Water is a chemical compound of hydrogen and oxygen (H2O) - a liquid without odor, taste, or color (bluish in thick layers); with a density of 1 g/cm³ at a temperature of 3.98 °C. At 0 "C water turns into ice, at 100 °C - into steam. The molecular weight of water is 18.0153. According to V.I. Vernadsky, the chemical composition of water can be represented by the formula H2O with the value of n, equal to 1 -6. Not all water molecules are identical: alongside ordinary molecules with a mass of 18, there are molecules with a molecular'mass of 19, 20, 21 and even 22.

DISTRIBUTION AND STATE OF WATER

Water is the most widespread substance on Earth. It exists in three phases; gaseous (water vapor), liquid and solid. There is atmospheric, surface (hydrosphere) and underground water.

In the atmosphere water occurs in vaporous form in the air envelope surrounding the Earth, in droplet-liquid form - in clouds, fogs and as rain, in solid form - as snow, hail and ice crystals of high clouds.

In liquid form water is found in the hydrosphere: the water of oceans, seas, lakes, rivers, swamps, ponds and reservoirs. In solid form water in the form of ice and snow is found at the planet's poles, on mountain peaks, and in winter covers water bodies over significant areas. In the rocks of the lithosphere water occurs in vapor form. There is capillary, gravitational, and crystallization water.

WORLD WATER RESERVES

The hydrosphere is the water envelope of the Earth, including oceans, seas, rivers, lakes, groundwater and glaciers, snow cover, as well as water vapor in the atmosphere. The Earth's hydrosphere is represented for 94% by the salt waters of oceans and seas; more than 75% of all fresh water is stored in the polar caps of the Arctic and Antarctic (Table 5.1).

T a b l e 1

Distribution of water masses in the Earth's hydrosphere

The total area of oceans and seas is 2.5 times larger than the area of land, and the volume of water on Earth amounts to 1.5*10' km³. More than 95% of it is salt.

The World Ocean occupies an area of 361 million km-, which amounts to 70.8% of the surface of the Earth. With an average ocean depth of 3800 m, the total volume of water reaches 1370 million km'.

The World Ocean. The total area of the World Ocean exceeds the area of land by 2.5 times. The main area of land is concentrated in the Northern Hemisphere, while the main area of water is in the Southern.

Ocean waters — are the main accumulator and distributor of solar energy. Oceans also produce up to 50% of atmospheric oxygen. Vegetation in the ocean is distributed at depths of up to 100 m, where the water's transparency is sufficient for normal photosynthesis, while animals inhabit the entire thickness of the ocean.

Waters of the land. These include continental waters carried by rivers, concentrated in lakes, swamps, glaciers, snow cover and enclosed in the Earth's crust. The largest river in the world is the Amazon; its discharge into the ocean amounts to 16% of the discharge of all the world's rivers. Its basin contains the largest forest area on the planet. The planetary reserve of high-quality fresh water is concentrated in Lake Baikal, which contains more fresh water than all the fresh lakes of the world combined. 2% of the Earth's territory is covered by swamps. More than 60% of them are located in Russia and Belarus.

Glaciers cover 16 million km² of land, most of them located in Antarctica. If all the glaciers melted, the level of the World Ocean would rise by 64 m compared to the present.

Underground waters (underground hydrosphere). Fresh, salt and geothermal (temperature above 30°C) waters lie beneath the soil at various depths in the Earth's crust. They often form water-bearing strata. The volume of fresh underground water is approximately 100 times greater than the volume of surface fresh water of lakes, rivers, swamps, etc.

Waters in the atmosphere. These are mainly water vapor or its condensate; almost all water vapor (90%) is concentrated in the troposphere.

Biological water. This is the most important component of living matter, accounting on average for 80% of the total mass of a living organism. The total volume of biological water is estimated at about 1000 km³. The need for water among organisms is very great. For example, a person consumes about 10 tons of water a year, and about 500 kg is spent to form 1 kg of biomass.

Water resources

Russia is washed by the waters of 12 seas belonging to three oceans. On the territory of Russia there are more than 2.5 million large and small rivers, and more than 2 million lakes. Russia's water resources consist of static (age-old) and renewable ones. The former are considered relatively constant over a long period of time, while renewable water resources are estimated by the volume of annual river runoff. River runoff is formed by the melting of snow and rainfall, and the sources feeding rivers are swamps and groundwater.

Table 2

Total water resources of Russia

More than 120 thousand rivers longer than 10 km flow through the territory of Russia, with a total length exceeding 2.3 million km. About 90% of Russia's annual river runoff falls on the basins of the Arctic and Pacific Oceans, and only 8% on the basins of the Caspian and Azov Seas. However, it is precisely in the basins of these seas that more than 80% of Russia's population lives, and the bulk of economic infrastructure is concentrated.

Russia has more than 2 million fresh and salt lakes. Among them are the deepest freshwater lake, Baikal, and the largest closed brackish body of water, the Caspian Sea. The bulk of lake freshwater resources is concentrated in the lakes: Baikal (23 thousand km³, or 20% of world reserves and 90% of national reserves), Ladoga (903 km³). Onega (285 km³), Chudsko-Pskovskoye (35.2 km³). The largest reservoirs of Russia contain about 450 km³ of fresh water.

Glaciers are a significant accumulator of water; they are concentrated mainly in circumpolar regions: in Antarctica, on Arctic islands, including the Russian sector of the Arctic, and in mountainous areas.

