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Water water hardness water softening methods. Water softening for the home in the best way with minimal investment. Why soften domestic water

Station for water purification from hardness salts
The indicator "hardness of water" displays the quantitative content of alkaline earth metals in it. Due to the fact that the main contribution is made by calcium and magnesium, the remaining alkaline earth metal ions are neglected. The term itself has a household origin: a fabric washed in water with a high content of calcium and magnesium becomes hard to the touch. Water hardness is divided into carbonate (temporary) and non-carbonate (permanent). Temporary - due to calcium and magnesium bicarbonates, permanent - mainly chlorides and sulfates. Temporary hardness is reduced by boiling due to the formation of insoluble carbonates. Ohigh water hardness, as well as an excess of iron, can be judged by the traces left in the form of scaleon heating elementsgray deposits on drying surfaces, dry tight skin, hard linen after washing.The process of removing hardness ions from water is called softening. Depending on the purpose of the water, the requirements for water hardness are different. For drinking water SanPiN 2.1.4.1074-01 sets the maximum concentration of 7 mg-eq / l, and according to the WHO recommendation, calcium in drinking water should contain 20-80 mg / l, magnesium - 10-30 mg / l, which corresponds to a hardness of 1.8-6 .5 mg-eq/l. For household appliances (washing machines, dishwashers, boilers), manufacturers recommend using water with a hardness of no more than 1.5 meq/l. The highest requirements for hardness are imposed on water for, the hardness of the prepared water should not exceed 5 µg-eq / l.

Water softening - terms

  • Thermal . When water is heated, calcium and magnesium bicarbonates turn into insoluble carbonates and settle on the walls of a water heater, kettle, etc. This method is applicable when there is a small need for water, for example, for a summer residence, and provided that most of the hardness is temporary (bicarbonate). The disadvantage of this method is also the difficulty of cleaning the heating surface from scale.
  • Reagent softening . The method is based on the introduction of slaked lime Ca (OH) 2 - liming, or slaked lime Ca (OH) 2 and soda Na2CO3 - soda-liming into water, to convert hardness salts into insoluble carbonates, with further precipitation or clarification. Additionally, coagulants and flocculants can be introduced. The method is used in industry for large volumes of water consumption with high carbonate hardness. When liming and soda-liming are used, alkalinity decreases simultaneously with hardness, suspended particles, including colloids, are removed during settling and clarification, and organic impurities can also be sorbed on sediment flakes. The disadvantages of this method are the high consumption of reagents, the need for a reagent economy, the large dimensions of the equipment when using sedimentation tanks, the formation of sludge that is difficult to dispose of. This method is not applicable to the preparation of drinking water, since softened water has a high pH value.
  • Ion exchange (Na-cationization) . The most common and accessible method, used for both industrial, and for private water treatment systems . The method is based on the replacement of calcium and magnesium ions with sodium ions when water passes through a strongly acidic cation exchanger in the Na-form. During the cleaning process, the ion-exchange resource of the load is exhausted and its regeneration is required. Restoration is carried out with a 6-10% solution of sodium chloride ( table salt), during regeneration, calcium and magnesium ions are again replaced by sodium ions, and the load is ready for further work. The frequency of regeneration is determined by the hardness of the source water.
  • Reverse osmosis and nanofiltration . These methods belong to membrane cleaning methods. At the core reverse osmosis and nanofiltration is based on the principle of filtration through a semi-permeable membrane. The cleaning process also removes other ions and contaminants, and reduces the overall mineralization of water. Installations are made both industrial, and household scale. Settings reverse osmosis indispensable for the purification of very hard water with an excess of salinity or sodium. The disadvantages of the method include high energy consumption compared to ion exchange.

Separately, you can specify the method of binding hardness salts with polyphosphate reagents, magnetic and pulsed processing, changes in the structure of hardness salts - all these methods do not remove calcium and magnesium ions from water, but only prevent the formation of scale.

Water treatment plants series - Water softening station
Purpose:
Water softening- extraction of calcium Ca2+ and magnesium Mg2+ ions from water, which determine its hardness. Hardness salts cause scale formation on heating elements and internal surfaces of pipes, increased consumption of detergents, and cloudy water.
Description:
The water softening station consists of a fiberglass body with an internal polyethylene liner, an Autotrol automatic control valve (Pentair Water, USA), a drainage distribution system, an ion exchange load, a gravel bed and a salt tank for regeneration.
Operating principle:
Water softening occurs by the mechanism of ion exchange, while calcium and magnesium ions are replaced by an equivalent amount of sodium ions. When the resource of the ion-exchange resin is exhausted, it is necessary to regenerate it with an 8-10% solution of common salt (NaCl). For this, special tableted salt is used, which is not subject to caking. The solution is prepared in a salt tank, the tank is filled with water automatically.The duties of the service personnel include filling the salt and monitoring its level.

"Lewatit" S1567 (Germany) is a strongly acidic helium cation exchanger in sodium form based on a styrene-divinylbenzene copolymer. Monodisperse granules have extraordinary chemical and mechanical stability and high osmotic resistance. The working exchange capacity is higher than that of most resins (taking into account aging) - 1200-1400 meq/l of resin is taken. Regeneration - with a solution of common salt (NaCl).

Source water requirements:

  • General hardness - up to 15 mg-eq / l, total salt content is not more than 1000 mg / l;
  • Lack of ferric iron in water;
  • The maximum content of dissolved iron in water is not more than 0.5 mg/l;
  • Permanganate oxidizability - no more than 3.0 mg O2/l;
  • Color - no more than 30 degrees;
  • Absence of suspensions, oil products, hydrogen sulfide and sulfides;
  • Content of free active chlorine - no more than 1 mg/l.

Specifications:

  • Water pressure at the filter inlet: minimum - 2.5 atm, maximum - 6.0 atm.;
  • Pumping equipment must provide a water flow rate not less than required during flushing (depending on the filter model);
  • The installation installation room must have an inlet and a drainage line;
  • Availability of stabilized power supply 220V (±5%), ~50Hz;
  • Room temperature: from +5 to +35˚С, humidity - no more than 70%, temperature of treated water from +2 to +45˚С.

Water softening stations in the cottage

A high level of hardness provokes the formation of scale, impairs the effectiveness of detergents. Under such adverse conditions, the risk of damage to functional components increases. heating equipment, other technology. Increased operating costs, the cost of complying with sanitary and hygienic rules.

Modern manufacturers offer different water softening methods and related equipment. Choose best option It will not be difficult after reading this publication. There is useful data here that will help you inexpensively and quickly implement the project.

Basic definitions

The overall level of hardness is defined as the sum of the permanent and temporary components. As a rule, the first part is of little practical importance, so it can be excluded from the review. The second is determined by the concentration of magnesium and calcium cations. These chemicals, when heated, are converted into an insoluble precipitate - scale.

It is they who clog the technical ducts, which is accompanied by a deterioration in the performance of the boilers. Such formations are characterized by porosity, low thermal conductivity. When accumulated on the surface of the heating element, this layer blocks the normal heat removal. If not applied effective method softening hard water, washing machine or other appliances with a heating element will be disabled due to scale.

In practice, they solve the issues of reducing the level of rigidity, or the complete elimination of harmful phenomena. The second option is better! It involves reliable protection of expensive products, effective prevention with the prevention of emergencies.

Method 1: Heating

The principle of operation of these water softening methods is clear from the general definition. Everyone knows that when boiling (heating) a layer of scale is actively formed on the walls of the kettle. After the procedure is completed, the stiffness will be reduced.

The theoretical simplicity of the method is the only advantage. A detailed study of the issue reveals the following shortcomings:

  • duration of the process;
  • not a large number of liquid that can be processed at home;
  • significant costs for electricity, gas, and other fuels.

It should not be forgotten that at the finishing stage it is necessary to remove strong scale. These are labor-intensive work operations that can spoil the working capacity.

Method 2: Treatment with an electromagnetic field

An intermediate conclusion can be drawn from the above descriptions. To remove harmful compounds using chemicals, ion exchange, boiling and membrane filtration, complex engineering problems have to be solved. This will be written below. The costs increase accordingly. Polyphosphate compounds are more effective. They are inexpensive, but reliably block the negative process. The method can be considered ideal if it were not for the contamination of the liquid.

