Self-purification of water in nature. Self-purification of water in a reservoir
In the process of self-purification, saprophytes and pathogenic microorganisms die off. They die as a result of: depletion of water with nutrients; bactericidal action of ultraviolet rays of the sun, which penetrate into the water column by more than 1 m; the influence of bacteriophages and antibiotic substances secreted by saprophytes; adverse temperature conditions; antagonistic effect of aquatic organisms and other factors. The processes of self-purification of water proceed more intensively in the warm season, as well as in flowing water bodies - rivers. The so-called saprophytic microflora and aquatic organisms are essential in the processes of water self-purification. Some representatives of the microflora of water bodies have antagonistic properties to pathogenic microorganisms, which leads to the death of these microbes.
The simplest aquatic organisms, as well as zooplankton (crustaceans, rotifers, etc.), passing water through their intestines, destroy a huge amount of bacteria. Bacteriophages that have fallen into the reservoir also have an effect on pathogens. One of the important processes of water self-purification is the mineralization of organic substances.
The first mineral product of the oxidation of nitrogen-containing organic substances is the ammonium ion or ammonia. The presence of the latter in high concentrations, in the absence of nitrites and nitrates, indicates the freshness of pollution. Ammonia (ammonium nitrogen), as a rule, in the presence of oxidizing agents passes into nitrites, but these compounds are very unstable and in the presence of oxygen are oxidized to nitrates. Nitrates are, as it were, the final substance in the mineralization of organic nitrogen-containing products.
Good aeration of water -- enrichment of water with oxygen --- provides activation of oxidative, biological and other processes, helps to purify water.
The rate of self-purification of water depends on many conditions: the amount of pollution entering the reservoir; its depth and the speed of the water flow; water temperature; presence of dissolved oxygen in water; composition of microfauna and flora, etc.
The ability to self-cleanse is not unlimited, on the contrary, it is very limited.
Compounds of lead, copper, zinc, mercury, which can get into water bodies with wastewater, have a toxic effect on the body of animals, and also slow down the processes of self-purification of water and worsen its organoleptic properties.
In small reservoirs, with a significant amount of protein pollutants in the water, intermediate substances of their decay (in particular, hydrogen sulfide, nitrites, diamines, etc.), which are highly toxic, can accumulate.
Self-purification of groundwater occurs due to filtration through the soil and due to the process of mineralization, as a result, water is completely freed from organic contaminants and microorganisms.
Veterinary and sanitary supervision of water sources includes: monitoring its veterinary and sanitary condition and organizing protection in order to prevent possible water pollution by organic and other waste and sewage; organization of sanitary and laboratory control of water quality and taking into account the constancy of its quality depending on the seasons of the year and soil conditions; establishing the relationship between the good quality of drinking water and animal diseases (sanitary passport).
For open reservoirs, an additional biochemical oxygen demand is determined for 5 days. (BOD3) in mg/l and dissolved oxygen in mg/l.
Regardless of the results of water analysis, only such water sources are allowed for use that can be provided or already have a sanitary protection zone (SPZ).
The ZSO is understood as the area around water supply sources and waterworks, where a specially established regime must be observed. The purpose of the organization of the ZSO is to ensure the protection of water sources, waterworks and the surrounding area from pollution.
It is necessary to create a sanitary protection zone, first of all, near surface water sources, which are easily accessible to pollution. This event is also very important in relation to the sanitary protection of underground water sources, since in the absence of the SSS, they can also be contaminated.
The ZSO for water pipelines taking water from open reservoirs consists of three belts: strict regime, restrictions and observations.
The first ZSO belt - strict regime - covers the territory in which there is a source of water supply and water intake and water facilities are located. In this zone, the residence and temporary stay of persons is prohibited. not working on waterworks. Construction is not allowed here, with the exception of facilities related to the technical needs of the water supply. The area of the strict regime belt when using underground sources is up to 1 ha with a radius of at least 50 m around the water intake site. When using interlayer waters, which are better protected, the belt area can be limited to 0.25 ha. The second belt - restrictions - is the territory directly surrounding the source of water supply. It is prohibited to use it for household needs (graze cattle, etc.).
The third belt - observations - covers the territory adjacent to the territory of the second belt. Here, the sanitary authorities keep a record of water infections and constant monitoring to prevent the spread of infectious diseases through water.
