Wastewater Story Class 7 Science Notes - Chapter 18

Wastewater is defined as used water. Used water is either rich in lather, mixed with oil, black– brown water that passes through the drains from sinks, toilets, laundries, showers, is dirty. We can reuse the wastewater by removing the pollutants.

  • Sewage – The used water or the water that is generated in industries, homes, agricultural fields, etc. is called sewage. It is a waste in the form of liquid. It causes soil and water pollution. The wastewater can be treated in a sewage treatment plant which reduces the pollutants present in used water.
  • Sludge – In the Wastewater treatment plant, during the process of settling of water in a large tank for solids to settle at the bottom. The solids settle at the bottom such as feaces are removed with a scraper. This removed waste is called sludge. The sludge is then transferred to a separate tank for decomposition by the anaerobic bacteria.The floatable liquids like grease and oil are removed by a skimmer. The water clarified in such a way is called clarified water.

Wastewater Story Class 7 Extra Questions

  1. What is wastewater?
  2. Can fats and oils be released in drains? Explain.
  3. How can untreated human excreta become a health hazard?
  4. What does the term sewage mean?
  5. How sanitation and disease are related?
  6. What are the steps involved to get clarified water?
  7. What does it mean to disinfect water? Name the chemicals used for the same process.
  8. Explain the process of water cleaning.
  9. What is onsite sewage?
  10. Define sludge. Explain its treatment.
  11. Fill in the blanks –
    1. Houses release wastewater called as _________.
    2. Usually the drainage block is due to _________ and ________.
  1. Answer true or false –
    1. Ozone is required for the breathing of living organisms.
    2. Ozone is used to disinfect water.
    3. Ozone absorbs ultraviolet rays.

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