Here in this post we provided NCERT Exemplar Problem Class 7 Science Wastewater Story Chapter 18 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Wastewater Story Class 7 Exemplar full Explanation:
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Multiple Choice Questions
1) Which of the following is waste water?
a) Water tricking from a damaged tap.
b) Water coming out of a shower.
c) Water flowing in a river.
d) Water coming out of a laundry.
Answer:- d) water coming out of a laundry.
Water coming out of Laundry is a waste water because it is used water in washing and it contains soap , detergent , dust etc. which makes it waste. Other sources given above are fresh water source which is not used.
2) Sewage is mainly a
a) Liquid waste.
b) Solid waste.
c) Gaseous waste.
d) Mixture of solid and gas.
Answer:- a) Liquid waste
It is mainly liquid waste because it contains maximum percentage of water in it. The sewage watercontains dissolvedimpurities in it .
3) Which of the following is / are products of wastewater treatment?
a) Biogas
b) Sludge
c) Both biogas and sludge
d) Aerator
Answer:- c) Both biogas and sludge
Biogas and sludge are products of wastewater treatment while the Aerator is the process where air is pumped into the wastewater treatment plant.
4) Open drain system is a breeding place for which of the following :
a) Files
b) Mosquitoes
c) Organisms which cause diseases
d) All of These
Answer:- d) all of these.
Open drain system is a breeding place for files, mosquitoes , and organisms which causes all of these diseases.
5) Water polluted by various human activities causes a number of water borne diseases. Which of the following is not a water borne diseases?
a) Cholera
b) Typhoid
c) Asthma
d) Dysentery
Answer:- C) asthma
Asthma is not a water borne disease, other are water borne diseases. Asthma is the breathing problem causes due to polluted air.
6) Pick form the following one chemical used to disinfect water.
a) Chlorine
b) Washing soda
c) Silica
d) Coal
Answer:- a) chlorine
Chlorine is a chemical which is used to disinfect the water. Other options given like washing soda , silica and coal act as an impurities in the water
7) The system of a network of pipes used for taking away wastewater from homes or public buildings to the treatment plant is known as
a) Sewers
b) Sewerage
c) Transport system.
d) Treatment plant
Answer:- b) sewerage
Sewerage is the system of a network of pipes used for taking away wastewater from homes or public buildings to the treatment plant .
8) Which of the following is a part inorganic impurities of the sewage?
a) Pesticides
b) Urea
c) Phosphates
d) Vegetable waste
Answer:- c) phosphates
Phosphates is a part of inorganic impurities of the sewage. Other are Organic impurities.
9) In a filtration plant water is filtered using layers of
a) Sand and clay.
b) Clay and fine gravel
c) Sand and fine gravel
d) Sand, fine gravel and medium gravel.
Answer:- d) sand, fine gravel and medium gravel.
In filtration plant water is filtered using layers of sand , fine gravel and medium gravel. This process is used in wastewater treatment plant.
10) Which of the following is not a source of waste water ?
a) Sewers
b) Homes
c) Industries
d) Hospitals
Answer:-a) sewers
Sewers is not a source of waste water. Sewer is the network of small and big pipes which carries waste water.
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Very Short Answer Questions
11) Why are open drains a concern ?
Answer:- Opendrainage is a concern because in the open drainage due to unhygienic and unsanitary condition flies, mosquitoes and other insects breed. Due to open drainage it easily comes out and comes in contact with human beings which lead to the disease like typhoid, cholera , dysentery etc. Sometimes dengue , and maleria also. This is very dangerous for human beings.
Also in open drainage situation goes worst in rainy reason. In the heavy rains drainage starts overflowing which is the worst condition in hygienic. Therefore the open drainage is a concern.
12) State whether the following statements are true or false. In case a statement is false, write the correct statement.
A) Sewage is a solid waste which causes water pollution and soil pollution.
Answer:- False
Sewage is a liquid waste which causes water pollution and soil pollution.
B) Used water is wastewater.
Answer:- True.
C) Wastewater could be reused.
Answer:- True
D) Where underground sewerage systems and refuse disposal systems are not available, the high cost on-site sanitation system can be adopted.
Answer:- False.
