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CBSE Class 7 Chemistry Notes- Chapter 7 Waste Water

The waste water released by homes, industries, hospitals, offices, etc. is called sewage. Sewage is basically liquid waste. The impurities that sewage contains are called contaminants.
Sewage treatment is the process of removing pollutants or contaminants from the waste water.

  • Large objects are removed by passing the waste water through bar screens
  • Grit and sand are removed by decreasing the speed of incoming wastewater, which allows to sand and pebbles to settle down.
  • The waste water, then enters tank sloped towards the middle. This removes solid wastes like faeces. This is called Sludge. The floatable solids like oil and grease are removed by a skimmer. This stage produces what we call clarified water.
  • Air is then pumped into the clarified water which helps the aerobic bacteria to grow. These bacteria consume any unwanted matter remaining in the water. These microbes then settle down at the bottom of the tank as activated sludge and water is removed from the top.

This treated water is then discharged into a water body.
Measures to reduce sewage and diseases

  • Drains should not be open as they lead to spreading of diseases.
  • Wastes should be disposed properly and responsibly.

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