What are the types of biological ponds? Biopond - wastewater treatment

K category: Cleaning of drains

Biological wastewater treatment in natural conditions

Biological wastewater treatment under natural conditions can be carried out in biological ponds, filtration fields and underground filtration structures, as well as in agricultural irrigation fields.

Biological ponds are artificially created shallow reservoirs in which biological wastewater treatment occurs on weakly filtering soils, based on the processes that occur during self-purification of reservoirs. Biological ponds can also be used for post-treatment of wastewater after it has passed through other biological treatment facilities. Ponds can be single (shallow, non-flowing with a depth of 0.6-1.2 m) or consisting of three to five ponds, through which clarified or biologically purified waste liquid on biofilters slowly flows.

For wastewater treatment in climatic region IV, biological ponds can be used all year round, in climatic regions II and III - only in the warm season, and in the cold season, provided that the water in the biological ponds has a temperature of at least 8°C.

Wastewater treatment in biological ponds can occur under anaerobic and aerobic conditions. Anaerobic ponds have a depth of 2.5-3 m, the BOD load for domestic wastewater is 300-350 kg/ /(ha-day). Aerobic bioponds with natural aeration can be used to treat wastewater with a BOD.5 concentration of no higher than 200-250 mg/l in climatic zone IV year-round, and in climatic zones II and III only during the warm period. The design load on ponds for settled wastewater is assumed to be up to 250 m3/(ha-day), for biologically treated water - up to 5000 m3/(ha-day). With a pond area of ​​0.5-0.25 hectares, the residence time of wastewater, depending on the load, ranges from 2.5 to 10 days.

For complete cleaning, it is advisable to carry out Bnoponds in two to three stages, taking in each stage the degree of purification according to BOD.5 equal to 70%. To intensify the wastewater treatment process, atmospheric oxygen is artificially supplied to bioponds. Such bioponds occupy a significantly smaller area and are less dependent on climatic conditions; they can operate at air temperatures from -15 to -20 °C, and on some days up to -45 °C.

Research by VNII VODGEO, MISS named after. V.V. Kuibysheva and TsNIIEP engineering equipment, as well as the results of production tests of the Belarusian Scientific Research Sanitary and Hygienic Institute confirmed the feasibility of using aerated bioponds for wastewater treatment in rural areas with a throughput capacity of 100-10,000 m3/day, and for post-treatment - up to 50,000 m3/day.

Aerated bioponds can be used for wastewater treatment with a BOD5 concentration of up to 500 mg/l; they provide effective wastewater treatment in climatic zones II and III. In the northern regions of climate zone II, as well as in areas with stable winds in winter time years, it is more advisable to use biological ponds with a recirculation cycle (return) of the sludge mixture, which have better thermal characteristics. Before bioponds, mechanical wastewater treatment should be provided. At a concentration of suspended substances up to 250 mg/l, the settling time can be taken equal to 0.5 hours, at a concentration of 250-500 mg/l - 1 hour.

Rice. 1. Plan of a biological wastewater treatment plant with a throughput capacity of 700 m3/day 1, 2, 3, 4 - aerated ponds, respectively, stages I, II, III, IV: 5 - settling pond; 6 - contact pond; 7 - production building: 8 - service water suction pipeline; 9 - air duct; 10 - pressure pipeline of technical water; 11 - receiving chamber; 12 - supply pipeline with a diameter of 300 mm; 13 - two-tier settling tank; 14, 17 - sand areas; 15 - sand pipeline; 16 - sludge beds

The construction of treatment facilities using aerated bioponds requires the least capital investment compared to treatment by other methods. Unit costs at these stations are 20-50% lower. In addition, aerated bioponds are characterized high level mechanization of excavation work and minimal consumption of reinforced concrete and other building materials.

Filtration fields can be used in some cases if there are land plots with filter soils unsuitable for agricultural use, and there is no danger of contamination of groundwater used for drinking needs. Land plots of filtration fields are specially prepared for biological wastewater treatment, preventing their use for agricultural purposes. Wastewater supplied to the fields is supplied to individual areas (maps) through a system of open trays or channels (diversion channels); the complex of these canals makes up the irrigation network. The collection and disposal of filtered purified water is carried out using drainage, which can be open in the form of ditches around the perimeter of the maps or closed, consisting of drainage pipes laid along the map at a depth of 1.5-2 m, and ditches. A system of drainage and ditches forms a drainage system. The channels are made of brick, rubble, reinforced concrete, concrete or made of earth. The channels have a rectangular or trapezoidal cross-section; they are placed along the enclosing earthen rolls.

When designing filtration fields, choose open, non-flooded ones spring waters areas with calm terrain with a natural slope of no more than 0.02. Areas located close to areas where aquifers pinch out, as well as peat and clay soils and saline soils, are not suitable for constructing filtration fields. Sandy and sandy loam soils are most suitable. It is recommended to locate the fields on the leeward side at a certain distance from residential areas depending on the wastewater flow rate: at a flow rate of up to 5000 m3/day this distance is taken to be 300 m, at 5000-50,000 m3/day -500 m and over 50,000 m3/day -1000 m. Willow and other moisture-loving plantings are usually planted along the contours of the fields. The width of the planting strip is 10-20 m, depending on the distance of the fields from populated areas.