SELF-CLEANING OF WATER. Reservoirs have the ability, under the influence of natural factors, to gradually clear themselves of contaminants that have fallen into them: suspended particles, bacteria, dissolved organic and inorganic substances. S.'s mechanism of century. from organic pollution consists of: 1) sorting of solid particles according to their beats. weight (their settling to the bottom), 2) the distribution of pollution in the mass of water of the reservoir, which leads to closer contact of pollution with 0 2 dissolved in water, which is one of the essential agents in the process of mineralization of organic matter, 3) biochemical. processes of destruction of organic substances as a result of the vital activity of bacteria and other representatives of the flora and fauna of the reservoir, Ch. image, their lower forms, and 4) chem. processes of exchange and oxidation of decay products of organic matter. As a result, biochem. decomposition processes, organic matter is destroyed and gives a number of final compounds - free carbonic acid and its salts, nitrogenous, sulfate and phosphate compounds, which are further involved in the circulation of substances by the plant population and microbes of the reservoir. - To factors that reduce the content of bacteria in water, belong to: 1) their sedimentation during the sedimentation of particles suspended in water to the bottom; 2) dilution of water by inflowing masses of purer waters; 3) the death of bacteria under the influence of direct sunlight; 4) the total loss of organic substances nutritious for bacteria in the water; and 5) the devouring of Protozoa bacteria. -from 6 to 18 days To determine the degree of self-purification of water from bacteriological methods, the determination of the total number of microbes and the titer of Escherichia coli, as well as B. proteus vulgaris and Streptococcus as satellites of Escherichia coli is used j% The role of Protozoa in the bacterial self-purification of water is evidenced by the experiments of Shepilevsky, who note the most intense clarification of bacterial suspensions during the reproduction of Protozoa in them. Of the Protozoa, colorless Flagellata play an important role in the bacterial self-purification of water, the development curve of which in rivers, after the introduction of pollution into them, repeats the development curve of bacteria with a shift downstream of the river, as can be seen from the data on the study of the river. Oka below the mouth of the river. Nara (Kononov). In r. Oka, along its left bank, from the side of which it flows into the river. Oku river Nara, receiving industrial and domestic waters of the city of Serpukhov, the content of bacteria and colorless Flagellata is expressed in the following quantities in 1 cm 3 water. Sampling site Number of bacteria Number of colorless Flagellata R. Oka, 4 km above the mouth of the R. Nara .......... R. Oka, 0.5 km below the mouth of the river. Planks......... 6,200-8,942 8,400 5,992 5,532 3,981 3,021,189 38-189 2 2U 2,740 2,098 1,021 Oka River, 6.0 km below the mouth of the River Oka, 13.0 km below the mouth of the River Oka, 22.5 km below the mouth of the River Oka, 30.5 km below the mouth of the river. Nara......... The role of colorless Flagellata in the process of bacterial self-purification is also confirmed by Kononov's observation of the water of the Moskva River ditch (Fig. 2) and Horowitz's experiments with Bact broth dilutions. coli with and without Flagellata. Particularly intensively Protozoa absorb those bacterial species that do not belong to the normal inhabitants of the water, namely pathogenic microorganisms and of them Vibrio cholerae, typhoid, intestinal, Pseudomonas aeruginosa, etc. - When a reservoir is polluted, the water in it changes its composition, the flora and the fauna of the reservoir, but later, as a result of self-purification processes, the normal picture of the reservoir is gradually restored. In the zone of maximum pollution (polysaprobic zone), the river is characterized by a high content of fresh organic matter. This zone is poor in dissolved 0 2 . It is inhabited by heterotrophic organisms (those that feed on organic substances dissolved and suspended in water). Down the river, in the mesosaprobic MG/L. 0" \ \ \ li \ \ \ \ \ l and ^ "consumption 0, 4 . 3 \ *-- H ( h occultability - %0b -- -^ t" 80 70 topics 1 literature "17 16 14 -f\-. 1 1 - ,- -"" ! ,P at | l1 V -J 20 10 -\ - /l % saturation Oh, in log. / / \ / / \ \ / \ / i/ / i f / / / / / \ \ <>at erni\ \ s ST.1 "lags Hat days! 234 56789 10 Figure 1. Figure 1. Chemical change in water composition and relative development of saprobic forms of benthos in the Yauza River under the influence of pollution from its tributary, the Rabotnya River, which receives wastewater from a viscose factory. Figure 2. Self-purification of water from the ditch of the Moskva River under laboratory conditions. zone contains a smaller amount of fresh organic matter compared to the polysaprobic zone, due to their partial decay. In this zone, there are a number of intermediate decay products of organic matter. Along with heterotrophic organisms, it is also inhabited by mixotrophic organisms (capable of assimilating both organic substances and nitrogenous products of their decay) and autotrophic (organisms with mineral nutrition). The mesosaprobic zone, in turn, is divided into a-mesosaprobic and