Chemical water purification. Methods used in household filters

The effectiveness of a water purification method depends on how correctly the type of pollution is determined. In order to learn more about the type and concentration of foreign substances in water, chemical and bacteriological analysis is carried out.

Almost always, several contaminants are present in water at once, so a complex is used various methods cleaning, several filters mounted in series.

Chemical methods

Chemical methods of water purification are based on the use of chemical interactions between various elements and compounds. Reagents are selected strictly based on the results chemical analysis water. The reagents enter into chemical reactions with contaminants, completely decomposing them, converting them into a form that is safe for humans, or into a solid sediment that is retained by the filter.

You can set up a chemical filter (select reagents) very precisely - so that only harmful impurities are removed from the water. At the same time, the purified water will not be “dead” or sterile - it will still contain the salts necessary to maintain the water-salt balance in the human body.

Chemical methods of water purification in combination with mechanical filtration are the main ones for an autonomous water supply system for a country house.

Capable of removing from water: hardness salts, dissolved iron, dissolved manganese, increased acidity, organic compounds, microbiological contamination, chlorides, sulfates, nitrates, nitrites, free carbon dioxide, free chlorine, silicon, dissolved gases.

Physical methods

Physical methods of water purification use one or another physical effect on water or pollution.

Capable of removing from water: coarse particles, microparticles, suspensions, colloids, dissolved gases, hardness salts, salts heavy metals, free chlorine, microbiological contamination.

Ultraviolet

Ultraviolet radiation can kill all microorganisms in water. The physical effect is that the wavelength of UV radiation effectively destroys the cells of pathogenic bacteria. Passing through the filter, the flow of water flows around the ultraviolet lamp, protected by quartz glass, from all sides. This effect makes the UV emitter one of the most effective water sterilizers.

Capable of removing from water: microbiological contamination of any type and level.

Thermal method

The process is based on the phenomenon of the transition of heated water into the vapor phase and the subsequent condensation of steam into liquid. At the same time, the level of salt concentration in the water changes. Boiling is the simplest way to partially soften water. At high temperature calcium bicarbonate (hardness salt) breaks down into carbon dioxide and calcium carbonate, the same white coating in a teapot. Heating water to 100C also reduces hardness caused by the presence of calcium sulfate.

Capable of removing from water: hardness, organic compounds, microbiological contamination.

Reverse osmosis

Under the influence of osmotic pressure, water containing contaminants penetrates through a special polymer membrane. The polymer membrane allows only water and oxygen molecules to pass through, retaining molecules of all foreign solutes, as well as bacteria and viruses. The reverse osmosis filter will not work if the pressure in the water supply is less than 2.5-3 atm.

Capable of removing from water: microparticles, suspensions, colloids, bacteria, viruses, molecules, ions, hardness salts, iron, manganese, total alkalinity, dissolved gases, chlorides, sulfates, nitrates, nitrites, silicon.

Very often, cleaning methods combine several principles at once. Thanks to this, physicochemical methods of water purification are more versatile and highly effective.

Physico-chemical water purification

Based on the flotation effect, it effectively removes fine and colloidal particles from water. The gas is passed through the liquid mass of waste. In this case, each gas bubble, under the influence of molecular forces, “sticks” with a particle of pollution. Bubbles accumulate on the surface in the form of foam, which can be easily removed mechanically.

Another example of a physical-chemical purification method: the electrochemical method of water purification or coagulation. The phenomenon of sedimentation of colloidal particles when exposed to direct current is used. The method is widely used in industry - mining, processing, etc.

Capable of removing from water: organic substances, fine particles, suspensions, colloids, hardness salts.

Biological methods

Systems biological treatment water use the ability of some microorganisms to absorb partially or completely various (most often biological) types of pollutants. This happens when the pollution provides a breeding ground for bacteria. Aerobic and anaerobic methods of wastewater treatment are well known. Two types of bacteria process the organic component of household wastewater from a country house.

