Construction of urban sewerage treatment facilities. Sewage treatment facilities OS, WWTP, BOS. Biological wastewater treatment

is a complex of special structures designed to purify wastewater from the contaminants it contains. Purified water is either used further or discharged into natural reservoirs (Great Soviet Encyclopedia).

Every settlement needs effective wastewater treatment facilities. The operation of these complexes determines what kind of water will enter the environment and how this will further affect the ecosystem. If liquid waste is not cleaned up at all, not only will plants and animals die, but the soil will also be poisoned, and harmful bacteria can enter the human body and cause serious consequences.

Every enterprise that has toxic liquid waste is required to deal with the system treatment facilities. Thus, this will affect the state of nature and improve human living conditions. If treatment systems work effectively, wastewater will become harmless when it enters the ground and water bodies. The size of treatment facilities (hereinafter - OS) and the complexity of treatment strongly depend on the contamination of wastewater and its volume. More details about the stages of wastewater treatment and types of O.S. read on.

Stages of wastewater treatment

The most indicative in terms of the presence of water purification stages are urban or local OS, designed for large populated areas. It is household wastewater that is most difficult to treat, as it contains various pollutants.

It is typical for sewerage water treatment facilities that they are built in a certain sequence. Such a complex is called a treatment plant line. The diagram starts with mechanical cleaning. Grates and sand traps are most often used here. This is the initial stage of the entire water treatment process.

This could be leftover paper, rags, cotton wool, bags and other debris. After the grates, sand traps come into operation. They are necessary in order to retain sand, including large sizes.

Mechanical stage of wastewater treatment

Initially, all water from the sewer enters the main pumping station into a special reservoir. This reservoir is designed to compensate for the increased load during peak hours. A powerful pump evenly pumps the appropriate volume of water to pass through all stages of cleaning.

catch large debris larger than 16 mm - cans, bottles, rags, bags, food, plastic, etc. Subsequently, this waste is either processed on site or transported to sites for processing solid household and industrial waste. Grids are a type of transverse metal beams, the distance between which is several centimeters.

In fact, they catch not only sand, but also small pebbles, glass fragments, slag, etc. Sand settles to the bottom quite quickly under the influence of gravity. Then the settled particles special device is raked into a depression at the bottom, from where it is pumped out. The sand is washed and disposed of.

. Here all impurities that float to the surface of the water (fats, oils, petroleum products, etc.) are removed. By analogy with a sand trap, they are also removed with a special scraper, only from the surface of the water.

4. Settling tanks– an important element of any treatment plant line. In them, water is freed from suspended substances, including helminth eggs. They can be vertical and horizontal, single-tier and two-tier. The latter are the most optimal, since in this case the water from the sewer in the first tier is purified, and the sediment (silt) that has formed there is discharged through a special hole into the lower tier. How does the process of releasing suspended solids from sewer water take place in such structures? The mechanism is quite simple. Sedimentation tanks are large tanks, round or rectangular shape, where sedimentation of substances occurs under the influence of gravity.

To speed up this process, you can use special additives - coagulants or flocculants. They promote the sticking together of small particles due to a change in charge; larger substances settle faster. Thus, sedimentation tanks are indispensable structures for purifying water from sewers. It is important to take into account that they are also actively used in simple water treatment. The principle of operation is based on the fact that water enters from one end of the device, while the diameter of the pipe at the exit becomes larger and the flow of liquid slows down. All this contributes to the sedimentation of particles.

Mechanical wastewater treatment can be used depending on the degree of water contamination and the design of a specific treatment facility. These include: membranes, filters, septic tanks, etc.

If we compare this stage with conventional water treatment for drinking purposes, then latest version such structures are not used, they are not necessary. Instead, processes of water clarification and discoloration occur. Mechanical cleaning is very important, since in the future it will allow for more effective biological treatment.

Biological wastewater treatment plants

Biological treatment can be either an independent treatment facility or important stage in a multi-stage system of large urban treatment complexes.

The essence biological treatment consists of removing various pollutants (organics, nitrogen, phosphorus, etc.) from water using special microorganisms (bacteria and protozoa). These microorganisms feed on harmful contaminants contained in the water, thereby purifying it.

From a technical point of view, biological treatment is carried out in several stages:

– a rectangular tank where water, after mechanical purification, is mixed with activated sludge (special microorganisms), which purifies it. There are 2 types of microorganisms:

Aerobic– using oxygen to purify water. When using these microorganisms, the water must be enriched with oxygen before entering the aeration tank.
Anaerobic– DO NOT use oxygen to purify water.

Necessary for removing unpleasantly smelling air with its subsequent purification. This workshop is necessary when the volume of wastewater is large enough and/or treatment facilities are located near populated areas.

Here the water is purified from activated sludge by defending it. Microorganisms settle to the bottom, where they are transported to the pit using a bottom scraper. A surface scraper mechanism is provided to remove floating sludge.

The purification scheme also includes sludge digestion. Of the treatment facilities, the digester is important. It is a reservoir for the fermentation of sludge, which is formed during settling in two-tier primary settling tanks. During the fermentation process, methane is produced, which can be used in other technological operations. The resulting sludge is collected and transported to special sites for thorough drying. Sludge beds and vacuum filters are widely used for sludge dewatering. After this, it can be disposed of or used for other needs. Fermentation occurs under the influence of active bacteria, algae, and oxygen. The sewer water purification scheme may also include biofilters.

It is best to place them before the secondary settling tanks, so that substances that are carried away with the flow of water from the filters can settle in the settling tanks. It is advisable to use so-called pre-aerators to speed up cleaning. These are devices that help saturate water with oxygen to accelerate aerobic processes of oxidation of substances and biological treatment. It should be noted that sewerage water purification is conventionally divided into 2 stages: preliminary and final.

The treatment plant system may include biofilters instead of filtration and irrigation fields.

- These are devices where wastewater is purified by passing through a filter containing active bacteria. It consists of solids, which can be granite chips, polyurethane foam, polystyrene foam and other substances. A biological film consisting of microorganisms forms on the surface of these particles. They decompose organic matter. As biofilters become dirty, they need to be cleaned periodically.

Wastewater is fed into the filter in doses, otherwise high pressure can destroy beneficial bacteria. After biofilters, secondary settling tanks are used. The sludge formed in them goes partly into the aeration tank, and the rest of it goes to the sludge compactors. The choice of one or another biological treatment method and type of treatment facility largely depends on the required degree of wastewater treatment, topography, soil type and economic indicators.