Domestic wastewater treated in filtration fields has a BOD of 10-15 mg/l, a stability of 99% (i.e. does not rot), and contains nitrates up to 25 mg/l. The number of bacteria is reduced by 99-99.9% compared to their content in the source water. No special disinfection is required. For successful operation of fields, it is necessary to supply them with wastewater that has been previously clarified, i.e. largely freed from suspended particles. In addition, when settling, up to 50-80% of helminths are precipitated from waste liquid, which reduces soil contamination by 7-10 times.

The required area for filtration fields is determined based on the load norm - the permissible amount of wastewater that can be purified per 1 hectare of field surface. In addition, the nature of the soil, groundwater level and average annual temperature according to load standards are taken into account. The norms for the load of clarified wastewater on filtration fields for areas with an average annual precipitation of 300-500 mm are given in SNiP 2.04.03-85.

For the construction of map fences, irrigation networks, roads and entrances to maps, additional area must be provided. Thus, with a useful area of ​​filtration fields up to 0.3 hectares, the additional area is provided equal to 100% of the usable area, with 0.5 hectares - 90, with 0.8-80, with 1 hectare - 60 and more than 1 hectare - 40% of the usable area fields.

When constructing filtration fields, permanent and temporary irrigation networks are usually provided. The permanent irrigation network (Fig. 2) consists of a main canal, group distribution canals and map irrigators serving individual cards. The Kartovyn sprinkler is the last element of the permanent network.

Rice. 2. Scheme of irrigation fields 1 - main and distribution canals; 2 - sled sprinklers; 3 - drainage ditches; 4 - drainage; 5 - roads

The irrigation network is designed from ceramic or asbestos-cement pipes with a diameter of 75-100 mm. It is allowed to use irrigation trays made of brick, concrete and other materials. Irrigation pipes are laid in sandy soils with a slope of 0.001-0.003, and horizontally in sandy soils. The distance between parallel irrigation pipes in sand is 1.5-2.0 m, in sandy loam - 2.5 m. Ceramic pipes are laid with gaps of 15-20 mm; Overlays should be provided over pipe joints. In asbestos-cement pipes of irrigation networks, cuts are made from below to half the diameter with a width of 15 mm. The distance between cuts should be no more than 2 m. For air flow, risers with a diameter of 100 mm are installed at the ends of the irrigation pipes, rising 0.5 m above the ground surface.

Rice. 3. Layout of underground filtration fields 1 - outlet from the building; 2 - three-chamber septic tank made of reinforced concrete rings; 3 - dosing chamber with dosing siphon; 4 - distribution chamber; 5 - drains

A drainage network on filtration fields is provided under unfavorable ground conditions. It consists of drainage, collection network, outlet lines and outlets. The drainage system is integral part fields, as it allows for the timely removal of excess soil moisture and promotes the penetration of air into the active layer, without which the aerobic oxidative process cannot take place. In low-permeability soils (loams), closed drainage is constructed; in permeable soils (sands, sandy loams), drainage is either not required at all, or open drainage ditches are installed.

The distance between drains depends on the degree of water permeability of the soil, the depth of the drained layer, the depth of drains, the amount of water drained, etc. For preliminary calculations, the distance between drains in sand is taken to be 16-25 m, in sandy loam 12-15 m and in light loam 8-10 m. In coarse sands, in some cases, drainage is constructed in the form of open drainage ditches with a distance between them of up to 100 m.

Closed drainage is made mainly from unglazed pottery pipes with a diameter of 75-100 mm.

Drains should be located perpendicular to the direction of groundwater flow with a slope of 0.0025-0.005. Gaps of 4-5 mm are left between the pipes. A clay cushion is placed under the joints, and the joints are covered with roofing felt or felt on top. Open drainage ditches, collection networks and outlets are arranged in the form of trapezoidal-shaped channels with side walls at the angle of natural slope of the soil.

In winter, after the soil freezes, the filtration of wastewater on the filtration fields slows down significantly, and sometimes stops completely, and the wastewater released onto the fields freezes. Therefore, in areas with cold and temperate climates, filtration fields should be checked for freezing. Typically, the height of the wastewater freezing layer is taken to be 0.6-0.8 m, according to which the height of the shafts enclosing the map is determined.

Underground filtration structures. To treat small quantities of wastewater, underground filtration fields are used. Wastewater from a building or group of buildings is sent for preliminary clarification to a septic tank (Fig. 3). The clarified water enters a network of pipelines laid at a depth of 0.3-1.2 m with unsealed joints, through which the wastewater penetrates into the ground, where it is further purified. Treated wastewater is not collected in the drainage network, but seeps into the soil or partially goes with the ground flow.