Underground waters together with the surface waters of rivers, lakes and ponds form the basis of Russia's water resource fund, serving drinking purposes. The natural resources of fresh underground water amount to 787.5 km per year, with the forecast usable amount being more than 300 km³/year. Resources are distributed unevenly across the country's territory. The bulk of them - 229.7 km³/year (72.5%) - is concentrated in four economic regions: West Siberian - 96.1 km^!/year (30.3%), Far Eastern - 58.2 km³/year (18.4%), East Siberian - 42.8 km-'/year (13.5%) and Northern - 32.6 km³/year (10.3%).

2. The role of water in nature

1. Water plays an extremely important role in nature. It creates favorable conditions for the life of plants, animals, and microorganisms. Water remains liquid within the temperature range most favorable for their vital processes, and for a huge mass of organisms it is a habitat. Organisms living in water are protected from sharp spontaneous fluctuations in temperature and composition, since they constantly adapt to slow rhythmic fluctuations - daily, seasonal, annual, and so on.

2. Water has a moderating effect on weather and climatic conditions. It constantly moves through all spheres of the Earth, together with the circulation flows of the atmosphere - over great distances.

3. The circulation of water in the ocean (sea currents) leads to planetary heat and moisture exchange (Stepanov, 1974). The role of water as a powerful geological factor is well known.

4. Water is the only source of the oxygen released into the atmosphere during photosynthesis. Water is necessary for the biochemical and physiological processes occurring in an organism. Living organisms, including humans, who consist of 80% water (Kuntzel, 1988), cannot do without it. Loss of 10-20% of water leads to their death.

5. Water plays a huge role in ensuring human livelihood. It is used directly for drinking and household needs, as a means of transportation and raw material for obtaining industrial and agricultural products, has recreational significance, and its aesthetic importance is great.

Composition of natural water

In nature water does not occur in chemically pure form. It represents solutions of complex composition, which include gases (O₂. CO2, H^S, CH₄ and others), organic and mineral substances. Suspended particles are present in moving water flows. The overwhelming majority of chemical elements have been found in natural waters. Ocean waters contain on average 35 g/dm³ (34.6-35.0%o) of salts. Their main part consists of chlorides (88.7%), sulfates (10.8%) and carbonates (0.3%). The least mineralized waters are those of atmospheric precipitation, ultra-fresh waters of mountain streams and fresh lakes.

Depending on the content of dissolved mineral substances, waters are distinguished: fresh with a dissolved salt content of up to 1 g/dm³, brackish - up to 1-25 g/dm³, salt - more than 25 g/dm³. The boundary between fresh and brackish waters is set by the average lower threshold of human taste perception. The boundary between brackish and salt waters is established on the grounds that at a mineralization of 25 g/dm-⁵ the freezing point and the point of maximum density quantitatively coincide.

The water cycle in nature

Water is constantly in motion - circulation (fig. 1). Its movement occurs as a result of mechanical motion - flows of water in rivers, currents in the ocean depths; as a result of changes in phase composition - water evaporates and enters the atmosphere by means of diffusion and convective flows. Thus, a continuous closed process of water circulation on Earth takes place, called the cycle, or moisture turnover. There are small, large and intracontinental cycles, the latter being part of the large one.

Water that has evaporated from the ocean surface mostly condenses and returns back in the form of atmospheric precipitation (the small, or oceanic, cycle) and is partly carried by air currents onto land. Atmospheric precipitation that has fallen on land, seeping into the soil and the aeration zone, creates reserves of soil moisture. Atmospheric precipitation that has penetrated deeper forms groundwater: ground, stratal and deep-horizon waters. Part of the atmospheric precipitation flows over the Earth's surface, forming streams and rivers, while the rest evaporates again. Eventually, the water brought by air currents onto land reaches the ocean again, completing the large water cycle on the globe. From the large cycle, a further local, or intracontinental, cycle can be distinguished, in which water evaporated from the land surface falls onto land again as atmospheric precipitation. A small part of the water from the total volume participating in the cycle, of the order of 7.7 thousand km³/year, completes its cycle within closed drainage areas.

Every year more than 1 million km³ of water participates in the cycle on the Earth's surface, which amounts to about 0.1% of the volume of actively exchanged waters. About 510 [thousand km3] evaporates annually from the surface of the seas and ocean, and about 70 thousand km-¹ from the land surface. 90% of the moisture evaporated from its surface returns to the ocean as precipitation, and 1% enters the ocean as river, underground and glacial waters. About 120 thousand km³ of water falls on land as atmospheric precipitation, of which 58% goes to evaporation, while 42% flows back into the seas and oceans (Klige, 1998).

3. Water consumption

At present humanity uses 3.8 thousand km³ of water annually, and consumption could be increased to a maximum of 12 thousand km³. At the current rate of growth in water consumption, this will be enough for the next 25 — 30 years. Pumping out groundwater leads to subsidence of soil and buildings (in Mexico City and Bangkok) and to a lowering of groundwater levels by tens of meters (in Manila).

Every inhabitant of the Earth consumes on average 650 m³ of water per year (1780 liters per day). However, 2.5 liters per day is enough to satisfy physiological needs, i.e. about 1 m³ per year. Agriculture requires a large amount of water (69%), mainly for irrigation; industry consumes 23% of the water; 6% is used in households.

Taking into account the water needs of industry and agriculture, water consumption in our country ranges from 125 to 350 liters per person per day (450 liters in St. Petersburg, 380 liters in Moscow).

In developed countries, each inhabitant accounts for 200 — 300 liters of water per day, in cities — 400 — 500, in New York — more than 1000, in Paris — 500, in London — 300 liters. At the same time, 60% of the Earth's land does not have a sufficient amount of fresh water. A quarter of humanity (about 1.5 billion) experiences a shortage of it, and another 500 million suffer from a shortage and poor quality of drinking water, which leads to intestinal diseases.

