Water purification technologies at Vodokanal stations. Analysis of tap water How water is purified at a water utility

Water at modern water supply stations undergoes multi-stage purification to remove solid impurities, fibers, colloidal suspensions, microorganisms, and to improve organoleptic properties. The highest quality result is achieved by a combination of two technologies: mechanical filtration and chemical treatment.

Features of cleaning technologies

Mechanical filtration. The first stage of water treatment allows you to remove visible solid and fibrous inclusions from the medium: sand, rust, etc. During mechanical treatment, water is successively passed through a series of filters with decreasing cell sizes.

Chemical treatment. Technology is used to bring chemical composition And quality indicators water to normal. Depending on the initial characteristics of the medium, treatment may include several stages: settling, disinfection, coagulation, softening, clarification, aeration, demineralization, filtration.

Methods of chemical water purification at waterworks

Advocacy

At water supply stations, special tanks with an overflow mechanism are installed or reinforced concrete settling tanks are installed at a depth of 4–5 m. The speed of water movement inside the tank is maintained at a minimum level, and the upper layers flow faster than the lower ones. Under such conditions, heavy particles settle to the bottom of the tank and are removed from the system through drainage channels. On average, it takes 5–8 hours for water to settle. During this time, up to 70% of heavy impurities settle.

Disinfection

Purification technology is aimed at removing dangerous microorganisms from water. Disinfection installations are present in all water supply systems without exception. Disinfection of water can be done by irradiation or the addition of chemicals. Despite the advent of modern technologies, the use of chlorine-based disinfectants is preferable. The reason for the popularity of the reagents is the good solubility of chlorine-containing compounds in water, the ability to remain active in a moving environment, and to have a disinfecting effect on the internal walls of the pipeline.

Coagulation

The technology allows you to remove dissolved impurities that are not captured by filter meshes. Polyoxychloride or aluminum sulfate and potassium-aluminum alum are used as coagulants for water. The reagents cause coagulation, that is, the sticking together of organic impurities, large protein molecules, and suspended plankton. Large heavy flakes form in the water, which precipitate, carrying with them organic suspensions and some microorganisms. To speed up the reaction, flocculants are used at treatment stations. Soft water is alkalized with soda or lime to quickly form flakes.

Softening

The content of calcium and magnesium compounds (hardness salts) in water is strictly regulated. To remove impurities, filters with cationic or anionic ion exchange resins are used. When water passes through the load, hardness ions are replaced by hydrogen or sodium, which is safe for human health and the plumbing system. The resin's absorption capacity is restored by backwashing, but the capacity decreases each time. Due to the high cost of materials, this water softening technology is used mainly in local treatment plants.

Lightening

The technique is used to purify surface waters contaminated with fulvic acids, humic acids, and organic impurities. Liquid from such sources often has a characteristic color, taste, and greenish-brown tint. At the first stage, water is sent to the mixing chamber with the addition of a chemical coagulant and a chlorine-containing reagent. Chlorine destroys organic inclusions, and coagulants remove them into sediment.

Aeration

The technology is used to remove ferrous iron, manganese, and other oxidizing impurities from water. With pressure aeration, the liquid is bubbled with an air mixture. Oxygen dissolves in water, oxidizes gases and metal salts, removing them from the environment in the form of sediment or insoluble volatile substances. The aeration column is not completely filled with liquid. An air cushion above the surface of the water softens water hammer and increases the area of contact with air.

Non-pressure aeration requires simpler equipment and is carried out in special shower installations. Inside the chamber, water is sprayed through ejectors to increase the area of contact with air. If the iron content is high, aeration complexes can be supplemented with ozonizing equipment or filter cassettes.

Demineralization

The technology is used to prepare water in industrial water supply systems. Demineralization removes excess iron, calcium, sodium, copper, manganese and other cations and anions from the environment, increasing the service life of process pipelines and equipment. To purify water, reverse osmosis, electrodialysis, distillation or deionization technology is used.

Filtration

Water is filtered by passing through carbon filters, or charcoalization. The sorbent absorbs up to 95% of impurities, both chemical and biological. Until recently, pressed cartridges were used to filter water at waterworks, but their regeneration is a rather expensive process. Modern complexes include a powdered or granular coal charge, which is simply poured into a container. When mixed with water, coal actively removes impurities without changing its state of aggregation. The technology is cheaper but just as effective as block filters. Coal loading removes heavy metals, organics, and surfactants from the water. The technology can be used at treatment plants of any type.

