Describe the various process involved in purification of water.

 The purification of water means making the unhealthy water potable. The purification of water involves following steps -

  1. Screening - The first step of purification of water is screening. In this step, the floating matter of large size present in the water is removed. Screening prevents the pumps and other equipments from the possible damage due to floating matter of sewage.
  2. Aeration - The process of exposing large surface of water to the atmospheric air is called aeration. After screening, water is collected in a large aeration tank and aerated by compressed air. This process removes volatile substances and gases like Hydrogen sulfide and carbon dioxide causing bad taste and odor. It increases the oxygen level in water. Due to aeration, precipitate of iron and magnese is formed which are separated from water.
  3. Sedimentation - The process by which suspended particles settle down under the action of gravity is known as sedimentation. Now, aerated water is placed in the sedimentation tank and stored for 10 - 14 days. It removes suspended particles to reduce the sediment load before treatment by other processes.
  4. Coagulation - It is chemical water treatment process used to remove solids from water, by manipulating electrostatic charges of particles suspended in water. Now, the water from sedimentation tank is placed in coagulation tank and ten some precipitating agents such as alum, lime etc., are added in water and mixed. These precipitating agents form precipitate of Aluminum hydroxide when dissolved in water. Suspended solids are absorbed on the surface of precipitate, so gradually mass of precipitate becomes heavier and finally settle down. This technique is used to remove very light suspended solids that do not settle by themselves during storage. The clean water above is transferred to a filtration tank with the help of a pump.
  5. Filtration - Water in the filtration tank has to pass through the levels of charcoal, pebbles and fine sand. There is a collection tank at the bottom of the filter bed to collect filtered water. This process removes approximately 99% of microorganisms and other impurities.
  6. Disinfection - Disinfection is generally done by chlorination. The application of chlorine to water for the purpose of disinfection is known as chlorination. Chlorine or bleaching powder is mixed with water in the tank. By doing this, harmful bacteria present in the water are destroyed and the water obtained thus is potable.

Above is the process of purification of water.

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