Where underground sewerage systems and refuse disposal systems are not available, the low cost on site sanitation system can be adopted.
13) How are open drains harmful for human health?
Answer:-
Open drainage is always a concern Because it leads to the unhygienic conditions. Flies, mosquitoes, and other harmful insects breed on the open drainage. Which comes in contact with the human beings, causing dengerous diseases like, typhoid , cholera , dysentery, maleria, dengue etc.
Open drainage is very unhygienic as it contains human excrete also but in the rainy season drainage gets fully overflow due to which the human faeces also flow in the form of sludge over the road. Which is also unhygienic for health. Also open drainage repelled very foul smell. Many times accident occurs in the rainy season people fall in the open drainage as they cannot see that. These are the harmful effects of open drains.
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Short Answer Questions
14) Name two inorganic impurities present in sewage .
Answer:-
Name of two inorganic impurities present in sewage are –
Nitrates and phosphates.
15) Animals waste, oil and urea are some of the organic impurities present in sewage. Name two more organic impurities present in sewage.
Answer:- Name of two organic impurities present in the sewage are –
Pesticides and herbicides, also fruit and vegetables waste.
16) Name two alternatives arrangements for sewage disposal where there is no sewerage system.
Answer:- To improve the sanitation facilities, low coast sewage disposal are being used now a days –
Septic tanks, composting pits and chemical toilets.
Are the alternative arrangements for sewage disposal if there is no sewerage system.
17) A man travelling in a train threw an empty packet of food on the platform. Do you think this is a proper waste disposal method? Elaborate.
Answer:- No. This is not a proper disposal method.
Now a days government of India is carrying out misson which is “swachhbharat”.
Under the mission proper waste disposal, sewage disposal, is started.
If there is a dry waste like food packet or something we should throw it in the dry waste dustbin which are always kept on any platforms. We should not throw it anywhere on the station. This is our responsibility to keep platform clean. Using dustbin for dry and liquid waste is necessary for today. Also it keeps hygiene in our surroundings.
18) Why should we not throw
a) Used tea leaves into sink?
Answer:- we should not throw used tea leaves in the sink as it may choke the drainage and sink pipes. They will not allow free flow of oxygen which will effect on degradation process.
b) Cooking oil and fats down the drain?
Answer:- cooking oil and fats can be Harden and block the pipes of drainage. Fats clog the soil pores in the open drainage which reduces the effectiveness of filtering water. Thus we should not throw cooking oil and fats in the drains but in the dustbins.
19) Match the items of Column I with the items of Column II with reference to sewage.
Column I | Column II |
a) Inorganic impurities | i) Phosphorus and nitrogen |
b) Organic impurities | ii) Nitrates and phosphates |
c) Nutrients | iii) Cholera and typhoid |
d) Bacteria | iv) Pesticides and herbicides |
Answer:-
a) Inorganic impurities → ii) nitrates and Phosphates
b) Organic impurities →iv) pesticides & Herbicides
c) Nutrients → i) phosphorus Andnitrogen
d) Bacteria → iii) cholera and Typhoid
20) Given below is a jumbled sequence of the processes involved in a wastewater treatment plant. Arrange them in their correct sequence.
A) Sludge is scraped out and skimmer removes the floating grease.
B) Water is made to settle in a large tank with a slope in the middle.
C) Large objects like plastic bags are removed by passing wastewater through bar screens.
D) Sand, grit and pebbles are made to settle by decreasing the speed of incoming wastewater.
E) Wastewater enters a grit and sand removal tank.
Answer:-
C) large objects like plastic bags are removed by passing wastewater through bar screens.
E) wastewater enters a grit and sand removal tank.
D) sand, grit and pebbles are made to settle by decreasing the speed of incoming wastewater.
B) water is made to settle in a large tank with a slope in the middle.
A) sludge is scraped out and skimmer removes the floating grease.
21) Three statements are provided here which defines the terms (a) sludge (b) sewage (c) wastewater. Pick out the correct definition for each of these terms.
A) The settled solids that are removed in wastewater treatment with a scraper.
Answer:- sludge
B) Water from kitchen used for washing dishes.