Wastewater tertiary treatment

After passing through the main stages of treatment, 90-95% of all contaminants are removed from wastewater. But the remaining pollutants, as well as residual microorganisms and their metabolic products, do not allow this water to be discharged into natural reservoirs. In this regard, the treatment plants introduced various systems wastewater tertiary treatment.

In bioreactors the process of oxidation of the following pollutants occurs:

organic compounds, which were too tough for microorganisms,
these microorganisms themselves,
ammonium nitrogen.

This happens by creating conditions for the development of autotrophic microorganisms, i.e. converting inorganic compounds into organic ones. For this purpose, special plastic backfill discs with a high specific surface area are used. Simply put, these are disks with a hole in the center. To speed up processes in the bioreactor, intensive aeration is used.

Filters purify water using sand. The sand is continuously updated automatically. Filtration is carried out in several installations by supplying water to them from the bottom up. In order to avoid using pumps and not wasting electricity, these filters are installed at a level lower than other systems. Filter washing is designed in such a way that it does not require a large amount of water. That's why they don't occupy the same amount large area.

Ultraviolet water disinfection

Disinfection or disinfection of water is an important component that ensures its safety for the body of water into which it will be discharged. Disinfection, that is, the destruction of microorganisms, is the final stage of sewerage wastewater treatment. A wide variety of methods can be used for disinfection: ultraviolet irradiation, alternating current, ultrasound, gamma irradiation, chlorination.

Ural irradiation is a very effective method that destroys approximately 99% of all microorganisms, including bacteria, viruses, protozoa, and helminth eggs. It is based on the ability to destroy the membrane of bacteria. But this method is not used so widely. In addition, its effectiveness depends on the turbidity of the water and the content of suspended substances in it. And UV lamps quickly become covered with a coating of mineral and biological substances. To prevent this, special emitters of ultrasonic waves are provided.

The most commonly used method after treatment facilities is chlorination. Chlorination can be different: double, superchlorination, with preammonization. The latter is necessary for warning unpleasant odor. Superchlorination involves exposure to very large doses of chlorine. Double action is that chlorination is carried out in 2 stages. This is more typical for water treatment. The method of chlorinating sewer water is very effective, in addition, chlorine has an aftereffect that other cleaning methods cannot boast of. After disinfection, the wastewater is discharged into a reservoir.

Phosphate removal

Phosphates are salts of phosphoric acids. They are widely used in synthetic detergents (washing powders, dishwashing detergents, etc.). Phosphates entering water bodies lead to their eutrophication, i.e. turning into a swamp.

Purification of wastewater from phosphates is carried out by dosed addition of special coagulants to the water before biological treatment facilities and before sand filters.

Auxiliary premises of treatment facilities

Aeration shop

- this is an active process of saturation of water with air, in in this case by passing air bubbles through water. Aeration is used in many processes in wastewater treatment plants. Air supply is carried out by one or more blowers with frequency converters. Special oxygen sensors regulate the amount of air supplied so that its content in the water is optimal.

Disposal of excess activated sludge (microorganisms)

At the biological stage of wastewater treatment, excess sludge is formed, as microorganisms actively multiply in aeration tanks. Excess sludge is dewatered and disposed of.

The dehydration process takes place in several stages:

Added to excess sludge special reagents, which suspend the activity of microorganisms and promote their thickening
IN sludge compactor the sludge is compacted and partially dewatered.
On centrifuge the sludge is squeezed out and any remaining moisture is removed from it.
In-line dryers With the help of continuous circulation of warm air, the sludge is finally dried. The dried sludge has a residual moisture content of 20-30%.
Then packed into sealed containers and disposed of
The water removed from the sludge is sent back to the beginning of the cleaning cycle.

Air cleaning

Unfortunately, wastewater treatment plants don't smell the best. The biological wastewater treatment stage is especially smelly. Therefore, if the treatment plant is located near populated areas or the volume of wastewater is so large that a lot of bad-smelling air is generated, you need to think about cleaning not only the water, but also the air.

Air purification usually takes place in 2 stages:

Initially, polluted air is supplied to bioreactors, where it comes into contact with specialized microflora adapted for recycling organic substances contained in the air. It is these organic substances that cause bad odors.
The air goes through a disinfection stage with ultraviolet light to prevent these microorganisms from entering the atmosphere.

Laboratory at wastewater treatment plants

All water that leaves treatment plants must be systematically monitored in the laboratory. The laboratory determines the presence of harmful impurities in water and whether their concentrations comply with established standards. If one or another indicator is exceeded, treatment plant workers conduct a thorough inspection of the corresponding treatment stage. And if a malfunction is detected, it is eliminated.

Administrative and amenity complex

The personnel servicing the treatment plant can reach several dozen people. For their comfortable work, an administrative and amenity complex is being created, which includes:

Equipment repair workshops
Laboratory
Control room
Offices of administrative and management personnel (accounting, human resources, engineering, etc.)
Head office.

Power supply O.S. performed according to the first reliability category. Since a long shutdown of O.S. due to lack of electricity may cause O.S. output. out of service.

To prevent emergency situations, power supply O.S. carried out from several independent sources. In the department transformer substation input is envisaged power cable from the city power supply system. As well as entering an independent source electric current, for example, from a diesel generator, in case of an emergency in the city power grid.

Conclusion

Based on all of the above, we can conclude that the design of treatment facilities is very complex and includes various stages of treating wastewater from sewers. First of all, you need to know that this scheme applies only to domestic wastewater. If industrial wastes occur, then in this case they additionally include special methods, which will be aimed at reducing the concentration of hazardous chemicals. In our case, the cleaning scheme includes the following main stages: mechanical, biological cleaning and disinfection (disinfection).

Mechanical cleaning begins with the use of grates and sand traps, which trap large debris (rags, paper, cotton wool). Sand traps are needed to sediment excess sand, especially coarse sand. This is of great importance for subsequent stages. After screens and sand traps, the sewer water treatment plant scheme includes the use of primary settling tanks. Suspended substances settle in them under the force of gravity. To speed up this process, coagulants are often used.

After settling tanks, the filtration process begins, which is carried out mainly in biofilters. The mechanism of action of the biofilter is based on the action of bacteria that destroy organic substances.