What quality of water does the consumer receive?

Water becomes potable only after undergoing a full range of treatment measures. Then it goes to city communications for delivery to the consumer.

It is necessary to take into account that even if the water parameters at treatment plants fully comply with sanitary and hygienic standards at the water collection points, its quality may be significantly lower. The reason is old, rusty communications. Water becomes contaminated as it passes through the pipeline. Therefore, the installation of additional filters in apartments, private houses and enterprises remains a pressing issue. Properly selected equipment ensures that water meets regulatory requirements and even makes it healthy.

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Rublyovskaya water treatment plant

Moscow's water supply is provided by four largest water treatment stations: Severnaya, Vostochnaya, Zapadnaya and Rublevskaya. The first two use Volga water supplied through the Moscow Canal as a water source. The last two take water from the Moscow River. The performance of these four stations does not differ very much. In addition to Moscow, they also provide water to a number of cities near Moscow. Today we will talk about the Rublevskaya water treatment station - this is the oldest water treatment station in Moscow, launched in 1903. Currently, the station has a capacity of 1,680 thousand m3 per day and supplies water to the western and northwestern parts of the city.

All main water supply and sewerage systems in Moscow are managed by Mosvodokanal, one of the largest organizations in the city. To give an idea of the scale: in terms of energy consumption, Mosvodokanal is second only to two others - Russian Railways and the metro. All water treatment and purification stations belong to them. Let's take a walk through the Rublevskaya water treatment plant.

The Rublevskaya water treatment station is located near Moscow, a couple of kilometers from the Moscow Ring Road, in the northwest. It is located right on the banks of the Moscow River, from where it takes water for purification.

A little further up the Moscow River is the Rublevskaya Dam.

The dam was built in the early 30s. It is currently used to regulate the level of the Moscow River so that the water intake of the Western Water Treatment Station, which is located several kilometers upstream, can function.

Let's go upstairs:

The dam uses a roller design - the gate moves along inclined guides in niches using chains. The mechanism drives are located on top of the booth.

Upstream there are water intake canals, the water from which, as I understand it, flows to the Cherepkovsky wastewater treatment plants, located near the station itself and being part of it.

Sometimes, Mosvodokanal uses a boat to take water samples from the river. air cushion. Samples are taken several times daily at several points. They are needed to determine the composition of water and select the parameters of technological processes for its purification. Depending on the weather, time of year and other factors, the composition of the water changes greatly and is constantly monitored.

In addition, water samples from the water supply system are taken at the exit from the station and at many points throughout the city, both by the Mosvodokanal workers themselves and by independent organizations.

There is also a small hydroelectric power station, which includes three units.

It is currently shut down and taken out of service. Replacing equipment with new ones is not economically feasible.

It's time to move to the water treatment station itself! First where will we go - pumping station first rise. It pumps water from the Moscow River and lifts it up to the level of the station itself, which is located on the right, high bank of the river. We enter the building, at first the atmosphere is quite ordinary - bright corridors, information stands. Suddenly there is a square opening in the floor, under which there is a huge empty space!

However, we will return to it later, but for now let’s move on. A huge hall with square pools, as far as I understand, these are something like receiving chambers into which water flows from the river. The river itself is on the right, outside the windows. And the pumps pumping water are on the lower left behind the wall.

From the outside the building looks like this:

Photo from the Mosvodokanal website.

There is equipment installed here, it looks like an automatic station for analyzing water parameters.

All the structures at the station have a very bizarre configuration - many levels, all kinds of stairs, slopes, tanks, and pipes-pipes-pipes.

Some kind of pump.

We go down about 16 meters and find ourselves in the machine room. There are 11 (three spare) high-voltage motors installed here that drive centrifugal pumps level below.

One of the spare motors:

For nameplate lovers :)

Water is pumped from below into huge pipes that run vertically through the hall.

All electrical equipment at the station looks very neat and modern.

Handsome guys:)

Let's look down and see a snail! Each such pump has a capacity of 10,000 m 3 per hour. For example, he could completely fill an ordinary three-room apartment with water from floor to ceiling in just a minute.

Let's go down one level. It's much cooler here. This level is below the level of the Moscow River.

