For the treatment of wastewater, mechanical, physicochemical and biological treatment is used. The purified waste liquid is subjected to disinfection before being discharged into the reservoir to destroy pathogenic bacteria.

Wastewater treatment technology is currently developing in the direction of intensifying biological treatment processes, carrying out successive biological and physical-chemical treatment processes in order to be able to reuse deeply treated wastewater in industrial enterprises.

As a result of mechanical treatment, undissolved and partially colloidal contaminants are removed from the waste liquid. Large dirt (rags, paper, vegetable and fruit residues) are retained gratings. Contaminants of mineral origin (sand, slag, etc.) are captured sand traps. The bulk of undissolved pollution of organic origin is retained in cesspools. In this case, particles with a specific gravity greater than the specific gravity of the waste liquid fall to the bottom, and particles with a lower specific gravity (fats, oils, oil) float up depending on their nature. grease traps, oil traps, oil separators etc. With the help of these facilities, industrial sewage is cleaned.

They are also used to treat industrial wastewater. flotation introducing air into the waste liquid. and foaming agents (surfactants, alumina, animal glue, etc.). Floating air bubbles and foaming particles absorb impurities and raise them to the surface of the liquid in the form of foam, which is continuously removed.

Mechanical cleaning facilities also include septic tanks, two-tier sedimentation tanks and clarifiers-decomposers, in which the liquid is clarified and the precipitate is processed.

To remove suspended solids of a large specific gravity from industrial wastewater, hydrocyclones.

Physical-chemical treatment is used mainly for the treatment of certain types of industrial wastewater. Physical and chemical cleaning methods include sorption, extraction, evaporation, electrolysis, ion exchange and etc.

The essence of biological treatment is the oxidation of organic substances by microorganisms. Distinguish biological wastewater treatment in artificially created conditions (biological filters and aeration tanks) and under conditions close to natural (filter fields and biological ponds).

Most commonly used for disinfection of treated wastewater chlorination.

Currently, the requirements for the degree of wastewater treatment are increasing, and therefore they are subjected to post-treatment. For this, apply sand filters, contact clarifiers, microfilters, biological ponds.

To reduce the concentration of organic contaminants in biologically treated wastewater, sorption on activated carbons or chemical oxidation with ozone can be used.

Sometimes the problem arises of removing nutrients from wastewater - nitrogen and phosphorus, which, getting into the reservoir, contribute to the enhanced development of aquatic vegetation. Nitrogen is removed by physicochemical and biological methods, phosphorus is usually removed by chemical precipitation using iron and aluminum salts or lime.

The large masses of sludge accumulated in the treatment facilities are processed not only in septic tanks, two-tier settling tanks and clarifiers-decomposers, but also in digesters. Septic tanks, two-tier settling tanks and clarifiers-decomposers are designed for clarification of waste liquid and sludge fermentation. Methane tanks serve only for sludge fermentation.

Rice. 111.24. Schemes of a station with mechanical wastewater treatmenta- option without digester; 6 - variant with digester

Sludge treatment consists in the decomposition (fermentation) of its organic part using anaerobic, i.e. living without oxygen, microorganisms. In recent years, along with anaerobic sludge digestion, aerobic stabilization it, the essence of which is to purge the sediment for a long time with air in structures arranged like aerotanks.

In most sewage treatment plants, sludge forms in primary and secondary clarifiers (see figure III below). This sediment has a high humidity, does not give off water well and is dangerous in sanitary terms. For its processing, as a rule, digesters are used. The sludge fermented in digesters gives off water well, is less dangerous in sanitary terms and contains significant amounts of nitrogen, phosphorus and potassium, i.e., it is a good fertilizer. It is used for dehydration. sludge platforms, vacuum filters, centrifuges, filter presses. Quite often, the precipitate dehydrated on vacuum filters is subjected to thermal drying.

Some types of industrial wastewater sludge containing harmful contaminants after pre-drying burn. When burned, the organic matter of the sediments is completely oxidized and a sterile residue is formed - ash.

Wastewater is usually treated at mechanical and biological treatment plants located in series. Mechanical cleaning facilities (grids, sand traps and settling tanks) are designed to retain the bulk of undissolved contaminants. In biological treatment facilities, the remaining undissolved and dissolved organic contaminants are oxidized. The cleaning method and the composition of the treatment facilities are selected depending on the required degree of purification, the composition of the waste liquid contaminants, the performance of the treatment plant, soil conditions and the capacity of the reservoir with an appropriate feasibility study.