Growing garden crops is allowed on the territory of underground filtration fields. The disadvantage of filtration fields is the need to create a wide sanitary break zone (200-300 m). For objects with a wastewater flow rate of up to 12 m3/day, in some cases (in the presence of filter soils, deep groundwater and there is no danger of contamination of aquifers used for drinking water supply), treatment facilities operating on the principle of underground filtration of wastewater can be adopted ( sand and gravel filters, filter trenches, filter wells). These structures are quite simple to construct and operate and are designed for complete biological treatment.

Underground filtration structures (as opposed to above-ground filtration fields) can be located near the buildings they serve and do not require the construction of a significant external sewer network. Wastewater flows to treatment plants by gravity, and therefore no pumping stations are required. It is advisable to install such structures in sandy, sandy loam and light loamy soils.

Wastewater from a building or group of buildings is sent to a septic tank for preliminary clarification. Clarified water, through a dosing chamber and a distribution well, enters drainage pipes located at least 1 m above the groundwater level, or a filter well. Through unsealed joints and cuts in pipes or holes in the walls of the well, the clarified liquid enters the ground, where it is further purified. When operating underground filtration systems, pollution of air and top layers of soil is eliminated.

Typical designs of treatment facilities for underground filtration systems are developed in accordance with a unified range of such structures with low productivity of 0.5-12 m3/day. The range of standard projects includes: septic tanks; systems with underground filtration fields and filter wells, used in sandy and sandy loam soils; systems with filter trenches and sand-gravel filters, used for loamy and clayey soils.

A septic tank is an underground structure in which wastewater flows at low speed, while suspended substances precipitate and the liquid is clarified within 1-4 days. The sediment that falls in the septic tank undergoes long-term rotting (fermentation) for 6-12 months under the influence of anaerobic microorganisms.

The calculated volumes of septic tanks should be taken from the conditions for cleaning them at least once a year. When the average winter temperature of wastewater is above 10°C or when the drainage rate is more than 150 l/(person-day), the total calculated volume of the septic tank can be reduced by 20%.

For wastewater consumption up to 1 m3/day, single-chamber septic tanks are provided, up to 10 m3/day - two-chamber septic tanks, and over 10 m3/day - three-chamber septic tanks. The volume of the first chamber in two-chamber septic tanks is taken equal to 0.75; in three-chamber - 0.5 calculated volume. In the latter case, the volume of the second and third chambers should be 0.25 of the calculated volume. In septic tanks made of concrete rings, all chambers can be of equal volume. At flow rates of more than 5 m3/day, each chamber should be divided by a longitudinal wall into two identical compartments. The minimum dimensions of a septic tank are: depth (from water level) 1.3, width 1, length or diameter 1 m. The maximum depth of a septic tank is no more than 3.2 m. Natural ventilation must be provided in septic tanks. In a typical project, septic tanks with a throughput capacity of 0.5-0.25 m3/day are developed (Fig. 4).

The sand and gravel filter is a pit in which the filter backfill is laid. Depending on the number of backfill layers, filters come in one- and two-stage types. In single-stage filters, coarse sand is used in a layer of 1-1.5 m; in two-stage filters, the first stage is loaded with gravel, coke, granulated slag in a layer of 1-1.5 m, the second is similar to a single-stage filter.

The filter trench is a structural type of sand and gravel filters - it consists of dispersed and elongated filters. Trenches are used in cases where the installation of sand and gravel filters is not allowed due to the proximity of groundwater and it is impossible to drain it with a drainage network due to the terrain. The design length of the filter trenches is taken depending on the wastewater flow and the load on the irrigation pipes, but not more than 300 m, the width of the trenches at the bottom is not less than 0.5 m.

In filter trenches, coarse and medium-grained sand and other coarse-grained materials with a layer thickness (between the irrigation and drainage pipes) of 0.8-1 m are used as loading material. For irrigation pipes and drainage filters and trenches, pipes with a minimum diameter of 100 mm are used, laying them in a gravel (or other coarse-grained materials) layer 5-20 cm thick. The depth of irrigation pipes from the ground surface should be at least 0.5 m. The distance between parallel irrigation pipes and between outlet drains in sand and gravel filters is 1- 1.5 m. The slope of irrigation and drainage pipes in filters and trenches is not less than 0.005.

Rice. 5. Wastewater treatment in septic tanks and filter wells 1 - sewer riser; 2- release from the building; 3 septic tank; 4 - drainage pipe; 5 - filter well

Filter wells - designed for the treatment of domestic wastewater coming from detached buildings with a calculated flow rate of no more than 1 m3/day, after pre-treatment in a septic tank. They are used in sandy and sandy loam soils in the absence of sufficient areas to accommodate underground filtration fields and the location of the well base at least 1 m higher maximum level groundwater (Fig. 5).

Round filter wells are made of reinforced concrete rings with a diameter of no more than 2 m, and rectangular ones are made of hard-burnt brick and rubble stone with a size of no more than 2x2 m in plan and 2.5 m in depth. Inside the well, a bottom filter up to 1 m high is installed from gravel, crushed stone, coke, well-sintered boiler slag and other materials. The outer walls and base of the well are covered with the same materials. Holes are drilled in the walls of the well below the supply pipe to release filtered water. The wells are covered with a slab with a hatch with a diameter of 700 mm and equipped with a ventilation pipe with a diameter of 100 mm.

