Wastewater treatment in biological ponds. Biological ponds: definition, classification, types, processes and biological water treatment

Biological ponds, also called lagoons, are specially created shallow reservoirs where natural processes of water self-purification take place with the participation of the organisms inhabiting them. Ponds can be used both as independent treatment systems and for post-treatment of wastewater after the removal of the bulk of contaminants. They are widely used for the treatment of domestic effluents, which most often come in undiluted form, and for the post-treatment of wastewater from enterprises in the food and processing, pulp and paper and other industries, livestock farms, for the treatment of surface (storm, melt) water, drainage agricultural water under irrigation conditions. agriculture. Purified water can be used in the recycling water supply system of enterprises, which reduces their overall water consumption.

Bioponds are divided into anaerobic, aerobic anaerobic (optionally aerobic) and aerobic, as well as high and low load, flow and contact. Aerobic (oxidation) ponds can be with natural and artificial aeration. Single ponds and cascading ponds can also be used.

Anaerobic conditions are observed in the presence of excess organic matter and lack of oxygen

• in ponds at BTG loads of about 300.. .600 kg/ha-day;
• in the bottom layers of water in ponds with a depth of 2.5 m or more, even when the water is saturated with oxygen in the surface layers;
• in contact (non-flowing) ponds in the first phases of cleaning after filling the pond with waste water;
• during the spring opening of biological ponds with intensive decomposition of organic compounds accumulated over the winter.

In a cascade of flowing ponds, the head pond, which takes on the bulk of pollution, can also be anaerobic.

The processes of nitrate reduction, sulfate reduction, methane fermentation, reduction of oxidized forms of metals and other substances occurring in anaerobic ponds lead to the decomposition of organic substances and the precipitation of heavy metal sulfides. The operation of such ponds usually provides for the possibility of separating activated sludge from treated wastewater (in settling tanks, emshers). Anaerobic treatment in ponds makes it possible to remove 80...90% of COD at 25°C (50% - at 10°C) with a residence time of water in the facility of 40...50 days, however, the content of contaminants in water after anaerobic treatment still remains high, therefore, its further purification is required in a cascade of flowing aerobic ponds or, if the contact method is adopted, in the same pond, but under aerobic conditions.

In Russia, anaerobic ponds are practically not used due to low average annual temperatures and the formation of a large amount of foul-smelling substances during the operation of such ponds.

Aerobic-anaerobic ponds have a depth of 1.5...2 m and are aerated by natural processes. In the surface layers of water there is dissolved oxygen coming from the atmosphere or formed as a result of photosynthesis. The supply of oxygen due to atmospheric aeration is limited and does not exceed a few grams of Og per 1 m 2 per day. During the day, photosynthesis enriches the water with oxygen, and at night, oxygen is consumed in the process of respiration by animals and plants, while oxygen deficiency can be observed in the water. In the bottom layers total absence oxygen, anaerobic processes, sulfate reduction, methane fermentation can occur. In such ponds great importance acquires the sedimentation of suspended solids and the formation of silt at the bottom.

Depending on climatic conditions, on the content of contaminants in wastewater and on the requirements for the quality of treated water, the load in aerobic-anaerobic ponds ranges from 10.. .300 kg VPK / ha? day

In aerobic ponds with natural aeration, oxygen saturation of water occurs due to atmospheric aeration and photosynthesis. Such ponds have a shallow depth (0.3 ... 1 m), are well lit and warmed up by the sun's rays, which leads to the intensive development of planktonic algae and benthic higher plants. The purified water moves in them at very low speeds. The residence time of water in these ponds ranges from 7 to 60 days. If the biological ponds are an independent treatment plant, the wastewater, having passed the settling tanks, is diluted with 3-5 volumes of technical water before entering the ponds. Load on them: for sludge wastewater without dilution - up to 250 m 3 / ha day, for biologically treated - up to 500 m 3 / ha? day

The advantages of ponds with natural aeration are ease of installation and maintenance, minimal operating costs. However, the rates of removal and biological oxidation of organic pollutants in such ponds are low, and large areas are required for cleaning.

