Wastewater treatment - methods and special equipment. Wastewater Treatment Methods - An overview of the three main water treatment methods.

Wastewater treatment means their special treatment in order to remove harmful substances present in it. At the moment, a lot of cleaning methods have been developed and used. The choice in favor of one or another method of wastewater treatment directly depends on the characteristics of pollution and a whole list of conditions. Let's take a quick look at each of these methods.

The essence of the mechanical method of wastewater treatment is that all kinds of impurities are excluded from the polluted wastewater by means of mechanical filtration. Particles of various kinds are retained by special fine grates, sieves, petrol catchers and other cleaning elements. Mechanical cleaning systems remove up to 70% of contaminants.

The essence of the chemical method is that specific chemicals are supplied to the wastewater, which affect the pollution, which leads to their precipitation in the form of precipitation. With the help of such wastewater treatment systems, a decrease in the index of insoluble impurities up to 95% is ensured. This method is considered one of the most effective among all existing ones.

The essence of the biological method is to use for the purification of the biochemical and physiological principles of self-purification of natural reservoirs. The main role in industrial biological treatment systems is played by bacteria, which are added to the effluent and which purify it. The biological treatment scheme is shown in the photo.

The essence of the physicochemical method of wastewater treatment is to remove finely dispersed substances from them and to destroy poorly oxidized compounds. Most modern industrial physical and chemical treatment plants and equipment use wastewater treatment methods such as sorption, coagulation and extraction.

Let's consider each cleaning method and each cleaning system in more detail.

Biological wastewater treatment

As already mentioned, this cleaning method is based on the ability of certain microorganisms to mineralize organic matter. It is according to this cleaning system that natural self-purification is carried out in reservoirs and rivers. To accelerate the cleaning by this method in biological plants and equipment, special bacteria are used, which accelerate the biological cleaning process and increase its efficiency.

The biological method uses aerobic and anaerobic microorganisms.

• Aerobic bacteria only exist in an environment where oxygen is present. Under the influence of such bacteria, organic substances are completely destroyed to carbon dioxide and water. The independent aerobic method is rarely used in biological purification: as a rule, it is used in conjunction with the anaerobic purification method.
• Anaerobic bacteria during biological treatment can exist in an environment in which there is no oxygen. Typically, anaerobic purification systems are used in conditions of high concentration of organic matter, which exceeds the acceptable level for aerobic microorganisms. Moreover, in the case of a low level of organic matter content, the anaerobic purification method is ineffective. That is why in most cleaning systems, after cleaning with anaerobic microorganisms, an additional cleaning is performed with aerobic bacteria.

The principle of biological treatment technology is discussed in detail in the video below.

Mechanical

The mechanical cleaning method is used to separate sufficiently large contaminants from wastewater by filtering or filtration. The main features of the mechanical cleaning method are as follows:

• To remove coarse-grained substances, a method of filtering effluents through gratings and all kinds of sieves is used.
• To exclude substances with a higher / lower particle density (in comparison with water) from the effluent, the sedimentation method is used. With the method of settling, the lightest compounds float to the surface, and the heaviest ones precipitate.
• To remove various mineral contaminants, the sedimentation method is used with the use of special sedimentation tanks. A photo of the sedimentation tanks is shown below.
• To remove light compared to water substances (oils, oil, fats), which float to the surface during cleaning, special treatment plants are used - oil catchers, oil catchers, etc. Most of this method and equipment are used for industrial wastewater treatment.

Most often, mechanical treatment methods and mechanical treatment equipment are used in the treatment of industrial wastewater. In all other cases, mechanical cleaning is used as an initial cleaning before biological treatment.

The technology of mechanical purification of effluents is discussed in detail in the video:

Chemical

Chemical wastewater treatment systems use special chemicals to remove contaminants. In particular, chlorine, lime, hydrochloric acid are used.

Chemical wastewater treatment is carried out in several stages:

1. Contamination neutralization. This method involves mixing acidic wastewater with alkaline and subsequent filtration through appropriate substances. At the same time, dolomite, cement, and ammonia water are used in the acid water neutralization technology.

