Introduction

Energy and environment

Wastewater characteristics

Justification for the choice of a wastewater treatment scheme

Wastewater treatment scheme

Conclusion

Literature

application

Introduction

For millennia, mankind exerted an extremely limited impact on the environment, but in the second half of the twentieth century, due to a sharp increase in anthropogenic pressure on it and severe environmental consequences, the most acute problem of environmental protection, finding a balance between ensuring the economic and social needs of society and preserving environment. In the context of the growing threat to the environment and public health, practically all countries of the world have adopted legislative acts that limit and regulate anthropogenic pressure on nature. At the same time, new technologies are being developed and introduced that exclude or minimize the harmful effects of production processes on air, water and soil.

The problem of utilization of rinse water is relevant for large water treatment plants in Russia. In the process of water treatment at filter stations, a large number of washing water of filters and contact clarifiers (15 - 30% of the volume of treated water). The wash water discharged from the stations is characterized by high concentrations of aluminum, iron, suspended solids, oxidizability, which negatively affects the state of water bodies that receive this type of wastewater.

According to SNiP 2.04.02-84, the wash water should be reused, however, in practice, it is not possible in this way to completely utilize the wash water for a number of reasons: deterioration of flocculation and sedimentation processes, reduction in the duration of filter cycles. At present, most (~ 75%) of wash water is either discharged into the domestic sewage system, or, after preliminary settling (or without it), into a natural reservoir. At the same time, in the first case, the load on the sewer networks and biological treatment facilities increases significantly, their normal operation is disrupted. In the second case, natural water bodies are polluted with toxic sediment, which negatively affects their sanitary condition.

Thus, new approaches are needed that exclude environmental pollution and allow obtaining an additional amount of purified water without increasing water intake.

In this work, we investigate the scheme of wastewater treatment of thermal power plants and their impact on the environment.

Problems of this work: study of wastewater emissions from industrial enterprises, the impact of wastewater on the environment.

1. Energy and environment

The modern period of human development is sometimes characterized through three parameters: energy, economy, ecology.

Energy takes a special place among these indicators. It is a defining indicator for both the economy and the environment. The economic potential of states and the welfare of people depend on energy indicators.

The demand for electricity and heat is growing every year, both in our country and abroad, respectively.

There is a need to increase the capacity of existing industries and modernize equipment in order to increase the production of energy and heat.

Meanwhile, getting more electricity negatively affects natural resources.

Large scale power generation affects:

atmosphere;

hydrosphere;

lithosphere;

biosphere.

At present, energy needs are met mainly from three types of energy resources: fossil fuel, water and the atomic nucleus. The energy of water and nuclear energy is used by humans after converting it into electrical energy.

Main types of electricity production in the Russian Federation

The modern energy complex of the Russian Federation includes almost 600 power plants with a unit capacity of over 5 MW. The total installed capacity of power plants in Russia is 220 thousand MW. The installed capacity of the park of operating power plants by types of generation has the following structure: 21% are hydropower facilities, 11% are nuclear power plants and 68% are thermal power plants.

Thermal energy

Thermal power plants are a complex of structures and equipment for generating electricity and heat.

Thermal power plants are distinguished:

By the degree of loading:

· Basic;

· Peak.

By the nature of the fuel consumed:

· On solid;

· Liquid;

· Gaseous.

These types of power plants, of high capacity, require a huge amount of water to cool the steam.

In this case, the incoming cooling water passes through the cooling devices and returns to the source.

In the Russian Federation, steam turbine types of thermal power plants are used.

Energy Yekaterinburg

The main type of development electrical energy in Yekaterinburg will fall on thermal power plants.

Energy saving in Yekaterinburg is provided by 6 thermal power plants and 172 boiler houses of various capacities from 0.1 to 515 Gcal / hour.

The installed electric capacity of the CHPP is 1,906 MW (generation of over 6.1 billion kWh per year).

The total heat capacity of the power sources is 9,200 Gcal / hour. More than 19 million Gcal of thermal energy are produced per year, including:

56% - at the Sverdlovenergo stations;

39% - boiler houses of industrial enterprises;

5% - by municipal boiler houses.

The annual fuel consumption is 3 million tons of fuel equivalent, more than 99% of which is natural gas, the rest is coal, fuel oil (the latter is used as a backup fuel).

The length of main heating networks in Yekaterinburg is 188 km, distribution and district heating networks - more than 3200 km.

Wastewater characteristics

It is customary to call waste water fresh water that has changed its physical, chemical and biochemical properties as a result of household and industrial activities of a person. By origin, wastewater is divided into the following classes: domestic, industrial and rainwater.

The degree of uniformity of distribution (frequency) of the polluting component.

Table 1 Composition and concentration of contaminants in waste water from CHPP

Table 2 Indicators of waste water from CHP

Justification for the choice of a wastewater treatment scheme

As we have already found out, the main type of electricity development in Yekaterinburg is thermal power plants. Therefore, in this work we analyze the impact of the development of thermal power plants and their impact on the environment.

The development of heat power engineering has an impact on:

atmosphere;

hydrosphere;

lithosphere;

biosphere.

Currently, this impact is becoming global in nature, affecting all structural components our planet.

The most important factors in the functioning of the environment is the living matter of the biosphere, which plays an essential role in the natural cycle of almost all substances.

The impact of thermal power plants on the environment

Nitrogen compounds practically do not interact with other substances in the atmosphere and their existence is almost unlimited.

Sulfur compounds are a toxic gaseous release from a thermal power plant, and when they are in the atmosphere, in the presence of oxygen, it is oxidized to SO 3 and reacts with water, and forms a weak solution of sulfuric acid.