Ponds with artificial aeration, due to the intensification of biochemical processes in them, occupy 10 ... 15 times less area, have a much smaller volume, and a depth of up to

4 ... .6 m. The required degree of water purification in them is usually achieved in 1 ... 3 days. The speed of water movement in such ponds exceeds 0.1 m/s, the oxidizing power is 5...20 g BOD/m 3 -h, the load achieved is 1000 kg BOD/extinguish and more. Waste water consumption can reach 10...25 thousand m 3 /h. Ponds of large industrial enterprises are structures with a volume of up to 1 million m 3, equipped with a large number of aerators. For aeration of water, devices of mechanical (mixing), pneumatic (air injection) or pneumo-mechanical types are used. The type of aerators, their required number and the volume of the zone served by each of the aerators are selected based on the conditions for maintaining active sludge in suspension, the amount and content of oxygen required to oxidize pollution and maintain aerobic conditions, and minimize the volume of stagnant zones.

The configuration of ponds is often determined by the topographic features of the area. Usually aerated ponds are earthen 2-5-section pools with a ratio of length to width of the pond of at least 20, with a dispersed supply and removal of waste water or sludge mixture and their subsequent settling for 2 ... 2.5 hours. At smaller ratios length to width, the location of the inlet and outlet devices is decided in such a way as to ensure the movement of water over the entire living section of the pond. In ponds with artificial aeration, the volume of stagnant zones does not exceed 10%.

Compared to ponds with natural aeration, algae develop less actively in bioponds with artificial aeration. This reduces the amount of secondary biomass and water pollution by algae metabolic products. However, the construction and operation of artificially aerated ponds are more expensive, and operating costs also increase.

In Russian practice, aerated ponds are most widely used in pulp and paper, food and a number of other industries.

The intensity of processes and the depth of post-treatment of wastewater in aerated biological ponds can be significantly increased by recycling activated sludge separated from treated water in secondary clarifiers (or other desilting facilities). In this mode, highly loaded aerobic ponds operate. Ponds with sludge recirculation can be used as independent treatment facilities or as one of the treatment stages. Low-load ponds are usually used for post-treatment of wastewater after aerotanks with MIC 25...50 mg/l. In this case, they work on the sludge carried out from the secondary settling tanks, as well as on the microflora that develops in the pond itself. To avoid siltation of the bottom, the water velocity in such ponds should be higher than 0.007 m/s.

In contact bioponds with artificial aeration, cleaning is carried out in two stages - aeration and sedimentation. During the aeration period, wastewater is fed into the pond, but not removed from it. When aeration stops, the silt settles and clarified water is discharged from the pond. The alternation of aeration and sedimentation is carried out in the automatic control mode.

In contact bioponds with natural aeration, settled wastewater, if necessary, is diluted with 3-5 volumes of clean water and released into shallow non-flowing ponds. After 20...30 days, the water descends and is refilled with diluted waste water. The quality of cleaning in such stagnant ponds is higher than in transparent ponds.

In cascade ponds, usually installed on sloping terrain, undiluted wastewater passes sequentially through a 4-6-stage cascade of ponds with an aerobic pond at the first stage, algae, crustaceans, and fish ponds. Breeding fish in such ponds is possible after passing 3-4 steps. For breeding fish in early spring, 500-2000 mothers per 1 ha are released into the pond. The growth of fish is by the end of the autumn period up to

500...800 kg per 1 ha. Fishing is carried out in late autumn. The presence of a large mass of nutrients in the water contributes to the intensive growth of algae (duckweed). To combat them, it is desirable to breed ducks in fish ponds, for which duckweed is a good food.

The feasibility of using biological ponds is determined by the concentration of pollutants and the flow of wastewater, as well as specific climatic, soil and topographic conditions, and the level of water mineralization. Sufficiently large land areas must be allocated for bioponds, therefore they are often created in floodplains, in shallow waters and in sections of rivers with small slopes. In such cases, with the abundant development of aerial-water and submerged vegetation in them, they are actually exploited as hydrobotanical sites, or bioplateaus (see below).