The calculated filtering surface area of ​​the well is determined by the sum of the areas of the bottom and surface of the internal walls of the well per filter height. The load per 1 m2 of filter surface area in sandy soils is assumed to be 80 l/day, and in sandy soils - 40 l/day. When installing filter wells in medium- and coarse-grained sands or when the distance between the base of the well and the groundwater level is more than 2 m, the load increases by 10-20% (the last figure is accepted when the drainage rate per person is more than 150 l/day or at the average winter wastewater temperature water above 10 °C). For seasonal facilities, the load can also be increased by 20%.

Agricultural irrigation fields, established on the lands of collective and state farms, are intended for year-round reception and neutralization of wastewater during its agricultural use. These fields have low load standards per 1 hectare of irrigation area, as well as a small amount of planning work. Year-round intake of wastewater, regardless of climatic conditions, is possible if the load rates do not exceed 5-20 m3/day per 1 hectare of irrigation area. Agricultural irrigation fields are located on soils suitable for agriculture, or that can be used after proper preparation (reclamation). The natural slope of land plots should not exceed 0.03 (the most acceptable slope is 0.005-0.015).

Municipal wastewater first enters a treatment plant, where it is pre-treated, i.e., it passes through a screen, sand trap and primary settling tanks. At night, water flows into the control tanks. After settling tanks, wastewater is supplied by gravity or using pumps to field command points.

Water is supplied to the fields through an irrigation network, which is divided into:
a) permanent, supplying wastewater to crop rotation fields and consisting of permanent main and distribution pipelines, laid mainly from asbestos-cement pipes;
b) temporary, consisting of portable pipelines, temporary sprinklers, hollows and drainage furrows;
c) irrigation, consisting of furrows, strips and subsoil moisturizers.

Pipelines of a permanent irrigation network are laid taking into account soil freezing on arable lands at a depth of 0.7-1.2 m, and under roads and in populated areas - below the soil freezing depth by 0.1 m to the pipe shelya. Water is released from a closed permanent network through special water outlets. Water outlet wells, depending on the terrain and the location of irrigation areas, are placed at a distance of 100-200 m for one-sided distribution, and 200-300 m for two-sided distribution.

Moisturizing and fertilizing standards for irrigation with wastewater on agricultural irrigation fields are established depending on the composition of crops and plantings, their need for mineral food and water, and sanitary and hygienic requirements associated with wastewater disposal. The estimated water consumption is 5-20 m3/day per 1 ha or 1800-7300 m3/year.

- Biological wastewater treatment in natural conditions

3.

Biological ponds ( Cleaning of drains )

Biological ponds with natural and artificial (pneumatic or mechanical) aeration. Used for purification and post-treatment of municipal, industrial and surface wastewater containing organic pollutants.

At the same time, depending on the purpose of the structure, the wastewater supplied to it must meet the requirements presented in table. 13, and allowable expenses in table. 14.

Table 13

BOD value of total wastewater suppressed into biological ponds

Aeration type	BOD total value of wastewater supplied to bioponds, mg/l, no more
	Cleaning of drains	Wastewater tertiary treatment
Natural aeration
Artificial aeration

Table 14

Allowable flow rates of wastewater supplied to biological ponds

Aeration type	Allowable flow rates of wastewater supplied to bioponds, m 3 /day, no more.
	Cleaning of drains	Wastewater tertiary treatment
Natural aeration		10000
Artificial aeration	10000	Unlimited

Note. If the total BOD value of wastewater supplied to bioponds for treatment exceeds the values ​​indicated in Table 13, then preliminary treatment of these waters should be provided.

Bioponds should be installed on non-filtering or weakly filtering soils. In case of unfavorable soils in terms of filtration, anti-filtration measures should be carried out, i.e. waterproofing of structures. In relation to residential buildings, they are located on the leeward side of the prevailing wind direction in the warm season. The direction of water movement in them should be perpendicular to this direction of the wind.

The pits for biological ponds are constructed using, if possible, natural depressions in the terrain. The shape of the ponds in plan is taken depending on the type of aeration, namely: with natural, mechanical and pneumatic aeration - rectangular; when using self-propelled aerators - round. In rectangular structures, smooth rounding of the corners is recommended to prevent the formation of stagnant zones in them.

The radius of these roundings must be at least 5 m. In addition, in ponds with natural aeration, in order to ensure a hydraulic regime of water movement close to the conditions of complete displacement, the ratio of the length of the structure to its width must be at least 20, and for smaller values ​​of this ratio design of inlet and outlet devices should be provided to ensure the movement of water throughout the entire living cross-section of the pond, i.e. dispersed wastewater inlets and outlets (Fig. 10). With artificial aeration, the aspect ratio of the sections can be any, but the speed of water movement maintained by the aerators at any point in the pond must be at least 0.05 m/s.

