Ph and alkalinity of recycled water. What is water alkalinity and pH calculation

In the tables of the SanPiN of the Russian Federation (“Drinking Water”), the maximum permissible concentration for alkaline indicators is not indicated, therefore, most sources when determining the alkalinity of water refer to WHO standards, the EU directive or sanitary rules of countries with similar regulatory procedures.

So, a value of 30 mg HCO3- / l is established in the EU directive when determining the quality of water intended for human consumption. In the Ukrainian current rules of the GSanPiN for tap water, the parameter is not set, and the value in< 6,5 ммоль/м 3 указывается только для фасованной и бюветной воды. Приведённые в российских тематических источниках значения чаще всего варьируются в пределах от 0,5 до тех же 6,5 ммоль/м 3 .

Moreover, there is GOST 31957-2012 - Interstate Standard, signed by standardization bodies of 6 countries and modified in relation to other international standards. Russia, along with Armenia, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan, is one of the countries that signed the document, which describes methods for determining alkalinity at a concentration of 0.1-100 mmol / dm 3.

Definition and content of the concept

The alkalinity of water ("SH" in the formulas) is the sum of the substances contained in it - hydroxyl ions / anions of weak acids - reacting with strong acids with the division into:

• bicarbonate (Щ b),
• carbonate (Щ to),
• hydrated (SH g) ,.

The unit is milligram equivalent of acid, written as mEq / L. Total alkalinity as the sum of anions of weak acids - silicates, borates, carbonates, bicarbonates, sulfides, hydrosulfides, sulfites, hydrosulfites, phosphates, anions of humic acids) is the ability to bind strong acids (their equivalent amount). The concentration of some ions is insignificant, therefore, when they talk about general alkalinity, they mainly mean the carbonate type (determined by carbonic acid ions), where hydrolyzed anions form hydroxide ions:

The alkaline indicator for surface waters is associated with the presence in them mainly of hydrocarbonates of alkaline earth metals (and alkaline metals to a lesser extent), and for natural waters with pH< 8,3 он определяется концентрацией гидрокарбонатов магния и кальция. При определённой обработке водоресурса и при pH >8.5 occurs hydration type.

An alkaline parameter is required for:

• determination of carbonate content, as well as the balance of carbonic acid (together with pH),
• dosing of chemicals used in water supply,
• reagent cleaning
• establishing the suitability of water for irrigation (with an excess of alkaline earth metals).

The northern regions of Russia with low alkaline values \u200b\u200band pH for natural water are characterized by increased corrosiveness, which affects pipelines and structures made of ferrous metals and concrete.

According to Japanese researchers, in areas where they drink more alkaline water (above 6.5, but below 9), life expectancy is 20-30% higher. In general, alkaline indicators should be sufficient to undergo chemical coagulation, but at the same time they should not be too high so as not to provoke physiological disorders in water consumers. The minimum alkaline values \u200b\u200bare +/- 30 mg / l, and the maximum within 450-500 mg / l.

The opinion spread among the owners of various modified aerators about their effect on the alkaline properties of the hydroflow is not confirmed. These aerators-economizers (http://water-save.com/) can reduce water consumption, but do not affect the chemical characteristics of the water resource.

Methods for determining the concentration of carbonates

The interstate standard describes 2 titrimetric methods for calculating water alkalinity:

1. Free and general alkalinity. For drinking - pre-packaged (non-carbonated) and from drinking water sources - natural, as well as wastewater by titration (gradual mixing) to a pH of 8.3, as well as 4.5. The obtained values \u200b\u200bare used to calculate the concentration of carbonates (in the range of 6-6000 mg / dm 3) and hydrocarbons (6.1-6100 mg / dm 3).
2. Carbonate alkalinity. For drinking, natural, technical water at different stages of technological processes by titration to a pH of 5.4 units.

The titration endpoint is determined by changing the value on the pH meter or when the indicator is colored:

• the pH transition from pink to colorless at 8.3-8.0 gives the value of the parameter “according to phenolphthalein”,
• the pH transition from orange to yellow at 4.4 gives a value for the “methyl orange” parameter.

