NCERT SOlutions for class 7 science Chapter 18

Wastewater Story

NCERT Solutions for Class 7 Science chapter 18 Exercise Question

Question 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 ____________.

Answer

(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 cooking oil and fats.

Question 2

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

Answer

Wastewater released by houses is called sewage . Untreated sewage should not be discharged untreated into the sea because sewage consists some harmful substances and microorganisms which cause disease for people .

Question 3

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

Answer

Oils and fats should not be released in the drain because They can harden the soil and block the pipes .

Question 4

Describe the steps involved in getting clarified water from wastewater.

Answer

• Step 1:impurities like stones, plastic bags, cans etc are removed by filtration and sedimentation processes.
  
• Step 2:Then the aeration process apply which allowed Bacteria to grow .
  
• Step 3: Bacteria eat away human waste from the wastewater.
  
• Step 4:Chlorination is used to kill the germs in clarified water.
  
• Step 5:So now the water becomes fit for human consumption.
  

Question 5

What is sludge? Explain how it is treated.

Answer

Solids like faeces settle at the bottom This is the sludge. Sludge is removed using a skimmer and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas.

Question 6

Untreated human excreta is a health hazard. Explain

Answer

Untreated human excreta is a health hazard because it contain some harmful disease-causing bacteria which infec soil and water .When people use this water they get diseases like Plague ,Syphilis ,Anthrax

Question 7

Name two chemicals used to disinfect water

Answer

Chlorine and Ozone .

Question 8

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

Answer

Bar screen removes large objects like plastic packets, cans and napkins.

Question 9

Explain the relationship between sanitation and disease.

Answer

Sanitation and diseases are related to each other as lack of sanitation can cause disease. When this infected water is used for drinking, it can cause diseases such as cholera and hepatitis etc. which may even lead to death.

Question 10

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

Answer

• Separate garbage as recycled waste and non-recycled waste
• Ensure that our surroundings are clean.
• The sewage system in the house should be properly managed
• Report to the concerned authoritive immediately in case of leakages in sewage pipes.

Question 11

Here is a crossword puzzle: Good luck!

Across

3. Liquid waste products

4. Solid waste extracted in sewage treatment

6. A word related to hygiene

8. Waste matter discharged from human body

Down

1. Used water

2. A pipe carrying sewage

5. Micro-organisms which causes cholera

7. A chemical to disinfect water

Answer

Across

3. Sewage

4. Sludge

6. Sanitation

8. Excreta

Down

1. Wastewater

2. Sewer

5. Bacteria

7. Ozone

Question 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

Answer

(ii) (b) and (c)