Wastewater Story (NCERT Solutions, Class 7)

(1) Fill in the blanks:

(a) Cleaning of water is a process of removing_____.

(b) Wastewater released by houses is called_____.

(c) Dried ____ is used as manure.

(d) Drains get blocked by __and ____.

Ans-

(a) Cleaning of water is a process of removing pollutants.

(b)Wastewater released by houses is called sewage.

(c) Dried sludge is used as manure.

(d) Drains get blocked by oil and fat.

(2) What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Ans- Sewage is a liquid waste, comes from homes, industries, hospitals, offices, and other users. It is harmful to discharge untreated sewage into rivers or seas because it causes water pollution. It becomes source of diseases like dysentery, cholera, typhoid etc.

(3) Why should oils and fats be not released in the drain? Explain.

Ans– Oils and fats should not be released in the drain. They can harden and block the pipes. We should not throw fats in open drain because they can clog the pores of soils and can reduce the filtration of water.

(4) Describe the steps involved in getting clarified water from wastewater.

Ans– Steps in getting clarified water from wastewater-

(i) Wastewater is passed through bar screens to remove large objects ( eg- rags, sticks , plastics, napkins etc.).

(ii)From bar screen water goes to a grit and sand removal tank, where speed of wastewater keep slow to settle down the sand, grit and pebbles.

(iii)The water is than allowed to settle in a large tank which is sloped towards the middle. Sludge (Solids like faeces) settle at the bottom and are removed with a scraper. Floatable solids (oil and grease) are removed by skimmer. The water than obtained is called clarified water.

(5) What is sludge? Explain how it is treated.

Ans-Solids like faeces settle at the bottom of the tank in wastewater treatment, is called sludge. It is removed with a scraper. 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.

(6) Untreated human excreta are a health hazard. Explain.

Ans- Untreated human excreta are a health hazard. It may cause water pollution and soil pollution. Both the surface water and ground water get polluted. Ground water is a source of water for wells, tube wells etc. So, it causes many water borne diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

(7) Name two chemicals used to disinfect water.

Ans- Two chemicals used to disinfect water are chlorine and ozone.

(8) Explain the function of bar screens in a wastewater treatment plant.

Ans- Wastewater is passed through bar screens to remove large objects ( eg- rags, sticks , plastics, napkins etc.).From bar screen water goes to a grit and sand removal tank, where speed of wastewater keep slow to settle down the sand, grit and pebbles.

(9) Explain the relationship between sanitation and disease.

Ans-People in our country do not have proper sewage facilities. So, they defecate in open. It may cause water pollution and soil pollution. When people drink polluted water, they become sick.  They may get diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery. Thus, poor sanitation and diseases travel together.

(10) Outline your role as an active citizen in relation to sanitation.

Ans-Role of an active citizen in relation to sanitation-

(i) We should always drink clean water.

(ii) We should always use toilets. We should not defecate in the open.

(iii)We should use low cost onsite sewage disposal systems (septic tanks, chemical toilets, composting pits) for the places where sewage is not available.

(iv)We should use hygienic onsite human waste disposal technology.

(v) We should always throw waste generated in public places in dustbins.

(11) Here is a crossword puzzle: Good luck!

Wastewater, q 11,NCERT,class 7

Across

  1. Liquid waste products
  2. Solid waste extracted in sewage treatment
  3. A word related to hygiene
  4. Waste matter discharged from human body

Down

  1. Used water
  2. A pipe carrying sewage
  3. Micro – organisms which causes cholera
  4. A chemical to disinfect water

Ans- Crossword Puzzle is solved and given below:

Wastewater, A 11,NCERT,class 7

(12) Study the following statements about ozone:

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.(c) It absorbs ultraviolet rays.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b),and (c)

(ii) (b) and (c)  

(iii) (a) and (d)

(iv)All four

Helping Topics

Wastewater Story

Practice sheet, class 7

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