Indirect indicators of microbial contamination of water supply networks. Water source pollution indicators. Pollution entering water bodies

Von + 2Vf = Vmo

)Vk = 2(Vmo - Vph)

5. Vph = Vmo. Both carbonates and bicarbonates are absent in the original sample, and acid consumption is due to the presence of strong alkalis containing hydroxo anions.
The presence of free hydroxo anions in appreciable amounts (cases 4 and 5) is possible only in wastewater.
The results of titration for phenolphthalein and methyl orange make it possible to calculate the alkalinity index of water, which is numerically equal to the number of acid equivalents used to titrate a 1 liter sample.
At the same time, acid consumption during titration by phenolphthalein characterizes free alkalinity, and by methyl orange - total alkalinity, which is measured in mg-eq / l. The alkalinity index is used in Russia, as a rule, in the study of wastewater. In some other countries (USA, Canada, Sweden, etc.), alkalinity is determined when assessing the quality of natural waters and is expressed as a mass concentration in CaCO3 equivalent.

It should be borne in mind that, when analyzing waste and polluted natural waters, the results obtained do not always correctly reflect the values ​​of free and total alkalinity, because in water, in addition to carbonates and hydrocarbonates, compounds of some other groups may be present (see "Alkalinity and acidity").

5.2. sulfates

Sulfates are common components of natural waters. Their presence in water is due to the dissolution of some minerals - natural sulfates (gypsum), as well as the transfer of sulfates contained in the air with rains. The latter are formed during oxidation reactions in an atmosphere of sulfur oxide (IV) to sulfur oxide (VI), the formation of sulfuric acid and its neutralization (complete or partial):

2SO2+O2=2SO3
SO3+H2O=H2SO4
The presence of sulfates in industrial wastewater is usually due to technological processes occurring with the use of sulfuric acid (production of mineral fertilizers, production of chemicals). Sulfates in drinking water do not have a toxic effect on humans, but worsen the taste of water: the taste sensation of sulfates occurs at their concentration of 250-400 mg/l. Sulfates can cause deposits in pipelines when two waters with different mineral compositions are mixed, such as sulfate and calcium (CaSO4 precipitates).

MPC of sulfates in the water of reservoirs for household and drinking purposes is 500 mg/l, the limiting indicator of harmfulness is organoleptic.

5.3. chlorides

Chlorides are present in almost all fresh surface and ground water ah, as well as in drinking water, in the form of metal salts. If sodium chloride is present in water, it has a salty taste already at concentrations above 250 mg/l; in the case of calcium and magnesium chlorides, water salinity occurs at concentrations above 1000 mg/l. It is by the organoleptic indicator - taste that the MPC for drinking water for chlorides (350 mg / l) was established, the limiting indicator of harmfulness is organoleptic.
Large quantities of chlorides can be formed in industrial processes of solution concentration, ion exchange, salting, etc., forming wastewater with a high chloride anion content.
High concentrations of chlorides in drinking water do not have toxic effects on humans, although saline waters are very corrosive to metals, adversely affect plant growth, and cause soil salinization.

6. Dry residue

The dry residue characterizes the content of non-volatile dissolved substances (mainly mineral) and organic substances in water, the boiling point of which exceeds 105-110 ° C.

The dry residue value can also be estimated by the calculation method. In this case, it is necessary to sum up the concentrations of mineral salts dissolved in water, as well as organic substances obtained as a result of analyzes (hydrocarbonate is summed up in an amount of 50%). For drinking and natural water, the dry residue is practically equal to the sum of the mass concentrations of anions (carbonate, bicarbonate, chloride, sulfate) and cations (calcium and magnesium, as well as those determined by the calculation method of sodium and potassium).

The value of dry residue for surface waters of reservoirs for household and domestic water use should not exceed 1000 mg/l (in some cases up to 1500 mg/l is allowed).

7. General hardness, calcium and magnesium

Water hardness is one of the most important properties that has great importance when using water. If there are metal ions in the water that form insoluble salts with soap fatty acids, then in such water it is difficult to form foam when washing clothes or washing hands, resulting in a feeling of hardness. Water hardness has a detrimental effect on pipelines when water is used in heating networks, leading to the formation of scale. For this reason, special “softening” chemicals have to be added to the water. Water hardness is due to the presence of soluble and slightly soluble mineral salts, mainly calcium (Ca2 + ") and magnesium (Mg2 +).

The value of water hardness can vary widely depending on the type of rocks and soils that make up the catchment basin, as well as on the season and weather conditions. The total hardness of water in lakes and rivers of the tundra, for example, is 0.1-0.2 mg-eq / l, and in the seas, oceans, groundwater reaches 80-100 mg-eq / l and even more (Dead Sea). In table. 11 shows the values ​​of the total water hardness of some rivers and reservoirs in Russia.

The values ​​of the total water hardness of some rivers and reservoirs in Russia

Of all salts related to hardness salts, bicarbonates, sulfates and chlorides are distinguished. The content of other soluble calcium and magnesium salts in natural waters is usually very low. The hardness attached to water by hydrocarbons is called hydrocarbonate, or temporary, because. Hydrocarbonates when boiling water (more precisely, at a temperature of more than 60 ° C) decompose with the formation of poorly soluble carbonates (Mg (HC03) 2 in natural waters is less common than Ca (HCO3) 2, since magnesite rocks are not common. Therefore in fresh waters, the so-called calcium hardness prevails):

CaHCO3>CaCO3v+H2O+CO2

IN natural conditions the above reaction is reversible, however, when underground (ground) waters, which have significant temporary hardness, come to the surface, the equilibrium shifts towards the formation of CO2, which is removed into the atmosphere. This process leads to the decomposition of bicarbonates and the precipitation of CaCO3 and MgCO3. In this way, varieties of carbonate rocks called calcareous tuffs are formed.
In the presence of dissolved in water carbon dioxide the reverse reaction takes place. This is how the dissolution, or washing out, of carbonate rocks occurs in natural conditions.