In the process of combustion in an atmosphere of atmospheric oxygen, nitrogen, in turn, forms a number of compounds: N 2 O, NO, N 2 O 3, NO 2, N 2 O 4 and N 2 O 5.

In the presence of moisture, nitric oxide (IV) easily reacts with oxygen, forming HNO 3.

The growth of emissions of toxic compounds into the environment, first of all, affects the health of the population, worsens the quality of agricultural products, reduces productivity, affects the climatic conditions of certain regions of the world, the state of the ozone layer of the Earth, and leads to the death of flora and fauna.

Physicochemical cleaning methods

These methods are used to remove dissolved impurities, and in some cases from suspended solids. Many methods of physicochemical purification require preliminary deep separation of suspended solids from wastewater, for which the coagulation process is widely used.

At present, in connection with the use of circulating water supply systems, the use of physical and chemical methods of wastewater treatment is significantly increasing, the main of which are:

flotation;

ion exchange and electrochemical cleaning;

hyperfiltration;

neutralization;

extraction;

evaporation;

evaporation, evaporation and crystallization.

Industrial waste water

Industrial wastewater is mainly polluted with industrial waste and emissions. The quantitative and qualitative composition of such effluents is diverse and depends on the industry sector and its technological processes. By composition, wastewater is divided into three main groups, containing:

Inorganic impurities (including toxic ones);

Organic impurities;

Inorganic and organic contaminants.

Waste water from thermal power plants

Wastewater treatment methods

Wastewater treatment - treatment of wastewater with the aim of destroying or removing harmful substances from it.

Wastewater treatment methods can be divided into:

mechanical;

chemical;

physical and chemical;

biological.

Wastewater treatment scheme

Wastewater treatment is carried out sequentially.

On the initial stage, wastewater is purified from undissolved contaminants, and then from dissolved organic compounds.

Chemical treatment is used to treat industrial wastewater (chemical production, thermal power plants).

Physicochemical methods of wastewater treatment can be carried out before biochemical treatment and after biochemical treatment.

Disinfection is usually carried out at the end of the waste water treatment process.

power plant waste water

Figure: 1. Scheme of mechanical and biochemical wastewater treatment

The sediment is fermented in digesters, dewatered and dried in sludge pads.

Mechanical cleaning consists in filtering waste liquid through grates.

Contaminants caught on the screens are crushed on special crushers and returned to the stream of purified water before or after the screens.

Biochemical cleaning is carried out by aerobic microorganisms.

The sediment from the secondary clarifiers is also sent to digesters.

Chlorine is used to disinfect water.

Disinfection of water takes place in contact tanks.

Figure: 2. Scheme of mechanical and biochemical wastewater treatment

In this scheme, aerotanks are used for biochemical treatment.

The principle of water purification in them is the same as in biological filters. Instead of a biological film, activated sludge is used here, which is a colony of aerobic microorganisms.

According to this scheme, the precipitate is dehydrated in vacuum filters and dried in thermal ovens.

The scheme of chemical treatment of industrial wastewater, along with the structures used for mechanical treatment of wastewater, includes a number of additional structures: reagents, as well as mixing them with water.

Conclusion

In this work, we have investigated wastewater treatment schemes.

It is customary to call waste water fresh water that has changed its physical, chemical and biochemical properties as a result of household and industrial activities of a person. By origin, wastewater is divided into the following classes: domestic, industrial and rainwater.

Industrial waste water is generated during the production activities of enterprises, factories, complexes, power plants, car washes, etc.

The main characteristics of wastewater are:

Types of pollution and their concentration (content) in wastewater;

The amount of wastewater, the rate of their entry, consumption;

The degree of uniformity of distribution (frequency) of the polluting component.

As we found out, the production of electricity leads to massive emissions of harmful compounds, which in turn adversely affect the atmosphere, hydrosphere, lithosphere and biosphere.

In the appendices, there are regulatory indicators for the composition and lists of substances that are discharged into the reservoir.

To reduce emissions of harmful substances into the environment, humanity needs to switch to alternative energy sources.

Alternative energy sources are aimed at solving global - environmental problems.

The cost of alternative energy sources is significantly lower than the cost of traditional sources, and the construction of alternative power plants pays off faster. Alternative energy sources will save the country's fuel resources for use in other industries, so the economic reason is being solved here.

Alternative energy sources will help preserve the health and life of many people.

Literature

1. V.I. Kormilitsyn, M.S. Tsitskshivili, Yu.I. Yalamov "Fundamentals of Ecology", publishing house - Interstyle, Moscow 1997.

2. N.A. Voronkov "Ecology - General, Social, Applied", publishing house - Agar, Moscow 1999.

3. V.M. Garin, I.A. Klenov, V.I. Kolesnikov "Ecology for technical universities", publishing house - Phoenix, Rostov-on-Don 2001.

4. Richter L.A. Thermal power plants and protection of the atmosphere. - M .: Energy, 1975.-131 p.

5. Romanenko V.D. et al. Methodology for environmental assessment of surface water quality according to the relevant criteria. - K., 1998.

6. Guidelines for organizing monitoring of the state of the natural environment in the area of \u200b\u200bNPP location. Control over radioactive contamination of the natural environment in the vicinity of NPP / Ed. K.P. Makhonko. - Obninsk: NPO Typhoon, 1989. - 350 p.

7. Semenov I.V. et al. Monitoring in the system of ensuring the ecological safety of hydraulic engineering facilities // Hydraulic engineering. - 1998. - No. 6.

8. Skalin F.V., Kanaev A.A., Koop L.Z. Energy and Environment. - L .: Energoizdat, 1981 .-- 280 p.

9. Tarkhanov A.V., Shatalov V.V. New trends in the development of the world and Russian mineral resource base of uranium // Mineral raw materials. Geological and economic series. - M .: VIMS, 2008. - No. 26. - 79 p.

