Biological pond for wastewater treatment. Bioprud - wastewater treatment

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

Biological ponds as independent treatment facilities according to SNiP are allowed to be used (with proper justification) for populated areas located in the IV climatic region. 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 according to the load of sewage (first case) water per 1 hectare of the water surface of the pond or according to the amount of reaeration (second case).

In the first case, this load is assumed to be (without dilution for settled wastewater) up 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 amount of reaeration equal to 6 - 8 g of oxygen per day from 1 m2 of the pond, depending on climatic conditions (SNiP).

The average depth of water in biological ponds is taken, depending on local conditions, within 0.5–1 m. When using ponds for fish breeding, clarified waste liquid, diluted with river water by 3–5 times, should be supplied to them. At the same time, biological ponds should include 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 is reduced by more than 100 times, the oxidizability is reduced by 90%, the amount of organic nitrogen is reduced by 88, ammonia by 97 and BOD by up to 98%. In autumn, ponds not intended for growing fish are emptied, and in winter they are used as storage ponds. In the spring, the ponds are filled with water and after about a month they begin to work for the channel. Contact operation of ponds is also possible. The bottom of the pond is recommended to be plowed annually. Wastewater should be in the ponds for 20-30 days. It is recommended to let sewage into the ponds during the daytime. Ponds should be located near natural water bodies. The amount of dissolved oxygen in water should not be less than 2.5 mg/l. The bottom of the pond is planned towards the outlet. The depth at the inlet is usually taken as 0.5 m, at the outlet - up to 1–2 m. Ponds are designed with an area of ​​0.5–1.5 ha or more.

When designing ponds with a natural catchment area, spillway structures must be designed for an additional pass of flood and storm flow. Depending on the conditions of release (emptying) dictated by the relief, the capacity of the pond can be formed by damming along thalwegs, using existing or creating artificial cuts (hollows), fencing the territory with rollers (dams). In the upper pond, 2-3 inlets are arranged. For a better distribution of the flow of waste fluid across the first pond, two rows of wattle fences are installed. Bypasses from the ponds are arranged in the form of trays 0.4 m wide every 30 m. Water is discharged from the last pond using shaft spillways.

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

The investigated channels were located in the thalwegs of dry beams with an average annual air temperature of the area of ​​6.8 + 7.1 ° C and an average annual rainfall of 500--510 mm. The speed of movement of waste water in these channels ranged from 0.01 to 0.05 m / s, the residence time of effluents in the channel was from 7 to 28 hours. The layer of water in the channel (excluding sediment) was taken within 0.025 - 0.15m, channel width - within 0.65--1.5m.

Wastewater flowing in channels with low speed and shallow depth, but relatively large flow width, is affected by sunlight, atmospheric oxygen and other climatic factors, which causes the concentration of contaminants in wastewater to decrease as it moves away from the discharge point. There is a natural self-purification of wastewater. Such channels are called natural oxidative channels, since they undergo oxidation processes similar to those occurring in biological ponds.

Artificial oxidizing channels are used abroad (Holland, USA, etc.) in climatic conditions with a minimum air temperature (up to -8 ° C) and give good results in the treatment of small amounts of wastewater. In such canals, the concentration of contaminants is reduced by BOD5 to 98%, bacterial contamination and the content of suspended solids drop sharply. Artificial oxidizing channels as treatment facilities in our conditions are still rarely used.

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 facilities, samples of wastewater were taken before septic tanks, after septic tanks and through channels every 100 m, for chemical and bacteriological analyzes. At both sites, the amount of wastewater fluctuated between 100-150 m3 per day. The primary settling tanks were septic tanks, poorly maintained (almost not cleaned).

The analyzes showed that the concentration of sewage pollution in the natural oxidizing channels has significantly decreased. During the studied 1000 m of the canal, waste water is purified both chemically and bacteriologically.

Biological ponds are artificially created reservoirs for biological wastewater treatment, based on the processes that occur during self-purification of reservoirs.

In the absence of good filtering soils for the construction of filtration fields or irrigation fields, ponds can be used as independent facilities for wastewater treatment, as well as for their post-treatment in combination with other treatment facilities.

Ponds make shallow depths - from 0.5 to 1 m. This allows you to create a significant surface of contact between water and air and ensure heating of the entire water column and its good mixing. Thus, favorable conditions are created for the mass development of aquatic organisms, in particular planktonic algae, which assimilate biogenic elements and, as a result of the synthesis process, enrich water with oxygen necessary for the oxidation of organic substances.

biological ponds provide a higher effect of bacterial self-purification than artificial biological treatment facilities. Thus, the number of Escherichia coli in ponds decreases w. 95.9 - 99.9% of the initial content. The content of helminth eggs in water that has passed through biological ponds is negligible.

Wastewater inlet and treated water discharge from ponds is carried out dispersed.

For the possibility of complete emptying of the ponds, their bottom should be given a slight slope towards the spillways.

The normal operation of ponds takes place in warm weather, and already at a water temperature below 6 ° C, it deteriorates sharply.

With a further decrease in temperature, and especially after the formation of an ice cover, when oxygen does not penetrate into the water, the process of oxidation of organic matter almost completely stops. During this period, only freezing of sewage can occur.

Biological ponds are usually calculated according to the load on the surface, depending on the concentration of contaminants and temperature conditions.

There are the following types of biological ponds: 1) ponds with dilution (fish-breeding); 2) ponds without dilution (multi-stage or serial); 3) ponds for post-treatment of wastewater.

In the first case, wastewater after preliminary clarification in settling tanks is mixed with fresh river water in proportions of 1:3-1:5 and sent to single-stage flow ponds, where the organic matter is oxidized. Waste water load is 125-300 m3/(ha-day). The size of each pond is 0.5-7 ha. Duration of stay of water (taking into account dilution) 8-12 days. You can breed fish in the ponds.