Hardness due to chlorides or sulfates is called constant, because. these salts are stable when heated and boiled in water.
Total water hardness, i.e. the total content of soluble salts of calcium and magnesium, is called "total hardness".

Due to the fact that hardness salts are salts of different cations having different molecular weights, the concentration of hardness salts, or water hardness, is measured in units of equivalent concentration - the number of g-eq / l or mg-eq / l. With a hardness of up to 4 mg-eq / l, water is considered soft; from 4 to 8 meq/l - medium hardness; from 8 to 12 meq/l - hard; more than 12 meq/l - very hard (there is also another classification of water according to degrees of hardness) /l), the limiting indicator of harmfulness is organoleptic.

The permissible value of the total hardness for drinking water and sources of centralized water supply is no more than 7 mg-eq / l (in some cases - up to 10 mg-eq / l), the limiting indicator of harmfulness is organoleptic.

8. Total salt content

To calculate the total salt content by the sum of the mass concentrations of the main anions in milligram equivalent form, their mass concentrations determined during the analysis and expressed in mg / l are multiplied by the coefficients indicated in Table. 12, after which they are summed up.

Concentration conversion factors

The concentration of the potassium cation in this calculation (for natural waters) is conventionally taken into account as the concentration of the sodium cation. The result obtained is rounded to whole numbers (mg/l)

9. Dissolved oxygen
Oxygen is always present in dissolved form in surface waters. The content of dissolved oxygen (DO) in water characterizes the oxygen regime of a reservoir and is of paramount importance for assessing the ecological and sanitary state of a reservoir. Oxygen must be contained in the water in sufficient quantities, providing conditions for the respiration of aquatic organisms. It is also necessary for self-purification of water bodies, since it participates in the processes of oxidation of organic and other impurities, and the decomposition of dead organisms. A decrease in the concentration of RK indicates a change in biological processes in the reservoir, pollution of the reservoir with biochemically intensively oxidized substances (primarily organic). Oxygen consumption is also determined by the chemical processes of oxidation of impurities contained in water, as well as by the respiration of aquatic organisms.
Oxygen enters the reservoir by dissolving it upon contact with air (absorption), as well as as a result of photosynthesis by aquatic plants, i.e. as a result of physicochemical and biochemical processes. Oxygen also enters water bodies with rain and snow water. Therefore, there are many reasons that cause an increase or decrease in the concentration of dissolved oxygen in water.
Oxygen dissolved in water is in the form of hydrated O2 molecules. The content of the RK depends on the temperature, atmospheric pressure, the degree of water turbulence, the amount of precipitation, the mineralization of water, etc. At each temperature value, there is an equilibrium concentration of oxygen, which can be determined from special reference tables compiled for normal atmospheric pressure. The degree of saturation of water with oxygen, corresponding to the equilibrium concentration, is assumed to be 100%. The solubility of oxygen increases with decreasing temperature and mineralization, and with increasing atmospheric pressure.
In surface waters, the content of dissolved oxygen can range from 0 to 14 mg/l and is subject to significant seasonal and daily fluctuations. Significant oxygen deficiency can occur in eutrophicated and heavily polluted water bodies. A decrease in the concentration of DO to 2 mg/l causes a massive death of fish and other aquatic organisms.

In the water of reservoirs in any period of the year until 12 noon, the concentration of RK should be at least 4 mg / l. MPC of oxygen dissolved in water for fishery reservoirs is set at 6 mg/l (for valuable fish species), or 4 mg/l (for other species).
Dissolved oxygen is a very unstable component of the chemical composition of waters. When determining it, sampling should be carried out with particular care: it is necessary to avoid contact of water with air until oxygen is fixed (binding it into an insoluble compound).
During the analysis of water, the concentration of RK is determined (in mg / l) and the degree of saturation of water with it (in%) in relation to the equilibrium content at a given temperature and atmospheric pressure.
The control of the oxygen content in water is an extremely important problem, in the solution of which practically all branches of the national economy are interested, including ferrous and non-ferrous metallurgy, the chemical industry, Agriculture, medicine, biology, fish and food industry, environmental services. The content of RK is determined both in uncontaminated natural waters and in wastewater after treatment. Wastewater treatment processes are always accompanied by the control of oxygen content. The definition of RK is part of the analysis while defining another the most important indicator water quality - biochemical oxygen demand (BOD).

10. Biochemical oxygen demand (BOD)
Organic substances are always present in the natural water of reservoirs. Their concentrations can sometimes be very low (for example, in spring and melt waters). Natural sources of organic substances are the decaying remains of organisms of plant and animal origin, both living in the water and falling into the reservoir from the foliage, through the air, from the shores, etc. In addition to natural, there are also man-made sources of organic substances: transport companies(petroleum products), pulp and paper and wood processing plants (lignins), meat processing plants (protein compounds), agricultural and fecal effluents, etc. Organic pollutants enter the reservoir in different ways, mainly with sewage and rain surface washouts from the soil.
Under natural conditions, organic substances in the water are destroyed by bacteria, undergoing aerobic biochemical oxidation with the formation of carbon dioxide. In this case, oxygen dissolved in water is consumed for oxidation. In water bodies with a high content of organic matter, most of the RA is consumed for biochemical oxidation, thus depriving other organisms of oxygen. At the same time, the number of organisms more resistant to a low content of RA increases, oxygen-loving species disappear and species tolerant of oxygen deficiency appear. Thus, in the process of biochemical oxidation of organic substances in water, the concentration of DO decreases, and this decrease is indirectly a measure of the content of organic substances in water. The corresponding indicator of water quality, which characterizes the total content of organic substances in water, is called biochemical oxygen demand (BOD).
The determination of BOD is based on measuring the concentration of RA in a water sample immediately after sampling, as well as after sample incubation. The sample is incubated without access to air in an oxygen flask (i.e., in the same vessel where the value of the RK is determined) for the time necessary for the biochemical oxidation reaction to proceed.
Since the rate of the biochemical reaction depends on temperature, incubation is carried out in a constant temperature mode (20 ± 1) °C, and the accuracy of the BOD analysis depends on the accuracy of maintaining the temperature value. Usually BOD is determined for 5 days of incubation (BOD5) (BOD10 for 10 days and BODtot for 20 days can also be determined (in this case, about 90 and 99% of organic substances are oxidized, respectively)), however, the content of some compounds is more informatively characterized by the value of BOD for 10 days or for the period of complete oxidation (BOD10 or BODtotal, respectively). An error in the determination of BOD can also be introduced by sample illumination, which affects the vital activity of microorganisms and can, in some cases, cause photochemical oxidation. Therefore, the incubation of the sample is carried out without access to light (in a dark place).
The value of BOD increases with time, reaching a certain maximum value - BODtotal; moreover, pollutants of various nature can increase (decrease) the BOD value. The dynamics of biochemical oxygen consumption during the oxidation of organic substances in water is shown in Fig. 8.