There are no listed shortcomings in the technology of electromagnetic processing. Exposure to a strong field changes the shape of scale particles. Created needle protrusions do not allow them to combine into large fractions. This blocks the process of scale formation.

To obtain a field of optimal power and configuration, a high-frequency generator of electromagnetic oscillations is used. It works according to a special algorithm that does not cause the effect of "addiction". A decrease in the positive impact is observed when working with permanent magnets.

In the course of studying current market offers, attention should be paid to modern high-quality models of electromagnetic water treatment devices:

  • perform their functions with minimal power consumption (5-20 W / h).
  • The coil is created from several turns of wire. The device is connected to the network. Additional configuration is not needed.
  • The range reaches 2 km, which is enough to protect the object as a whole.
  • The durability of the devices exceeds 20 years.

In any case, you need to choose a manufacturer who has solid experience in the core field of activity!

Chemical methods of water softening

A well-known technique for specialized specialists is the addition of slaked lime to the solution. Chemical reactions bind calcium and magnesium molecules, followed by the formation of an insoluble precipitate. As it accumulates at the bottom of the working tank, it is removed. Fine suspended particles are retained through the phosphate method. A similar technology is used to reduce the non-carbonate component with soda.

The main disadvantage of this and other methods in this category is the contamination of the liquid with chemicals. In order for such processing to be safe, it is necessary to strictly observe the optimal dosages, carefully control all important steps. High-quality reproduction of technology at home is not possible without excessive difficulties and costs. It is used at municipal and collective water treatment plants of a professional category.

However, one "chemical" technique has become popular in everyday life. The researchers found that polyphosphate compounds form shells around the smallest insoluble fractions. They prevent coalescence into large particles, attachment to pipe walls and external surfaces of heating devices.

This useful property used by manufacturers of phosphate washing powders. Also, specialized flow tanks are used, in which polyphosphate salts are placed. The devices are mounted on the inlet pipe in front of the boilers and washing machines. The method is not suitable for the preparation of drinking water.

Filtration

The desired effect can be obtained by reducing the size of the cells to the size of molecules. Such microscopic ducts are created in membranes reverse osmosis. They can only pass clean water. Contaminated liquid accumulates in front of the barrier, is removed to the drain.

Problem solved? You should not jump to conclusions. The filtration technique is really good, but only for processing 180-220 liters/day. Such is the performance of serial at a reasonable cost. This amount is not enough for a single shower, to meet other household needs.

To increase productivity, several membranes are installed in parallel. For the operation of the kit, it is necessary to raise the pressure of a special pumping station. Such equipment for water filtration is expensive and takes up a lot of space.

Water softening by ion exchange

Reduce initial and operating costs with the help of equipment in this category. A special backfill is used that traps calcium and magnesium ions. At the same time, the liquid is filled with harmless sodium compounds.

The benefits are listed below:

  • In addition to the salty taste, the initial characteristics of the water do not change for the worse.
  • After processing a certain amount of liquid useful features backfills are restored by washing and regeneration.
  • These procedures are performed repeatedly in automatic mode, without careful control and intervention by the user.
  • If the operating rules are followed, the filling of resins remains operational for more than six years.

It is necessary to emphasize the availability of the regeneration mixture. This is an inexpensive solution of ordinary table salt (well purified).

As before, here are the nuances that deserve to be mentioned for a complete analysis of water softening by the ion-exchange method:

  • The ion-exchange method of water softening interrupts the supply of the object during regeneration (lasting more than an hour). To eliminate this disadvantage, two functional containers are installed in parallel.
  • A set with high performance for a family of 2-3 people occupies several square meters. meters of area.
  • Work publishes loud noise during the washing process, therefore, effective sound insulation of the room is needed.
  • Any significant change in hardness level must be corrected by manual adjustment.
  • A well-equipped set with an automation unit and several working tanks is expensive.

Ultrasonic exposure

Processing vibrations of the appropriate frequency range is used to reduce the level of rigidity. At the same time, a layer of old scale is destroyed, which is useful for cleaning pipes without aggressive chemical compounds.

Ultrasound is used with professional precautions to clean and protect industrial equipment. Large elements of these structures and threaded connections have better resistance to strong vibration effects.

Which water softening methods are suitable for different properties?

The optimal technique is chosen taking into account the actual conditions of future operation. Experienced professionals advise to create common project with mechanical and other filters for precise matching of all functional components.

In a city apartment, you can count on maintaining an acceptable quality of hard water. The corresponding obligations are specified in the contract with the supplying organization. However, at home, accidents on highways and pressure surges are not ruled out. To protect against these negative effects, a phosphate or mechanical filter with a pressure regulator and control pressure gauges is installed at the inlet. It is necessary to emphasize the advantages of an electromagnetic transducer, taking into account the features of objects of this category:

  • compactness;
  • light weight;
  • no noise;
  • cute appearance.

For autonomous suburban water supply, prudent owners prefer to use an artesian well. Such a source provides a high degree of purification by natural filtration. But at great depths, the concentration of impurities washed out of the rocks increases. Among them are compounds of salts in a sufficiently high concentration.

In a private house it is easier to find a free place for technological equipment. Here you can install kits for water softening by ion exchange. The necessary network engineering. We must not forget about good insulation. It is necessary to maintain the manufacturer's temperature regime. Chlorine and other chemical compounds that can damage the existing backfill should be removed.

It is impossible to analyze the problems of excessive hardness of modern water without a detailed study of the diversity water softening methods. The abundance of filters on the shelves of shops and markets makes you think that choosing a device for an apartment is not so simple. And in order to choose the right softener option, you need to familiarize yourself with at least different types water softening methods. Without knowing the basics, it is impossible to understand the topic.

Although we know quite a lot about scale, there are still too many prejudices regarding filtering devices, as well as myths about uselessness, at least for domestic conditions. Excessive hardness of water leads to a large number of undesirable phenomena. The price of scale formation and poor solubility of any detergents with harsh poor-quality water is too expensive to neglect the issues of water softening today.

For some reason, we believe that excessive hardness in water is a myth, and that the use of filters is pumping money out of gullible citizens. At the same time, everyone perfectly saw and knows what scale is and how difficult it is to deal with it, how difficult it is to remove it, constantly from month to month. If you have any doubts about the degree of hardness of your water, you can always carry out a chemical analysis of the water. It will always help you not only determine how clean and edible your water is. Based on its results, you can make the correct one, that is, competent.

The fact that you use poor-quality water, you will learn by many signs, so familiar to all of us. Excessive rigidity will manifest itself even when cooking. Such water causes the meat to become tougher. Vegetables fall apart when boiled in such water. And the eternal edge of the sediment of hardness salts. If you already have such kettles or pans with eternal hard edges inside on the surfaces, then one hundred percent hardness in your water has long exceeded the permissible limits. You will learn about the presence of such water in the apartment not only by limescale inside the kettle, water will leave its mark, and even when washing dishes in dishwasher. It would seem that glasses and plates after washing in such a machine should come out creaky and perfectly clean, but not in the case of hard water. The use of such water can be recognized by the treacherous white stains on the glasses, by the barely noticeable white coating on the plates.

Rigidity also affects the quality of cooked dishes, and tea and coffee. Real natural coffee brewed in good water has a completely different taste, and if you are a real coffee lover, then the question of creating a hardness cleaning system will never confuse you. One has only to try good coffee on the right water.

Poorly washed clothes will also tell about the presence of excess calcium salts with magnesium in the water. Scale formation is far from all that working with such water leads to. She also has such a feature - as poor solubility, that of powder, that of soap with detergent for dishes. Working with hard water, it will not be possible to save in any way. This feature leads to rapid wear of fabrics, they begin to crack and tear literally before our eyes. And it is worth installing one AquaSHIELD electromagnetic water softener in front of the washing machine and the problem with increased water hardness will be solved. But many people think that the device on magnets cannot clean water. So far, they are not convinced by their own example how rationally and economically water softening methods work.

And one more thing - the use of low-quality water for personal use, in the end, will negatively affect our health. It is impossible to drink such water with impunity. And your body will respond to you with different chronic diseases, early skin aging and hair loss. Only not all people can immediately identify the cause of such diseases in water hardness.

