Sources of contamination of water and their prevention

Pure and uncontaminated water does not occur in nature. It contains impurities of various kinds of natural and man made. The natural impurities dissolved gases (e.g. carbon dioxide, nitrogen, hydrogen sulphide etc which may be pick up during rainfall), dissolved minerals (e.g. salts of calcium, magnesium, sodium etc), which are naturally constitutes of water following its contact with soil, and suspended impurities (e.g. clay, silt, sand and mud) and microscopic organisms. These impurities are derived from the atmosphere, catchments area and the soil.
A more serious aspect of water pollution is that caused by human activities urbanization and industrialization.
The sources of pollution resulting from
1. Sewage- It contains 99.9% of water and 0.1% of solid contains and mostly contains decomposable organic matter and pathogenic agents. The offensive nature of the sewage is mainly due to the organic matter.
2. Industrial and trade wastes- Which contain toxic agents ranging from metal salts to complex synthetic organic chemicals.
3. Agriculture and livestock pollutants, which comprises, chemical fertilizer, pesticides, animals dung and urine.
4. Physical pollutants viz heat (thermal pollution) and radioactive substances. The indicators of pollution include the amount of total suspended solids, biochemical oxygen demand (BOD) at 200C.

Prevention of water pollution- Various legislative measures should be employed to control the water pollution. Strict check should be maintained on the quality of drinking water. Should be introduced improved methods for handling and disposal of sewage, garbage and night soil. To control the epidemics and other diseases, proper methods for sterilizing water supplies drawn from shallow well safeguard the health of millions of people are enable to sporadic outbreaks of epidemics to be contained. The effluents from the industries should be neutralized and properly treated and suspended matter to removed by settlement or filtration. From the industrial effluents, specific poisons have to be removed by chemical methods before discharge into streams. Public sewers should be connected to biological treatment plants.

Farm sewage and refuse treatment-
It is estimated that one gram of faeces may contain about 1000million of E. coli, 10-100 million of faecal Streptococci, and 1-10million spores of Cl. perfringens besides several others. The average adult person excretes daily some 100grams of faeces.
Raw sewage or inadequately disposed sewage should not be discharged into rivers, sea or other sources of water supply. The oxygen in the water supply is used up by the numerous aerobic bacteria, which are found in sewage. Depletion of oxygen may cause to the death of the plant and animal life in the water. The water may yield an offensive smell because of the release of hydrogen sulphide.
The main aim of sewage disposal is to “stabilized” the organic matter so that it can be disposed off safely, and to convert the sewage water into and effluent of an acceptable standard of purity, which can be disposed off into land, rivers or sea.
Grading of sewage- The strength of the sewage is expressed in terms of-
Biological oxygen demand (BOD)- it is the most important test done on sewage. It is defined as the amount of oxygen absorbed by a sample of sewage during a specified period, generally 5days at a specified temperature, generally 20 days for the aerobic destruction or use of organic matter by living organisms. BOD values range from about 1mg/l for natural water to about 300mg/l for untreated water.
Chemical Oxygen Demand (COD)- The COD test measures the oxygen equivalent of that portion of the organic matter in a sample, which is susceptible to oxidation by a strong chemical oxidizer. If wastes contain toxic substances, this test may be the only practical method for determining the organic load.
Suspended solids- The suspended solids are yet amount of suspended solids is 100mg/l, the sewage is said to the weak, if the amount is 500mg/l the sewage is said to be strong.


For this reason, modern refuse treatment is of great necessity. And water must be consumed by treatment only