The anaerobic method is more effective, since microorganisms develop more intensively in an oxygen environment. In addition, oxygen serves as an additional source of oxidation reactions and decomposition of organic matter.

Various types of bacteria are capable of processing different types pollution, including those that are not at all “edible” in our opinion: bacteria that eat plastic have recently been discovered.

Taking into account the accelerated development of genetic engineering biological methods water purification will constantly develop, expanding the scope of application. Perhaps soon, thanks to omnivorous bacteria, humanity will finally get rid of giant landfills.

Capable of removing from water: organic matter, dissolved ferrous iron.

Chemical water treatment has become widespread today. Substances with which water is saturated, which are suitable for chemical water purification, are very extensive. Therefore, the application of water treatment with ultrafiltration is extensive. Complete water purification can be achieved using a combination of several reagents for any contamination. Usually, chemical methods Wastewater treatment is used more in industry than in everyday life. Its purpose is to remove fine suspended particles, organics, dissolved gases and minerals.

Typically, the use of a fairly delicate method - chemical water treatment - in a house, country house or cottage allows you to take into account all the small details, and this is exactly what this one does water treatment method the most effective. The choice of reagent depends on the composition of the water to be purified. It is worth doing a water analysis first.

Myself chemical cleaning process carried out using filters and is a rather complex procedure that depends on many factors. Reagents for chemical water treatment use various oxidizing agents, such as chlorine, ozone, potassium permanganate, as well as alkalizing substances (for example, sodium hydroxide, soda, lime and acidifying substances such as sulfuric acid and hydrochloric acid).

Oxidation as chemical water treatment. This cleaning method is applicable when the water is full harmful substances, and if they cannot be extracted in any other way. These substances are cyanide compounds, which are most often found in wastewater. industrial waters(usually they are contaminated with various industrial wastes).

Oxidizing agents used for chemical cleaning waters that can cope with cyanide compounds are sodium hypochlorite and chlorine. It is used most often due to its relatively low cost. At chemical water purification procedure Constant monitoring of the acidity level of the water is necessary because the reaction can only occur at a certain pH level. Purified water must have the pH level of the reservoir to which it will be returned after the purification procedure.

Chemical water treatment is as important as ozonation and electrochemical oxidation. , like electrochemical oxidation at the anode, allows you to extract acids, metals and other substances found in waste solutions. One of the most safe methods of water treatment Ozonation is precisely what it is, because it is used most often for the reuse of wastewater. Ozonation has a high reaction rate, which ensures the decomposition of ozone into oxygen. The advantages are also the complete absence of traces of the reaction and the possibility of obtaining ozone at the site where the reaction is carried out.

Keeps its acid-base balance normal, without increasing the salt content, as happens with other chemical reagents. Ozone is a derivative of oxygen, which is what explains the speed of the reaction: during the ozonation process, the rate of release of the oxygen atom to other substances is very high. Ozone is perhaps the most effective metal oxidizer among the reagents used in water treatment.

Neutralization using alkalizing or acidifying agents is another method of water purification. As a rule, this chemical cleaning method used in the treatment of industrial wastewater whose pH is disturbed. This method has been successfully used to remove heavy metals from water.

The neutralization method is the interaction of alkalis and acids that stabilize the pH level (and according to standards it should not exceed a coefficient of 8.5, and also should not fall below 6.5). Water must be chemically treated before being released into a city sewer or reservoir if the acid-base balance does not meet these standards. The process usually takes place in special contact or flow-type neutralizers combined with a settling tank. After chemical purification, the water must be clarified.

Chemical water treatment wastewater is the most advanced method of chemical treatment because it occurs complete cleansing water without causing unwanted side effects. This method is not yet widely used due to its high cost.

We use water everywhere: swimming pools, baths, heating, cooking... It's no secret that water becomes polluted over time, so what to do? Here elements from the periodic table will come to our aid, with the help of which we can perform chemical purification of water. Many substances can be used in chemical water purification. Below are the popular chemicals used for water purification.

