Educational program on water treatment and explanations of chemical analysis of water

Scale formation and other negative manifestations are explained by the presence of calcium and magnesium compounds in the liquid. To extend the service life of boilers and other equipment, manufacturers indicate the permissible degree of contamination (water hardness) in mmol/l, degrees, and other units. This article contains information that will help you correctly evaluate the results of laboratory analysis. Professional recommendations will help you choose the right specialized equipment for reproducing protective and preparatory technologies.

The concept of rigidity, basic definitions

Specific terms are used in the relevant literature, so a few clarifications are necessary. The value of temporary hardness is usually determined by the amount of divalent cations calcium (Ca2+) and magnesium (Mg2+). This specific name refers to positively charged particles. They combine with negatively charged compounds (anions of sulfates, chlorides, nitrates, bicarbonates and silicates).

This type of hardness is called “temporary” based on a relatively simple method for removing impurities. When boiled, they are converted into an insoluble precipitate, which is filtered using conventional mechanical techniques.

To accurately determine water hardness in mmol, the following nuances should be noted:

• The level of hardness is also determined by strontium, manganese cations and other impurities. However, their influence is much less, so they are neglected. Of course, special corrections are made for abnormally high concentrations of such contaminants.
• Trivalent compounds of aluminum and iron can change the level of hardness. However, under natural conditions they are extremely rare, since a certain pH value is required for a stable state.
• Permanent hardness is not eliminated even with prolonged high temperature exposure. The corresponding impurities are created from sulfuric salts and other strong acids.

Water hardness in mmol l, use of other units of measurement

According to the standards in force since January 1, 2014 (GOST 31865-2012) in Russia, this parameter is expressed in degrees of hardness, designated “°Zh”. It denotes the combination of the parameters noted above. Moreover, it is especially emphasized that the main active ingredients are elements of the alkaline earth category. To calculate the value, use the formula Ж = ∑ (KP/KM), where:

• KP – actual concentration of hardness impurities in g per cubic meter. (or mg per dm3) in the control sample;
• KM is a concentration equal to half a mole in the same units of measurement.

Similar rules apply in countries that have approved relevant interstate agreements. In addition to the Russian Federation, they were joined by: Armenia, the Republic of Belarus, Kyrgyzstan, Moldova, Uzbekistan and Tajikistan.

The noted standards are not global. In the USA, degrees of hardness (ppm) are also used. The unit of measurement is the concentration of one part of calcium carbonate (CaCO3) in 100 thousand parts of water. This corresponds to 10 mg of impurities per liter of liquid. More common in practice in this country is gpg (grain per gallon).

If we convert to units of measurement familiar to Europeans, the concentration of hardness salts will be 17.12 mmol l. The definition scale shows conversion factors for converting different units of measurement:

The Russian degree of hardness °Zh corresponds to the content of 50.05 mg of calcium carbonate in one liter of liquid. This is equivalent to 20.04 mmol l in terms of divalent calcium cations. To convert hardness to mmol/l, multiply this value by 2.

How does water hardness occur?

The definition scale notes that this standard applies to all types of natural sources. It is used to evaluate the quality of bottled water and filtration technologies. The main pollutants, cations, enter the liquid from dolomites and other rocks. They are sometimes present in industrial effluents. The concentration of such impurities is much lower in open reservoirs (wells) compared to deep wells.

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A pattern has been noted of an increase in the concentration of magnesium components as mineralization increases to several grams per liter of liquid. The content of calcium cations decreases accordingly, but can also reach a value of 1-1.5 mmol l. Hardness levels in surface waters are highly susceptible to seasonal fluctuations. This explains the need for more thorough testing. To select suitable cleaning equipment, you have to do several laboratory tests per year.

Where does hardness and softness come from?

Despite the simple chemical formula of H2O, in fact, it is a very complex substance of natural origin with a large number of trace elements. Any organic material contains a water base with varying degrees of hardness. What does this indicator mean?

Even by touch you can determine in what liquid the items were washed. Fabrics cleaned in a soft environment are more fluffy and soft, while in a hard environment they are rough and thin to the touch. This is explained by the fact that tissues are able to accumulate ions of mineral elements.

Sources of calcium (Ca2+), magnesium (Mg2+) and other alkali metals are natural deposits of limestone, dolomite and gypsum. Ions of these microelements enter the liquid as a result of the reaction of carbon dioxide with minerals, as well as as a result of the process of chemical decomposition of rocks. The microbiological processes occurring in the soil in the catchment area are also the supplier of these particles.

• A liquid medium with a high salt content is considered hard;
• soft water is characterized by their low content.

Generally, in low-mineralized liquid media, hardness based on calcium ions prevails, but in rare cases, magnesium ionization predominates. With an increase in the level of water mineralization, the percentage of calcium ions rapidly decreases and rarely exceeds 1 g/l. The content of magnesium ions in a highly mineralized environment can reach 5-71 g/l, and in salt lakes – 10-20 g/l.