Untreated water from the river flows through pipes into the treatment plant block:

There are several such blocks at the station. But before we go there, let's first visit another building called the Ozone Production Workshop. Ozone, also known as O3, is used to disinfect water and remove harmful impurities from it using the ozone sorption method. This technology has been introduced by Mosvodokanal in recent years.

To produce ozone, the following technical process is used: air is pumped under pressure using compressors (on the right in the photo) and enters the coolers (on the left in the photo).

In a cooler, the air is cooled in two stages using water.

Then it is fed to dryers.

A dehumidifier consists of two containers containing a mixture that absorbs moisture. While one container is in use, the second one restores its properties.

On the reverse side:

The equipment is controlled using graphic touch screens.

Next, the prepared cold and dry air enters the ozone generators. An ozone generator is a large barrel, inside of which there are many electrode tubes, to which high voltage is applied.

This is what one tube looks like (in each generator out of ten):

Brush inside the tube :)

Through the glass window you can look at the very beautiful process of producing ozone:

It's time to inspect the wastewater treatment plant. We go inside and climb the stairs for a long time, as a result we find ourselves on a bridge in a huge hall.

Now is the time to talk about water purification technology. I’ll say right away that I’m not an expert and I only understood the process in general terms without much detail.

After the water rises from the river, it enters the mixer - a structure of several successive basins. There, different substances are added to it one by one. First of all, powdered activated carbon (PAC). Then a coagulant (polyoxychloride of aluminum) is added to the water - which causes small particles to collect into larger lumps. Then a special substance called a flocculant is introduced - as a result of which the impurities turn into flakes. The water then enters settling tanks, where all impurities are precipitated, and then passes through sand and carbon filters. Recently, another stage has been added - ozone sorption, but more on that below.

All main reagents used at the station (except liquid chlorine) in one row:

In the photo, as far as I understand, there is a mixer room, find the people in the frame :)

All kinds of pipes, tanks and bridges. Unlike sewer treatment plants, everything here is much more confusing and not so intuitive, in addition, if most of the processes there take place outside, then water preparation takes place entirely indoors.

This hall is only a small part of a huge building. Part of the continuation can be seen in the openings below, we will go there later.

There are some pumps on the left, huge tanks with coal on the right.

There is also another stand with equipment measuring some characteristics of water.

Tanks with coal.

Ozone is an extremely dangerous gas (first, highest hazard category). A strong oxidizing agent, inhalation of which can be fatal. Therefore, the ozonation process takes place in special indoor pools.

All kinds of measuring equipment and pipelines. On the sides there are portholes through which you can look at the process, on top there are spotlights that also shine through the glass.

The water inside is bubbling very actively.

The spent ozone goes to an ozone destructor, which consists of a heater and catalysts, where the ozone is completely decomposed.

Let's move on to filters. The display shows the speed of washing (blowing?) the filters. Filters become dirty over time and need to be cleaned.

Filters are long tanks filled with granular activated carbon (GAC) and fine sand according to a special pattern.

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The filters are located in a separate space, isolated from the outside world, behind glass.

You can estimate the scale of the block. The photo was taken in the middle, if you look back you can see the same thing.

As a result of all stages of purification, the water becomes suitable for drinking and meets all standards. However, such water cannot be released into the city. The fact is that the length of Moscow's water supply networks is thousands of kilometers. There are areas with poor circulation, closed branches, etc. As a result, microorganisms can begin to multiply in the water. To avoid this, the water is chlorinated. Previously, this was done by adding liquid chlorine. However, it is an extremely dangerous reagent (primarily from the point of view of production, transportation and storage), so now Mosvodokanal is actively switching to sodium hypochlorite, which is much less dangerous. A special warehouse was built a couple of years ago for its storage (hello HALF-LIFE).

Again, everything is automated.

And computerized.

Eventually, the water ends up in huge underground reservoirs on the station grounds. These tanks fill and empty within 24 hours. The fact is that the station operates with more or less constant productivity, while consumption varies greatly during the day - in the morning and evening it is extremely high, at night it is very low. The tanks serve as a kind of water accumulator - at night they are filled with clean water, and during the day it is taken from them.

The entire station is controlled from a central control room. Two people are on duty 24 hours a day. Everyone has workplace with three monitors. If I remember correctly, one dispatcher monitors the water purification process, the second monitors everything else.

