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Water Pollution and its control

AIPMT Biology Aspirants, read out the next AIPMT Biology Study material/ Notes of Water pollution, important for AIPMT Biology.Free online notes for AIPMT. What are the major causes of water pollution, how the waste water is treated. Sewage treatment plant important for AIPMT biology.

  • Contamination of water bodies by industrial effluents, domestic sewage, human activities etc. can lead to undesirable change in physical, chemical and biochemical characteristics of water called as water pollution.
  • Water (Prevention and Control of Pollution) Act passed in 1974, to maintain the cleanliness and preserve water bodies.
  • Composition of Waste water: Water with only 0.1% impurities can be considered as waste water and is unfit for human consumption.The impurities in waste water can be 1) Suspended solids: sand, silt, clay

                     2) Colloidal material: Fecal matter, cloth and paper fiber, bacteria

                    3) Dissolved material: like nutrients-nitrate, ammonia, sodium, calcium, phosphate, metal ions, organic compounds

Biological Oxygen Demand:  Also called as Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen used (demanded) by micro-organisms in water to break down organic matter present in water under certain conditions. OR BOD refers to the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.

  • Domestic sewage consists of large amount of biodegradable organic matter, which is decomposed by bacteria and other microbes present in water. Micro-organisms also use suspended nutrients in water as substrates to multiply.
  • Micro-organisms involved in biodegradation of organic matter consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen of water, which causes mortality of fish and other aquatic creatures.
  • BOD is used as a measure to estimate the amount of organic matter in sewage water.
  • More the value of BOD= Less Dissolved Oxygen= Highly Polluted Water
  • Large amount of nutrients in water can also lead to Algal Bloom (excessive growth of free-floating algae in water). Algal blooms make water quality poor, toxic for consumption, and also decreases dissolved oxygen (leads to fish mortality).
  • Aquatic floating weed Water Hyacinth (Eichhornia crassipes) – introduced in India for its beautiful flowers but lead to havoc by their excessive growth which causes blocks in our waterways. It grows excessively in Eutrophic lakes and creates imbalance in aquatic system by consuming nutrients and oxygen. Called as Terror of Bengal.
  • Water pollution can lead to Biomagnification in aquatic food chain and Eutrophication of water bodies.
  • Industrial effluents contains heavy metals like mercury, cadmium, copper, lead, etc. which are toxic in nature lead to water pollution
  • Hospital discharge contain many undesirable pathogenic microorganisms, and its disposal into a water without proper treatment may cause outbreak of serious diseases, such as, dysentery, typhoid, jaundice, cholera, etc.

SEWAGE TREATMENT: Domestic sewage contains large amount of human excreta which contains organic matter and microbes so it is treated in Sewage Treatment Plants (STPs) before disposal. Treatment is done in 2 stages: (a) Primary treatment, (b) Secondary treatment or Biological treatment.

(a) Primary treatment: It involves physical removal of large and small particles through filtration and sedimentation. Filtration removes floating debris and sedimentation removes grit (soil and small pebbles). Then solids settle as primary sludge, and the supernatant forms the effluent. Effluent from the primary settling tank is taken for secondary treatment.

(b) Secondary treatment or Biological treatment: Done by using heterotrophic micro-organisms present in water.

  • Primary effluent is first passed through large aeration tanks.
  • In aeration tanks, effluent is agitated and air is pumped into it constantly, which allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria with fungal filaments to form mesh like structures).
  • Due to excessive growth of microbes in effluent, microbes consume organic matter present in the effluent, which sharply reduces the BOD of the effluent.
  • Primary effluent is treated till the BOD is reduced.
  • Once the BOD of primary effluent is reduced significantly, effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called Activated sludge.
  • Small portion of the activated sludge is pumped back into the aeration tank to serve as inoculum. Remaining major part of the sludge is pumped into large tanks called Anaerobic Sludge Digesters.
  • In Anaerobic Sludge Digesters, anaerobic bacterial growth is promoted to digest the bacteria and the fungi flocs in the sludge. During this digestion, anaerobic bacteria produce a mixture of gases such as Methane, Hydrogen sulphide and Carbon dioxide. These gases together form Biogas. Biogas can be used as source of energy as it is inflammable.
  • Finally, effluent from the secondary treatment plant is safe to be released into natural water bodies like rivers.

NOTE: Ganga Action Plan and Yamuna Action Plan: Initiative by Ministry of Environment and Forests to save rivers from pollution. Purpose is to build large number of sewage treatment plants.

  • Integrated Waste Water Treatment: Approach used in California. Water treatment occurs in two stages – (a) firstly, conventional methods of sedimentation, filtering and chlorine treatments are used (b) then plants, algae, fungi and bacteria are used which neutralise, absorb and assimilate the heavy pollutants from water.
  • ‘EcoSan’ toilets: Used in Kerala and Sri Lanka. These are dry composting toilets for handling human excreta. Human excreta can be used as natural fertilizer after dry composting. It is a practical, hygienic, efficient and cost-effective solution to human waste disposal which otherwise pollutes water.
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