Definition of transparency. Main indicators of water quality Odors of natural origin

The transparency of water depends on the amount of mechanical suspended substances and chemical impurities it contains. Turbid water is always suspicious from an epizootic and sanitary point of view. There are several methods for determining water transparency.

Comparison method. The test water is poured into one colorless glass cylinder, and distilled water into the other. Water can be rated as clear, slightly clear, slightly opalescent, opalescent, slightly turbid, turbid and very turbid.

Disk method. To determine the transparency of water directly in a reservoir, a white enamel disk is used - a Secchi disk (Fig. 2). When a disc is immersed in water, the depth at which it ceases to be visible and at which it becomes visible again when removed is noted. The average of these two values ​​shows the transparency of the water in the reservoir. In clear water the disk remains visible at a depth of several meters; in very turbid water it disappears at a depth of 25-30 cm.

Type Method (Snellen). More accurate results are achieved when using a glass calorimeter with a flat bottom (Fig. 3). The calorimeter is installed at a height of 4 cm from standard font No. 1:

After shaking, the water to be tested is poured into the cylinder. Then they look down through the column of water at the font, gradually releasing water from the calorimeter tap until it is possible to clearly see font No. 1. The height of the liquid in the cylinder, expressed in centimeters, is a measure of transparency. Water is considered transparent if the font is clearly visible through a column of water of 30 cm. Water with a transparency of 20 to 30 cm is considered slightly turbid, from 10 to 20 cm - cloudy, up to 10 cm is unsuitable for drinking purposes. good clear water does not leave sediment after standing.

Ring method. Water transparency can be determined using a ring (Fig. 3). To do this, use a wire ring with a diameter of 1-1.5 cm and a wire cross-section of 1 mm. Holding it by the handle, the wire ring is lowered into a cylinder with the water being tested until its contours become invisible. Then use a ruler to measure the depth (cm) at which the ring becomes clearly visible when removed. An indicator of acceptable transparency is considered to be 40 cm. The obtained data “by ring” can be converted into readings “by font” (Table 1).

Table 1

Converting water transparency values ​​“by ring” to values ​​“by font”

Transparency of water according to the Secchi disk, according to the cross, according to the font. Turbidity of water. The smell of water. Color of water.

Water clarity

There are suspended substances in water that reduce its transparency. There are several methods for determining water transparency.

1. According to the Secchi disk. To measure transparency river water, use a Secchi disk with a diameter of 30 cm, which is lowered on a rope into the water, attaching a weight to it so that the disk goes vertically down. Instead of a Secchi disk, you can use a plate, lid, or bowl placed in a mesh. The disc is lowered until it is visible. The depth to which you lowered the disk will be an indicator of the transparency of the water.
2. By the cross. Find the maximum height of the water column through which a pattern of a black cross on a white background with a line thickness of 1 mm and four black circles with a diameter of 1 mm can be seen. The height of the cylinder in which the determination is carried out must be at least 350 cm. At the bottom there is a porcelain plate with a cross. The bottom of the cylinder should be illuminated by a 300 W lamp.
3. By font. A standard font is placed under a cylinder 60 cm high and 3-3.5 cm in diameter at a distance of 4 cm from the bottom, the test sample is poured into the cylinder so that the font can be read, and the maximum height of the water column is determined. The method for quantifying transparency is based on determining the height of the water column at which it is still possible to visually distinguish (read) black type with a height of 3.5 mm and a line width of 0.35 mm on a white background or see an adjustment mark (for example, a black cross on white paper) . The method used is standardized and complies with ISO 7027.

Water turbidity

Water has increased turbidity due to the content of coarse inorganic and organic impurities in it. The turbidity of water is determined by the gravimetric method and a photoelectric colorimeter. The weight method is that 500-1000 ml muddy water filtered through a dense filter with a diameter of 9-11 cm. The filter is pre-dried and weighed on an analytical balance. After filtering, the filter with the sediment is dried at a temperature of 105-110 degrees for 1.5-2 hours, cooled and weighed again. Based on the difference in filter masses before and after filtration, the amount of suspended substances in the test water is calculated.

In Russia, water turbidity is determined photometrically by comparing samples of the water being tested with standard suspensions. The measurement result is expressed in mg/dm 3 using the basic standard kaolin suspension (turbidity for kaolin) or in TU/dm 3 (turbidity units per dm 3) when using a basic standard formazin suspension. The last unit of measurement is also called Turbidity Unit according to Formazin(EMF) or in Western terminology FTU (formazine Turbidity Unit). 1FTU=1EMF=1EM/dm 3.