The parameter is equal to zero if for the analyzed sample the pH<4,5.

Alkalinity is the content in water of substances that react with strong acids. These substances include:

- strong grounds;

- weak bases: ammonia, aniline, pyridine, etc .;

- weak acid anions:, anions of humic acids.

There are three forms of alkalinity: free, carbonate and total.

Free alkalinity is due to hydroxyl and carbonate ions. It is determined by the amount of acid used to titrate water to a pH of 8.3.

Carbonate alkalinity depends on the presence of only carbonic acid ions in water, i.e. carbonate and bicarbonate ions, and is determined by the amount of acid used to titrate water to pH ≈ 4.

The general alkalinity is due to the presence in the water of anions of weak acids of organic and inorganic origin, as well as hydroxyl ions.

In fresh uncontaminated waters, the carbonate alkalinity is so great compared to the alkalinity introduced by other anions that it can be taken equal to the total alkalinity.

The main source of carbonate and bicarbonate ions in surface waters is the chemical weathering and dissolution of carbonate rocks such as limestone and dolomite. For example,

CaCO 3 + H 2 O + CO 2 ↔ Ca 2+ + 2;

MgCO 3 + H 2 O + CO 2 ↔ Mg 2+ + 2.

Some of the hydrocarbonate ions appear as a result of metamorphization of products of chemical weathering of igneous rocks:

CO 2 → + SiO 2;

OH - + CO 2 →.

Significant amounts of bicarbonate ions come from precipitation and groundwater.

Hydrocarbonate and carbonate ions are discharged into water bodies with sewage from chemical, silicate, and soda enterprises, etc.

With the accumulation of hydrocarbonate and especially carbonate ions, the latter, forming poorly soluble compounds with calcium ions, may precipitate:

Ca (HCO 3) 2 → CaCO 3 ↓ + H 2 O + CO 2;

Ca 2+ + \u003d CaCO 3 ↓.

This process is very important in nature, since the formation of carbonate rock strata depends on it.

In surface waters, hydrocarbonate and carbonate ions are present mainly in the dissolved state. Some of the carbonate ions may be in suspension and close to the colloidal state in the form of fine particles of calcium carbonate.

In the solution between bicarbonate and carbonate ions, there is a mobile equilibrium determined by dissociation constants characterizing the first and second stage of carbonic acid dissociation

H 2 CO 3 ↔ H + + ↔ H + +.

In river waters, the content of bicarbonate ions varies from 30 to 400 mg / dm 3, in lakes - from 1 to 500 mg / dm 3. Their concentration in seawater varies within a narrower range from 100 to 200 mg / dm 3, in atmospheric precipitation it is 30 - 100 mg / dm 3, in groundwater - from 150 to 300 mg / dm 3. In underground waters, their content noticeably increases from 150 to 900 mg / dm 3.

Alkalinity is an important characteristic of surface waters, by which one can judge the most important hydrochemical and geochemical processes, such as the formation of the chemical composition of water, erosion of the earth's surface, the formation of carbonate rocks, etc.

In technology, the alkalinity is very significant, since it affects the corrosion of concrete and the loss of carbonate scale in boilers that feed various steam-powered plants.

The following methods are used to determine the alkalinity of waters: direct titration, back titration and potentiometric.

Direct titration methods are based on titration of a water sample with strong acid (HCl, H 2 SO 4) in the presence of various indicators with a color transition at an equivalence point in the pH range from 3 to 4. These include methyl orange, bromphenol blue, methyl yellow. The disadvantage of this simplest and fastest method is the uncertainty of the pH value at the end point of the titration. To determine the free alkalinity, phenolphthalein is usually used, having a range of pH transition and color indicator 8.2 - 10.0.

The methods of back titration are more accurate, which are based on adding an excess of strong acid to the water sample and its titrimetric determination in the presence of an indicator. These methods are most widely used, however, when analyzing waters with a low alkalinity (less than 10 mg / dm 3), as well as colored and turbid waters, significant errors of up to 20% are possible.