On fig. II 1.24 shows diagrams of a station with mechanical wastewater treatment. The waste liquid passes through a grate designed to trap large contaminants, a sand trap that serves to trap contaminants of mineral origin (sand, slag, etc.), a sump in which the bulk of organic contaminants are deposited, a mixer where the waste liquid is mixed with chlorine, contact a tank that serves to react chlorine with waste liquid g in order to disinfect it, and then is discharged into a reservoir. The sludge from the settling tank is sent to dewatering plants or to a digester (see Fig. III.24, b) for fermentation. The digested sludge is dried on sludge beds.

For stations of high productivity, the scheme shown in Fig. II 1.25. Mechanical wastewater treatment is carried out on grates, sand traps, preaerators and settling tanks. Preaerators are used for preliminary aeration of the waste liquid in order to improve the conditions for its subsequent clarification in settling tanks. Biological treatment is carried out in aeration tanks. Activated sludge is deposited in the secondary settling tanks. Part of the activated sludge from the secondary settling tanks is pumped to the aeration tanks (circulating activated sludge), and part of it (excess activated sludge) is transferred to the sludge thickeners. After the sludge thickeners, the sludge enters the digesters, where it is fermented along with the sludge from the primary settling tanks. Waste water after disinfection is discharged into the reservoir.

→ Solutions for wastewater treatment plants

Examples of wastewater treatment plants in major cities

Before considering specific examples of wastewater treatment plants, it is necessary to define what the concepts of the largest, large, medium and small city mean.

With a certain degree of conventionality, it is possible to classify cities by the number of inhabitants or, taking into account professional specialization, by the amount of wastewater entering the treatment plant. So for the largest cities with a population of more than 1 million people, the amount of wastewater exceeds 0.4 million m3 / day, for large cities with a population of 100 thousand to 1 million people, the amount of wastewater is 25-400 thousand m3 / day . In medium-sized cities, 50-100 thousand people live, and the amount of wastewater is 10-25 thousand m3 / day. In small towns and urban-type settlements, the number of inhabitants is from 3-50 thousand people (with a possible gradation of 3-10 thousand people; 10-20 thousand people; 25-50 thousand people). At the same time, the estimated amount of wastewater varies in a fairly wide range: from 0.5 to 10-15 thousand m3 / day.

The share of small towns in the Russian Federation is 90% of the total number of towns. It should also be taken into account that the water disposal system in cities can be decentralized and have several treatment facilities.

Let's consider the most significant examples of large treatment facilities in the cities of the Russian Federation: Moscow, St. Petersburg and Nizhny Novgorod.

Kuryanovskaya aeration station (KSA), Moscow. Kuryanovskaya aeration station is the oldest and largest aeration station in Russia; using its example, one can quite clearly study the history of the development of equipment and technology for wastewater treatment in our country.

The area occupied by the station is 380 ha; design capacity - 3.125 million m3 per day; of which almost 2/3 are domestic and 1/3 industrial wastewater. The station has four independent blocks of structures.

The development of the Kuryanovskaya aeration station began in 1950 after the commissioning of a complex of facilities with a capacity of 250 thousand m3 per day. An industrial-experimental technological and constructive base was laid on this block, which was the basis for the development of almost all aeration stations in the country, and was also used in the expansion of the Kuryanovskaya station itself.

On fig. 19.3 and 19.4 are technological schemes for wastewater treatment and sludge treatment of the Kuryanovskaya aeration station.

Wastewater treatment technology includes the following main facilities: gratings, sand traps, primary settling tanks, aerotanks, secondary settling tanks, wastewater disinfection facilities. Part of the biologically treated wastewater undergoes post-treatment on granular filters.