Answer:- wastewater
C) Wastewater released form homes, industries, hospitals and other public buildings.
Answer:- sewage
22) A mixture (x) in water contains suspended solids, organic impurities , inorganic impurities (a), nutrients (b), disease causing bacteria and other microbes. Give names for (x) , (a) and(b)?
Answer:- As per given statement ,
X is the sewage a mixture which contains suspended solids, organic impurities , inorganic impurities and nutrients.
A is nitrates, phosphates and metal which are inorganic impurities in the sewage.
B is phosphorus and nitrogen are nutrients bacteria and other microbes.
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Long Answer Questions
23) What are the different types of inorganic impurities and organic impurities generally present in sewage?
Answer:-
Organic impurities are fruit and Vegetables wastes, animal waste, urea , pesticides and herbicides, human faeces, oil, etc
Inorganic impurities are nitrates, phosphates, and metals which are generally present in sewage.
24) The terms sewage, sewers and sewerage are interlinked with each other. Can you explain, how?
Answer:-
Sewage – sewage is a mixture of wastewater from the homes, hospitals , industries , offices and other users, it also contains rainwater which runs on the roads . Sewage is a liquid waste.
Sewers-pipes which carry the sewage is known as sewers.
Sewerage- small and big pipes which carry sewage forms a network of pipe is known as sewerage.
25) Fill in the blanks in the following statements using words given in the box.
Air, handpumps, cholera, water, large , ground
A very __________ number of our people defecate in the open . It may cause ___________ pollution and soil pollution. Both the surface water and ___________ water gets polluted. ____________ water is the source for wells, tubewells and ____________. Thus it becomes the most common route for _________ borne diseases like ___________ , dysentery, etc.
Answer:-
A very large number of our people defecate in the open. It may cause water pollution and soil pollution. Both the surface water and ground water get polluted. Ground Water is the source for wells, tubewells and handpumps thus it becomes the most common route for water borne diseases like cholera, dysentery, etc.
26) Describe various steps of cleaning wastewater in a treatment plant.
Answer:-
Steps of cleaning wastewater in the treatment plant are-
Waste water contains physical, chemical and biological matter which contaminates the wastewater.
Which is removed by treatment of physical, chemical and biological processes.
1) For removing large objects like rags, sticks , cans , plastic packets, and napkins wastewater is passed through bar screens.
2) After removing these large sized waste water goes further to grid and sand removal tank. Speed of water decreases for allow sand , grit and pebbles to settle down.
3) After that water is settled in large sized tanks which have slopes in the middle. In which solids like faeces settled at bottom remove with a scraper which is known as sludge.
4) Floatable solids like oil and grease is removed by the skimmer. Now the water is known as clarified water.
5) Sludge is then transferred to the separate tank where it is decomposed with the help of anaerobic bacteria.
6) This biogas produced over here can be used as fuel or to produce electricity.
7) After that air is pumped into the clarified water which help the aerobic bacteria to grow.
8) These bacteria consume the human waste , food waste, other unwanted matter and soaps .
9) The suspended microbes settle at the bottom of tank. It becomes activated sludge after several hours.
10) Water is removed from the top of these tanks.
11) These activated sludge is 97% water.
12) These water is removed by machines or sand drying beds .
13) The dried sludge is used as manure, which in turns return the organic matter and nutrients into the soil.
14) The treated water is discharged into the sea or river or into the ground water .
15) Sometimes it is disinfect with chemicals like chlorine and ozone.
Thus the process of waste water treatment plant is carried out.
27) Think and suggest some ways to minutes waste and pollutants at their source, taking your home as an example.
Answer:-
To minutes waste and pollutants at their sources we should not throw used tea leaves and the remained solid food in the sink. Which blocks the sink pipe and the drainage. We should throw that solid waste in the dustbins.
Cooking oil and fats block the sink, these Harden and block the pipes, which further clog the soil pores reduce the effectiveness of filtering water.
We should not throw chemicals in the sink. Like paints, solvents, motor oil, medicines which kill microbes, insecticides, etc. We should throw it in dustbins.
Soft toys, cotton and sanitary napkin etc. Should be thrown in dustbins not in the drain. These waste choke the drainage and hampers the degradation process.