Algaecides This chemical compounds, which when added to water kills blue and green algae. Examples of such connections:

• copper sulfate,
• iron salts,
• amine salts and benzalkonium chloride.

Algaecides are very effective at controlling algae, but they are not very useful against algae blooms in the environment.

Note! The problem with algaecides is that they kill all the algae present, but do not neutralize the toxins released by the algae before they are killed.

Anti-foaming agents

Foam is a mass of bubbles formed when certain types gases disperse into liquid. Foam formation is a complex topic of research in physical chemistry, but its presence is known to cause serious problems during industrial processes and quality finished products. When foam formation is not controlled, it can reduce the ability of equipment to operate.

The antifoam mixture contains oils combined with a small amount of silica. These compounds break up foam due to two properties of silica: incompatibility with aqueous systems and ease of spread. Antifoaming agents are available either as a powder or as a pure emulsion product.

Powder

Powdered antifoam agents are a group of products based on modified polydimethylsiloxane. These products differ in basic characteristics, but as a group perform very well in preventing foam in a wide range of applications and conditions.

Antifoam agents are chemically inert and do not react with the environment. They are odorless, tasteless, non-volatile or toxic and do not cause corrosion of materials. The only drawback of the crushed product is that it cannot be used in an aqueous solution.

Emulsions

Emulsions, i.e. Antifoaming agents are polydimethylsiloxane in liquid form. They have the same properties as in powder form. The only difference is that they can be used in aqueous solutions.

Coagulants

As far as coagulants are concerned, positive ions with high valence are preferred. Typically aluminum and iron ions are used as Al2(SO4)3- (“aluin”) and iron as FeCl3 or Fe2(SO4)3. A relatively cheap form of FeSO4 can also be used, provided that it is mixed with hydrogen peroxide and Fe3+ under aeration.

Coagulation is highly dependent on the dose of coagulants, pH and colloid concentration. To adjust the pH, Ca(OH)2 is also used as a flocculant. Doses typically range between 10 and 90 mg Fe3+/L.

Corrosion inhibitors

Corrosion is a general term that defines the transition of a metal to a soluble form.
Corrosion can lead to destruction important elements boiler systems, the deposition of corrosion products on the corresponding surfaces of the heat exchangers, and a general decrease in system performance.

Therefore, corrosion inhibitors are often used in water applications. heating systems. These chemical compounds react with the metal surface, giving it a certain level of protection. Inhibitors often act by adsorption onto the metal surface, protecting it - forming protective layer on inside pipelines.

There are five various types corrosion inhibitors. This:

1. Passive inhibitors(“passivators”). They cause a shift in the corrosion potential. Examples of such inhibitors are oxidizing anions such as chromate, nitrite and nitrate, and non-flammable ions such as phosphate and molybdate. These inhibitors are the most effective and therefore most widely used.
2. Cathode inhibitors. Some, such as arsenic and antimony compounds, work by inhibiting recombination and releasing hydrogen. Other ions, such as calcium, zinc or magnesium, can be deposited as oxides, forming a protective layer on the metal surface.
3. Organic Inhibitors. They affect the entire surface of corrosive metal liquids when present in appropriate concentrations. Organic inhibitors protect metals by creating a film (layer) and a hydrophobic group on its surface.
4. Precipitation-causing inhibitors. These are compounds that cause the formation of a deposition product on the metal surface, thereby creating a protective film. The most popular inhibitors in this category are silicates and phosphates.
5. Volatile corrosion inhibitors(VCI). These connections are made in a closed volatilization corrosion environment from the source. Examples of such inhibitors are morpholine, hydrazine and volatile solids such as dicyclohexylamine salts, cyclohexylamine and hexamethylene. Upon contact with a metal surface, the vapor of these salts condenses and hydrolyzes with moisture to release protective ions.