1. Oxidation. Oxidation is performed to decontaminate contaminants in the wastewater treatment process. Sodium chlorate, ozone, liquefied chlorine, etc. are used as oxidants. It should be noted that the most effective oxidizing agent is fluorine. However, it is rarely used at stations and in systems, since it is a rather corrosive chemical. Chlorine is the most common oxidizing agent used in industrial plants and chemical wastewater treatment systems.

Chemical wastewater treatment is discussed in detail in the video.

Physicochemical cleaning methods

This cleaning method can be used both independently and in conjunction with other methods and technologies - chemical, mechanical and biological cleaning.

The most common methods of physicochemical purification of wastewater include coagulation, ion exchange, and flotation. Let's consider each of these methods in more detail:

1. The coagulation method involves the preparation of special solutions containing flocculants and coagulants. Such solutions are added to the wastewater plant. As a result of the reaction, flakes are formed from the contaminants, which are subsequently removed by the mechanical processing system.
2. The method of ionic cleaning involves the selection of ions from a special electrolyte solution in exchange for the same amount of ion exchanger ions. This wastewater treatment method is reversible and can be used not only for wastewater treatment, but also in equipment and installations designed to soften water.
3. The flotation method involves the introduction of air bubbles into the wastewater. In doing so, dirt particles adhere to these bubbles, which leads to the formation of foam on the surface. If the contaminating particles, due to their properties, do not adhere to the bubbles, then special reagents are added to the cleaning system. Subsequently, foam with contaminants is removed mechanically. A photo of the foamy substance is shown below.

Equipment for cleaning by flotation method is used most often in industrial and manufacturing enterprises involved in the processing of petroleum products. Photo of waste water flotation system.

The technology of physicochemical removal of contaminants is discussed in the video below.

Wastewater treatment equipment

For maximum clarity, we will consider modern systems, equipment and installations used for the treatment of industrial and domestic sewage.

Sewage pumping station

Such a station is designed and used for pumping wastewater in cases where it is not possible to transport it by gravity. Depending on the requirements and operating conditions, industrial pumping stations for pumping sewage can be self-priming or submersible. A photo pump station presented below.

Station for mechanical wastewater treatment

The system is intended for the initial treatment of wastewater from pollution by sedimentation. The main structural element of most industrial mechanical cleaning stations is a sand separator. It is with the help of this system that wastewater is purified from coarse pollutants. A photo of an industrial plant for mechanical wastewater treatment is shown below.

Grease system

The grease collection system is designed to separate fats of various origins from waste water. The grease trap is an obligatory equipment of the sewer system, since the accumulation of fat significantly reduces the throughput of the entire system. Grease collection systems are used in the treatment of industrial polluted water. The fat trapping system is shown in the photo below.

Biological wastewater treatment plant

Such a station is a kind of square-shaped container made of stainless steel alloy or fiberglass. The principle of operation of such a system is based on the use of certain microorganisms and the alternation of aerated zones with sludge recirculation. This method and such systems are widely used in the organization of household, non-industrial sewer systems. A photo of an industrial station for biological wastewater treatment is displayed below.

Equipment for biological treatment can be buried or above ground. In industry, as a rule, underground biological treatment plants are used. Ground-based biological treatment plants are used if an underground installation is impossible or it is necessary to obtain a mobile wastewater treatment plant. A photo of the mobile cleaning station is shown below.

It should be noted: very often a biological treatment plant is called an aeration tank. This name was given to the biological treatment plant due to the use of treatment technology by means of aerobic bacteria. A photo of the aerotank is displayed below.

Chemical wastewater treatment plant

Plants that use chemical technology for wastewater treatment are intended primarily for building treatment systems in large industries. It should be noted that there are no universal industrial installations for such waste treatment, as well as universal treatment technologies. In each specific case, a specific station is required, which is designed to carry out chemical cleaning of certain contaminants and uses an appropriate cleaning method in its work. If the system of chemical purification cannot be limited to only one such technology is used in combination with mechanical or physicochemical purification of wastewater.