Note. In biological ponds with artificial aeration of wastewater, the ratio of length to width in which is 1...3, a hydraulic mode of fluid movement should be adopted that corresponds to the conditions of ideal (complete) mixing.

Structurally, biological ponds consist of at least two parallel sections with 3...5 consecutive stages in each (for example, Fig. 11). In this case, it should be possible to disconnect any section for cleaning or preventative repairs without disrupting the operation of the others. Sections and stages of bioponds are separated by enclosing dams and dams made from soils that can retain their shape. Their minimum width at the top should be 2.5 m.

Note. For biological ponds with an area of ​​less than 0.5 hectares, the width of the enclosing dams and dams at the top can be reduced to 1.0...15 m.

If there is filtration through protective dams and dams, their “clothing” should be provided in the form of an anti-filtration screen made of clay (0.3 m thick) or polymer films. The steepness of the slopes is taken based on the characteristics of the soil (Table 15).

Table 15

The steepness of the slopes of dividing and protective dams and dams

Type of soil	Slope steepness
Wet clay and loamy soils
Wet sandy and sandy loam soils
Dry clay and loamy soils	1:1,5
Dry sandy and sandy loam soils

Wastewater inlets into biological ponds, as well as liquid overflows between treatment stages, are carried out using wells equipped with devices that allow changing the filling level of the stages. The mark of the bypass (inlet) pipe tray should be 0.3...0.5 m above the bottom of the pond. In this case, water is injected into ponds with artificial pneumatic aeration through a horizontal pipeline, the outlet of which is located on a concrete pad and is directed upward at an angle of 90 0 and is located below the expected ice level, and with mechanical aeration - through the pipeline directly into the active mixing zone. In addition, at the exit point of the overflow pipe, in order to avoid erosion of the slope, its corresponding members are strengthened with stone or concrete slabs. To release wastewater from the structure (stage), a collection device is designed, located below the water level at 0.15...0.20 of the working depth of the pond (water depth).

In order to provide wave erosion of the internal slopes of the dams, as well as the development of higher aquatic vegetation, they are laid out with stone, slabs and covered with asphalt over crushed stone preparation with a strip 1.5 m wide (1 m below the water level and 0.5 m above). To prevent the slabs from sliding, a ledge is made to serve as a stop for them. The outer slope of dams should be seeded with slow-growing, low-stand grass that can prevent erosion, such as blue wheatgrass. The excess of the construction height of the dam above the design water level in the pond should be less than 0.7 m.

To increase the efficiency of wastewater treatment to BOD total = 3 mg/l, as well as to reduce the content of nutrients in them (primarily nitrogen and phosphorus), it is recommended to use higher aquatic vegetation (reeds, cattails, reeds, etc.) in ponds. This vegetation should be placed in the last stage of the pond. Moreover, the area occupied by higher aquatic vegetation can be determined by the load of 10,000 m 3 /day per 1 Ha with a planting density of 150...200 plants per 1 m 2.

1.1.Aerobic: aeration tank (biotank), biofilter, soil methods, bioponds.

The essence of the biochemical purification method
The biological (or biochemical) method of wastewater treatment is used to purify industrial and domestic wastewater from organic and inorganic pollutants. This process is based on the ability of some microorganisms to use wastewater pollutants for nutrition during their life processes.
The main process that occurs during biological wastewater treatment is biological oxidation. This process is carried out by a community of microorganisms (biocenosis), consisting of many different bacteria, protozoa, fungi, etc., interconnected in single complex complex relationships (metabiosis, symbiosis and antagonism).
The dominant role in this community belongs to bacteria.
Wastewater treatment using the method under consideration is carried out under aerobic (i.e. in the presence of oxygen dissolved in water) and anaerobic (in the absence of oxygen dissolved in water) conditions.
Wastewater treatment in natural conditions
Aerobic processes of biochemical purification can occur in natural conditions and in artificial structures. Under natural conditions, purification occurs in irrigation fields, filtration fields and biological ponds. Artificial structures are aeration tanks and biofilters of various designs. The type of structures is selected taking into account the location of the plant, climatic conditions, source of water supply, volume of industrial and domestic wastewater, composition and concentration of pollutants. In artificial structures, cleaning processes occur at a faster rate than in natural conditions.
Irrigation fields
These are specially prepared land plots used simultaneously for wastewater treatment and agricultural purposes. Wastewater treatment under these conditions occurs under the influence of soil microflora, sun, air and under the influence of plant life.
The soil of irrigation fields contains bacteria, actinomycetes, yeasts, fungi, algae, protozoa and invertebrate animals. Wastewater contains mainly bacteria. In mixed biocenoses of the active soil layer, complex interactions between microorganisms of a symbiotic and competitive order arise.