The next stage is secondary settling tanks. The silt that was carried away by the current of liquid settles in them. After them, it is advisable to use a digester, in which the sludge is fermented and transported to sludge sites.

The next stage is biological treatment using an aeration tank, filtration fields or irrigation fields. The final stage is disinfection.

Types of treatment facilities

A variety of structures are used for water treatment. If it is planned to carry out this work on surface water immediately before its supply to the city’s distribution network, then the following structures are used: settling tanks, filters. For wastewater, a wider range of devices can be used: septic tanks, aeration tanks, digesters, biological ponds, irrigation fields, filtration fields, and so on. There are several types of treatment plants depending on their purpose. They differ not only in the volume of water being purified, but also in the presence of stages of its purification.

City wastewater treatment plants

Data from O.S. are the largest of all, they are used in large cities and towns. In such systems they are especially used effective methods liquid treatment, eg chemical treatment, digester tanks, flotation units These are designed for the treatment of municipal wastewater. These waters are a mixture of domestic and industrial wastewater. Therefore, there are a lot of pollutants in them, and they are very diverse. The waters are purified to meet the standards for discharge into fishery reservoirs. The standards are regulated by Order of the Ministry of Agriculture of Russia dated December 13, 2016 No. 552 “On approval of water quality standards water bodies fishery significance, including standards for maximum permissible concentrations harmful substances in the waters of water bodies of fishery importance.”

In OS data, as a rule, all stages of water purification described above are used. The most illustrative example is the Kuryanovsky wastewater treatment plant.

Kuryanovsky O.S. are the largest in Europe. Its capacity is 2.2 million m3/day. They serve 60% of Moscow's wastewater. The history of these objects goes back to 1939.

Local treatment facilities

Local treatment facilities are structures and devices designed to treat the subscriber's wastewater before discharging it into the public sewerage system (defined by Decree of the Government of the Russian Federation of February 12, 1999 No. 167).

There are several classifications of local OS, for example, there are local OS. connected to central sewer and autonomous. Local O.S. can be used on the following objects:

In small towns
In the villages
In sanatoriums and boarding houses
At car washes
On personal plots
At manufacturing plants
And at other facilities.

Local O.S. can vary greatly from small units to capital structures that are maintained daily by qualified personnel.

Treatment facilities for a private home.

Several solutions are used to dispose of wastewater from a private home. They all have their advantages and disadvantages. However, the choice always remains with the home owner.

1. Cesspool. In truth, this is not even a treatment facility, but simply a tank for temporary storage of wastewater. When the pit is filled, a sewage disposal truck is called, which pumps out the contents and takes it away for further processing.

This archaic technology is still used today due to its cheapness and simplicity. However, it also has significant disadvantages, which sometimes negate all its advantages. Wastewater can enter the environment and groundwater, thereby polluting it. It is necessary to provide a normal entrance for the sewer truck, since it will have to be called quite often.

2. Storage. It is a container made of plastic, fiberglass, metal or concrete into which wastewater is drained and stored. They are then pumped out and disposed of by a sewer truck. The technology is similar cesspool, but the waters do not pollute the environment. The disadvantage of such a system is the fact that in the spring, when there is a large amount of water in the ground, the storage tank can be squeezed out to the surface of the earth.

3. Septic tank- are large containers, in which substances such as coarse dirt, organic compounds, stones and sand precipitate, and elements such as various oils, fats and petroleum products remain on the surface of the liquid. The bacteria that live inside the septic tank extract oxygen for life from the fallen sediment, while reducing the level of nitrogen in the wastewater. When the liquid leaves the sump, it becomes clarified. It is then purified using bacteria. However, it is important to understand that phosphorus remains in such water. For final biological treatment, irrigation fields, filtration fields or filter wells can be used, the operation of which is also based on the action of bacteria and activated sludge. It will not be possible to grow plants with a deep root system in this area.

A septic tank is very expensive and can take up a large area. It should be borne in mind that this is a structure that is designed to treat small amounts of domestic wastewater from the sewer system. However, the result is worth the money spent. The structure of a septic tank is shown more clearly in the figure below.

4. Deep biological treatment stations are already a more serious treatment facility, unlike a septic tank. This device requires electricity to operate. However, the quality of water purification is up to 98%. The design is quite compact and durable (up to 50 years of operation). To service the station, there is a special hatch at the top, above the ground surface.

Stormwater treatment plants

Although rainwater It is considered quite clean, but it collects various harmful elements from asphalt, roofs and lawns. Garbage, sand and petroleum products. To ensure that all this does not end up in nearby water bodies, stormwater treatment facilities are being created.

In them, water undergoes mechanical purification in several stages:

Sump. Here, under the influence of the Earth's gravity, large particles - pebbles, glass fragments, metal parts, etc. - settle to the bottom.
Thin layer module. Here, oils and petroleum products collect on the surface of the water, where they are collected on special hydrophobic plates.
Sorption fiber filter. It catches everything that the thin-layer filter missed.
Coalescent module. It helps to separate oil particles that float to the surface, the size of which is greater than 0.2 mm.
Carbon filter after purification. It finally rids the water of all petroleum products that remain in it after passing through the previous stages of purification.

Design of wastewater treatment plants

Design of O.S. determine their cost, choose the right treatment technology, ensure reliable operation of the structure, and bring wastewater to quality standards. Experienced specialists will help you find effective installations and reagents, draw up a wastewater treatment plan and put the installation into operation. Another important point– drawing up an estimate that will allow you to plan and control expenses, as well as make adjustments if necessary.

For the project O.S. The following factors greatly influence:

Wastewater volumes. Design of structures for personal plot this is one thing, but the design of wastewater treatment facilities for a cottage community is another. Moreover, it must be taken into account that the capabilities of O.S. must be greater than the current amount of wastewater.
Terrain. Wastewater treatment facilities require access to special vehicles. It is also necessary to provide for the power supply of the facility, the removal of purified water, and the location of the sewage system. O.S. may occupy a large area, but they should not interfere with neighboring buildings, structures, roads and other structures.
Wastewater pollution. Cleaning technology storm water very different from household cleaning.
Required level of cleaning. If the customer wants to save on the quality of purified water, then it is necessary to use simple technologies. However, if you need to discharge water into natural reservoirs, then the quality of treatment must be appropriate.
Competence of the performer. If you order O.S. from inexperienced companies, then get ready for unpleasant surprises in the form of an increase in construction estimates or a septic tank floating in the spring. This happens because they forget to include quite critical points in the project.
Technological features. The technologies used, the presence or absence of treatment stages, the need to construct systems servicing the treatment facility - all this must be reflected in the project.
Other. It is impossible to foresee everything in advance. As the treatment plant is designed and installed, various changes may be made to the design plan that could not be foreseen at the initial stage.