The problem of the shortage of fresh water

Fresh water resources. Fresh waters make up an insignificant (about 2% of the hydrosphere) share of the total water reserves in nature. Fresh water available for use is found in rivers, lakes and groundwater. Its share of the entire hydrosphere is 0.3%.

Causes of the fresh water shortage. The problem of the fresh water shortage arises for several reasons, the main ones being: uneven distribution of water in time and space, growth of its consumption by humanity, losses of water during transportation and use, deterioration of water quality and its pollution.

1. The anthropogenic causes of depletion and pollution of fresh water include the following: withdrawal of surface and underground waters; mine and tunnel dewatering; development of deposits - solid minerals, oil and gas, industrial waters, sulfur smelting; urbanization - residential development, energy facilities (nuclear power plants, thermal power plants). Fresh waters are heavily polluted by enterprises of the chemical, food, pulp-and-paper, ferrous and non-ferrous metallurgy, oil-refining, construction-materials, and machine-building industries.

2. The growth of fresh water consumption by the planet's population is estimated at 0.5- 2% per year. Water consumption is increasing due to rising prosperity, as can be seen in the following example. Water consumption by one urban resident of the southern regions of Russia amounts to: in a house without sewerage 75, in a house with sewerage 120, with a gas water heater 210 and with all amenities 275 liters/day, and with centralized hot water supply 250-350 liters/day.

3. Losses of fresh water grow with the growth of its per-capita consumption and are related to the use of water for household needs. Most often this is explained by the imperfection of technology in industrial and agricultural production and municipal services. Losses of water from water-carrying communications in Russian cities amount to 30-35%.

4. In a number of cases the shortage of fresh water is related to the unpredictability of the negative consequences of human activity. Thus, the construction of canals (Volga-Chogray, Volga-Ural), cascades of reservoirs, irrigation and watering of pastures, drainage of swamps, etc. did not lead to the expected positive effects; on the contrary, these projects ended in the loss and pollution of water resources. When creating reservoirs, the increase in filtration into their banks and the increase in evaporation with an increase in the water surface are not always taken into account.

5. Deterioration of water quality is related to the entry of the products of human activity both directly into the water of rivers and other surface water bodies and groundwater, and through the atmosphere and soils. Deterioration of the quality of fresh waters is the most dangerous and is becoming threatening to human health and to the spread of life on Earth. Its extreme state is catastrophic pollution of waters.

4. Sources of pollution of water bodies

Sources of pollution are recognized as objects from which discharge or other entry into water bodies of harmful substances occurs, worsening the quality of surface waters, limiting their use, as well as negatively affecting the state of the bottom and shore water bodies.

The main pathways of pollution of the hydrosphere:

1) pollution by oil and oil products. This leads to the appearance of oil slicks, which impede the processes of photosynthesis in water due to the cutting off of sunlight, and also causes the death of plants and animals. Each ton of oil creates an oil film over an area of up to 12 km². Restoration of affected ecosystems takes 10—15 years

1. pollution by wastewater as a result of industrial production, mineral and organic fertilizers as a result of agricultural production, as well as by municipal and domestic effluents. This leads to eutrophication of water bodies — their enrichment with nutrients, leading to excessive development of algae and the death of other ecosystems of water bodies with stagnant water (lakes and ponds), and sometimes to waterlogging of the terrain;

2. pollution by heavy metal ions. This disrupts the vital activity of aquatic organisms and humans;

4) pollution by acid rain. Leads to acidification of water bodies and death of ecosystems;

1. radioactive pollution. Related to the discharge of radioactive waste;

2. thermal pollution. Caused by the discharge into water bodies of heated waters from thermal and nuclear power plants. Leads to the mass development of blue-green algae, the so-called blooming of water, a reduction in the amount of oxygen, and negatively affects the flora and fauna of water bodies;

3. mechanical pollution. Increases the content of mechanical impurities;

4. bacterial and biological pollution. Related to various pathogenic organisms, fungi and algae.

The world economy discharges 1500 km³ of wastewater of varying degrees of treatment per year, which requires 50—100-fold dilution to give it natural properties and further purification in the biosphere.

The main sources of pollution of water bodies are enterprises of ferrous and non-ferrous metallurgy, chemical and petrochemical, pulp-and-paper, and light industry.

Ferrous metallurgy. The volume of discharged wastewater amounts to 11,934 million m³, and the discharge of polluted wastewater reached 850 million m³. Enterprises in Magnitogorsk, Lipetsk, Yekaterinburg, Chelyabinsk, Cherepovets, and Novokuznetsk do not provide standard treatment of wastewater.

Non-ferrous metallurgy. The volume of discharge of polluted wastewater exceeded 537.6 million m³. Wastewater is polluted with mineral substances, flotation reagents (cyanides, xanthates), salts of heavy metals (copper, lead, zinc, nickel, mercury, etc.), arsenic, chlorides, etc.

Woodworking and pulp-and-paper industry. The main source of wastewater formation in the branch is pulp production, based on the sulfate and sulfite methods of wood cooking and bleaching.

Oil-refining industry. 543.9 million m³ of wastewater was discharged into surface water bodies by enterprises of the branch. As a result, oil products, sulfates, chlorides, nitrogen compounds, phenols, salts of heavy metals and others entered water bodies in significant quantities.