The screens display a huge number of various parameters and graphs. Surely this data is taken, among other things, from those devices that were above in the photographs.

Extremely important and responsible work! By the way, practically no workers were seen at the station. The whole process is highly automated.

In conclusion, a bit of surreality in the control room building.

Decorative design.

Bonus! One of the old buildings left over from the time of the very first station. Once upon a time it was all brick and all the buildings looked something like this, but now everything has been completely rebuilt, only a few buildings have survived. By the way, in those days water was supplied to the city using steam engines! You can read a little more detail (and look at old photos) in my last report.

The report turned out to be voluminous, although only a small part of the station is shown, and even less is told, even from what I know :)

I express my deep gratitude to the press service of Mosvodokanal for the invitation!

Also thank you very much walsk for good company and help in preparing the report!

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The technological process of water treatment includes the following main stages:

ammoniation of water (ammonium sulfate is used)
water disinfection (sodium hypochlorite is used)
coagulation of pollutants (aluminum sulfate is used)
flocculation (cationic flocculant is used)
filtration through sand loading on contact clarifiers (single-stage cleaning scheme)
settling and filtration through sand loading on rapid filters ( two-stage scheme cleaning)
UV disinfection

New water treatment unit K-6 at the Southern Waterworks

Ozonator at block K-6

Since 2007 operates in Vodokanal unique two-stage technology complex disinfection of drinking water at water supply stations in St. Petersburg.
It includes the use of a highly effective and at the same time safe reagent - sodium hypochlorite (chemical method) and ultraviolet water treatment (physical method). This combination allows us to fully guarantee the epidemiological safety of the water supply of St. Petersburg, as well as full compliance of microbiological indicators of water quality with current standards.

St. Petersburg became the first metropolis in which all drinking water is treated with ultraviolet light and which completely abandoned the use of liquid chlorine for water disinfection.

The removal ceremony of the last chlorine cylinder took place June 26, 2009 at the Northern Waterworks. Chlorine (the use of which posed a serious danger from the point of view of storage and transportation) was replaced by the safe reagent sodium hypochlorite. There are two plants producing low-concentrated sodium hypochlorite in St. Petersburg - at the Southern Waterworks Station (since 2006) and at the Northern Waterworks Station (since 2008).

Another technology that has been used by Vodokanal for more than several years is powder dosing system activated carbon(PAH), ensuring the removal of odors and petroleum products.

Since 2011 At the Southern Waterworks there is a new block K-6, which uses the most modern water treatment technologies to cope with any changes in the condition of the water in the Neva.

The main stages of drinking water production at K-6:

preliminary ozonation of water (ozone is obtained from the air on the station territory);
water clarification: coagulation, flocculation and settling in a shelf settling tank;
filtration through rapid gravity filters with double-layer loading (sand and activated carbon);
first stage of disinfection: sodium hypochlorite in combination with ammonium sulfate (sodium hypochlorite successfully fights bacteria);
second stage of disinfection: ultraviolet treatment (this allows you to destroy viruses).

Advantages of the new block:

high quality drinking water is guaranteed regardless of the condition of the water in the Neva;
reducing the environmental load on the Neva (the water used to wash the filters is not discharged into the river, but is purified and reused);
treatment (dewatering) of sludge formed during water purification.

The pride of Vodokanal is unique biomonitoring system water quality. Its operating principle is based on diagnosing the functional state of crayfish and fish.

The method, developed at the Research Center for Environmental Safety of the Russian Academy of Sciences, involves measuring the heart rate of native crayfish and analyzing the behavior of fish. If the water taken from the Neva contains toxic substances, the crayfish’s heart rate will increase, and the fish’s behavior will change dramatically. Now the biomonitoring system is used at all water stations in the city.

At the Main Waterworks in the “state” there are 12 crayfish. Working schedule: two days in the aquarium under supervision, then four days of rest and active eating. Only male crayfish are accepted into service at Vodokanal.

Concluding the series of articles on urban wastewater treatment, we will talk about sludge treatment - the last stage of the entire process. The article turned out to be long, but the topic of sludge treatment when treating urban wastewater is as interesting as it is large-scale. It concerns many aspects: from complex technologies and their many types, to the economic feasibility of their use and compliance with environmental standards. To begin with, let us recall that a full technological scheme FGP cleaning should include 4 main processes: mechanical treatment, biological treatment, purified water disinfection and sludge treatment. In some cases, so-called “stripped-down schemes” can be used, in which some process is missing - this is justified under exceptional conditions.