IN Lately The photometric method for measuring turbidity using formazin has become the main method throughout the world, which is reflected in the ISO 7027 standard (Water quality - Determination of turbidity). According to this standard, the unit of measurement for turbidity is FNU (formazine Nephelometric Unit). Security Agency Environment USA (U.S. EPA) and World Organization The World Health Organization (WHO) uses the turbidity unit NTU (Nephelometric Turbidity Unit).

The relationship between the basic units of turbidity is as follows:

1 FTU=1 FNU=1 NTU

WHO does not standardize turbidity based on health effects, but from the point of view appearance recommends that turbidity be no higher than 5 NTU (nephelometric turbidity unit) and, for disinfection purposes, no more than 1 NTU.

Determining the smell of water

Odors in water may be associated with vital activity aquatic organisms or appear when they die - these are natural odors. The smell of water in a reservoir can also be caused by sewage and industrial wastes entering it - these are artificial odors. First, a qualitative assessment of the smell is given according to the relevant criteria:

• swamp,
• earthy,
• fish,
• putrefactive,
• aromatic,
• oil, etc.

The strength of the smell is assessed on a 5-point scale. The flask with a ground-in stopper is filled 2/3 with water and immediately closed, shaken vigorously, opened and immediately noted the intensity and character of the odor.

Determination of water color

A qualitative assessment of color is made by comparing the sample with distilled water. To do this, separate test and distilled water is poured into colorless glass glasses, examined from above and from the side against the background of a white sheet in daylight, the color is assessed as the observed color; in the absence of color, the water is considered colorless.

The main pollutants present in wastewater urban wastewater treatment plants, grouped into groups and presented in diagram 1

Organic substances in wastewater in their physical state can be in undissolved, colloidal and dissolved states, depending on the size of their constituent particles (Table 1). As the particle size of pollutants changes, they are consistently removed at all stages of biological treatment (Scheme 2).

Table 1 Composition of organic substances in untreated wastewater by particle size

Scheme 1

Water clarity

The transparency of wastewater is due to the presence of undissolved and colloidal impurities in it. A measure of transparency is the height of a column of water at which a font of a certain size and type can be read through it. Municipal wastewater entering for treatment has a transparency of 1-5 cm. The treatment effect is most quickly and simply assessed by the transparency of the treated water, which depends on the quality of treatment, as well as on the presence in the water of small activated sludge flakes that do not settle in two hours and dispersed bacteria. The grinding of sludge flakes can be a consequence of the disintegration of larger, older flakes, the result of their rupture by gases, or under the influence of toxic wastewater. Small flakes can stick together again, but, having reached a certain small size, they do not enlarge further. Transparency is the most efficient, responsive to violations, indicator of the quality of cleaning. Any, even minor, unfavorable changes in the composition of wastewater and in the technological mode of its treatment lead to the dispersion of sludge flakes, disruption of flocculation, and, consequently, to a decrease in the transparency of purified water.

Biological wastewater treatment must provide at least 12 cm of purified water transparency. With complete, satisfactory biological treatment, transparency is 30 centimeters or more, and with such transparency, all other sanitary indicators of contamination, as a rule, correspond to a high degree of purification.

Transparency is determined in shaken (characterizes the presence of suspended and colloidal substances) and settled (presence of colloidal substances) samples. Transparency in a settled sample characterizes the operation of aeration tanks, transparency in a shaken sample characterizes the operation of secondary settling tanks.

Examples. If the transparency of purified water in a shaken sample is 19 cm, and in a settled sample it is 28 cm, we can conclude that the aeration tanks are operating satisfactorily (colloidal substances are well removed) and secondary settling tanks (we can expect that the removal of suspended substances in purified water will not exceed 15 mg/dm3 ),

Scheme 2 Sequential removal of organic particles (depending on their size) at different stages of wastewater treatment

If, according to the test results, the transparency in the shaken sample is 10 cm, and in the settled sample 30 cm, this means that colloidal substances are well removed from wastewater in aeration tanks, but secondary settling tanks work unsatisfactorily and provide low transparency of purified water.