In the second case, waste water after preliminary settling is sent to the pond without dilution with clean water. Such biological ponds were first built on the initiative of prof. S. N. Stroganova on Moscow filtration fields.

The duration of wastewater treatment in ponds of this type is longer than in ponds of the first type; water exchange takes up to 30 days. Wastewater load is about the same as in dilution ponds [in Moscow 125-150 m3/(ha-day)].

The construction and operating costs of constructing ponds without dilution are significantly lower than those of diluted ponds.

In order to ensure proper water purification, ponds without dilution are arranged in 4-5 stages (serial ponds), which the water passes through sequentially. The degree of purity of water with each successive stage gradually increases. Ponds of each stage usually have an area of ​​2-2.5 hectares.

The lower stages of serial biological ponds without dilution can be used for breeding fish, mainly carp.

When breeding fish in early spring, 500-2000 fry per 1 ha are released into the pond. The growth of fish by the end of the autumn period is up to 500-800 kg per 1 ha. Fishing is done 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.

When constructing biological ponds, land plots are used more fully than when constructing irrigation fields or filtration fields. In addition, ponds can be built on soils that are unsuitable for fields.

Wastewater that has passed biological ponds can be used for irrigation. In this case, watering machines, firth irrigation, long furrows, sprinkling, subsoil irrigation can be used.

If necessary, according to local conditions, increased wastewater treatment for their post-treatment (after artificial treatment facilities), it is recommended to arrange biological ponds of the third type. The number of steps in such ponds should be: when biologically treated wastewater enters them, 2-3 steps, when settled wastewater enters, 4-5 steps. The load on the ponds should be taken taking into account their reaeration, which gives 6-7 g of oxygen per 1 m2 of the pond. This is sufficient to treat 100-250 m3/(ha-day) of settled wastewater (without dilution) or 4000-5000 m3/(ha-day) of biologically treated wastewater.

Ponds intended for post-treatment of wastewater can also be used for fish farming. In these cases, additional small ponds with a depth of at least 2.5 m should be provided for fish to stay in them in winter.

Recently, ponds with photosynthetic phytoplankton organisms, in particular with chlorella algae, have become widespread for wastewater treatment.

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 with wastewater is also increasing, setting the experts a difficult task - how to cause the least harm to nature 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.

The useful life of these structures is 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

Treatment facilities, 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, various types of studies are used, 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.

Aerobic processes of biochemical purification can occur in natural conditions and in artificial structures. Under natural conditions, cleaning occurs in irrigation fields, filtration fields and biological ponds. Artificial structures are aerotanks and biofilters of various designs. The type of facilities is chosen taking into account the location of the plant, climatic conditions, the source of water supply, the volume of industrial and domestic wastewater, the composition and concentration of pollution. In artificial structures, cleaning processes proceed 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 is under the influence of soil microflora, sun, air and under the influence of plant life.

Agricultural irrigation fields have the following advantages over aeration tanks:

• 1) capital and operating costs are reduced;
• 2) discharge of runoff outside the irrigated area is excluded;
• 3) high and stable yields of agricultural plants are ensured;
• 4) low-productive lands are involved in agricultural turnover.

In the process of biological treatment, wastewater passes through the filter layer of the soil, in which suspended and colloidal particles are retained, forming a microbial film in the pores of the soil. Then the resulting film adsorbs colloidal particles and substances dissolved in wastewater. Oxygen penetrating from the air into the pores oxidizes organic substances, turning them into mineral compounds. The penetration of oxygen into the deep layers of the soil is difficult, so the most intense oxidation occurs in the upper layers of the soil (0.2-0.4 m). With a lack of oxygen in the ponds, anaerobic processes begin to predominate.

Irrigation fields are best arranged on sandy, loamy and chernozem soils. Groundwater should be no higher than 1.25 m from the surface. If the ground hearths lie above this level, then it is necessary to arrange drainage.

[taken equal to 5-20 m 3 (ha * day)]

In winter, wastewater is directed only to reserve filtration fields. Since during this period the filtration of wastewater either stops completely or slows down, the reserve filtration field is designed taking into account the freezing area Fn (in m 2):

where Q - wastewater consumption, m 3 / day; Tn - number of days of freezing; ? - coefficient characterizing the value of winter filtration; hn and ho are the heights of the layers of freezing and winter precipitation, respectively, m; ?l - ice density, kg/m 3 .

biological ponds

They are a cascade of ponds, consisting of 3-5 steps, through which clarified or biologically treated wastewater flows at a low speed.

The ponds are designed 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 warmed up by the sun and are inhabited by aquatic organisms.

3.

biological ponds ( Cleaning of drains )

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. 14.

Table 13

BOD value of total sewage released into biological ponds

Type of aeration	The value of BOD is full of wastewater supplied to bioponds, mg/l, not more than
	Cleaning of drains	Post-treatment of wastewater
natural aeration
artificial aeration

Table 14

Permissible flow rates of wastewater supplied to biological ponds

Type of aeration	Permissible flow rates of wastewater supplied to bioponds, m 3 /day, no more.
	Cleaning of drains	Post-treatment of wastewater
natural aeration		10000
artificial aeration	10000	Not limited

Note. If the value of BOD full of wastewater supplied for treatment into bioponds exceeds the values ​​\u200b\u200bgiven in Table 13, then preliminary treatment of these waters should be provided.

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

Soil type	slope steepness
Wet clay and loamy soils
Wet sandy and sandy soils
Dry clay and loamy soils	1:1,5
Dry sandy and sandy 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 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, placed 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 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 in ponds (reed, cattail, reed, etc.). 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.