WATER SUPPLY
Water is an important part of nature which surrounds us and of those natural conditions we are changing constantly and more intensively: the flora, the soil, the mountains, mineral resources, the deserts, the marshes, the steppes and the taiga.
Water passes through a very interesting natural cycle. The atmosphere which surrounds the earths surface contains water which varies in amount in direct proportion to the temperature of its gases. Water is also evaporated into atmosphere. Atmosphere which has become saturated with water precipitates its moisture when the temperature lowers. This phenomenon is termed rainfall. The moisture falls to the earth and finds its way into a number of reservoirs provided by nature.
Vast depressions in the earth are filled with water through the medium of natural water sources such as rivers lakes, etc. over the earths surface. These bodies of water are classified as inland lakes and are excellent sources of water.
Sometimes the rainfall finds its way into the soil and forms water bodies at various levels because of the impervious nature of the undersoil. Often a water body deep in the soil consists of a sand or gravel stratum which connects or empties into the basin of an inland lake and provides a splendid source of water supply through the medium of a drilled well.
Man uses water for domestic and sanitary purposes and returns it to the source through sewage disposal system. Industry likewise replaces water diverted to its use. Hence the cycle is completed but it is of prime importance that the supply be protected against pollution, for if it fouls no one can predict how disastrous may be the results.
An adequate supply of pure, wholesome and palatable water is essential to the maintenance of high standards of health and to provide the convenience modern society demands. In some localities water is available in unlimited quantities and converting it to use is not a difficult problem. This is especially true of towns situated on large inland lakes or rivers. On the other hand there are cities where geographical location requires elaborate systems of water supply, and to provide a satisfactory supply of water in these localities becomes a large engineering task.
The importance of a sufficient supply of water for domestic and industrial purpose has long been a deciding factor in the location of cities. The earliest settlers realized this need and took advantage of natural water sources by establishing colonies in close proximity to them.
Water may be taken from any sources of water for human consumption after it has undergone a preliminary treatment to assure its purity. As mans communities grew in population, the demand for water increased and the need for protection of the source of water supply against the possibility of contamination became evident. Progress and civilization have called for elaborate and various systems and methods of water treatment.
Ex.2 Answer the questions.
|
|
|
1. What cycle does water pass through?
2. How are vast depressions filled with water?
3. What bodies of water are classified as inland lakes?
4. What does a water body consist of?
5. How is splendid source of water got?
6. What purposes does a man we water for? How does a man we water?
7. What is essential to the maintenance of high standards of health?
8. When does become a large engineering taste to provide people with water?
9. What is done to assure purity of water?
TEXT 9
Ex.1 Read the text and translate it into Russian.
SEWERAGE
The problem of protecting natural water resources has grown very pressing for many countries since the beginning of the second half of the 20th century. The development of human society, the growth of civilization and social and technical progress have resulted in the changing of the composition of natural water resources. The rivers, lakes and ground-waters contain today a considerable amount of the products of mechanical, chemical and biological pollution.
The waste products that result from the daily activities in a community are of two general types: namely, the liquid waste, known as sewage and the solid wastes, known as refuse. The different wastes of which sewage is composed are the following: the wastes from lavatories, baths, sinks, and laundry tanks in residences, institutions, and business buildings; certain liquid wastes from various types of manufacturing or industrial plants, and, in many communities, the surface run-off that results from storms or street-flushing operations.
Sewage may also be divided according to its source into the following three classes. The sewage from residences, institutions and business buildings is called domestic sewage, sanitary sewage or house sewage; that resulting from manufacturing or industrial processes is known as industrial waste; and that from run-off during or immediately following storms is called storm sewage. A combination of domestic sewage, industrial waste and storm water is called combined sewage.
Both sewage and refuse must be removed promptly in order to avoid endangering the health of the community and also present decomposition of the materials of animal or vegetable origin and the subsequent production of nuisances and odours.
The removal of all kinds of sewage is usually accomplished by means of sewers. The sewers are placed in the streets at several feet below the ground surface. The general process of removing sewage is designated as sewerage and the entire systems of sewers including a sewage treatment plant is known as a sewerage system.
The method of sewage treatment to be adopted in a particular case will depend almost entirely on local conditions. It may consist only of the discharge of the raw sewage into a stream or a large body of water. The usual methods of sewage treatment consist either of preliminary treatment alone or of primary treatment followed by secondary treatment.
During primary treatment the larger and heavier solid particles settle out from the liquid. These solid particles that settle out form a slimy paste which is known as sludge.
The partly clarified sewage that has been given primary treatment generally contains much decomposable materials. Therefore, further treatment which is known as secondary treatment, is usually required.
An auxiliary treatment which may be used with either primary or secondary treatment is disinfection or the killing of the most of the bacteria in the sewage by means of chemicals.
