Water Pollution & Soil Pollution | Chemistry for JAMB PDF Download

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, agriculture wastage, domestic wastage, hot water of thermal plant and nuclear reactors etc.

• Water having D.O. (Dissolved Oxygen) content below 8.0 mgL^–1 may be considered as contaminated and below 4.0 mgL^–1 as heavily polluted.
• 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 of dissolved oxygen (D.O. = Dissolved Oxygen) needed by bacteria in decomposing the organic wastes present in water.

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

• Daphnia is the indicator of B.O.D.
• Biochemical oxygen demand [BOD] is the amount of oxygen taken up by the micro organisms present in water. BOD is measured by keeping a sample of water containing known amount of oxygen for 5-days at 20ºC in the dark. At the end of this period, the oxygen content is again measured. A high BOD indicates intense level of microbial pollution.

Fig.: Effect of sewage discharge on some important characteristics of a river

2. Chemical Oxygen Demand (C.O.D.) :
It is the oxygen requirement by chemicals 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 (Alkyl benzene sulphonate) are not decomposed by micro-organisms.

They get accumulated in tissue in increasing concentration along the food chain, called biological magnification. The highest concentration occurs in top consumer.

Note : High concentration of DDT disturb calcium metabolism in birds, which causes thinning of egg shell and their premature 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 ageing of a lake by biological enrichment of its water. Natural ageing of a lake may span thousands of years and lake finally gets converted into land due to deposition of silt. Pollutants from man's activities like effluents from the industries and homes can radically accelerate the ageing process, this phenomenon is called accelerated eutrophication.
• B.O.D. of Eutrophic lake is very high.

Water Pollution can be caused by the following man made sources:

1. Household Detergents : The house hold detergents include the compounds of phosphate, nitrate, ammonium and alkyl-benzene sulphonate (ABS) etc. harmful substances which are gathered in water. Alkyl benzene sulphonate is non degradable, so its concentration increases which is harmful for aquatic life.

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, their carbonic material decomposes and gets deprived of oxygen, which causes death of aquatic organisms. 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 considered best for this purpose.

2. 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 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.

3. 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 rate of reoxygenation is reduced as compared to deoxygenation in water reservoirs. The acceleration of microbial activity increases BOD of water. This indicates the essential amount of oxygen for decomposition in bacteria.

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

Method of water purification :

Water (prevention and control of pollution) Act. 1974 passed by Government of India.

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 in tanks.

2. Secondary treatment :- This is a biological process and is carried out by microorganisms. 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 of CO₂ and this CO₂ 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, phosphorus 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 in irrigation.

Daphnia, trout fishes and larva of stone fly are sensitive to water pollution and show the intensity of water pollution.

Some animals are very specific to their habitat, other have wider choice or tolerance levels. For example, Tubifex (an annelid) and many insect larva such as chironomous larva lives in polluted water. They can survive in water with very low oxygen quantity and high organic content. Certain fishes like trout can live only in fresh water, whereas others like Hilsa can live in both fresh water and saline water.

SOIL POLLUTION

Soil is also polluted through polluted water and air. These pollutants are mixed into the soil through the rain water.

Such as H₂SO₄ acid is formed by mixing of SO₂ with rainy water in the air. The fertilizers, pesticides and weedicides are being sprayed over the crops. All these are mixed with soil to produce harmful effects. The growth of plants is inhibited or reduced due to this type of pollution and sometime their death also takes place.

Excluding these, soil pollution is also caused by the disposal of house hold detergents, sewage, flowing oils, radio active substances and hot water etc. The main pollutants of soil are D.D.T. and weedicides [2, 4D ( 2, 4 dichlorophenoxy acetic acid), 2, 4, 5-T ( 2, 4, 5, tri chloropheinoxy acetic acid)].

Control : Soil pollution can be controlled through biological degradation of waste materials. The various carbonic materials of agriculture waste, cattle dung etc. can be minimized by the use of bio-gas plants which can produce energy also. Inspite of all the measures, pesticides and weedicides should be used in limited quantity only when it is required.

Plant indicators :- "Such type of plants which give additional information about the environment or habitat are called plant indicators". e.g. growing of Viola plants indicates the presence of Zinc in soil. Occimum shows presence of copper in soil. Silene (a plant) indicates presence of cobalt. The presence of Lichens shows that atmosphere is free from the pollutants like CO and SO₂.