In the process of biological treatment, wastewater passes through a filter layer of soil, in which suspended and colloidal particles are retained, forming a microbial film in the pores of the soil. The resulting film then adsorbs colloidal particles and substances dissolved in the wastewater. Oxygen penetrating from the air into the pores oxidizes organic substances, turning them into mineral compounds. The penetration of oxygen into deep layers of soil is difficult, so the most intense oxidation occurs in upper layers soil (0.2–0.4 m). With a lack of oxygen in ponds, anaerobic processes begin to predominate.
Biological ponds
They are a cascade of ponds consisting of 3-5 stages, through which clarified or biologically treated wastewater flows at a low speed. The ponds are intended for biological treatment and for post-treatment of wastewater in combination with other treatment facilities. There are ponds with natural or artificial aeration. Ponds with natural aeration have a shallow depth (0.5-1 m), are well heated by the sun and are populated by aquatic organisms. The residence time of water in ponds with natural aeration ranges from 7 to 60 days. Together with wastewater, activated sludge, which is a seed material, is removed from secondary settling tanks.

Microfilters and precoat filters
Microfilters are mesh rotating drums partially lowered into liquid. Waste water is fed into the drum, contaminated inner surface washed with jets of water at the top of the drum. The efficiency of treatment when supplied with biologically treated wastewater is 20-30%, and for suspended solids 65-70%. Microfilters are easy to use and do not require daily maintenance. Pre-coated filters are tanks with mesh filter elements installed inside. Filtration is carried out through meshes with filter material washed on them. Therefore, before the operating cycle, a pulp of filter material is fed into the filter. The same material is introduced into the purified water in small doses during the operating cycle. The quality of post-treatment is high: in terms of suspended solids content (4 mg/l) and (3 mg/l), wastewater is close to clean river water.
Filter wells, cassettes
The use of biological treatment facilities located in natural conditions (filtration wells and cassettes, underground filtration fields) in the technological scheme allows for simultaneous deep cleaning and disinfection of wastewater and does not require additional installation of post-treatment facilities. A survey of about 50 systems showed that a completely satisfactory sanitary environment is created near properly installed and operated filter wells. At most of the objects surveyed, even at a distance of 1-2 meters around the filter well, no pollution of the atmospheric air or soil surface was observed. The results of studies of experimental installations show that even at a distance of 0.8-1 meters from filter wells there is a significant reduction in pollution in wastewater. Natural wastewater treatment facilities, such as filter wells and biological ponds, can be used as post-treatment facilities in various wastewater treatment technology schemes. These structures are usually located after biological treatment plants.
Cleaning in biofilters
Biofilm grows on the biofilter filler; it has the appearance of mucous fouling with a thickness of 1-3 mm or more. This film consists of bacteria, fungi, yeast and other organisms. The number of microorganisms in biofilm is less than in activated sludge.
Biological filters are widely used for the treatment of domestic and industrial wastewater with a volumetric flow rate of up to 30 thousand m3/day.
Biofilters - artificial biological treatment structures are round or rectangular structures loaded with filter material, on the surface of which a biofilm is grown; They are made of reinforced concrete or brick. Wastewater is filtered through a loading layer coated with a film of microorganisms; the spent (dead) biofilm is washed off by flowing wastewater and removed from the biofilter.
Based on the type of loading material, biofilters are divided into two categories: with volumetric (granular) and flat loading. Crushed stone, gravel, pebbles, slag, expanded clay, ceramic and plastic rings, cubes, balls, cylinders, etc. are used as granular loading. Flat loading is metal, fabric and plastic mesh, gratings, blocks, corrugated sheets, films, etc., often rolled into rolls.

Biotank- the biofilter is a housing that contains loading elements arranged in a checkerboard pattern. These elements are made in the form of semi-cylinders, irrigated from above with water, which, filling the loading elements, flows down through the edges. A biofilm forms on the outer surfaces of the elements, and biomass resembling activated sludge forms in the elements. The design provides high performance and cleaning efficiency.
According to the principle of air flow into the thickness of the aerated load, filters can be with natural and forced aeration. When receiving wastewater with a BOD > 300 mg/l, in order to avoid frequent silting of the biofilter surface, recirculation is provided - the return of part of the purified water for dilution with waste water.
The use of biofilters is limited by the possibility of their silting, a decrease in oxidative power during operation, the appearance of unpleasant odors, and the difficulty of uniform film growth.
Cleaning in aeration tanks
Aerobic biological treatment of large volumes of water is carried out in aeration tanks - rectangular reinforced concrete structures with free-floating activated sludge in the volume of treated water, the biopopulation of which uses wastewater pollution for their livelihoods.

The main technological schemes for cleaning in aeration tanks are shown in Figure 52.

The aeration system is a complex of structures and special equipment that supplies the liquid with oxygen, maintains sludge in suspension and constantly mixes wastewater with sludge. For most types of aeration tanks, the aeration system ensures that these functions are performed simultaneously. According to the method of dispersing air in water, three aeration systems are used in practice: pneumatic, mechanical and combined.
Oksitenki
Oxyten tanks are biological treatment facilities in which technical oxygen or air enriched with oxygen is used instead of air.
The main difference between an oxytank and an aeration tank operating on atmospheric air, is an increased concentration of sludge. This is due to increased oxygen mass transfer between the gas and liquid phases.
It is a tank, round in shape with a cylindrical partition, which separates the aeration zone from the sludge separation zone.

