3. Sewage of industrial enterprises

3.1. Natural water

One of the most valuable natural riches is water. Without water the life is inconceivable. Water is the building material of cells, the solvent delivering the necessary nutrients to organisms and removing waste products of ability to live from organisms. Water is an integral part of economic, industrial and agricultural activity of people.

The total of water on the ground (volume of hydrosphere) is estimated in 1400 millions km³. However stationary stocks of fresh waters, suitable for use, including river, lake and underground, make only 0,3 % of volume of hydrosphere (about 4 million km³).

Water on our planet is in condition of circulation. Under action of a solar energy water evaporates from a surface of the World Ocean and a land, and then drops out as an atmospheric precipitation. From a surface of World Ocean evaporates about 448 thousand km³ of water in year, and quantity of the atmospheric precipitations which is dropping out on surface of the seas and oceans, makes about 412 thousand km³ one year. The difference represents a river drain from a land in the seas and oceans.

The one time stock of water in all rivers of globe makes approximately 1200 km³, and this volume renews on the average each 12 day. The river drain consists from underground and superficial drains. The most valuable to use is the first source, but it makes the smaller part from total amount of the river drain.

In nature the pure water is not present. Even an atmospheric precipitation contain up to 100 mg / l of impurity.

On a degree of a mineralization water shares on 4 groups:

- water of low mineralization (up to 200 mg / l of salts);

- water of average mineralization (200-500 mg / l);

- water of the raised mineralization (500-1000 mg / l);

- water of high mineralization (over 1000 mg / l).

Water of the majority of Kazakhstan river concerns to the first and second groups. The content of salts in river water changes within one year. During the high water content of salts is reduced.

Waters of open reservoirs are polluted with humus substances. There are the complex organic compounds which are contained in river waters and content on the average makes 5-10 mg / l, in lake waters changes from 1 up to 150 mg / l. Natural waters contain also colloidal, fine dispersed and rough dispersed impurities. It is necessary to note the biological pollution of reservoirs (microorganisms, the elementary organisms, seaweed, etc.).

Natural waters contain the dissolved gases - oxygen, carbon dioxide, etc. The рН size in waters of rivers and lakes, as a rule, makes 6,5-8,5.

Lake water usually contains few suspended substances. Salt content of waters of various lakes essentially differs. For example, general rigidity of water of lake Baikal makes about 1,1 mg - eqv/ l, lakes Ladoga - 0,5 mg - eqv/l, and lake Balkhash - 14,4 mg - eqv/l.

Sea water contains on the average 35 g/l of salts though in the various seas the salt content strongly changes: in Baltic Sea - 5 g/l, in Black - 18 g/l, in Red - 41 g/l. The structure of these salts includes chlorides of Na, K, Ca - about 89 %, sulfates of Na, K, Mg - about 10 %, carbonates of Na and Ca - up to 1 %.