In these cases, various variants of potentiometric methods are preferred, in which a sample of the test water is titrated with strong acid to a certain pH value determined using a pH meter. The results are not affected by traces of active chlorine, turbidity and color of the water.

Natural waters usually have a slightly alkaline reaction. These waters acquire an acid reaction with a significant content of humic acids or in the presence of a large amount of free carbon dioxide. [...]

Natural surface water (like groundwater of the active water exchange zone) in its composition, as a rule, is quite suitable directly for drinking purposes. Improvement of organoleptic properties is easily achieved at waterworks by coagulation, filtration and oxidation processes, as a result of which for unpolluted natural water sources the scope of analytical control could be limited to determining turbidity (transparency) and color of water. Requirements for water quality from industrial water users depend on the characteristics of the technological use of water, which determine the minimum necessary analytical control of the source water. The most typical determination of the composition and quality of water. In water, they determine: hardness, acidity, turbidity, pH, color, alkalinity, electrical conductivity, oils, as well as the content of boron, fluorine, iron, calcium, sodium, magnesium, manganese, nickel, copper, lead, zinc, chromium (VI) ortho and polyphosphates, nitrate, nitrite, sulfate, sulfide, sulfite, chloride ions, silicic acid, ammonia, carbon dioxide, dissolved oxygen, hydrazine, tannin, lignin; in addition, determine the weight of the solids - before and after filtration. [...]

Natural waters of the northern regions with low alkalinity and pH are characterized by increased corrosiveness in relation to pipelines and structures made of concrete and ferrous metals. A variety of compounds may be present in wastewater that enhance the corrosive effects of water on concrete and metals. [...]

The alkalinity of the water should be sufficient to effect chemical coagulation, but not so high as to cause physiological disorders in consumers. The minimum alkalinity is about 30 mg / l, and the maximum should not exceed 400-500 mg / l. Fluorine ions are resistant to conventional cleaning processes, with the exception of softening water with lime; therefore, the permissible fluorine concentrations for natural water are the same as for drinking water (see table [...]

The alkalinity of natural waters depends mainly on the content of salts of carbonic acid. If the color of water is more than 40 ° and the need to accurately determine the concentration of hydrocarbonate and carbonate ions, the value of humate alkalinity should be taken into account separately (see below). [...]

Alkalinity of water. Under the general alkalinity of water is meant the sum of the "hydroxyl ions (OH-) contained in the water and the weak acid anions, for example, carbonic (HCO - ions, COg-). Since carbon dioxide predominates in most natural waters, usually only bicarbonate and carbonate alkalinity are distinguished. With some methods of water treatment and at a pH above 8.5, hydrated alkalinity occurs. [...]

Natural water used for water supply may have one of these properties. In case of stability violation, in which pipe damage due to corrosion or unacceptable deposits of calcium carbonate are possible, water undergoes special (stabilization) treatment. If prone to carbonate deposits, add acid or sodium hexametaphosphate to the water; in the presence of aggressive carbon dioxide, the water is treated with an alkaline reagent, usually lime. [...]

Alkalinity is the content in water of substances that react with strong acids, i.e., hydrogen ions. This is one of the most important characteristics of natural water. The alkalinity of water is significantly affected by the state of carbon dioxide compounds, which therefore should be considered in more detail. [...]

Alkali metals. Of alkaline ions! The most common metals in water are Na + and K +, which enter the water as a result of dissolution of ■ bedrock. The main source of sodium in natural waters is salt deposits. In natural waters, sodium contains - more than potassium. This is due to the best absorption of the latter by the soils, as well as its greater extraction from water by plants. [...]

Under natural conditions, soda is formed by weathering igneous and sedimentary rocks containing a certain amount of sodium. The bases released during weathering (Ca, My, No., etc.) interact with the carbon dioxide of the soil solution and form the corresponding carbonates, including sodium carbonate. Soda can occur as a result of the interaction of neutral salts rising with ascending solutions from groundwater, with carbonates of alkaline soil: Na2504 + Ca (HC03) 2 -\u003e CaBO, + 2NaCN03. [...]