Rice. 0 Purification stages in a full-fledged technological scheme of GSV

Fact 1. Technically speaking, wastewater is a "liquid waste"

Wastewater is waste that, with the help of water, acquires a fluid consistency that allows it to be discharged to a wastewater treatment facility. The goal of wastewater treatment is to reliably and economically remove unwanted pollutants from it, which, when discharged into a body of water, can cause unacceptable stress on its ecosystem. For this purpose, methods are used that ultimately contribute to the separation of the original wastewater into treated wastewater and residual substances - sludge.

The resulting residual substances (Fig. 1) can be divided into the following groups:

Waste retained on screens or sieves;
Sand retained in sand traps;
Oils and fats;
Sewage sludge (primary, secondary and tertiary).

Sludge from screens/sieves, sand from sand traps, as well as fats and oils are already removed from the wastewater during mechanical pre-treatment so that they do not interfere with further treatment processes. Sewage sludge, on the other hand, is the actual product of wastewater treatment, which contains substances that are removed from the wastewater by treatment. Compared to other residual substances, sewage sludge occurs in significantly larger quantities. The issue of expedient economic and at the same time environmental use of sludge has not yet been clearly resolved.

Rice. 1. The occurrence of residual substances in the treatment plant depending on the stages of the process

In general, all wastewater treatment residuals require reliable, environmentally friendly disposal. It is true of all residual substances that, according to the natural law of conservation of matter and energy, they cannot be destroyed in the proper sense of the word, as a result of which only two methods are available:

Return to the cycle of substances (recycling);
Removal from the cycle of substances (elimination).

However, as a rule, residual substances have various critical properties/components that prevent their direct return to the substance cycle or removal from it. As a consequence, pre-treatment, “removal-oriented” treatment, becomes necessary to modify the critical properties/components so that the residual substances no longer cause critical environmental loads.

Fact 2: The type and extent of sludge treatment depends on the amount and structure of the sewage sludge, as well as the disposal methods available

The task of sludge treatment is to prepare the sludge resulting from wastewater treatment in such a way that it can be disposed of in accordance with regulations, economically and harmlessly, i.e. without negative general environmental impact. The purpose of sludge treatment is to change or improve the most important properties of sludge (volume, odor, hygiene, etc.). Reducing the content of harmful substances in sludge is not the task of sludge treatment. This requires measures on the part of the source, i.e. wastewater producers. The most important properties of sludge that can and should be changed during its processing include high proportions of water, organic matter and pathogens.

If sewage sludge is to be used in agriculture or agriculture, it must be hygienically impeccable and stable, because There should be no odor formation due to rapid bacterial decomposition. To be disposed of in landfills, organic solids must be substantially completely removed (PP< 5%). В обоих случаях осадок сточных вод должен транспортироваться, вследствие чего требуется отделить воду для уменьшения количества и объема. Как можно меньшее содержание воды важно также при термическом удалении в целях экономии применяемой энергии.

To solve the problems posed for sludge treatment, many methods are available, which can be systematically combined into four main operations (Table 1).

Basic operation	Target	Examples of possible technologies
Water separation	Reduction in volume and mass	Compaction, dehydration, drying
Stabilization	Partial decomposition of organic impurities (reduced odor formation)	Biological aerobic (composting); biological anaerobic (fermentation)
Disinfection/disinfection	Killing or reducing the number of germs	Exposure to high temperature. pH value shift, ionized irradiation
Mineralization / inertization	Complete decomposition of organic impurities	Burning. Gasification and degassing. Wet oxidation

Table 1. Basic operations for treating sewage sludge

Numerous method options are combined as modules of disposal processes, taking into account the quality and quantity of sewage sludge and according to the desired disposal objectives. Flexibility in the removal process is important for safe removal. It is achieved when the first modules of the selected removal process allow the maximum number of insertion locations for modules of alternative removal processes. Typically, water separation and stabilization come first.

Let us consider the above operations sequentially.

Fact 3. Sludge is formed in wastewater treatment plants with a water content of 96 to 99.5%

Water separation.