For the normal operation of bioponds, it is necessary to maintain optimal pH values ​​​​and wastewater temperatures. The temperature must be at least 6 °C. Since the mode of operation of bioponds depends on temperature and light levels, this creates certain difficulties for stabilizing cleaning.

When using bioponds as independent treatment systems, wastewater pollution should not exceed BOD P0L11 = 200 mg/l for ponds with natural aeration and over 500 mg/l for ponds with artificial aeration. When BOD total is higher than 500 mg/l, preliminary wastewater treatment is necessary. Wastewater is sent to post-treatment ponds after biological or physico-chemical treatment with BOD full. Bioponds are often used to remove excess nitrogen and phosphorus from wastewater. However, sometimes the self-purification processes occurring in bioponds, especially in the initial period of their operation, are limited by biogenic elements, an insufficient number of microorganisms involved in the removal of pollution. In bioponds with a balanced ratio of carbon flux and nutrient content, the concentration of the IN/ ion is not more than 0.2 mg/l, NaEz~

During the operation of biological ponds, careful monitoring of the condition is necessary. ground water(their water content, the entry of pollutants into groundwater and the dynamics of their distribution). If an artificial biopond is used, then in order to reduce the filtration flow of water into the soil, the bed of the biopond during its creation is laid out with clay, other waterproof materials, or conditions are created that contribute to the further formation of such a waterproof layer (for example, with the development of anaerobic microbiological processes, silting and gleying of the bottom layer ).

As a result of photosynthesis, primary production is formed in ponds, therefore, the increase in biomass in biological ponds often exceeds the amount of organic substances contained in wastewater, reaching 100 ... and products of their metabolism, the decomposition of which causes additional oxygen consumption and an undesirable increase in nutrients in the reservoir. Compounds that are more difficult to oxidize sink to the bottom and contribute to siltation of water bodies. With the excessive development of algae and plants, not only the quality of the water deteriorates, but floating carpets of dead parts form on the surface of the pond, and the shore becomes polluted. To avoid these problems, excess biomass must be periodically removed from the pond: surface phytomass annually, usually at the end of the growing season, and plants such as duckweed at least once a week.

Under the conditions of Russia, bioponds cannot be used during the cold season; in autumn they are emptied or used in winter as wastewater storage tanks. In the spring, before putting into operation, in bioponds with natural aeration, the bottom is plowed and, if necessary, vegetation is planted. Then they fill it with waste water, withstand until the almost complete disappearance of ammonium nitrogen and transfer to the channel with the calculated load. The maturation period of ponds for central Russia is about 1 month.

Intensive growth of biomass often serves as an obstacle to the use of ponds in the treatment plant system, and effective methods Algae removal has not yet been developed. At the same time, on the basis of the collected biomass of algae and plants, healthy foods: feed, bio-composts, biogas, liquid hydrocarbons, paper, etc. So, from 1 hectare of algae ponds, fertilizers can be obtained for 10 ... 50 hectares of fields. In areas with high insolation, it is advisable to specially grow algae or cyanobacteria in bioponds, for example, those that clean the effluents of livestock and poultry fattening enterprises. About 40% of the nitrogen in the effluents of such enterprises is fixed by algae, which are then fed to animals. The biomass of cultivated green algae contains 50...60% protein, and the biomass of blue-green algae contains 60...70%.

In Belgium, the green alga Bubgosnsiop geisi!umm is grown together with duckweed in shallow ponds, where runoff from the livestock complex and other polluted waters are directed. For better development of algae, the water temperature is adjusted to 20 ... 30 ° C. Biomass is processed into biogas or a protein feed additive for fish and chickens, dyes, and cosmetics are obtained from it. The sludge, rich in mineral components, remaining after biogasification is used to intensify the cultivation of the unicellular green algae Bsepebrus Br. Thus, a biotechnological system with a partially closed cycle of the circulation of substances is realized.

Water hyacinth, microalgae of the genera Lovyococcus, chiatubotopase, eupailena, and some others are capable of synthesizing and accumulating hydrocarbons and polyhydric alcohols in their cells. The green alga Bipaepa lambauer accumulates glycerol (up to 85% of the DM). Algae LoHyococsie Lgainn - hydrocarbons of composition from to C 34 in an amount of up to 75% of dry matter. Hydrocarbon-filled cells b. bruin float on the surface of ponds. After collecting and drying plants and algae, hydrocarbons can be recovered by extraction with organic solvents and distillation.

