Treatment of Effluents

Primary, Secondary, and Tertiary Treatment of Effluents are

Primary Treatment of Effluents

  • In the first stage of primary treatment, large particles such as rags and sticks are removed from the water.
  • To remove inorganic solids such as silt, eggshells along with bone chips and seeds, known as grit, the wastewater is made to enter a grit chamber where the speed of water is decreased. The grit then settles and is removed manually or mechanically from the grit chamber.
  • Water then flows into a sedimentation tank. In the process of sedimentation, water is stored in large basins where sand particles, silt, and other particles settle. The impurities or sludge are then removed.
  • The process in which sedimented water is subjected to a chemical process is known as coagulation or flocculation.
  • In the process of filtration, suspended impurities are removed by making water pass through a barrier of sand matrix.

Secondary Treatment of Effluents

  • In this method, the organic matter which is present in water is biologically degraded by microorganisms. When water enters a tank, it comes into contact with microorganisms.
  • Air is introduced into the tank through diffusers. Microorganisms in the presence of oxygen break the organic matter and the impurities then settle at the bottom of the tank which is later removed.
  • Water is then treated with chlorine gas which then kills the rest of the harmful organisms.

Tertiary Treatment of Effluents

Tertiary treatment: In this method, nutrients such as nitrogen or phosphorus are removed. This water can be reused for industrial, agricultural, and domestic purposes.


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