10. Explanatory dictionary of environmental terms / G.А. Tkach, E.G. Bratuta et al. - К .: 1993. - 256 p. Tupov V.B. Environmental protection from noise in the energy sector. - M .: MPEI, 1999 .-- 192 p. Khodakov Yu.S. Nitrogen oxides and heat power engineering. - M .: OOO "EST-M", 2001. - 370 p.

application

List of pollutants removed from wastewater at biological treatment facilities

LIST of contaminants that cannot be removed from wastewater at biological treatment plants

List of substances and materials prohibited for discharge into sewage systems of settlements

1. Substances and materials that can clog pipelines, wells, gratings or be deposited on their walls:

metal shavings;

construction waste and garbage;

solid household waste;

industrial waste and sludge from local (local) treatment facilities;

floating substances;

insoluble fats, oils, resins, fuel oil, etc.

colored waste water with an actual dilution ratio exceeding the standard values general properties wastewater more than 100 times;

biologically hard surfactants (surfactants).

Substances that have a destructive effect on the material of pipelines, equipment and other structures of sewage systems:

alkalis, etc.

Substances that can form toxic gases, explosive, toxic and flammable gases in sewer networks and structures:

hydrogen sulfide;

carbon disulfide;

carbon monoxide;

hydrogen cyanide;

vapors of volatile aromatic compounds;

solvents (gasoline, kerosene, diethyl ether, dichloromethane, benzenes, carbon tetrachloride, etc.).

Concentrated and mother liquors.

Wastewater with a fixed toxicity category "hypertoxic";

Wastewater containing microorganisms that cause infectious diseases.

Radionuclides, the discharge, removal and neutralization of which is carried out in accordance with the "Rules for the Protection of Surface Waters" and the current radiation safety standards

Average characteristics of the quality of household wastewater discharged by subscribers of the housing stock of settlements

Note: If necessary, the data given in the table can be refined and corrected based on the conducted field studies.

The state of the environment directly depends on the degree of industrial wastewater treatment of closely located enterprises. Recently, environmental issues have become very acute. Over the past 10 years, many new and effective technologies for industrial wastewater treatment have been developed.

Treatment of industrial wastewater from different objects can take place in one system. Representatives of the enterprise can agree with the utilities to discharge their wastewater into the general centralized sewage system. settlementwhere it is located. To make this possible, a chemical analysis of the effluents is preliminarily carried out. If they have an acceptable degree of pollution, then industrial wastewater will be discharged together with domestic wastewater. It is possible to pre-purify waste water from enterprises with specialized equipment to eliminate pollution of a certain category.

Standards for the composition of industrial wastewater for discharge into the sewer

Industrial waste water can contain substances that will destroy the sewer pipeline and city treatment plants. If they get into water bodies, they will negatively affect the mode of water use and life in it. For example, when the maximum permissible concentration is exceeded, toxic substances will harm the surrounding water bodies and, possibly, humans.

To avoid such problems, the maximum permissible concentrations of various chemical and biological substances are checked before cleaning. Such actions are preventive measures for the correct operation of the sewer pipeline, the functioning of treatment facilities and the ecology of the environment.

The requirements for drains are taken into account during the design, installation or reconstruction of all industrial establishments.

Plants should strive to operate on technologies with little or no waste. The water must be reused.

Wastewater discharged to the central sewerage system must comply with the following standards:

• BOD 20 must be less than the permissible value of the design documentation for a sewage treatment plant;
• drains should not cause malfunctions or shutdown of the sewage system and the treatment plant;
• wastewater should not have a temperature higher than 40 degrees and a pH of 6.5-9.0;
• waste water should not contain abrasive materials, sand and shavings that can form sediment in the sewage system;
• there should be no impurities that clog pipes and gratings;
• drains should not have aggressive components leading to the destruction of pipes and other elements of treatment plants;
• waste water should not contain explosive components; non-biodegradable impurities; radioactive, viral, bacterial and toxic substances;
• COD should be 2.5 times less than BOD 5.

If the discharged water does not meet the specified criteria, then local pretreatment of wastewater is organized. An example would be the treatment of waste water from an electroplating industry. The quality of the cleaning must be agreed by the installer with the municipal authorities.

Types of industrial wastewater pollution

Water purification must remove environmentally negative substances. The technology used must neutralize and recycle the components. As can be seen, treatment methods should take into account the initial composition of the effluent. In addition to toxic substances, water hardness, its oxidizability, etc. should be monitored.

Each harmful factor (HF) has its own set of characteristics. Sometimes one indicator can indicate the existence of several EFs. All VFs are divided into classes and groups, which have their own cleaning methods:

• coarse suspended impurities (suspended impurities with a fraction of more than 0.5 mm) - sifting, settling, filtration;
• coarse emulsified particles - separation, filtration, flotation;
• microparticles - filtration, coagulation, flocculation, pressure flotation;
• stable emulsions - thin-layer sedimentation, pressure flotation, electroflotation;
• colloidal particles - microfiltration, electroflotation;
• oils - separation, flotation, electroflotation;
• phenols - biological treatment, ozonation, sorption by activated carbon, flotation, coagulation;
• organic impurities - biological treatment, ozonation, sorption by activated carbon;
• heavy metals - electroflotation, sedimentation, electrocoagulation, electrodialysis, ultrafiltration, ion exchange;
• cyanides - chemical oxidation, electroflotation, electrochemical oxidation;
• tetravalent chromium - chemical reduction, electroflotation, electrocoagulation;
• trivalent chromium - electroflotation, ion exchange, precipitation and filtration;
• sulfates - sedimentation with reagents and subsequent filtration, reverse osmosis;
• chlorides - reverse osmosis, vacuum evaporation, electrodialysis;
• salts - nanofiltration, reverse osmosis, electrodialysis, vacuum evaporation;
• Surfactants - sorption by activated carbon, flotation, ozonation, ultrafiltration.