During alkaline cleaning of petroleum products, natural gas and gas condensate from sulfur-containing compounds, alkaline wastewaters are formed containing sulfides and mixtures of lower alkyl mercaptides. These wastewaters are difficult to process and create an unfavorable environmental situation around oil and gas refineries. [...]

Total alkalinity (t). Measure 100 ml of the sample or use the solution after determining the free alkalinity, add 0.15 ml (3 drops) of the mixed indicator or 0.1 ml (2 drops) of methyl orange. Then blow air and at the same time titrate on a white background 0.1 n hydrochloric acid solution until the green color of the mixed indicator turns into dirty gray or until the color of methyl orange changes from yellow to orange. Continue to purge the air and after 5 minutes, if necessary, titrate. With electrometric determination, blowing is carried out in the same way, but titrated to pH 4.5. With less stringent requirements for accuracy, methyl orange titration is carried out without purging. Titrate from a burette with a division price of 0.1 ml, the reading accuracy is up to 0.05 ml. Otherwise, the above procedure should be followed. When analyzing natural waters having a low total alkalinity, they are titrated from microburettes and counted to the accuracy of 0.005 ml. [...]

Of the alkali metal ions in natural waters, especially in marine waters, there are large amounts of sodium ions, and smaller ones contain potassium, as well as rubidium (about 0.2 mg / l) and lithium (about 0.1 mg / l). In terms of prevalence in natural waters, No. + ranks first, making up more than half of all cations contained in them. The amount of K + usually amounts to 4-10% of the number of Na + ions present in water (in low-mineralized waters ■ a large percentage). [...]

Usually, in natural waters, alkali metal ions — potassium and sodium — are contained in small amounts. In addition, ferrous and oxide iron ions may be present in them. In waters of surface sources, iron is often a part of organo-mineral complexes, in underground waters - in the form of bicarbonates, less often - chlorides and sulfates. Manganese is present in natural waters in much smaller quantities than iron; according to the standard, the total content of iron and manganese in drinking water should not exceed 0.3 mg / l. Non-ferrous metal ions - copper, zinc, lead, as well as arsenic can enter the water only when it is contaminated with industrial effluents or due to corrosion of valves. [...]

The water quality of natural sources of water supply is mainly characterized by the content of coarse suspensions, color (due mainly to dissolved humic substances), total organic matter, taste and smell, alkalinity (content of bicarbonates, carbonates and other salts of weak acids) and the concentration of mineral salts, in including stiffness cations. Absolute or conditional criteria have been introduced to evaluate each of these indicators. [...]

Acidic or alkaline effluents entering the water body can be neutralized in a certain amount by the carbonate buffer system of natural waters, consisting of free carbonic acid and bicarbonates. This also helps to maintain a constant pH of water during the introduction of reagents during processing. In alkaline waters (at pH\u003e 8.5), the buffering properties of natural waters are determined by a second carbonate buffer system consisting of hydrocarbonates and medium carbonates (for example, NaC03 and Na2CO3). [...]

Since alkalinity in natural waters is usually determined by the presence of alkaline earth metal bicarbonates, the state of carbon dioxide compounds in water should be considered in more detail. [...]

The stability of water characterizes its property of not emitting and not dissolving calcium carbonate. The stability analysis results are expressed in the form of a fraction, the numerator of which is alkalinity or an indicator of the concentration of hydrogen ions of the studied water in its natural state, and the denominator is the same indicators after the maximum saturation of water with calcium carbonate. Free carbon dioxide contained in natural waters does not all have the ability to dissolve carbonate rocks. [...]

If there are several substances in the wastewater with an organoleptic hazard indicator of the same effect (\u003e by smell, taste, color) and similar substances are found in the water of the reservoir to the place of the planned release, the maximum permissible concentration of substances should be taken taking into account the instructions for protecting water bodies from pollution, related to the case of water pollution by a complex of substances with the same limiting hazard indicator. As for the salt composition of natural waters, it is known that the pleasant and refreshing taste of water is mainly associated with the content of alkali and alkaline earth metal bicarbonates in it, which make up about 70% of the total number of cations and anions. However, increased concentrations of chlorides, sulfates and nitrates can dramatically impair the taste of water. [...]