A photo of the chemical treatment station is shown below.

Membrane cleaner

This system can be called one of the most advanced among all existing ones. The main advantage of such a plant is the treatment of waste water at the molecular level. After passing through such a system, the purified water can subsequently be used for certain technological and production processes. Photos of industrial membrane equipment:

Wastewater treatment plant

Let us consider in detail the most common options for wastewater treatment plants that are used in household wastewater treatment systems. Most often, when creating sewage systems in private houses, biological wastewater treatment plants are used. The principle of operation of such a system is as follows:

Initial wastewater treatment is carried out in the so-called septic tank. A septic tank is a special chamber in which organic pollutants are decomposed by anaerobic bacteria. Of course, to ensure the fermentation process in the septic tank, oxygen is excluded. A photo of the septic tank is displayed below.

Anaerobic purification technology is carried out by hydrolysis of organic compounds into less complex particles. In order to increase the efficiency of anaerobic cleaning, use special equipment - a bioreactor, which is a special filler that has a honeycomb with anaerobic bacteria. Thanks to these cells, the efficiency of the treatment plant is significantly increased. A photo of the bioreactor is shown below.

Wastewater treatment technology: video

For maximum clarity, we suggest you watch a video in which the wastewater treatment technology is discussed in detail.

In rivers and other bodies of water, a natural process of self-purification of water takes place. However, it is slow. While industrial discharges were small, the rivers themselves coped with them. In our industrial age, due to a sharp increase in waste, water bodies can no longer cope with such significant pollution. It became necessary to neutralize, purify waste water and dispose of it.

Wastewater treatment - treatment of wastewater with the aim of destroying or removing harmful substances from it. Elimination of pollution from wastewater complex production. In it, as in any other production, there are raw materials (waste water) and finished products (purified water)

Wastewater treatment methods can be divided into mechanical, chemical, physicochemical and biological, but when they are used together, the method of purification and disposal of wastewater is called combined. The application of this or that method in each specific case is determined by the nature of the pollution and the degree of harmfulness of impurities.

The essence of the mechanical method is that mechanical impurities are removed from wastewater by sedimentation and filtration. Coarse particles, depending on their size, are captured by gratings, sieves, sand traps, septic tanks, manure catchers of various designs, and surface contaminants - by oil traps, oil separators, sedimentation tanks, etc. up to 95%, many of which are used as valuable impurities in production.

The chemical method consists in the fact that various chemical reagents are added to wastewater, which react with pollutants and precipitate them in the form of insoluble sediments. Chemical cleaning achieves a reduction of insoluble impurities up to 95% and soluble impurities up to 25%.

With the physicochemical method of treatment, finely dispersed and dissolved inorganic impurities are removed from wastewater and organic and poorly oxidizable substances are destroyed, most often from physicochemical methods coagulation, oxidation, sorption, extraction, etc. are used. Electrolysis is also widely used. It consists in the destruction of organic substances in wastewater and the extraction of metals, acids and other inorganic substances. Electrolytic cleaning is carried out in special structures - electrolyzers. Wastewater treatment using electrolysis is effective in lead and copper plants, paint and varnish and some other industries.

Contaminated waste water is also treated with ultrasound, ozone, ion exchange resins and high pressure, cleaning by chlorination has proven itself well.

Among the methods of wastewater treatment, a biological method based on the use of the laws of biochemical and physiological self-purification of rivers and other bodies of water should play an important role. There are several types of biological wastewater treatment devices: biofilters, biological ponds, and aeration tanks.

In biofilters, wastewater is passed through a layer of coarse-grained material covered with a thin bacterial film. Thanks to this film, biological oxidation processes proceed intensively. It is she who serves as an active principle in biofilters.

In biological ponds, all organisms that inhabit the reservoir take part in wastewater treatment.