Chemical and petrochemical industry. oil products, suspended substances, total nitrogen, ammonium nitrogen, nitrates, chlorides, sulfates, total phosphorus, cyanides, thiocyanates, cadmium, cobalt, manganese, copper, nickel, mercury, lead, chromium, zinc, hydrogen sulfide, carbon disulfide, alcohols, benzene, formaldehyde, furfural, phenols, surfactants, carbamides, pesticides, and semi-finished products entered water bodies.

Machine building. primarily with oil products, sulfates, chlorides, suspended substances, cyanides, nitrogen compounds, salts of iron, copper, zinc, nickel, chromium, molybdenum, phosphorus, cadmium.

5. Pollution of oceans and seas

Every year more than 10 million tons of oil enter the World Ocean, and up to 20 % of the World Ocean is already covered with an oil film. This is primarily due to the fact that the extraction of oil and gas in the World Ocean has become the most important component of the oil and gas complex. In 1993, 850 million tons of oil were extracted in the ocean (almost 30% of world production). About 2500 wells have been drilled in the world.

Pollution of the hydrosphere by water transport occurs through two channels: firstly, sea and river vessels pollute it with waste obtained as a result of operational activity, and secondly, by emissions in the event of accidents involving toxic cargoes, mostly oil and oil products. The power plants of ships (mainly diesel engines) constantly pollute the atmosphere, from where toxic substances partially or almost completely enter the waters of rivers, seas and oceans.

1. Oil and oil products are the main pollutants of the water basin. On tankers carrying oil and its derivatives, before each new loading, the tanks are, as a rule, washed to remove the remnants of previously transported cargo. The washing water, and with it the remnants of the cargo, are usually dumped overboard. Among the most widespread and harmful pollutants is oil, whose annual influx into seas and oceans, according to UN data, reaches 6...7 million tons.

Enormous damage was inflicted on the Ocean by the wreck of the American supertanker «Torrey Canyon» off the southwestern coast of England in March 1967: 120 thousand tons of oil spilled into the water and was set on fire with incendiary bombs from aircraft. The oil burned for several days. The beaches and coast of England and France were polluted.

In the decade following the disaster of the tanker «Torrey Canyon», more than 750 large tankers were lost in the seas and oceans. Most of these wrecks were accompanied by mass discharges of oil and oil products into the sea.

Fields of oil pollution, forming local zones, remain stable over time, so ocean circulations play a huge role in their spread. It is they that carry oil pollution into the cleanest areas of the World Ocean, including the Arctic Ocean.

Oil products that have entered the water degrade as a result of chemical, photochemical and bacterial decomposition, as well as the activity of certain marine organisms and higher plants. However, the «process» of natural neutralization of oil products is quite lengthy and can take from one to several months.

Thus, oil films are the technogenic factor that influences the formation and course of hydrological and hydrochemical processes in the surface layers of the water of seas and oceans.

Oil pollution also affects living organisms, screening solar radiation and slowing the renewal of oxygen in the water. As a result, plankton - the main food source of marine inhabitants - stops reproducing. Thick oil films often become the cause of death of sea birds.

Oil negatively affects the physiological processes occurring in living organisms, causes pathological changes in tissues and organs, disrupts the work of the enzymatic apparatus and the nervous system. Oil is a kind of narcotic for marine inhabitants. It has been noted that some fish, having once «had a taste» of oil, no longer strive to leave the poisoned zone. In addition, it negatively affects the taste qualities of the meat of marine inhabitants.

2. Pollution of the World Ocean also occurs through other types of industrial waste. About 20 billion tons of garbage have been dumped into all the seas of the world (1988). It has been calculated that on average 17 tons of waste fall per 1 km² of ocean. It was recorded that in one day 98,000 tons of waste were dumped into the North Sea (1987).

Up to 2 million sea birds and 100 thousand marine animals, including up to 30 thousand seals, die every year after swallowing some plastic items or becoming entangled in scraps of nets and ropes.

Germany, Belgium, Holland, England dump toxic acids into the North Sea, mainly 18 — 20% sulfuric acid, heavy metals in the sediment and deposits of wastewater containing arsenic and mercury, as well as hydrocarbons, including toxic dioxin (1987).

145 million tons of ordinary garbage were dumped from ships annually. England dumped 5 million tons of sewage effluent per year.

As a result of oil extraction from pipelines connecting oil platforms with the mainland, about 30 thousand tons of oil products leaked into the sea every year. The consequences of this pollution are not hard to see. A whole number of species that once inhabited the North Sea, including salmon, sturgeon, oysters, rays and haddock, have simply disappeared. Seals are dying, other inhabitants of this sea often suffer from infectious skin diseases, have deformed skeletons and malignant tumors. Birds that feed on fish or are poisoned by seawater are dying. Blooms of toxic algae were observed, which led to a decrease in fish stocks (1988).

In the Baltic Sea, 17 thousand seals died during 1989. Studies conducted showed that the tissues of the dead animals were literally saturated with mercury, which entered their bodies from the water.

In 1992, ministers of 12 states and a representative of the European Community signed a new Convention on the Protection of the Environment of the Baltic Sea Basin.

The Mediterranean Sea is threatened with the fate of turning into a garbage dump, a sewage pit for three continents. Every year 60 thousand tons of detergents, 24 thousand tons of chromium, and thousands of tons of nitrates used in agriculture enter the sea. 85% of the waters discharged from 120 large coastal cities are not treated, and self-purification (complete renewal of waters) of the Mediterranean Sea takes place through the Strait of Gibraltar (1989) over 80 years.

Due to pollution, the Aral Sea has completely lost its fishery significance since 1984. Its unique ecosystem has died.