Rice. 19.3. Technological scheme of wastewater treatment of the Kuryanovskaya aeration station:
1 - lattice; 2 - sand trap; 3 - primary sump; 4 - aeration tank; 5 - secondary sump; 6 - flat slotted sieve; 7 - quick filter; 8 - regenerator; 9 - the main machine building of the CBO; 10 – sludge thickener; 11 – gravity belt thickener; 12 – flocculant solution preparation unit; 13 - industrial water pipeline structures; 14 – sand processing shop; 75 - incoming waste water; 16 - wash water from quick filters; 17 - sand pulp; 18 - water from the sand shop; 19 - floating substances; 20 - air; 21 – sludge from primary settling tanks at sludge treatment facilities; 22 - circulating activated sludge; 23 - filtrate; 24 - disinfected process water; 25 - technical water; 26 - air; 27 - thickened activated sludge for sludge treatment facilities; 28 - disinfected industrial water to the city; 29 - purified water in the river. Moscow; 30 - additionally treated wastewater in the river. Moscow

The KSA is equipped with mechanized gratings with 6 mm gaps with continuously moving scraper mechanisms.

Three types of sand traps are operated at KSA - vertical, horizontal and aerated. After dehydration and processing in a special workshop, sand can be used in road construction and for other purposes.

Radial type settlers with diameters of 33, 40 and 54 m are used as primary settling tanks at KSA. The design duration of settling is 2 hours. Primary settling tanks in the central part have built-in preaerators.

Biological wastewater treatment is carried out in four-corridor displacer aerotanks, the percentage of regeneration is from 25 to 50%.

Air for aeration is supplied to the aeration tanks through filter plates. At present, to select the optimal aeration system in a number of sections of aerotanks, tubular polyethylene aerators from the Ecopolymer company, plate aerators from the Greenfrog and Patfil companies are being tested.

Rice. 19.4. Technological scheme for processing sediments of the Kuryanovskaya aeration station:
1 – loading chamber of the digester; 2 – digester; 3 – unloading chamber of digesters; 4 - gas holder; 5 – heat exchanger; 6 - mixing chamber; 7 - washing tank; 8 – digested sludge compactor; 9 - filter press; 10 – flocculant solution preparation unit; 11 - silt platform; 12 – sludge from primary settling tanks; 13 - excess activated sludge; 14 - gas per candle; 15 - fermentation gas to the boiler room of the aeration station; 16 - industrial water; 17 - sand on sand platforms; 18 - air; 19 - filtrate; 20 - drain water; 21 - sludge water to the city sewer

One of the sections of the aeration tanks was reconstructed to operate on a single-sludge nitride-denitrification system, which also includes a phosphate removal system.

Secondary settling tanks, as well as primary ones, are of the radial type, with diameters of 33, 40 and 54 m.

About 30% of biologically treated wastewater undergoes post-treatment, which is first treated on flat slotted sieves and then on granular filters.

For sludge digestion at the KSA, buried methane tanks with a diameter of 24 m made of monolithic reinforced concrete with earthen sprinkling are used, ground-based ones with a diameter of 18 m with thermal insulation of the walls. All digesters operate according to the flow scheme, in thermophilic mode. The escaping gas is diverted to the local boiler house. After the digesters, the fermented mixture of raw sludge and excess activated sludge is subjected to compaction. Of the total amount of the mixture, 40-45% is sent to sludge sites, and 55-60% is sent to the mechanical dehydration shop. The total area of ​​silt pads is 380 ha.

Mechanical dehydration of sludge is carried out on eight filter presses.

Luberetskaya aeration station (LbSA), Moscow. More than 40% of wastewater in Moscow and large cities of the Moscow region is treated at the Luberetskaya aeration station (LbSA), located in the village of Nekrasovka, Moscow region (Fig. 19.5).

LbSA was built in the pre-war years. The technological process of cleaning consisted in the mechanical treatment of wastewater and subsequent treatment in the fields of irrigation. In 1959, by decision of the government, construction of an aeration station began on the site of the Lyubertsy irrigation fields.

Rice. 19.5. The plan of the treatment facilities of the Luberetskaya and Novoluberetskaya aeration stations:
1 – wastewater supply to LbSA; 2 – wastewater supply to NLbSA; 3 - LbSA; 4 - NLbSA; 5 – facilities for sludge treatment; b - releases of treated wastewater

The technological scheme of wastewater treatment at the LbSA practically does not differ from the adopted scheme at the KSA and includes the following facilities: grids; sand traps; primary settling tanks with preaerators; aeration tanks-displacers; secondary clarifiers; sludge treatment and wastewater disinfection facilities (Fig. 19.6).

In contrast to the structures of the KSA, most of which were built of monolithic reinforced concrete, prefabricated reinforced concrete structures were widely used at the LbSA.