Wastewater types

Wastewater pollution are:

• mechanical;
• chemical - organic and inorganic substances;
• biological;
• thermal;
• radioactive.

In each industry, the composition of wastewater is different. There are three classes that contain:

1. inorganic pollution, including toxic;
2. organics;
3. inorganic impurities and organic matter.

The first type of pollution is present in soda, nitrogen, sulphate plants that work with various ores with acids, heavy metals and alkalis.

The second type is characteristic of oil industry enterprises, organic synthesis plants, etc. Water contains a lot of ammonia, phenols, resins and other substances. Impurities during oxidation lead to a decrease in oxygen concentration and a decrease in organoleptic qualities.

The third type is obtained in the process of electroplating. The effluent contains a lot of alkalis, acids, heavy metals, dyes, etc.

Wastewater treatment methods for enterprises

Classic cleaning can take place using various methods:

• removal of impurities without changing their chemical composition;
• modification of the chemical composition of impurities;
• biological methods of purification.

Removing impurities without changing their chemical composition includes:

• mechanical cleaning using mechanical filters, settling, filtering, flotation, etc .;
• with a constant chemical composition, the phase changes: evaporation, degassing, extraction, crystallization, sorption, etc.

The local wastewater treatment system is based on many treatment methods. They are selected for a specific type of wastewater:

• suspended particles are removed in hydrocyclones;
• fines contamination and sediment are removed in continuous or batch centrifuges;
• flotation plants are effective in cleaning from fats, resins, heavy metals;
• gaseous impurities are removed by degassers.

Wastewater treatment with a change in the chemical composition of impurities is also divided into several groups:

• transition to poorly soluble electrolytes;
• the formation of fine or complex compounds;
• decay and synthesis;
• thermolysis;
• redox reactions;
• electrochemical processes.

The effectiveness of biological treatment methods depends on the types of impurities in the effluent, which can accelerate or slow down the destruction of waste:

• the presence of toxic impurities;
• increased concentration of minerals;
• biomass nutrition;
• impurity structure;
• biogenic elements;
• activity of the environment.

In order for industrial wastewater treatment to be effective, a number of conditions must be met:

1. Existing impurities must be biodegradable. The chemical composition of effluents affects the rate of biochemical processes. For example, primary alcohols oxidize faster than secondary alcohols. With an increase in oxygen concentration, biochemical reactions proceed faster and better.
2. The content of toxic substances should not negatively affect the operation of the biological installation and treatment technology.
3. PKD 6 should also not disrupt the vital activity of microorganisms and the process of biological oxidation.

Stages of industrial wastewater treatment

Wastewater treatment takes place in several stages using different methods and technologies. This can be explained quite simply. Do not perform fine cleaning if coarse substances are present in the effluent. Many methods provide concentration limits for certain substances. Thus, the waste water must be pre-treated before the main treatment method. A combination of several methods is the most economical in industrial enterprises.

Each production has a certain number of stages. It depends on the type of treatment plants, treatment methods and composition of wastewater.

The most expedient method is a four-stage water purification.

1. Removal of large particles and oils, neutralization of toxins. If the wastewater does not contain this type of impurities, then the first stage is skipped. It is pre-cleaning. It includes coagulation, flocculation, mixing, settling, sieving.
2. Removal of all mechanical impurities and water preparation for the third stage. It is the primary stage of purification and can consist of sedimentation, flotation, separation, filtration, demulsification.
3. Removal of contaminants up to a certain predetermined threshold. Secondary treatment includes chemical oxidation, decontamination, biochemistry, electrocoagulation, electroflotation, electrolysis, membrane purification.
4. Removal of soluble substances. It is a deep purification - sorption by activated carbon, reverse osmosis, ion exchange.

The chemical and physical composition determines the set of methods at each stage. It is allowed to exclude some stages in the absence of certain contaminants. However, the second and third stages are mandatory in industrial wastewater treatment.

If you comply with the listed requirements, then the disposal of waste water from enterprises will not damage the ecological situation of the environment.

This article is for informational purposes only. Quant Mineral does not share all the provisions of this article.

Industrial waste water classification

Since various technologies are used at different enterprises, the list of harmful substances that enter industrial waters during technological processes is very different.

The conventional division of industrial wastewater into five groups by types of pollution is accepted. with this classification, it differs within the same group, and the similarity of the used cleaning technologies is taken as a systematizing feature:

• group 1: impurities in the form of suspended solids, mechanical impurities, incl. metal hydroxides.
• group 2: impurities in the form of oil emulsions, oil-containing impurities.
• group 3: impurities in the form of volatile substances.
• group 4: impurities in the form of washing solutions.
• group 5: impurities in the form of solutions of organic and inorganic substances with toxic properties (cyanides, chromium compounds, metal ions).

Industrial wastewater treatment methods

Several methods have been developed to remove contaminants from industrial wastewater. The choice in each case is carried out based on the required quality composition of the purified water. Since in some cases the contaminating components are related to different types, then for such conditions it is advisable to use combined cleaning methods.

Methods for cleaning industrial effluents from oil products and suspended solids

For the treatment of industrial effluents of the first two groups, sedimentation is most often used, for which sedimentation tanks or hydrocyclones can be used. Also, depending on the amount of mechanical impurities, the size of suspended particles and the requirements for treated water, flotation is carried out in the treatment plant. It should be borne in mind that some types of suspended impurities and oils have polydisperse properties.