Ministry of Education and Science of the Republic of Kazakhstan

Karaganda state Technical University

ESSAY

by discipline: Ecology

Topic: __________ Biological cleaning methods

Supervisor

_________________

(assessment) (surname, initials)

(signature) (date)

Student

(Group)

(surname, initials)

(signature) (date)

2009

Biological methods are used to purify household and industrial wastewater from a variety of dissolved organic and some inorganic (hydrogen sulfide, ammonia, etc.) compounds. The cleaning process is based on the ability of microorganisms to use these substances for nutrition in the process of life. Known aerobic and anaerobic methods of biological wastewater treatment.

Aerobicmethod based on the use aerobic microorganisms, for the vital activity of which a constant supply of oxygen and a temperature in the range of 20 ... 40 ° C are necessary. In aerobic treatment, microorganisms are cultivated in activated sludge or as a biofilm. Activated sludge consists of living organisms and a solid substrate. Living organisms are represented by bacteria, protozoan worms and algae. The biofilm grows on the biofilter filler and looks like mucous fouling with a thickness of 1...3 mm or more. The biofilm is made up of bacteria, protozoan fungi, yeasts, and other organisms.

Aerobic scavenging occurs in natural conditions as well as in artificial structures.

Cleaning in natural conditions occurs in irrigation fields, filtration fields and biological ponds.

Irrigation fields- these are areas specially prepared for wastewater treatment and agricultural purposes. Cleaning proceeds under the influence of soil microflora, sun, air and under the influence of plants. In the soil of irrigation fields there are bacteria, yeast, algae, protozoa. Wastewater contains mostly bacteria. In the mixed biocenoses of the active soil layer, complex interactions of microorganisms occur, as a result of which the wastewater is freed from the bacteria contained in it. If the fields do not grow crops, and they are only for the biological treatment of waste iodine, then they are called filtration fields.

biological ponds- this is a cascade of ponds, consisting of 3 ... 5 steps, through which clarified or biologically treated wastewater flows at a low speed. Such ponds are intended for biological treatment of wastewater or post-treatment of wastewater in combination with other treatment facilities.

Cleaning in artificial structures is carried out in aerotanks and biofilters. Aerotanks have found wider application.

Aerotanks- these are reinforced concrete tanks, which are open pools equipped with devices for forced aeration. The depth of the aeration tank is 2...5m.

anaerobic method cleaning proceeds without air access. It is mainly used for the neutralization of solid sediments, which are formed during mechanical, physico-chemical and biological wastewater treatment. These solid sludges are fermented by anaerobic bacteria in special hermetic tanks called digesters. Depending on the final product, fermentation can be alcoholic, lactic acid, methane, etc. Methane fermentation is used to ferment sewage sludge.

Soil and soil-forming factors

The soil- This is a loose surface layer of the earth's crust, which has fertility. The soil is constantly changing under the influence of climate, biological factors and human activities.

The main quality of the soil - fertility, which is determined by the ability to satisfy the needs of humans and other living organisms for nutrients, water and air.

Kazakhstan has large land resources. Natural chernozem lands are located in a narrow strip in the northern and northwestern parts of the republic, where temperature conditions and precipitation make it possible to grow stable crops. The eastern and central parts are considered a zone of risky agriculture due to the often recurring dry years. The southern part of the republic is located in the semi-desert and desert zones, and agriculture here is only irrigated.

AT last years the growth of arable land has ceased, convenient and suitable lands have been developed, and inconvenient solonetzes, solonchaks and sands remain. Despite this, the allocation of agricultural land for non-agricultural needs continues: for the construction of roads, industrial enterprises, housing and other facilities. Annually 18..20 thousand hectares are withdrawn for these purposes

Types of negative impact on the soil and measures to combat them

The decrease in soil fertility and its complete loss occur as a result of erosion, salinization, waterlogging, pollution and direct destruction during construction, mining and other works.