Rice. 8. Dynamics of biochemical oxygen consumption:

a - easily oxidized ("biologically soft") substances - sugars, formaldehyde, alcohols, phenols, etc.;
c - normally oxidizing substances - naphthols, cresols, anionic surfactants, sulfanol, etc.;
c - heavily oxidized ("biologically rigid") substances - non-ionic surfactants, hydroquinone, etc.

Thus, BOD is the amount of oxygen in (mg) required for the oxidation of organic matter in 1 liter of water under aerobic conditions, without access to light, at 20 ° C, for a certain period as a result of biochemical processes occurring in water.
It is tentatively assumed that BOD5 is about 70% BODtot, but can be from 10 to 90% depending on the oxidizing substance.
A feature of the biochemical oxidation of organic substances in water is the accompanying nitrification process, which distorts the nature of oxygen consumption.

2NH4++ЗO2=2HNO2+2H2О+2Н++Q
2HNO2+O2=2HNO3+Q
where: Q is the energy released during reactions.

Rice. 9. Change in the nature of oxygen consumption during nitrification.

Nitrification proceeds under the influence of special nitrifying bacteria - Nitrozomonas, Nitrobacter, etc. These bacteria provide the oxidation of nitrogen-containing compounds that are usually present in polluted natural and some waste waters, and thereby contribute to the conversion of nitrogen, first from ammonium to nitrite, and then to nitrate forms

The process of nitrification also occurs during the incubation of the sample in oxygen bottles. The amount of oxygen used for nitrification can be several times greater than the amount of oxygen required for the biochemical oxidation of organic carbon-containing compounds. The beginning of nitrification can be fixed at a minimum on the graph of daily BOD increments over the incubation period. Nitrification begins approximately on the 7th day of incubation (see Fig. 9), therefore, when determining BOD for 10 or more days, it is necessary to introduce special substances into the sample - inhibitors that suppress the vital activity of nitrifying bacteria, but do not affect the usual microflora (i.e. on bacteria - oxidizers of organic compounds). As an inhibitor, thiourea (thiocarbamide) is used, which is injected into the sample or into dilution water at a concentration of 0.5 mg/ml.

While both natural and domestic wastewater contains a large number of microorganisms that can develop due to the organic matter contained in the water, many types of industrial wastewater are sterile, or contain microorganisms that are not capable of aerobic processing of organic matter. However, microbes can be adapted (adapted) to the presence of various compounds, including toxic ones. Therefore, in the analysis of such wastewater (they are usually characterized by an increased content of organic substances), dilution with water saturated with oxygen and containing additives of adapted microorganisms is usually used. When determining the BODtot of industrial wastewater, the preliminary adaptation of the microflora is crucial to obtain correct results analysis, because the composition of such waters often includes substances that greatly slow down the process of biochemical oxidation, and sometimes have a toxic effect on the bacterial microflora.
For the study of various industrial wastewaters that are difficult to biochemically oxidize, the method used can be used in the variant of determining the "total" BOD (BODtotal).
If the sample is very high in organic matter, dilute water is added to the sample. To achieve maximum BOD analysis accuracy, the analyzed sample or the mixture of the sample with diluting water should contain such an amount of oxygen that during the incubation period there was a decrease in its concentration by 2 mg/l or more, and the remaining oxygen concentration after 5 days of incubation should be at least 3 mg/l. If the content of RA in the water is not enough, then the water sample is pre-aerated to saturate the air with oxygen. The most correct (accurate) result is considered to be the result of such a determination, in which about 50% of the oxygen originally present in the sample is consumed.
In surface waters, the BOD5 value ranges from 0.5 to 5.0 mg/l; it is subject to seasonal and daily changes, which mainly depend on temperature changes and on the physiological and biochemical activity of microorganisms. Changes in BOD5 of natural water bodies are quite significant when polluted by sewage.

Standard for BODtot. should not exceed: for reservoirs of domestic and drinking water use - 3 mg / l for reservoirs of cultural and domestic water use - 6 mg / l. Accordingly, it is possible to estimate the maximum permissible BOD5 values ​​for the same water bodies, which are approximately 2 mg/l and 4 mg/l.

11. Biogenic elements

Biogenic elements (biogens) are traditionally considered elements that are included, in significant quantities, in the composition of living organisms. The range of elements classified as biogenic is quite wide, these are nitrogen, phosphorus, sulfur, iron, calcium, magnesium, potassium, etc.
The issues of water quality control and environmental assessment of water bodies have introduced a broader meaning into the concept of biogenic elements: they include compounds (more precisely, water components), which, firstly, are the waste products of various organisms, and secondly, are " building material» for living organisms. First of all, these include nitrogen compounds (nitrates, nitrites, organic and inorganic ammonium compounds), as well as phosphorus (orthophosphates, polyphosphates, organic esters of phosphoric acid, etc.). Sulfur compounds are of interest to us in this regard, to a lesser extent, since we considered sulfates in the aspect of a component of the mineral composition of water, and sulfides and hydrosulfites, if present in natural waters, then in very small concentrations, and can be detected by smell.

