Without regeneration (LF and return sludge are fed into 1 corridor, biological treatment is carried out by 4 corridor)

With 25% regeneration

With 50% regeneration

With 75% regeneration

Aeration tanks - sedimentation tanks

A characteristic feature of these structures is the structural combination of an aeration tank and a secondary settling tank in one structure.

The part of the structure in which the aeration of the sludge mixture is carried out is called the aeration zone, and the other is called the settling zone.

Both areas are connected by holes, windows and crevices. Providing the overflow of the sludge mixture from the aeration zone to the settling tank and returning the sludge from the settling zone to the aeration zone without the use of additional equipment.

Aeration tank - sedimentation tank "Oksikompakt"

1.SG inlet

2.discharge of purified water

3.sludge area

4.Remove excess sludge

5.air supply

The LF after the primary sedimentation tanks is supplied to the aeration zone located in the center of a rectangular tank, on both sides of the central aeration zone there are settling zones, which are separated by partitions and have overflow windows in the upper part and slots in the lower part. These holes are used to circulate the sludge.

Excess sludge is removed from the lower part of the sedimentation zone through special pipelines located at a certain distance from each other. Air is supplied through cap aerators mounted in the bottom plate, blocking the air channels, or into air ducts laid along the bottom along the aeration zone. The depth of the structure is taken to be about 4 m, the length is from 15 to 70 m (depending on performance).

The advantage of this type of structure is the recirculation of activated sludge without auxiliary devices, as well as an increase in the dose of sludge in the aeration tanks.

Extended aeration aeration tank

The aeration time in aeration tanks of this type can reach 20 hours or more, which significantly exceeds the aeration time in conventional aeration tanks (from 2 to 8 hours). During this time, in the aeration tank, not only biological treatment of SF is carried out, but also the oxidation of activated sludge in the phase of endogenous respiration. This is due to the fact that activated sludge is under conditions of low organic load, and microorganisms are in the starvation stage, as a result of which the cells of microorganisms undergo self-oxidation. Return activated sludge after aeration tanks of extended aeration does not require regeneration, and excess activated sludge does not need additional processing and can be immediately sent for dehydration.

This scheme is a combined installation that combines an extended aeration tank and a secondary settling tank. From the aeration zone, the sludge mixture through a special window enters the degassing zone, where air bubbles are separated from the sludge flocks.

In the sedimentation zone, the separation of the purified liquid and activated sludge is carried out, while the water in the sump moves from bottom to top passing through the layer of suspended sediment, which intensifies the clarification process. The residence time in the settling zone is from 2 to 4 hours. The separated sludge is removed outside the structure under hydrostatic pressure and fed to the sludge pumping station. ANN returns part of the sludge to the aeration tank, and the excess is supplied or pumped for dewatering.

An aeration tank is a rectangular structure through which wastewater mixed with activated sludge flows. Biochemical wastewater treatment is carried out in this tank. The aeration tank must be completed with an aerator (mechanical or pneumatic). Thanks to the aeration system, the activated sludge effluent is saturated with oxygen, which is vital for aerobic microorganisms. This biological treatment scheme is implemented only under conditions of sufficient saturation of effluents with activated sludge, as well as with a continuous supply of oxygen. Only under such conditions active biochemical oxidation of organic matter is ensured, which guarantees high efficiency of biological treatment facilities.

There are several types of aeration tanks, depending on what technological cleaning schemes are provided in them. So, the following types of biological treatment facilities are distinguished:

1. Displacers. These are structures whose operation scheme is based on the supply of wastewater from one side and the outlet of treated wastewater from the opposite side.
2. Mixers. In these structures, the supply of wastewater and the outlet of the treated liquid are carried out simultaneously.
3. Constructions in which there is a dispersed infusion of water... In this case, the scheme provides that the polluted medium enters the structure from several points, is collected in one tank and, after cleaning, leaves through one hole.
4. Aeration tank with uneven dispersion of liquid... In such structures, the entry of contaminated water occurs from several points. After a certain time after cleaning, the liquid is also discharged into the ground through several outlet pipes.