The hardness of surface waters is generally less than the hardness of underground environments. The hardness of surface waters is prone to significant seasonal fluctuations, reaching its highest point at the end of winter and its lowest point during the flood stage, when it is thoroughly diluted by soft rain and melt liquid. Marine and ocean environments have a very high degree of hardness - 90-300 or more mEq/dm3.

Qualitative indicators

Under natural conditions, there are sources with very hard water of more than 10 mmol l. The use of such liquid to supply household real estate is accompanied by the following problems:

• unpleasant bitterness spoils the taste of dishes, cold and hot drinks;
• mechanical contaminants get into food;
• persistent plaque worsens the appearance of dishes, cutlery, and plumbing fixtures;
• a porous layer of calcium compounds disrupts heat transfer and disables equipment;
• solid scale particles clog not only narrow technological openings, but also reduce the internal diameter of pipes.

It is clear that such conditions do not meet modern standards of quality housing. It is necessary to use special protective measures to reduce the concentration of harmful impurities. They prevent emergency situations and are therefore economically feasible, taking into account the increased service life of the connected equipment.

Official standards and recommendations from professionals on choosing the optimal level of hardness

If the impurity content is less than indicated in the example, you should not be careless. Scale forms actively and at lower concentrations. Such situations are even more dangerous, since harmful processes are invisible to users. Industry standards for professional boiler houses contain recommendations for reducing hardness to 0.1 mmol l or less. However, there are no such restrictions in the official general rules.

It should be noted that the World Health Organization does not set a high stringency limit. Separate issue papers from this organization have noted an increase in cardiovascular disease in control groups. However, a direct connection has not been identified specifically taking into account this indicator. Many specialists consider this attitude to be incorrect.

Domestic standards define the permissible level of 7 mEq/liter as a significant deterioration in taste parameters. But some people feel the concentration is 2-3 times less. It is necessary to make corrections taking into account personal physiological characteristics.

Medical recommendations do not take into account the harm of scale to equipment. Meanwhile, it is this factor that has a strong negative effect even at a minimum concentration. The process of converting solution into solid particles occurs especially quickly in heating zones. For this reason, without preventive measures, high-quality heating boilers, boilers, dishwashers and washing machines, irons and coffee machines become unusable.

A more strict approach to determining the permissible concentration of pollutants is manifested in statistical data. Thus, in different areas of the capital of the Russian Federation, according to current measurements, the hardness ranges from 2 to 5.5 mEq/liter. In New York, when converted into domestic units, it does not exceed 0.4 °W.

Educational program on water treatment and explanations of chemical analysis of water

Ecology of consumption. Science and technology: The story will be about what pollutes water, how it is cleaned and why I calmly drink from a spring containing a lot of nitrates.

For the last five years I have been doing chemical analysis of water and have been in contact with water treatment engineers. A variety of people come to us: for some, a water purification system is a very expensive but vital purchase, others have simply read horror stories on the Internet and want “living water.” But for us, as for doctors, all our customers are the same. They have water - well water, coming from a city or village water supply, well, river - and it must be purified to established standards. This story will tell you about what pollutes water, how it is cleaned and why I calmly drink from a spring containing a lot of nitrates. But no company names, geographical references or other individualizing information will be indicated - I just want to share five years of my observations of the process, because many cottage owners could be less nervous if they took care of water treatment at the stage of pouring the foundation.

But first, let's define the process structure and terminology in order to communicate in the same language. Strictly speaking, without a water analysis, not a single normal organization involved in water treatment will even let you in. It all starts with water analysis.

How to correctly select water for analysis?
The care with which you take your water sample can ultimately have a significant impact on the cost of installation. Here are general recommendations.

1. Take a clean 1.5 liter plastic bottle. Under no circumstances use bottles that previously contained liquids containing organic substances (kvass, beer, kefir, white spirit) or highly mineralized water. Drinking water bottles will do. The ideal option is to buy a new bottle where they sell drinks by the glass.
2. If you have a well, fill it to a constant consistency. Your well drillers should provide recommendations on how to do this. Some of our customers said that their well was in operation for two to three weeks.
3. Open the tap closest to the well to any existing filters, tanks or other devices that may affect the composition of the water, and run for a few minutes to refresh the water in the pipes.
4. Rinse the bottle twice with the selected water, then pour water right up to the neck, screw on the cap, lightly squeeze the sides of the bottle so that water flows over the edge, and screw the cap all the way. Goal: collect water without an air bubble.
5. Deliver the water to the laboratory the same day. If this is not possible, store the water in the refrigerator for no more than two days.

