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Class 7 NCERT SCIENCE Chap 18

 Chapter 18 

Waste Water Story

Here is some important points and answer of chapter 18 Waste Water Story NCERT science of class 8 which helps students to understand topics of chapter.The answer of textbook question of CHAPTER 18 Waste Water Story of CLASS 8 SCIENCE NCERT help students to better understand the topics of chapter.

Important Points:-

1) Aeration:- Cleaning of waste water with the help of moving air instrument is called aeration.

2)Aerobic bacteria:- Bacteria which do respiration in the presence of oxygen is called aerobic respiration.

3) Anaerobic Bacteria:- Bacteria which do respiration  in the  presence of oxygen is called anaerobic respiration.

4)Biogas:- Gas which release during waste water treatment from sludge and use as fuel is known as biogas.

5) Contaminant:- Impurities or waste particles is called contaminant.

6) Sanitation:- Proper disposal of  waste and human extract without harming environment is called sanitation.

7)Sewage:- Waste or used water which released from houses, hospitals,schools etc.

8)Sewer:- Network of small and large drain is called sewer.

9) Sewage:- A way or big drain is called drain.

10)Sludge:- Human, animals solid extract which remain and convert in urea.
 
11)Waste water:- Untreated or water  which released after use is called waste water.

Exercise Questions-
1.Fill in the blanks:
a) Cleaning of water is a process  of removing    ________
b)Waste water released by houses is called________.
c)Dried_______ is used as manure.
d)Drains get blocked by _______and _______.

Ans. a) Pollutants
b) Sewage 
c)Sludge
d) oil and fat

Ques 2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans. Sewage is the waste released from  homes, factories and other activities in which water is used, it is a mixture of suspended organic and inorganic solids, nutrients and some microorganisms. Micro organisms like bacteria  that cause Cholera and typhoid and microbes that cause dysentery, are present in sewage water. Hence, untreated sewage should not be discharged into rivers and seas as it may lead to the spread of diseases.

Ques 3. Why should oils and fats be not released in the drain? Explain.
Ans .Cooking oils and fats harden the pipes and block them they clog the soil pores in an open, there by reducing it water filtering capacity. Hence, oils and fats should not be released into a drain.

Ques 4. Describe the steps involved in getting clarified water from waste water.
Ans. The steps involved in getting clarified water are as follows:- 
I)Waste water is passed through bar screens that remove large objects like rags, plastic bags, cans etc.
II) Water then moves to a grit and sand removal tank here, the speed of water is reduced to allow sand,grit and small stones to settle.
III) This water is then allowed to settle in a large tank is stopped towards the centre, solid waste, like faeces, settles at the bottom and is removed by a scraper as sludge. 
IV) A skimmer is used to  remove solids like oil or grease.
V) Water cleared this way is called clarified water.

Ques 5. What is sludge? Explain how it is treated. 
Ans. Sludge is solid waste like faeces that is removed by using a scraper it is the leftover of clarified water the sludge is transfered to a special tank containing anaerobic bacteria. Decomposition of sludge occurs here and biogas released. Biogas thus produced is used as fuel on to produce electricity.

Ques 6. Untreated  human excreta is a health hazard. Explain.
Ans.  Due to poor sanitation facilities, a very large section of people defecates in open areas, near railway tracks or rivers. This may cause water and soil pollution. Thus, surface water as well as ground water as polluted. Ground water is a source of water for wells, tube wells and rivers. Water borne diseases like Cholera, polio, hepatitis and meningitis spread due to this pollution. Hence, untreated human excreta is a source of contagious and a health hazard.

Ques 7. Name two chemicals used to disinfect water.
Ans. Two chemicals used to distinct water  are chlorine and ozone.

Ques 8. Explain the function of bar screens in a waste water treatment plant.
Ans. The first step in waste water treatment is the physical removal of large objects. Waste water is first passed through bar screens and thereby objects like plastic bags, rags cans and napkins are removed.

Ques 9. Explain the relationship between sanitation and disease.
Ans. Proper sanitation is very important for maintaining hygienic conditions in society. Many contagious diseases occurs. Due to poor sanitation and contamination of drinking water and food. So, sanitation is directly related to the society's health.

Ques 10. Outline your role as an active citizen in relation to sanitation.
Ans. I) We should not scatter litter anywhere.
II) If proper disposal of waste is not available outside, carry it home and throw it into the dustbin.
III)We should try to educate rural people about the benefits of proper sanitation.
IV) Diseases the relation between sanitation and disease to bring awareness among friends.

Ques 11. Here is a crossword puzzle:- Good luck!
class-7-waste-water-story


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.Microorganisms which causes Cholera.
7.A chemical to disinfect water.

Ans. Across
3.Sewage
4. sludge
6.Sanitation
 8.Excreta
Down 
1.Excreta
2.Sewer
5.Bacteria
7.ozone

Ques 12. Study the following statement about ozone:-
a) It is essential for breathing of living organisms.
b)It is used to disinfect water.
c)It absorbs ultraviolet rays.
d)It's 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
Ans. ii (b) and (c)


THE SOLUTION OF CHAPTER 18 WASTE WATER STORY OF SCIENCE NCERT OF CLASS 7 IS GIVEN ACCORDING TO LATEST SYLLABUS CBSE 2020-2021. 



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