the sump is combined with a flocculation chamber, which is located instead of the central pipe. In this case, water flows from the nozzle tangentially at a speed of 2 - 3 m/s, creating conditions for flocculation. To dampen the rotational movement, gratings are arranged in the lower part of the sump. Settling time in vertical settling tanks - 2 hours.

Radial settling tanks are round tanks with a slightly conical bottom, used in industrial water supply, with a high content of suspended particles with a capacity of more than 40,000 m 3 / day.

Water is supplied to the center and then moves in a radial direction to the collection tray along the periphery of the sump, from which it is discharged through a pipe. Lightening also occurs due to the creation of low speeds of movement. The settling tanks have a shallow depth of 3–5 m in the center, 1.5–3 m at the periphery, and a diameter of 20–60 m. The sediment is removed mechanically, with scrapers, without stopping the operation of the settling tank.

Clarifiers. The clarification process in them is more intense, because. water after coagulation passes through a layer of suspended sediment, which is maintained in this state by a stream of water (Fig. 1.9).

Particles of suspended sediment contribute to a greater coarsening of the coagulant flakes. Large flakes can retain more suspended particles in the water to be clarified. This principle is the basis for the operation of suspended sludge clarifiers. Clarifiers with equal volumes with settling tanks have greater productivity, require less coagulant. To remove air, which can stir up suspended sediment, water is first sent to the air separator. In the corridor-type clarifier, clarified water is supplied through a pipe from below and is distributed by perforated pipes in the side compartments (corridors) in the lower part.

The upward flow velocity in the working part must be 1-1.2 mm/s so that the coagulant flakes are in suspension. When passing through a layer of suspended sediment, suspended particles are retained, the height of suspended sediment is 2 - 2.5 m. The degree of clarification is higher than in the sump. Above the working part there is a protective zone where there is no suspended sediment. Then the clarified water enters the collection tray, from which it is fed through the pipeline to the filter. The height of the working part (clarification zone) is 1.5-2 m.

Water filtration. After clarification, the water is filtered; for this, filters are used that have a layer of filtering fine-grained material, in which particles of fine suspension are retained during the passage of water. Filter material - quartz sand, gravel, crushed anthracite. Filters are fast, ultra-high-speed, slow: fast - work with coagulation; slow - without coagulation; high-speed - with and without coagulation.

There are pressure filters (super-high-speed), non-pressure (fast and slow). In pressure filters, water passes through the filter layer under pressure created by pumps. In non-pressure - under pressure created by the difference in water marks in the filter and at the outlet of it.

Rice. 1.9. In-line suspended sludge clarifier

1 - working chamber; 2 – sediment thickener; 3 - windows covered with visors; 4 - pipelines for supplying clarified water; 5 - pipelines for the release of sediment; 6 - pipelines for water withdrawal from the sludge thickener; 7 - valve; 8 - gutters; 9 - collection tray

In open (non-pressure) fast filters, water is supplied from the end into the pocket and passes from top to bottom through the filter layer and the supporting layer of gravel, then through the perforated bottom it enters the drainage, from there through the pipeline into the clean water tank. The filter is washed by reverse current through the discharge pipeline from the bottom up, the water is collected in the washing gutters, then discharged into the sewer. The thickness of the filter load depends on the size of the sand and is assumed to be 0.7 - 2 m. The estimated filtration rate is 5.5-10 m / h. Washing time - 5-8 minutes. The purpose of drainage is the uniform removal of filtered water. Now two-layer filters are used, first (from top to bottom) crushed anthracite (400 - 500 mm) is loaded, then sand (600 - 700 mm), supporting the gravel layer (650 mm). The last layer serves to prevent washing out of the filter media.

In addition to a single-flow filter (which has already been mentioned), two-flow ones are used, in which water is supplied in two streams: from above and below, the filtered water is removed through one pipe. Filtration speed - 12 m / h. The performance of a dual-stream filter is 2 times that of a single-stream one.

Water disinfection. When settling and filtering, most of the bacteria are retained up to 95%. The remaining bacteria are destroyed as a result of disinfection.

Water disinfection is achieved in the following ways:

1. Chlorination is carried out with liquid chlorine and bleach. The effect of chlorination is achieved with the intensity of mixing chlorine with water in a pipeline or in a special tank for 30 minutes. 2-3 mg of chlorine is added to 1 liter of filtered water, and 6 mg of chlorine is added to 1 liter of unfiltered water. Water supplied to the consumer must contain 0.3 - 0.5 mg of chlorine per 1 liter, the so-called residual chlorine. Usually double chlorination is used: before and after filtration.