Next, based on the analysis, engineers select and calculate the water treatment system, and if you are satisfied with the commercial offer and you pay for it, installers come to you with equipment. The installers will need from you an inlet, an outlet and a drainage - where to get water from, where to supply it and where to drain it. Particular attention should be paid to the sewerage system. If you have a hole and you are pumping it out, make sure that it can simultaneously absorb 2-3 cubic meters of water without consequences. Why? Filters allow dirty water to pass through them, and the dirt settles on the filter material. Over time, the capacity of the filter material is exhausted and it needs to be backwashed - with a flow of water from the bottom up, all the dirt from it is washed off into the sewer. One flush can take from one hundred liters to one and a half cubic meters of water, depending on the type of filter and the level of contamination. And all this amount will drain into the drainage in about 20 minutes for cabinet filters and in about an hour for column-type backfill filters.

Note. Here and further I will give values ​​on the scale of private household ownership.

By the way, if your septic tank uses biological treatment, the drainage water can kill it. The installers will also require you to have an electrical outlet nearby (the filters are equipped with controllers - electronic control brains that themselves know when it’s time to start washing). And also keep in mind that any filters must be operated at a temperature not lower than +5 °C, and the space they take up, depending on the model, is up to two square meters in area and up to two meters in height (although the smallest filter with all the piping can fit in cubic meter). Yes, don't forget about the inlet water pressure! If it is less than 2-3 atmospheres, you cannot do without a booster pump. For comparison, city water canal systems usually supply water to apartments at a pressure of about 4 atmospheres.

At the inlet, coarse cleaning is installed in front of the filters - mesh filters, mechanics up to 20 microns - to protect more expensive equipment from sand, rust and other large particles. At the outlet after installation, it is recommended to install final purification (usually coal - removes odors, chlorine and small particles). The most expensive configuration may also include an ultraviolet lamp for disinfection at the outlet and protection against leaks on the floor, but these are all options. But if your water contains a lot of iron, then an engineer can design water treatment using tanks that take up significant space.

How much is a lot of iron?

Now we can talk about things closer to my profession. And we'll start with units of measurement. In Russia and abroad, paradoxically, completely different units of measurement are used, although the chemistry is the same. We use mg/l and mEq/l, they use ppm.

mg/l (read: milligrams per liter) is the mass of the particles under study contained in one liter of solution (not solvent!). If we study the ionic composition of water, then the mass of particles will mean the mass of atoms of the same type. For example, 10 mg/l of iron means that in 1 liter of solution you contain 10 mg of atomic iron - the same one whose molar mass, according to the periodic table, is 56 g/mol. And it doesn’t matter in what form this iron is - a divalent or trivalent ion. It’s just some kind of abstraction - iron, as it is in the periodic table. And if we measure the content of some salt, then the mass of the particles will mean the mass of the molecule of this salt. For example, 10 mg of sodium chloride NaCl in 1 liter of solution.

mg-eq/l (read: milligram equivalent per liter) - from this moment special black magic begins. Jeremiah Richter, a German chemist, discovered the law of equivalents (and the portal to hell) in 1792. The law states: substances react in quantities proportional to their equivalents, or m1E2 = m2E1. Try to find a chemist who gets excited about counting equivalents! I have not yet encountered such maniacs, although I have been studying chemistry for 14 years. Let's start from afar. Let's take the usual reaction between chalk and hydrochloric acid:

CaCO3 + 2HCl = CaCl2 + H2O + CO2

Let's discard the escaped carbon dioxide and water as unimportant, and highlight the most important thing in this reaction:

Ca2+ + 2Cl- = CaCl2 (in ionic form)

Now let’s take each of the ions and force it to enter into a hypothetical hydrogenation reaction with a hydrogen cation, regardless of the sign of the charge (yes, we chemists love all sorts of perversions; but in fact, the mass of the hydrogen cation is taken as one, and now we need to find the quantity other ions equivalent to this unit).

1/2Ca2+ + H+ = CaH (equivalence factor = 0.5, and the hydrogen equivalent is a 1/2Ca2+ particle)

Cl- + H+ = ClH (equivalence factor = 1, and the equivalent of hydrogen is the Cl- particle)

So, either one chlorine anion or half a calcium cation can (conditionally) react with one hydrogen cation. The numerical expression of the fraction of a substance equivalent to one hydrogen cation is called the equivalence factor. Now we can draw a simple conclusion:

1/2Ca2+ = Cl- (1 equivalent of calcium = 1 equivalent of chlorine)

Let's imagine that we are titrating alkalinity with hydrochloric acid (more on these scary words later). A variety of salts (hydrocarbonates, carbonates, hydroxides...) of a wide variety of ions (calcium, magnesium, sodium...) can react with hydrochloric acid. How can we express all this in one unit of measurement? We do not have the right to use here the unit of measurement mg/l, which is already familiar to us, because it is simply not clear - milligram of what? Calcium? Magnesium? Mixtures of them? In what ratio? But with equivalents this problem goes away by itself:

Cl- = 1/2Ca2+ = 1/2Mg2+ = Na+ = 1/3Al3+, etc.