11.1. Nitrates
Nitrates are salts of nitric acid and are commonly found in water.. The nitrate anion contains a nitrogen atom in the maximum oxidation state "+5". Nitrate-forming (nitrate-fixing) bacteria convert nitrite to nitrate under aerobic conditions. Under the influence of solar radiation, atmospheric nitrogen (N2) is also converted predominantly into nitrates through the formation of nitrogen oxides. Many mineral fertilizers contain nitrates, which, if applied excessively or inappropriately to the soil, lead to water pollution. The sources of nitrate pollution are also surface runoff from pastures, stockyards, dairy farms, etc.
The increased content of nitrates in water can serve as an indicator of pollution of the reservoir as a result of the spread of fecal or chemical pollution (agricultural, industrial). Ditches rich in nitrate water worsen the quality of water in a reservoir, stimulating the mass development of aquatic vegetation (primarily blue-green algae) and accelerating the eutrophication of reservoirs. Drinking water and foods containing high amounts of nitrates can also cause illness, especially in infants (so-called methemoglobinemia). As a result of this disorder, the transport of oxygen with blood cells worsens and the “blue baby” syndrome (hypoxia) occurs. At the same time, plants are not as sensitive to an increase in nitrogen content in water as phosphorus.

11.2. Phosphates and total phosphorus
In natural and waste waters, phosphorus can be present in different types. In a dissolved state (sometimes they say - in the liquid phase of the analyzed water) it can be in the form of orthophosphoric acid (H3P04) and its anions (H2P04-, HP042-, P043-), in the form of meta-, pyro- and polyphosphates (these substances use to prevent the formation of scale, they are also part of detergents). In addition, there are a variety of organophosphorus compounds - nucleic acids, nucleoproteins, phospholipids, etc., which can also be present in water, being products of vital activity or decomposition of organisms. Organophosphorus compounds also include some pesticides.
Phosphorus can also be contained in an undissolved state (in the solid phase of water), present in the form of sparingly soluble phosphates suspended in water, including natural minerals, protein, organic phosphorus-containing compounds, remains of dead organisms, etc. Phosphorus in the solid phase in natural water bodies is usually found in the bottom sediments, but can occur, and in large quantities, in waste and polluted natural waters.
Phosphorus is an essential element for life, but its excess leads to accelerated eutrophication of water bodies. Large amounts of phosphorus can enter water bodies as a result of natural and anthropogenic processes - surface soil erosion, improper or excessive use of mineral fertilizers, etc.
MPC of polyphosphates (tripolyphosphate and hexametaphosphate) in the water of reservoirs is 3.5 mg/l in terms of orthophosphate anion PO43-, the limiting indicator of harmfulness is organoleptic.

11.3. Ammonium

Ammonium compounds contain a nitrogen atom in the minimum oxidation state "-3".
Ammonium cations are a product of microbiological decomposition of proteins of animal and vegetable origin. The ammonium formed in this way is again involved in the process of protein synthesis, thereby participating in the biological cycle of substances (nitrogen cycle). For this reason, ammonium and its compounds in small concentrations are usually present in natural waters.
There are two main sources of environmental pollution with ammonium compounds. Ammonium compounds in large quantities are part of mineral and organic fertilizers, the excessive and improper use of which leads to the corresponding pollution of water bodies. In addition, ammonium compounds are present in significant amounts in sewage (faeces). Impurities not properly disposed of can penetrate into groundwater or be washed away by surface runoff into water bodies. Effluent from pastures and livestock gathering places, wastewater from livestock complexes, as well as domestic and domestic fecal effluents always contain large amounts of ammonium compounds. Dangerous contamination of groundwater with domestic fecal and domestic wastewater occurs when the sewerage system is depressurized. For these reasons, elevated levels of ammonium nitrogen in surface waters are usually a sign of household faecal contamination.
MPC for ammonia and ammonium ions in the water of reservoirs is 2.6 mg/l (or 2.0 mg/l for ammonium nitrogen). The limiting indicator of harmfulness is general sanitary.

11.4. Nitrites

Nitrites are salts of nitrous acid.
Nitrite anions are intermediate products of biological decomposition of nitrogen-containing organic compounds. and contain nitrogen atoms in the intermediate oxidation state "+3". Nitrifying bacteria convert ammonium compounds to nitrites under aerobic conditions. Some types of bacteria can also reduce nitrates to nitrites in the course of their life activity, but this occurs already under anaerobic conditions. Nitrites are often used in industry as corrosion inhibitors and in the food industry as preservatives.
Due to the ability to convert to nitrates, nitrites are generally absent from surface waters. Therefore, the presence of an increased content of nitrites in the analyzed water indicates water pollution, and taking into account the partially transformed nitrogenous compounds from one form to another.
MPC of nitrites (according to N02-) in the water of reservoirs is 3.3 mg/l (or 1 mg/l of nitrite nitrogen), the limiting indicator of harmfulness is sanitary-toxicological.

12. Fluorine (fluorides)

Fluorine in the form of fluorides can be contained in natural and ground waters, which is due to its presence in the composition of some soil-forming (parent) rocks and minerals. This element can be added to drinking water in order to prevent caries. However, excessive amounts of fluoride have a harmful effect on humans, causing the destruction of tooth enamel. In addition, an excess of fluorine in the body precipitates calcium, which leads to disturbances in calcium and phosphorus metabolism. For these reasons, the determination of fluoride in drinking water, as well as groundwater (eg water from wells and artesian wells) and water from drinking water bodies, is very important.
MPC for fluorine in drinking water for different climatic regions ranges from 0.7 to 1.5 mg/l, the limiting indicator of harmfulness is sanitary-toxic.