After the construction and commissioning in 1984 of the first block, and subsequently the second block of the treatment facilities of the Novoluberetskaya aeration station (NLbSA), the design capacity of the LbSA is 3.125 million m3 / day. The technological scheme of wastewater treatment and sludge treatment at LbSA is practically no different from the classical scheme adopted at KSA.

However, in recent years, a lot of work has been carried out at the Lyubertsy station to modernize and reconstruct wastewater treatment facilities.

New foreign and domestic small-gauge mechanized gratings (4-6 mm) were installed at the station, as well as the modernization of existing mechanized gratings was carried out according to the technology developed at the MGP "Mosvodokanal" with a decrease in the size of the gaps to 4-5 mm.

Rice. 19.6. Technological scheme of wastewater treatment of the Luberetskaya aeration station:
1 - waste water; 2 - gratings; 3 - sand traps; 4 - preaerators; 5 - primary settling tanks; 6 - air; 7 - aeration tanks; 8 - secondary settling tanks; 9 – sludge thickeners; 10 - filter presses; 11 – dehydrated sludge storage areas; 12 - reagent facilities; 13 – digested sludge compactors before filter presses; 14 - sludge preparation unit; 15 – digesters; 16 - sand bunker; 17 - sand classifier; 18 - hydrocyclone; 19 - gas holder; 20 - boiler room; 21 - hydraulic presses for waste dewatering; 22 - emergency release

Of greatest interest is the technological scheme of block II of the NLbSa, which is a modern single-silt scheme of nit-ri-denitrification with two stages of nitrification. Along with the deep oxidation of carbon-containing organic substances, a deeper process of nitrogen oxidation of ammonium salts occurs with the formation of nitrates and a decrease in phosphates. The introduction of this technology makes it possible in the near future to obtain purified wastewater at the Lyubertsy aeration station, which would meet modern regulatory requirements for discharge into fishery water bodies (Fig. 19.7). For the first time, about 1 million m3/day of wastewater at LbSA is subjected to deep biological treatment with the removal of nutrients from treated wastewater.

Almost all raw sludge from primary clarifiers, before fermentation in digesters, undergoes preliminary processing on grates. The main technological processes for the treatment of sewage sludge at LbSA are: gravity compaction of excess activated sludge and raw sludge; thermophilic fermentation; washing and compaction of digested sludge; polymer conditioning; mechanical neutralization; deposit; natural drying (emergency silt pads).

Rice. 19.7. Technological scheme of wastewater treatment at LbSA according to the single-silt scheme of nitrification-denitrification:
1 - initial waste water; 2 – primary settler; 3 - clarified waste water; 4 - aerotank-denitrifier; 5 - air; 6 - secondary sump; 7 - treated waste water; 8 - recirculating activated sludge; 9 - raw sediment

For sludge dehydration, new frame filter-presses were installed, which make it possible to obtain a cake with a moisture content of 70-75%.

Central aeration station, St. Petersburg. The treatment facilities of the Central Aeration Station in St. Petersburg are located at the mouth of the river. Neva on the artificially reclaimed Bely Island. The station was put into operation in 1978; the design capacity of 1.5 million m3 per day was reached in 1985. The built-up area is 57 hectares.

The central aeration station of St. Petersburg receives and processes about 60% of domestic and 40% of industrial wastewater in the city. St. Petersburg is the largest city in the Baltic Sea basin, which places a special responsibility for ensuring its environmental safety.

The technological scheme of wastewater treatment and sludge treatment of the Central aeration station in St. Petersburg is shown in fig. 19.8.

The maximum flow rate of wastewater pumped by the pumping station in dry weather is 20 m3/s and in rainy weather - 30 m/s. Wastewater coming from the inlet collector of the city drainage network is pumped into the mechanical treatment inlet chamber.

The structure of mechanical treatment facilities includes: a receiving chamber, a grate building, primary settling tanks with grease collectors. Initially, wastewater is treated on 14 mechanized rake and stepped screens. After the screens, the wastewater enters the sand traps (12 pcs.) and then through the distribution channel is discharged to three groups of primary sedimentation tanks. Primary settling tanks of radial type, in the amount of 12 pieces. The diameter of each sump is 54 m at a depth of 5 m.