Sludge formation leads to technical problems in all subsequent treatment processes (or disposal) and increases construction, equipment and operating costs. Therefore, each sludge treatment process must contain one or more stages in which water is separated from the sludge in order to provide optimized conditions for the following stages. Methods for separating water are divided depending on the ability to isolate various types water from suspended sewage sludge:

For compaction (natural or mechanical) - removal of water from the intermediate space to approximately 15% CO (85% water content (SWd/WG));
Dehydration (natural or mechanical) - removal of capillary and partly surface bound water to approximately 45% Co (55% SVd);
Drying - removing remaining surface bound water and internal water more than 95% CO (5% SVd).

Seal.

Compaction is the simplest and least expensive form of increasing concentration solids or separation of the solid fraction from the liquid during the treatment of sewage sludge and is used in almost every treatment plant. In addition to its main purpose - volume reduction - compaction has a positive effect on the treatment process in the intermediate storage area, on process stabilization, as well as on optimization of results and costs (smaller containers, pumps, stirring and heating devices, as well as lower transport costs).

Typically, compaction methods may vary depending on whether natural (gravitational) or artificial forces are at work (Figure 2). Methods are also divided according to the technology used - static and mechanical.

Rice. 2. Methods for compacting sewage sludge

Dehydration.

The purpose of dewatering is to reduce the volume of sewage sludge as much as possible in order to prepare the sludge for subsequent disposal processes (e.g. composting, drying, incineration) and transportation. The most common practice is to dewater the stabilization sludge. In principle, in addition to conventional mechanical methods, natural ones are also available, but due to the large space requirements and odor problems, they lose their importance.

Drying.

If residual water is to be removed from the sludge after mechanical dewatering, it must be evaporated or evaporated by drying. The following arguments speak in favor of drying after dehydration:

The amount of sewage sludge is reduced and the calorific value increases;
Storability and transportability are improved;
Improved handling and dosing capabilities;
Microbiological and hygienic safety is stabilized;

For subsequent thermal removal, the last point is primarily important, since the solid content achieved by dewatering is often insufficient to ensure an autothermal combustion process. Autothermicity is possible, as a rule, for fermented sludge at CO = 40-45%, and for untreated sludge at CO = 35%.

However, for technical reasons, further drying may be required before burning.

Rice. 3. Types of dryers for drying sewage sludge depending on the application

Stabilization.

Stabilization of sewage sludge is the most important of the basic sludge treatment operations. The main purpose of stabilization is to act on sludge impurities or decompose them so that the formation of odors and other hygienic or aesthetic disturbances can be avoided during further treatment of sewage sludge. In fact, this can be achieved by biological, chemical and thermal methods.

The effective reduction of odor-forming impurities and organic sludge solids required for this results in a number of positive effects, namely:

Reduce sediment/solids;
Improved sludge dewatering capabilities;
Reducing the number of pathogens (partial disinfection);
Production of biogas (only with anaerobic stabilization).

Biological aerobic stabilization.

Aerobic stabilization of sludge is based on the same metabolic processes that are known from biological wastewater treatment (Fig. 4): decomposing organic matter, when consumed O 2, is oxidized to inorganic end products (CO 2, H 2 O, NO 3) (dissimilation) or when energy is consumed, it is used for the construction of new cellular substances and for the formation of reserve substances (assimilation). Unlike wastewater treatment, the available substrate concentration must be so low that the sludge begins to consume itself, i.e. so that the rate of death of microorganisms is greater than the increase in biomass.

Rice. 4. Metabolic processes during aerobic stabilization of sediment

Biological anaerobic stabilization (fermentation).

Anaerobic decomposition of organic components of sewage sludge (carbohydrates, fats, proteins) to inorganic final products and gases is carried out within the framework of a four-stage system (hydrolysis, acidogenesis, acetogenesis and matanogenesis) with close spatial proximity of various groups of microorganisms. First, at the hydrolysis stage, high-molecular, often insoluble substrates (carbohydrates, proteins and fats) are converted using exoenzymes into low-molecular fragments (monosaccharides, glycerol, residues fatty acids and amino acids), from which, during acidogenesis, fermentative bacteria (facultative or obligate anaerobic) then form short-chain organic acids (for example, butyric, propionic, acetic acids), as well as alcohols, carbon dioxide and hydrogen. Of these intermediates, only acetic acid (acetate), CO 2 and H 2 can be directly converted by acetotrophic methanogenic bacteria into methane and carbon dioxide. Other organic acids and alcohols must first be converted by acetogenic bacteria to acetic acid through the process of acetogenesis. Then, methanogenic microorganisms, in the process of methanogenesis, form the final product - methane - from acetic acid, as well as from CO 2 and H 2. In general, about 60-70% of all converted carbon is decomposed to methane through an intermediate product - acetic acid - by methanogenic microorganisms. The remaining 30-40% is obtained by direct conversion of intermediately produced CO 2 and H 2 into methane by hydrogen bacteria.