13. Metals

13.1. Iron total

Iron is one of the most common elements in nature. Its content in earth's crust is about 4.7% by weight, so iron, in terms of its prevalence in nature, is commonly called a macronutrient.
Over 300 minerals containing iron compounds are known. Among them are magnetic iron ore α-FeO(OH), brown iron ore Fe3O4x H2O, hematite (red iron ore), hemite (brown iron ore), hydrogoethite, siderite FeCO3, magnetic pyrites FeSx, (x = 1-1.4), ferromanganese nodules and others. Iron is also a vital microelement for living organisms and plants; an element necessary for life in small quantities.
In low concentrations, iron is always found in almost all natural waters (up to 1 mg/l with MPC for the amount of iron 0.3 mg/l) and especially in wastewater. Iron can get into the latter from wastewater (wastewater) from pickling and electroplating shops, metal surface preparation areas, wastewater from fabric dyeing, etc.
Iron forms 2 kinds of soluble salts, forming Fe2+ and Fe3+ cations, however, iron can be found in solution in many other forms, in particular:
1) in the form of true solutions (aquacomplexes) 2+ containing iron (II). In air, iron (II) is rapidly oxidized to iron (III), the solutions of which have a brown color due to the rapid formation of hydroxo compounds (the solutions of Fe2+ and Fe3+ themselves are practically colorless);
2) in the form of colloidal solutions due to peptization (decomposition of aggregated particles) of iron hydroxide under the influence of organic compounds;
3) in the form of complex compounds with organic and inorganic ligands. These include carbonyls, arene complexes (with petroleum products and other hydrocarbons), 4-hexacyanoferrates, etc.
In an insoluble form, iron can be present in the form of various solid mineral particles of various compositions suspended in water.
At pH>3.5, iron (III) exists in an aqueous solution only in the form of a complex, gradually turning into a hydroxide. At pH>8, iron (II) also exists in the form of an aqua complex, undergoing oxidation through the stage of iron (III) formation:

Fe (II) > Fe (III) > FeO (OH) x H2O

Thus, since iron compounds in water can exist in various forms, both in solution and in suspended particles, accurate results can only be obtained by determining the total iron in all its forms, the so-called "total iron".
Separate determination of iron (II) and (III), their insoluble and soluble forms, gives less reliable results regarding water pollution by iron compounds, although sometimes it becomes necessary to determine iron in its individual forms.
The transfer of iron into a soluble form suitable for analysis is carried out by adding a certain amount of strong acid (nitric, hydrochloric, sulfuric) to the sample to pH 1-2.
The range of determined concentrations of iron in water is from 0.1 to 1.5 mg/l. Determination is also possible at an iron concentration of more than 1.5 mg/l after appropriate dilution of the sample with clean water.

MPC of total iron in the water of reservoirs is 0.3 mg/l, the limiting indicator of harmfulness- organoleptic.

13.2. Amount of heavy metals
Speaking about the increased concentration of metals in water, as a rule, they imply its pollution with heavy metals (Cad, Pb, Zn, Cr, Ni, Co, Hg, etc.). Heavy metals, getting into water, can exist in the form of soluble toxic salts and complex compounds (sometimes very stable), colloidal particles, precipitation (free metals, oxides, hydroxides, etc.). The main sources of water pollution with heavy metals are galvanic production, mining, ferrous and non-ferrous metallurgy, machine-building plants, etc. Heavy metals in the reservoir cause a number of negative consequences: getting into the food chain and violating the elemental composition of biological tissues, they thereby have a direct or indirect toxic effects on aquatic organisms. Heavy metals enter the human body through food chains.
According to the nature of the biological effect, heavy metals can be divided into toxicants and microelements, which have a fundamentally different nature of the effect on living organisms. The nature of the dependence of the effect exerted by an element on organisms, depending on its concentration in water (and, therefore, as a rule, in body tissues), is shown in Fig. 10.

As can be seen from fig. 10, toxicants have a negative effect on organisms at any concentration, while trace elements have an area of ​​deficiency that causes a negative effect (less than Ci), and an area of ​​concentrations necessary for life, when exceeded, a negative effect occurs again (more than C2). Typical toxicants are cadmium, lead, mercury; microelements - manganese, copper, cobalt.
Below we provide brief information about the physiological (including toxic) of some metals, usually classified as heavy.

Copper. Copper is a trace element found in the human body mainly in the form of complex organic compounds and plays an important role in the processes of hematopoiesis. The reaction of Cu2+ cations with SH-groups of enzymes plays a decisive role in the harmful effects of excess copper. Changes in the content of copper in serum and skin cause the phenomena of skin depigmentation (vitiligo). Poisoning with copper compounds can lead to disorders of the nervous system, impaired liver and kidney function, etc. MPC of copper in the water of reservoirs for drinking and cultural purposes is 1.0 mg/l, the limiting indicator of harmfulness is organoleptic.

Zinc. Zinc is a trace element and is included in the composition of some enzymes. It is found in blood (0.5-0.6), soft tissues (0.7-5.4), bones (10-18), hair (16-22 mg%), (a unit of measurement of low concentrations, 1 mg %=10-3) i.e. mainly in bones and hair. It is in the body in dynamic equilibrium, which shifts under conditions of increased concentrations in environment. The negative impact of zinc compounds can be expressed in the weakening of the body, increased morbidity, asthma-like phenomena, etc. The MPC of zinc in the water of reservoirs is 1.0 mg/l, the limiting indicator of harmfulness is general sanitary.

Cadmium. Cadmium compounds are highly toxic. They act on many systems of the body - the respiratory organs and the gastrointestinal tract, the central and peripheral nervous systems. The mechanism of action of cadmium compounds is to inhibit the activity of a number of enzymes, disruption of phosphorus-calcium metabolism, metabolic disorders of microelements (Zn, Cu, Pe, Mn, Se). The MPC of cadmium in the water of reservoirs is 0.001 mg/l, the limiting indicator of harmfulness is sanitary-toxicological.