Despite the fact that sedimentation is a widely used cleaning method, it has several disadvantages. The settling of industrial effluents to obtain a good degree of purification, as a rule, takes a very long time. 50-70% of oils and 50-60% of cleaning for suspended solids are considered to be good indicators of purification during settling.

A more efficient method of wastewater clarification is flotation. Flotation units can significantly reduce the time of wastewater treatment, while the degree of treatment for contamination with oil products and mechanical impurities reaches 90-98%. Such a high degree of purification is obtained by flotation for 20-40 minutes.

At the outlet of the flotation plants, the amount of suspended particles in the water is about 10-15 mg / l. At the same time, this does not meet the requirements for circulating waters of a number of industrial enterprises, and the requirements of environmental legislation for the discharge of industrial effluents on the relief. For better removal of pollutants from industrial effluents, filters are used at treatment plants. The filtering filler is a porous or fine-grained material, for example, quartz sand, anthracite. Filtration plants of the latest modifications often use foam urethane and polystyrene foam fillers, which have a larger capacity and are capable of being repeatedly regenerated for reuse.

Reagent method

Filtration, flotation and settling make it possible to remove mechanical impurities from 5 microns and more from wastewater, the removal of smaller particles can be carried out only after preliminary. The addition of coagulants and flocculants to industrial wastewaters causes the formation of flocs, which, during the precipitation process, cause the sorption of suspended solids. Some types of flocculants accelerate the self-coagulation of particles. The most common coagulants are ferric chloride, aluminum sulphate, ferrous sulfate, and as flocculants - polyacrylamide and activated silicic acid. Depending on the technological processes used in the main production, auxiliary substances generated at the enterprise can be used for flocculation and coagulation. An example of this is the use of spent pickling solutions containing ferrous sulfate in the engineering industry.

Reagent treatment increases the performance of industrial wastewater treatment up to 100% of mechanical impurities (including finely dispersed), and up to 99.5% of emulsions and oil products. The disadvantage of this method is the complication of maintenance and operation of the treatment plant, therefore, in practice, it is used only in cases of increased requirements for the quality of wastewater treatment.

In steelworks, suspended solids in wastewater can be more than half of iron and iron oxides. This composition of industrial water allows the use of reagent-free coagulation for cleaning. In this case, the coagulation of contaminating iron-containing particles will be carried out by a magnetic field. Treatment plants in such a production are a complex of a magnetic coagulator, magnetic filters, magnetic filter cyclones and other installations with a magnetic principle of operation.

Methods for cleaning industrial wastewater from dissolved gases and surfactants

The third group of industrial effluents is gases and volatile organic matter dissolved in water. Their removal from wastewater is carried out by stripping or desorption. This method consists in passing small air bubbles through the liquid. Bubbles rising to the surface capture dissolved gases and remove them from the effluent. Bubbling air through industrial wastewater does not require special additional devices, except for the bubbling installation itself, and the released gases can be utilized, for example,. Depending on the amount of waste gas, in some cases, it is advisable to burn it in catalytic plants.

A combined cleaning method is used for cleaning effluents containing detergents. This could be:

• adsorption on inert materials or natural sorbents,
• ion exchange,
• coagulation,
• extraction,
• foam separation,
• destructive destruction,
• chemical precipitation in the form of insoluble compounds.

The combination of the methods used to remove contaminants from water is selected according to the composition of the source wastewater and the requirements for treated wastewater.

Methods for purification of solutions of organic and inorganic substances with toxic properties

Most of the effluents of the fifth group are formed on galvanic and pickling lines and are concentrates of salts, alkalis, acids and wash water with various acidity indices. Wastewater of this composition at treatment plants is reagent treated in order to:

1. lower acidity,
2. lower alkalinity,
3. coagulate and precipitate heavy metal salts.

Depending on the capacities of the main production, concentrated and diluted solutions can either be mixed and then neutralized and clarified (small pickling departments), or in large pickling departments, separate neutralization and clarification of solutions of various kinds can be performed.

Neutralization of acidic solutions is usually carried out with a 5-10% solution of slaked lime, with the formation of water and precipitation of insoluble salts and metal hydroxides:

In addition to slaked lime, alkalis, soda, ammonia water can be used as a neutralizer, but their use is advisable only if they are generated as waste at a given enterprise. As can be seen from the reaction equations, when the sulfuric acid effluent is neutralized with slaked lime, gypsum is formed. Gypsum tends to settle on the inner surfaces of pipelines and thereby cause a narrowing of the bore, especially metal pipelines are susceptible to this. As a preventive measure, in such a situation, it is possible to clean the pipes by flushing, as well as use polyethylene pipelines.

They are subdivided not only by acidity, but also by their chemical composition. In this classification, three groups are distinguished:

This division is due to specific wastewater treatment technologies in each case.

Chromium Waste Treatment

Ferrous sulfate is a very cheap reagent, therefore, in the past years, this method of neutralization was very common. At the same time, storage of iron (II) sulfate is very difficult, since it quickly oxidizes to iron (III) sulfate, therefore it is difficult to calculate the correct dosage for a treatment plant. This is one of two disadvantages of this method. The second drawback is the large amount of precipitation in this reaction.

Modern gas is used - sulfur dioxide, or sulfites. The processes occurring in this case are described by the following equations:

The rate of these reactions is influenced by the pH of the solution, the higher the acidity, the faster the hexavalent chromium is reduced to trivalent. The most optimal acidity indicator for the chromium reduction reaction is pH \u003d 2-2.5, therefore, if the acidity of the solution is insufficient, it is additionally mixed with concentrated acids. Accordingly, mixing chromium-containing wastewater with wastewater of lower acidity is unreasonable and economically unprofitable.

