Environmental Issues

Water pollution and its control


  • Water pollutants may be of three types on the basis of their nature - biological, chemical and physical.
  • Water pollution may be either natural (or) man made
  • Municipal waste water contain sewage, detergents, animal as well as industrial wastes.
  • Industrial waste water contain hot water which contain a variety of organic and inorganic residues.
  • Domestic sewage is rich in biodegradable organic matter which stimulates the activity of decomposer organisms collectively called sewage fungus.
  • The property of organic wastes in getting decomposed through microbial activity is known as putrescibility.
  • Degree of impurity of water due to organic matter is measured in terms of B.O.D [Biological oxygen demand].
  • A healthy ecosystem has Do 14 units. Do below 8 units indicates pollution, below 4 units is considered as heavy pollution.
  • Eutrophication is natural ageing of water body by biological enrichment of its water.
  • The excess growth of planktonic algae in nitrate and 'P' rich polluted water that causes coloration of water and unpleasant odour is called algal bloom.
  • BGA sevetes Neurotoxins which paralyse the animal driving this water.
  • Algal blooms cause mortality of fishes.
  • Over the centuries, as silt and organic debris file up, the lakes glow shall over, warmer, poor in oxygen receives more light, support growth of warm water organisms and marshy plants such lakes are called Eutrophic lakes which would later converted into land.
  • Sewage pollution can be prevented by treating sewage by passing into water course, in sewage (or) effluent treatment plant which involves 3 steps.
  • Primary treatment is a physical process and involves filtration and sedimentation. By screening large objects floating polythene bags are removed. This step allows the suspended particles to settle down @ bottom within 2-3 hours to form a sludge.
  • 1° / primary treatment removes BOD to about 35% and 60% of TSS.
  • 2°/ secondary treatment is a biological aerobic method, in which the organic matter is decomposed by micro organisms which involves decomposition and chlorination by involving sodium Hypochlorite.
  • Decomposition of organic matter can be carried out by trickling filter method, activated sludge method (or) water Hyacinth ponds construction.
  • Secondary treatment thus removes suspended as well as dissolved organic substances from sewage which removes BOD and TSS to the level of 25-30 units but not less than 85% level.
  • Tertiary treatment is physico - chemical process which involves precipitation, filtration [by passing over activated charcoal], aeration and purification (or) desalination.
  • The final process removes both BOD and TSS to level less than 9 mg/L (or) removal of 95% BOD and TSS.
  • Industrial waste water pollutants may have toxic heavy metals like mercury, cadmium, copper, lead, acid / alkalies and hot water etc.
  • Heavy metals list with its highlights are given below.
  • Copper: Hypertension, anaemia, Uremia and coma.
  • Lead: Haem synthesis interference, Liver / Kidney / Brain damage. lead poisoning (plumbism) causes brain damage and madness.
  • Chromium: Gastro - intestinal ulcers, nephritis, cancer.
  • Cadmium: Itai - Itai [skeletal deformities, reported in 1947 from Toyomacity, Japan]
  • Arsenic: black foot disease, ICC (Indian Childhood Cirrhosis)
  • Excess Nitrates: blue body syndrome - called cyanosis [methaemoglobinamia]
  • Fluorides: Teeth mottling, knocking knee, fluorosis ; safe limit of water fluoride level ⇒ 0.5 to 0.8 mg/l

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