Monday , July 6 2020
7th Class CBSE Science NCERT Book

Wastewater Story: 7th Class NCERT CBSE Science Ch 18

Wastewater Story 7th Class NCERT CBSE Science Chapter 18

Question: Wastewater is fit for human consumption or not. Give reason to support your answer.

Answer: No, because it is dirty and has many diseases causing organisms like cholera, typhoid etc.

Question: Name two chemicals used to disinfect wastewater.

Answer: Chlorine and ozone

Question: Special type of toilets has been designed in aeroplanes, name it.

Answer: Vacuum toilets

Wastewater Story NCERT – Question: Name the toilets used in areas with limited water supply.

Answer: Vermi-processing toilets

Question: Name the type of toilets which are most suitable for holding an outdoor music festival in a park.

Answer: Chemical toilets

Question: Name two things that can be made from sludge extracted during treatment of sewage.

Answer: Biogas and manure

Wastewater Story NCERT – Question: The Eucalyptus trees are planted along sewage ponds. Give reason.

Answer: The Eucalyptus trees are planted along sewage ponds because these trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.

Question: One can avoid the addition of the load in WWTP. Justify.

Answer: By following proper sanitation and house-keeping practices, by creating less waste at an individual level, we can avoid the addition of the load in wastewater treatment plant.

Question: Name two inorganic impurities present in sewage.

Answer: Inorganic impurities present in sewage are nitrates and phosphates.

Question: Mention the use of dried sludge.

Answer: It is used as manure, thus returning organic matter and nutrients to the soil.

Question: In which type of toilets, human excreta is treated by earthworm?

Answer: Vermi-processing toilets

Question: Give some examples of onsite sewage disposal systems.

Answer: Chemical toilets, septic tanks, composting pits, etc.

Question: Sewage contains some organic impurities in it. Name them.

Answer: Human feces, animal wastes, oil, urea pesticides, herbicides, fruits and vegetables are the organic impurities present in sewage.

Question: Mention the common process of cleaning of wastewater.

Answer: Sewage treatment

Question: World Water Day is celebrated on

Answer: 22 March

Question: Mention the period proclaimed as the International Decade for action on Water for Life.

Answer: 2005 – 2015 is the period proclaimed as the International Decade for action on Water for Life.

Question: Name the three processes involved in treatment of wastewater.

Answer: Treatment of wastewater involves physical, chemical and biological processes for removing different types of contaminants.

Question: Explain sewers and sewage.

Answer: Sewers are the pipes acting as a transport system that carries sewage from point of origin to the point of disposal. The wastewater released from homes, industries, hospitals, offices and other uses is called sewage.

Question: The used water should not be wasted. Do you agree? Justify.

Answer: The used water should not be wasted but it should be cleaned.

Question: Bleaching powder is mixed in water, why? Think and give appropriate reason for it.

Answer: Bleaching powder is mixed in water to make it safe for drinking because it kills the harmful germs present in water.

Question: Natural water is the purest form of water. Explain why or why not.

Answer: Natural water is not pure always. It is because all types of water except rainwater contain salts dissolved in it. These salts make the water impure.

Wastewater Story NCERT – Question: Mention the role of effluent treatment plants in cities.

Answer: The effluent treatment plants filter out undissolved materials form water.

Question: Protozoa is causative organism of which waterborne disease?

Answer: Dysentery

Question: In the chemical process of water treatment, water is treated with some chemicals. Describe chlorination in light of it.

Answer: Chlorination is the process of adding chlorine (chemical) in water to make it safe for drinking.

Question: Sanitation can be improved. Explain, what step should be taken to improve it.

Answer: Low cost onsite sewage disposal system must be encouraged to improve sanitation.

Wastewater Story NCERT – Question: Give the percentage of water being activated in sludge.

Answer: About 97% of water is being activated in sludge.

Question: Animal waste, oil and urea are some of the organic impurities present in sewage. Name two more organic impurities present in sewage.

Answer: Fruits and vegetable wastes, pesticides and herbicides are organic impurities present in sewage other than animal wastes, oil and urea.

Wastewater Story NCERT – Question: Open drain is a big concern now-a-days. Justify.

Answer: Open drain is a big concern for the society now-a-days because they create unhygienic conditions. It provides favorable conditions to flies, mosquitoes and other insects to breed and spread a number of diseases.

Question: Explain, how sewage is disposed of in an aeroplane.

