WATER POLLUTION AND ITS CAUSE AND TREATMENT

                  WATER POLLUTION

 The water pollution is caused by the addition of organic and Inorganic chemicals as well as the biological materials which change the physical and chemical properties of water. This harmful process is called water pollution.

The water pollution is caused by many sources such as sewage matter, industrial wastage, agricultural water domestic wastage, hot water of thermal plant and nuclear reactors etc. 

Note : A mere 0.1 per cent impurities make domestic sewage unfit for human use (Figure).

   1)  Domestic sewage primarily contains biodegradable organic matter. 

    2)  Water hyacinth (Eichhornia crassipes), the world's most problematic aquatic weed, also called 'Terror, Bengal'. 

  3) Unlike domestic sewage, waste water from industries like petroleum, paper manufacturing, metal extraction and processing, paper manufacturing, metal extraction and processing, chemical manufacturing, metal extractie and processing, chemical manufacturing, etc., often contain toxic substance, notably heavy metals (defineda elements woth density > 5 g/cm³ such as mercury, cadmium, copper, lead, etc.) and a variety of organ compounds. 

      À) Water having D. O. content below 8.0 mgl may be considered as contaminated and below 4.0 mgl heavily polluted.

   B).  D. O. is measured by oximeter 1. Biochemical Oxygen Demand (B.O.D.): 

The water pollution by organic wastes is measured in terms of Biochemical oxygen demand. It is the amount dissolved oxygen (D.O. - Dissolved Oxygen) needed by bacteria in decomposing the organic was present in water.

 B.O.D. increased =water polluted 

B.O. D.  Directly proportional to input of organic wastes

 If B.O. D. is increased dissolved oxygen is decreased in water. Higher amount of organic waste increase the rates of decomposition in water. O² is rspidly consumed by microbes,thereby causing drop in D.O content in water

Note: Daphnia is the indicator of B.O.D.

Graph of indicator

  2.  Chemical Oxygen Demand (C. O. D.):

It is the oxygen requirement by chemical for oxidation of total organic matter (biodegradable +

non biodegradable) in water.

Note : C. O. D. value is always higher than B. O. D. value.

 3. Biological magnification :-

The non biodegradable pollutant like Al, Hg, Fe, D.D. T. pesticides, phenolic compound ABS (Alkylbenzene sulphonate) are not decomposed by micro-organisms.

They get accumulated in tissue in increasing concentration along the food chain is called biological magnification. The highest concentration occur's in top consumer.

The concentration of DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts per billion) in water, it can ultimately can reach 25 ppm (ppm - part per million) in fish-eating

birds, through biomagnification

Water ► Phytoplankton ZP > Small fish ► Large fish Fish eating birds

Note : High concentration of DDT distrub calcium metabolism in birds, which causes thinning of egg shell and

their permature breaking, eventually causing decline in bird populations.

    4.  Eutrophication :-

The process of nutrient enrichment of water and consequent loss of species diversity (or death of aquatic

animals) is referred to as eutrophication and lake is known as eutrophic lake. In this process presence of

nutrients in lake stimulates growth of algae (algal bloom) increase organic loading and bring about reduction

in the oxygen content of water causing death of aquatic animals.

Note :

Eutrophication is the natural aging of a lake by biological enrichment of its water. Natural aging of a lake may span thousands of years and lake finally converted into land due to deposition of silt. Pollutants from man's activities like effluents from the industries and homes can radically accelerate the aging process, this phenomenon is called accelerated eutrophication.

During eutrophication due to organic matter lake become shallow and warmer. Due to warming of lake water, growth of cold water organisms stop and growth of warm water organisms increases.

B.O.D. of Eutrophic lake is very high.

Water Pollution can be caused by the following man made sources

1. Household Detergents : - The household detergents include the compounds of phosphate, nitrate, ammonium

and alkyl-benzene sulphonate etc. harmful substances which are gathered in water.

Inorganic phosphorus and Nitrogen - The growth of algae is very fast due to presence of higher concentration of these substances. After the death of algae organic matter increase. The presence of large amount of organic material leads to eutrophication because of this, amount of oxygen in water decreases. Some of the algae also secrete toxic materials. The drinking of such polluted (toxic) water causes death of the cattles.

For the control of this pollution, lime ferric chloride, etc. are used to precipitate the phosphate. Zirconium is considered best for this purpose.

II. Industrial waste :- The wastes of industries are discharged into the running water of rivers and canals

Industrial waste mainly contains inert suspended particles such as dust, coal, toxins like acid, base phenols. cyanides, mercury, zinc etc., inorganic reduced material like-ferrous salts sulphide, oils and other residues of organic material and hot water. The water polluted by mercury, lead etc metals when used which causes

disorganisation of nervous system. It means it produces insanity. The minamata disease was caused in Japan by eating of polluted fishes from the water polluted by mercury. So, many humans died because of this disease.

For the control of the industrial wastes and toxic components should be purified before draining into rivers, lakes and ponds or sea. So the water pollution by industrial effluents can be controlled by suitably treating the pollutants.

III. Sewage - Sewage contains highest amount of carbonic materials and biological material, as pollutants.

These carbonic materials increase the number of decomposers like bacteria and fungus. The acceleration of microbial activity increases BOD of water.

BOD is very less in pure water. The higher BOD is the indication of water pollution and the water of polluted reservoir can not be utilized and very bad smell spreads around the locality. The infections or infectious diseases also takes place.

Method of water purification :

The industrial and municipal waste water are treated in "Effluent Treatment Plant" (ETP).

Generally following treatments are given in ETP.

1. Primary treatment :- This physical process involves the separation of large debris (particles), followed by

sedimentation intanks.

2. Secondary treatment :- This is a biological process and is carried out by microorganism. In this process, the

waste water is pumped in shallow stabilisation or oxidation ponds or activated sludge chamber, where the

microbes oxidise its organic matter. The process results in release CO, and this CO, is used by algae in photosynthesis. In photosynthesis process algae release O²,

3. Tertiary treatment :- This physiochemical process removes turbidity in waste water caused by the presence of

nutrients (nitrogen, phophorus etc.), dissolved organic matter, metals or pathogens.

This step involves chemical oxidation of waste water by strong oxidising agents, such as chlorine gas, perchlorate

salts, ozone gas and UV radiations.

After tertiary treatment, the waste-water can be discharged into natural water sources or used irrigation.