Erosion- this is the process of destruction of the upper, most fertile horizons of the soil and soil by water or wind. 9/10 of all losses of arable land falls on its share.

In Kazakhstan, eroded lands make up about 18...20 thousand hectares, and are located in the northern, western and central steppe regions.

Erosion is mainly due to the fault of man. It affects dry, grassless and treeless lands. On the contrary, wooded areas are moisture accumulators and counteract the occurrence of erosion. Each hectare of forest holds more than 500 m3 of water.

There are two types of erosion; wind and water.

Wind erosion proceeds with a strong wind (of the order of 18 ... 20 or more m / s). Local wind erosion can also appear at a speed of 5...6 m/s. In this case, the upper horizon up to 15 ... 20 cm thick can be blown out, and sometimes the entire arable layer.

Water erosion occurs during heavy rains, intense snowmelt, destroys the soil cover, and ravines form.

Measures to combat soil erosion are carried out using the following measures:

organizational and economic activities- differentiated use of land, cultivation of crops, fertilization, application different types crop rotation, location of soil-protective perennial plantations, irrigation and drainage systems, roads, cattle trailers, etc.;

agricultural practices, which provide optimal conditions for the food, water, air and thermal regime of the soil for the growth, development and formation of the crop of cultivated crops. Such agrotechnical methods include: regulation of the depth of plowing, non-moldboard or flat-cut tillage, plowing on slopes of more than 5 °, the use of forest reclamation and hydrotechnical measures.

Salinization occurs when the content of easily soluble salts (sodium carbonate, chlorides, sulphates) in the soil is increased, caused by ground or surface water (primary salinization), but often caused by improper irrigation (secondary salinization). Soils are considered saline if they contain more than 0.1% by weight of salts toxic to plants. An increase in salt on irrigated lands up to 1% reduces the yield by 1/3, and up to 2...3% leads to the death of crops. The reason for the occurrence of salinization is the irrigation of fields by the method of flooding or the construction of ditches. With this practice, first the water filters the large ones, the salts are washed down, the yield increases. After a few years, the reverse process occurs: the groundwater level rises, filtration decreases, evaporation increases, and salts are carried to the soil surface.

desertification. In the world, 50...60 thousand km 2 of land is annually lost as a result of desertification. The total area of ​​deserts has reached 20 million km.

As a result of desertification, the biological diversity of regions decreases, weather conditions change, water resources are reduced, which leads to a shortage of food resources.

The main measure to protect land from desertification is to prevent soil erosion through forest plantations and the creation of artificial annual pastures.

Waterlogging takes place in areas where the amount of precipitation exceeds the amount of moisture evaporating from the soil surface, and then waterlogging of the lands occurs. There are no swamps on the territory of Kazakhstan, and wetlands occupy insignificant areas. For the agricultural use of wetlands, it is necessary to drain them by carrying out drainage work in combination with other agrotechnical measures.

soil depletion. This phenomenon is associated with the overload of arable land, the removal of nutrients from the soil on a large scale. Soils lose organic matter, the soil structure, water and air regime deteriorate, compaction appears, the biogenic and redox regime deteriorate. Meadows and pastures are depleted as a result of overgrazing.

Land reclamation and irrigation measures are an important direction in the fight against depletion.

Reclamation- this is a set of organizational, economic, technical measures aimed at improving soils and their fertility.

Reclamation happens:

Hydrotechnical (irrigation, drainage, washing of saline soils);

Chemical (liming, gypsum, introduction of other chemical ameliorants);

Agrobiological (agroforestry, etc.);

Improving the physical and structural properties of the soil (sanding clay and claying sandy and peat soils).

Permissible anthropogenic loads on the environment

Any load on ecological systems that has arisen due to any impact that can bring them out of a normal state is defined as an ecological load. Permissible anthropogenic load on the environment is a load that does not change the quality environment or changes it within acceptable limits, in which the existing ecological system is not disturbed and adverse consequences do not occur in the most important populations. If the load exceeds the permissible one, then the anthropogenic impact causes damage to populations, ecosystems or the biosphere as a whole.