A change in the transparency of the silt water can serve as a prompt signal of changes in the purification process even when other methods of physical and chemical control do not yet detect deviations, since all violations are accompanied by grinding of activated sludge flakes, which is immediately recorded by the reduced transparency of the silt water.

Water clarity

Transparency- a value indirectly indicating the amount of suspended particles and other pollutants in ocean water. It is determined by the depth of disappearance of a flat white disk with a diameter of 30 cm. The transparency of water is determined by its selective ability to absorb and scatter light rays and depends on the surface lighting conditions, changes in the spectral composition and attenuation of the light flux. With high transparency, water acquires intense Blue colour, which is typical for open ocean. In the presence of a significant amount of suspended particles that strongly scatter light, the water has a blue-green or green color, characteristic of coastal areas and some closed seas. At the confluence large rivers, carrying a large number of suspended particles, the color of the water takes on yellow and brown shades. The maximum value of relative transparency (66 m) was noted in the Sargasso Sea (Atlantic Ocean); in the Indian Ocean it is 40-50 m, in the Pacific Ocean 59 m. In general, in the open part of the ocean transparency decreases from the equator to the poles, but in the polar regions it can also be significant.

Water clarity- an indicator characterizing the ability of water to transmit light. In laboratory conditions, transparency is taken to be the thickness of the water layer through which a standard font is visible.

In natural reservoirs, a Secchi disk is used to assess transparency. This is a white metal disk with a diameter of 30 cm. It is lowered to such a depth that it completely disappears from view, this depth is considered transparency. This method of measurement was first used in the US Navy in 2017. Currently there are also a number electronic devices for measuring water clarity.

Transparency is usually determined by the turbidity of the water and its color.

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See what “Water transparency” is in other dictionaries:

WATER TRANSPARENCY- the ability of water to transmit light. Usually measured by a Secchi disk. Depends mainly on the concentration of suspended and dissolved organic and inorganic substances in water. May decline sharply as a result of anthropogenic pollution and... ... Ecological dictionary

Turbidity is an indicator of water quality caused by the presence in water of undissolved and colloidal substances of inorganic and organic origin. Turbidity in surface waters is caused by silt, silicic acid, iron and aluminum hydroxides, organic colloids, microorganisms and plankton. In groundwater, turbidity is caused primarily by the presence of undissolved minerals, and when wastewater penetrates into the ground, it is also caused by the presence of organic substances. In Russia, turbidity is determined photometrically by comparing samples of the test water with standard suspensions. The measurement result is expressed in mg/dm3 when using a basic standard suspension of kaolin or in TU/dm3 (turbidity units per dm3) when using a basic standard suspension of formazin. The last unit of measurement is also called Formazine Turbidity Unit (FTU) or in Western terminology FTU (Formazine Turbidity Unit). 1FTU=1EMF=1EM/dm3. Recently, the photometric method for measuring turbidity using formazin has become established as the main method throughout the world, which is reflected in the ISO 7027 standard (Water quality - Determination of turbidity). According to this standard, the unit of measurement for turbidity is FNU (Formazine Nephelometric Unit). The U.S. Environmental Protection Agency (U.S. EPA) and the World Health Organization (WHO) use the Nephelometric Turbidity Unit (NTU). The relationship between the basic units of turbidity is as follows: 1 FTU=1 FNU=1 NTU.

WHO does not standardize turbidity based on health effects, but from an appearance point of view it recommends that turbidity should not exceed 5 NTU (nephelometric turbidity unit), and for disinfection purposes - no more than 1 NTU.

A measure of transparency is the height of the water column at which one can observe a white plate of a certain size lowered into water (Secchi disk) or distinguish a font of a certain size and type on white paper (Snellen font). Results are expressed in centimeters.

Characteristics of water by transparency (turbidity)

Chroma

Color is an indicator of water quality, mainly due to the presence of humic and sulfic acids, as well as iron compounds (Fe3+) in water. The amount of these substances depends on the geological conditions in the aquifers and on the number and size of peatlands in the basin of the river under study. Thus, the surface waters of rivers and lakes located in areas of peat bogs and swampy forests have the highest color, and the lowest color in steppes and steppe zones. In winter, the content of organic matter in natural waters minimal, while in the spring during the period of high water and floods, as well as in the summer during the period of mass development of algae - water blooms - it increases. Groundwater, as a rule, has less color than surface water. Thus, high color is an alarming sign indicating trouble in the water. In this case, it is very important to find out the cause of the color, since the methods for removing, for example, iron and organic compounds are different. The presence of organic matter not only worsens the organoleptic properties of water and leads to the appearance of foreign odors, but also causes a sharp decrease in the concentration of oxygen dissolved in water, which can be critical for a number of water treatment processes. Some, in principle, harmless organic compounds, entering into chemical reactions(for example, with chlorine) are capable of forming compounds that are very harmful and dangerous to human health.