Stages of designing a treatment plant:

Preliminary work. They include studying the site, clarifying the customer’s wishes, analyzing wastewater, etc.
Collection of permits. This point is usually relevant for the construction of large and complex structures. For their construction, it is necessary to obtain and approve the relevant documentation from the supervisory authorities: MOBVU, MOSRYBVOD, Rosprirodnadzor, SES, Hydromet, etc.
Choice of technology. Based on points 1 and 2. a choice is made necessary technologies used for water purification.
Drawing up an estimate. Construction costs O.S. must be transparent. The customer must know exactly how much the materials cost, what the price of the installed equipment is, what the workers' wage fund is, etc. You should also consider the costs of subsequent system maintenance.
Cleaning efficiency. Despite all the calculations, the cleaning results may be far from desired. Therefore, already at the planning stage O.S. it is necessary to conduct experiments and laboratory studies that will help avoid unpleasant surprises after construction is completed.
Development and approval of project documentation. To begin construction of treatment facilities, it is necessary to develop and agree on the following documents: a draft sanitary protection zone, a draft standards for permissible discharges, a draft maximum permissible emissions.

Installation of treatment facilities

After the O.S. project has been prepared and all necessary permits have been obtained, the installation stage begins. Although the installation country septic tank is very different from the construction of a wastewater treatment plant in a cottage community, but they still go through several stages.

First, the area is prepared. A pit is being dug to install a treatment plant. The floor of the pit is filled with sand and compacted or concreted. If the treatment facility is designed for a large number of wastewater, then, as a rule, it is built on the surface of the earth. In this case, the foundation is poured and a building or structure is already installed on it.

Secondly, the installation of equipment is carried out. It is installed, connected to the sewerage and drainage system, and to the electrical network. This stage is very important because it requires personnel to know the specifics of the operation of the equipment being configured. It is incorrect installation that most often causes equipment failure.

Thirdly, inspection and delivery of the object. After installation, the finished treatment facility is tested for the quality of water treatment, as well as for its ability to operate under high load conditions. After checking O.S. is handed over to the customer or his representative, and also, if necessary, undergoes a state control procedure.

Treatment plant maintenance

Like any equipment, the treatment plant also needs maintenance. Primarily from O.S. It is necessary to remove large debris, sand, and excess silt that are formed during cleaning. On large O.S. the number and type of elements removed can be significantly greater. But in any case, they will have to be deleted.

Secondly, the functionality of the equipment is checked. Malfunctions in any element can lead not only to a decrease in the quality of water purification, but also to the failure of all equipment.

Thirdly, if a breakdown is detected, the equipment must be repaired. And it’s good if the equipment is under warranty. If the warranty period has expired, then repair O.S. you will have to do it at your own expense.

Before designing treatment facilities for domestic wastewater or other types of wastewater, it is important to find out their volume (the amount of wastewater generated over a certain period of time), the presence of impurities (toxic, insoluble, abrasive, etc.) and other parameters.

Types of wastewater

Wastewater treatment plants are installed for various types of wastewater.

Domestic wastewater– these are drains from plumbing fixtures (washbasins, sinks, toilets, etc.) of residential buildings, including private houses, as well as institutions, public buildings. Household wastewater is dangerous as a breeding ground for pathogenic bacteria.
Industrial effluents are formed in enterprises. The category is characterized by the possible presence of various impurities, some of which significantly complicate the purification process. Industrial wastewater treatment plants are usually complex in design and have several stages of treatment. The completeness of such structures is selected in accordance with the composition of the wastewater. Industrial wastewater can be toxic, acidic, alkaline, containing mechanical impurities and even radioactive.
Storm drains due to the method of formation they are also called superficial. They are also called rain or atmospheric. Drains of this type is a liquid formed on roofs, roads, terraces, and squares during precipitation. Stormwater treatment plants typically include multiple stages and are capable of removing impurities from the liquid various types(organic and mineral, soluble and insoluble, liquid, solid and colloidal). Storm drains are the least dangerous and least polluted of all.

Types of treatment facilities

In order to understand what blocks a treatment complex may consist of, you should know the main types of wastewater treatment facilities.

These include:

mechanical structures,
biorefinery installations,
oxygen saturation units that enrich already purified liquid,
adsorption filters,
ion exchange blocks,
electrochemical installations,
physical and chemical cleaning equipment,
disinfection installations.

Effluent treatment equipment also includes structures and tanks for storage and storage, as well as for processing filtered sludge.

Operating principle of the wastewater treatment complex

The complex can implement a scheme of wastewater treatment facilities with above-ground or underground design.
Treatment facilities for domestic wastewater are installed in cottage villages, as well as in small settlements (150-30,000 people), at enterprises, in regional centers, etc.

If the complex is installed on the surface of the earth, it has a modular design. In order to minimize damage, reduce costs and labor costs for repairing underground structures, their bodies are made of materials whose strength allows them to withstand soil pressure and groundwater. Among other things, such materials are durable (up to 50 years of service).

To understand the operating principle of wastewater treatment plants, let’s consider how the individual stages of the complex function.

Mechanical cleaning

This stage includes the following types of structures:

primary settling tanks,
sand traps,
debris-retaining grates, etc.

All these devices are designed to eliminate suspended matter, large and small insoluble impurities. The largest inclusions are retained by the grill and fall into a special removable container. The so-called sand traps have limited productivity, therefore, when the intensity of wastewater supply to treatment plants is more than 100 cubic meters. m per day, it is advisable to install two devices in parallel. In this case, their efficiency will be optimal; sand traps will be able to retain up to 60% of suspended matter. The retained sand with water (sand pulp) is discharged to sand pads or to a sand bunker.

Biological treatment

After removing the bulk of insoluble impurities (cleaning the wastewater), the liquid for further purification enters the aeration tank - a complex multifunctional device with extended aeration. The aeration tanks will be divided into sections of aerobic and anaerobic purification, due to which, simultaneously with the breakdown of biological (organic) impurities, phosphates and nitrates are removed from the liquid. This significantly increases the efficiency of the second stage of the treatment complex. The active biomass released from the wastewater is retained in special blocks loaded with polymer material. Such blocks are placed in the aeration zone.