D-mesosaprobic zones, of which the first one approaches the polysaprobic zone in terms of pollution, the second one approaches the subsequent oligosaprobic zone. The /3-mesosaprobic zone is characterized by a high content of mineral nitrogenous compounds and, as a result, is distinguished by the lush development of plant plankton with autotrophic nutrition. Characteristic of the /2-mesosaprobic zone in summer during the daytime is a sharp increase in the content of dissolved 0 2 due to the processes of photosynthesis of free coal to-you. Even further down the river, in the oligo-saprobic zone, the river is already free of organic nitrogen-containing substances; its plant plankton is represented by organisms with autotrophic nutrition, which, due to the already low content in the water of nitrogenous decomposition products of organic matter consumed by plant plankton in the previous /9-mesosaprobic zone, produce less production here compared to the /5-mesosaprobic zone. The content of dissolved 0 2 in this zone corresponds to its absorption by water from the air. On fig. 1 shows an example of the course of river cleansing processes. Efficiency of processes of natural S. of century. is directly dependent on the 0 2 dissolved in water and the degree of population of the reservoir by plant and animal organisms, including microbes. When draining wastewater into public water bodies, with the expectation of their natural self-purification, it is necessary to take into account the capacity of the reservoir, the ratio of the quantity and quality of water in the reservoir to the quantity and quality of wastewater discharged, in particular the need for oxygen for biochemical. splitting of organic substances of the waste liquid and the content of dissolved 0 2 in the water of the reservoir. Based on the minimum allowable according to the norms of the NKZdr. decrease in the reservoir of dissolved O 2 in 4 mg for 1 l water, when calculating the discharge of wastewater into the river, the formula is adopted _Q(g-4) " " *" where J)-biochem. the need for 0 2 waste water, Q is the flow of water in the river, g is the flow of waste water discharged into the river, a- the content of dissolved 0 2 in the water of the river. - When raising the question of the point where one can expect the end of the self-purification of the river after the descent of pollution into it, it is always necessary to take into account, among other factors, also the speed of the river, which is associated with the mechanical transfer of pollution down the river and the process mixing of a jet of waste liquid with river water. The study of the latter issue has shown that in individual rivers, when sewage is discharged into them or when tributaries flow into them, the observed heterogeneity of the composition of the water of the river below the outflow or tributary can persist for a long distance. So, the mixing of the jet of a heavily polluted river. Yauzy river with water Moscow takes place at 2-3 km below the mouth of the river. Yauza along the river. Moscow; jet mixing of a heavily polluted river. Tmaki (in the city of Kalinin, former Tver) with the water of the river. Volga ends only at 11 km below the mouth of the river. Tmaki along the Volga River; mixing of industrial and fecal effluents from the city of Orekhovo-Zuyevo with water from the river. Klyazma ends at the river. Klyazma at 10 km below drains; R. Volga after the confluence of the river. Oki over 180 km from the city of Gorky to the city of Vasil-Sursk has a heterogeneous composition of water due to the incomplete displacement of the river jet. Oki with water Volga.-Great influence on the processes of natural S. century. provide the seasons of the year. In the winter season, when life in the reservoir freezes, they also manifest themselves to a weak degree and biochemical. processes; in the same season of the year, due to the presence of the ice cover, the re-aeration of the reservoir is also disturbed - all this has as a consequence the pollution of rivers when organic pollutants descend into them in the winter season for a longer distance compared to the summer. Lit.: G o r o v i ts L., On the bacteriological study of air, soil and water (chapter in the book The Teaching about Microorganisms, S. Zlatogorov, part 2, P., 1916); Dolgov G., On the heterogeneity of water in the river, Rus. hydrobiol. journal, vol. VII, № 3-4, 1928; Dolgov G. and Kononov V., Biological survey of the Klyazma River within the Bogorodsky and Orekhovo-Zuevsky counties, Proceedings of San. in-ta Moszdravotd. them. Erisman, no. 3, M., 1928; Dolgov G. and Nikitinsky Ya., Hydrobiological methods of research (Standard methods for the study of drinking and waste water, M., 1927, lit.); Zlatogorov S, Demchenko B., M o-gilevskaya B. and Kalmykova M., Bacteriological study of the water of the rivers: Northern Donets, Udy, Lopan, Proceedings of the commission for the sanitary and bacteriological examination of these rivers, issue 2, Kharkov, 1928; S erbinov I., General microbiology (chapter in the book "Teaching about microorganisms", [S. Zlatogorov, part 1, P., 1916).V. Kononov.From a sanitary point of view, the processes of natural water purification, or self-purification of water bodies, are of great interest. The process of self-purification does not occur in clean waters, but develops only in connection with the ingress of pollution.
