Living Science Solutions for Class 7 Science Chapter 20 Wastewater Management are provided here with simple step-by-step explanations. These solutions for Wastewater Management are extremely popular among Class 7 students for Science Wastewater Management Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of Class 7 Science Chapter 20 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class Class 7 Science are prepared by experts and are 100% accurate.

Page No 229:

Question 1:

What is sewage?

Answer:

Sewage is waste water generated from houses, industries, hospitals etc. It also includes rainwater that runs over land. It is carried away in sewers or drains.

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Question 2:

Why is it necessary to treat sewage before disposing it off in a water body?

Answer:

Untreated sewage contains a wide variety of dissolved and suspended impurities. Hence, it is necessary to treat sewage before disposing it in a water body to remove its impurities and to prevent its devastating effect on humans, animals, fishes and birds.

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Question 3:

Name four diseases that can be used by an improper drainage system.

Answer:

Cholera, typhoid, malaria and jaundice are four diseases that can be caused by an improper drainage system.

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Question 4:

Why is cholera outbreak common after floods?

Answer:

During floods, huge amount of water comes down in a short time. Hence, water starts overflowing on the streets. The excess water then contaminates the drinking water supplies, bursts pipelines and causes sewers to reverse their course of flow. This leads to major health risks as excreta flows on the surface and contaminates the water. The contaminated water provides a breeding ground for the cholera bacteria. Hence, cholera outbreak is common after floods.

Page No 229:

Question 5:

In a city, there are separate pipes for disposing sewage and storm water. Why is this necessary?

Answer:

There are separate pipes for disposing sewage and storm water because storm water infiltration into wastewater system can cause sewage overflow, which may lead to several environmental damages.

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Question 6:

What processes does sewage treatment involve?

Answer:

Sewage treatment involves three processes, namely physical, chemical and biological. They remove physical, chemical and biological contaminants present in the wastewater.

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Question 7:

How can contamination of drinking water occur from sewage even in a covered drainage system?

Answer:

In areas where drinking water pipe and sewage line are close, damages and leaks in the water pipe joints can sometimes lead to contamination of drinking water.

Page No 229:

Question 1:

List the ways in which wastewater present in sewage is generated and the kind of contaminants present in each.

Answer:

 Sewage wastewater includes:
(i) Waste water generated in houses during bathing, washing and cleaning kitchen utensils, which contains detergent and dirt as well as faeces and urine.
(ii) Wastewater generated in industries and hospitals, which contains poisonous chemicals.
(iii) Rainwater that has run down, which contains harmful substances.

Page No 229:

Question 2:

What problems can arise due to improper drainage?

Answer:

Improper drainage can create unhygienic and unsanitary conditions in our neighbourhood. Open, dirty and stagnant water serves as breeding place for flies and mosquitoes. Sometimes, the river water and groundwater, which are sources of drinking water, get contaminated with human excreta and can spread water-borne diseases like cholera, typhoid etc.

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Question 3:

What dangers result from improper storm water drainage system in a city?

Answer:

Improper storm drainage system in a city can lead to contamination of drinking water, bursting of pipelines and back flow of sewers. It is dangerous for public health and property. Contamination of drinking water can spread water-borne diseases like cholera, typhoid etc.

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Question 4:

Outline the main steps used in sewage treatment.

Answer:

Following are the steps involved in the sewage treatment :
(i) The sewage entering into the sewage treatment plant is first passed through vertical bars to remove large rubbish objects like rags, sticks, cans, plastic bags etc.
(ii) Then the water is made to flow through settling tank. This is done to remove the grit and sand present in it.
(iii) The wastewater is then passed through the first sedimentation tank and allowed to stay there for a while.
(iv) The sludge is then taken out from the bottom and put into a large, closed tank called digester tank.
(v) The floating materials are removed by a skimmer.
(vi) The clarified water is then passed through the aeration tank, where aerobic bacteria consume or digest organic wastes such as human waste, food waste, soap and other unwanted materials.
(vii) From the aeration tank, treated water goes to the second sedimentation tank and allowed again to stay there for a while.
(viii) The treated water left in the second sedimentation tank has low level of organic materials and suspended impurities. The treated water is then released in the river.