Color is measured in degrees on the platinum-cobalt scale and ranges from units to thousands of degrees - Table 2.

Characteristics of waters by color

Taste and smack

The taste of water is determined by substances of organic and inorganic origin dissolved in it and varies in character and intensity. There are four main types of taste: salty, sour, sweet, bitter. All other types of taste sensations are called tastes (alkaline, metallic, astringent, etc.). The intensity of taste and aftertaste is determined at 20 °C and assessed using a five-point system, according to GOST 3351-74*.

The qualitative characteristics of shades of taste sensations - taste - are expressed descriptively: chlorine, fishy, ​​bitter, and so on. The most common salty taste of water is most often caused by sodium chloride dissolved in water, bitter by magnesium sulfate, sour by excess free carbon dioxide, etc. The threshold of taste perception of salty solutions is characterized by the following concentrations (in distilled water), mg/l: NaCl – 165; CaCl2 – 470; MgCl2 – 135; MnCl2 – 1.8; FeCl2 – 0.35; MgSO4 – 250; CaSO4 – 70; MnSO4 – 15.7; FeSO4 – 1.6; NaHCO3 – 450.

According to the strength of their effect on the taste organs, ions of some metals are arranged in the following rows:

O cations: NH4+ > Na+ > K+; Fe2+ ​​> Mn2+ > Mg2+ > Ca2+;

O anions: OH->NO3->Cl->HCO3->SO42-.

Characteristics of waters by taste intensity

Intensity of taste and aftertaste	The nature of the appearance of taste and aftertaste	Intensity rating, point
	Taste and aftertaste are not felt
Very weak	Taste and aftertaste are not perceived by the consumer, but are detected during laboratory testing.
	Taste and aftertaste are noticed by the consumer if they pay attention to it
Noticeable	Taste and aftertaste are easily noticed and cause disapproval of water
Distinct	Taste and aftertaste attract attention and make you refrain from drinking
Very strong	The taste and aftertaste are so strong that they make the water unfit for consumption.

Smell

Odor is an indicator of water quality, determined by the organoleptic method using the sense of smell based on the odor strength scale. The smell of water is influenced by the composition of dissolved substances, temperature, pH values ​​and a number of other factors. The intensity of the odor of water is determined by experts at 20 ° C and 60 ° C and measured in points, according to the requirements.

The odor group should also be indicated according to the following classification:

By nature, odors are divided into two groups:

• natural origin(organisms living and dying in water, decaying plant debris, etc.)
• artificial origin (impurities of industrial and agricultural wastewater).

Odors of the second group (artificial origin) are named by the substances that determine the odor: chlorine, gasoline, etc.

Natural scents

Odor designation	Character of the smell	Approximate type of smell
	Aromatic	Cucumber, floral
	Bolotny	Muddy, muddy
	Putrefactive	Fecal, waste
	Woody	The smell of wet wood chips, woody bark
	Earthy	Rotten, smell of freshly plowed earth, clayey
	moldy	Musty, stagnant
		Fish oil smell, fishy
	Hydrogen sulfide	Rotten egg smell
	Grassy	The smell of cut grass and hay
	Uncertain	Odors of natural origin that do not fall under the previous definitions

The intensity of the odor according to GOST 3351-74* is assessed on a six-point scale - see the next page.

Characteristics of water by odor intensity

Odor intensity	Character of the odor	Intensity rating, point
	The smell is not felt
Very weak	The smell is not perceived by the consumer, but is detected during laboratory testing
	The smell is noticed by the consumer if you draw his attention to it
Noticeable	The smell is easily noticed and causes disapproval of the water
Distinct	The smell attracts attention and makes you refrain from drinking
Very strong	The smell is so strong that it makes the water unfit for consumption.

