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Water Pollution: Sources, Effects, Prevention and Control

Updated on June 25, 2017
Waste water discharge into water body.
Waste water discharge into water body.

Water Pollution is the contamination of water bodies with unwanted and harmful substances. Water is said to be polluted when there is any physical, biological or chemical change in its quality that adversely affects living organisms and makes it unfit for use.

Generally, there are two types of sources of water pollution- Point sources and non point sources. Point sources are those which are fixed at a place and have a specific location for discharging pollutants into a particular water body. These include factories, power plants, underground coal mines and oil wells situated close to the water source. Non point sources are those which are scattered and do not have any specific location for discharging into a particular water body. These include run-offs from fields, lawns, gardens, construction sites, logging areas, etc.

Water Pollutants

Substances which pollute the water are called water pollutants. Some of these are natural whereas others are man-made.

  • Natural pollutants in water are calcium and magnesium compounds which get dissolved in water from natural deposits. Microorganisms such as protozoa, bacteria and virus, which are vectors of diseases also pollute water.
  • Man-made pollutants are oils, heavy metals, detergents, domestic sewage, industrial waste, chemical fertilisers and radioactive wastes which are discharged into water bodies.

Sources of Water Pollution

Pathogens: Disease causing agents are called pathogens. It includes bacteria and other organisms that enter into water bodies from domestic sewage and animal excreta.

Industrial Wastes: The discharge of wastes from industries into rivers and lakes pollutes water as it contains harmful chemicals including acids and alkalies.

Sewage: Dumping of sewage into rivers and lakes without treatment pollutes water.

Synthetic Detergents: Excessive use of synthetic detergents for washing purposes produces a lot of foam and pollutes water.

Chemical Fertilisers: Herbicides and pesticides used in agriculture may contaminate water bodies.

Oil Discharges: The leakage of petroleum oil into the sea during drilling and shipping operations pollutes sea water causing problems for aquatic life.

Radioactive Waste:The wastes from atomic reactor plants affect aquatic life to a great extent.

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Thermal Pollution: Hot water from thermal power plants constitute another major source of water pollution.

Groundwater Pollution: Human activities such as improper sewage disposal, dumping of farm yard manures and agricultural chemicals, industrial effluents cause groundwater pollution.

Eutrophication: It is a process in which extra nutrients are added to a water body leading to tremendous growth of algal plants resulting in reduction of dissolved oxygen.

Effects of Water Pollution

  • Human beings become victims of several waterborne diseases such as typhoid, cholera, dysentery, hepatitis and jaundice.
  • Acids and alkalies present in polluted water kill and destroy the useful microorganisms which are natural cleansing agents of water.
  • Metals like lead, zinc, arsenic, copper, mercury and cadmium in industrial waste waters adversely affect humans and animals. It can cause skin lesions, rough skin, dry and thickening of skin and skin cancer.
  • The sewage waste and chemical fertilisers often leads to eutrophication and deoxygenation of water bodies killing the aquatic animals.
  • The toxic industrial wastes kills the fish and other animals living in fresh water.
  • Oil discharges in sea water often results in death of thousands of marine organisms and pollute the surrounding environment.
  • Pollution of water bodies by mercury causes Minamata disease in humans and dropsy in fishes. Lead causes displexia, cadmium poisoning causes Itai–Itai disease etc.
  • Discharge of hot water in water body affects feeding in fishes, increases their metabolism and affects their growth. Their resistance to diseases and parasites decreases. Due to thermal pollution biological diversity is reduced.

Pollutants
Sources
Organic wastes
Domestic sewage, animal excreta and waste, decaying animals and plants, discharge from food processing factories.
Plant nutrients
Chemical fertilizers
Microorganisms
Domestic sewage
Heavy metals
Industries and chemical factories
Pesticides
Chemicals used for killing insects, fungi and weeds
Radioactive substances
Mining of uranium containing minerals
Sources of Water Pollutants

Prevention and Control of Water Pollution:

  • Sewage treatment: Sewage should be treated before it is discharged into the river.
  1. Primary Treatment: First the sewage is passed through a grinding mechanism, then it is passed through several settling chambers and lime is added to neutralise it.
  2. Secondary Treatment: Also known as biological treatment. In this process, the neutralised sewage is sent to a reactor and anaerobic bacteria decomposes the biodegradable organic matter present in the sewage. This process removes foul odour and gives out methane gas. After this, water is sent to aeration tanks containing air and bacteria. Bacteria consumes most of organic matter.
  3. Tertiary Treatment: It is a disinfection process to remove dissolved inorganic solids and traces of organic matter. Tertiary methods are chlorination, evaporation and exchange of absorption to obtain clean and pure drinking water.
  • Industrial wastes should be treated chemically to neutralise the harmful substances present in them before discharging into rivers.
  • Waste paper, plastics, waste food materials and decaying fruits and vegetables should not be thrown into open drains.
  • Solid wastes containing organic matter and effluents from distilleries should be sent to biogas plants for generation of energy.
  • Oil slick should be skimmed off from its surface with suction device. Moreover, bioremediation techniques could be used to degrade harmful pollutants in oil spills.
  • To reduce thermal water pollution, hot water from thermal power plants should be stored in cooling ponds before releasing into any water body.
  • Organic farming and efficient use of animal residues as fertilisers should be promoted.
  • Proper filtration systems should be used in homes.

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