3. Heavy metals. Large masses of these compounds enter the ocean through the atmosphere. For marine biocenoses, mercury, lead and cadmium are the most dangerous, since they retain their toxicity for an indefinitely long time. For example, mercury-containing compounds (especially methylmercury) are the most powerful poisons, acting on the nervous system, and pose a threat to the life of all living things. In the 1950s-60s of the 20th century, in the area of Minamata Bay (Japan), a mass poisoning was registered, the victims of which numbered tens of thousands of people who had eaten contaminated fish. The cause of the contamination was an enterprise discharging mercury into the bay's water.

The owners of the «Chisso» chemical plant in the town of Minamata on the island of Kyushu (Japan) for many years discharged wastewater saturated with mercury into the ocean. The coastal waters and fish turned out to be poisoned, and since the 1950s 1200 people have died, and 100 thousand received poisoning of varying severity, including psycho-paralytic diseases.

Up to 2 million tons of lead, up to 20 thousand tons of cadmium and up to 10 thousand tons of mercury enter the World Ocean per year. Once in seawater, heavy metals are concentrated mainly in the surface film, in the bottom sediment and in the biota, whereas in the water itself they remain only in relatively small concentrations. The surface film is especially significant here, usually extending to a depth of 50...500 microns. It is precisely in this region that all the equilibrium processes of mass exchange between water and the atmosphere take place.

Large amounts of heavy metals become concentrated in bottom sediments. This is confirmed by the fact that the concentration of metals in the sediment can be several orders of magnitude higher than in the water.

4. Radioactive waste. A serious ecological threat to life in the World Ocean and, consequently, to humans is posed by the burial of radioactive waste on the sea bottom and the discharge of liquid radioactive waste into the sea. Western countries (USA, Great Britain, France, Germany, Italy and others) and the USSR began actively using the ocean depths from 1946 in order to get rid of radioactive waste.

In 1959, the US Navy sank a failed nuclear reactor from a nuclear submarine 120 miles from the Atlantic coast of the USA. According to Greenpeace, the USSR dumped about 17 thousand concrete containers with radioactive waste into the sea, as well as more than 30 ship nuclear reactors.

The most severe situation has developed in the Barents and Kara Seas around the nuclear test site on Novaya Zemlya. There, in addition to a countless number of containers, 17 reactors have been sunk, including with nuclear fuel, several emergency nuclear submarines, as well as the central compartment of the nuclear icebreaker «Lenin» with three emergency reactors. The Pacific Fleet of the USSR buried nuclear waste in 10 locations in the Sea of Japan and the Sea of Okhotsk — not far from the shores of Sakhalin and from Vladivostok, including 18 reactors.

The USA and Japan dumped the waste products of nuclear power plants into the Sea of Japan, the Sea of Okhotsk and the Arctic Ocean.

The USSR discharged liquid radioactive waste into the Far Eastern seas from 1966 to 1991 (mainly near the southeastern part of Kamchatka and in the Sea of Japan). The Northern Fleet annually dumped 10 thousand m³ of such waste into the water.

In 1972, the London Convention was signed, prohibiting the dumping of radioactive and toxic chemical waste onto the bottom of seas and oceans. Russia also joined this convention.

6. Pollution of surface continental waters

In general terms, continental waters are usually divided into surface, soil, and underground.

Fresh waters are distributed extremely unevenly over the Earth's surface. Thus, in Europe and Asia, where 70% of the world's population lives, only 39% of the world's river waters are concentrated. In Russia's territory, 82% of river runoff falls on the northern regions of the country, which, due to climatic conditions, are poorly suited for the development of agriculture and are significantly less populated than the southern regions, which are economically more developed but experience a shortage of fresh water.

The uneven distribution of precipitation and the ever-increasing pollution of the hydrosphere have led to the fact that a shortage of fresh water is felt in many countries. At present about 300 million people experience problems related to the shortage of fresh water, and this number may increase tenfold by 2025.

Large amounts of wastewater, oil products and even liquid radioactive waste enter the rivers and lakes of various regions of the world.

1. Pesticides pose a particular danger. Once in lakes, they quickly disperse and practically do not threaten the 35 million Americans and Canadians who use lake drinking water. But moving up the food chain, agrochemicals reach a high degree of concentration. According to some scientists, in 1991 it was such that a meal of lake trout contained more toxic substances than all the water a person drinks in a lifetime, water in which the trout lives. About 40% of US water resources are unfit for drinking, and 34 rivers and lakes are so polluted that one can neither swim nor fish in them (1994).

2. Along the entire course of the Rhine, in the 70s — 90s of the 20th century, a huge number of treatment facilities were built, into which more than 50 billion dollars have been invested. Water quality gradually began to improve. However, a fire that occurred in November 1986 at the warehouses of the large chemical-pharmaceutical company «Sandoz» in Switzerland caused a release of about 30 tons of pesticides and oxidation products into the waters of the Rhine, as a result of which almost all living things in the river died as far as the city of Karlsruhe (Germany).

3. In Russia, out of 60 km³ of wastewater, at least a third enters the environment without any treatment at all. The most polluted water sources are in the south of Russia, as well as in the Moscow region. From the basin of the river Kuban, in 1991, 80% of the annual runoff was withdrawn for production purposes, and from the Don — 65%. From the Terek and the Ural, current economic management withdraws on average 50% of their runoff. More than half of the withdrawn water is returned to the rivers without treatment. The water does not have time to self-purify.