It doesn’t matter to us what type of cation or anion we titrated, but we know that one equivalent of spent hydrochloric acid will always correspond to one equivalent of an unknown thing that can react with this acid. Okay, we’ve more or less figured out the equivalent. What is a milligram equivalent? This is the mass of one equivalent in milligrams. Roughly - calculated according to the periodic table as molar mass multiplied by the equivalence factor. For the above relation it would look like this:

35.45 mg Cl- = 20.04 mg Ca2+ = 12.15 mg Mg2+ = 22.99 mg Na+ = 8.99 mg Al3+

Note that the molar mass of, for example, calcium is 40.08 g/mol, but only half of calcium can react with 1 gram of hydrogen - 20.04 grams. This figure - 20.04 - will be the gram equivalent of calcium. Or milligram equivalent. Or microgram equivalent. This unit is convenient because if we ever figure out which compound reacted in that reaction with hydrochloric acid, we can always multiply the number of milligram equivalents by the mass of one equivalent - and thus convert milligram equivalents into ordinary milligrams for a particular compound . So, mEq/L is the number of milligram equivalents of a substance in one liter of solution.

ppm (read: pi-pi-em, parts per million) - number of particles per million. Shows how many dissolved particles under study are in one million particles of solution (not solvent!). The unit of measurement is used almost everywhere in the West. Corresponds to our mg/l (because a milligram is, like, also a millionth part of a liter, provided that the density of the solution is 1.00, but with such a dilution the change in density can still be neglected).

μS/cm (read: microsiemens per centimeter) is a unit of measurement of the electrical conductivity of water. Take two electrodes and immerse them in water. A known amount of current is supplied to one, and the second is used to measure how much has reached. Since charge carriers in an aqueous solution are ions, the number of electrons transferred from one electrode to another can be used to draw a conclusion about the total proportion of ions in the solution. Siemens is the reciprocal unit of resistance (1 cm = 1 ohm-1). Measuring electrical conductivity can sometimes give a fairly accurate idea of ​​the total salinity content of water. If the water is relatively clean, then we can conventionally assume that 1 µS/cm ≈ 0.5 mg/l of salts. And now we come close to the essence of water analysis.

Here we need to digress and clarify that there are many types of water tests. Offhand, there are chemical and microbiological. And also organoleptic, radiometric, there are countless of them. I deal directly with the chemical analysis of water, and we’ll talk about it. In Russia, the document regulating the quality of water for domestic needs is called “SanPiN 2.1.4.1074-01”. And there are a lot of controlled parameters there. It is appropriate to note here that such a concept as “process water” does not exist in any official document. Moreover, what the common people usually mean by technical water is precisely water that can be drunk, but cannot be used in that very equipment. Sometimes completely demineralized (deionized) water must be supplied to production or to a steam boiler.

Looking at all the parameters implied by SanPiN in the laboratory is crazy. Firstly, it will take a week to analyze one sample (while analysis of 12 indicators is done in 2 hours). And secondly, existing filter materials still purify water only from a finite number of pollutants. And, of course, most of the pollutants listed in SanPiN are practically not found in ordinary natural waters or are found in such quantities that they obviously comply with the standards. Let's go in order with all the comments (in what order exactly - I haven't decided yet).

Iron. It is present in almost all underground waters, but in surface waters - rivers, lakes - it can rarely be found. It comes in two forms: soluble or divalent Fe2+ and oxidized or trivalent Fe3+. Divalent iron salts dissolve perfectly in water (many gardeners will find iron sulfate FeSO4 ∙ 7H2O in specialized stores), but they are very quickly oxidized by atmospheric oxygen and turn into ferric iron compounds. But ferric iron compounds are insoluble in water - everyone has seen rust, and rust is a mixture of Fe2O3 ∙ nH2O and Fe(OH)3.

FeCl3 dissolves well in water, after which it hydrolyzes to oxychloride and precipitates. The same applies to other soluble ferric iron compounds - they are subject to hydrolysis in an aqueous solution to form insoluble products.

Therefore, there is little iron in surface sources: even if it was there initially, it quickly oxidized upon contact with the atmosphere and went into silt. In addition to the atmosphere, the natural enemy of ferrous iron is iron bacteria, which live off the energy released when they oxidize divalent iron. But he has a faithful ally in the form of hydrogen sulfide. Groundwater often contains large amounts of hydrogen sulfide, which is a strong reducing agent and prevents iron from oxidizing even when in contact with the atmosphere. In general, the dependence of the form of iron in solution on the redox potential and pH value is clearly displayed in Pourbaix diagrams. Iron is one of the microelements and is necessary for the human body (daily requirement - 10 mg), and is absorbed, including from water. Of course, the iron content affects the organoleptic properties of water (if it is more than 1-2 mg/l), and its excess intake into the body can provoke various health problems. Well, it's always like that. Everything is medicine and everything is poison, it’s all a matter of dose, said Paracelsus.

