NCERT solution for class 7// Science //Chapter 18 - Wastewater story

 NCERT solution  > class 7 > Science 

Chapter 18  - Wastewater story 

Exercise 

Q1. Fill in the blanks 

1. Cleaning of water is a process of removing pollutants

2. Wastewater released by houses is called sewage .

3. Dried sludge is used as manure .

4. Drains get blocked by cooking oil and fats

Q2. What is sewage explain why it is harmful to discharge untreated sewage into rivers or seas? 

Answer- Sewage is the waste water containing both liquid and solid impurities from homes, industries, hospital, officers it contain the various contamination include disease-causing bacteria organic and inorganic waste etc. If untreated sewage is discharged into rivers or sea then it polluted the water and unsafe for drinking it also can cause Cholera typhoid and dysentery like disease so it is harmful to discharge untreated sewage into the rivers or sea

Q3. Why should oils and fat be not released in the drain explain.

Answer- oil and fats deposited on the walls of the sewage and it block the sewage pipes in an open drain and so fats block the porosity of the soil and which affect the water filtration efficiency . So It should not be released in the drain.

Q4. Describe the steps involved in getting clarified water from what wastewater ? 

Answer- The step involved in getting clarified water as follow 

1.  Water passes through the screen bar that's why the solid impurities is remove

2. Use aerator to bubble air through wastewater to reduce the bad order from waste water.   

3. Then water is filtered through the layers of sand fine gravel and medium gravel to clean the various type of pollutants .

4. Then chlorine tablet is added in the filtrate water and stirred continuously  to obtain completely clear water .

Q5. What is sludge explain how it is treated ? 

Answer- Semi solid such as faeces settle down during the wastewater treatment are called sludge .It is remove and transfer to the another tank and decomposers with an aerobic bacteria to produce biogas .Biogas is used as a fuel for cooking and heating and produced electricity.

Q6. Untreated human excreta is a health hazard explain? 

Answer- Untreated human excreta contain the various disease causing microorganisms if it mixes with soil causing the pollution of soil as well as water it contaminate the drinking water and causes disease like Cholera typhoid hepatitis dysentery etc.

Q7. Name two chemicals used to disinfect water? 

Answer- Chlorine and ozone are used to disinfectant water

Q8. Explain the function of bar screens in a wastewater treatment plant? 

Answer- In wastewater treatment plant the bar screen remove the large solid objects of the water like a clothes ,napkins ,cans, plastic bags, polythene etc.

Q9. Explain the relationship between sanitation and diseases?

Answer- Sanitation and disease are related to each other is a lack of sanitation can causes disease in our country nowadays large number of the peoples have not a sewage facilities they dumped their all garbage and household water in open space and that water contaminate the underground water sources and that contaminated water used for drinking it can causes the disease such as Cholera typhoid he pet it is dysentery etc therefore the lack of sanitation in drinking water can cause  health problem

Q10. Outline your role as an active citizen in relation to sanitation 

Answer- A citizen has many responsibilities to maintain the sanitation 

1. To keep his surrounding both inside as well as outside our clean 

2. The sewage system in a house is properly managed.

3. If some leakage or other problem in sewage system he should be reported to the municipality

Q11. Here is a crossword puzzle  

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. Microorganism which causes cholera .

7. Chemical to disinfect water. 

Answer 

Q12. Study the following statement about ozone 

a) It is essential for breathing of living organisms  

b) It is used to disinfect water 

c) It absorb of ultraviolet rays .

d) Its proportion in air is about 3%.

Which of these statements are correct 

a) a,b and c 

b) b and c 

c) a and d 

d ) all four .

Answer -  b and c 


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