1.2.Anaerobic biological wastewater treatment.

The anaerobic treatment method can be considered as one of the most promising in the presence of high concentrations in wastewater organic matter or for the treatment of domestic wastewater. Its advantage over aerobic methods is a sharp reduction in operating costs (anaerobic microorganisms do not require additional aeration of water) and the absence of problems associated with the disposal of excess biomass.

Anaerobic degradation of organic substances is carried out as a multi-stage process, in which the participation of at least four groups of microorganisms is necessary:

· hydrolytics,

· wanderers,

acetogens

· methanogens.

Cleaning mechanism.

During the anaerobic transformation of organic substrates into methane under the influence of microorganisms, 4 stages of decomposition must be sequentially implemented. Certain groups of organic contaminants (carbohydrates, proteins, lipids/fats) are first converted into corresponding monomers (sugars, amino acids, fatty acid). Further, these monomers, during enzymatic decomposition (acytogenesis), are converted into short-chain organic acids, alcohols and aldehydes, which are then oxidized further into acetic acid, which is associated with the production of hydrogen. Only after this does it come to the formation of methane at the stage of methanogenesis. Along with methane, carbon dioxide is also produced as a by-product.

All transformation processes are closely interconnected with each other and must occur in the anaerobic reactor tank in a strictly established order, because any violation of one of the intermediate stages leads to a disruption of the entire process. Therefore, precise design of wastewater treatment plants and their adjustment to the appropriate wastewater is required.

Figure 1: Decomposition steps of anaerobic conversion

Post-treatment of wastewater in ponds occurs both due to additional longer and deeper settling, and due to biological processes(during the warm season). Currently, ponds are operated at sewerage facilities of a number of industrial enterprises (Kstovo, Severodonetsk, Karaganda, 1 Ozopolotsk, etc.).[...]

Observations of the operation of naturally aerated ponds at the Novo-Gorkovsky oil refinery, carried out by the Department of Sewerage of the Moscow Institute of Engineering and Design named after. V.V. Kuibysheva, together with the plant’s laboratory, made it possible to establish the reasons for the low efficiency of such ponds and showed the feasibility of using Russian aeration. For this purpose, a surface-type floating aerator design was developed and applied.[...]

In Fig. Figure 6.11 shows aerated biological ponds intended for post-treatment of wastewater. The ponds are designed on an area of ​​7.25 hectares with a depth of 3 m. The load per 1 hectare is 3448 m3/day, the duration of water residence in the ponds is 8.7 days. The ponds have two sections, each section consisting of five stages. There are bypasses between steps and sections. The first four stages of the ponds are equipped with mechanical aerators, the fifth stage is a settling stage. The cleaning effect for BOD20 is up to 75%, for suspended solids - up to 80%.[...]

Aerated biological ponds are also used with recirculation of activated sludge, which can significantly increase the intensity of the cleaning process. The use of recirculation is advisable when the concentration of incoming WASTEWATER by BODtotal is above 300 mg/l.[...]

Aerated biological ponds can also be intended for post-treatment of wastewater from the dairy, meat and yeast industries with a BOD concentration of up to 40-60 mg/l in climatic regions I, III and IV. The duration of post-treatment of wastewater in aerated ponds can be determined in the same way as the duration of wastewater treatment in ponds, and the purification effect for one stage should also be rationally taken to be 50%. Biological ponds can be single-stage, depending on the concentration of contaminants entering the water for post-treatment and the required concentration after post-treatment. The specific oxygen consumption for aeration in biological ponds for post-treatment should be 2 mg/mg of removed BODtotal. The aeration system can be mechanical or pneumatic.[...]

When treating wastewater in aerated biological ponds, it is recommended to use movable aerators (Fig. 6.12). When the aerator operates, a pair of reactive LEDs appears, and the rotation of the aerator around its own axis causes it to rotate around a fixed support. When designing movable aerators on a draft, a hinge should be installed to absorb wave influences on the pond. Pontoons should be located at a distance of at least two diameters of the aerator O from its center. It is recommended to take the distance from the support to the center of the aerator rotor equal to the radius of action of the aerator (up to b). The operating area of ​​each aerator can be increased by at least 4-5 times compared to permanently installed aerators. The minimum distance between aerator supports should be £10>. The depth of the pond is allowed to be at least 3 m.[...]

To increase the traction force of the aerator, it is advisable to provide for the possibility of a slight deviation of the aerator axis from the vertical in the plane of the aerator and handle axes. In this case, the blades external to the fixed support will be deeper and an additional rowing effect will occur. In algalized biological ponds, along with bacterial microflora, microalgae also take a significant part in the process of changing the value of the WPC. In the wastewater entering biological ponds, a pronounced process of transformation of organic substances of wastewater into the substance of microalgae cells is observed, and this leads to an increase in the WIC.[...]