The factors of self-purification of water bodies from incoming pollution, including from foreign microorganisms (biological self-purification) are numerous and diverse. Conventionally, they can be divided into three groups - physical, chemical, biological.
Physical factors. Among these factors, dilution, dissolution and mixing of incoming contaminants are of paramount importance. The settling of insoluble sediments in water also contributes to self-purification. The microflora of water is affected by solar radiation, hydrostatic pressure, temperature, etc.
Dilution. Rapid and intensive dilution of polluting waters with pure water of the reservoir leads to a drop in the concentration of organic compounds, i.e. a decrease in the concentration of nutrients, which leads to an acceleration of the death of bacteria that have come from outside, including pathogenic ones. Self-purification of running water in rivers is more intense than in stagnant waters (lakes, ponds).
As a result of dilution of wastewater that has entered the reservoir with a significant amount of pure water, their transparency increases, which contributes to a deeper penetration of ultraviolet rays of sunlight, which have a detrimental effect on both saprophytic and pathogenic microorganisms. The degree of dilution is also taken into account when rationing chemical pollutants entering water bodies.
subsidence insoluble sediments in water, sedimentation of polluted waters also contributes to the self-purification of water bodies. Microorganisms, by virtue of their own gravity or adsorption on other organic and inorganic particles, gradually settle to the bottom, are subjected to the subsequent action of other self-purification factors.
Temperature. There are differences in the intensity of self-purification of water bodies in summer and winter, as well as in hot, temperate and cold climatic zones. In the summer, microorganisms begin to actively multiply already in the drains, and in the water of reservoirs their number decreases. In winter, the processes of microbial self-purification slow down: bacteria multiply only near drains, the rate of death decreases, and the high content of microorganisms in the reservoir lasts longer than in summer. Therefore, the sanitary condition of reservoirs in winter is worse, in addition, lowering the temperature contributes to the preservation of enterobacteria in it - the causative agents of intestinal infections. The water way of spreading intestinal infections is observed more often in winter.
Chemical Factors. The process of self-purification is affected by the oxidation of some organic and inorganic substances, aeration of the water of reservoirs, the presence of some salts (for example, NaCl), halogens (iodine, bromine, etc.), and the pH of the water.
The intake of a large amount of harmful chemical compounds (detergents, petroleum products, pesticides) in the wastewater suppresses the reproduction of saprophytic flora, inhibits biocenoses that are actively involved in self-purification processes. All this can help prolong the survival of pathogenic microorganisms in water, which increases the epidemic danger of the reservoir.
Biochemical factors. Some chemical self-purification factors (changes in pH, the appearance of metabolic products, etc.) are closely related to biological factors, most often they are a subsequent regular stage in the manifestation of their action. These factors are the link between chemical and biological factors. Sometimes they are isolated in an independent group.
Biological factors. The rate of self-purification of water bodies is influenced by competitive relationships that develop between different groups of microorganisms in the struggle for oxygen and nutrients.
The essence of the antagonistic action of autochthonous microflora against allochthonous bacteria, viruses, microscopic fungi is the release of toxic substances and compounds such as antibiotics by antagonist microbes. The water of some lakes and especially sea water has bactericidal properties.