BIOLOGICAL POND

BIOLOGICAL POND artificial reservoirs used for wastewater treatment of small settlements, industrial (mainly food) enterprises, etc.

Ecological encyclopedic dictionary. - Chisinau: Main edition of the Moldavian Soviet Encyclopedia. I.I. Grandpa. 1989

BIOLOGICAL PONDS Ponds used for biological wastewater treatment. They act on the principle of self-purification of water by organisms living in it, as a result of which a silt-like mass accumulates, which can be used in agriculture as a fertilizer or as a raw material for its production.

Ecological dictionary, 2001

• BIOLOGICAL METHODS OF PLANT PROTECTION
• BIOLOGICAL RESOURCES

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Every year there is an increase in water consumption, which is associated with an increase in the number of inhabitants of most regions of the country, as well as the continued growth of industry. This leads to the fact that pollution of the environment by wastewater is also increasing, putting before the experts difficult task- how to cause as little harm to nature as possible with the least loss for progress. There is a need to develop effective methods of wastewater treatment, among the most effective of them is the creation of biological ponds. Let's get to know them better, find out the essence of this term, varieties and specifics of arrangement and application.

concept

Now they are not uncommon. And biological ponds are among them, however, they are distinguished from other varieties by their purpose - in such ponds, conditions are created as close to natural as possible, in which wastewater will be self-purified. You can also find other names of structures - lagoons, simple ponds, stabilization ponds, post-treatment ponds.

The main "inhabitants" of such reservoirs are green algae, which actively release oxygen during their life, and this chemical element, in turn, leads to an acceleration of the decay of organic matter. In addition, the decomposition process is influenced by the following groups of factors:

• Temperature.
• Aeration.
• Water speed.
• Vital activity of bacteria.

Thus, water purification occurs - quite naturally and quite quickly. In just 5 days, you can make a complete cleaning of the reservoir. In addition, plants will accumulate heavy metals inside them, which naturally decompose for a long time.

Characteristic

Let's get acquainted with the main parameters of bioponds:

• The optimal depth is small - from 0.5 to 1 meter.
• The shape is a rectangle.
• The ratio of length and width depends on the method of aeration: if it is artificial, then the proportion is 1:3, if natural - 1:1.5.

It is under such conditions that the mass development of planktonic algae and other beneficial microorganisms occurs. In order for bioponds to perform their immediate functions, the following plants are planted next to them: reed, calamus, reed, broad-leaved cattail, water hyacinth and some others.

Duration beneficial use these structures - more than 20 years.

Varieties

Biological ponds for water can be of three main types, information about them is presented in table format for ease of perception.

In addition, another classification can be found - the division into flow and contact, while the former, in turn, can be multi- and single-stage.

Also, bioponds can be divided into three groups depending on the biotic cycle: anaerobic, aerobic and facultative-aerobic.

• Anaerobic are most often used for partial water treatment. Living organisms living in them need a large amount of oxygen. An essential point of such reservoirs are the unpleasant smells of decay.
• Aerobic are the most powerful in terms of the degree of purification, since the living organisms living in them, primarily algae, take part in the oxidation of wastewater.
• Optional aerobic - an intermediate option that combines the unpleasant smell of rot and more efficient cleaning.

With multi-stage cleaning, fish can be bred in the ponds of the last stage, most often it is carp.

Application

Studies have proven that the simplest and at the same time effective water purification system is the use of natural methods, in particular plant organisms. For algae, improving water quality is a natural function, since they need potassium, phosphorus and nitrogen for normal life, and microorganisms responsible for the oxidation of organic matter are formed in the root system. The work of artificial reservoirs is based on these factors.

Bioponds are used both for independent water purification and as part of a whole complex of similar structures, for example, anticipating the use of agricultural irrigation fields or for post-treatment at aeration stations. For wastewater treatment, biological ponds are preferably used in those regions where the air temperature is at least +10 ° C on average throughout the year and a moderately humid climate.

