Class 7 Biology Wastewater Story Waste water treatment plan

Waste water treatment plan (WWTP )

  • Physical, chemical and biological processes are involved in the treatment of waste water.
  • Treatment removes physical, chemical and biological contaminants.
  • Procedure of waste water treatment
  1. Through bar screens waste water is passed and here large objects like rags, cans, sticks, bottles, large food materials are removed.
  2. Water is then passed to a grit and sand removal tank, where sand, grit and pebbles settle down by decreasing the speed of entering wastewater.
  • Water is then allowed to settle in a large tank and sludge is removed
  1. The water from which the floatable solids like oil and grease are removed is called clarified water.
  2. Clarified water is then transferred to a separate tank for decomposition by the anaerobic bacteria.
  3. The biogas produced during decomposition can be used as fuel or used to produce electricity.
  • Air is pumped into clarified water to grow the bacteria which consume the left out contaminants in the waste water.
  • After several hours of decomposition in the tank, the microbes settle down in the bottom as activated sludge.
  1. The water is then removed from the top by sand drying beds or machines.
  2. The treated water with very low amount of suspended matter is discharged into water bodies where it is further cleaned by nature.
  3. Chlorine and ozone are also used sometimes before releasing into the water bodies.

Fig. Water purification  

Dried sludge can be used as manure which in turn returns organic matter and nutrients to the soil.

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