Rice. 19.8. Technological scheme of wastewater treatment and sludge treatment of the Central Station of St. Petersburg:
1 - sewage from the city; 2 - main pumping station; 3 - supply channel; 4 - mechanized gratings; 5 - sand traps; 6 - garbage; 7 - sand; 8 - sand; sites; 9 - primary settling tanks; 10 – raw sediment reservoir; 11 - aeration tanks; 12 - air; 13 - superchargers; 14 - return activated sludge; 15 - sludge pumping station; 16 - secondary settling tanks; 17 - release chamber; 18 - Neva river; 19 - activated sludge; 20 - sludge thickeners; 21 - receiving tank;
22 - centrifuges; 23 – cake for combustion; 24 - sludge incineration; 25 - furnace; 26 - ash; 27 - flocculant; 28 - drain water of sludge thickeners; 29 - water; 30 - solution
flocculant; 31 - centrifuge

The structure of biological treatment facilities includes aerotanks, radial settling tanks and the main machine building, which includes a block of blowers and sludge pumps. Aerotanks consist of two groups, each of which is six parallel three-corridor aerotanks 192 m long with a common upper and lower channels, the width and depth of the corridors are 8 and 5.5 m, respectively. Air is supplied to the aerotanks through fine-bubble aerators. The activated sludge regeneration is 33%, while the return activated sludge from the secondary settling tanks is fed into one of the aerotank corridors, which serves as a regenerator.

From the aerotanks, purified water is sent to 12 secondary settling tanks to separate activated sludge from biologically treated wastewater. Secondary settling tanks, as well as primary ones, are of a radial type with a diameter of 54 m and a settling zone depth of 5 m. From the secondary settling tanks, activated sludge enters the sludge pumping station under hydrostatic pressure. After the secondary settling tanks, the purified water is discharged into the river through the outlet chamber. Neva.

In the shop for mechanical sludge dewatering, raw sludge from primary settling tanks and compacted activated sludge from secondary settling tanks are processed. The main equipment of this workshop is ten centrifuges equipped with systems for preheating a mixture of raw sludge and activated sludge. To increase the degree of moisture transfer of the mixture, a flocculant solution is fed into the centrifuges. After processing in centrifuges, the moisture content of the cake reaches 76.5%.

In the sludge incineration shop, 4 fluidized bed furnaces (French company OTV) are installed.

A distinctive feature of these treatment facilities is that there is no pre-digestion in digesters in the sludge treatment cycle. Dehydration of the mixture of sediments and excess activated sludge occurs directly in the centrifuges. The combination of centrifuges and incineration of compacted sludge dramatically reduces the volume of the final ash product. Compared to conventional mechanical sludge treatment, the resulting ash is 10 times less than dehydrated cake. Using the method of burning a mixture of sludge and excess activated sludge in fluidized bed furnaces guarantees sanitary safety.

Aeration station, Nizhny Novgorod. The Nizhny Novgorod aeration station is a complex of facilities designed for complete biological treatment of domestic and industrial wastewater in Nizhny Novgorod and the city of Bor. The following structures are included in the technological scheme: mechanical treatment unit - gratings, sand traps, primary settling tanks; biological treatment unit - aerotanks and secondary settling tanks; post-treatment; sludge treatment facilities (Figure 19.9).

Rice. 19.9. Technological scheme of wastewater treatment at the Nizhny Novgorod aeration station:
1 - wastewater receiving chamber; 2 - gratings; 3 - sand traps; 4 - sand platforms; 5 - primary settling tanks; 6 - aeration tanks; 7 - secondary settling tanks; 8 - pumping station for excess activated sludge; 9 - airlift chamber; 10 - biological ponds; 11 - contact reservoirs; 12 - release in the river. Volga; 13 – sludge thickeners; 14 – raw sludge pumping station (from primary settling tanks); 75 – digesters; 16 - sludge pumping station; 17 - flocculant; 18 - filter press; 19 - silt pads

The design capacity of the facilities is 1.2 million m3/day. The building has 4 mechanized gratings with a capacity of 400 thousand m3/day each. Waste from the grates is moved by means of conveyors, dumped into bunkers, chlorinated and taken to the landfill for composting.

Sand traps include two blocks: the first consists of 7 horizontal aerated sand traps with a capacity of 600 m3/h each, the second - of 2 horizontal slotted sand traps with a capacity of 600 m3/h each.