Disinfectants

Disinfectants kill unwanted microorganisms present in water. There are many various types disinfectants:

• Chlorine (dose 2-10 mg/l);
• Chlorine dioxide;
• Ozone;
• Hypochlorite.

Disinfection with chlorine dioxide

ClO2 is used as primary disinfectant for surface waters with odor and taste problems. This chlorine contains the biocide in concentrations as low as 0.1 ppm and over a wide pH range. ClO 2 penetrates the cell wall and reacts with amino acids in the cell cytoplasm to kill microorganisms.

Chlorine dioxide disinfects according to the same principle as chlorine. However, unlike chlorine, chlorine dioxide does not have any harmful effects on human health.

Hypochlorite

Hypochlorite is used in the same way as chlorine dioxide and chlorine. Hypo-chlorination is a disinfection method that Lately is not widely used, since it has been proven that during disinfection, a bromate consistency appears in the water.

Ozone disinfection

Ozone is a powerful oxidizing agent with a surprisingly short life. It consists of particles with an extra oxygen atom to form O3. When ozone comes into contact with the cause of odor, bacteria or viruses, the additional O-atom breaks them down through the process of oxidation. The extra oxygen molecule is so “used up” that the end result is only oxygen.

Disinfectants can be used in many industries. Ozone is used in the pharmaceutical industry to prepare drinking water, in the treatment of water for various processes in the production of ultrapure water, as well as for the disinfection of surfaces.
Chlorine dioxide is used primarily for the preparation of drinking water and disinfection of pipelines.

Flocculants

Promote the formation of flocs in water, which contain suspended solid particles of polymer flocculants (polyelectrolytes). They promote the formation of bonds between molecules. These polymers have very specific effects, depending on their charge, molecular weight, and degree of molecular branching.

The polymers are soluble in water and their molecular weight ranges from 10.5 to 10.6 g/L. In this case, there may be slightly different costs of one flocculant. Cationic polymers based on nitrogen, and anionic polymers based on carboxylic acids and zwitterions carry both positive and negative ions.

Neutralizing agents (alkalinity control)

To neutralize the acid, sodium hydroxide (NaOH), calcium carbonate or lime (Ca(OH)2) is used to raise the pH. To lower the pH, use diluted sulfuric acid(H 2 SO 4) or dilute hydrochloric acid (HCl). The dose of neutralizing agents depends on the pH of the water in the reaction tank. Neutralization of the reaction causes an increase in temperature.

Oxidizing agents

Chemical oxidative processes require the use of (chemical) oxidizers to reduce COD/BOD levels and to remove organic and inorganic oxidation components.
There are many oxidizing compounds. Examples include:

• Hydrogen peroxide;
• Ozone;
• Combination of ozone and peroxide;
• Oxygen.

Chemical methods of wastewater treatment include neutralization, oxidation and restoration of contaminants in waters. The oxidation method includes electrochemical treatment of wastewater, which is used to ensure circulating water supply by extracting dissolved impurities.

Sometimes the process in question is carried out before the wastewater is sent to bioremediation. In this case, the efficiency of chemical cleaning increases. More often, the above methods are used for post-treatment of wastewater before discharging it into water bodies or onto the terrain.

How to neutralize wastewater

Neutralization of wastewater helps to normalize the pH value. Such chemical composition water is not dangerous for humans and nature. It can be reused for various needs.

The neutralization process is based on the use of reagents that are used taking into account the concentration and constituent elements acidic environment. Experts distinguish 3 types of wastewater with acids:

• predominance of weak acids;
• presence of strong acids;
• predominance of sulfuric and sulfurous acid.

Neutralization of waters with sulfuric acid depends on the reagent used. The process occurs at different levels. If you use lime milk, then plaster will fall out as a residue. It will settle on the walls of the pipes.