Aerotanks are huge reinforced concrete reservoirs. Here, the cleansing principle is activated sludge from bacteria and microscopic animals. All these living things develop rapidly in aeration tanks, which is facilitated by organic matter of wastewater and excess oxygen entering the structure by the flow of supplied air. The bacteria stick together in flakes and secrete enzymes that mineralize organic pollution. Sludge with flakes quickly settles, separating from the purified water. Ciliates, flagellates, amoebas, rotifers and other tiny animals, devouring bacteria that do not stick to flakes, rejuvenate the bacterial mass of sludge.

Wastewater is subjected to mechanical treatment before biological treatment, and then to remove pathogenic bacteria and chemical treatment, chlorination with liquid chlorine or bleach. Other physicochemical methods are also used for disinfection (ultrasound, electrolysis, ozonation, etc.)

The biological method gives great results in the treatment of municipal wastewater. It is also used in the treatment of waste from oil refining, pulp and paper industries, and the production of artificial fibers.

One of the signs of the improvement of the building is the presence of water in the house, and where there is a water supply system, there must be drainage and sewage treatment. Where central sewerage systems have been built, waste disposal is the concern of Vodokanal. But the solution to the problem of water supply and wastewater disposal in a private house is, often, the concern of the owner.

One of the major sources of pollution of water bodies and groundwater is sewage. Of course, today nowhere is polluted wastewater simply dumped onto the ground or into the river. Wastewater is collected and processed in special installations. Let's consider what modern technologies for wastewater treatment can be used.

What is waste water?

Before the technological scheme of wastewater treatment is developed, it is necessary to figure out what exactly is planned to be treated. Waste water is water that has been somehow contaminated during its use for industrial or domestic needs.

The nature of wastewater pollution

To choose the right equipment for wastewater treatment, you need to know the nature of their pollution. Allocate the following types contaminants that may be present in wastewater:

• Mineral pollution. This type of pollution includes all types of impurities that are of inorganic origin. These can be soil particles, various salts and other inorganic chemical compounds.
• Organic. Organic impurities include sewage, which contains residues of plant and animal origin. This group of impurities includes pollution, which includes various organic chemical compounds, including polymeric ones.

• Biological. The category of biological pollution includes the content of various microorganisms in the effluent, for which the wastewater is a nutrient medium.

Advice! As a rule, the effluents contain all three components in different proportions. In ordinary household wastewater, the ratio of organic and mineral impurities is 3 to 2. The composition and amount of the biological component depends on the presence of microorganisms in the environment, as well as on the specific content of the wastewater.

Cleaning standards

The used wastewater treatment technology must ensure the required degree of processing. It must be said that strict standards exist only in industry.

Moreover, it regulates the content of each individual substance in purified water. For example, purification of waste water from iron should be done so that the content of this substance at the outlet from the installation does not exceed 0.1 mg per liter.

The treatment of domestic wastewater is not so strictly regulated, however, the owners of private houses and summer cottages should be aware that if untreated wastewater is discharged onto the ground, and even more so into water bodies, they may be brought to administrative responsibility.

Advice! To date, only the maximum permissible content of various substances in wastewater discharged into the reservoir has been legally regulated. But during the inspection, the regulatory authorities may impose similar requirements in the event that the effluents are discharged onto the relief (into a ravine, a ditch dug with a slope, etc.).

This approach is motivated by the considerations that when discharged onto the relief, the runoff will sooner or later fall into the reservoir. When discharging onto the ground, there are no such strict requirements, but since in this case, the ecology of his own site may first of all suffer, the owner himself should be interested in ensuring a high degree of water purity at the outlet of the installation.

Household wastewater treatment methods

Consider what methods of wastewater treatment are used for a cottage or in the country. Modern installations and filters for wastewater treatment can achieve such a degree of filtration that the water can be reused.

Of course, not as drinking, but for household use. For example, for watering the garden, washing paths, etc. In installations used in the country or for a cottage, the following cleaning methods are used:

• Mechanical (filtration, settling).
• Biological (waste processing by bacteria).
• Physicochemical (coagulation, adsorption, etc.) and chemical (due to the addition of various chemicals).