Water softening methods involve the use special devices. Their task is to remove the excess of two carbonate salts from the water. But there are also more primitive ways. They are almost never used today, but sometime before the invention, our ancestors used them in an effort to somehow protect themselves from the harmful effects of calcium and magnesium.

Thus in a simple way Water softening is the application of a simple piece of silicon. All you need to get soft water is to buy a piece of silicon about 5x5 cm in size and put it in a bottle (3 liters) with tap water. In a week you will be able to drink "charged" water and it will not be moldy, but soft and tasty, also with medicinal properties. Such is the effect of silicon on calcium and magnesium salts. Very often in ancient times, a well was lined with silicon in order to get good water.

Today, the use of such a silicon water softening method has the right to life, but it is unlikely that it will be possible to purify a large amount of water with its help. Therefore, only therapeutic, medicinal use of this method.

For industry, the use of primitive methods of water softening is impossible. In this situation, even the use of a carefully thought-out, based on chemical analysis water, the water treatment system is not a complete protection against the formation of scale. So in the thermal power industry, you still have to clean up from limescale. And the difference is that after work, a weak plaque forms, but it grows more slowly and, importantly, it is quite easily eliminated. You don't even have to buy for it special means. A simple rinse with water is sufficient.

The formation of scale is no worse than poor solubility in water, it harms household appliances and equipment. The problem is that if the scale is not removed in a timely manner, then it begins to grow even faster, and even more confidently. And in the wake of it, corrosion begins to slowly develop its activity. These two phenomena are inextricably linked.

Not only is scale not aesthetically pleasing, ugly, and of little use, but along with the formation of scale, the threat of losing equipment and expensive equipment increases. Scale problems, especially in industry, are always very expensive. Water softening methods. both reagent and non-reagent could not appear just like that. There must have been good reasons for their creation. This is the reason for the scale.

In boiler houses, especially steam rooms, this is a whole story. In order for the steam boiler to work, the quality of the steam must be very high, and during the cleaning time, that water and steam go through a huge number of instances, which later helps steam power plants to last much longer than when working with untreated water.

What causes bad water? She is being warmed up. Hardness salts during the heating process form a poorly soluble precipitate, that is, scale, which, when heated, settles precisely on the heated surface. The formed layer, although it was formed during the heating process, does not absorb or transmit heat by itself. And we remember that it was deposited just on the heating surface. Over time, the density of the scale layer reaches such limits that the heat absolutely ceases to be transferred to the water.

During this period of time, fuel consumption grows simply unimaginably. After all, the device or equipment is trying to work. And their job is to heat water. And in order to do this, you need to try to heat the scale so that it gives at least 10 percent of the heat transferred to it into the water. To do this, you have to spend a lot of fuel. It takes a lot of time and the surfaces suffer frantic overloads. Naturally, this cannot go on forever. Metals, as if they fall into an open-hearth furnace, if they are covered with a layer of scale.

So it turns out that a household appliance can turn off so as not to burn out, but a solid fuel boiler cannot do this. It can only break from such an effect. Here, human sacrifices are also possible. Therefore, it must be treated very correctly and carefully. It is absolutely impossible to miss descaling, especially in industry.

Any descaling of industrial equipment implies a mandatory shutdown of the system. This is downtime, this is again products not delivered on time, these are expenses. It is not possible to perform descaling with the equipment running. Just stop and clean up. And most often collapsible cleaning, because. equipment, both in boiler rooms and in metallurgy, is complex. It will not be possible to reach the most remote places immediately. Here also consider, whether removal is so cheap. Installation crews, surface cleaning crews, downtime, cleaning supplies. You definitely won’t be able to save on descaling.

And no matter how hard you try, it will definitely not be possible to carry out any kind of anti-scale cleaning without a trace. There will always be scratches, mechanical cleaning removes not only the protective coating, it will also touch the base layer. Well, any damaged surface - favorite place scale deposits. So it turns out that by eliminating one scale, we stimulate the rapid formation of other layers. So, it is unprofitable to constantly remove scale, not at all profitable.

Now, as for the ways to soften hard water. Although it may seem at first glance that there are many softening devices, nevertheless, there are not so many ways to soften hard water, although there is some choice. Methods can be safely divided into chemical and physical. Chemical water treatment involves the use of various reagents, during which hardness salts become slightly soluble, precipitate and are easily removed from systems where water is used. Let's learn more about these ways to soften hard water. Their types and benefits.

Physical methods of water softening

The group physical methods of water softening works without the use of any chemicals. This group is ideal for purifying tap water, that is, the water that is also used for personal use - to drink and eat. There the water should be soft by default.

Membrane methods of water softening

You can also select a group membrane methods of water softening. This includes reverse osmosis, which is very popular in the industry. This is a fine cleaning method using pressure. Inside such a device is a thin membrane made of expensive materials. The entire surface of such a membrane is dotted with holes. The diameter of such holes does not exceed the size of a water molecule. Such a semi-permeable surface makes it possible to eliminate almost any impurities from water that are larger than a water molecule.

With such a device, you can easily get water ideal for the same pharmacology or for the production of drinking water. The distillate is obtained by nanofiltration. This is another type of reverse osmosis, only low-pressure.

The main trump card of this method of water softening is the highest degree of purification, the ability to obtain water with the desired characteristics, only by changing the membrane. But reverse osmosis, like other membrane methods of water purification, has its drawbacks. When the appliance is in operation, there is a lot of water inside the appliance. This happens for several reasons. Firstly, the percolation rate through the membrane is far from being that high, plus the device includes more than one filter. The installation may include reverse osmosis, mechanical filter and air conditioning. The latter is mandatory put on installations for the production of drinking water. This method of water softening very well eliminates any impurities up to bacteria with viruses, which is important for drinking water. Then, without conditioning, such water becomes unsuitable for personal use. Well, then the use of reverse osmosis significantly limits the cost of installation. Not everyone in everyday life can afford to use such an installation.

Chemical method of water softening

Chemical method of water softening as we have said, involves the use of chemicals. This includes sodium chloride and phosphates. For such softening, dispensers are most often used, which are mounted on a water pipe. Such methods are bad in that chemicals can form other impurities in the water and the same precipitate is obtained. Only it is also very poorly eliminated. At the same time, chemical restoration of the filtering parts of devices also belongs to the chemical method of water softening. Therefore, the most famous of this method is ion exchange. Here the cartridge is reconstituted with a very saline solution. Once restored, the cartridge will be able to work again.

Ion-exchange method of water softening

Ion exchange, as a way to soften water is one of the simplest. It does not require any special structures. The basis, as the name implies, is ion exchange. A gel-like resin works inside such a device. It contains a large amount of sodium, which very quickly, upon contact with hard water, is replaced by crystals of calcium and magnesium salts. So it turns out a simple and quick cleaning process, without any effort. After a certain period of time, all sodium from the cartridge is washed out.

In industry, the cartridge is restored by washing with a solution, but in everyday life they simply change it, because. drinking water does not tolerate reagents. The cleaning speed is excellent, but the cost of cartridges or their restoration is quite high. Yes, and in everyday life, a filter jug ​​is able to clean you a couple of three liters on the strength. For complete protection against scale and hardness, it is imperative to use another filter.

Reagent-free water softening

bright representative reagentless method of water softening is the magnetic force. Powerful magnets form the basis of such devices. Definitely permanent. You are just mounting such a device, and the magnetic field is already working. At the same time, the device is easy to install, easy to remove. It does not require maintenance, it does not need cartridges and cleaning. He works. The magnetic force field thus permeates the water, so that the hardness salts in it lose their former shape. Now these are sharp needles. They rub surfaces with old scale, removing it very efficiently. But the magnetic effect is very picky about water. He needs water room temperature, flowing in one direction and at a certain speed. It was possible to remove all the disadvantages of the magnetic method of water softening only by adding electric current. So they invented the electromagnetic installation.

Getting to know everyone water softening methods, one must conclude that today to refuse softening means risking the health of one's family and a complete lack of foresight. Therefore, more and more people choose this path today.