8 primary radial settling tanks with a diameter of 54 m were built at the station. To remove floating impurities, the settling tanks are equipped with grease collectors.
4-corridor aeration tanks-mixers are used as biological treatment facilities. The dispersed inlet of wastewater into the aerotanks allows changing the volume of regenerators from 25 to 50%, ensuring good mixing of incoming water with activated sludge and uniform oxygen consumption along the entire length of the corridors. The length of each aeration tank is 120 m, the total width is 36 m, and the depth is 5.2 m.

The design of the secondary settling tanks and their dimensions are similar to the primary ones; in total, 10 secondary settling tanks were built at the station.

After the secondary settling tanks, the water is sent for post-treatment to two biological ponds with natural aeration. Biological ponds are built on a natural foundation and lined with earthen dams; the water surface area of ​​each pond is 20 ha. The residence time in biological ponds is 18-20 hours.

After bioponds, treated wastewater is disinfected in contact tanks using chlorine.

Purified and disinfected water through the Parshal trays enters the drainage canals and, after saturation with oxygen in the spillway overflow device, enters the river. Volga.

A mixture of raw sludge from primary settling tanks and compacted excess activated sludge is sent to digesters. Thermophilic mode is maintained in the digesters.

The digested sludge is partly fed to sludge beds and partly to a belt filter press.

The waste disposal system is an integral part of any city. It is she who provides the residential area, the normal functioning and compliance with sanitary standards in urban conditions. Wastewater that enters urban wastewater treatment plants contains a wide variety of organic and mineral compounds that can cause enormous damage to the environment if not properly disposed of.

The treatment plant includes four special treatment units. The first mechanical cleaning unit is used to remove sand and large debris (as a rule, large waste screened out at the first stage is much easier to dispose of). Then, at the next stage, in another block, a complete biological treatment takes place, and at the same time nitrogen compounds and the maximum possible amount of organic compounds are removed. After that, in the third block, further post-treatment of waste is already taking place - they are cleaned at a deeper level and disinfected. And in the fourth block, the process of processing the remaining precipitation takes place. Further, in order to better understand the essence of the process, we will consider in more detail how exactly this happens.

Due to mechanical, physical, chemical and biological treatment, sediment is separated from polluted water, which is then screened out in settling tanks specially designed for this purpose, and then, when activated sludge is formed, it passes into secondary settling tanks. Activated sludge is a very viscous substance that contains various simple organisms, bacteria and flakes formed from various chemical compounds. The sludge screened out by the settling tanks has almost one hundred percent moisture, but it is incredibly difficult to remove excess moisture, since the substances are highly bound together and have a low moisture yield. With the help of special sludge thickeners, the sludge is processed and compacted by two to three percent.

Unfortunately, the resulting substance cannot be used as fertilizer, because, despite the fact that potassium, nitrogen and phosphorus are present in activated sludge, they are poorly absorbed by plants, and in addition to microorganisms dangerous to humans, it also contains helminth eggs. Next, we will consider in more detail the types and principles of operation of facilities for the treatment of urban wastewater. In sewage treatment plants for mechanical water treatment, to remove sand and large debris, specialized nets or strainers with cells no larger than two millimeters are used. For finer sand, sand traps are used. This is a completely mechanized procedure. Structures for mechanical cleaning look like eleven meters high and up to twenty-two meters in diameter, reservoirs created on the basis of oil. From above they are closed with lids and equipped with a ventilation system. In lighting and heating, such structures need minimal quantities, since the largest volume in it is occupied by wastewater, for which it is not necessary to raise the temperature (it should be in the range of about twelve to sixteen degrees).

Biological treatment involves complex chemical processes that oxidize and break down liquids, using pumps that transport contaminated water from one area to another. In addition, the system is equipped with an anaerobic stabilizer that contains a sludge thickener. Currently, various types of treatment facilities are used in the city, local, which are designed for private and country houses, and industrial ones, which are necessary in order to purify water from industrial waste.

With particular strict adherence to environmental standards, they treat enterprises that produce any type of product (especially those from whose activities waste heavy metals and chemical compounds remain). Therefore, only after preliminary treatment, waste from industrial enterprises associated with the production of chemical, light, oil refining and other industries can be discharged into the central sewage system or reused. What processes should be carried out when treating water from an industrial enterprise is determined by the industry. The site, which is used for the construction of large ones, must be selected taking into account the convenient access of vehicles, the presence of a reservoir into which it is planned to discharge already treated water and the features of the terrain (in particular, the composition of the soil and the level of groundwater).