Let's consider them in more detail.

Mechanical method

Mechanical wastewater treatment, in most cases, is used at the initial stage of wastewater filtration measures, but the country sewage system can use this method as the main one. Its main purpose is to separate coarse inclusions. This can be done by installing filters or using sedimentation tanks.

Advice! The efficiency of wastewater treatment by the mechanical method is low, the filtration level is 60-70%. Sedimentation is widely used in the processing of industrial effluents. It is with the help of mechanical methods that most of the oil products can be removed from wastewater, therefore this way widely used in oil refineries and car washes.

In addition, mechanical cleaning methods are the simplest and cheapest. There are three main methods:

• Defending;
• Filtration;
• Straining.

The mechanical method is used to treat storm wastewater, since it contains mainly only large debris - soil particles, leaves, branches, etc. As a rule, in systems storm sewer the so-called sand traps are installed - a system of sedimentation tanks that does not allow debris to enter the system.

Biological method

In most cases, domestic wastewater treatment is carried out using biological methods. This method is based on the natural ability of the environment to clean itself. Today, several types of biological wastewater treatment plants are used:

• Biofilter. Biofilters for wastewater treatment function as follows: water seeps through a layer of coarse-grained material (for example, sand or crushed stone), covered with a thin film of bacteria. Local sewerage installations such as filter wells or aeration fields work according to this principle. In biofilters, aerobic and anaerobic wastewater treatment can be used simultaneously.
• Bioponds. Biological ponds are natural or artificially created reservoirs in which wastewater is purified by natural biological processes.
• Aeration tanks are closed tanks for biological wastewater treatment, in which oxygen is forcedly supplied. Aerotanks are used in deep cleaning stations, which provide a full cycle of wastewater filtration, that is, a set of methods is used inside. The main stages of wastewater treatment: preliminary sedimentation and mixing with activated sludge. Activated sludge is a symbiosis of bacteria and other microorganisms that promote the decomposition of organic matter. This is followed by aerobic wastewater treatment: wastewater flows into aeration tanks, where activated sludge filters wastewater. At the next stage, the water containing activated sludge leaves the aeration tanks and is sent for additional sedimentation, where the activated sludge is deposited. After that, water is supplied to the outlet.

Advice! Periodically, aeration tanks will need to be cleaned by pumping activated sludge. The pumped out substance can be used to fertilize plantings in the country.

• Membrane waste water treatment. A membrane bioreactor is used to treat domestic wastewater in industrial sewerage systems. Filtration using membranes allows you to remove even the smallest suspended matter.

Physicochemical and chemical methods

Household, that is, intended for servicing housing, wastewater treatment scheme rarely includes physical, chemical and chemical methods of wastewater treatment, but in the construction of industrial facilities, biochemical wastewater treatment is widely used.

For example, the coagulation method improves the efficiency of the deposition processes, as it promotes the "sticking" of the smallest particles into larger compounds. The adsorption method is also effective, which allows you to separate most of the harmful inclusions contained in the effluents.

Adsorption purification is used to extract certain substances as an auxiliary method. Using adsorbents, you can effectively purify water from impurities of fertilizers, surfactants, dyes, etc.

Chemical types of purification are considered to be the disinfection of primary purified waters by treatment with chlorine, potassium permanganate or other substances that can destroy pathogenic inclusions.

How to choose a treatment plant?

If a purification unit is selected, the following criteria should be followed:

• Reliability and durability. Ideally, the resource of the treatment plant should be comparable to the service life of the building.
• Ease of operation. A good installation requires a minimum of maintenance.
• Cleaning quality. The selected structure must provide a high degree of wastewater treatment.
• Adequate performance. The selected installation must be able to efficiently process the amount of wastewater that is generated in the house.

So, the treatment of domestic wastewater is a mandatory measure when building a residential building with a sewage system. Various types of treatment can be used for wastewater treatment, their choice is carried out depending on the nature of wastewater pollution.