For most natural waters, HCO ions are associated only with calcium and magnesium ions. Therefore, in cases where the alkalinity for phenolphthalein is zero, we can assume that the total alkalinity of water is equal to its carbonate hardness. [...]

The active reaction of water - its acidity or alkalinity, is characterized by the activity of hydrogen ions. The active reaction of natural waters is close to neutral, i.e. pH 6.8-7.3. [...]

The taste properties of water are due to the presence of substances of natural origin or substances that enter the water as a result of pollution by its effluents. Groundwater, containing only inorganic solutes, has a specific taste, which is caused by the presence of iron, manganese, magnesium, sodium, potassium, chlorides and carbonates. Determine (organoleptically) the taste of only drinking water; describe him verbally. There are four main tastes: salty, sweet, bitter, sour. In addition to them, some flavors can also be noted (for example, alkaline, metallic, etc.). [...]

Analysis of treated wastewater and natural waters containing volatile phenols in very low concentrations. To the distillate obtained from 1 l of the analyzed water, add 1.5 ml of 1 N. sodium hydroxide solution and saturated with sodium chloride at room temperature. Then the solution is transferred to a separatory funnel, add 2 ml of 1 N. hydrochloric acid and extraction is carried out by adding 50 ml of diethyl ether and shaking for 10 minutes. Transfer the ether layer to a small separatory funnel and remove volatile phenols from it, adding 10 ml of a 1.5% potassium hydroxide solution, and strongly; shake up. All obtained alkaline solution is used to obtain azo dyes. To do this, it is introduced into a small separatory funnel, 1 ml of diluted (1: 4) sulfuric acid, 10 ml of 2 N are added. sodium carbonate solution and 1.5 ml of diazotized ga-nitroaniline solution. After the formation of a mixture of dyes, they are extracted with 10 ml of diluted (1: 4) sulfuric acid and 5 ml of ether, shaking vigorously. [...]

Carbonate ions are formed in natural waters from HCO ions when part of the equilibrium CO2 is lost or when the alkaline reaction of the medium is strengthened. Their content in fresh waters in the presence of Ca2 + ions is, as a rule, small due to the low solubility of CaCO3 (see Section 2.4.4). Usually a significant part of natural waters is in a state of saturation with calcium carbonate, which is of great geochemical importance and is essential for water treatment technology. In sea waters, at a salt concentration of 35 g / kg and Ca2 + - 0.0104 mol / kg, the content of COz ions reaches 6 mg / kg due to an increase in the interionic interaction and, consequently, with a decrease in the ion activity coefficients (see 2.14.4 ) In natural soda lakes, where the content of Ca2 + is low, the total concentration of [NSO] and (СО§] can reach up to 250 mg equiv / l. [...]

Of inorganic compounds, most salts of acids and bases are soluble in water. Solutions of these substances are electrolytes. Hydrocarbonates are found in the largest quantities in natural waters; chlorides and sulfates of alkaline earth and alkali metals; to a lesser extent, nitrates, nitrites, silicates, fluorides, phosphates and salts of other acids. [...]

By evaporation of natural or artificial brines, as well as aqueous solutions of salt on salt towers, “boiled salt” (table salt) is obtained. In this case, foreign salts accompanying the starting material remain in the mother liquor, part of which is used in a circular process to dissolve subsequent quantities of rock salt. Upon reaching a high concentration of side salts, the mother liquor should be discharged and replaced with fresh water. The mother liquor is the only component that generates wastewater from salt mines and cooling towers. They usually contain a lot of sulfate and chloride salts, alkali and alkaline earth metals. Sometimes brines and mother liquors are used for therapeutic baths, as a result of which there is a discharge of saline, hygienically unclean wastewater. [...]

The same main groups of waste water are formed during the production of ammonia from natural gas. Cooling water is not contaminated; Contaminated water is formed during gas compression, copper-ammonia and alkaline gas purification and regeneration of a copper-ammonia solution, during monoethanolamine purification, liquefaction of ammonia, and purging of boilers when burning CO-fraction. [...]