To neutralize alkaline waters, acids or acid gases are used. Using the latest technology, simultaneous neutralization of wastewater and purification of harmful gas components is carried out. To calculate the amount of acid gas required, the level of mass transfer is determined. This technology is considered resource-saving, as it eliminates wastewater discharge, reducing fresh water consumption, saving thermal energy to heat it up.

When developing a technological scheme for wastewater neutralization, the following is taken into account:

• possible simultaneous neutralization of alkalis and acids entering with wastewater;
• presence of alkaline reserve;
• natural neutralization of water bodies.

To implement the process under consideration, special equipment is used. Neutralization is carried out in a storage tank, settling tank or illuminator. The choice of equipment depends on climatic conditions, duration of wastewater storage.

To implement neutralization, various chemicals are added to the wastewater, which react with acids or alkalis to form a suspension. It precipitates. Its volume is determined by the following indicators:

• the amount of metals, acid ions in the source water;
• quantity and water of the reagent used;
• the level of lightening used.

Neutralization with reagents is used if the balance between acid and alkali is disturbed in the wastewater. In such cases, the possibility of implementing the process in question by mixing water is excluded. To solve the problem, missing chemicals are added to the wastewater. This technology is most often used in the presence of acidic waters.

Their neutralization is based on the use of waste from various industries (sludge that is formed after chemical cleaning at thermal power plants). In the presence of sulfuric acid, steelmaking slags are used.

The effectiveness of this technology is based on the presence in them of a large amount of magnesium and calcium oxide compounds. The following data is taken into account:

• the amount of calcium salts inherent in water and capable of dissolving well;
• the amount of calcium salts that are poorly soluble in water.

Lime is introduced into drains in the form of milk or dry powder. The most economical option is to use fluff lime. If it is necessary to process up to 200 cubic meters. water, then use soda.

Water purification through oxidation

This technique is used in the following cases:

• for neutralization of wastewater derivatives from toxins;
• when there is no need to extract compounds from wastewater;
• it is unprofitable or impractical to use other methods.

To implement the method under consideration, various oxidizing agents are used, including chlorine dioxide, chlorine of various consistencies, sodium hypochlorite, potassium dichromate, ozone and other compounds. They enter the water by binding to chemical toxins. As a result of the reaction, toxic impurities appear, for the removal of which other technologies are used.

Chlorine is considered a strong oxidizing agent. It is aggressive, therefore it is not in great demand for the implementation of various modern technologies in the field of wastewater treatment. It is often replaced with ozone, less often with potassium permanganate or hydrogen peroxide.

The technology under consideration is to purify water by oxidizing its contaminants. After such a chemical reaction, substances of less toxicity are formed, which are easily removed from the liquid. The activity of the oxidizing agent used is the value of the oxidation potential. The first and most effective oxidizing agent is fluorine. It is highly aggressive, so it is not used in practice. For other substances the value of this indicator does not exceed 2.1.

To clean the liquid from hydrogen sulfide, phenol, hydrosulfide, chlorine is used. If ammonia or its derivatives are present in the wastewater, chlorine reacts with them to form diclo- and monochloramines.

Oxidative technology can be based on the use of oxygen. Such a reaction occurs in the liquid phase if observed high pressure and temperature. If a similar situation is observed in the case of the use of sulfides, then the depth of their oxidation increases.

Oxygen is used to remove iron from the liquid. To destroy sulfide compounds, carbon dioxide is used in the flue gas.

Water purification with ozone

Wastewater treatment technology based on the use of ozone is aimed at destroying many impurities and organic matter. Simultaneously with oxidation, the liquid becomes discolored and disinfected. Odors and taste are removed from it. Ozone is an oxidizing agent that affects organic and inorganic substances that are part of wastewater in dissolved form.

