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Class 7 science Wastewater stories Short answers


Additional Questions

Objective Questions

A. Fill in the blanks;

1. ————-released by houses is called Sewage.

2. Dried———– is used as manure.

3. ————-get blocked by Solid food remains; and sanitary towels.

4. Untreated human excreta may cause _____ pollution and pollution.

5. Vermin-processing toilets use————— to treat human waste.

6. Vacuum toilets are usually used in———————.


1. Wastewater

2. Sludge

3. Drains

4. Soil; Water

5. Earthworms

6. Aeroplanes

B. Very short answer type questions:

1. What is wastewater?

Answer: The disposed water which is rich in a lather, mixed with oil, black-brown water that goes down the drains from sinks, showers, toilets, laundries is dirty and is called wastewater.

2. When do we celebrate world water day?

Answer: 22 March.

3. What is meant by cleaning of water?

Answer: Removal of pollutants before it enters a water body or is reused is the cleaning of water.

4. What is sewage treatment?

Answer: The sewage treatment is the process of wastewater treatment (cleaning of wastewater).

5. What is sludge?

Answer: it is thick, soft, wet mud or a similar viscous mixture of liquid and solid components, which is the product of an industrial or refining process.

6. Name one microbe.

Answer: Protozoa.

7. Name one disease which is caused by bacteria.

Answer: Cholera.

8. Give the name of some inorganic impurities.

Answer: Nitrogen, Phosphates, etc.

Short answer type questions

1. Why is it harmful to discharge untreated sewage into rivers, lakes or ground.

Answer: Sewage contains various contaminants including disease-causing bacteria and other microbes, which are harmful to live beings.

2. What are the organic impurities?

Answer: Human faeces, animal waste, oil, urea, pesticides, etc. are organic impurities.

3. Describe disease-causing bacteria which are found in sewage or wastewater with the name of diseases.

Answer: Vibrio cholera, Salmonella paratyphi are some harmful bacteria which are found in sewage. Cholera, typhoid respectively are the diseases which are caused by them.

4. When and why do we celebrate World Water Day?

Answer: The United Nations General Assembly designated 22 March 1993 as the first World Water Day. Because an international day to celebrate freshwater was recommended at the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro.

5. Describe the types of sewage and their points of origin.

Answer: There are three types of sewage:

  • Sullage water
  • Foul water
  • Trade water

Their points of origin are as follows:

  • Sullage water: Kitchen
  • Foul water: Toilets
  • Trade water: Industrial and commercial organisations

6. How are the manholes located in sewerage?

Answer: Manholes are located at every 50 m to 60 m in the sewerage and at the junction of two or more sewers and at points where there is a change in direction.

7. What is chlorination?

Answer: Chlorine is added to drinking water to disinfect it and kill germs. This process of adding chlorine is chlorination.

8. Describe the term aeration.

Answer: When air is circulated through, mixed with or dissolved in a liquid or substance the process is called Aeration.

9. What is the treatment of wastewater?

Answer: Physical, a chemical and biological process to remove physical, chemical and biological matter that contaminates the wastewater is called the treatment of wastewater.

10. Why should we not throw Chemicals like paints, solvents, insecticides, motor oil, etc. in the drain?

Answer: Chemicals like paints, solvents, insecticides, motor oil, etc., kill good microbes that purify water. So don’t throw them down the drain.