After the aeration tank, the sludge mass passes into a secondary settling tank, where it is separated into activated sludge and treated wastewater.

Additional treatment

Post-treatment of wastewater is carried out using self-cleaning sand filters or using modern membrane filters. At this stage, the amount of suspended solids present in the water is reduced to 3 mg/l.

Disinfection

Disinfection of treated wastewater is carried out by treating the liquid with ultraviolet light. To increase the efficiency of this stage, biological wastewater treatment plants are equipped with additional blowing equipment.

Effluents that have passed all stages of the treatment complex are safe for the environment and can be discharged into a reservoir.

Design of treatment systems

Treatment facilities for industrial wastewater are designed taking into account the following factors:

burial level groundwater,
design, geometry, location of the supply manifold,
completeness of the system (type and number of blocks determined in advance based on biochemical analysis of wastewater or its predicted composition),
location of compressor units,
availability of free access for vehicles that will remove waste trapped by grates, as well as for sewage disposal equipment,
possible placement of the purified liquid outlet,
need to use additional equipment(determined by the presence of specific impurities and other individual characteristics object).

Important: Surface wastewater treatment facilities should be designed only by companies or organizations with an SRO certificate.

Installation of installations

The correct installation of treatment facilities and the absence of errors at this stage largely determine the durability of the complexes and their efficiency, as well as the uninterrupted operation - one of the most important indicators.

Installation work includes the following steps:

development of installation diagrams,
inspection of the site and determination of its readiness for installation,
construction works,
connecting installations to communications and connecting them to each other,
commissioning, adjustment and adjustment of automation,
delivery of the object.

The full range of installation work (list of necessary operations, volume of work, time required to complete them and other parameters) are determined based on the characteristics of the object: its productivity, completeness), as well as taking into account the characteristics of the installation site (type of relief, soil, location of groundwater and etc.).

Treatment plant maintenance

Timely and professional maintenance of wastewater treatment plants ensures the efficiency of the equipment. Therefore, such work must be performed by specialists.

The scope of work includes:

removal of retained insoluble inclusions (large debris, sand),
determining the amount of sludge formed,
checking oxygen content,
control of work according to chemical and microbiological indicators,
checking the functioning of all elements.

The most important stage in the maintenance of local treatment facilities is monitoring the operation and prevention of electrical equipment. Typically, blowers and transfer pumps fall into this category. Ultraviolet disinfection installations also require similar maintenance.

The Village continues to explain how the things that citizens use every day work. In this issue - the sewerage system. After we press the flush button on the toilet, turn off the tap and go about our business, tap water turns into waste water and begins its journey. To get back into the Moscow River, she needs to walk kilometers sewer networks and several stages of cleaning. The Village learned how this happens after visiting the city's wastewater treatment plants.

Through the pipes

At the very beginning, water enters the internal pipes of the house with a diameter of only 50–100 millimeters. Then it goes along the network a little wider - the courtyards, and from there - to the street ones. At the border of each yard network and at the point where it transitions to the street network, a manhole, through which you can monitor the operation of the network and clean it if necessary.

The length of city sewer pipes in Moscow is more than 8 thousand kilometers. The entire territory through which the pipes pass is divided into parts - pools. The section of the network that collects wastewater from the pool is called a collector. Its diameter reaches three meters, which is twice as large as a pipe in a water park.

Basically, due to the depth and natural topography of the territory, water flows through the pipes on its own, but in some places pumping stations are required, there are 156 of them in Moscow.

Wastewater goes to one of four treatment plants. The cleaning process is continuous, and peaks in hydraulic load occur at 12 noon and 12 noon. The Kuryanovsky treatment plant, which is located near Maryin and is considered one of the largest in Europe, receives water from the southern, southeastern and southwestern parts of the city. Sewage from the northern and eastern parts of the city goes to the treatment plant in Lyubertsy.

Treatment

Kuryanovsky treatment facilities are designed for 3 million cubic meters of wastewater per day, but only one and a half are received here. 1.5 million cubic meters is 600 Olympic swimming pools.

Previously, this place was called an aeration station; it was launched in December 1950. Now the treatment plant is 66 years old, and Vadim Gelievich Isakov worked here for 36 of them. He came here as a foreman of one of the workshops and became the head of the technological department. When asked whether he expected to spend his whole life in such a place, Vadim Gelievich replies that he no longer remembers, it was so long ago.

Isakov says that the station consists of three cleaning blocks. In addition, there is a whole complex of facilities for processing sediments that are formed in the process.

Mechanical cleaning

Turbid and foul-smelling wastewater arrives at the treatment plant warm. Even in the coldest time of the year, its temperature does not drop below plus 18 degrees. Wastewater is met by a receiving and distribution chamber. But we won’t see what’s happening there: the chamber was completely closed so that the smell wouldn’t spread. By the way, the smell of the huge (almost 160 hectares) wastewater treatment area is quite tolerable.

After this, the mechanical cleaning stage begins. Here, special grates trap debris that floats along with the water. Most often these are rags, paper, personal hygiene products (wipes, diapers), and also food waste - for example, potato peelings and chicken bones. “You won’t meet anything. It happened that bones and skins arrived from meat processing plants,” they say with a shudder at the treatment plants. The only pleasant thing was gold jewelry, although we did not find any eyewitnesses of such a catch. Seeing the debris-retaining grate is the most terrifying part of the excursion. In addition to all sorts of nasty things, there are many, many lemon slices stuck in it: “You can guess the time of year by the contents,” the employees note.

A lot of sand comes with wastewater, and to prevent it from settling on structures and clogging pipelines, it is removed in sand traps. Sand in liquid form is supplied to a special area, where it is washed with industrial water and becomes ordinary, that is, suitable for landscaping. Treatment plants use sand for their own needs.

The stage of mechanical cleaning in the primary settling tanks is completed. These are large tanks in which fine suspended matter is removed from the water. The water comes here cloudy and leaves cleared.