Mercury . Mercury belongs to ultramicroelements and is constantly present in the body, acting with food. Inorganic mercury compounds (first of all, Hg cations react with SH-groups of proteins (“thiol poisons”), as well as with carboxyl and amine groups of tissue proteins, forming strong complex compounds - metalloproteins. As a result, deep dysfunctions of the central nervous system occur , especially its higher departments. Of the organic compounds of mercury, methylmercury plays the most important, which is highly soluble in lipid tissues and quickly penetrates into vital organs, including the brain. As a result, changes occur in the autonomic nervous system, peripheral nerve formations, in heart, blood vessels, hematopoietic organs, liver, etc., disturbances in the immunobiological state of the body Mercury compounds also have an embryotoxic effect (lead to damage to the fetus in pregnant women). sanitary and toxicological.

Lead. Lead compounds are poisons that affect all living things, but cause changes especially in the nervous system, blood and blood vessels. Suppress many enzymatic processes. Children are more susceptible to lead exposure than adults. They have embryotoxic and teratogenic effects, lead to encephalopathy and liver damage, and suppress immunity. Organic lead compounds (tetramethyl lead, tetraethyl lead) are strong nerve poisons, volatile liquids. They are active inhibitors of metabolic processes. All lead compounds are characterized by a cumulative effect. The MPC of lead in the water of reservoirs is 0.03 mg / l, the limiting indicator is sanitary-toxicological.
The approximate maximum allowable value for the amount of metals in water is 0.001 mmol/l (GOST 24902). The MPC values ​​for the water of reservoirs for individual metals are given earlier when describing their physiological impact.

14. Active chlorine

Chlorine can exist in water not only in the composition of chlorides, but also in the composition of other compounds with strong oxidizing properties. Such chlorine compounds include free chlorine (CL2), hapochlorite anion (СlO-), hypochlorous acid (НClO), chloramines (substances that, when dissolved in water, form monochloramine NH2Cl, dichloramine NHCl2, trichloramine NCl3). The total content of these compounds is called the term "active chlorine".
Substances containing active chlorine are divided into two groups: strong oxidizing agents - chlorine, hypochlorites and hypochlorous acid - contain the so-called "free active chlorine", and relatively less weak oxidizing agents - chloramines - "bound active chlorine". Due to their strong oxidizing properties, active chlorine compounds are used for disinfection (disinfection) of drinking water and water in swimming pools, as well as for the chemical treatment of some wastewater. In addition, some compounds containing active chlorine (for example, bleach) are widely used to eliminate the foci of the spread of infectious pollution.
The most widely used for the disinfection of drinking water is free chlorine, which, when dissolved in water, disproportionates according to the reaction:

Сl2+Н2О=Н++Сl-+HOСl

In natural water, the content of active chlorine is not allowed; in drinking water, its content is set in terms of chlorine at the level of 0.3-0.5 mg / l in free form and at the level of 0.8-1.2 mg / l in bound form (In this case, the concentration range of active chlorine is given , because at lower concentrations, an unfavorable situation is possible in terms of microbiological indicators, and at higher concentrations, an excess directly on active chlorine.). Active chlorine in the indicated concentrations is present in drinking water for a short time (no more than a few tens of minutes) and is completely removed even with short-term boiling of water. For this reason, the analysis of the selected sample for the content of active chlorine should be carried out immediately.
Interest in the control of chlorine in water, especially in drinking water, has increased after the realization that chlorination of water leads to the formation of appreciable amounts of chlorinated hydrocarbons that are harmful to public health. Of particular danger is the chlorination of drinking water contaminated with phenol. MPC for phenols in drinking water in the absence of chlorination of drinking water is 0.1 mg/l, and under conditions of chlorination (in this case, much more toxic and pungent characteristic odor chlorophenols are formed) - 0.001 mg/l. Similar chemical reactions can occur with the participation of organic compounds of natural or technogenic origin, leading to various toxic organochlorine compounds - xenobiotics.
The limiting indicator of harmfulness for active chlorine is general sanitary.

15. Integral and comprehensive assessment of water quality

Each of the indicators of water quality separately, although it carries information about the quality of water, still cannot serve as a measure of water quality, because. does not allow to judge the values ​​of other indicators, although sometimes it happens indirectly, it is associated with some of them. For example, an increased value of BOD5 compared to the norm indirectly indicates an increased content of easily oxidizable organic substances in water, an increased value of electrical conductivity indicates an increased salt content, etc. At the same time, the result of assessing water quality should be some integral indicators that would cover the main indicators of water quality (or those for which problems are recorded).
In the simplest case, if there are results for several evaluated indicators, the sum of the reduced concentrations of the components can be calculated, i.e. the ratio of their actual concentrations to MPC (summation rule). The criterion for water quality when using the summation rule is the fulfillment of the inequality:

It should be noted that the sum of the given concentrations according to GOST 2874 can only be calculated for chemicals with the same limiting hazard indicator - organoleptic and sanitary-toxicological.
If the results of analyzes are available for a sufficient number of indicators, it is possible to determine water quality classes, which are an integral characteristic of surface water pollution. Quality classes are determined by the water pollution index (WPI), which is calculated as the sum of the actual values ​​of 6 main water quality indicators reduced to MPC according to the formula:

The WPI value is calculated for each sampling point (site). Further on the table. 14, depending on the WPI value, determine the water quality class.

Characteristics of the integral assessment of water quality

Among the 6 main, so-called "limited" indicators, when calculating WPI are, without fail, dissolved oxygen concentration and BOD5 value, as well as the values ​​of 4 more indicators that are the most unfavorable for a given reservoir (water), or that have the highest reduced concentrations (Ci/MPCi ratio). Such indicators, according to the experience of hydrochemical monitoring of water bodies, are often the following: the content of nitrates, nitrites, ammonium nitrogen (in the form of organic and inorganic ammonium compounds), heavy metals - copper, manganese, cadmium, etc., phenols, pesticides, petroleum products, synthetic surfactants ( Surfactants - synthetic surfactants.There are non-ionic, as well as cationic and anionic surfactants.), Lignosulfonates. To calculate the WPI, indicators are selected regardless of the limiting sign of harmfulness, however, if the given concentrations are equal, preference is given to substances that have a sanitary and toxicological sign of harmfulness (as a rule, such substances have a relatively greater harmfulness).