Discharge into the environment of domestic and industrial wastewater without preliminary treatment would entail a real environmental disaster.

As the chemical composition of waste becomes more diverse and aggressive as technology develops, wastewater treatment methods are constantly being improved.

Due to the wide variety of soluble and insoluble pollutants in wastewater, it is not possible to create a universal method for their neutralization and removal.

Therefore, a whole set of techniques is used at treatment plants, each of which is focused on working with one or another group of substances.

All these techniques can be divided into several categories:

1. Mechanical.
2. Chemical.
3. Biological and biochemical.
4. Physicochemical.

Each of the listed cleaning technologies includes several stages that require the use of certain technical devices, chemicals and biologically active preparations.

Wastewater treatment methods

Let us consider in more detail how exactly the waste disposal is carried out. See below for physicochemical and other wastewater treatment methods.

Chemical methods of wastewater treatment

Based on the use of chemicals, resulting in one of three processes:

1. Neutralization: this method is designed to neutralize acids and alkalis by converting them into harmless substances. These pollutants have to be dealt with in wastewater treatment industrial enterprises... If both acidic and alkaline effluents are available, they can be neutralized by simple mixing. To neutralize acidic waters, alkaline waste, caustic soda, soda, chalk and limestone are used. To implement this method, filters and various devices are installed at enterprises.
2. Oxidation: those types of pollution that cannot be neutralized by other means are subjected to oxidation. Oxygen, potassium dichromate and permanganate, sodium and calcium hypochlorite, bleach and other reagents are used as oxidants.
3. Recovery: using this method, you can neutralize compounds of chromium, mercury, arsenic and some other elements that are easily recoverable. The reagents are sulfur dioxide, sodium hydrosulfite, hydrogen and ferrous sulfate.

Industrial water treatment

Disinfection of purified water is carried out using gaseous chlorine or bleach.

Biochemical

Within the framework of this technique, in addition to chemical reagents, various microorganisms are used that consume organic contaminants as food. Treatment plants, the operation of which is based on this principle, can be divided into two groups:

1. Working in natural conditions: they can be reservoirs (bioponds), or "land" structures (irrigation field and filtration field), in which soil additional treatment of wastewater takes place. Such stations have low efficiency, require large areas and are highly dependent on climatic factors.
2. Working under artificial conditions: by artificially creating more comfortable conditions for microorganisms, the effectiveness of cleaning can be significantly increased.

The structures in the latter category are divided into three types:

• aerotanks;
• biofilters;
• aerofilters.

Anaerobic cleaning system with subsequent MBR cleaning

Biofilter Is an installation in which there is a filter bed made of expanded clay, slag, gravel, or similar material. Colonies of microorganisms form a film on it.

Air filter is arranged in a similar way, but it provides for forced air supply to the filter layer. This makes it possible to increase its power up to 4 meters and make the oxidation processes much more intense.

In aeration tanks useful biomass exists in the form of activated sludge, which, using various mechanical devices mixed with incoming wastewater into a homogeneous mass.

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Biological

A biological method is used to process wastewater containing only organic pollution. It differs from biochemical only in the absence of chemicals.

The most productive are aerobic microorganisms, which require oxygen to function.

If they work in a structure with artificial conditions, or in a biopond, air has to be pumped into the drains using a compressor. Less costly, but also less productive are anaerobic bacteria that do not use oxygen.

To increase the degree of biological filtration, the processed wastewater is subjected to additional treatment. In most cases, multi-layer sand filters or so-called contact clarifiers are used for this. In rare cases, microfilters are used.

If the effluent contains substances that are difficult to oxidize, they can be filtered using activated carbon or other sorbent, or chemical oxidation can be used, for example, using ozone.

In the course of biological purification, the water gets rid of toxic substances, but is saturated with phosphorus and ammonium nitrogen.

If such water is discharged into a natural reservoir, these elements will provoke a "population explosion" among algae (phosphorus in an amount of 1 mg provides the appearance of 115 mg of biomass), which is undesirable for the ecosystem of the reservoir.