The photo below shows the main types of aeration tanks: the first diagram shows displacers, the second - mixers, the third diagram in the photo shows the principle of operation of structures with dispersion.

Efficiency

As you already understood, active sludge is needed for efficient operation of the aeration tank. Its formation, viability, as well as the level of biological treatment are significantly influenced by temperature, the presence of a nutrient medium, the concentration of oxygen in the sludge mass, the acidity of the medium, and the presence of toxins. Also, for satisfactory operation, the technological mode in which the aeration tank works is important, namely:

• It is necessary to observe the basic relationships between the degree of pollution of wastewater and the amount of activated sludge. If the dose of sludge is less, then the load increases and the quality of purification decreases. If the dose of sludge is more than necessary, then the process of separating sludge from water in the secondary clarifier becomes more complicated.
• Another basic condition that must be strictly observed is the contact time of the contaminated liquid with the sludge, that is, the residence time in the sump.
• It is equally important that the amount of oxygen in the system is sufficient.

Important: the load on the sludge is the amount of pollution that the sludge must be processed in wastewater. The oxidizing ability of sludge depends on the dose of dry matter in one liter of liquid. Different sludge dosages are used in different aeration tanks. Usually it is 1-20 gr. per liter.

Features and differences from a septic tank

As you already understood, an aeration tank is a biological treatment facility that needs a continuous supply of air. Thanks to this, the oxidation of organic components of wastewater is faster and better. When using such a purification scheme, purified water is formed, which can be used for watering the garden, as well as for various technical purposes. In addition, activated sludge is successfully used for fertilizing fields and vegetable gardens. The collection of treated waste water takes place in the second settling tank.

Do not confuse a conventional septic tank equipped with a biofilter and an aeration tank. The main differences between them are as follows:

• To pump air into the aeration tank, you need a compressor that runs on electricity. Therefore, this type of structure can be called volatile.
• Wastewater enters the biofilter in small portions, and the aeration tank is filled with wastewater to the full.
• The scheme of purification of polluted water in a biofilter is very similar to the principles of biological purification in soil. However, in a septic tank, wastewater is treated faster and in smaller areas. The aeration tank uses the same cleaning scheme, but the speed of all processes is much higher. This high biological cleaning rate is achieved through the use of an aerator and oxygenation.

Principle of operation

The basic principles of aeration tank operation differ from a septic tank and are as follows:

1. Contaminated waste water flows into the central part of the structure. This is a primary sump, which closely resembles the sump used in a two-chamber septic tank.
2. After partial purification of wastewater, they are pumped by airlift into the aeration tank. Here they are mixed with activated sludge, which is already present in this chamber. Activated sludge is a special substance consisting of plant residues, bacterial colonies, which are involved in the processing of organic components of wastewater. As a rule, aerobic microorganisms live in activated sludge, which need oxygen during their life. Oxygen access is provided by forced aeration.

Important: a compressor is used to pump air, and an air duct system is used to distribute it along the aerotank. At the same time, the oxygen concentration in the treated water at the exit from the structure is at least 2 mg / l. Sometimes, to measure the oxygen level, built-in automation is used, which itself increases the supply of oxygen when its concentration in the liquid at the outlet decreases.

1. After staying in the aeration tank, the effluent enters the secondary clarifier. At the same time, microorganisms and activated sludge that have settled to the bottom return to the aeration tank. The residence time of the sludge in the secondary clarifier is limited, since a special pump is used for pumping back.
2. In the secondary sedimentation tank, the water stays for a sufficient time in order to pass the final stage of purification.

Since they constantly multiply during the life of bacteria, their number does not decrease for some time, but only increases. This contributes to the fact that the cleaning efficiency during the operation of the aeration tank only increases.

Biological treatment facilities can be made in the form of a single container, which is internally divided into separate compartments, or in the form of a multi-chamber structure from separate blocks. Usually, when using a multi-chamber design, secondary sedimentation tanks are equipped to collect sludge with the subsequent discharge of the treated water into drainage ditches or into storage tanks, from where the liquid will be used for watering the garden. In this case, the volume of water entering the secondary sedimentation tank should not exceed 8-10 liters per second.