Hydrogen value (pH)

Hydrogen index (pH) - characterizes the concentration of free hydrogen ions in water and expresses the degree of acidity or alkalinity of water (the ratio of H+ and OH- ions in water formed during the dissociation of water) and is quantitatively determined by the concentration of hydrogen ions pH = - Ig

If the water has a reduced content of free hydrogen ions (pH>7) compared to OH- ions, then the water will have an alkaline reaction, and with an increased content of H+ ions (pH<7)- кислую. В идеально чистой дистиллированной воде эти ионы будут уравновешивать друг друга. В таких случаях вода нейтральна и рН=7. При растворении в воде различных химических веществ этот баланс может быть нарушен, что приводит к изменению уровня рН.

Determination of pH is carried out using a colorimetric or electrometric method. Water with a low pH reaction is corrosive, while water with a high pH reaction tends to foam.

Depending on the pH level, water can be divided into several groups:

Characteristics of water by pH

Control over the pH level is especially important at all stages of water treatment, since its “change” in one direction or another can not only significantly affect the smell, taste and appearance of water, but also affect the effectiveness of water treatment measures. The optimal pH value required varies for different water treatment systems according to the composition of the water, the nature of the materials used in the distribution system, and depending on the water treatment methods used.

Typically, the pH level is within the range at which it does not directly affect the consumer quality of water. Thus, in river waters the pH is usually in the range of 6.5-8.5, in precipitation 4.6-6.1, in swamps 5.5-6.0, in sea waters 7.9-8.3. Therefore, WHO does not propose any medically recommended value for pH. At the same time, it is known that at low pH water is highly corrosive, and at high levels (pH>11) water acquires characteristic soapiness, bad smell, may cause irritation to eyes and skin. That is why the optimal pH level for drinking and domestic water is considered to be in the range from 6 to 9.

Acidity

Acidity is the content of substances in water that can react with hydroxide ions (OH-). The acidity of water is determined by the equivalent amount of hydroxide required for the reaction.

In ordinary natural waters, acidity in most cases depends only on the content of free carbon dioxide. The natural part of acidity is also created by humic and other weak organic acids and cations of weak bases (ammonium ions, iron, aluminum, organic bases). In these cases, the water pH does not fall below 4.5.

Polluted water bodies may contain large amounts of strong acids or their salts due to the discharge of industrial wastewater. In these cases the pH may be below 4.5. Part of the total acidity that reduces pH to values< 4.5, называется свободной.

Rigidity

General (total) hardness is a property caused by the presence of substances dissolved in water, mainly calcium salts (Ca2+) and magnesium (Mg2+), as well as other cations that appear in much smaller quantities, such as ions: iron, aluminum, manganese (Mn2+) and heavy metals (strontium Sr2+, barium Ba2+).

But general content in natural waters, calcium and magnesium ions are incomparably greater than the content of all other listed ions - and even their sum. Therefore, hardness is understood as the sum of the amounts of calcium and magnesium ions - the total hardness, which consists of the values ​​of carbonate (temporary, eliminated by boiling) and non-carbonate (permanent) hardness. The first is caused by the presence of calcium and magnesium bicarbonates in water, the second by the presence of sulfates, chlorides, silicates, nitrates and phosphates of these metals.

In Russia, water hardness is expressed in mEq/dm3 or mol/l.

Carbonate hardness (temporary) – caused by the presence of calcium and magnesium bicarbonates, carbonates and hydrocarbons dissolved in water. During heating, calcium and magnesium bicarbonates partially precipitate in solution as a result of reversible hydrolysis reactions.

Non-carbonate hardness (constant) - caused by the presence of calcium chlorides, sulfates and silicates dissolved in water (they do not dissolve and do not settle in the solution when the water is heated).

Characteristics of water by value overall hardness

Water group	Unit of measurement, mmol/l
Very soft
Medium hardness
Very tough

Alkalinity

Water alkalinity is the total concentration of weak acid anions and hydroxyl ions contained in water (expressed in mmol/l), which react during laboratory tests with hydrochloric or sulfuric acids to form chloride or sulfuric acid salts of alkali and alkaline earth metals.

The following forms of water alkalinity are distinguished: bicarbonate (hydrocarbonate), carbonate, hydrate, phosphate, silicate, humate - depending on the anions of weak acids that determine the alkalinity. Alkalinity of natural waters, the pH of which is usually< 8,35, зависит от присутствия в воде бикарбонатов, карбонатов, иногда и гуматов. Щелочность других форм появляется в процессах обработки воды. Так как в природных водах почти всегда щелочность определяется бикарбонатами, то для таких вод общую щелочность принимают равной карбонатной жесткости.