The maximum permissible concentration for total iron in domestic water is 0.3 mg/l. In the city water supply, approximately 0.10...0.15 mg/l flies from the pipes when they rust (where I live). Iron is removed simply: first it is oxidized to be sure (let me remind you that oxidized iron is insoluble in water), then the resulting particles are coagulated (enlarged), and this entire structure is caught mechanically - on the loading layer. There are different catalytic loads, on the surface of which all these processes occur. They are sand coated with a layer of manganese oxide - the same catalyst for iron oxidation - and require periodic reagent washing with a solution of potassium permanganate (no, manganese compounds are not washed off from the load and do not end up in purified water - well, unless, of course, you want mix the catalytic material with citric acid). There are also reagent-free loads, but before them, preliminary oxidation of the iron is required, and the engineer will decide which method - atmospheric air, ozone or chlorine. If your water contains up to 5 mg/l of iron, consider yourself very lucky: the installation will be cheaper. If iron is 10 mg/l, it’s already expensive. But 30 mg/l and above - you can say goodbye to your planned trip to warm countries. Such an installation can cost several hundred thousand rubles. In general, the main cost of most semi-industrial filtration systems depends on the iron concentration. The more it is, the more expensive it is. That’s why it’s so important to thoroughly drain the water before taking a sample - stagnant water in metal pipes can pick up iron, and the engineer will offer you a setup for analysis that Elon Musk doesn’t have enough money for. But that's not all. Separately, it is worth mentioning the so-called organic iron - complex organic compounds containing an iron atom in the molecule (usually humates - complexes of humic acids). It is not easy to knock iron out of such complexes, and it does not oxidize in air. Removing organic iron from water can be difficult.

Manganese. Manganese causes a gray coating to appear on plumbing fixtures, so it is strictly regulated. The human body also needs this microelement (daily requirement 2 mg [1]). Easily absorbed from water. It is also found in beets and half of vegetables in general. Manganese has seven valences; it makes no sense to consider it in detail. Divalent manganese is highly soluble, trivalent and tetravalent manganese usually undergo hydrolysis and precipitate in the form of insoluble hydroxides. Unlike iron, manganese is more common in surface waters. Especially if these are wells, and the underground water feeding them contains some kind of divalent manganese ion. The fact is that manganese is not easily oxidized by atmospheric air. Can be captured by precipitating iron and removed along with it. The loadings are still the same, because the principle is the same: oxidation, enlargement and mechanical filtration. MPC 0.1 mg/l.

Rigidity. Hardness closes the top three parameters that almost all semi-industrial water purification systems are aimed at. Yes, yes, there are deferrization filters (remove iron, manganese and some other heavy metals) and softening filters (remove hardness). Of course, there are other types of filters that work, for example, by oxidation, but ultimately for industrial needs you will be offered reverse osmosis with pre-treatment, then the output water will be as per GOST for laboratories: 3...5 µS/cm. But we digress. At school you were told that hardness is a combination of calcium and magnesium ions. It is they that fall out in the form of scale when water boils. In fact, this definition is not entirely correct. Yes, a significant proportion of hardness is made up of calcium and magnesium ions, but in general hardness is the sum of all alkaline earth ions, as well as some divalent heavy metal ions. Zinc, barium, cadmium, even divalent iron are all hardness. Another thing is that a chemist in the laboratory will mask ferrous ions when measuring hardness. But cadmium will have quite an effect on the amount of hardness. But I hasten to reassure you: calcium ions make up the majority of hardness - usually 80 percent, and another 15 percent magnesium. Hardness is standardized solely to reduce the amount of scale in kettles, and especially zealously in industry standards for all boiler houses, where there should be no hardness in the water at all. Sometimes you may hear that you should only use soft water in your household, and that hard water is supposedly harmful. Hard water increases the cost of soap, reduces the life of the washing machine... They may begin to convince you, arguing that calcium is still not absorbed from water, and the body gets it from milk and cheese. It is not correct.

Let's take a break and briefly talk about the process of souring milk. Milk contains calcium caseinate and the milk sugar lactose. Microorganisms that get into the milk begin to ferment lactose, gradually turning it into lactic acid. Lactic acid knocks calcium out of calcium caseinate and replaces it with a hydrogen ion. Calcium caseinate is converted into casein, the milk protein that makes up the entire cottage cheese. And calcium remains in the serum in the form of calcium lactate. So cottage cheese and cheese are low in calcium. And in natural fresh milk - yes, there is calcium. But in order to be absorbed, it must first be knocked out of the caseinate by the hydrochloric acid of the stomach. In water, calcium is already ready - immediately in ionic form, and is absorbed instantly. Therefore, water is one of the most important sources of calcium in the body, and we need a lot of it - the daily requirement is at least 1000 mg. Maximum permissible concentration for hardness is 7 mEq/l. If we convert this into calcium, then the water may contain (7 ∙ 20.04) 140 mg/l of calcium. So you will need to drink 7-8 liters of water to get your daily requirement. However, scale begins to noticeably form already at a hardness content of about 4 mEq/l. Hand-made bar soap - a mixture of sodium salts of higher fatty acids - upon contact with hard water turns into a mixture of calcium salts of higher fatty acids, and calcium salts of soap dissolve poorly in water. But now manufacturers add softening agents to soap - for example, Trilon B, which neutralize this process. Synthetic detergents - powders, gels and other lauryl sulfates - are generally not afraid of hardness and are not precipitated by it. Conclusion? It is useful to drink hard water (7 mEq/l according to SanPiN), wash your hands with soap in water with a hardness content of 2...4 mEq/l, supply soft water to the washing machine and dishwasher (<0.1 mEq/l) , and then only to prevent the heating element from fouling. As for kettles, with a hardness of about 2 mEq/l, the formation of scale on the heating element is almost invisible. Please note that not all calcium and magnesium compounds form as scale when boiled. Strictly speaking, this is characteristic only of bicarbonates, and all sorts of chlorides and sulfates floated in the water before boiling, and will float after. Typically, in river water (and rivers provide water to most of our settlements), the hardness value, depending on the season, is 2..4 mEq/l (lower in winter).