Sanitary supervision

Wastewater treatment plant, including bioponds, are under constant sanitary control, the task of which is carried out by sanitary and epidemiological stations. The following specialists are required to monitor the condition of such reservoirs:

For the purpose of control, different kinds research, including bacteriological. Compliance with measures to prevent the discharge of wastewater not subjected to preliminary treatment and disinfection into water bodies is also checked.

Benefit

Biological purification of water in a pond, in addition to its simplicity and effectiveness, is also very useful for a person. First of all, ordinary natural processes are used, so there is no talk of artificial interference in the life of the natural community. Such reservoirs can be used both for self-treatment and for post-treatment. In addition, bioponds help in the following cases:

• Destroy up to 99% of Escherichia coli.
• The content of helminth eggs is reduced to almost 100%.

However, it is important to note a significant disadvantage of such reservoirs - at low temperatures, the efficiency of their use decreases significantly, and covered with ice cover, they can no longer perform their functions: oxygen does not penetrate into the water, so the process of organic oxidation stops.

The use of bioponds - reservoirs in which living organisms live - is the simplest and most profitable system of biological pond cleaning. This method helps to achieve significant savings in energy and resources, and the result will be very high quality. In addition, compliance with any special conditions is not required, maintenance of the structure is as simple as possible.

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

At the same time, depending on the purpose of the facility, the wastewater supplied to it must meet the requirements presented in Table. 13, and allowable costs in table. fourteen.

Table 13

BOD value of total sewage released into biological ponds

Table 14

Permissible flow rates of wastewater supplied to biological ponds

Note. If the value of BOD total of wastewater supplied for treatment into bioponds exceeds the values ​​\u200b\u200bspecified in Table 13, then it should be provided preliminary cleaning these waters.

Bioponds should be arranged on non-filtering or weakly filtering soils. In case of soils unfavorable in terms of filtration, anti-filtration measures should be carried out, i.e. waterproofing of buildings. In relation to residential development, 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.

Ditches of biological ponds are arranged using, if possible, natural depressions in the terrain. The shape of the ponds in the 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 corners is recommended to prevent the formation of stagnant zones in them.

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

Note. In biological ponds with artificial aeration of waste water, in which the ratio of length to width is 1 ... 3, it is necessary to take the hydraulic mode of fluid movement corresponding to the conditions of ideal (complete) mixing.

Structurally, biological ponds consist of at least two parallel sections with 3 ... 5 consecutive steps in each (for example, Fig. 11). At the same time, it should be possible to turn off any section for cleaning or preventive maintenance 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. In biological ponds with an area of ​​less than 0.5 ha, the width of the enclosing dams and dams along the top can be reduced to 1.0 ... 15 m.

In the presence of filtration through protective dams and dams, their "clothes" should be provided in the form of an impervious 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

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 level of filling of the stages. The mark of the tray of the bypass (inlet) pipe should be 0.3 ... 0.5 m above the bottom of the pond. In this case, water is admitted to ponds with artificial pneumatic aeration through a horizontal pipeline, the outlet of which is located on a concrete pad, directed upwards at an angle of 90 0 and is below the estimated ice level, and with mechanical aeration - through the pipeline directly to the zone of active mixing. In addition, at the exit point of the bypass pipe, in order to avoid erosion of the slope, its respective participants are reinforced with stone or concrete slabs. To release wastewater from the structure (stage), a collection device is designed, which is placed below the water level by 0.15 ... 0.20 of the working depth of the pond (water depth).

In order to provide wave erosion of the inner slopes of the dams, as well as the development of higher aquatic vegetation, they are laid out with stone, slabs and covered with asphalt for crushed stone preparation with a strip with a width of 1.5 m (1 m below the water level and 0.5 m above). To prevent the plates from slipping, a ledge is made, which serves as an emphasis for them. The outer slope of the dams should be planted with slow growing grass with a low herbage that can prevent erosion, for example, blue wheatgrass. The excess of the construction height of the dam above the calculated 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 biogenic elements in them (primarily nitrogen and phosphorus), it is recommended to use higher aquatic vegetation (reeds, cattail, reeds, etc.) in ponds. This vegetation should be placed in the last step 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 at a planting density of 150...200 plants per 1 m 2.