Iron, manganese

Iron, manganese - in natural water appear mainly in the form of hydrocarbons, sulfates, chlorides, humus compounds and sometimes phosphates. The presence of iron and manganese ions is very harmful to most technological processes, especially in the pulp and textile industries, and also worsens the organoleptic properties of water.

In addition, the content of iron and manganese in water can cause the development of manganese bacteria and iron bacteria, colonies of which can cause clogging of water supply networks.

Chlorides

Chlorides – The presence of chlorides in water can be caused by the leaching of chloride deposits, or they can appear in the water due to the presence of effluent. Most often, chlorides in surface waters act in the form of NaCl, CaCl2 and MgCl2, and always in the form of dissolved compounds.

Nitrogen compounds

Nitrogen compounds (ammonia, nitrites, nitrates) arise mainly from protein compounds that enter the water along with wastewater. Ammonia present in water can be organic or inorganic. In the case of organic origin, increased oxidation is observed.

Nitrites arise mainly due to the oxidation of ammonia in water; they can also penetrate into it along with rainwater due to the reduction of nitrates in the soil.

Nitrates are a product of the biochemical oxidation of ammonia and nitrites, or they can be leached from the soil.

Hydrogen sulfide

O at pH< 5 имеет вид H2S;

O at pH > 7 appears as the HS- ion;

O at pH = 5:7 can be in the form of both H2S and HS-.

Water. They enter the water due to the leaching of sediment rocks, soil leaching and sometimes due to the oxidation of sulfides and sulfur - protein breakdown products from wastewater. A high content of sulfates in water can cause diseases of the digestive tract, and such water can also cause corrosion of concrete and reinforced concrete structures.

Carbon dioxide

Hydrogen sulfide gives water an unpleasant odor, leads to the development of sulfur bacteria and causes corrosion. Hydrogen sulfide, mainly present in groundwater ah, can be of mineral, organic or biological origin, and in the form of dissolved gas or sulfides. The form under which hydrogen sulfide appears depends on the pH reaction:

• at pH< 5 имеет вид H2S;
• at pH > 7 it appears as an HS- ion;
• at pH = 5: 7 can be in the form of both H2S and HS-.

Sulfates

Sulfates (SO42-) – along with chlorides, are the most common types of contaminants in water. They enter the water due to the leaching of sedimentary rocks, leaching of soil and sometimes due to the oxidation of sulfides and sulfur - protein breakdown products from wastewater. A high content of sulfates in water can cause diseases of the digestive tract, and such water can also cause corrosion of concrete and reinforced concrete structures.

Carbon dioxide

Carbon dioxide (CO2) – depending on the reaction, the pH of water can be in the following forms:

• pH< 4,0 – в основном, как газ CO2;
• pH = 8.4 – mainly in the form of bicarbonate ion HCO3-;
• pH > 10.5 – mainly in the form of carbonate ion CO32-.

Corrosive carbon dioxide is the portion of free carbon dioxide (CO2) that is needed to keep hydrocarbons dissolved in water from decomposing. It is very active and causes corrosion of metals. In addition, it leads to the dissolution of calcium carbonate CaCO3 in mortars or concrete and therefore must be removed from water intended for construction purposes. When assessing the aggressiveness of water, along with the aggressive concentration of carbon dioxide, the salt content of the water (salinity) should also be taken into account. Water with the same content of aggressive CO2 is more aggressive, the higher its salinity.

Dissolved oxygen

Oxygen enters a body of water by dissolving it upon contact with air (absorption), as well as as a result of photosynthesis aquatic plants. The content of dissolved oxygen depends on temperature, atmospheric pressure, the degree of water turbulization, water salinity, etc. In surface waters, the content of dissolved oxygen can range from 0 to 14 mg/l. There is practically no oxygen in artesian water.

The relative content of oxygen in water, expressed as a percentage of its normal content, is called the degree of oxygen saturation. This parameter depends on water temperature, atmospheric pressure and salinity level. Calculated using the formula: M = (ax0.1308x100)/NxP, where

M – degree of water saturation with oxygen, %;

A – oxygen concentration, mg/dm3;

R - Atmosphere pressure in a given area, MPa.