Fact 4. The decision in favor of anaerobic digestion of sludge using biogas is decisive for the energy balance of the treatment plant

Production and use of biogas.

Due to the nature of the system, the production of biogas and its use to generate energy (heat and current) is only possible with anaerobic stabilization of sewage sludge. The purpose of using biogas is to fully cover the heat consumption of the treatment plant and partially cover its electricity consumption.

The standard level of equipment for metatanks today and the course of the technological process with optimal operation ensures high gas emission. Full use of this energy potential makes it possible to replace energy consumed from other sources and reduce the resulting energy consumption, as a result of which the use of biogas as a secondary energy carrier is strongly recommended from an economic point of view.

Disinfection.

In general, disinfection of sewage sludge by chemical, biological and physical methods is possible using one of the following three mechanisms of action:

High temperature;
Increasing the pH value;
Combination of exposure to high temperature and increased pH value.

In all cases, the appropriate duration of exposure to these mechanisms is a condition for the infectious safety of the sediment. Since the named mechanisms partly operate at other technological stages of sludge processing (stabilization, conditioning, drying), it is possible and advisable to define disinfection as a secondary goal of these technological stages. With the inclusion of disinfection in the existing treatment process, in addition to reducing the cost of adapting the process, no other costs arise. Disinfection can also be carried out in a separate place with special units (pasteurization).

Inertization.

The purpose of inertization is the destruction or as complete transformation of organic components as possible and, as a result, the conversion of sewage sludge into a mineral substance suitable for storage or use. This is required primarily when sewage sludge, due to its structure and quantity, should not be used in the surrounding area for either agricultural or agricultural purposes, but should be disposed of in landfills.

Various thermal methods are used to inertize sludge. Here are the most famous of them:

Incineration (separate and joint);
Gasification;
Pyrolysis (combined with either combustion or gasification);
Wet oxidation.

Burning.

Incineration of sewage sludge provides mainly the following advantages:

Reduction of mass and volume by evaporation of water and almost complete mineralization of the organic fraction in sewage sludge;
Destruction of harmful organic substances contained in sludge;
Concentration and binding of harmful organic substances in combustion residue and in gas purification products;
Utilization of the sludge's own energy content.

Therefore, regarding protection natural resources burning sewage sludge is ambiguous: on the one hand, valuable nutrients for plants, and on the other hand, under certain limiting conditions, the energy of fossil substances can accumulate. The use of waste from the combustion of sewage sludge can be considered in terms of energy production and the possible use of the resulting ash or slag in the production of building materials.

Gasification.

Gasification refers to the conversion of a hydrocarbon-containing solid or liquid substance (e.g. coal, biomass, oil) with a gasifying agent (oxygen/air, water vapor) into gaseous products. This produces synthesis gas, which contains H2, H2O, CO, CO2, CH4 as its main components. Other components include H 2 S, COS, HCl, NH 3 , HCN and - depending on the process - higher concentrations of hydrocarbons or resin oils. The exact composition of the synthesis gas depends on:

Composition of the substance used;
Type and quantity of gasification means(s);
Reaction conditions - temperature and pressure;
Kinetic limiting conditions determined by the selected gasification method.

When gasifying sewage sludge, due to the presence of a mineral content in it, along with synthesis gas, granulates or slags also appear that are prone to the formation of deposits and are suitable for use (for example, in the production of building materials). The temperature should be at least 850 o C, and during gasification followed by melting of the slag - at least 1300 o C. Usually, the sediment is dried to CO > 90%. Depending on which method is used, sewage sludge must be prepared differently (Table 2).

Table 2. Methods for gasification of sewage sludge

Degassing/pyrolysis.