Basic water softening methods


Thermochemical method of water softening

Water softening by dialysis

Magnetic water treatment

Literature


Theoretical basis water softening, classification methods

Water softening refers to the process of removing hardness cations from it, i.e. calcium and magnesium. In accordance with GOST 2874-82 "Drinking water" water hardness should not exceed 7 mg-eq / l. Separate types of industries impose requirements on process water for its deep softening, i.e. up to 0.05.0.01 mg-eq / l. Commonly used water sources have a hardness that meets the standards of domestic and drinking water, and do not need softening. Water softening is carried out mainly during its preparation for technical purposes. Thus, the hardness of water for feeding drum boilers should not exceed 0.005 mg-eq / l. Water softening is carried out by methods: thermal, based on heating water, its distillation or freezing; reagent, in which Ca (II) and Mg (II) ions in water are bound by various reagents into practically insoluble compounds; ion exchange based on filtration of softened water through special materials that exchange Na (I) or H (1) ions included in their composition for Ca (II) and Mg (II) ions contained in dialysis water; combined, representing various combinations of the above methods.

The choice of water softening method is determined by its quality, the required depth of softening and technical and economic considerations. In accordance with the recommendations of SNiP, when softening groundwater, ion-exchange methods should be used; when softening surface water, when water clarification is also required, the lime or lime-soda method is used, and when the water is deeply softened, subsequent cationization. The main characteristics and conditions for the use of water softening methods are given in Table. 20.1.

softening water dialysis thermal

To obtain water for household and drinking needs, only a certain part of it is usually softened, followed by mixing with the source water, while the amount of softened water Q y is determined by the formula

where J o. and. - total hardness of the source water, mg-eq/l; F 0. s. - total hardness of water entering the network, mg-eq / l; F 0. y. - softened water hardness, mg-eq/l.

Water softening methods

Indicator thermal reagent ion exchange dialysis
Process characteristic Water is heated to a temperature above 100 ° C, while carbonate and non-carbonate hardness is removed (in the form of calcium carbonate, hydroxide and magnesium and gypsum) Lime is added to the water, which eliminates carbonate and magnesium hardness, as well as soda, which eliminates non-carbonate - second hardness. Softened water is passed through cationite filters Raw water is filtered through a semi-permeable membrane
Purpose of the method Elimination of carbonate hardness from water used to feed low and medium pressure boilers Shallow softening with simultaneous clarification of water from suspended solids Deep softening of water containing a small amount of suspended solids Deep water softening
Water consumption for own needs - No more than 10% Up to 30% or more in proportion to the hardness of the source water 10
Conditions effective application: turbidity of source water, mg/l Up to 50 Up to 500 No more than 8 Up to 2.0
Water hardness, mg-eq/l Carbonate hardness with a predominance of Ca (HC03) 2, non-carbonate hardness in the form of gypsum 5.30 Not higher than 15 Up to 10.0
Residual hardness of water, mg-eq/l Carbonate hardness up to 0.035, CaS04 up to 0.70 Up to 0.70 0.03.0.05 prn for single-stage and up to 0.01 for two-stage cationization 0.01 and below
Water temperature, ° С Up to 270 Up to 90 Up to 30 (glauconite), up to 60 (sulfonated coal) Up to 60
thermal method water softener

It is advisable to use the thermal method of water softening when using carbonate waters used to feed boilers. low pressure, as well as in combination with reagent methods of water softening. It is based on the shift of the carbon dioxide equilibrium when it is heated towards the formation of calcium carbonate, which is described by the reaction

Ca (HC0 3) 2 -\u003e CaCO 3 + C0 2 + H 2 0.

The equilibrium is shifted by a decrease in the solubility of carbon monoxide (IV), caused by an increase in temperature and pressure. Boiling can completely remove carbon monoxide (IV) and thereby significantly reduce calcium carbonate hardness. However, this hardness cannot be completely eliminated, since calcium carbonate, although slightly (13 mg / l at a temperature of 18 ° C), is still soluble in water.

In the presence of magnesium bicarbonate in water, the process of its precipitation occurs as follows: first, a relatively well-soluble (110 mg / l at a temperature of 18 ° C) magnesium carbonate is formed

Mg (HCO 3) → MgC0 3 + C0 2 + H 2 0,

which is hydrolyzed during prolonged boiling, as a result of which a precipitate of slightly soluble precipitates (8.4 mg / l). magnesium hydroxide

MgC0 3 + H 2 0 → Mg (0H) 2 + C0 2.

Consequently, when water is boiled, the hardness due to calcium and magnesium bicarbonates decreases. Boiling water also reduces the hardness determined by calcium sulfate, the solubility of which drops to 0.65 g/l.

On fig. 1 shows a thermal softener designed by Kopiev, which is characterized by a relative simplicity of the device and reliable operation. The treated water, preheated in the apparatus, enters through the ejector to the outlet of the film heater and is sprayed over vertically placed pipes, and flows down through them towards the hot steam. Then, together with the blowdown water from the boilers, it enters the clarifier with suspended sediment through the central supply pipe through the perforated bottom.

Carbon dioxide and oxygen released from the water, together with excess steam, are discharged into the atmosphere. The calcium and magnesium salts formed during the heating of water are retained in the suspended layer. After passing through the suspended layer, the softened water enters the collector and is discharged outside the apparatus.

The residence time of water in the thermal softener is 30.45 min, the speed of its upward movement in the suspended layer is 7.10 m/h, and in the openings of the false bottom 0.1.0.25 m/s.

Rice. 1. Thermal softener designed by Kopiev.

15 - discharge of drainage water; 12 - central supply pipe; 13 - false perforated bottoms; 11 - suspended layer; 14 - sludge discharge; 9 - collection of softened water; 1, 10 - supply of initial and removal of softened water; 2 - purge of boilers; 3 - ejector; 4 - evaporation; 5 - film heater; 6 - steam discharge; 7 - annular perforated pipeline for water drainage to the ejector; 8 - inclined separating partitions


Reagent methods of water softening

Water softening by reagent methods is based on its treatment with reagents that form sparingly soluble compounds with calcium and magnesium: Mg (OH) 2, CaCO 3, Ca 3 (P0 4) 2, Mg 3 (P0 4) 2 and others, followed by their separation in clarifiers , thin-layer settling tanks and clarification filters. Lime, soda ash, sodium and barium hydroxides and other substances are used as reagents.

Water softening by liming is used when it has high carbonate and low non-carbonate hardness, and also in the case when it is not required to remove salts of non-carbonate hardness from water. Lime is used as a reagent, which is introduced in the form of a solution or suspension (milk) into preheated treated water. Dissolving, lime enriches water with OH - and Ca 2+ ions, which leads to the binding of free carbon monoxide (IV) dissolved in water with the formation of carbonate ions and the transition of hydrocarbonate ions to carbonate:

C0 2 + 20H - → CO 3 + H 2 0, HCO 3 - + OH - → CO 3 - + H 2 O.

An increase in the concentration of CO 3 2 - ions in the treated water and the presence of Ca 2+ ions in it, taking into account those introduced with lime, leads to an increase in the solubility product and precipitation of poorly soluble calcium carbonate:

Ca 2+ + C0 3 - → CaC0 3.

With an excess of lime, magnesium hydroxide also precipitates.

Mg 2+ + 20Н - → Mg (OH) 2

To accelerate the removal of dispersed and colloidal impurities and reduce the alkalinity of water, coagulation of these impurities with iron (II) sulfate is used simultaneously with liming. FeS0 4 * 7 H 2 0. The residual hardness of softened water during decarbonization can be obtained by 0.4.0.8 mg-eq / l more than non-carbonate hardness, and the alkalinity is 0.8.1.2 mg-eq / l. The dose of lime is determined by the ratio of the concentration of calcium ions in water and carbonate hardness: a) at the ratio [Ca 2+ ] /20<Ж к,

b) with the ratio [Ca 2+] / 20 > W to,

where [СО 2 ] is the concentration of free carbon monoxide (IV) in water, mg/l; [Ca 2+ ] - concentration of calcium ions, mg/l; Zhk - carbonate hardness of water, mg-eq / l; D to - dose of coagulant (FeS0 4 or FeCl 3 in terms of anhydrous products), mg / l; e c is the equivalent mass of the active substance of the coagulant, mg/mg-eq (for FeS0 4 e c = 76, for FeCl 3 e c = 54); 0.5 and 0.3 - an excess of lime to ensure a greater completeness of the reaction, mg-eq / l.