Ozone easily removes phenol, petroleum products, hydrogen sulfide, and cyanide. At the same time, it affects different microbes. In the process of ozonation at the local treatment station, 2 technologies are used:

• catalysis;
• ozonolysis

In this case, ozone acts according to one of the following principles:

1. Application of 1 oxygen atom.
2. Ozone attaches to the substance, promoting the formation of ozonide.
3. Increased exposure to atmospheric oxygen.

Electrochemical wastewater treatment technology is based on their electrolysis. The chemical transformation of substances depends on the type and material of the electrodes used. The technique is based on cathodic reduction, anodic oxidation of wastewater.

This technique is considered energy-intensive. The technology works slowly, so it is used to purify small volumes of water or when there are concentrated contaminants in the liquid. Graphite, ruthenium, and magnesium are used as anodes.

A dangerous phenomenon in the process of electrochemical oxidation technology is the displacement of gases that are released during the cleaning process. This could cause an explosion. To prevent this, diaphragms of asbestos, ceramics and glass are installed between the electrodes.

To clean wastewater, use a large number of oxidizing particles and high-energy radiation. If the technique is used at a local treatment plant, then radioactive cesium or cobalt is used as a radiation source.

If arsenic and chromium need to be removed from wastewater, recovery technology is used. An inorganic mercury compound is converted into a metal compound using reagents. Then flotation, filtration and sedimentation are carried out.

Sulfur dioxide is used to bind arsenic. The resulting compounds are removed from wastewater by precipitation. Chromium with 6 valences is reduced to the trivalent level. Various reagents are used for this. The hydroxide then settles in a settling tank.

Equipment used

The process under consideration proceeds normally if a filter installation that has not failed is used for its implementation. It is presented in the form of a multicomponent device with an antiseptic and a biological filter. An antiseptic with a chemical reagent is used to disinfect wastewater. They selectively act on the pollutant.

Purification plants are capable of filtering different volumes of water per day. This indicator depends on the power of the equipment used. Its advantages include:

• long-term operation;
• simple maintenance;
• accessibility to different equipment units.

The following types of cleaning units are used to filter wastewater:

• with filter baffle;
• with a non-cohesive filter layer.

The first group includes traps of useful elements contained in wastewater. Similar equipment is used for cleaning with low-humidity sludge. The second group includes granular filters that purify a large amount of wastewater.

System units that have a fixed filter partition are equipped with a belt, sheet, drum or disk filter. Installations with a non-cohesive layer are equipped with non-pressure or pressure filters.

The following devices are used as settling tanks in equipment:

• hydrocyclones – purify wastewater from chemical plants;
• scrubbers and thermal units – purify from sulfates and radioactive substances;
• hydraulic – neutralize acids;
• adsorbers and desorbers - bind or remove organic and volatile inorganic substances, including gases.

The installations described above are installed in various industries and in everyday life. The type of installation is selected taking into account the composition of the water and the type of production. Equipment that purifies wastewater from mechanical particles and petroleum products is more often used. Chemical wastewater treatment technologies are based on adding various chemical reagents to contaminated water. The substances used, reacting with pollutants, contribute to their precipitation in the form of insoluble particles. They are then removed from the wastewater by filtration. The chemical purification technique helps remove up to 95% of insoluble and up to 25% of soluble substances from water.

Chemical water treatment is one of the most important factors in the service life of the boiler. The higher the quality of the water, the longer the overall water supply system will last you.

The main tasks of water treatment and rational organization of the water chemistry regime of boilers, steam generators, feed water path and heating networks are:

· Prevention of the formation of scale deposits, iron oxides, etc. on the heating surfaces of boilers, heat exchangers and other parts of heating systems,

· Corrosion protection of structural metals of the base and auxiliary equipment heating systems in conditions of their contact with water and steam, as well as when they are in reserve, long-term downtime or conservation.

Requirements for the quality of make-up and network water are established depending on the type of heating network:

For a heating network with an open water intake, the treated water must meet:
requirements for household and drinking water, the quality of which is regulated by SanPIN 2.1.4.559-96, in particular GOST “Drinking Water”. Magnitude overall hardness should not exceed 7 mg-eq/l, iron - 0.3 mg/l, pH value - 9.0.