Degassing or pyrolysis (as well as semi-coking, carbonization or dry distillation) is the thermal decomposition of organic material by removing oxygen. The products of the pyrolysis reaction are, on the one hand, gases and gaseous hydrocarbons (pyrolysis gas), and on the other hand, a solid coke-like residue containing remaining inert materials (pyrolysis coke). Pyrolysis gas cannot be stored for a long time, and pyrolysis coke cannot be placed in landfills, so both must be burned or gasified immediately after degassing. So, as regards the resulting products, degassing must be considered as a pre-treatment step that leads to a combination of methods for the purpose of final treatment only in combination with a second thermal treatment step.

There are two main implemented combinations of methods: the semi-coking-combustion method (pyrolysis + combustion) (Fig. 5) and the Thermoselect method (pyrolysis + gasification) (Fig. 6).

Rice. 5. Semi-coking and combustion method

The semi-coking and combustion method was the first combined method to be successfully tested in pilot plants.

Rice. 6. Thermoselect method

Wet oxidation methods.

The concept of “wet oxidation” generally describes the flameless oxidation of substances in aqueous solutions or in dispersed form with oxygen, air or other oxidizing substances at elevated pressure and temperature. The main stages of the wet oxidation reaction are thermal decomposition, hydrolysis and subsequent oxidation. Instead of wet oxidation, the methods are briefly called LoPrOx and VerTech.

According to the FerTech method, the reaction takes place in an underground reactor at a depth of 1200 -1500 m (Fig. 7).

Rice. 7. FerTech method

We have looked at 4 main municipal sewage sludge treatment operations, which include many different methods and technologies. The use of each of these methods requires economic and environmental justification in each individual application.

The series of articles devoted to the treatment of urban wastewater is coming to an end. We talked about the 4 main stages of wastewater treatment in a complete technological scheme: mechanical treatment, biological treatment, disinfection of purified water and sludge treatment - and examined in detail the methods and technologies of each of them.

When writing the article, materials from the manuals were used: “Wastewater treatment using centralized drainage systems of settlements and urban districts”, “Industrial wastewater treatment”, St. Petersburg: New Journal

One of the main objectives of the enterprise is the effective purification of water obtained from natural surface sources in order to provide residents with high-quality drinking water. The classic technological scheme used at Moscow water treatment stations allows this task to be accomplished. However, ongoing trends in the deterioration of water quality in water sources due to anthropogenic impact and the tightening of drinking water quality standards dictate the need to increase the degree of purification.

With the beginning of the new millennium in Moscow, for the first time in Russia, in addition to the classical scheme, highly efficient innovative technologies for the preparation of drinking water of a new generation are being used. Projects of the 21st century are modern treatment facilities, in which classical technology is supplemented with ozonation and sorption processes on activated carbon. Thanks to ozone sorption, water is better purified from chemical contaminants, unpleasant odors and tastes are eliminated, and additional disinfection occurs.

The use of innovative technologies eliminates the influence of seasonal changes in the quality of natural water, ensures reliable deodorization of drinking water, and its guaranteed epidemic safety even in cases of emergency contamination of the water supply source. In total, about 50% of all treated water is prepared using new technologies.

Along with the introduction of new methods of water purification, disinfection processes are being improved. In order to increase the reliability and safety of drinking water production by eliminating liquid chlorine from circulation, in 2012 the transition of all water treatment stations to a new reagent - sodium hypochlorite was completed. Due to the tightening state standard to control the content of chloroform in drinking water, targeted testing of disinfection regimes was carried out, as a result of which the concentration of chloroform in Moscow tap water, according to average data for 2018, did not exceed 5 - 13 μg/l, with a standard of 60 μg/l.

Process flow diagrams for cleaning artesian waters are individual for each object, taking into account the characteristics of the water quality of the exploited aquifers and contain the following steps: deferrization; softening; water conditioning using carbon sorption filters; removal of heavy metal impurities; disinfection with sodium hypochlorite or using ultraviolet lamps.

Today, in the Troitsky and Novomoskovsky administrative districts of Moscow, about half of the water intake units supply water that has undergone technological processing.

The phased introduction of new technologies is carried out in accordance with the General Scheme for the development of the water supply system, which provides that the complete reconstruction of all water treatment facilities will make it possible to supply water of the highest quality to all residents of the Moscow metropolis.