Obviously, not all of the listed water quality indicators can be determined by field methods. The tasks of the integrated assessment are further complicated by the fact that in order to obtain data when calculating the WPI, it is necessary to analyze a wide range of indicators, with the selection of those for which the highest reduced concentrations are observed. If it is impossible to conduct a hydrochemical survey of a reservoir for all indicators of interest, it is advisable to determine which components can be pollutants. This is done on the basis of an analysis of the available results of hydrochemical studies of past years, as well as information and assumptions about the likely sources of water pollution. If it is impossible to perform analyzes for this component by field methods (surfactants, pesticides, oil products, etc.), samples should be taken and preserved in compliance with the necessary conditions (see Chapter 5), after which the samples should be delivered to the laboratory for analysis at the required time.

Thus, the tasks of the integral assessment of water quality practically coincide with the tasks of hydrochemical monitoring, since for the final conclusion about the class of water quality, the results of analyzes for a number of indicators over a long period are needed.

An interesting approach to assessing water quality, developed in the United States. The National Sanitary Foundation of this country in 1970 developed a standard generalized indicator of water quality (CQI), which has become widespread in America and some other countries. When developing the PCV, expert assessments were used based on extensive experience in assessing the quality of water when it is used for domestic and industrial water consumption, water recreation (swimming and water entertainment, fishing), protection of aquatic animals and fish, agricultural use (watering, irrigation), commercial use (navigation, hydropower, thermal power), etc. PCV is a dimensionless value that can take values ​​from 0 to 100. Depending on the value of PCV, the following estimates of water quality are possible: 100-90 - excellent; 90-70 - good; 70-50 - mediocre; 50-25 - bad; 25-0 is very bad. It has been established that the minimum value of PCV, at which the majority of state water quality standards are met, is 50–58. However, the water in the reservoir may have a PCV value greater than the specified one, and at the same time not meet the standards for any individual indicators.

PCV is calculated based on the results of determination 9 the most important characteristics water - private indicators, and each of them has its own weighting coefficient characterizing the priority of this indicator in assessing water quality. Particular indicators of water quality used in the calculation of PCV, and their weighting factors are given in Table. 15.

Weighting coefficients of indicators in the calculation of PCV according to the data of the National Sanitary Foundation of the USA

As follows from the table. 15 data, the most significant indicators are dissolved oxygen and the number of Escherichia coli, which is quite understandable if we recall the most important ecological role of oxygen dissolved in water and the danger to humans caused by contact with water contaminated with feces.

In addition to weight coefficients that have a constant value, weight curves have been developed for each individual indicator, characterizing the level of water quality (Q) for each indicator, depending on its actual value determined during the analysis. Graphs of the weight curves are shown in fig. 11. Having the results of analyzes for particular indicators, the weight curves determine the numerical values ​​of the assessment for each of them. The latter are multiplied by the appropriate weighting factor, and receive a quality score for each of the indicators. Summing up the scores for all defined indicators, the value of the generalized PCV is obtained.

The generalized PCV largely eliminates the shortcomings of the integral assessment of water quality with the calculation of the WPI, since contains a group of specific priority indicators, which include an indicator of microbial contamination.
When assessing water quality, in addition to the integral assessment, which results in the determination of the water quality class, as well as hydrobiological assessment by bioindication methods, as a result of which the purity class is established, sometimes there is also the so-called integrated assessment, which is based on biotesting methods.

The latter also refer to hydrobiological methods, but differ in that they allow one to determine the reaction of aquatic biota to pollution using various test organisms, both protozoa (ciliates, daphnia) and higher fish (guppies). Such a reaction is sometimes considered the most revealing, especially in relation to the assessment of the quality of polluted waters (natural and waste) and even makes it possible to determine quantitatively the concentrations of individual compounds.

The safety of drinking water chemical composition determined by its compliance with the following standards:

A list of harmful substances that may be contained in drinking water, their sources and the nature of the impact on the human body.