Sometimes, instead of conventional flow-through or contact biological ponds, biological oxidation, contact stabilization (BOX) ponds are used for post-treatment of wastewater, in which algalization occurs with specially selected microalgae grown on wastewater, which ensures complete biological disinfection of wastewater. This type of pond was developed at the All-Russian Research Institute for Agricultural Use of Wastewater and is widely used in areas with warm climates.

Biological ponds are a cascade of ponds consisting of 3-5 stages through which clarified or biologically treated wastewater slowly flows. Ponds are constructed for biological wastewater treatment under natural conditions on low-filtration soils in the form of separate reservoirs. As a result of the vital activity of plankton (phytoplankton), free and bicarbonate acids are assimilated, due to which the pH of the water during the day rises to 10 - 11, which leads to the rapid death of bacteria.

Biological ponds as independent treatment facilities according to SNiP can be used (with proper justification) for populated areas located in climatic region IV. Ponds can also be designed for post-treatment of wastewater in combination with other treatment facilities.

In biological ponds there should be 2-3 stages when biologically treated wastewater enters and 4-5 stages when settled wastewater enters.

Biological ponds are calculated based on the load of wastewater (first case) per 1 hectare of water surface of the pond or by the amount of reaeration (second case).

In the first case, this load is assumed to be equal (without dilution for settled wastewater) to 250 m3/ha per day and for biologically treated wastewater - up to 5000 m3/ha per day; in the second case - based on the value of reaeration equal to 6 - 8 g of oxygen per day per 1 m2 of pond, depending on climatic conditions (SNiP).

The average water depth in biological ponds is taken to be within 0.5-1 m depending on local conditions. When using ponds for fish farming, clarified waste liquid must be supplied to them, diluted with river water 3-5 times. At the same time, biological ponds must contain a small pond with a depth of at least 2.5 m, intended for fish in winter.

When treating wastewater in biological ponds, the number of bacteria decreases by more than 100 times, oxidation decreases by 90%, the amount of organic nitrogen decreases by 88, ammonia by 97 and BOD by up to 98%. In the fall, ponds not intended for growing fish are emptied, and in winter they are used as storage tanks. In the spring, the ponds are filled with water and after about a month they begin to flow. Contact operation of ponds is also possible. It is recommended to plow the bottom of the pond annually. Wastewater should remain in ponds for 20-30 days. It is recommended to release wastewater into ponds during the daytime. Ponds should be located near natural bodies of water. The amount of dissolved oxygen in water must be at least 2.5 mg/l. The bottom of the pond is planned towards the outlet. The depth at the inlet is usually 0.5 m, at the outlet - up to 1-2 m. Ponds are designed with an area of ​​0.5-1.5 hectares or more.

When designing ponds that have a natural drainage area, spillway structures must be designed to accommodate additional flood and storm flows. Depending on the release (emptying) conditions dictated by the topography, the pond's capacity can be formed by constructing dams along thalwegs, using existing or creating artificial excavations (depressions), or fencing the area with rollers (dams). 2-3 inlets are installed in the upper pond. For better distribution of wastewater flow, two rows of wattle fences are installed across the first pond. Overflows from the ponds are arranged in the form of trays 0.4 m wide every 30 m. From the last pond, water is released using mine spillways.

After leaving the treatment plant, wastewater is discharged into the thalwegs of gullies and ravines, where channels with a slight slope are constructed, the length of which reaches hundreds of meters and sometimes several kilometers.

The studied channels were located in the thalwegs of dry beams with an average annual air temperature of 6.8 + 7.1 ° C and an average annual precipitation of 500-510 mm. The speed of movement of wastewater in these canals ranged from 0.01 to 0.05 m/sec, the residence time of wastewater in the canal was from 7 to 28 hours. The layer of water in the canal (not counting sediment) was taken to be in the range of 0.025 to 28 hours. 0.15 m, channel width - within 0.65--1.5 m.

Wastewater flowing in channels with low speed and shallow depth, but a relatively large flow width, is affected by Sun rays, air oxygen and other climatic factors, which is why the concentration of contaminants in wastewater decreases as it moves away from the point of release. Natural self-purification of wastewater occurs. Such channels are called natural oxidation channels because they undergo oxidation processes similar to those occurring in biological ponds.

Artificial oxidation channels are used abroad (Holland, USA, etc.) in climatic conditions with minimal air temperatures (up to -8°C) and give good results when treating small quantities of wastewater. In such channels, the concentration of contaminants in terms of BOD5 is reduced to 98%, bacterial contamination and the content of suspended solids drop sharply. Artificial oxidation channels are still rarely used as treatment facilities in our conditions.

The degree of wastewater treatment in natural channels depends on the length of the discharge channel and its slope.

When treating wastewater in natural oxidation channels at two sites, wastewater samples were taken in front of septic tanks, after septic tanks and along the channels every 100 m for chemical and bacteriological analyses. At both sites, the amount of wastewater fluctuated between 100-150 m3 per day. The primary settling tanks were septic tanks that were poorly maintained (almost never cleaned).

Analyzes showed that the concentration of wastewater contaminants in natural oxidation channels was significantly reduced. Over the studied 1000 m of canal, wastewater is purified both chemically and bacteriologically.