The expression D to /e to is taken with a minus sign if the coagulant is introduced before lime, and with a plus sign if together or after.

In the absence of experimental data, the dose of the coagulant is found from the expression

D c \u003d 3 (C) 1/3, (20.4)

where C is the amount of suspension formed during water softening (in terms of dry matter), mg/l.

In turn, C is determined using the dependency

The lime-soda water softening method is described by the following main reactions:

According to this method, the residual hardness can be increased to 0.5.1, and the alkalinity from 7 to 0.8.1.2 meq/l.

Doses of lime D and and soda D s (in terms of Na 2 C0 3), mg / l, are determined by the formulas

(20.7)

where is the content of magnesium in water, mg/l; Zh n. k. - non-carbonate hardness of water, mg-eq / l.

With the lime-soda method of water softening, the formed calcium carbonate and magnesium hydroxide can supersaturate the solutions and remain in a colloidal-dispersed state for a long time. Their transition to coarse sludge takes a long time, especially when low temperatures and the presence of organic impurities in the water, which act as protective colloids. With a large number of them, water hardness with reagent water softening can be reduced by only 15.20%. In such cases, before or during softening, organic impurities are removed from the water with oxidizing agents and coagulants. With the lime-soda method, the process is often carried out in two stages. Initially, organic impurities and a significant part of the carbonate hardness are removed from the water using aluminum or iron salts with lime, carrying out the process at optimal conditions coagulation. After that, soda and the rest of the lime are introduced and the water is softened. When removing organic impurities simultaneously with water softening, only iron salts are used as coagulants, since at a high pH value of water necessary to remove magnesium hardness, aluminum salts do not form sorption-active hydroxide. The dose of coagulant in the absence of experimental data is calculated by the formula (20.4). The amount of suspension is determined by the formula

where W o is the total hardness of water, mg-eq / l.

Deeper softening of water can be achieved by heating it, adding an excess of a precipitant and creating contact of the softened water with previously formed precipitation. When water is heated, the solubility of CaCO 3 and Mg (OH) 2 decreases and softening reactions proceed more fully.

From the graph (Fig. 2, a) it can be seen that the residual hardness, close to the theoretically possible, can be obtained only with significant heating of the water. A significant softening effect is observed at 35.40°C, further heating is less effective. Deep softening is carried out at temperatures above 100 ° C. It is not recommended to add a large excess of a precipitant during decarbonization, since residual hardness increases due to unreacted lime or if there is magnesium non-carbonate hardness in the water due to its transition to calcium hardness:

MgS0 4 + Ca (OH) 2 \u003d Mg (OH) 2 + CaS0 4

Rice. Fig. 2. Effect of temperature (a) and dose of lime (b) on the depth of water softening by the lime-soda and lime methods

Ca (0H) 2 + Na 2 C0 3 \u003d CaC0 3 + 2NaOH,

but an excess of lime leads to an inefficient waste of soda, an increase in the cost of water softening and an increase in hydrated alkalinity. Therefore, an excess of soda is taken about 1 mg-eq / l. The hardness of water as a result of contact with the previously precipitated precipitate is reduced by 0.3-0.5 mg-eq / l compared to the process without contact with the precipitate.

The control of the water softening process should be carried out by adjusting the pH of the softened water. When this is not possible, it is controlled by the value of hydrated alkalinity, which is maintained within 0.1.0.2 meq/l during decarbonization, and 0.3.0.5 meq/l during lime-soda softening.

With the soda-sodium method of softening water, it is treated with soda and sodium hydroxide:

Due to the fact that soda is formed by the reaction of sodium hydroxide with bicarbonate, the dose required for adding to water is significantly reduced. With a high concentration of bicarbonates in water and low non-carbonate hardness, excess soda can remain in softened water. Therefore, this method is used only taking into account the ratio between carbonate and non-carbonate hardness.

The soda-sodium method is usually used to soften water, the carbonate hardness of which is slightly higher than non-carbonate. If the carbonate hardness is approximately equal to non-carbonate, soda can be omitted altogether, since the amount necessary to soften such water is formed as a result of the interaction of bicarbonates with caustic soda. The dose of soda ash increases as the non-carbonate hardness of the water increases.

The soda regenerative method, based on the renewal of soda during the softening process, is used in the preparation of water to feed low-pressure steam boilers

Ca (HC0 3) 2 + Na 2 C0 3 \u003d CaC0 3 + 2NaHC0 3.

Sodium bicarbonate, getting into the boiler with softened water, decomposes under the influence of high temperature

2NaHC0 3 \u003d Na 2 C0 3 + H 2 0 + C0 2.

The resulting soda, together with the excess, first introduced into the water softener, immediately hydrolyzes in the boiler with the formation of sodium hydroxide and carbon monoxide (IV), which enters the water softener with purge water, where it is used to remove calcium and magnesium bicarbonates from the softened water. The disadvantage of this method is that the formation of a significant amount of CO 2 during the softening process causes corrosion of the metal and an increase in the dry residue in the boiler water.

The barium method of water softening is used in combination with other methods. First, barium-containing reagents are introduced into water (Ba (OH) 2, BaCO 3, BaA1 2 0 4) to eliminate sulfate hardness, then after clarification of the water, it is treated with lime and soda for additional softening. The chemistry of the process is described by the reactions:

Due to the high cost of reagents, the barium method is rarely used. Due to the toxicity of barium reagents, it is unsuitable for the preparation of drinking water. The resulting barium sulfate precipitates very slowly, so settling tanks or clarifiers are needed large sizes. To introduce BaCO3, flocculators with mechanical agitators should be used, since BaCO 3 forms a heavy, rapidly settling suspension.

The required doses of barium salts, mg/l, can be found using the expressions: barium hydroxide (a product of 100% activity) D b =1.8 (SO 4 2-), barium aluminate D b =128W 0 ; barium carbonate D in \u003d 2.07γ (S0 4 2-);

Barium carbonate is used with lime. By the action of carbon dioxide on barium carbonate, barium bicarbonate is obtained, which is dosed into the softened water. In this case, the dose of carbon dioxide, mg/l, is determined from the expression: D ang. = 0.46 (SO 4 2-); where (S0 4 2-) is the content of sulfates in the softened water, mg/l; γ=1.15.1.20 - coefficient taking into account the loss of barium carbonate.

The oxalate water softening method is based on the use of sodium oxalate and on the low water solubility of the resulting calcium oxalate (6.8 mg/l at 18°C)

The method is distinguished by the simplicity of technological and instrumental design, however, due to the high cost of the reagent, it is used for softening small quantities water.

Phosphating is used to soften water. After reagent softening by the lime-soda method, the presence of residual hardness (about 2 mg-eq/l) is inevitable, which can be reduced to 0.02-0.03 mg-eq/l by phosphate additional softening. Such deep post-treatment allows, in some cases, not to resort to cationic water softening.

Phosphating also achieves greater water stability, reducing its corrosive effect on metal pipelines, and preventing carbonate deposits on the inner surface of pipe walls.

As phosphate reagents, hexametaphosphate, tripolyphosphate (orthophosphate) sodium, etc. are used.

The phosphate method of water softening using tri-sodium phosphate is the most effective reagent method. The chemistry of the process of water softening with trisodium phosphate is described by the reactions

As can be seen from the above reactions, the essence of the method lies in the formation of calcium and magnesium salts of phosphoric acid, which have low solubility in water and therefore precipitate quite completely.

Phosphate softening is usually carried out by heating water to 105.150 ° C, reaching its softening to 0.02.0.03 mg-eq / l. Due to the high cost of trisodium phosphate, the phosphate method is usually used to re-soften water previously softened with lime and soda. The dose of anhydrous trisodium phosphate (Df; mg/l) for additional softening can be determined from the expression

D F \u003d 54.67 (W OST + 0.18),

where F ost - residual hardness of softened water before phosphate softening, mg-eq / l.