Aeration tanks, which consist of three structures in the form of a primary sedimentation tank, aeration tank and a secondary sedimentation tank, provide better water purification. However, such designs require difficult maintenance.

To operate the aeration tank, the following resources are needed:

• Electricity with a voltage of 220 V. Depending on the modification, it can be consumed from 80 W. For the efficient operation of the structure, there must be no power outages.
• Aerobic microorganisms.

Advantages and disadvantages

The advantages of aeration tanks include the following points:

1. The whole structure is very compact, which allows installation even in a small area.
2. Since gases are not emitted during the life of aerobes, there is absolutely no unpleasant odor from the structure.
3. Such a structure does not need to be insulated for the winter, since a large amount of energy is released during the processing of organic waste, which allows maintaining the required temperature inside the structure even in winter.

However, such products also have their drawbacks:

1. Without electricity, a sufficient level of cleaning cannot be achieved. Since the compressor will not work, bacteria and activated sludge will die.
2. High price of factory products.
3. The complex equipment used in the operation of the aeration tank needs constant monitoring.
4. If you do not use the sewer for a long time, then there will be no breeding ground for bacteria, and they will die.

Important: when the compressor is running and there is no wastewater flow, the activated sludge retains its viability for 3 months. If the electricity is turned off, the sludge will die in three months.

To prevent the death of activated sludge, a mixture of dry activated sludge with water is poured into the structure of the aeration tank. This should be done once a month. If, for some reason, the sludge died, then the aeration tank will have to be restarted. To do this, do the following:

• Free the aerotank from dead silt. To do this, rinse it with water.
• Live activated sludge can be taken in another aeration tank. To avoid problems with this, it is necessary to sign a maintenance agreement for the aeration tank when purchasing it.

Installation

Usually, the installation of the aeration tank is carried out by specialists of the company where you purchased the equipment. Since the installation requirements may slightly differ from model to model, before installing the product, you must carefully read the instructions, which provide detailed instructions for installation.

The installation of a factory product is usually carried out in several stages:

1. The pit is dug, based on the dimensions of the product. Usually its dimensions are 180x180x260 cm.
2. A sand pillow 15 cm high is made at the bottom of the pit.
3. We lower the structure into the pit.
4. Before backfilling, water is poured into the aeration tank. In this case, the water is poured gradually as you fall asleep. The water level should always be 15-20 cm above the filling level. This is to ensure that the soil pressure does not damage the walls of the structure. We do the filling up to the level of the location of the pipes for fastening communications.
5. We connect communications to the aerotank.
6. We carry out the installation of the compressor.
7. We connect electricity.
8. We complete the backfill and ram the soil.

Aeration tanks-settling tanks are designed in the form of rectangular tanks of structures that combine aeration tanks with extended aeration (aeration part) and secondary sedimentation tanks of a vertical type (settling part). Both structures are interconnected by overflow windows that ensure the flow of the sludge mixture from the aeration zone to the settling zone.

The extended aeration mode, which is also called the complete oxidation method, is distinguished by a significantly longer residence time of wastewater in aeration tanks. The duration of aeration of wastewater in the extended mode is 1-3 days. depending on the initial concentration of wastewater by BOD. Aeration tanks with extended aeration operate at doses of activated sludge on a dry matter basis of 3-6 g / l per day.

Aeration tanks operating in full oxidation mode can be operated with or without excess activated sludge removal. In the latter case, excess activated sludge is removed from the secondary clarifier, which reduces the quality of treatment. Therefore, for a higher degree of purification, the project provides for the removal of excess sludge from the system, especially since its low increase allows this operation to be performed at significant intervals.

The use of the extended aeration mode is due to a slight increase in activated sludge and a high degree of its mineralization, ease of operation, stability of operation in modes of uneven flow of wastewater flow.