Biological treatment

Biological treatment begins. It occurs in structures called aeration tanks. They artificially support the vital activity of a community of microorganisms called activated sludge. Organic contaminants in water are the most desirable food for microorganisms. Air is supplied to the aeration tanks, which prevents the sludge from settling so that it comes into contact with waste water as much as possible. This continues for eight to ten hours. “Similar processes occur in any natural body of water. The concentration of microorganisms there is hundreds of times lower than what we create. Under natural conditions, this would last for weeks and months,” says Isakov.

An aeration tank is a rectangular tank divided into sections in which waste water snakes. “If you look through a microscope, everything there is crawling, moving, moving, swimming. We force them to work for our benefit,” says our guide.

At the outlet of the aeration tanks, a mixture of purified water and activated sludge is obtained, which now need to be separated from each other. This problem is solved in secondary settling tanks. There, the sludge settles to the bottom and is collected by suction pumps, after which 90% is returned to the aeration tanks for a continuous cleaning process, and 10% is considered excess and is disposed of.

Return to the river

Biologically purified water undergoes tertiary treatment. To check, it is filtered through a very fine sieve, and then discharged into the station’s outlet channel, on which there is an ultraviolet disinfection unit. Ultraviolet disinfection is the fourth and final stage of cleaning. At the station, the water is divided into 17 channels, each of which is illuminated by a lamp: the water in this place acquires an acidic tint. This is a modern and largest such block in the world. Although according to the old project it was not available, previously they wanted to disinfect the water with liquid chlorine. “It’s good that it didn’t come to that. We would destroy every living thing in the Moscow River. The reservoir would be sterile, but dead,” says Vadim Gelievich.

In parallel with water purification, the station deals with sediment. Sludge from primary settling tanks and excess activated sludge are processed together. They enter digesters, where at a temperature of plus 50–55 degrees, the fermentation process takes place for almost a week. As a result, the sediment loses its ability to rot and does not emit an unpleasant odor. This sludge is then pumped to dewatering complexes outside the Moscow Ring Road. “30–40 years ago the sediment was dried on sludge beds in natural conditions. This process lasted from three to five years, but now dehydration is instantaneous. The sediment itself is valuable. mineral fertilizer, V Soviet times he was popular, state farms took him with pleasure. But now no one needs it, and the station pays up to 30% of the total cleaning costs for disposal,” says Vadim Gelievich.

A third of the sludge breaks down into water and biogas, saving on disposal costs. Part of the biogas is burned in the boiler room, and part is sent to the combined heat and power plant. A thermal power plant is not an ordinary element of a wastewater treatment plant, but rather a useful addition that gives treatment plants relative energy independence.

Fish in the sewer

Previously, on the territory of the Kuryanovsky treatment plant there was an engineering center with its own production base. Employees carried out unusual experiments, for example, breeding sterlet and carp. Some of the fish lived in tap water, and part of it is in the sewer, which has been cleaned. Nowadays, fish are found only in the discharge canal; there are even signs saying “Fishing is prohibited.”

After all the purification processes, the water flows through the discharge canal - a small river 650 meters long - into the Moscow River. Here and wherever the process takes place in the open air, many seagulls swim on the water. “They don’t interfere with the processes, but they spoil the aesthetic appearance“Isakov is sure.

The quality of treated wastewater discharged into the river is much better than the water in the river in terms of all sanitary indicators. But drinking such water without boiling is not recommended.

The volume of treated wastewater is equal to approximately a third of all water in the Moscow River above the discharge. If the treatment plants failed, settlements downstream would be on the verge of environmental disaster. But this is practically impossible.

Construction country house comes with some inconveniences. One of them is the lack centralized system sewerage. Today no one wants to install “conveniences” in the yard. The solution to the problem was autonomous stations. Modern sewage treatment plants are quite compact and are able to cope with the task assigned to them.

Sewage treatment plants: operating principle

The modern market offers a huge range of treatment facilities. But the principle of operation is the same for everyone.

Stage 1. Mechanical wastewater treatment, after which the water is almost completely free of suspended impurities. Methods:

settling;
fat removal;
filtration.

Stage 2. Breakdown of organic matter remaining in clarified waters.

Clarified water is usually called the water that comes after mechanical purification. At this stage, it enters biofilters, where organic matter is broken down. As a result, sludge forms and gases are released.

Stage 3. Additional water disinfection. It happens thanks to chemical means.

Technically pure water discharged into a reservoir or onto the ground.

In conditions big city, where there is a central sewer system, the problem of wastewater bypasses private parties (subject to the proper approach of the city administration to this issue). In small villages, in country cottages you have to solve all problems yourself.

First, a design estimate for sewerage treatment facilities is drawn up. It is extremely difficult to do this without an engineering education. It is necessary to understand that no one will pat you on the head for environmental pollution in the case of an improperly constructed wastewater disposal system.

The next stage is the selection of a treatment facility. Determining indicators – type, performance.

Sewage treatment facilities for the village:

1) Storage capacity.

One of the simplest methods of organizing a local sewage system. This is a plastic container for collecting and temporarily storing wastewater. In the future, periodic pumping out of the collected material using sewage disposal equipment is required.

Advantages of sewer storage tank:

low cost;
simplest installation.

Flaws:

expensive servicing (you will have to pay for the services of vacuum cleaners every time).

It is better to choose a storage tank when a small volume of waste is expected. It is good to install it in a country house used for periodic recreation.

2) Septic tank.

Non-volatile installation made of plastic. Wastewater treatment occurs by mechanical settling and with the help of anaerobic bacteria.

You can make septic tanks yourself from

reinforced concrete;
well rings;
bricks

It is important to properly seal the chambers so that wastewater does not enter the ground.

Disadvantages of homemade septic tanks:

large amount of space for construction;
labor intensity of the construction process.

Installation finished septic tank can be completed within two to three days.

Water released from the installation cannot be discharged directly into a reservoir. It's not clean enough yet. The system needs to be further developed soil filtration. This can only be done in light soils. Build a post-treatment system in clay soils very expensive.

A layer of sand and crushed stone for post-treatment of wastewater in a professional environment is called a filtration field. Average term The service life of this field is ten years. Then you need to change the drainage layer or the location of the filtration field.

3) Aeration unit.

Device for biological wastewater treatment. Waste is not collected in any container and is not settled. Aerobic microorganisms destroy organic matter. At the exit - process water and il. A striking example aeration plant – sewage treatment plant Topas (not “Topaz”; TOP is part of the surname of Jan Topol, the developer of the system; AC – activation system).