To remove hardness salts from water, cation exchange resins are used, which simultaneously bind most other cations, including manganese and divalent iron. Therefore, there are filter options that simultaneously remove iron, manganese and hardness in one load, but there are nuances - iron and manganese must be contained in small quantities in the water, and the iron must be divalent (in ionic form). Such filters require regeneration with a saline solution, so the consumable material here is tableted salt (just as in iron removers, potassium permanganate can be a consumable material). The cation exchange resin is charged with sodium ions. Hard water, passing through a layer of such loading, will exchange ions with the resin - give up calcium/magnesium, take away sodium. Eventually, the charge of sodium ions on the resin will be used up, after which the controller will turn off the consumers and pour a strong sodium chloride solution into the filter. A reverse replacement will occur, all the hardness ions deposited on the resin will go into the solution, which will then merge into the drainage. And the resin, recharged with sodium ions, can continue to purify water.

Separately, I would like to talk about Chinese pocket devices that supposedly measure hardness. In fact, these devices are ordinary conductivity meters, or TDS meters. They measure the specific electrical conductivity of water in µS/cm, the resulting value is multiplied by about 0.5 and a certain value is obtained in ppm. And they cheerfully report to you that the hardness of your water is, say, 250 ppm. Firstly. In the West, hardness is actually measured in ppm, and they calculate it using calcium carbonate.

The molar mass of calcium carbonate is 100 mg/mmol, the equivalence factor is 0.5, therefore, one milligram equivalent of calcium carbonate “weighs” 50 mg. Since mg/l and ppm are practically the same thing, when converted to our native units of measurement, 50 ppm = 1 mEq/l of hardness. Secondly, the conductometric method, as I already said, determines the total salt content, the sum of all anions and cations in the solution. It is almost impossible to measure hardness separately using this method (it is possible if you first find out in the laboratory what percentage calcium and magnesium ions make up of the sum of all ions in a given water, calculate the correction factor and then measure this same water conductometrically). And all these supposed hardness meters simply determine the total salt content on the assumption that nothing except calcium carbonate is dissolved in the water.

Alkalinity. Not standardized, represents everything that can react with a 0.1 M solution of hydrochloric acid. In our natural waters these are mainly carbonates and bicarbonates. Based on alkalinity, you can roughly estimate what percentage of carbonate (temporary) hardness is in your water. The rest of the hardness will be non-carbonate, that is, that which does not precipitate during boiling (chlorides, sulfates...). This parameter is more needed by engineers in their calculations (it is especially interesting to look at the buffering capacity of water). There are no specific methods for removing alkalinity, and it is not required to remove it.

Nitrogen compounds: nitrates, nitrites, ammonium. As soon as watermelons appear on sale at the beginning of summer, everyone around them begins to discuss nitrates. Meanwhile, nitrates are completely safe. Their maximum permissible concentration is 45 mg/l. But nitrites... Once in the blood, nitrites bind to hemoglobin, turning oxyhemoglobin into methemoglobin, which is unable to carry oxygen. The maximum permissible concentration of nitrites in domestic water is 3 mg/l. But why doesn’t anyone panic when they read the line “nitrite-curing mixture” in the sausage? After all, it is a mixture of sodium nitrite and sodium chloride. Due to its ability to bind to blood proteins, as well as to enter into azo coupling reactions, nitrite helps color meat red. Without the use of nitrites in sausage, you would be eating completely gray and unsightly products. But they would be healthier, right? Let's take a closer look at this point. Manufacturers claim that their curing mixture contains only 0.6% sodium nitrite. A person also has the enzyme methemoglobin reductase, which is capable of repairing broken hemoglobin, so it’s too early to cover yourself with a sheet and crawl to the cemetery with sausage in your teeth. The transformation of nitrates into nitrites in the human body (and this is what they may intimidate you with, appealing to the mysterious enzyme nitrate reductase), strictly speaking, is impossible by the body’s own forces. It is believed that animals and humans lack this enzyme, and I have not yet seen articles proving otherwise. But in our oral cavity there live microorganisms that produce this enzyme. Indeed, they are capable of converting nitrates into nitrites. We're all going to die, right? No. The process of reducing nitrates is not fast, and the efficiency is not high. And the final products are consumed, in fact, by those microorganisms that produce the enzyme. This is how they absorb nitrogen.