Hydrolytic microorganisms promote purification by decomposing proteins, fats, carbohydrates of dead plants and animals. Oil-oxidizing bacteria are of great importance in self-purification from oil pollution. Microorganisms are also involved in the destruction of carcinogenic hydrocarbons.
Biological self-purification is also associated with the action of phages, which enter water bodies in abundance along with the bacteria themselves. An increase in the concentration of phages of pathogenic enterobacteria is found near settlements. However, a relatively high temperature is required for the manifestation of phage activity.
Some representatives of phytoplankton, protozoa, aquatic plants, and animals (for example, biofiltering mollusks) take part in the process of water self-purification.
The combination of all these factors leads to the fact that even in very polluted reservoirs, as you move away from the source of pollution and over time, the water becomes cleaner and its hygienic qualities improve.
Each body of water is a complex system inhabited by bacteria, higher aquatic plants, and various invertebrates. Their combined activity ensures self-purification of water bodies. One of the environmental tasks is to support the ability of self-purification of water bodies from impurities.
The factors of self-purification of water bodies can be conditionally divided into three groups: physical, chemical and biological.
Among the physical factors, the dilution, dissolution and mixing of incoming contaminants is of paramount importance. Good mixing and reduction of suspended solids concentrations is ensured by the rapid flow of the rivers. It contributes to the self-purification of water bodies by settling to the bottom of insoluble sediments, as well as settling polluted waters. In zones with a temperate climate, the river cleans itself after 200-300 km from the place of pollution, and in the Far North - after 2 thousand km.
Disinfection of water occurs under the influence of ultraviolet radiation from the sun. The effect of disinfection is achieved by the direct destructive effect of ultraviolet rays on protein colloids and enzymes of the protoplasm of microbial cells, as well as spore organisms and viruses.
Of the chemical factors of self-purification of water bodies, oxidation of organic and inorganic substances should be noted. Self-purification of a water body is often assessed in relation to easily oxidized organic matter or in terms of the total content of organic substances.
The sanitary regime of a reservoir is characterized primarily by the amount of oxygen dissolved in it. It should beat at least 4 mg per 1 liter of water at any time of the year for reservoirs for reservoirs of the first and second types. The first type includes water bodies used for drinking water supply of enterprises, the second - used for swimming, sporting events, as well as those located within the boundaries of settlements.
The biological factors of self-purification of the reservoir include algae, molds and yeast fungi. However, phytoplankton does not always have a positive effect on self-purification processes: in some cases, the mass development of blue-green algae in artificial reservoirs can be considered as a process of self-pollution.
Representatives of the animal world can also contribute to the self-purification of water bodies from bacteria and viruses. Thus, the oyster and some other amoeba adsorb intestinal and other viruses. Each mollusk filters more than 30 liters of water per day.
The purity of reservoirs is unthinkable without the protection of their vegetation. Only on the basis of a deep knowledge of the ecology of each reservoir, effective control over the development of various living organisms inhabiting it, can positive results be achieved, transparency and high biological productivity of rivers, lakes and reservoirs can be ensured.
Other factors also adversely affect the processes of self-purification of water bodies. Chemical pollution of water bodies with industrial wastewater, biogenic elements (nitrogen, phosphorus, etc.) inhibits natural oxidative processes and kills microorganisms. The same applies to the discharge of thermal wastewater from thermal power plants.
A multi-stage process, sometimes stretching for a long time - self-cleaning from oil. Under natural conditions, the complex of physical processes of self-purification of water from oil consists of a number of components: evaporation; settling of lumps, especially those overloaded with sediment and dust; adhesion of lumps suspended in the water column; floating lumps forming a film with inclusions of water and air; reducing the concentration of suspended and dissolved oil due to settling, floating and mixing with clean water. The intensity of these processes depends on the properties of a particular type of oil (density, viscosity, coefficient of thermal expansion), the presence of colloids in water, suspended and entrained plankton particles, etc., air temperature and sunlight.
Pollution entering the reservoir causes a violation of the natural balance in it. The ability of a reservoir to resist this disturbance, to get rid of the pollution introduced, is the essence of the self-purification process.
Self-purification of water systems is due to many natural and sometimes man-made factors. These factors include various hydrological, hydrochemical and hydrobiological processes. Conventionally, three types of self-purification can be distinguished: physical, chemical, biological.