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Question 5:

In what ways is the sludge obtained from a WWTP used?

Answer:

The sludge obtained from a wastewater treatment plant (WWTP) is used as manure and biogas. The dried manure returns the nutrients to the soil, whereas biogas is used as a fuel.

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Question 6:

How can each one of us help in making the sewage treatment in our city more efficient?

Answer:

Sewage treatment can be made more efficient by taking following precautions:
(i) Do not throw wastes such as solid food remains like tea leaves, sanitary towels, polythene bags, soft toys etc. down the drain.
(ii) Do not throw waste cooking oil and fat in kitchen sink as they can harden and block the drainage pipe.
(iii) Do not throw chemicals like paint, solvent, insecticides, medicines etc. in the drainage pipe.

Page No 229:

Question 1:

Which of these diseases is not caused by improper disposal of sewage?

(a) cholera
(b) heart attack
(c) jaundice
(d) typhoid

Answer:

(b) heart attack
Cholera, jaundice and typhoid are water-borne diseases. They are caused due to improper disposal of sewage.

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Question 2:

The solid matter produced during sewage treatment is

(a) slurry
(b) fertiliser
(c) sludge
(d) humus

Answer:

(c) sludge

The solid matter produced during sewage treatment is known as sludge.

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Question 3:

Which of these is a part of the wastewater treatment plant?

(a) clarifier
(b) vertical bars
(c) aeration tank
(d) all of them

Answer:

(d) all of them
Clarifier, vertical bars and aeration tank - all of these are parts of a wastewater treatment plant.

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Question 4:

Which of these methods should NOT be used for disposal of urine and faeces if no sewage system is available?

(a) allowing untreated sewage to flow into rivers
(b) making septic tanks for sewage to flow into
(c) allowing sewage to flow into a biogas plant
(d) using a vermicomposting toilet

Answer:

(a) allowing untreated sewage to flow into rivers

Disposal of untreated sewage directly into rivers can result in serious water pollution. This, in turn, can result in major health hazard for fish, birds, animals and humans. Polluted water is unsuitable for drinking, agriculture and industry.

Page No 229:

Question 1:

Stagnant water in blocked drains is a good breeding place for flies and ___________.

Answer:

Stagnant water in blocked drains is a good breeding place for flies and mosquitoes.

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Question 2:

Domestic wastewater does not contain microorganisms. True of false?

Answer:

False. Domestic sewage is likely to contain disease-causing microorganisms.

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Question 3:

Organic matter discharged into water bodies uses up substantial ___________ dissolved in water.

Answer:

Organic matter discharged into water bodies uses up substantial oxygen dissolved in water.

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Question 4:

After proper sewage treatment, wastewater can be used for agriculture. True of false?

Answer:

True. After proper sewage treatment, wastewater can be used for agriculture.



Page No 230:

Question 7:

Mention three ways that can be used for sewage disposal if a proper sewage treatment plant is not available.

Answer:

Followings are the three ways that can be used for sewage disposal if a proper sewage treatment plant is not available:
(i) Making septic tanks or septic tank toilets: It is suitable for places that have no sewerage system.
(ii) Making vermi-processing toilet: Here, the sewage is treated by earthworms in a pit. The earthworms gradually eat all the organic matters and decompose it.
(iii) Use of human excreta in biogas plants: Here, the human excreta from the toilet seats in the homes travels directly to biogas plants through covered drains.

Page No 230:

Question 1:

Which pipes should be bigger-those used for sewage disposal or those used for storm water disposal? Why?

Answer:

The pipe used for storm water disposal should be bigger, i.e., it should have large diameter. This is because, when it rains very heavily, large amount of water comes down in a short time. If the diameter of the pipe is small, water will overflow on the streets and may cause major health risks by contaminating drinking water supplies.

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Question 2:

We realise that plastics, being non-biodegradable, are an environment hazard. However, while discussing the choking of sewage drains by plastics, why do we only talk about plastic carry bags and not of other plastic products?

Answer:

In recent times, usage of plastic carry bags has increased at an alarming rate than other plastic products. Plastic carry bags are often thrown here and there. This clogs up gutters and drains and causes water and sewage to overflow in our homes and public areas.



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