N is the normal oxygen concentration at a given temperature and total pressure of 0.101308 MPa, given in the following table:

Oxygen solubility depending on water temperature

Water temperature, °C

Oxidability

Oxidability is an indicator characterizing the content of organic and mineral substances in water that are oxidized by a strong oxidizing agent. Oxidability is expressed in mgO2 required for the oxidation of these substances contained in 1 dm3 of the tested water.

There are several types of water oxidation: permanganate (1 mg KMnO4 corresponds to 0.25 mg O2), dichromate, iodate, cerium. The highest degree of oxidation is achieved by dichromate and iodate methods. In water treatment practice, permanganate oxidation is determined for natural, slightly polluted waters, and in more polluted waters, as a rule, dichromate oxidation (also called COD - chemical oxygen demand). Oxidability is a very convenient complex parameter that allows one to assess the overall contamination of water with organic substances. Organic substances found in water are very diverse in nature and chemical properties. Their composition is formed both under the influence of biochemical processes occurring in the reservoir, and due to the influx of surface and groundwater, atmospheric precipitation, industrial and domestic wastewater. The amount of oxidizability of natural waters can vary widely from fractions of milligrams to tens of milligrams of O2 per liter of water.

Surface waters have a higher oxidizability, which means they contain high concentrations of organic substances compared to underground waters. So, mountain rivers and lakes are characterized by oxidability of 2-3 mg O2/dm3, lowland rivers – 5-12 mg O2/dm3, rivers fed by swamps – tens of milligrams per 1 dm3.

Groundwater has an average oxidizability at a level of from hundredths to tenths of a milligram of O2/dm3 (exceptions include water in areas of oil and gas fields, peat bogs, heavily swampy areas, and groundwater in the northern part of the Russian Federation).

Electrical conductivity

Electrical conductivity is a numerical expression of the ability of an aqueous solution to conduct electricity. The electrical conductivity of natural water depends mainly on the degree of mineralization (concentration of dissolved mineral salts) and temperature. Thanks to this dependence, the value of electrical conductivity can be used to judge the mineralization of water with a certain degree of error. This measurement principle is used, in particular, in fairly common instruments for operational measurement of total salt content (so-called TDS meters).

The fact is that natural waters are solutions of mixtures of strong and weak electrolytes. The mineral part of the water consists mainly of sodium (Na+), potassium (K+), calcium (Ca2+), chlorine (Cl–), sulfate (SO42–), and hydrogen carbonate (HCO3–) ions.

These ions mainly determine the electrical conductivity of natural waters. The presence of other ions, for example, ferric and divalent iron (Fe3+ and Fe2+), manganese (Mn2+), aluminum (Al3+), nitrate (NO3–), HPO4–, H2PO4–, etc. does not have such a strong effect on electrical conductivity (provided, of course, that these ions are not contained in the water in significant quantities, as, for example, this can be in industrial or domestic wastewater). Measurement errors arise due to the unequal specific electrical conductivity of solutions of various salts, as well as due to an increase in electrical conductivity with increasing temperature. However, the modern level of technology makes it possible to minimize these errors, thanks to pre-calculated and stored dependencies.

Electrical conductivity is not standardized, but a value of 2000 µS/cm approximately corresponds to a total mineralization of 1000 mg/l.

Redox potential (redox potential, Eh)

The oxidation-reduction potential (a measure of chemical activity) Eh, together with pH, ​​temperature and salt content in water, characterizes the state of stability of water. In particular, this potential must be taken into account when determining the stability of iron in water. Eh in natural waters varies mainly from -0.5 to +0.7 V, but in some deep zones Earth's crust can reach values ​​of minus 0.6 V (hydrogen sulfide hot waters) and +1.2 V (superheated waters of modern volcanism).

Groundwater is classified:

• Eh > +(0.1–1.15) V – oxidizing environment; water contains dissolved oxygen, Fe3+, Cu2+, Pb2+, Mo2+, etc.
• Eh – 0.0 to +0.1 V – transitional redox environment, characterized by an unstable geochemical regime and variable content of oxygen and hydrogen sulfide, as well as weak oxidation and weak reduction of various metals;
• Eh< 0,0 – восстановительная среда; в воде присутствуют сероводород и металлы Fe2+, Mn2+, Mo2+ и др.

Knowing the pH and Eh values, using the Pourbaix diagram it is possible to establish the conditions for the existence of compounds and elements Fe2+, Fe3+, Fe(OH)2, Fe(OH)3, FeCO3, FeS, (FeOH)2+.