Biological water treatment at the enterprise

Two methods are used to remove nitrogen:

1. Physico-chemical: water is subjected to liming, due to which its pH increases to 10-11 units. The resulting ammonia is removed in the cooling towers by air stripping.
2. Biological.

The biological method is carried out in stages:

• First, with the help of special bacteria in the aerotank, the purified water is nitrified.
• Further, the liquid enters a hermetically sealed container - a denitrifier, where bacteria without access to air destroy the molecules of nitrites and nitrates (molecular nitrogen is released) by splitting off the oxygen necessary for life.

To remove phosphorus, lime is added to the water, as well as aluminum or iron salts. Phosphorus reacts to form precipitated compounds.

Physicochemical cleaning methods

1. Coagulation: special reagents are added to the effluents - the so-called coagulants and flocculants. Their action is accompanied by various effects: soluble contaminants can turn into insoluble flakes, which can be removed by straining; hazardous components break down into safe ones; the reaction of the waste masses changes, for example, from acidic to neutral.
2. Ion exchange method: most often used for the purpose of water softening. The essence of the method consists in replacing "unwanted" ions (in the case of softening - magnesium and calcium) with "harmless" ones, for example, sodium.
3. Flotation: the wastewater treatment method is aimed at separating oil products. Air is supplied to the waste mass, forming a lot of bubbles. Particles of petroleum products tend to stick to such bubbles, as a result of which they appear on the surface in the form of foam. It can be removed by means of special scrapers or by raising the water level - while the foam itself will drain into the receiving tray.

Physical and chemical water treatment process

If the contaminants do not have sufficient "stickiness", it is stimulated by the introduction of special reagents.

There are several types of flotation: pressure, mechanical, biological, foam, pneumatic.

In addition to these methods, within the framework of physicochemical cleaning, reverse osmosis, evaporation, extraction and more.

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Mechanical and physical methods

Mechanically get rid of insoluble inclusions. In most cases, this stage is preliminary and is used in combination with other types of cleaning. This technique includes three stages.

Upholding

Also often referred to as gravity cleaning. In the course of settling, impurities with a higher density than that of water are collected at the bottom, and the lungs float. The latter include many impurities characteristic of industrial effluents: oils (the sump is called an oil catcher), fats (grease traps), oil (oil traps) and resins (resin traps). Previously, separate grease traps were also used for cleaning domestic wastewater, but today their function is assigned to special devices that are equipped with sedimentation tanks.

To remove sand and other suspensions of a mineral nature, a special type of sedimentation tank is used - sand traps. They can be tubular, static and dynamic.

Gravity Sump

Due to the peculiarities of the technology, only 80% of the impurities amenable to such treatment can be isolated by the gravity cleaning method. On average, this amount is only 60% of the total volume of undissolved impurities. To make sedimentation more effective, methods such as clarification with a weighted filter, biocoagulation and preareration (sometimes with or without excess sludge) are used.

Straining

To screen out large suspended particles (the density is almost equal to the density of water), the effluents are filtered through grates and sieves installed in their path.

Filtration

The method is similar to filtering, but aimed at removing impurities of smaller fractions.

Instead of sieves, cloth, porous or fine-grained filters are used.

There are special devices - micro-strainers, which are a drum equipped with a mesh. The sifted impurities are washed into the trapping hopper by a stream of water beating from special nozzles.

Video on the topic

Wastewater is treated different ways: mechanical, chemical, mechanochemical, physicochemical and biochemical (or biological).

Mechanical cleaning used to remove suspended solids and partially colloidal contaminants from wastewater. For mechanical cleaning, grids, sand traps, sedimentation tanks, grease traps, oil traps, oil separators, hydrocyclones, filters and other structures are used. The grates are used to trap large contaminants (rags, washcloths, paper, etc.), sand traps - to trap undissolved mineral impurities (sand, slag, glass breakage, etc.), sedimentation tanks - to purify wastewater from suspended solids.