Advantages of aeration units:

compact size, no need to equip a filtration field;
absence of noise and odor;
degree of wastewater treatment up to 98%;
the ability to choose the station’s performance (from installation for one house to installation for an entire village).

Flaws:

high cost of the station;
Requires electricity to operate.

To select a treatment facility, you need to analyze the following parameters:

the volume of waste per day (depends on the number of people living in the house and the number of plumbing fixtures; the average water consumption per person is two hundred liters);
how often will the sewer be used (only one season, like in a country house, or all year round);
topography and geology of the site (nature of the soil, depth of groundwater, distance from open reservoirs and wells, size of the site, level of soil freezing in winter time and so on.).

Storm sewer treatment facilities

Storm sewers are designed to collect and transport melted rainwater. Regular sewerage treatment not suitable for these purposes. Therefore, special structures were developed storm sewer. Their main task is to remove precipitation from the foundation of the house, lawns, road surfaces, beds, etc.

Storm drainage system:

gutters installed on the roof to collect melt water;
funnels and drainpipes, directing and transporting water to the rainwater inlet (it is equipped with a filter that prevents large debris from entering the system);
a system of pipes and trays through which water enters storage well or the nearest ravine.

Sand traps with waste collection containers are installed at various parts of the transportation system. These devices filter the flow. They will need to be cleaned periodically.

Modern sewage treatment plants are convenient installations, effectively purifying wastewater. Their proper use will ensure comfort for residents and preserve the ecology of the area.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

Operating principle of wastewater treatment plants

Treatment facilities are facilities designed to remove contaminants contained in domestic and industrial wastewater.

Water purification occurs in several stages.

Mechanical stage: wastewater treatment

Sewage carries with it a lot of garbage. To get rid of it, there are grates at the entrance. The first one is large, filters out the largest debris and protects the following gratings from damage.

The next stage of cleaning is sand traps, oblong concrete containers in which the flow of water slows down and all heavy particles precipitate.

Primary settling tanks, where water enters at the next stage, are designed to settle suspended organic matter.

These are reinforced concrete “basins” five meters deep and 40 and 54 meters in diameter. Drains are supplied to their centers from below, the sediment is collected in a central pit by scrapers running along the entire plane of the bottom, and a special float from above drives all the contaminants lighter than water into the bunker. As a result of mechanical cleaning, up to 60-70% of mineral contaminants are removed, and BOD (Biochemical Oxygen Demand) is reduced by 30%. Biological oxygen demand (BOD) is the amount of oxygen consumed for biochemical oxidation under the influence of bacteria and decomposition of unstable organic compounds contained in the water being tested. BOD is one of the the most important criteria level of pollution of the reservoir with organic substances.

It determines the amount of oxygen needed to decompose organic pollutants.

Biological Stage. From a technical point of view, there are several options for biological treatment. At the moment, the main ones are activated sludge (aeration tanks), biofilters and digesters (anaerobic fermentation)

Aerotank is a device for biological wastewater treatment, the main and most difficult stage. In the aeration tank, contaminants are decomposed and oxidized by activated sludge

For example: At the Lyubertsy wastewater treatment plant, aeration tanks are huge concrete pools 300 meters long, divided into four paths that form a “snake”. The paths are made to increase the mileage of water and to highlight special zones, each of which has its own stage of purification.

In addition to dissolved and suspended organic matter, it is necessary to remove nutrients from wastewater. These include phosphates and nitrogen compounds: nitrites, nitrates, ammonium nitrogen. Once in water bodies, they act as fertilizers. Their accumulation leads to excessive flowering, and then to the death of water bodies.

Activated sludge is flakes, which are a collection of various microorganisms that decompose and oxidize dissolved contaminants. Its composition is very diverse: mainly bacteria, as well as protozoa, rotifers, worms, aquatic fungi, and yeast.

When the oxygen supply and mixing are turned off, the activated sludge begins to die, and it can take about six months to restore it.

After the aeration tanks, the water flows into secondary settling tanks, where the remaining activated sludge is removed. The water obtained at the outlet of the secondary settling tanks is sent for post-treatment - filtration using a fine mesh of 1.6 mm. The final stage should be disinfection,

To improve cleaning parameters, various chemical methods, as well as physical and chemical methods, can be used.

For the final disinfection of wastewater intended for discharge onto the terrain or into a reservoir, ultraviolet irradiation installations are used.

To disinfect biologically treated wastewater, along with ultraviolet irradiation, which is usually used in wastewater treatment plants in large cities, chlorine treatment is also used for 30 minutes.

Chlorine has long been used as the main disinfectant in almost all wastewater treatment cities in Russia. Since chlorine is quite toxic and dangerous, treatment plants in many Russian cities are already actively considering other reagents for wastewater disinfection such as hypochlorite, desavid and ozonated.

After water purification, sediment obtained from the primary and secondary settling tanks remains. For example, Moscow wastewater treatment plants produce more than 10 million tons of sludge per year.

The sludge released from wastewater is sent for digestion into digesters - huge reinforced concrete tanks 24 meters high and with a volume of 8 thousand cubic meters. The sediment is kept in them for about seven days. The biogas obtained during the fermentation process (a mixture of methane and carbon dioxide) is burned in a boiler room located right there, the heat of which is used to heat the digesters themselves, as well as for the economic needs of the enterprise.

Digester is a device for anaerobic fermentation (methane fermentation of organic substances with the release of free methane.) of liquid organic waste to produce methane.

Purpose

Digester is one of the important elements treatment facilities. Unlike aeration tanks, they receive not the waste liquid itself, but the concentrated sediment that falls in the settling tanks.

Biological cleaning methods are based on the oxidation of organic residues using microorganisms. Unrotted sludge cannot be disposed of. In digesters, organic residues are converted into a non-decaying form without access to oxygen. The first experiments on methane fermentation of sewage waste began at the end of the 19th century. In the mid-1920s, industrial operation of digesters began in Germany, Great Britain, the USA and the USSR

Structurally, a digester is a cylindrical or, less commonly, rectangular tank that can be completely or partially buried in the ground. The bottom of the digester has a significant slope towards the center. The roof of the digester can be rigid or floating. In digesters with a floating roof, the risk of increasing pressure in the internal volume is reduced.

The walls and bottom of the digester are usually made of reinforced concrete.