Adsorption methods for extracting water-soluble organic substances from natural waters are based on the use of activated carbon (AC). When treating AC water in static or dynamic conditions, the color of the water decreases, odors and flavors are eliminated. Activated carbon has a highly developed surface due to the presence of thin channels and pores. It is a good sorbent for phenols, alcohols, surfactants, and waste products of aquatic organisms. The sorption capacity of AC increases with increasing molecular weight of the adsorbed organic matter. The sorption capacity of AC in an alkaline medium decreases. Typically, for deodorizing water, the dose of coal is 10-15 mg / l with a contact time of 10-20 minutes with water. Since the concentration of organic substances in natural waters, causing a deterioration in organoleptic properties, are very small, the sorption capacity of AC in static conditions for these substances is insufficient. [...]

The calculation of the sodium content and the total alkali metal content from the difference in the sums of equivalents of anions and cations is based on the fact that in solution the sum of equivalents of anions. should be equal to the sum of the equivalents of cations. In natural waters, the main mass of anions consists of chlorion, as well as sulfate and bicarbonate ions (in some cases it is necessary to take into account the nitrate ion). The bulk of the cations consists of calcium, magnesium, sodium and potassium ions. [...]

Determination of anionic surfactants. Extraction-photometric methods based on the formation of ionic associations of the surface-active anion with cations of the main dyes are mainly used for the quantitative determination of surfactants in natural and waste waters. The definition of anionic surfactants in wastewater and natural waters with a fentiazine dye methylene blue is widespread. After extraction of the ionic associate with chloroform from an alkaline medium, the organic phase is washed with an acidic reagent solution (to remove low molecular weight impurities) and photometric at 670 nm. Due to the low degree of extraction of the ionic associate with chloroform (84%), the extraction is carried out several times. The determination is hindered by sulfide, polysulfide and thiosulfate ions, which destroy hydrogen peroxide, as well as large quantities of nonionic surfactants. Methylene blue forms an ionic associate extracted with chloroform with humic acids, the absorption maximum of which lies at 550 nm. The interfering effect of humic acids can be reduced by measuring with a high monochromatization spectrophotometer. The range of surfactant concentrations determined with methylene blue is 0.01-0.80 mg / ml with a sample volume of 250 ml; determination accuracy of 2%. [...]

Studies have shown that the absorption spectra of light with colored natural waters are identical to the absorption spectra observed by soil scientists for various humic substances (monotonically decreasing curves in the wavelength range 220–700 nm, Fig. 23a). The presence of such a continuous spectrum is characteristic of substances that are copolymers when several isolated chromophore systems arise during the formation of a macromolecule. The spectrum of these substances is formed by summing up the absorption of individual chromophore systems. It can be assumed that they are multinuclear aromatic groups, the phenolic nature of which is confirmed by an increase in the visible region of the color intensity of aqueous humates in an alkaline medium. Along with a change in the color of the Dnieper water as a result of acidification or alkalization, there is also a change in the spectral characteristic of the impurities staining it. This is due to an increase or suppression of the dissociation of functional groups of high molecular weight humic substances at different pH environments. Shevchenko gives data on a sharp jump in color in the pH range 3-5, which, apparently, is explained by the formation of undissociated humic acid molecules or their associates during acidification of water. [...]

Since hydrolysis of the coagulant leads to a decrease in pH, with a lack of natural alkalinity, lime or soda is added to the water, calculating their doses in accordance with the instructions. [...]

As a result of the studies performed by us in laboratory conditions, it turned out that when pure natural water was infected (chloride content 15-20 mg / l) with coli bacteria (50,000 bacteria per 1 ml), a dose of silver in the amount of 0.05 mg / l provided water suitable for drinking after 2-3 hours. At a dose of 0.2 mg / l, bacteria died after 1-2 hours, at a dose of 0.5 mg / l - after 30-60 minutes and at a dose of 1.0 mg / l - after 30 minutes Moreover, an increase in temperature and an increase in alkalinity strengthened the effect, and a decrease in these values \u200b\u200bweakened it. [...]