Also, in order to save money, chromium wastewater after recovery should not be neutralized separately from other wastewater. They are combined with the rest, including those containing cyanogen, and subjected to general neutralization. To prevent reverse oxidation of chromium due to excess chlorine in cyanide effluents, you can use one of two methods - either increase the amount of reducing agent in chromium effluents, or remove excess chlorine in cyanide effluents with sodium thiosulfate. Precipitation occurs at pH \u003d 8.5-9.5.

Cyanide-containing effluent treatment

Cyanides are highly toxic substances, therefore technology and methods must be followed very strictly.

It is produced in a basic environment with the participation of chlorine gas, bleach, or sodium hypochlorite. The oxidation of cyanides to cyanates occurs in 2 stages with the intermediate formation of cyanogen chloride, a very toxic gas, while the conditions in the treatment plant must be constantly maintained when the rate of the second reaction exceeds the rate of the first:

By calculation, the following optimal conditions for this reaction were derived, and later practically confirmed: pH\u003e 8.5; t wastewater< 50°C; концентрация цианидов в исходной сточной воде не выше 1 г/л.

Further neutralization of cyanates can be performed in two ways. The choice of method will depend on the acidity of the solution:

• at pH \u003d 7.5-8.5, oxidation to carbon dioxide and gaseous nitrogen is carried out;
• at pH<3 производится гидролиз до солей аммония:

An important condition for the use of the hypochlorite method for neutralizing cyanides is their compliance with no higher than 100-200 mg / l. A large concentration of a toxic substance in effluents requires a preliminary reduction of this indicator by dilution.

The final stage in the treatment of cyanide galvanic wastewater is the removal of heavy metal compounds and neutralization in terms of pH. As noted above, it is recommended to neutralize cyanide effluents in conjunction with two other types of effluents - chromium-containing and acidic with alkaline. It is also more expedient to separate and remove hydroxides of cadmium, zinc, copper and other heavy metals in the form of suspensions in mixed waste streams.

Purification of various effluents (acidic and alkaline)

Formed by degreasing, pickling, nickel plating, phosphating, tinning, and more. They do not contain cyanogen compounds or, that is, they are not toxic, and detergents (surfactants) and emulsified fats act as pollutants. Purification of acidic and alkaline waste water from galvanic workshops consists in their partial mutual neutralization, as well as in neutralization with the help of special reagents, such as solutions of hydrochloric or sulfuric acid and milk of lime. In general, in this case, the neutralization of effluents is more correctly called pH correction, since solutions of different acid-base composition will eventually be brought to an average acidity.

The presence of surfactants and oil-fatty inclusions in solutions does not interfere with neutralization reactions, but reduces the overall quality of wastewater treatment, therefore fats are removed from wastewater by filtration, and only mild detergents that are capable of biodegradation must be used as surfactants.

After neutralization, acidic and alkaline wastewater as part of mixed wastewater is sent to clarification tanks or centrifuges. This completes the chemical method of cleaning wastewater from galvanic lines.

In addition to the chemical method, galvanic wastewater treatment can be carried out by electrochemical and ion-exchange methods.

The operation of thermal power plants is associated with the use of a large amount of water. The bulk of water (more than 90%) is consumed in cooling systems of various devices: turbine condensers, oil and air coolers, moving mechanisms, etc.

Wastewater is any stream of water discharged from the power plant cycle.

Sewage or waste water, except for cooling system waters, includes: waste water from hydraulic ash collection systems (HSS), spent solutions after chemical washing of heat power equipment or its conservation: regeneration and sludge water from water treatment (water treatment) plants: oil-contaminated wastewater, solutions and suspensions, arising from washing of external heating surfaces, mainly air heaters and water economizers of boilers burning sulfurous fuel oil.

The compositions of the listed effluents are different and are determined by the type of TPP and main equipment, its capacity, the type of fuel, the composition of the source water, the method of water treatment in the main production and, of course, the level of operation.

Water after cooling the condensers of turbines and air coolers, as a rule, carry only the so-called thermal pollution, since their temperature is 8 ... 10 С higher than the temperature of water in the water source. In some cases, cooling waters can introduce foreign substances into natural water bodies. This is due to the fact that the cooling system also includes oil coolers, the violation of the density of which can lead to the penetration of oil products (oils) into the cooling water. Fuel oil TPPs generate waste water containing fuel oil.

Oils can also get into wastewater from the main building, garages, open switchgears, oil farms.

The amount of water in cooling systems is mainly determined by the amount of exhaust steam entering the turbine condensers. Consequently, most of these waters are at condensing TPPs (CES) and NPPs, where the amount of water (t / h) cooling turbine condensers can be found by the formula Q \u003d KWwhere W- plant capacity, MW; TO- coefficient, for TPP TO\u003d 100 ... 150: for NPP 150 ... 200.

In power plants using solid fuels, the removal of significant amounts of ash and slag is usually done hydraulically, which requires a lot of water. At a thermal power plant with a capacity of 4000 MW, operating on Ekibastuz coal, up to 4000 t / h of this fuel is burned, while about 1600 ... 1700 t / h of ash is formed. To evacuate this amount from the station, at least 8000 m 3 / h of water is required. Therefore, the main direction in this area is the creation of recirculating systems of the hydraulic power plant, when the clarified water freed from ash and slag is sent back to the TPP in the water supply system.

Waste waters from the GZU are significantly polluted with suspended solids, have increased mineralization and, in most cases, increased alkalinity. In addition, they may contain compounds of fluorine, arsenic, mercury, vanadium.