Among physical processes, dilution (mixing) is of paramount importance. Good mixing and a reduction in the concentration of suspended particles is ensured by the intensive flow of rivers. Contributes to the self-purification of water bodies by settling polluted waters and settling to the bottom of insoluble sediments, sorption of pollutants by suspended particles and bottom sediments. For volatile substances, evaporation is an important process.
Among the chemical factors of self-purification of water bodies, the main role is played by the oxidation of organic and inorganic substances. Oxidation occurs in water with the participation of oxygen dissolved in it, therefore, the higher its content, the faster and better the process of mineralization of organic residues and self-purification of the reservoir proceeds. With severe pollution of the reservoir, the reserves of dissolved oxygen are quickly consumed, and its accumulation due to the physical processes of gas exchange with the atmosphere proceeds slowly, which slows down self-purification. Self-purification of water can also occur as a result of some other reactions in which hardly soluble, volatile or non-toxic substances are formed, for example, hydrolysis of pesticides, neutralization reactions, etc. Calcium and magnesium carbonates and bicarbonates contained in natural water neutralize acids, and carbonic acid dissolved in water neutralizes alkalis.
Under the influence of ultraviolet radiation of the sun in the surface layers of the reservoir, photodecomposition of some chemicals, such as DDT, and water disinfection occur - the death of pathogenic bacteria. The bactericidal action of ultraviolet rays is explained by their influence on the protoplasm and enzymes of microbial cells, which causes their death. Ultraviolet rays have a detrimental effect on vegetative forms of bacteria, fungal spores, protozoan cysts, and viruses.
Each body of water is a complex living system inhabited by bacteria, algae, higher aquatic plants, and various invertebrates. The processes of metabolism, bioconcentration, biodegradation lead to a change in the concentration of pollutants. Algae, molds and yeast fungi also belong to the biological factors of self-purification of a reservoir, however, in some cases, the massive development of blue-green algae in artificial reservoirs can be considered as a process of self-pollution. Representatives of the animal world can also contribute to the self-purification of water bodies from bacteria and viruses. So, oysters and some amoeba adsorb intestinal and other viruses. Each mollusk filters more than 30 liters of water per day. Common reed, narrow-leaved cattail, lake bulrush and other macrophytes are able to absorb from water not only relatively inert compounds, but also physiologically active substances such as phenols, toxic salts of heavy metals.
The process of biological purification of water is associated with the content of oxygen in it. With a sufficient amount of oxygen, the activity of aerobic microorganisms that feed on organic substances is manifested. When organic matter is broken down, carbon dioxide and water are formed, as well as nitrates, sulfates, and phosphates. Biological self-purification is the main link in the process and is considered as one of the manifestations of the biotic cycle in a reservoir.
The contribution of individual processes to the ability of the natural aquatic environment to self-purify depends on the nature of the pollutant. For the so-called conservative substances that do not decompose or decompose very slowly (metal ions, mineral salts, persistent organochlorine pesticides, radionuclides, etc.), self-purification has an apparent character, since only the redistribution and dispersion of the pollutant in the environment occurs, pollution adjacent objects to them. The decrease in their concentration in water occurs due to dilution, removal, sorption, bioaccumulation. With regard to biogenic substances, biochemical processes are most important. For water-soluble substances that are not involved in the biological cycle, the reactions of their chemical and microbiological transformation are important.
For most organic compounds and some inorganic substances, microbiological transformation is considered one of the main ways of self-purification of the natural aquatic environment. Microbiological biochemical processes include reactions of several types. These are reactions involving redox and hydrolytic enzymes (oxidases, oxygenases, dehydrogenases, hydrolases, etc.). Biochemical self-purification of water bodies depends on many factors, among which the most important are temperature, active reaction of the environment (pH), and the content of nitrogen and phosphorus. The optimum temperature for biodegradation processes is 25-30ºС. Of great importance for the vital activity of microorganisms is the reaction of the environment, which affects the course of enzymatic processes in the cell, as well as changes in the degree of penetration of nutrients into the cell. For most bacteria, a neutral or slightly alkaline reaction of the medium is favorable. At pH<6 развитие и жизнедеятельность микробов чаще всего снижается, при рН <4 в некоторых случаях их жизнедеятельность прекращается. То же самое наблюдается при повышении щелочности среды до рН>9,5.