Answer: Aeroplanes have their closed waste sewage tanks in them, which suck the wastewater and collect it in their tanks. Once the aeroplane lands on the ground, the crew disposed of the sewage properly into airport sewage facility.

Question: Sewage also contains some nutrients Comment.

Answer: Sewage is a complex mixture which contains suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes. The nutrients present in sewage are phosphorus and nitrogen.

Question: Suggest two alternative arrangements for sewage disposal where there is no sewerage system.

Answer: The two alternative arrangements for sewage disposal, where there is no sewerage system are as below

  1. Septic tanks
  2. Composting pits.

Question: Recall and enlist some better house keeping practices.

Answer: We must minimize and manage waste at our houses before its disposal in the following manner:

  1. Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water. Throw oil and fats in the dustbin.
  2. Used tea leaves, solid food remains, soft toys, cotton, sanitary towels, etc., should also be thrown in the dustbin. These wastes choke the drains. They do not allow free flow of oxygen. This hampers the degradation process.
  3. The chemicals like paints, solvents, insecticides, medicines and motor oils should 1 State the role of screen bars in wastewater treatments, not be thrown in drains as they kill helpful 2 Chlorination makes water fit for human consumption. How? microbes which digest the organic waste.

Question: Water in a river is cleaned naturally. Do you agree? Think and explain.

Answer: Yes, river water is cleaned naturally by a process that is similar to wastewater treatment plant. As muddy water when flows through grass or weeds on its way to a stream, mud and solid particles get filtered out. At the bottom of a lake or stream, microorganism brings chemical changes in the water. The natural filtration process removes pollution from the groundwater throughout the process making it clean and fit for drinking.

Question: The terms sewage, sewers and sewerage are interlinked with each other. Can you explain, how?

Answer: The terms like sewage, sewers and sewerage are interlinked with each other because sewage is a mixture of wastewater coming out of homes and other places. Sewers are pipes which carry sewage and sewerage is a network of sewage carrying pipes.

Wastewater Story NCERT – Question: Describe onsite disposal systems.

Answer: Some organisations offer hygienic onsite human waste disposal technology. These toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The biogas produced is used as a source of energy.

Question: A sewage treatment plant involves few steps in its working. Aeration tank, grit and sand removal tank, second sedimentation tank, bar screen, first sedimentation tank.

  1. Arrange all the above steps in the correct order in which they occur in the sewage treatment plant.
  2. Which step gives most of the sludge?

Answer:

  1. Bar screen, grit and sand removal tank, first sedimentation tank, aeration tank, second sedimentation tank.
  2. First sedimentation tank.

Question: Give reasons for each of the following.

  1. We should not throw used tea leaves into sink.
  2. We should not throw cooking oil and fats down the drain.

Answer:

  1. We should not throw used tea leaves into sink because it may choke the drain-pipe of the sink.
  2. We should not throw cooking oil and fats down the drain as it can harden and block the drain-pipes.

Question: 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 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: The correct sequence of wastewater treatment in treatment plant is

(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.

Question: Can we contribute in sanitation at public places? Explain.

Answer: Yes, we all have a role to play in keeping our environment clean and healthy. All of us can contribute in maintaining sanitation at public places. We should not scatter litter anywhere. If there is no dustbin in sight, we should carry the litter home and throw it in the dustbin.

Question: Three statements are provided here which define the terms, i.e. sludge, sewage and wastewater.

Pick out the correct definition for each of these terms.

  1. The settled solids that are removed in wastewater treatment with a scraper.
  2. Water from kitchen used for washing dishes.
  3. Wastewater released from homes, industries, hospitals and other public buildings.

Answer:

  1. The settled solids that are removed in wastewater treatment with a scraper is sludge.
  2. Water from kitchen which is used for washing dishes is wastewater.
  3. Wastewater released from homes, industries, hospitals and other public buildings is sewage.

Question: 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, one must always put the waste in a nearby dustbin or carry it home and dispose it in dustbins there.
Waste, not properly disposed may enter into the drains and choke them. It also makes public places dirty and unhygienic.

Question: With reference to the treatment of polluted water at home by aeration, filtration, chlorination processes answer the following questions.

  1. What changes did we observe in the appearance of liquid after aeration? Did aeration change the odour?
  2. What is removed by the sand filter?
  3. Does chlorine change the colour of treated water?
  4. Do chlorine have an odour?

