Active Science Solutions for Class 7 Science Chapter 18 The Management Of Wastes are provided here with simple step-by-step explanations. These solutions for The Management Of Wastes are extremely popular among Class 7 students for Science The Management Of Wastes Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Active Science Book of Class 7 Science Chapter 18 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Active Science Solutions. All Active Science Solutions for class Class 7 Science are prepared by experts and are 100% accurate.

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Question 1:

A disease that is spread through polluted water is
(a) chicken pox.
(b) jaundice.
(c) cough and cold.
(d) flu.

Answer:

(b) jaundice

Jaundice is a disease that spreads through polluted water.

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Question 2:

Muncipal drains should be cleaned regularly
(a) to avoid overflowing.
(b) to avoid choking.
(c) for easy movement of the sewage.
(d) all the above.

Answer:

(d) all the above

Municipal drains, if not cleaned regularly, may overflow. Cleaning of drains is also necessary to avoid choking and for easy movement of sewage.



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Question 3:

The decomposition of sewage is carried out by
(a) algae.
(b) insects.
(c) bacteria.
(d) chlorine.

Answer:

(c) bacteria
The decomposition of sewage is carried out by bacteria. The bacteria present in the sewage decompose the organic matter present in it.

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Question 4:

In biological  treatment, the sewage is treated by
(a) microorganisms
(b) aquatic plants
(c) chlorine.
(d) passing through screens.

Answer:

(a) microorganisms
In biological treatment, the sewage is treated by microorganisms such as useful bacteria. These bacteria break down the harmful products into harmless ones. 

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Question 5:

Waste water that flows out from our homes is called ________________.
(a) garbage
(b) sludge
(c) sewage sewer
(d) sewer

Answer:

(c) sewage sewer
Wastewater that comes out from our homes is called sewage. It contains suspended and dissolved impurities.

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Question 6:

After treatment sludge is used as _______________.
(a) food for animals
(b) insecticide
(c) poison to kill microbes
(d) fertiliser

Answer:

(d) fertiliser
After treatment, sludge can be used as fertiliser.

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Question 7:

Underground pipes that carry waste water are called
(a) tanks.
(b) sewage.
(c) sewers.
(d) drains.

Answer:

(d) drains
Underground pipes that carry wastewater are called drains.

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Question 8:

In which stage is the liquid sewage treated with chemical disinfectants?
(a) primary treatment
(b) secondary treatment
(c) biological treatment
(d) tertiary treatment

Answer:

(d) tertiary treatment
Tertiary treatment is the final stage of sewage treatment in which the liquid sewage is treated with chemical disinfectants such as chlorine to get rid of harmful microorganisms.

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Question 9:

Which of the following is not a correct step towards preventing water pollution?
(a) throwing waste paper into drains
(b) developing good sanitation system in rural areas
(c) disposing waste oil in your kitchen drains
(d) treatment of sewage before it is released into rivers

Answer:

(a) and (c)
To prevent water pollution, waste paper and plastic bags should not be thrown into drains. Moreover, waste oil should not be disposed in kitchen drains.

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Question 10:

Explain the following terms:
sewage, sewage system, sludge

Answer:

Domestic liquid waste is called sewage. It contains various suspended impurities.

Sewage system is a network of sewers that collects sewage from various parts of the city.

Sludge is the waste that remains after the treatment of sewage. It contains all the poisonous and harmful wastes.

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Question 11:

Describe the various stages in the treatment of sewage.

Answer:

Treatment of sewage involves three stages:
(a) Primary treatment: This stage is a mechanical process that involves screening and settling of large particles from sewage using vertical bars and grit chambers. After screening, water is passed through sedimentation tanks.

(b) Secondary treatment: This stage is a biological process. It involves breaking down of organic matters obtained from primary treatment with the help of bacteria to produce biogas. Water is sent to aeration tanks and air is blown through them to speed up the treatment of water.

(c) Tertiary treatment: This stage is a chemical process. It is the last stage in the treatment of sewage. Chemicals are added to remove phosphorous and nitrogen from sewage. Bacteria and other germs are killed by the addition of chlorine.

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Question 12:

What can happen when drinking water gets mixed with sewae water?

Answer:

Sewage water contains germs of waterborne diseases such as diarrhoea, dysentery, cholera. When drinking water gets mixed with sewage water, the germs of waterborne diseases enter the drinking water and cause serious health problems.

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Question 13:

What is the role of bacteria in the treatment of sewage?

Answer:

The bacteria decompose the sewage and convert its harmful products into harmless ones. They are involved in the sewage treatment plants to get rid of harmful substances from the sewage.

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Question 14:

Why is treatment of sludge a major problem?

Answer:

Sludge consists of poisonous and harmful wastes. Treatment of sludge is a major problem because it is very costly and takes time.

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Question 15:

Why is sewage disinfected at the last stage of treatment?

Answer:

Sewage is disinfected by adding chlorine at the last stage of treatment because chlorine helps in getting rid of harmful microorganisms.

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Question 16:

Fill in the blanks with suitable words.
(a) The ______________ removes solid insoluble matter.
(b) The insoluble matter that settles at the bottom of the settlement tank is _______________.
(c) In the secondary stage, sewage is treated with _____________.
(d) ________________ percent of pollution is removed in the secondary stage.
(e) In the tertiary stage, _________________ is carried out.

Answer:

(a) The primary treatment removes solid insoluble matter. 
(b) The insoluble matter that settles at the bottom of the settlement tank is sludge.
(c) In the secondary treatment, sewage is treated with bacteria.
(d) 85 percent of pollution is removed in the secondary stage.
(e) In the tertiary stage, disinfection is carried out.

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Question 17:

Name four diseases caused by water pollution.

Answer:

Jaundice, cholera, dysentery and diarrhoea are four diseases caused by water pollution.



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