More than 1 million m³ of pollutants enter the Neva every day, including 20% of the city's sewage effluent discharged without treatment. In the Ural rivers — Chusovaya, Iset, Tagil and Tura — concentrations of copper, nickel, and chromium are 5 —20 times above the maximum permissible norms. The Yenisei, the Angara and the Lena are polluted with copper, zinc and phenols. The Ob is polluted along its entire course from source to mouth with oil products and phenol at concentrations from 5 to 17 times the maximum permissible concentration.

The waters of the Amur are polluted with copper and chromium (5—15 times above the maximum permissible concentration). The Volga is in a difficult ecological situation; 60 million people live on its banks, and 30% of the country's industrial and agricultural output is produced there. Water withdrawal from the Volga equals 33% (data for 1992). The volume of polluted wastewater discharged into its basin amounts to 37% of their total volume across the territory of Russia.

On the whole, about half of Russia's population in 1994 was forced to use water that did not meet hygienic norms and the requirements of the State standard.

A great threat is posed by liquid radioactive waste from the production of nuclear fuel and weapons-grade plutonium.

In 1991, the consequences became known of accidents that had occurred at the «Mayak» chemical plant near Chelyabinsk, where, since the late 1940s, weapons-grade plutonium had been produced, and radioactive waste had been discharged into the Techa river. In 1951 an accident occurred; 124 thousand people were irradiated, and 28 thousand received doses of up to 170 rem (rem — the biological equivalent of a roentgen), and a dose of 100 rem leads to chronic radiation sickness. In 1957 one of the tanks with liquid waste exploded, releasing into the air almost half the dose of the Chernobyl disaster. The radioactive cloud covered 23 thousand km², where 270 thousand people lived. In the Chelyabinsk, Sverdlovsk and Kurgan regions, 450 thousand people were irradiated. 2.5 Chernobyl doses are contained in the waste dumped into Lake Karachay, and in the water lens beneath it, which could flow into the rivers of the Ob basin and cause an ecological catastrophe in Western Siberia all the way to the Arctic Ocean.

Almost 20 Chernobyl doses are contained in tanks like the one that exploded in 1957. There are also 200 burial sites with 500 thousand tons of solid waste and 500 billion m³ of radioactive water in a series of artificial reservoirs in the upper reaches of the Techa river (1991 data).

In 1996, 20 European countries agreed to combine efforts to reduce harmful discharges into shared rivers and lakes. The agreement covers 150 rivers and 20 lakes, including the Ural and the Dnieper, and the Aral Sea.

7. Self-purification of water bodies

The factors of self-purification of water bodies are diverse. Conventionally they can be divided into three groups: physical, chemical and biological.

Among physical factors, the primary importance belongs to dilution, dissolution and mixing of incoming pollutants. Good mixing and reduction of concentrations of suspended particles is ensured by the intensive flow of rivers. Self-purification of water bodies is aided by the settling of insoluble sediments to the bottom, as well as the settling of polluted waters. Microorganisms, under their own weight or by settling on other organic and inorganic particles, gradually sink to the bottom, are subjected to the action of physical factors, which promotes the rapid die-off of the polluting microflora. This process is slowed down by a decrease in water temperature, which favors the prolonged preservation of bacteria and viruses that have entered a water body. Thus, in zones with a temperate climate, a river self-purifies within 200-300 km from the site of pollution, while in the Far North — within 2 thousand km.

Disinfection of water occurs under the influence of the Sun's ultraviolet radiation. The disinfecting effect is achieved by the direct destructive action of ultraviolet rays on the protein colloids and enzymes of the protoplasm of microbial cells, as well as on spore-forming organisms and viruses.

Among chemical factors of self-purification of water bodies, the oxidation of organic and inorganic substances should be noted. An assessment of the self-purification of a water body is often made in relation to easily oxidizable organic matter (determined by biochemical oxygen demand — BOD) or by the total content of organic substances (determined by chemical oxygen demand — COD). An assessment of self-purification is also made by the content of specific compounds or their groups (phenols, hydrocarbons, resins).

The sanitary regime of a water body is characterized above all by the amount of oxygen dissolved in it. It should be no less than 4 mg per 1 liter of water at any period of the year for water bodies of the first and second types. The first type includes water bodies used for the drinking water supply of enterprises, and the second — those used for swimming, sports events, as well as those located within the boundaries of populated areas. Water bodies intended for the preservation and reproduction of valuable fish species must contain no less than 6 mg of dissolved oxygen per liter of water.

Among the biological factors of self-purification of a water body are algae, mold and yeast fungi. However, phytoplankton does not always have a positive effect on self-purification processes: in certain cases, the mass development of blue-green algae in artificial water bodies can be regarded as a process of self-pollution.

The self-purification of water bodies from bacteria and viruses can also be aided by representatives of the animal world. Thus, the oyster and certain amoebas adsorb intestinal and other viruses. Every mollusk filters more than 30 liters of water per day.

A multistage process, sometimes stretching over a long period of time, is the self-purification of water from oil. Microorganisms actively oxidize aromatic hydrocarbons, as a result of which aromatic alcohols and acids are formed. Part of the organic matter from the oil film passes into the water in the form of soluble compounds, and part is deposited on the bottom as resinous substances. Treated wastewater from oil-refining plants turned out to be toxic to algae and daphnia even after 6—9 months of settling.

8. Drinking water

The World Health Organization warns that 80% of diseases on the planet are caused by the consumption of poor-quality drinking water. The problem of clean water confronts many countries. Every fifth American in 1991 drank water polluted with toxic substances (50 million people).