Figure 4.4 Aeration tanks-settling tanks: 1 - aeration tank, 2 - sedimentation tank, 3 - sewage supply pipeline for treatment, 4 - purified water discharge pipeline, 5 - aeration system, 6 - circulating sludge pipeline, 7 - excess sludge discharge pipeline, 8 - air duct, 9 - airlift, 10 - chute, 11 - toothed weir

Table 4.2 Initial data for calculating aeration tanks-sedimentation tanks

Options	Parameter values
Daily waste water consumption, m3 / day
Average hourly flow rate, m3 / h
Maximum hourly flow rate, m3 / h
BOD20 of incoming effluent, mg / l
The same treated effluent, mg / l
The concentration of suspended solids in the treated effluent, mg / l
Average annual temperature of wastewater, ° С
Sludge dose in aerotanks, g / l
Silt index, cm3 / g
Concentration of ammonium nitrogen in feed water, mg / l
The same in purified water

Aeration tank

The calculation of aeration tanks is carried out according to the extended aeration mode. The duration of aeration is:

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Aerobic biological treatment of large volumes of water is carried out in aeration tanks - rectangular in terms of reinforced concrete structures with activated sludge freely floating in the volume of treated water, the bio-population of which uses wastewater pollution for its life.

Aerotanks can be classified according to the following criteria:

1. according to the flow structure - aeration tanks-displacers, aeration tanks-mixers and aeration tanks with a dispersed inlet of waste fluid (intermediate type) Figure 51;

Figure 51 - Schemes of aeration tanks
a - aeration tank-displacer; b - aeration mixer; c - intermediate type aeration tank;
1 - waste water; 2- return activated sludge; 3- aerotank; 4 - silt
mixture.

2. by the method of activated sludge regeneration - aerotanks with separate or combined sludge regenerators;
3. by load on activated sludge - high-load (for incomplete cleaning), normal and low-load (with extended aeration);
4. by the number of stages - one-, two-, and multi-stage;
5. according to the mode of input of wastewater - flowing, semi-flowing, with a variable working level, contact;
6. by the type of aeration - pneumatic, mechanical, combined hydrodynamic or pneumomechanical;
7. by design features - rectangular, round, combined, mine, filter tanks, flotation tanks, etc.

Aeration tanks are used in an extremely wide range of wastewater flow rates from several hundred to millions of cubic meters per day.

In mixing aeration tanks, water and sludge are introduced evenly along the long walls of the aerotank corridor. Complete mixing of waste water with a sludge mixture in them ensures the equalization of sludge concentrations and rates of the biochemical oxidation process. The load of contaminants on the sludge and the rate of oxidation of contaminants are practically unchanged along the length of the structure. They are most suitable for purification of concentrated (BODp up to 1000 mg / l) industrial wastewater with significant fluctuations in their consumption and concentration of contaminants. In aeration tanks, water and sludge are supplied to the beginning of the structure, and the mixture is removed at the end of it. The aeration tank has 3-4 corridors. Theoretically, the flow regime is piston without longitudinal mixing. In practice, there is significant longitudinal mixing. The load of contaminants on the sludge and the rate of oxidation vary from the highest values ​​at the beginning of the structure to the lowest at its end. Such structures are used in the event that a sufficiently easy adaptation of the activated sludge is ensured. In aeration tanks with a dispersed water supply along its length, unit loads on sludge decrease and become more uniform. Such facilities are used for the treatment of mixtures of industrial and municipal wastewater.

The operation of the aeration tank is inextricably linked with the normal operation of the secondary clarifier, from which the return activated sludge is continuously pumped into the aeration tank. Instead of a secondary clarifier, a skimmer can be used to separate sludge from water.