Generally speaking, in the above expression, the difference (Ek and Ia) should always be positive, since any natural water contains alkali metals. The latter, apparently, can be explained by the presence of unaccounted acids in the water, for example, humic, silicic, nitric, phosphoric, etc., therefore, the weight of all components that are of practical importance in this sum should be entered in the amount of mEq. [.. .]

The product of the equivalent weight of sodium in the sum of milligram equivalents of sodium and potassium obtained for the water under study will give the alkali metal content in it, expressed in milligrams of sodium. Such a recount is allowed because potassium in natural waters is usually found in quantities significantly less than sodium. In the above example, the sum of milligram equivalents of anions is 7.896, and the sum of milligram equivalents of calcium and magnesium is 1.752 - - 3.923 \u003d 5.675. [...]

Based on these reactions, it can be assumed that 1.0 mg / l of alum with a molecular weight of 600 reacts with 0.50 mg / l of substances that determine the natural alkalinity, calculated as CaCO3, with 0.39 mg / l of E5% slaked lime Ca (OH) 2 or with 0.33 mg / L of 18% quicklime CaO and with 0.53 mg / L of calcined Na2CO3 soda. When lime or soda ash reacts with aluminum sulfate, the natural alkalinity of the water does not change. Sulfate ions, introduced with alum, remain in the treated water. The interaction of substances that cause natural alkalinity, and soda ash emits carbon dioxide. The dosage of alum used in water treatment ranges from 5 to 50 mg / l, and higher concentrations are required to clarify cloudy surface waters. Coagulation using alum is usually effective at pH ranging from 5.5 to 8.0. [...]

It is necessary to distinguish between the concepts of carbonate and disposable stiffness. Upon the transition of НСООГ into СОЗ and upon the precipitation of calcium and magnesium carbonates in water, a certain amount of Ca2 +, М 2+, ООз ions remains, corresponding to the solubility product of calcium carbonate and basic magnesium carbonate. In the presence of foreign ions, the solubility of these compounds increases. The difference between carbonate and disposable hardness due to calcium and magnesium carbonates characterizes the value of residual hardness. In some natural waters, the ratio of HCO3\u003e Ca2 + -A / 2+ is observed, i.e., the total alkalinity exceeds the sum of the concentrations of Ca2 + and g2 + ions. For such waters, the total hardness is conventionally taken as carbonate, and the non-carbonate value is not calculated. [...]

The technical capabilities of conductometers, which form the basis of the first coagulant dosing systems, are such that they could be used in low-mineralized natural waters with a content of not more than 100 mg / l of dissolved salts and with an alkalinity of not more than 1.5 mEq / l. Their use was limited by the minimum dose of coagulant. For example, on the water of the river. Moscow, which is one of low and medium mineralized (200 - 400 mg / l), dispensers Cheyshvili - Krymsky could not be used. [...]

The hydrogen index is expressed by pH, which is the decimal logarithm of the concentration of hydrogen ions, taken with the opposite sign; The pH is determined in the range from 1 to 14. In most natural waters, the pH is in the range of 6.5 to 8.5 and depends on the ratio of the concentrations of free carbon dioxide and bicarbonate ion. Lower pH values \u200b\u200bcan be observed in acidic swamp waters. In summer, during intense photosynthesis, the pH can increase to 9.0. The pH value is affected by the content of carbonates, hydroxides, hydrolyzed salts, humic substances, etc. This indicator is an indicator of pollution of open water bodies when acidic or alkaline wastewater is released into them. [...]

If the concentration of metals is too low, then resort to enrichment of the sample. Typically, complexing agents are added to the solution and the complexes of the elements to be determined are extracted with solvents that are not miscible with water, "es": ["AIoJSA3Yrks"], "pt": ["Op7tt597C0o", "YdZdIdmBXyI", "Op7tt597C0o"], "cs": [ "V-e46dCtbzc"], "pl": ["TqQpMqKwGBk"], "lt": ["- mxQe9MsaIE"])