In Russia, every fifth sample of tap water does not meet sanitary-chemical norms, every eighth — microbiological ones, and 90% of drinking water in the country does not meet recommended sanitary norms and chemical and microbiological standards. This water is used by 70% of cities and populated areas. What spoils our lives the most is chlorine, used for water disinfection. Although at first it saves us from infections, later its derivatives begin to slowly kill us, since they have a carcinogenic, mutagenic effect and affect heredity. According to American researchers, people who constantly consume chlorinated water have a 21% higher probability of bladder cancer and a 38% higher probability of rectal cancer than those who drink purified but unchlorinated water. Nevertheless, in the USA 86% of the population uses chlorinated water (2002).

In Japan water is purified with the help of ozone, although one of its drawbacks is that it does not have as long-lasting an effect as chlorine compounds.

Before use, tap water should be purified. To free it from chlorine, it is advisable to let the water settle (from several hours to a day). To free it from microbes and chlorine, water must be boiled for no more than 1 — 3 minutes.

Recently, various household filters have come into use for further purification of water. A filter must remove microbes, chlorine and its derivatives, heavy metals, oil products, nitrates and nitrites, and pesticides. However, secondary contamination of water by microorganisms that have settled on the filter itself is also dangerous.

The Japanese and Americans are now switching to electrochemical filters. One such filter is the Russian-English filter «Izumrud». Its principle of operation is based on a chemical reaction proceeding under the action of a strong electric field in the presence of a catalyst. As a result, the water is completely purified of microorganisms, organic compounds and heavy metal ions.

The domestic filter «Aquaphor», made in the form of a faucet attachment, has proven itself well. In this filter, deep purification of water is achieved through the use of aqualen — a new-generation sorbent. This substance is used in medicine to purify blood. The filter effectively counteracts any pollution: bacterial, heavy metals, phenol, chloroform, benzopyrene.

Purification of drinking water.

The main elements of water purification:

• introduction of copper sulfate and subsequent aeration to remove unpleasant taste and odor;

• first chlorination to remove disease-causing microorganisms

• coagulation and precipitation of pollutants from water;

• filtration to remove disease-causing microorganisms;

• final chlorination to complete the destruction of microorganisms.

To prevent the growth of algae and aquatic plants, copper sulfate (blue vitriol) is introduced into storage reservoirs. Next, the water is subjected to aeration (i.e. it is exposed to air), by spraying it in the air with rows of fountains or passing it through a mesh. After aeration, gaseous chlorine is added to the water to destroy disease-causing microorganisms. The finest suspended particles that do not dissolve in water, which give it one color or another, are called colloidal. To remove these particles from water, a process called coagulation is used. At the first stage of coagulation, either ammonium sulfate or iron is added to the water, as a result of which a flaky suspension forms in the water. Settling to the bottom of the settling tank, it mixes with the particles suspended in the water and captures them. The sediment from the bottom of the settling tank is removed with scrapers.

At many water treatment plants, a small amount of crumbled activated carbon, which binds colloidal particles present in the water well, is introduced into the water together with ammonium sulfate or iron. In addition, treatment with activated carbon not only decolorizes the water, but also significantly improves its taste and odor

After passing through the settling tank, the water is filtered through a layer of sand, i.e. it is purified of relatively large particles, which could clog the filter that ensures the effectiveness of the next stage of purification. Filtration through sand ensures further removal of particles from the water, but the main purpose of the filter is to capture and retain bacteria, viruses and other microorganisms. The sand in the filters must be periodically rinsed in order to preserve its ability to effectively retain microorganisms.

Despite the high efficiency of sand filters for removing microbes and viruses from water, the water is not completely freed of them. An additional stage of purification - the second chlorination of water - destroys any microorganisms remaining after filtration through sand. Chlorine also reacts with ammonia, which may be present in the water.

This leads to the appearance of «free» (i.e. unreacted) chlorine in the solution. One of the reasons why chlorination is such a preferred disinfection method for public water sources is that this excess or residual chlorine provides a quick and simple test for its presence.

It should be noted that as a result of chlorination, a small amount of chlorinated hydrocarbons may form in water, some of which have been found to have carcinogenic properties.

One of the alternatives to chlorination of water is its disinfection with the help of ozone. Ozonation, like chlorination, is carried out simply by bringing water into contact with the gas. Unlike chlorination, in which chlorine can combine with hydrocarbons contained in the water, in ozonation chlorinated hydrocarbons are not formed; on the contrary, ozone can destroy hydrocarbons present in the water through their oxidation.

9. Methods of water purification

Methods of water purification, for all their diversity, can be divided into three groups: mechanical, physico-chemical and biological.

Mechanical purification

is used primarily for separating solid and suspended substances. The most typical methods in this group are straining, settling, inertial separation, filtration and oil-trapping (as a variety of settling), — all of them are used for treating wastewater. For water treatment, settling and filtration are the most widely used methods from this group.

1. Straining — the primary stage of wastewater treatment — the water is passed through special metal grates with a spacing of 5—25 mm, installed at an incline. Periodically they are cleaned of sediment with the help of special rotary devices.

2. Settling takes place in special tanks, which, according to the direction of water movement, are divided into horizontal, vertical, radial and combined ones. Common to them is the discharge of purified water from the upper part of the settling tank and the gravitational principle of particle settling, with particles collecting at the bottom. A variety of settling tank is the sand trap, used for separating sand particles in the effluents of foundry shops, and scale — in the effluents of forging-and-pressing and rolling shops, etc. As a rule, the residence time of water in sand traps is much shorter than in settling tanks, where it can reach up to 1.5 hours (for wastewater).