Chlorine is dosed in special chlorinators, which are pressure and vacuum. Pressure chlorinators have a disadvantage: liquid chlorine is under pressure above atmospheric, so gas leaks are possible, which is toxic; vacuum - do not have this drawback. Chlorine is delivered in liquefied form in cylinders, from which chlorine is poured into an intermediate one, where it passes into a gaseous state. The gas enters the chlorinator, where it dissolves in tap water, forming chlorine water, which is then introduced into the pipeline transporting water intended for chlorination. With an increase in the dose of chlorine, an unpleasant odor remains in the water, such water must be dechlorinated.

2. Ozonation is the disinfection of water with ozone (oxidation of bacteria with atomic oxygen obtained by splitting ozone). Ozone eliminates color, odors and tastes of water. For disinfection of 1 liter of underground sources, 0.75 - 1 mg of ozone is needed, 1 liter of filtered water from surface sources - 1-3 mg of ozone.

3. Ultraviolet irradiation is produced using ultraviolet rays. This method is used to disinfect low-flow underground sources and filtered water from surface sources. Mercury-quartz lamps of high and low pressure serve as radiation sources. There are pressure units that are installed in pressure pipelines, non-pressure - on horizontal pipelines and in special channels. The disinfection effect depends on the duration and intensity of the radiation. This method is not suitable for highly turbid waters.

Water network

Water supply networks are divided into main and distribution networks. Trunk - transport the transit masses of water to the objects of consumption, distribution - supply water from the mains to individual buildings.

When tracing water supply networks, the layout of the water supply facility, the location of consumers, and the terrain should be taken into account.

Rice. 1.10. Schemes of water supply networks

a - branched (dead end); b - ring

According to the outline in the plan, water supply networks are distinguished: dead-end and ring.

Dead-end networks are used for those water supply facilities that allow a break in the water supply (Fig. 1.10, a). Ring networks are more reliable in operation, because in the event of an accident on one of the lines, consumers will be supplied with water through another line (Fig. 1.10, b). Fire water supply networks must be ring.

For external water supply, cast-iron, steel, reinforced concrete, asbestos-cement, polyethylene pipes are used.

Cast iron pipes with anti-corrosion coating are durable and widely used. The disadvantage is poor resistance to dynamic loads. Cast-iron pipes are socketed, with a diameter of 50 - 1200 mm and a length of 2 - 7 m. Pipes are asphalted from inside and outside to prevent corrosion. The joints are sealed with a tarred strand using a caulk, then the joint is sealed with asbestos cement with a seal using a hammer and chasing.

Steel pipes with a diameter of 200 - 1400 mm are used when laying water conduits and distribution networks at a pressure of more than 10 atm. Steel pipes are connected by welding. Water and gas pipelines - on threaded couplings. Outside, steel pipes are covered with bituminous mastic or kraft paper in 1 - 3 layers. According to the method of manufacturing pipes, they distinguish: longitudinally welded pipes with a diameter of 400 - 1400 mm, a length of 5 - 6 m; seamless (hot-rolled) with a diameter of 200 - 800 mm.

Asbestos-cement pipes they are produced with a diameter of 50 - 500 mm, a length of 3 - 4 m. The advantage is dielectricity (they are not exposed to stray electric currents). Disadvantage: exposed to mechanical stress associated with dynamic loads. Therefore, care must be taken when transporting. Connection - coupling with rubber rings.

Reinforced concrete pipes with a diameter of 500 - 1600 mm are used as conduits, the connection is pin.

Polyethylene pipes are resistant to corrosion, strong, durable, have less hydraulic resistance. The disadvantage is a large coefficient of linear expansion. When choosing a pipe material, design conditions and climatic data should be taken into account. For normal operation, valves are installed on water supply networks: shut-off and control valves (gate valves, valves), water folding (columns, taps, hydrants), safety valves (check valves, air vents). In the places of installation of fittings and fittings, manholes are arranged. Water wells on networks are made of precast concrete.

The calculation of the water supply network consists in establishing the diameter of the pipes, sufficient to skip the estimated costs, and determining the pressure loss in them. The depth of laying of water pipes depends on the depth of freezing of the soil, the material of the pipes. The depth of laying pipes (to the bottom of the pipe) should be 0.5 m below the estimated depth of soil freezing in a given climatic region.