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

Figure 52 - Basic technological schemes for wastewater treatment in aeration tanks
a - one-stage aerotank without regeneration; b - one-stage aerotank with regeneration; c - two-stage aeration tank without regeneration; d - two-stage aeration tank with regeneration; 1 - waste water supply; 2 - azrotenc; 3 - release of sludge mixture; 4 - secondary sedimentation tank; 5 - outlet of purified water; 6 - release of exfoliated activated sludge; 7 - sludge pumping station; 8 - supply of returnable activated sludge; 9 - release of excess activated sludge; 10 - regenerator; 11 - discharge of waste water after the first stage of treatment; 12 - second stage aeration tank; 13 - second stage regenerator.

In a one-stage scheme without a regenerator, it is impossible to intensify the wastewater treatment process. In the presence of a regenerator, oxidation processes end in it and the sludge acquires its original properties. The two-stage scheme is used when the initial concentration of organic pollutants in the water is high, as well as in the presence of substances in the water, the oxidation rate of which is sharply different. At the first stage of treatment, the BOD of wastewater is reduced by 50-70%.

To ensure the normal course of the biological oxidation process, air must be continuously supplied to the aerotank. Aeration must provide a large contact surface between air, waste water and sludge, which is a prerequisite for effective cleaning.

The aeration system is a complex of structures and special equipment that supplies oxygen to the liquid, maintains the sludge in suspension and constantly mixes waste water with sludge. For most types of aeration tanks, the aeration system provides the simultaneous performance of these functions. According to the method of dispersing air in water, in practice, three aeration systems are used: pneumatic, mechanical and combined.

With mechanical aeration, mixing is carried out by mechanical devices (agitators, turbines, shields, etc.), which provide crushing of the air jets drawn directly from the atmosphere by the rotating parts of the aerator (rotor).

Pneumatic aeration, in which air is pumped into the aeration tank under pressure, is divided into three types depending on the size of the air bubbles: fine-bubble (1-4 mm), medium-bubble (5-10 mm), large-bubble (more than 10 mm). devices for air in a fine-bubble aeration system, diffusers made of ceramics are used. Plastics, fabrics in the form of filter plates, tubes, domes. To obtain medium-bubble aeration, perforated pipes, slotted and other devices are used. Large bubble aeration is created by open pipes, nozzles, etc.

A modern aerotank is a technologically flexible structure, which is a corridor-type reinforced concrete tank equipped with an aeration system. The working depth of the aeration tanks is from 3 to 6 m, the ratio of the width of the corridor to the working depth is from 1: 1 to 2: 1. For aeration tanks and regenerators, the number of sections must be at least two; with a productivity of up to 50 thousand m3 / day, 4-6 sections are assigned, with a higher productivity of 8-10 sections, all of them are working. Each section consists of 2-4 corridors.

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SEWERAGE - OUTDOOR NETWORKS AND STRUCTURES - SNiP 2-04-03-85 (approved by the Decree of the State Construction Committee of the USSR from 21-05-85 71) (revised from 20-05-86) ... Actual in 2018

Aeration plants for complete oxidation (aeration tanks with extended aeration)

6.166. Aeration plants for complete oxidation should be used for biological wastewater treatment.

Before supplying wastewater to the installation, it is necessary to provide for the retention of large mechanical impurities.

6.167. The duration of aeration in aeration tanks for complete oxidation should be determined by the formula (48), while it should be taken:

р - average oxidation rate according to BOD_full - 6 mg / (g x h);

a_i - sludge dose - 3 - 4 g / l;

s - ash content of sludge - 0.35.

The specific air consumption should be determined by the formula (61), while it should be taken:

q_O - specific oxygen consumption, mg / mg of removed BOD_full, - 1.25;

K_1, K_2, K_T, K_3, C_a - according to the data given in clause 6.157.

6.168. The duration of the wastewater stay in the sedimentation zone at the maximum inflow should be at least 1.5 hours.

6.169. The amount of excess activated sludge should be taken as 0.35 kg per 1 kg of BOD_full. Removal of excess sludge is allowed to be provided both from the settling tank and from the aeration tank when the sludge dose reaches 5 - 6 g / l.

The moisture content of the sludge removed from the settling tank is 98%, from the aeration tank 99.4%.

6.170. The load on the sludge pads should be taken as for sediments fermented in mesophilic conditions.

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