Answer:

  1. Aerated water contains some suspended impurities and the foul odour of the polluted water disappears completely after aeration.
  2. Sand filter removes tiny suspended impurities.
  3. Chlorine makes the water clear and colorless.
  4. Yes, chlorine have a peculiar odour which is not worse than wastewater.

Question: Observe the given figure and answer the following:

  1. What does this figure show?
  2. State the functions of each part of the figure?

Answer:

  1. This figure shows the supply of drinking water, its processing and its source as well. Functions of each part of the figure.
  2. Functions of each part:
    1. River It is the source of water.
    2. Pumping station Pump the water to collect it in reservoir.
    3. Sedimentation tank Impurities are settle in the bottom of tank.
    4. Sand and gravel and sand filter Remove the dirt from the water.
    5. Chlorinating tank Chlorine is mixed in water to disinfect the eater and to kill the germs.
    6. To overhead tank Purified water is stored in this tank for supply to the households for drinking.

Question: Complete the table given below of the contaminant survey.

Types of sewage Point of origin Substances which contaminate Any other remark
Sullage water Kitchen
Foul waste Toilets
Trade waste Industrial and commercial organisations

Answer: Given below is the table of contaminant survey explaining types of sewage with their point of origin an contaminate in them.

Type of sewage Point of origin Substances which contaminate Any other remark
Sullage water Kitchen Cooking oils, fats, etc. May choke drains
Foul waste Toilets Feces and urine Cause diseases like dysentery, cholera etc
Trade waste Industrial and commercial organisations Chemicals like paints, solvents, motor oil, etc. Causes water and soil pollution

Question: Explain the different types of inorganic and organic impurities generally present in sewage.

Answer: It is wastewater released by homes, industries agricultural fields and other human activities. It also includes rainwater that has run down the street during a storm or heavy rain and it is a liquid waste. Most of its water has dissolved and suspended impurities called contaminants.

Composition of Sewage: The following components make the sewage:

  1. The organic impurities present in sewage are human feces, animal wastes (like animal dung), urea (as urine), oil, fruits and vegetable wastes, pesticides, herbicides, etc.
  2. The inorganic impurities present in sewage are nitrates, phosphates and metals.
  3. The nutrients present in sewage are nitrogen and phosphorus.
  4. The bacteria present in sewage include those bacteria which cause water-borne diseases such as cholera and typhoid.
  5. The other microbes present in sewage are Protozoa which cause a water-borne disease called dysentery.

Question: Describe septic tank. How does it function?

Answer: Low cost outside sewage disposal system have been developed to take care of places where there is no sewage system, e.g. rural areas, isolated buildings. These are described below:

  1. Septic tanks Septic tank is a low cost onsite sewage disposal system. Septic tanks are suitable where there is no sewerage made. These tanks need cleaning every four to six months.
    A septic tank usually consists of a big, covered underground tank made of concrete having an inlet pipe at one end and on outlet pipe at the other end. The toilet seat is connected to the inlet pipe of the septic tank. The human excreta from the toilet seat enters into the septic tank through the inlet pipe. The solid part of excreta keeps on collecting at the bottom of the septic tank in the form of a sludge whereas watery waste remains above it.
    The anaerobic bacteria breakdown most of the solid organic matter present in human excreta due to which the volume of solid waste is reduced too much. The digested solid waste keeps on depositing at the bottom of septic tank. The watery waste is also cleaned by anaerobic bacteria. The excess water goes out of the septic tank through the outlet pipe and get absorbed in soil.
  2. Composting pits These are self sustained human waste disposal units which is not connected to a sewer line or a septic tank. A composting toilet breaks down and dehydrate human waste to compost.
  3. Chemical toilets These toilets have limited storage capacity for human waste and need to be emptied periodically. These are the toilets which use chemically treated reservoir located just below the toilet seats. The chemicals reduce the foul smell coming out of human excrete and carry out partial disinfection of human waste.

Question: Discuss vermi-processing toilets. Name the useful product obtained from such toilets.

Answer: In the vermi-processing toilet, the human excreta is treated by earthworms in a pit. The earthworms gradually eat up all the organic matter present in human excreta, decompose it and pass out from their body in the form of warm casting (also called vermi cakes).

The useful product obtained from a vermi-processing toilet is vermi cakes which is kind of high quality manure.

Question: One day Sachin had gone to his uncle who lives in a village. He saw there a large number of people defecate in an open area because proper toilet facilities are not there. He wondered about the groundwater contamination, as he studied in his class that this act may cause water-borne diseases. He convinced village people to make toilets to avoid such an out break of water-borne diseases.