Water quality for a closed network determined by the type of heating equipment used (boiler, boiler, etc.). Due to the lack of direct water supply for the needs of the population, less stringent requirements are imposed on the quality of water for a closed network; the main task is to ensure scale-free operation of the heating equipment used (boilers, boilers) and the regulatory permissible level of corrosion activity. Thus, it may be acceptable to increase the pH value to 10.5 with simultaneous deep softening; the determining indicator is the value of the carbonate index, which in turn determines the permissible level of scale formation - not higher than 0.1.

The main indicator of scale-free mode is the value of the carbonate index - the product of total alkalinity and calcium hardness, which has different meanings for a given temperature regime.

The main modern methods of water preparation:

Softening by Na-cation using modern methods ion exchange, using filter materials and corresponding filter designs;

· Decarbonization of water using modern new types of filter materials (weak acid cation exchangers) and corresponding filter designs instead of H - cationization with “hungry” regeneration;

· Water purification using membrane water treatment technologies;

· Application of chemical treatment programs for make-up water using dosing of modern, more effective reagents (corrosion inhibitors, dispersants and scale inhibitors)

· Also a combination of all the above methods;

· Alternative methods - mainly various “hardness salt converters” based on physical methods water treatment;

Let's consider the use of the first two ion exchange methods - softening by Na-cation and decarbonization of water using modern new types of filter materials (weak acid cation exchangers).

Softening

The method of single-stage parallel-precise Na-cationization is most widely used. This process implemented in filters (of various designs and sizes depending on performance, requirements for the process itself, etc.). The ion exchange process itself occurs when water is filtered through a layer ion exchange resin(which is a strongly acidic cation exchanger in Na-form), loaded into a filter and periodically, when exhausted, regenerated with a solution of table salt. In this case, calcium salts (Ca2+), magnesium (Mg2+) are replaced with sodium (Na+) according to the following scheme:

Thus, instead of calcium (Ca2+), magnesium (Mg2+), an equivalent amount of sodium (Na+) is introduced. The result is softened water, but the alkalinity of the source water practically does not change during processing, and if its value is increased, the water will have enhanced corrosive properties due to the decomposition of alkalinity when heated. Strongly acidic cation exchangers like KU2-8 or sulfonated carbon, regenerated with table salt, are usually used as filter media.

The disadvantages of this method are:

· Increased (usually threefold) consumption of the reagent (NaCl salt) relative to stoichiometry;

· Increased water consumption for own needs;

· Increased content of chlorides and sodium in waste water, often exceeding the norm;

· To obtain deeply softened water, a second stage is required;

Modern methods ionization and the use of new types of cation exchangers make it possible to significantly optimize the process of Na - cationization - reduce the consumption of reagents for regeneration, reduce water consumption for own needs, and reduce the number of equipment (filters) involved. These methods include countercurrent cationization, in which the filtrate and regeneration flows have opposite directions. In particular, almost the entire volume of the filter is used for loading cation resin. The percentage of own needs is reduced to 3-4%, salt consumption is reduced by 15-20%. It becomes possible to obtain a filtrate after the first stage with a water hardness quality of no higher than 10–15 mcg-eq/l, that is, the second cationization stage is eliminated. But this technology requires high degree organization of operation and automation of technological processes is desirable.

It should be especially noted that transferring a cation exchange resin from one form to another directly at the consumer not only leads to increased labor costs and additional consumption of water and reagents, but also often leads to a decrease in performance indicators, primarily the dynamic exchange capacity. The explanation for this is the very procedure of converting from the H-form to the Na-form, in which it is first necessary to “deplete” the cation exchanger by pouring acidic water into the sewer (which leads not only to wastewater pollution, but also to corrosion of pipelines), and only then twice regenerate with sodium chloride solution and convert to Na-form. It should also be noted that a strong acid cation exchanger in the H-form, when initial water is passed through it until “depletion”, in addition to hardness salts, captures other ions from it, including metal ions (iron, aluminum, etc.), which, with subsequent regenerations with a solution of table salt are not removed. Consequently, some functional groups are blocked, resulting in exchange capacity cation exchange resin decreases after such procedures. These negative processes do not occur if cation exchangers in Na-form are specially used for water softening processes.