3. Inertial separation is carried out in hydrocyclones, the operating principle of which is similar to cyclones for gas purification. Open and pressure hydrocyclones are distinguished, with the former having greater capacity and lower head losses, but losing out in purification efficiency (especially for fine particles).

4. Filtration is most often carried out through porous bonded or unbonded materials. As a rule, filters purify water of finely dispersed impurities even at low concentrations. Filter materials are quite diverse: quartz sand, gravel, anthracite, metal particles, etc. Sand filters — are the main purifiers in water treatment. An effective filter made of sand-and-gravel fractions bonded with special resins was developed by a group of staff from RGUPS (L.F. Bykadorov, V.I. Korenevsky, T.A. Shatikhina).

5. Oil traps in their simplest design are settling tanks in which the discharge of purified water occurs from below, while the oil film collects on top.

Physico-chemical purification

ensures the separation of both solid and suspended particles and dissolved impurities. It includes many different methods, the most important of which are extraction, flotation, neutralization, oxidation, sorption, coagulation, ion-exchange methods and others.

1. Extraction — the process of separating impurities in a mixture of two insoluble liquids (extractant and wastewater). For example, in special columns (hollow or packed with filler), the effluent is mixed with an extractant that removes harmful substances: for example, phenol is removed with benzene.

2. Flotation — the process of impurities (most often oil products) floating up when enveloped by air bubbles fed into the wastewater. In some cases a reaction occurs between the bubbles and the impurities. A variant of the method is electroflotation, in which the water is additionally disinfected due to redox processes at the electrodes.

3. Neutralization — treatment of water with alkalis or acids, lime, soda, ammonia, etc. in order to ensure a set value of the hydrogen index pH. The simplest way to neutralize wastewater — is mixing acidic and alkaline effluents, if they are available at the enterprise.

4. Oxidation — is used both in water treatment and in the treatment of wastewater for disinfecting water and destroying toxic biological impurities. The most widespread method — chlorination — is fraught, as noted earlier, with the appearance of dioxins (especially with a forced increase in the chlorine dose in summer or during the flood period, so-called hyperchlorination). It is necessary to gradually switch to other methods, for example, to a combination — ozonation and chlorination. Ozonation — is expensive and has a shorter-lasting effect, but it is more promising. At present combinations of reagents with ultraviolet treatment of water are being worked out. In any case, water used for drinking and containing the characteristic smell of chlorine should be settled and boiled before use, as a minimum.

5. Sorption, as in the treatment of gas emissions, is capable of ensuring effective purification of water from salts of heavy metals, unsaturated hydrocarbons, particles of coloring substances, etc. The best sorbent here too is activated carbon; this also applies to various minerals (shungite, zeolite, etc.), specially treated sawdust, soot, titanium particles, etc. Many household water filters operate on these sorbents: «Rodnichok», «Rosa» and others.

6. Coagulation — treatment of water with special reagents in order to remove undesirable dissolved impurities. Widely used in water treatment. Treatment is carried out with aluminum or iron compounds, in which case solid insoluble impurities form, which are separated by ordinary methods. Electrocoagulation is widely used for wastewater, in which ions form near the electrodes (a result of anodic dissolution of the electrode material) that react with impurities. This is how heavy metals, cyanides and others are separated.

7. Ion-exchange methods are quite effective for purification from many solutions and even from heavy metals. Purification is carried out with synthetic ion-exchange resin and, if it is preceded by mechanical purification, makes it possible to obtain metals extracted from water in the form of relatively pure concentrated salts.

Recently abroad (especially for water treatment), reverse osmosis installations have been used. In them, water is forced through a set of special micro-membranes at high pressure (up to 30 MPa). These installations are extremely effective as final stages (i.e. for fine purification). But they are quite expensive and energy-intensive.

Biological purification

is possible in natural conditions and in artificial structures. In both cases organic impurities are processed by reducing agents (bacteria, protozoa, algae, etc.) and are turned into mineral substances. Under natural conditions, purification is carried out at filtration or irrigation fields (through the soil) or in biological settling ponds, in which the concentration of pollutants is reduced to the required norms due to self-purification processes carried out by microorganisms, algae, and invertebrates; ponds can have air blown in (with artificial aeration).

Higher aquatic plants (HAP) for water purification (reeds, rushes, water milfoil, duckweed, etc.) are of great interest. The ability of HAP to accumulate, utilize, and transform many pollutants makes them indispensable in the overall process of self-purification of water bodies. Recently a tropical flowering plant — Eichornia crassipes — water hyacinth, has become widely used on the territory of the Russian Federation. Water hyacinth can be used where, for at least two months, the effluent temperature is no lower than 16 °C. Water hyacinth is capable of absorbing everything unwanted that pollutes water: oil products, phenols, sulfates, phosphates, chlorides, nitrates, surfactants, alkalis, heavy metals... It improves BOD and COD. It destroys pathogenic putrefactive microorganisms, normalizes the total microbial count and the coli index. Water hyacinth can be used for the additional treatment of wastewater at municipal treatment facilities, as well as in agricultural and industrial effluents. There is experience of using this plant to purify the Temernik river (Rostov-on-Don).

Aeration tanks, oxytanks, methane tanks and biofilters can be used as artificial structures.

1. Trickling biofilter

The trickling biofilter — is the most widespread type of bioreactor with a fixed biofilm, used for treating effluents. Essentially, it is a reactor with a fixed bed and counterflow of air and liquid. Biomass grows on the surface of the packing in

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Часть 1 Lecture 3: Pollution and Protection of the Hydrosphere. Properties of Water, Pollution and Purification of
Часть 2 10. Pollution of surface and groundwater in Omsk - Lecture