Ca 3 (P0 4) 2 and Mg 3 (P0 4) 2 precipitates formed during phosphate softening adsorb organic colloids and silicic acid well from softened water, which makes it possible to identify the feasibility of using this method for preparing feed water for boilers of medium and high pressure(58.8.98.0 MPa).

A solution for dosing hexametaphosphate or sodium orthophosphate with a concentration of 0.5-3% is prepared in tanks, the number of which should be at least two. The inner surfaces of the walls and bottom of the tanks must be covered with a corrosion-resistant material. The preparation time of a 3% solution is 3 hours with obligatory stirring with a stirrer or bubbling (using compressed air) way.

Technological schemes and structural elements of chemical water softening plants

In the technology of reagent water softening, equipment for the preparation and dosing of reagents, mixers, thin-layer sedimentation tanks or clarifiers, filters and installations for stabilizing water treatment are used. The diagram of a pressure water softener is shown in fig. 3

Rice. 3. Water softener with vortex reactor.

1 - hopper with contact mass; 2 - ejector; 3, 8 - supply of initial and removal of softened water; 4 - vortex reactor; 5 - input of reagents; 6 - quick clarification filter; 9 - dumping of the contact mass; 7 - softened water tank

There is no flocculation chamber in this plant because the calcium carbonate precipitate flocculates in the contact mass. If necessary, the water in front of the reactors is clarified.

The optimal structure for softening water using lime or lime-soda methods is a vortex reactor (pressure or open spirator) (Fig. 20.4). The reactor is a reinforced concrete or steel body, narrowed downwards (taper angle 5.20°) and filled to about half the height with a contact mass. The speed of water movement in the lower narrow part of the vortex reactor is 0.8.1 m/s; the speed of the upward flow in the upper part at the level of the drainage devices is 4.6 mm/s. As a contact mass, sand or marble chips with a grain size of 0.2-0.3 mm are used at the rate of 10 kg per 1 m3 of the reactor volume. With a helical upward flow of water, the contact mass is weighed, the grains of sand collide with each other, and CaCO 3 intensively crystallizes on their surface; Gradually, the grains of sand turn into balls of the correct shape. The hydraulic resistance of the contact mass is 0.3 m per 1 m of height. When the diameter of the balls increases to 1.5.2 mm, the largest, heaviest contact mass is released from the bottom of the reactor and the fresh one is loaded. Vortex reactors do not retain magnesium hydroxide sediment, so they should be used in conjunction with filters installed behind them only in cases where the amount of magnesium hydroxide sediment formed corresponds to the dirt capacity of the filters.

With a dirt capacity of sand filters equal to 1.1.5 kg/m 3 and an 8-hour filter cycle, the allowable amount of magnesium hydroxide is 25.35 g/m 3 (magnesium content in the source water should not exceed 10.15 g/m 3). It is possible to use vortex reactors with a higher content of magnesium hydroxide, but at the same time after them it is necessary to install clarifiers to separate magnesium hydroxide.

The consumption of fresh contact mass added using an ejector is determined by the formula G = 0.045QЖ, where G is the amount of added contact mass, kg/day; W - water hardness removed in the reactor, mg-eq/l; Q - installation capacity, m 3 / h.

Rice. 4. Vortex reactor.

1.8 - supply of initial and removal of softened water: 5 - samplers; 4 - contact mass; 6 - air discharge; 7 - hatch for loading the contact mass; 3 - input of reagents; 2 - removal of spent contact mass

In technological schemes of reagent water softening with clarifiers, vertical mixers are used instead of vortex reactors (Fig. 5). In clarifiers, a constant temperature should be maintained, avoiding fluctuations of more than 1 ° C, for an hour, since convection currents, sediment agitation and its removal occur.

A similar technology is used to soften turbid waters containing a large amount of magnesium salts. In this case, the mixers are loaded with contact mass. When using clarifiers designed by E.F. Kurgaev, mixers and flocculation chambers are not provided, since the mixing of reagents with water and the formation of sediment flakes occur in the clarifiers themselves.

Significant height with a small volume of sediment thickeners allows them to be used for water softening without heating, as well as for desiliconization of water with caustic magnesite. The distribution of the source water by nozzles causes its rotational movement in the lower part of the apparatus, which increases the stability of the suspended layer with fluctuations in temperature and water supply. Water mixed with reagents passes through horizontal and vertical mixing baffles and enters the zone of sorption separation and regulation of the sludge structure, which is achieved by changing the conditions for sludge sampling along the height of the suspended layer, creating prerequisites for obtaining its optimal structure, which improves the effect of water softening and clarification. Clarifiers are designed in the same way as for conventional water clarification.

At the expense of softened water up to 1000 m 3 /day, a water treatment plant of the "Jet" type can be used. The treated water with the reagents added to it enters the thin-layer sump, then to the filter.

A reagentless electrochemical water softening technology has been developed at the Institute of Mining of the Siberian Branch of the Russian Academy of Sciences. Using the phenomenon of alkalinization at the anode and acidification at the cathode when a direct electric current is passed through an aqueous system, the water discharge reaction can be represented by the following equation:

2Н 2 0 + 2е 1 → 20Н - + Н 2,

where e 1 is a sign indicating the ability of hardness salts to dissociate into Ca (II) and Mg (II) cations.

As a result of this reaction, the concentration of hydroxyl ions increases, which causes the binding of Mg (II) and Ca (II) ions into insoluble compounds. From the anode chamber of a diaphragm (diaphragm made of belting-type fabric) electrolyzer, these ions pass into the cathode chamber due to the potential difference between the electrodes and the presence of an electric field between them.

On fig. 6 shown technology system installations for water softening by electrochemical method.

The production plant was installed in the district boiler house, which lasted for about two months. The mode of electrochemical treatment turned out to be stable, no sedimentation was observed in the cathode chambers.

The voltage on the supply tires was 16 V, the total current was 1600 A. The total capacity of the installation was 5 m3/h, the speed of water in the anode chambers was 0.31 n-0.42 m/min, in the gap between the diaphragm and the cathode 0.12- 0.18 m/min.

Rice. 5. Installation of lime-soda water softening. 1.8 - supply of initial and removal of softened water; 2 - ejector; 3 - hopper with contact mass; 5 input of reagents; 6 - clarifier with a layer of suspended sediment; 7 - clarification quick filter; 4 - vortex reactor

Rice. 6. Scheme of installation of electrochemical water softening I - rectifier VACG-3200-18; 2 - diaphragm electrolyzer; 3, 4 - analyte and catalyte; 5 - pump; 6 - pH meter; 7 - clarifier with a layer of suspended sediment; 8 - clarification fast filter; 9 - discharge into the sewer; 10, 11 - removal of softened and supply of source water; 12 - flow meter; thirteen - exhaust hood

It has been established that from water with W o = 14.5-16.7 mg-eq/l, an anolyte with a hardness of 1.1-1.5 mg-eq/l at pH = 2.5-3 and a catholyte with a hardness of 0 are obtained ,6-1 mg-eq/l at pH=10.5-11. After mixing the filtered anolyte and catholyte, the indicators of softened water were as follows: the total hardness W o was 0.8-1.2 meq/l, pH = 8-8.5. The cost of electricity amounted to 3.8 kWh/m 3 .

Chemical, X-ray diffraction, IR spectroscopic and spectral analyzes found that the precipitate mainly contains CaC0 3 , Mg (OH) 2 and partially Fe 2 0 3 *H 2


Water is a forced and expensive undertaking, which is a rather difficult task associated with a wide variety of pollutants and the appearance of new compounds in their composition. Water treatment methods can be divided into 2 large groups: destructive and regenerative. Destructive methods are based on the processes of destruction of pollutants. The resulting decomposition products are removed ...

It is produced through the middle and upper collection and distribution devices by directing a part of the spent regeneration solution or supplying raw water through the recirculation circuit. 1. TYPES OF FILTERS AND FEATURES OF THEIR STRUCTURE Ionic filters are classified depending on the principle of operation, as well as on the goals pursued when water passes through them. 1.1 FIP filters, ...

Federal State Educational Institution of Higher Professional Education

"SIBERIAN FEDERAL UNIVERSITY"

Polytechnical Institute

abstract

Methods for clarifying and softening water.