Operating principle

From above, sediment and activated sludge enter the digester through a pipe. To speed up the fermentation process, the digester is heated and the contents are mixed. Heating is carried out by a water or steam radiator. In the absence of oxygen, organic substances (fats, proteins, etc.) are formed fatty acid, from which methane and carbon dioxide are formed during further fermentation.

Digested sludge high humidity removed from the bottom of the digester. The resulting gas is removed through pipes in the roof of the digester. From one cubic meter of sediment in the digester, 12-16 cubic meters of gas are obtained, about 70% of which is methane.

The main technological parameters when calculating digesters are the temperature at internal space, fermentation duration, dry organic matter productivity, concentration of processed sludge and loading mode. The most widely used modes are mesophilic (at a temperature of 32--35 °C) and thermophilic mode (at a temperature of 52--55 °C). The mesophilic mode is less energy-intensive, while the thermophilic mode allows the use of smaller volume digesters. Abroad, the mesophilic regime is more often used. At the end of the 20th century, instead of methane tanks, mechanical dewatering and chemical conditioning of unstabilized biological sediments began to be used, but these methods are less energetically profitable.

Methamn is the simplest hydrocarbon, a colorless gas (under normal conditions) and odorless.

When methane accumulates indoors, it is explosive. Explosive at concentrations in air from 4.4% to 17%. Most explosive concentration 9.5%

Explosions of steam (gas) clouds pose a serious danger. Such phenomena occur when gas leaks or evaporates flammable liquids in confined spaces (rooms), where the concentration of flammable elements quickly increases to the limit at which the cloud ignites.

On October 7, 2008, in Nizhny Tagil, on the territory of the Vodokanal-NT treatment plant, a burst of methane gas occurred in the settling chamber. 4 people were injured and received 1st and 2nd degree burns. During the investigation, it was established that the explosion occurred due to non-compliance with safety precautions: when welding a metal container that contained residual methane vapor.

Hazards associated with flammable gases

An explosion is a fairly simple chemical reaction in which oxygen quickly combines with other substances, releasing energy.

An explosion always requires three factors:

1. Ignition source (spark, flame)

2. Oxygen

3. Fuel in the form of gas or steam

Therefore, the goal of any fire protection system is to eliminate at least one of these three potential hazards.

The formation of an explosive mixture occurs only in a certain range of gas/air concentrations. This range is specific to each gas and vapor and is limited by an upper level known as the “upper explosive limit” and a lower level known as the “lower explosive limit.”

At values below the lower explosive limit there is not enough gas to explode (that is, the mixture is not concentrated enough), and at values above the upper explosive limit there is not enough oxygen in the mixture (that is, the mixture is too concentrated). Therefore, the flammability range is between the lower explosive limit and the upper explosive limit for each gas or mixture of gases. Outside these limits, the mixture is not capable of burning.

On average industrial enterprise There are usually no gases that can be released into the environment. In extreme cases, only minor background levels of gas present are observed. Therefore, detection and system early warning necessary only for the purpose of detecting gas concentrations between zero and the lower explosive limit. Once this concentration is reached, equipment shutdown or area cleanup procedures will be required. In reality, this is done at a concentration of less than 50% of the LEL, thus providing the necessary safety margin.

However, it must always be remembered that in confined or unventilated areas, concentrations in excess of the upper explosion limit may be formed. Therefore, during the inspection, it should be remembered that when doors and hatches are opened and air enters from outside, a decrease in the concentration of gases can lead to the formation of a dangerous, flammable mixture.

Properties of methane

Ignition temperature.

Combustible gases have a temperature at which ignition occurs, even if there is no ignition source, such as a spark or flame. This temperature is called the ignition temperature..(595. °C)

Flash point (<-20 °C)

The flash point of a flammable liquid is the lowest temperature at which the surface of the liquid will give off sufficient vapor to cause ignition from a small flame.

Vapor Density(0.55)

Helps solve the issue of sensor location

Gas/vapour density is determined in comparison with air

Other accidents

Causes of accidents at wastewater treatment plants:

Power outage;

Depreciation of equipment;

Weather and natural disasters (severe frost, floods);

Human factor (inattention of personnel, terrorist attacks);

Non-standard operation of treatment facilities (the volume of contaminated material is greater than planned, treatment facilities are not designed to destroy individual substances and components, etc.).

Consequences of accidents at wastewater treatment plants:

The main consequence of accidents at wastewater treatment plants is environmental pollution, up to and including environmental disaster.

Examples of accidents:

In Zaporozhye, due to the failure of water treatment facilities, untreated sewage water entered water bodies.

Due to a hole in the cable, there was a disconnection from the power supply at KNS-7 (the sewerage and pumping station of the Vodokanal utility company), the Zaporozhye territorial department of the Ministry of Emergency Situations reported. Thousands of cubic meters of untreated sewage flowed into the Mokraya Moskovka River, which flows into the Dnieper.

In the Kharkov region, 4.5 thousand cubic meters of sewage flowed into the Udy River, the reason for this was an accident at the treatment facilities in the village of Eskhar. The equipment failed partly due to severe frosts, and partly due to the fact that it was not repaired for almost a third of a century.

Posted on Allbest.ru

Construction of urban sewerage treatment facilities. Sewage treatment facilities OS, WWTP, BOS. Biological wastewater treatment

Stages of wastewater treatment

Mechanical stage of wastewater treatment

Biological wastewater treatment plants

Wastewater tertiary treatment

Ultraviolet water disinfection

Phosphate removal

Auxiliary premises of treatment facilities

Aeration shop

Disposal of excess activated sludge (microorganisms)

Air cleaning

Laboratory at wastewater treatment plants

Administrative and amenity complex

Conclusion

Types of treatment facilities

City wastewater treatment plants

Local treatment facilities

Treatment facilities for a private home.

Stormwater treatment plants

Design of wastewater treatment plants

Installation of treatment facilities

Treatment plant maintenance

Types of wastewater

Types of treatment facilities

Operating principle of the wastewater treatment complex

Mechanical cleaning

Biological treatment

Additional treatment

Disinfection

Design of treatment systems

Installation of installations

Treatment plant maintenance

Through the pipes

Treatment

Mechanical cleaning

Biological treatment

Return to the river

Fish in the sewer

Sewage treatment plants: operating principle

Storm sewer treatment facilities

Send your good work in the knowledge base is simple. Use the form below

Similar documents