In addition, this exogenous nitrate cycle plays a huge role in maintaining and improving our health, if only because it normalizes blood pressure, protects against caries and kills bacteria. In addition to nitrate reductase, living creatures in our oral cavity also produce nitrite reductase, which converts nitrite further into ammonium ion. Ammonium ion affects the acid-base balance of body fluids. There is evidence that if there is an excess, it can alkalize the blood. Our body itself releases ammonium during the breakdown of proteins and then binds it into urea (that is, neutralization methods exist). The maximum permissible concentration of ammonium in domestic water is 2.6 mg/l (in SanPiN: 2 mg/l for nitrogen). As a rule, nitrates, nitrites and ammonium in natural waters do not exceed the maximum permissible concentration, although there are rare exceptions. The removal of these compounds from water is more or less guaranteed only by reverse osmosis. Of course, nitrates and nitrites will sit on the anion exchange resin, and ammonium on the cation exchange resin, but due to their physicochemical properties they can be quickly knocked out of the resin by other ions contained in the water.

Oxidability. Otherwise - chemical oxygen consumption. This is everything that can be oxidized by potassium permanganate in a sulfuric acid environment: organic molecules, unicellular algae, divalent iron... True, the analytical chemist will subtract iron when measuring oxidability. In general, oxidability can be used to indirectly judge the biological contamination of water. The unit of measurement for oxidability is mgO/l (the number of milligrams of atomic oxygen absorbed by a liter of the test solution). Organic iron and oxidability may be related. The maximum permanganate oxidation concentration is 5 mgO/l. There are loads that work by oxidation. But if its content in your water reaches a threshold level, the engineer will most likely suggest a carbon filter.

Hydrogen sulfide and radon. Hydrogen sulfide is poisonous and smells bad, radon is radioactive. They should not be present in water at all, because they have no benefit. Hydrogen sulfide can be oxidized to elemental sulfur using special charges, but only to a certain concentration. The most reliable method for removing both of these dissolved gases from water is stripping. Atmospheric air is bubbled through the water, as a result of which both gases are blown out of the water and go along with the supplied air into the surrounding atmosphere, poisoning everything around. The room in which this process takes place must be technical (non-residential) with good ventilation.

Sulfates, chlorides. MPC of the first is 500 mg/l, the second is 350 mg/l. No toxicology. They are rationed because of the taste: sulfates are bitter, chlorides are salty. Removed by reverse osmosis.

Osmotic pressure, due to which plants absorb water from the soil, acts on the following principle: if two solutions are separated by a semi-permeable partition through which water molecules can penetrate, but ions cannot, then the solvent flows from an area with a lower concentration to an area with a higher one, equalizing the concentrations . Reverse osmosis uses exactly the same semi-permeable membrane, but artificially creates pressure just in the area of ​​​​higher concentration, as a result of which the solvent flows into the area of ​​​​lower concentration, and the solution is concentrated. In this case, the incoming water flow is divided into two: permeate (pure water) and concentrate, which is discharged into the drainage. In household osmosis systems, the permeate: concentrate ratio is approximately 1: 3 (3 parts of the input water are drained into the drain). In expensive industrial ones, this process is compensated, otherwise the losses will be terrible.

Hydrogen index. Aka pH. We'll wrap it up there. It is a negative decimal logarithm of the concentration of hydrogen ions and indicates the acidity of the medium. Normalized in the range of 6-9 units. pH. A more acidic solution will dissolve your teeth, a more alkaline solution will begin to irritate the stomach lining. A very important parameter for selecting equipment is that many loads operate in a certain pH range. In natural waters it is almost always near the level of 7 units. pH, in some extraordinary cases, an engineer may suggest dosing alkali or acid into the water to achieve a given acidity value.

At the end I want to add a few words about filter types. I mentioned cabinet systems and column-type filters in the text. In essence, they are the same thing. There is a certain cylinder, inside of which there is a drainage and distribution system and filter material. Only in cabinet systems is everything compressed into a small volume and placed in a case the size of a washing machine. One of the advantages is lower consumption of water and reagents for washing; the disadvantage is one filter material for all parameters. Column-type filters are more flexible in setting - for example, if an office worker immediately removes iron, manganese and hardness to zero for you, and you do nothing about it, then by placing two columns in series - one for iron, the second for hardness - you can adjust the output water hardness so that you feel comfortable taking a shower (so that you don’t feel like the soap isn’t being washed off), and there will be no iron or manganese in the purified water. Remember that the size of the cylinder depends on your water consumption, and you cannot use the smallest cylinder for a water consumption of two cubic meters per hour. Contaminants will simply start leaking through, and eventually you will kill the filter material. Filter materials, by the way, usually last 5-7 years, after which they need to be replaced. But first, I recommend analyzing the outlet water, because I personally tested the filter, which has been working properly for 11 years on one load.