Under the influence of gravity of the particle, specific gravity which is more than the specific gravity of water, fall to the bottom of the structures, forming a sediment. At the same time, particles whose specific gravity is less than the specific gravity of water (fats, oils, oil) float to the surface. Sediment and floating contaminants are removed from structures and sent for treatment.

Grids, sand traps and sedimentation tanks are indispensable components of the complex of structures used for the treatment of domestic wastewater.

Grease traps, oil traps and oil separators are used to remove large amounts of fats, oil and oils from industrial wastewater. These facilities are similar to sedimentation tanks, but have equipment to remove large amounts of floating contaminants. At the same time, they also serve to purify water from settling substances.

Hydrocyclones can be used to clean industrial waste water from suspended solids with a large specific gravity (mineral pollution). Their body has a cylindrical-conical shape. Water is supplied to the body of the apparatus tangentially at high speeds. The release of suspended matter occurs under the action of centrifugal force. To purify industrial wastewater from fine suspended solids, fabric, mesh or sand filters are used.

Chemical cleaning consists in the separation of contaminants from wastewater by carrying out reactions between them and the reagents introduced into the water. These reactions are oxidation and reduction reactions, reactions of formation of precipitated compounds, and reactions accompanied by gas evolution. Chemical treatment is used to treat only some industrial wastewater.

Mechanochemical cleaning used to separate undissolved contaminants from wastewater. Its essence lies in the fact that coagulants are added to the water, which help to remove impurities from it during its mechanical cleaning.

Physical and chemical methods wastewater treatment includes sorption, extraction, evaporation, coagulation, flotation, electrolysis, ion exchange, crystallization, etc.

Biochemical (biological) treatment consists in the oxidation of organic contaminants remaining in the water after mechanical cleaning with the help of microorganisms capable of mineralizing organic substances in the course of their vital activity. Biochemical wastewater treatment can occur in conditions close to natural (irrigation fields, filtration fields and biological ponds), and in artificially created conditions (biological filters and aerotanks).

Irrigation fields, bioplato and filtration fields are specially prepared and planned land plots that are periodically flooded with sewage. Microbial life develops in the upper layer of earth or rubble. The biological film of microorganisms formed on the particles of the earth, crushed stone, adsorbs and mineralizes organic substances. Oxygen, necessary for the life of microorganisms, penetrates into the soil from the air or through the roots of plants, for example, reeds, reeds. Irrigation fields are used simultaneously for wastewater treatment and for agricultural purposes (for growing crops) and are divided into communal and agricultural irrigation fields. Filtration fields are only used for waste water treatment. In biological ponds, wastewater treatment is also carried out by microorganisms-mineralizers, and the oxygen necessary for their life comes from the air through the surface of the water in the reservoir.

Wastewater treatment in irrigated fields, bioplato and filtration fields is rather slow. It is carried out much more intensively on biological filters and in aeration tanks.

For disinfection (disinfection) of wastewater, they are treated with bleach or chlorine.

For contact of bleach or chlorine with water, contact tanks are constructed, the design of which is similar to the design of sedimentation tanks.

The treatment of the sludge formed during the wastewater treatment process consists in fermentation (decomposition), dehydration and drying. Fermentation is a biochemical process of decomposition of the solid phase of the sediment under the action of anaerobic microorganisms without access to oxygen. In the process of fermentation, up to 30-40% of organic matter decomposes. The sediment loses its ability to decay. At low wastewater flow rates - up to 10000m 3 / day - the facilities for sludge digestion are combined with sedimentation tanks. Such combined structures include septic tanks and two-tier sedimentation tanks. With significant wastewater consumption - more than 10,000 m 3 / day - independent structures - digesters - are used for sludge digestion. Dehydrate the sludge or sludge beds, or mechanically on vacuum filters, filter presses or centrifuges. In some cases, the precipitate is subjected to thermal drying.

Sediments of domestic and industrial wastewater in some industries are a good fertilizer and are used in agriculture.