Structure and properties of sewage

Sewage of industrial enterprises

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 %.


Structure and properties of sewage

Water is turned into waste water by the addition of water-carried waste from private households, business, and industry. The mixture of water and waste is generally called sewage. The composition of sewage depends on it source. Domestic sewage consists of used water containing human excreta and all kinds of substances typical of domestic activities and hospitals. Industrial sewage is composed of used water and solid and liquid wastes resulting from the operation of slaughterhouses, dairies, tanneries, paper mills, food processors, and various other industrial enterprises. Many of these waste waters may be harmful to public health and cause epidemics of various kinds.

Sewage contains solid and liquid pollutants in suspension and solution. Untreated or improperly treated sewage that is discharged into rivers, lakes and the open sea, may cause the formation of sludge banks of obnoxious matter. Sludge banks are primarily found in so-called dead spaces of two- or three-dimensional flow fields, and this may also be the case in waste water treatment plants. From a chemical point of view, sewage contains matter of animal, vegetable and mineral origin. Organic matter contributes 40 to 70 % of the solids in urban sewage and is readily decomposed by biological or chemical methods. This decomposition process may take place under conditions that require oxygen, thereby endangering fish life in rivers, lakes and coastal waters. Other decomposition process does not require oxygen, but may result in objectionable odors and poisoning of the water, that will also endanger fish life.

Waste water is collected and transported to treatment plants by a system of pipes and conduits called sewers. Sewers are graded so that the sewage may flow downstream at a rate sufficient to prevent particulates from settling out.

Sewage of chemical manufactures is polluted with various organic and inorganic substances. For example, depending on kind of manufacture, characteristic pollutions can be:


Source of pollution Structure of pollution
Manufactures of mineral and inorganic salts Inorganic acids, alkalis, salts (fluorides, sulfates, phosphates, etc.)
Manufactures of the basic organic and petrochemical synthesis Fat acids, aromatic compounds, spirits, aldehydes, ethers, etc.
Oil refining factories, the enterprises on thermal processing of firm fuels Mineral oil, oils and pitches, phenols, surface active substances, etc.
Manufactures of synthetic pitches, polymers, synthetic fibres, etc. High-molecular substances, monomers, particles of polymers, etc.


Except for the dissolved organic and inorganic substances sewage can contain colloidal impurities, and also suspended (fine dispersed and rough dispersed) substances, which density can be less or more the density of water. In some cases sewage contains the dissolved gases (hydrogen sulphide, etc.). More often sewage represents the complex systems containing mixes of various substances.

The degree of damage of sewage depends on toxicity of substances polluting it. Sewage of high toxicity contains salts of heavy metals, cyanides, hydrogen sulphide, cancerogenic substances, benzene and many other substances.

Sewage of chemical manufactures can contain inflammable and explosive substances, and also the compounds, polymerized in a water solution, that can lead to contamination of pipelines.

It is necessary to take into account aggression of sewage in relation to materials of pipelines, sewer collectors and devices of clearing constructions. Aggression of sewage depends from рН, presence of some salts and gaseous products. Sewage of manufactures of acids, phosphoric and other fertilizers, oil refining factories, manufacture of synthetic fat acids and etc. concern to number of very aggressive sewage.

Frequently sewage contains the substances possessing sharp, unpleasant smell (sulfides, disulfides, hydrogen sulphide, merkaptides, etc.). A lot of sewage is painted owing to pollution by dyes or the substances having painting.

Presence of surface active substances in sewage causes their foaming ability.

Hit of household waters in industrial sewage leads to biological pollution of them.

The temperature of sewage can change over wide range.

Methods of research of sewage. Complex structure, wide interval of impurities concentration, change of structure of sewage in time complicate the research of qualitative and quantitative structure of sewage. Research of sewage of unknown structure (for example, biologically cleared waters) is especially complex.

Frequently at the analysis of sewage there are the difficulties connected to presence of accompanying and preventing substances, not stipulated in standard techniques.

Special value has application of automatic devices, which:

- Allow to increase labour productivity of chemists-analysts;

- To lower cost of analyses;

- To carry out the continuous control over structure of sewage and work of clearing constructions;

- Immediately to fix any infringements.

The general parameters of pollution. To the general parameters of sewage pollution are concerned:

- The parameters, describing the general properties of water (organoleptic - color, taste, smell, transparency, turbidity; physical and chemical - density, optical density, chromaticity, рН, temperature, electrical conductivity, alkaliness, acidity viscosity, surface tension, etc.);

- Insoluble impurity (the content of the suspended substances);

- Dissolved substances (the general content of organic and inorganic impurities, "organic" carbon, definition of bichromate and permanganate oxidability, biochemical consumption of oxygen, etc.).


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