The material turned out to be great, you can read it at night to fall asleep faster and sleep more soundly. I tried to embrace the immensity, told the very essence and now I will add, perhaps, about bacteriological purification. There is only one method to kill living creatures in water - to oxidize it. To do this, in the simplest case, chlorine in the form of hypochlorite will be dosed into the water or an ultraviolet lamp will be placed at the outlet. Ultraviolet ionizes oxygen dissolved in water, and active oxygen will kill bacteria. The best option is an ozonizer. A UV lamp or ozonizer is placed at the outlet after all cleaning, immediately before supplying water to the consumer, and chlorine, on the contrary, at the beginning. Because chlorine is a slower oxidizing agent and needs to be given time, and then the excess chlorine must be neutralized using a carbon filter.

There are still a lot of nuances and pitfalls in water treatment. But... “This is indescribable!” - said Moska, looking at the baobab tree. published

Author: Dmitry Filatov

If you have any questions on this topic, ask them to the experts and readers of our project here.

PS And remember, just by changing your consumption, we are changing the world together! © econet

How to maintain water hardness level in mmol l using modern technologies

Since domestic supply organizations are not required to maintain or reduce the hardness level below 7 mmol l, the appropriate preparation must be carried out independently. Owners of individual suburban plots must solve these problems when connecting to personal/collective artesian wells.

In the standard version, calcium and calcium compounds are extracted from the liquid stream using ion exchange technology. The active filler in granules is poured into a special container. Initially, and for regeneration, it is impregnated with a harmless solution of sodium salts. The washing and restoration work cycles are automated using specialized automation/control units.

Other methods of dealing with scale

If the concentration of impurities is not high, flow filters or autonomous jugs are used. They install cartridges filled with ion exchange resins. Some designs imply the possibility of repeatedly restoring lost properties using washing in a solution of citric acid.

The next method of preparing drinking water is reverse osmosis. Household installations provide a productivity of no more than 220-240 liters per week. But this is enough to meet the needs of the average family. For reserve, the kit is supplemented with a storage tank of 80-14 liters.

Electromagnetic converters are used instead of ion exchange units. These modern devices take up a minimum of space, but prevent the formation of scale at a distance of up to 2 km from the installation site of the induction coil. Unlike reverse osmosis and other technologies, they do not change the water hardness in mmol l or mEq l in any way. Accordingly, components valuable for human physiology are preserved.

How to determine compliance or non-compliance with the rigidity standard

As in the case of the level of hot water heating, the consumer has the right to make claims against the supplying organization if we are talking about temporary rigidity. The abundance of magnesium or calcium ions above the norm not only changes the taste of drinking water, but also has a harmful effect on human health and damages household appliances.

The supplier may have one of many water softening devices at his disposal. However, unscrupulous companies ignore existing regulatory requirements. In order to talk about the inadmissibility of an indicator existing in drinking water, it is necessary to make certain measurements and compare it with the hardness standard.

In this case, home-grown criteria, such as soap that lathers poorly even in hot water, or scale that quickly forms on a kettle, are unacceptable.

Water samples can be taken to the SES, where pathogenic microorganisms, organic impurities, and toxic inclusions such as nitrates will be identified. For home express analysis, you can use test strips, the cost of which does not exceed 500 rubles.

If we are talking about independent water supply to a mansion, cottage or country house from improvised sources, such as an artesian well, you can do a comprehensive analysis in a specialized laboratory, the cost of which varies.

In the laboratory of Moscow State University, an analysis of water hardness will not be cheap, but at a local one it can range from 1200 to 4500 rubles, if an extended one is required. But having all the indicators in hand and having identified inconsistencies with any hardness standards in the source used, you can choose one of the many water purification systems.

This will help protect your own health from future troubles and feel comfortable. These measures will also ensure the safety of household appliances.

The effect of hard water on human health

The effect of salts contained in an aqueous solution on the human body has not been sufficiently studied. But, according to research, impurities have a negative impact on:

1. Cardiovascular system.
2. Kidneys. A large amount of salts in the body leads to the formation of stones.
3. Skin. Soap interacts with calcium and magnesium salts and forms an indelible film that breaks the protective layer of the skin. Irritation and allergies are a consequence of using hard water.
4. Hair. They become brittle.
5. Gastrointestinal tract. Salts settle on the walls of the stomach, their accumulation in the body can lead to dysbiosis and other digestive disorders.
6. Joints. A large amount of impurities in water contributes to the development of arthrosis.

Table 1

Let's consider the types of rigidity

This indicator is usually divided into the following categories.

• Constant - is a constant indicator that depends on the content of sulfates and chlorides.
• Temporary - due to the content of calcium and magnesium bicarbonates. This type of hardness gets its name from its ability to be almost completely neutralized as a result of boiling.
• General stiffness is obtained by adding the constant and temporary indicators.

In order to accurately determine this indicator, you need to know what units of measurement can be used.