Since the treatment plant is a structure that can have a direct impact on the environment, it must comply with strictly defined standards and norms. The perimeter of a wastewater treatment plant must always be enclosed by a fence, and only urban-made tanks are used on the station itself. In addition, the treatment facilities are subject to strict control by the Ministry of Ecology and Bioresources, which arranges inspection of all facilities at the station.

Different conditions for dealing with plums and the difference in the tasks solved in this case led to the creation of different types of treatment facilities. For example, stormwater treatment facilities, in terms of their configuration and capabilities, are designed to treat surface runoff; local, depending on the equipment, are used for preliminary treatment of polluted waters of certain workshops, industries.

The urban type of treatment facilities, unlike others, is more versatile and can treat any type of liquid waste, but under one condition (which distinguishes it from others) - all of them must be brought to certain characteristics established by the standards. Among them: the concentration of impurities; effluent acidity (pH), which should be between 8.5 and 6.5.

City drains

This type of effluent is distinguished by the content of various organic compounds and particles of inorganic substances as pollutants. Some of them are quite harmless (for example, sand, particles of dust, dirt), others (oil, oil products, toxins, heavy metals) are dangerous and, when released into nature, cause irreparable harm to it, cause deterioration in human health, and lead to epidemics.

According to experts, urban wastewater to be treated contains on average (in mg/l):

• PVA ………………………………………..…………....10;
• dry residue ………………………….…………… 800;
• suspended solids ……………………….……....259;
• nitrogen of ammonium salts …………………………...30;
• total nitrogen ……………………..……..……………..45;
• phosphates ……………………..…………………..…….15;
• chlorides ………………………….………………..…...35;
• BODfull ……………………………………..……….. 280;
• BOD5 …………………………………………..………..200.

Description of treatment facilities for the city

Most often, urban treatment facilities include four units of treatment equipment: mechanical (or preliminary), biological, deep treatment, final treatment of wastewater.

In the first, mechanical, sand and large debris are removed from the drains. To do this, when treating urban wastewater, sieves, screens of various designs (mechanical drum, screw, rake, etc.), sand traps, and sand separators are used.

The pre-treated effluents received at the second block are freed from nitrogen compounds and most organic impurities. This is done using special bioreactors, the operation of which is based on the ability of microorganisms to process pollution included in the effluent during their life. At the same time, hazardous impurities "pass" into the category of non-hazardous and in suspension, which are removed in the following stages.

The third unit at the municipal wastewater treatment plant is engaged in the treatment of wastewater from suspended solids that appeared during previous operations and those that cannot be removed by biomethods. Various equipment helps to make this: flotation plants, settling tanks, separators, filters. At the final stage, the purified water is disinfected, and finally brought to the standards that comply with the requirements established by the sanitary and epidemiological rules.

In addition to the above, there are sections at the city sewage treatment plants that are engaged in the processing and disposal of sludge formed during the treatment of urban wastewater. They are equipped with installations where sludge is freed from excess moisture (belt and chamber filter presses, decanters). There are filtration fields and bioponds.

All facilities related to urban wastewater treatment facilities are always fenced and closed from unauthorized access by outsiders. They constantly monitor the indicators of wastewater treatment, the state of atmospheric air.

Improving urban wastewater treatment facilities

This type of treatment system is capital intensive. It requires high construction costs, constant cash costs during operation. Therefore, any measures that allow to reduce costs, and even more so to bring the process to a level of self-sufficiency, self-sufficiency, and even better - to profit, are considered by specialists very carefully and with interest.

Among these is a recently published report on studies conducted with drains from different US cities by specialists from the University of Arizona. They once again confirmed the possibility of making money on the treatment of urban wastewater, extracting them and sludge, metals and substances valuable for industry.

The increased interest in the results of their research is caused by the fact confirming the presence of precious metals in the effluents. Moreover, their presence is quite large and amounts to ¾ g for gold, 16.7 g for silver. According to their estimates, only the extraction of these metals will allow the treatment facilities of a million-plus city to earn up to 2.6 million US dollars a year.