A further improvement of countercurrent processes was the development of ion exchangers in the form of monospheres, i.e. resins having a narrow fractional effective composition of granules (the number of particles of an effective size of about 0.5-0.6 mm reaches 95%, whereas for conventional ion exchangers it is approximately 40-45%).

However, good results can be achieved if cation exchangers are used with the usual granular composition (0.3-1.2 mm), but manufactured and supplied to consumers in Na-form. For example, strong acid cation exchanger Tulsion T-42 in Na-form, with a fractional composition of 0.3-1.2 mm.

Decarbonization

When preparing make-up water for hot water supply systems, the water preparation technology N - cationization with “hungry” regeneration is also used.

The H-cationization technology with “hungry” regeneration can significantly reduce the carbonate hardness of water with a partial decrease in non-carbonate hardness. All hydrogen ions introduced into the cation exchanger with the regeneration solution are completely retained, and as a result there is practically no acid in the waste water. The consumption of the regenerating reagent - sulfuric acid - is stoichiometric, i.e. calculated.

The disadvantages of this method when using sulfonated coal in the H-form are reduced performance characteristics, in particular:

· Low filtration speed (up to 10 m 3 / h);

· Low exchange capacity (200-250 g-eq/m3), as a consequence
- high costs of reagents and water for own needs
-increased number of filters
- difficulty in controlling the process and, as a result, unstable water quality

There are weak acid cation exchangers, often called carboxylic cation exchangers, which are specifically designed to remove carbonate hardness i.e. decarbonization. These include, in particular, the weakly acidic cation exchanger Tulsion SKhO-12.

With the ion exchange method of decarbonization of water on a weakly acidic carboxyl cation exchanger to the hydrogen form (as the most economical), calcium salts (Ca2+), magnesium (Mg2+) are replaced with hydrogen (H+) according to the following scheme:

Thus, instead of calcium (Ca2+), magnesium (Mg2+), an equivalent amount of hydrogen (H+) is introduced. Next, the HCO3- anions interact with the resulting H+ cations.

As a result, the concentration of bicarbonates decreases through their “destruction” and the resulting formation of carbon dioxide. At the same time, the pH of the water decreases. Further, to stabilize the pH of the water, it is required to be blown off using a degasser.

For example, let’s consider a technological scheme that involves the use of a decarbonization process on a weakly acidic cation exchanger instead of H-cationization with “hungry regeneration” and softening on a strong acid cation exchanger supplied immediately in Na - form. Considering that the source of source water is drinking chlorinated water from the city water supply, to increase the service life of cation exchangers, pre-cleaning in the form of a filled filter activated carbon. After this, the water goes to three decarbonization filters filled with weakly acidic cation exchanger, one/two in operation, one in reserve. The resulting carbon dioxide after the ion exchanger is blown off in the degasser (decarbonizer) and enters through the deaerator for heating. Part of the decarbonized water is supplied to a two-stage softening unit to produce make-up water for steam boilers. Schematic diagram is presented in Figure 10, in the form of direct-flow filters with the organization of an upper distribution system and an inert layer to increase the efficiency of filtering and washing the cation exchanger.

Figure 10 - Fundamental technology system HVO boiler room

Figure 11 - Photo of the chemical treatment plant

The total amount of water added from chemical water treatment consists of the following losses:

1) Condensate losses from process consumers:

In the absence of condensate from process consumers kg/s.

2) Loss of purge water kg/s.