Use of an IOMS inhibitor.

Head ________________ Yakovenko A.A.

Student TE 06 - 03 ________________ Minaeva D.S

Krasnoyarsk 2009

Water clarification methods.

Water clarification is understood as the release of suspended solids from it during the continuous movement of water through special structures (settlers, clarifiers) at low speeds. At low speeds of water movement, the suspended solids contained in it, the specific gravity of which is greater than the specific gravity of water, settle under the action of gravity, forming a sediment in the sump.

Technological schemes for water treatment are determined in each case depending on the requirements and include the following stages of work:

    technological research and preliminary laboratory testing of the reagents used;

    selection and calculation of equipment for dosing and mixing reagents;

    selection of equipment for thin-layer clarification and suspension compaction;

    selection and calculation of fast filters with granular loading, both pressure and open type;

    selection of technology and equipment for sludge dehydration with subsequent disposal;

    selection of equipment for disinfection by dosing a solution of chlorine reagent (sodium hypochlorite) and quality control of treated water.

Depending on the direction of water movement, sedimentation tanks are divided into horizontal, vertical and radial.

The horizontal settling tank (Fig. 1) is a tank of rectangular section, the longitudinal (longer) axis of which is directed along the movement of water. The clarified water is directed through the pipe 1 to the distribution chute 2, which has a number of holes that serve to more evenly distribute the water flow over the cross section of the sump. The speed of water movement in these holes should not exceed 0.4 m/s. The clarified water enters another gutter 3 and is discharged from it through a pipe 4 to the filters. Settled particles (sludge) accumulate on the bottom, which should have a slope opposite to the movement of water.

The settling time for horizontal settling tanks is usually taken for a coagulated mixture no more than 4 hours. Horizontal settling tanks for clarification of large amounts of water can be divided in height into several compartments (floors) connected in parallel. The advantages of storey settling tanks (proposed by Prof. P.I. Piskunov) are a small building area and less concrete consumption. Such a sump was built at one of the largest treatment plants in the Soviet Union.

Rice. 1. Scheme of a horizontal sump: 1 - tray; 2 - receiving chamber; 3 - receiving chute; 4 - on the filter; 5 - to remove sediment

Rice. 2. Scheme of a vertical sump 1 - central pipe; 2-tray; 3- outlet pipe; 4 - pipeline for sediment removal

Vertical settling tanks (Fig. 2) are a round in plan, sometimes square, tank with a conical bottom and a central pipe, into which clarified water is supplied from the flocculation chamber.

Upon exiting the central pipe into the sump, the water moves upwards at a low speed and drains already clarified through the side of a concentrically located gutter, from where it is discharged to the filter. The sediment falling to the bottom of the sump is periodically removed.

The water flow rate in the central pipe is taken from 30 to 75 mm/sec. The settling time of water in the sump T = 2 hours. The speed of the upward movement of water is 0.5-0.6 mm/sec.

The diameter of the sump should not exceed 12 m, and the ratio of the diameter to the height of the sump is usually taken no more than 1.5.

Radial settling tanks are round tanks with a slightly conical bottom. Water enters the central pipe and from it is directed in the radial direction to the collection tray along the periphery of the sump. Settling tanks have a shallow depth, the sediment is removed mechanically without disturbing the operation of the settling tank. Radial settling tanks are constructed with a diameter of 10 l * or more at a depth of 1.5-2.5 m (at the wall of the settling tank) to 3-5 m (in the center).

The choice of the type of settling tank depends on the daily capacity of the station, its general layout, terrain, nature of the soil, etc. Vertical settling tanks are recommended for use with a daily capacity of up to 3000 m3. Horizontal settling tanks are used when the station capacity is more than 30,000 m3/day, both in the case of water coagulation and without it.

Radial settling tanks are expedient at high water flow rates (more than 40,000 m3/day). The advantage of these settling tanks compared to rectangular horizontal ones is the mechanized removal of sediment without stopping the operation of the settling tank. They are used for high turbidity of river water (with and without coagulation) mainly for clarification of industrial water.

Clarifiers with suspended sludge. The clarification process proceeds much more intensively if the water to be clarified after coagulation is passed through a mass of previously formed sediment, maintained in suspension by current

Rice. 3. Clarifiers: a - original design; b - corridor type: 1 - distribution pipes; 2 - gutters with flooded holes; 3 - working part of the clarifier; 4- protective zone; 5 - outlet tray; 6 - pipe for sediment suction; 7 - precipitation windows; 8-sludge thickener; 9 - pipes for sludge discharge) 10 - pipe for draining clarified water

Such clarifiers provide a higher effect of water clarification than in conventional settling tanks, which is explained by faster coarsening and retention of suspension when coagulated water passes through suspended sediment.

The use of a clarifier with a suspended residue makes it possible, compared with a conventional sedimentation tank, to reduce the consumption of coagulant, reduce the size of structures and obtain a higher effect of water clarification.

The clarifier of the original design is a cylindrical tank with a sludge thickener in its central part (Fig. 3, a). Here, the water with the reagent enters the air separator, then passes down into the perforated distribution pipes 1, and then into the holes of the perforated bottom 2.

Water, passing through the layer of suspended sediment 3, enters the clarification zone 4 and overflows into the discharge troughs. An excess of suspended sediment enters the sludge accumulator 5, from where it is periodically removed to the sewer.

The corridor-type clarifier (see Fig. 3, b) is a rectangular tank. The coagulated water enters the clarifier through pipe 1 and is distributed through perforated pipes 2 in the lower (working) part 3 of the clarifier. The speed of water movement in the working part should be such that the coagulant flakes are in suspension. This layer contributes to the retention of suspended particles. The degree of water clarification is much higher than in a conventional sump.

Above the working part there is a protective zone 4, where there is no suspended layer. Clarified water is discharged by tray 5 and pipes 10 for further processing. Excessive amount of sediment by suction into pipe 6 is discharged through windows 7 to sediment thickener 8, where the sediment is compacted and periodically discharged into the sewer through pipes 9.

The ascending flow rate in the working part of the clarifier is assumed to be 1-1.2 mm/sec.

Water softening methods.

The removal of hardness salts from water, i.e. its softening, must be carried out to feed boiler plants, and the hardness of water for medium and low pressure boilers should be no more than 0.3 mg.eq / l. Softening water is also required for such industries as textile, paper, chemical, where water should have a hardness of not more than 0.7-1.0 mg.eq / l. Softening of water for household and drinking purposes is also advisable, especially if it exceeds 7 mg.eq / l.

The following main methods of water softening are used:

1) reagent method. - by introducing reagents that contribute to the formation of poorly soluble calcium and magnesium compounds and their precipitation;

2) cationite method, in which softened water is filtered through substances that have the ability to exchange the cations (sodium or hydrogen) contained in them for calcium and magnesium cations, salts dissolved in water. As a result of the exchange, calcium and magnesium ions are retained and sodium salts are formed that do not give water hardness;

3) the thermal method, which consists in heating water to a temperature above 100 °, while carbonate hardness salts are almost completely removed.

Often, softening methods are used in combination. For example, some of the hardness salts are removed by the reagent method, and the rest by cation exchange.

Of the reagent methods, the soda-lime softening method is the most common. Its essence is reduced to obtaining, instead of Ca Mg salts dissolved in water, insoluble salts of CaCO 3 and Mg (OH) 2 that precipitate.

Both reagents - soda Na 2 C0 3 and lime Ca (OH) 2 - are introduced into the softened water simultaneously or alternately.

Salts of carbonate, temporary hardness are removed with lime, non-carbonate, permanent hardness - soda. Chemical reactions when removing carbonate hardness proceed as follows:

Ca (HC0 3) 2 + Ca (OH) 2 \u003d 2 CaCO 3 + 2H 2 0.

In this case, calcium carbonate CaCO3 precipitates. When magnesium bicarbonate Mg (HC0 3) 2 is removed, the reaction proceeds as follows:

Mg (HCOa) 2 + 2Ca (OH) 2 \u003d Mg (OH) 2 + 2CaCO 3 + 2H 2 0.