The effluents after chemical washing or conservation of heat-power equipment are very diverse in their composition due to the abundance of washing solutions. For washing, hydrochloric, sulfuric, hydrofluoric, sulfamic mineral acids, as well as organic acids: citric, orthophthalic, adipic, oxalic, formic, acetic, etc. are used. Trilon B, various corrosion inhibitors, surfactants, thiourea, are used along with them. hydrazine, nitrites, ammonia.

As a result of chemical reactions in the process of washing or preserving equipment, various organic and inorganic acids, alkalis, nitrates, ammonium, iron, copper, Trilon B, inhibitors, hydrazine, fluorine, urotropin, captax, etc. can be released. Such a variety of chemicals requires an individual solution for the neutralization and disposal of toxic waste from chemical washings.

Water from washing the outer heating surfaces is formed only at TPPs using sulfurous fuel oil as the main fuel. It should be borne in mind that the neutralization of these washing solutions is accompanied by the production of sludge containing valuable substances - vanadium and nickel compounds.

During the operation of demineralized water treatment at TPPs and NPPs, there are effluents from the storage of reagents, washing of mechanical filters, removal of sludge water from clarifiers, and regeneration of ion exchange filters. These waters contain significant amounts of calcium, magnesium, sodium, aluminum, and iron salts. For example, at a CHP with a chemical water treatment capacity of 2000 t / h, salts are discharged up to 2.5 t / h.

Pretreatment (mechanical filters and clarifiers) discharges non-toxic sediments - calcium carbonate, iron and aluminum hydroxide, silicic acid, organic matter, clay particles.

Finally, power plants that use fire resistant fluids such as ivviol or OMTI in steam turbine lubrication and control systems generate a small amount of wastewater contaminated with this substance.

The main regulatory document establishing the surface water protection system is the "Rules for the protection of surface waters (standard provision)" (Moscow: Goskomprirody, 1991).

5.21.1. The main problems of wastewater in the energy sector

The operation of modern thermal power plants is associated with the appearance of a number of liquid waste water. These include water after cooling of various devices - turbine condensers, oil and air coolers, moving mechanisms, etc .; waste water from hydraulic ash removal systems (HSS); spent solutions after chemical cleaning of heat-power equipment or its conservation; regeneration and sludge water from water treatment plants; oil-contaminated sewage; solutions arising from washing the external heating surfaces, mainly of air heaters and water economizers of boiler units operating on sulphurous fuel oil. The compositions of all these effluents and their quantities are very different; they are determined by the type of TPP and the equipment installed on it, its capacity, the type of fuel used, the composition of the source water, the adopted method of water treatment in the main production and other less significant circumstances. In recent years, significant work has been carried out in the power industry to reduce the amount of wastewater, the content of various pollutants in them and to create circulating water use systems. The ways of creating completely internal drainage thermal power plants are outlined, which requires the solution of a number of complex technical and organizational problems, as well as certain capital investments.

The creation of TPPs that do not pollute natural water bodies is possible in two ways - deep purification of all effluents to maximum permissible concentrations (MPC) or organization of wastewater reuse systems. The first way is unpromising, since the bodies of protection of water bodies are constantly increasing the requirements for the degree of purification of waters discharged by industrial enterprises. So, several years ago, the purification of effluents from oil products to a residual content of 0.3 mg / l was considered sufficient. Later it was adopted as the maximum permissible concentration of 0.1 mg / l. Now this norm has been reduced to 0.05 mg / l, and it is not excluded that its further reduction will occur for fishery reservoirs. It should also be borne in mind that the use of new materials and reagents in water treatment technology will also require setting MPC for them. Increasing the depth of wastewater treatment will require a significant increase in the costs of both the construction of the relevant installations and their operation. All these circumstances make the first way very unpromising. The second way is more realistic - the creation of circulating systems with repeated use of water. At the same time, deep purification of effluents is no longer required, it is enough to bring their quality to a level acceptable for the implementation of the corresponding technological processes. This way gives a significant reduction in water consumption, that is, the amount of water that the company takes from the water source sharply decreases. In addition, this approach sharply reduces the number of issues to be agreed with the bodies that control the quality of effluents. That is why the development of drainless TPPs is going on.

The amount of water formed after cooling the equipment is mainly determined by the amount of exhaust steam entering the turbine condensers. Water after cooling the condensers of turbines and air coolers, as a rule, carries only the so-called thermal pollution, since their temperature is 8-10 ° C higher than the temperature of water in the water source. However, in some cases, cooling waters can introduce foreign matter into natural water bodies. This is due to the fact that the cooling system also includes oil coolers, the violation of the density of which can lead to the penetration of oil products (oils) into the cooling water.

The most reliable way to solve this problem is to separate the cooling of such devices as oil coolers and the like into a special autonomous system, separated from the cooling system of "clean" devices.

At TPPs using solid fuels, the removal of significant amounts of ash and slag is usually carried out hydraulically, which requires a large amount of water. Thus, a TPP with a capacity of 2400 MW, operating on Ekibastuz coal, burns up to 2500 t / h of this fuel, while forming up to 1000 t / h of ash and slag. To evacuate this amount from the station to ash and slag fields, at least 5000 m3 / h of water is required. Therefore, the main direction in this area is the creation of a recirculating system of the GZU, when the clarified water freed from particles of ash and slag is again sent through the return pipeline to the TPP to perform the same function. Part of the water during this circulation leaves the system, as it is retained in the pores of the settled ash, enters into chemical compounds with the components of this ash, and also evaporates and in some cases seeps into the ground. At the same time, water flows into the system mainly due to atmospheric precipitation. Therefore, the most important issue in the creation of circulating systems of the hydraulic system is to ensure a balance between the flow and consumption of water, which must be taken into account in various technological processes, including ash collection. For example, when using wet ash collectors, the main role in solving this problem is played by the organization of their supply with clarified water. The lack of balance creates the need for a systematic discharge of part of the water from the MS system.

