Describe various steps of cleaning wastewater in a wastewater treatment plant

cbse
cbse-class-7-science
waste-water-story

#1

Describe various steps of cleaning wastewater in a wastewater treatment plant.

Answer:

  • Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
  • Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
  • The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.
  • The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.
  • Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.
  • { After several hours, the suspended microbes settle at the bottom of the tank as
  • activated sludge. The water is then removed from the top.