Water sampling and conservation

Sampling - operation, on the correct implementation of which the accuracy of the results obtained largely depends. Sampling during field analyzes must be planned, outlining the points and depths of sampling, the list of indicators to be determined, the amount of water taken for analysis, the compatibility of methods for preserving samples for their subsequent analysis. Most often, so-called one-time samples are taken on the reservoir. However, when examining a reservoir, it may be necessary to take a series of periodic and regular samples - from the surface, deep, bottom layers of water, etc. Samples can also be taken from underground sources, water pipes, etc. The averaged data on the composition of the waters give mixed samples.
IN normative documents(GOST 24481, GOST 17.1.5.05, ISO 5667-2, etc.) defines the basic rules and recommendations that should be used to obtain representative10 samples. Different types of reservoirs (water sources) cause some features of sampling in each case. Let's consider the main ones.
Samples from rivers and streams are selected to determine the quality of water in the river basin, the suitability of water for food use, irrigation, for watering livestock, fish farming, bathing and water sports, and to identify sources of pollution.
To determine the influence of the place of wastewater discharge and tributary water, samples are taken upstream and at the point where the water has completely mixed. It should be borne in mind that pollution can be unevenly distributed along the river flow, therefore, samples are usually taken in places of the most turbulent flow, where the flows mix well. Samplers are placed downstream of the stream at the desired depth.
Samples from natural and artificial lakes (ponds) are taken for the same purposes as water samples from rivers. However, given the long existence of lakes, monitoring of water quality over a long period of time (several years), including in places intended for human use, as well as establishing the consequences of anthropogenic water pollution (monitoring its composition and properties) comes to the fore. Sampling from lakes must be carefully planned to provide information to which statistical evaluation can be applied. Slowly flowing reservoirs have a significant heterogeneity of water in the horizontal direction. The quality of water in lakes often varies greatly in depth due to thermal stratification, which is caused by photosynthesis in the surface zone, water heating, the effect of bottom sediments, etc. Internal circulation may also appear in large deep reservoirs.
It should be noted that the quality of water in reservoirs (both lakes and rivers) is cyclical, with daily and seasonal cyclicity observed. For this reason, daily samples should be taken at the same time of day (eg 12 noon) and the duration of seasonal studies should be at least 1 year, including studies of series of samples taken during each season. This is especially important for determining the quality of water in rivers with sharply different regimes - low water and high water.
Wet precipitation samples (rain and snow) are extremely sensitive to contamination that may occur in the sample when using insufficiently clean dishes, ingress of foreign (non-atmospheric) particles, etc. It is believed that wet sediment samples should not be taken near sources of significant atmospheric pollution - for example, boiler houses or thermal power plants, open warehouses materials and fertilizers, transport hubs, etc. In such cases, the sediment sample will be significantly affected by the indicated local sources of anthropogenic pollution.
Precipitation samples are collected in special containers made from neutral materials. Rainwater is collected by means of a funnel (at least 20 cm in diameter) into a measuring cylinder (or directly into a bucket) and stored there until analysis.
Snow sampling is usually carried out by cutting cores to the full depth (down to the ground), and it is advisable to do this at the end of the period of heavy snowfalls (in early March). The volume of snow converted to water can also be calculated using the formula above, where D is the core diameter.
Groundwater samples are selected to determine the suitability of groundwater as a source of drinking water, for technical or agricultural purposes, to determine the impact on the quality of groundwater of potentially hazardous economic facilities, while monitoring groundwater pollutants.
Groundwater is studied by sampling from artesian wells, wells, and springs. It should be borne in mind that the quality of water in different aquifers can vary significantly, therefore, when sampling groundwater, an assessment should be made of accessible ways the depth of the horizon from which the sample was taken, the possible gradients of underground flows, information about the composition of the underground rocks through which the horizon lies. Since a concentration of various impurities can be created at the sampling point, different from the entire aquifer, it is necessary to pump out from the well (or from the spring, making a recess in it) water in an amount sufficient to renew the water in the well, water pipe, recess, etc.
Water samples from water supply networks are selected in order to determine the general level of tap water quality, search for the causes of contamination of the distribution system, control the degree of possible contamination of drinking water with corrosion products, etc.
To obtain representative samples when sampling water from water supply networks, the following rules are observed;
- sampling is carried out after the water has been drained for 10-15 minutes - the time usually sufficient to renew the water with accumulated pollutants;
- for sampling, do not use the end sections of water supply networks, as well as sections with pipes of small diameter (less than 1.2 cm);
- for selection, whenever possible, areas with turbulent flow are used - taps near valves, bends;
— When sampling, water should slowly flow into the sampling container until it overflows.
Sampling to determine the composition of water (but not quality!) Is also carried out when studying wastewater, water and steam from boiler plants, etc. Such work, as a rule, has technological goals, requires special training and compliance with additional safety rules from personnel. Field methods can be quite (and often very effectively) used by specialists in these cases, however, for the reasons indicated, we will not recommend them for work. educational institutions, the public and the public, and describe appropriate sampling techniques.
When sampling, attention should be paid (and recorded in the protocol) to the hydrological and climatic conditions that accompanied sampling, such as precipitation and its abundance, floods, low water and stagnant water, etc.
Water samples for analysis can be taken both immediately before the analysis and in advance. For sampling, experts use standard bottles or bottles with a capacity of at least 1 liter, which open and fill at the required depth. Due to the fact that 30-50 ml of water is usually sufficient for field analysis for any one indicator (with the exception of dissolved oxygen and BOD), sampling immediately before analysis can be done in a 250-500 ml flask (for example, from the laboratory kit, measuring kit, etc.).
It is clear that the sampling vessel must be clean. The cleanliness of dishes is ensured by pre-washing them with hot soapy water (do not use washing powders and chromium mixture!), Repeated rinsing with clean warm water. In the future, it is desirable to use the same glassware for sampling. Vessels intended for sampling are thoroughly washed beforehand, rinsed at least three times with sampled water and sealed with glass or plastic stoppers boiled in distilled water. Between the stopper and the sample taken in the vessel, air with a volume of 5-10 ml is left. A sample is taken into a common dish for analysis only of those components that have the same conditions of preservation and storage.
Sampling not intended for analysis immediately (i.e., taken in advance) is carried out in a hermetically sealed glass or plastic (preferably fluoroplastic) container with a capacity of at least 1 liter.
To obtain reliable results, water analysis should be performed as soon as possible. The processes of oxidation-reduction, sorption, sedimentation, biochemical processes caused by the vital activity of microorganisms, etc. take place in water. As a result, some components can be oxidized or reduced: nitrates - to nitrites or ammonium ions, sulfates - to sulfites; oxygen can be spent on the oxidation of organic substances, etc. Accordingly, the organoleptic properties of water can also change - smell, taste, color, turbidity. Biochemical processes can be slowed down by cooling the water to a temperature of 4-5 ° C (in the refrigerator).
However, even if you know the field methods of analysis, it is not always possible to perform the analysis immediately after sampling. Depending on the expected storage time of the collected samples, it may be necessary to preserve them. There is no universal preservative, so samples for analysis are taken in several bottles. In each of them, water is preserved by adding the appropriate chemicals, depending on the components being determined.
In table. methods of conservation, as well as features of sampling and storage of samples are given. When analyzing water for certain indicators (for example, dissolved oxygen, phenols, oil products), special requirements are imposed on sampling. So, when determining dissolved oxygen and hydrogen sulfide, it is important to exclude the contact of the sample with atmospheric air, so the bottles must be filled with a siphon - a rubber tube lowered to the bottom of the bottle, ensuring that water overflows when the bottle is overfilled. Details of specific sampling conditions (if any) are given in the description of the respective analyses.

Methods of conservation, features of sampling and storage of samples

It should be borne in mind that neither conservation nor fixation ensures the constancy of the composition of water indefinitely. They only keep the corresponding component in the water for a certain time, which makes it possible to deliver samples to the place of analysis, for example, to a field camp, and, if necessary, to a specialized laboratory. The sampling and analysis protocols must indicate the dates of sampling and analysis.