The need to create recirculating systems for hydraulic control systems is also due to the fact that in some cases such waters contain an increased concentration of fluorides, arsenic, vanadium, less often mercury and germanium (Donetsk coals) and some other elements with harmful properties. HZU waters also often contain carcinogenic organic compounds, phenols, etc.

Effluents after chemical washing or conservation of heat power equipment are very diverse in their composition due to the abundance of recipes for washing solutions. In addition to mineral acids - hydrochloric, sulfuric, hydrofluoric, sulfamic, many organic acids are used (citric, orthophthalic, adipic, oxalic, formic, acetic, etc.). Along with them, trilon and various mixtures of acids, which are industrial waste, are used, and captax, surfactants, sulfonated naphthenic acids, etc. are introduced as corrosion inhibitors. Thiourea is introduced into the copper complex for binding to the copper complex. Preservation solutions contain hydrazine, nitrites, ammonia.

Most of the organic compounds used in flushing solutions are biologically recyclable and, therefore, can be sent together with domestic wastewater to appropriate plants. Before that, it is necessary to remove toxic substances that have a detrimental effect on the active microflora from the spent flushing and conservation solutions. These substances include metal nones - copper, zinc, nickel, iron, as well as hydrazine and captax. Trilon refers to biologically "hard" compounds, moreover, it suppresses the activity of biological factors, but in the form of calcium complexes it is permissible in rather high concentrations in wastewater sent for biological processing. All these conditions dictate a specific technology for processing wastewater from chemical treatment of equipment. They must be collected in a container in which the acid mixture is neutralized, and hydrates of iron, copper, zinc, nickel oxides are precipitated, etc. If a trilon was used for cleaning, then only iron can be precipitated during neutralization, while copper complexes, zinc and nickel are not destroyed even at high pH values. Therefore, to destroy these strong complexes, the precipitation of metals in the form of sulfides is used by introducing sodium sulfide into the liquid.

The precipitation of sulfides or hydrates of oxides occurs slowly, therefore, after adding the reagents, the liquid is kept for several days. During this time, complete oxidation of hydrazine with atmospheric oxygen takes place. Then a transparent liquid containing only organic substances and an excess of precipitating reagents is gradually pumped out into the mains of domestic wastewater.

The vacated container is filled with effluents from the next washing and the deposition operation is repeated. Sediments accumulated after several cleanings are evacuated; these sediments often contain significant amounts of valuable metals that can be recovered by metallurgists. In cases where a TPP is located far from settlements that have devices for biological treatment of domestic wastewater, the clarified liquid can be sent for irrigation of sites or into a closed cooling system as additional water. At TPPs with hydraulic ash removal, wastewater after chemical cleaning of equipment, often even without preliminary precipitation of metals (iron, copper, zinc, etc.), can be discharged into the slurry pipeline. Crushed ash particles have a high absorption capacity in relation to impurities in spent solutions after chemical cleaning of equipment.

Water from washing the external heating surfaces is formed only at TPPs using sulfurous fuel oils as the main fuel. Ash elements formed during the combustion of fuel oil have a high stickiness and settle mainly on the surface of air heater elements, which, as a result, have to be regularly cleaned. Periodically cleaning is done by washing; the result is a wash fluid containing free sulfuric acid and sulfates of iron, vanadium, nickel, copper and sodium. Other metals are also present as minor impurities in this liquid.

Neutralization of these washing solutions is accompanied by the production of sludge containing valuable substances - vanadium, nickel, etc.

During the operation of water treatment plants at power plants, effluents arise from the washing of mechanical filters, from the removal of sludge water from clarifiers and as a result of the regeneration of cationic and anionic materials.

The flushing water contains only non-toxic sediments - calcium carbonate, magnesium, iron and aluminum hydroxides, silicic acid, organic, mainly humic substances, clay particles. Since all these impurities are not toxic, these effluents can be discharged after the separation of the sludge into water bodies. At modern thermal power plants, these waters, after some clarification, are returned to water treatment, namely, to its head part.

Regeneration effluent contains a significant amount of calcium, magnesium and sodium salts in the solution.

In order to reduce saline discharges from chemical water purification, various methods of preliminary treatment of water entering the water purification are proposed. For example, in electrodialysis plants or in reverse osmosis plants, the mineralization of the source water can be slightly reduced. However, the amount of saline effluents even with these methods remains significant, since in all cases pure water is taken, and the salts contained in it are returned to the reservoir with one or another amount of reagents.

It is proposed to replace the chemical desalination with evaporators or to use them for the evaporation of saline effluents. The installation of evaporators instead of chemical desalination is possible at purely condensing TPPs, but it is very burdensome at TPPs with a high steam output to its industrial consumers. Evaporation of saline wastewater, obviously, does not solve the problem of their removal, but only reduces the volume of objects to be evacuated.

The following scheme of waste treatment seems somewhat more attractive: after mixing acidic (from H-cationite) and alkaline (from anionite) wastewater, they are treated with lime and soda to precipitate calcium and magnesium ions. The solution after separation from the formed precipitates contains only sodium salts, chlorides and sulfates. This solution is subjected to electrolysis, thus obtaining acidic and alkaline solutions. They are sent instead of imported acids and alkalis for the regeneration of the corresponding filters. Calculations show that in this way the amount of excess salts can be reduced several times.