Magnesium oxide hydrate Mg(OH) 2 coagulates and precipitates. To eliminate non-carbonate hardness, Na 2 C0 3 is introduced into the softened water. The chemical reactions when removing non-carbonate hardness are as follows:

Na 2 C0 8 + CaS0 4 \u003d CaCO 8 + Na 2 S0 4;

Na 2 CO 3 + CaCl 2 \u003d CaC0 3 + 2NaCl.

As a result of the reaction, calcium carbonate is obtained, which precipitates.

For deep softening, auxiliary measures are used, such as heating the treated water to about 90, while the residual hardness can be increased to 0.2-0.4 mg.eq / l.

Without heating, water treatment is carried out with large excess doses of lime, followed by removal of these excesses by purging the water with carbon dioxide. The last process is called recarbonization.

On fig. 4 shows a diagram of a reagent water softening plant, which includes a device for preparing and dosing reagent solutions, mixers, reaction chambers, clarifiers, and filters.

To soften uniformly supplied water that flows continuously, the same soda and lime solution dispensers are used as in coagulation. If the flow of softened water fluctuates, so-called proportional dispensers are used.

Rice. 4. Scheme of reagent water softening: 1 - reaction chamber (vortex reactor); 2 - clarifier; 3 - quartz filter; 4 - mixer; 5, 6 and 7 - dispensers of reagent solutions; 8, 9 and 10 - tanks for dissolving coagulants and soda for making milk of lime; 11 - tank; 12 - pump; 13 - air separator.

The soda-lime method is suitable for softening water with any ratio of carbonate and non-carbonate hardness.

The disadvantages of the soda-lime softening method are as follows: 1) the water is not softened completely; 2) installations for softening bulky; 3) a careful dosage of soda and lime is necessary, which is difficult to achieve due to the inconstancy of the composition of the softened water and reagents.

The cationic softening method is based on the ability of substances called cationites to exchange the sodium cations Na + or hydrogen H + contained in them for calcium or magnesium cations dissolved in water. In accordance with this, sodium-cationite and hydrogen-sodium are distinguished: cationite methods of water softening.

With the help of cation exchangers, water is softened in an installation consisting of several metal pressure tanks loaded with cation exchange resin (Fig. 5).

Raw water enters the filter through pipes A, B and C; softened water is released through pipe G. When the filter is operating, valves 2 and 5 are open, and the rest (1, 3, 4 and 6) are closed. Wash the filter before regeneration.

To wash the filter, water from tank D is supplied through pipe E and passes through drains from bottom to top. The duration of washing is 20-30 minutes, the intensity is 4-6 l / s per 1 m2. Rinse water from the filters is discharged through pipes C, B, G, with valves 4 and 3 open, and the rest closed.

The regenerating solution of the cation exchanger during regeneration is supplied through pipe B, passes the filter from top to bottom and is discharged through the pipe. In this case valves 1 and 6 are open, the rest (2-5) are closed; the duration of regeneration is about 30-60 minutes, and washing from the regenerating solution is 40-60 minutes.

Rice. 5. Diagram of a cationic water softener

The advantages of the cationite method are as follows: 1) the water softens almost completely; 2) it is necessary to dose only a solution of common salt or sulfuric acid; 3) filters are manufactured in a factory way. The disadvantages of this method include the need for preliminary clarification of water, since colloidal and organic substances envelop grains of cation exchangers and reduce their exchange capacity.

Reagents used in water treatment are introduced into the water in the following places:

a) chlorine (with preliminary chlorination) - into the suction pipelines of the pumping station of the first lift or into the conduits supplying water to the treatment station;

b) coagulant - into the pipeline before the mixer or into the mixer;

c) lime for alkalization during coagulation - simultaneously with the coagulant;

d) activated carbon to remove odors and tastes in water up to 5 mg/l - before filters. At high doses, coal should be introduced to the pumping station of the first lift or simultaneously with the coagulant into the mixer of the water treatment plant, but not earlier than 10 minutes after the introduction of chlorine;

e) chlorine and ammonia for water disinfection are introduced to treatment facilities and into filtered water. In the presence of phenols in the water, ammonia should be introduced both during preliminary and final chlorination.

The coagulant solution is prepared in solution tanks; from where it should be released or pumped into service tanks. To supply water with a given amount of coagulant solution, the installation of dispensers should be provided.

When using automatic dispensers based on the principle of changing the electrical conductivity of water depending on impurities, lime for alkalization should be introduced after the selection of coagulated water going to the dispenser.

Special types of water purification and treatment include: desalination, desalination, iron removal, removal of dissolved gases from water and stabilization.

Mechanism of action of IOMS inhibitors.

When water is heated during the operation of the heating system, the thermal decomposition of the bicarbonate ions present in it occurs with the formation of carbonate ions. Carbonate ions, interacting with calcium ions present in excess, form the embryos of calcium carbonate crystals. More and more carbonate ions and calcium ions are deposited on the surface of the nuclei, as a result of which crystals of calcium carbonate are formed, in which magnesium carbonate is often present in the form of a substitutional solid solution. Settling on the walls of heat engineering equipment, these crystals coalesce, forming scale (Fig. 6, a).

The main component providing the antiscale activity of all the considered inhibitors are organophosphonates - salts of organic phosphonic acids. When organophosphonates are introduced into water containing calcium, magnesium and other metal ions, they form very strong chemical compounds - complexes. (Many modern inhibitors contain organophosphonates already in the form of complexes with transition metals, mainly with zinc.) Since one liter of natural or industrial water contains 1020–1021 calcium and magnesium ions, and organophosphonates are introduced in an amount of only 1018–1019 molecules per liter of water, all molecules of organophosphonates form complexes with metal ions, and complexons as such are not present in water. Complexes of organophosphonates are adsorbed (precipitated) on the surface of calcium carbonate crystal nuclei, preventing further crystallization of calcium carbonate. Therefore, when 1–10 g/m3 of organophosphonates are introduced into water, scale does not form even when very hard water is heated (Fig. 6b).

Complexes of organophosphonates can be adsorbed not only on the surface of crystal nuclei, but also on metal surfaces. The resulting thin film hinders the access of oxygen to the metal surface, as a result of which the metal corrosion rate decreases. However, the most effective metal protection against corrosion is provided by inhibitors based on complexes of organic phosphonic acids with zinc and some other metals, which were developed and put into practice by Professor Yu.I. Kuznetsov. In the surface layer of the metal, these compounds can decompose with the formation of insoluble compounds of zinc hydroxide, as well as complexes of a complex structure, in which many zinc and iron atoms participate. As a result of this, a thin, dense film is formed that is firmly adhered to the metal and protects the metal from corrosion. The degree of metal protection against corrosion when using such inhibitors can reach 98%.

Modern preparations based on organophosphonates not only inhibit scale and corrosion, but also gradually destroy old deposits of scale and corrosion products. This is explained by the formation of surface adsorption layers of organophosphonates in the scale pores, the structure and properties (for example, thermal expansion coefficient) of which differ from the structure of scale crystals. The fluctuations and temperature gradients arising during the operation of the heating system lead to wedging of crystalline scale aggregates. As a result, the scale is destroyed, turning into a fine suspension, which is easily removed from the system. Therefore, when introducing preparations containing organophosphonates into heating systems with a large amount of old deposits of scale and corrosion products, it is necessary to regularly drain sediment from filters and sumps installed at the lowest points of the system. The sludge should be drained, depending on the amount of deposits, 1–2 times a day, at the rate of feeding the system with clean, inhibitor-treated water in the amount of 0.25–1% of the water volume of the system per hour. It should be noted that with an increase in the concentration of the inhibitor above 10–20 g/m3, the scale is destroyed with the formation of very coarse suspensions that can clog the bottlenecks of the heating system. Therefore, an overdose of the inhibitor in this case threatens to clog the system. The most effective and safe cleaning of heating systems from old deposits of scale and corrosion products is achieved by using preparations containing surfactants, for example, the KKF composition.

a) b)

Rice. 6. Section of the intra-quarter 89 mm hot water pipeline:

a - after two years of operation on water with a hardness of 8–12 meq/dm3;

b - six months after the start of water treatment with an IOMS-1 inhibitor.