No less interesting are reports about the possibility of obtaining electricity during the treatment of urban wastewater. Realization of this is possible along the path of creating microbiological fuel cells, which is what many scientists in the industry are doing. Until recently, the effectiveness of the direction was low, but everything changed radically after the discovery of engineers working at the University of Oregon in the USA.

Thanks to the use of a reduced cathode-anode arrangement, a developed bacterial environment and new separating materials, they managed to obtain an amount of electricity in the process of processing wastewater that exceeds previous achievements by 100 times. Such a result, according to the estimates of the same engineers, allows us to assert the effectiveness of the technology and the possibility of transferring experiments to real treatment facilities.

Hopes to turn the process of treating municipal wastewater into a self-sufficiency in the production of their own electricity may be too optimistic. But even with their partial implementation, the effect of this event is expected to be stunning, and therefore deserves attention and prompt implementation.

Kuryanovsk treatment facilities (KOS) design capacity 2.2 million m 3 / day, which are the largest in Europe, provide reception and treatment of domestic and industrial wastewater from the northwestern, western, southern, southeastern regions of Moscow (60% of the city) and, in addition, a number of cities and towns of the Moscow region.
The composition of the WWTP includes three independently functioning wastewater treatment units: the old station (KTPst.) with a design capacity of 1.0 million m 3 per day and the II block of the Novokurianovsk treatment facilities (NKOS-II) - 600 thousand m 3 per day.

WWTPs operate according to the technological scheme of complete biological treatment, including at the reconstructed facilities of NKOS-I and NKOS-II with the removal of biogenic elements: the first stage is mechanical treatment, including filtering water on grates, trapping mineral impurities in sand traps and settling water in primary sedimentation tanks ; the second stage is the biological treatment of water in aerotanks and secondary settling tanks. Part of the biologically treated wastewater undergoes post-treatment on fast filters and is used for the needs of industrial enterprises instead of tap water.

With sewage, a large number of different types of waste enter the WWTP: household items of citizens, waste from food production, plastic containers and plastic bags, as well as construction and other waste. To remove them at the WWTP, mechanized gratings with 10 mm gaps are used.

The second stage of mechanical wastewater treatment is sand traps - structures that serve to remove mineral impurities contained in incoming water. Mineral contaminants in wastewater include: sand, clay particles, solutions of mineral salts, mineral oils. Various types of sand traps are operated at the WWTP - vertical, horizontal and aerated.

After passing the first two stages of mechanical treatment, wastewater enters the primary settling tanks, designed to precipitate undissolved impurities from wastewater. Structurally, all primary clarifiers at the WWTP are of open type and have a radial shape, with different diameters - 33, 40 and 54 m.

The clarified wastewater after the primary settling tanks is subjected to complete biological treatment in aeration tanks. Aerotanks – open reinforced concrete structures of rectangular shape, 4-corridor type. The working depth of the aerotanks of the old unit is 4 m, the aerotanks of the NKOS - 6 m. Biological wastewater treatment is carried out using activated sludge with forced air supply.

The sludge mixture from the aeration tanks enters the secondary settling tanks, where the activated sludge is separated from the treated water. Secondary clarifiers are structurally similar to primary clarifiers.

The entire volume of wastewater treated at the WWTP is delivered to the post-treatment facilities. The productivity of the straining section is 3 million m 3 /day, which allows the entire volume of biologically purified water to be passed through flat slotted sieves. Part of the water after filtering is filtered on fast filters and used for technical needs as a circulating water supply.

Starting from 2012, all wastewater that has undergone a full treatment cycle at the Kuryanovsk treatment facilities is subjected to ultraviolet disinfection before being discharged into the Moskva River (capacity 3 million m 3 /day). Thanks to this, the indicators of bacterial contamination of the biologically purified water of the WWTP reached the standard values, which had a beneficial effect on the quality of the water of the Moscow River and the sanitary and epidemiological state of the water area as a whole.

Sludge generated at various stages of wastewater treatment is fed to a single sludge treatment complex, which includes:

• belt thickeners to reduce sludge moisture,
• digesters for digestion and stabilization of sludge in thermophilic mode (50-53 0 C),
• decanter centrifuges for sludge dewatering using flocculants.

The dehydrated sludge is taken out by third parties outside the territory of the treatment facilities for the purpose of neutralization/utilization and/or use for the production of finished products.