  1. Name two water-borne diseases.
  2. Explain vermi-composting toilets.
  3. What values are shown by Sachin?

Answer:

  1. Typhoid and cholera.
  2. In vermi-composting toilets, human excreta is treated by earthworms in a pit.
  3. He is intelligent and conscious about health.

Wastewater Story NCERT – Question: There are many alternative sewage disposal systems which have been developed as per needs of the community, persons, occasions, etc. Few situations / specifications of the sewage need are given below. Write the name of sewage which can be used in the following conditions.

  1. A toilet which can provide high quality manure.
  2. The toilet which is used in aeroplane during flight.
  3. A toilet which can be used in some out door gathering.
  4. A toilet used in limited water supply.
  5. A toilet which contaminates water of hand pump installed nearby.

Answer:

  1. Vermi-composting toilets
  2. Vacuum toilets
  3. Chemical toilets
  4. Composting toilets
  5. Septic tank toilets

Question: Think and suggest some ways to minimize waste and pollutants at their source, taking your home as an example.

Answer: We can minimize waste and pollutants entering the water and create less wastewater by taking following few steps at home:

  • By not throwing used tea leaves, solid food remains, etc., in the drain. We should throw it in the dustbin.
  • By not throwing chemicals like medicines, paints, insecticides, etc., in the drain as they increase the pollution load of the sewage.

Question: Trisha has seen huge garbage dumps outside the school campus which are not being regularly disposed of by municipality of the area. She discussed the problem with her biology teacher and decided to organize a rally to spread awareness among local people.

Next day she delivered this information in the assembly and convinced the school mates to join her. She also explained them about the importance of sanitation at public places which she had recently studied in biology.

  1. In your views, who is responsible to maintain sanitation at public places?
  2. What would happen, if all the wastes produced at public places are not disposed of regularly?
  3. What are the values shown by Trisha?

Answer:

  1. In my opinion, municipality is responsible to maintain sanitation at public places.
  2. If all the wastes produced at public places are not disposed of regularly and properly epidemics could break out.
  3. Responsibility, sensitivity and awareness towards public hygiene.

Fill in the Blanks: Wastewater Story NCERT

  1. Untreated human excreta is a ………………. hazard.
  2. Vermi-composting toilets use ………………. to treat human waste.
  3. Poor sanitation is crowded public places can result in spread of ………………. .
  4. Dried sludge is used as ………………. .
  5. 5. Wastewater is treated in ………………. treatment plant.
  6. 6. Wastewater released by houses is called ………………. .
  7. 7. Stagnant water blocked in drains is good breeding place for ………………. .
  8. 8. All portable toilets are ………………. toilets.
  9. 9. The full form of WWTP is ………………. .
  10. 10. Bacteria play important ………………. in sewage treatment.

Answers:

  1. health
  2. earthworms
  3. diseases
  4. sludge activator
  5. waste
  6. sewage
  7. insect vectors
  8. chemical
  9. wastewater treatment plant
  10. role

True / False

  1. Sewage is a solid waste which causes water pollution and soil pollution.
  2. Used water is wastewater.
  3. Wastewater could be reused.
  4. Where underground sewerage systems and refuse disposal systems are not available, the high cost onsite sanitation system can be adopted.
  5. We should not defecate is open because untreated human waste is a health hazard.
  6. Cooking oil, fats should not be thrown in the drainage system directly.
  7. Microorganisms are present in the domestic waste also.
  8. Poor sanitation and contaminated drinking water is the cause of a large number of diseases.
  9. Wastewater is transparent, colorless, odorless.
  10. Tuberculosis is a water-borne disease.
  11. Aerobic bacteria produces biogas sludge in the digester tank.
  12. urea is an inorganic impurity present in sewage.

Answers:

  1. False, sewage is a liquid waste which causes water pollution and soil pollution.
  2. True
  3. True
  4. False, where underground sewerage systems and refuse disposal systems are not available, the low cost onsite sanitation system can be adopted.
  5. True
  6. True
  7. True
  8. True
  9. False, potable water is transparent, colorless and odorless.
  10. False, water-borne diseases are cholera, typhoid, dysentery, etc.
  11. False, anaerobic bacteria produce biogas.
  12. False, urea is an organic impurity present in sewage.

Wastewater Story NCERT – Question: Match the Column I with Column II.

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:

  1. (a) – (ii)
  2. (b) – (iv)
  3. (c) – (i)
  4. (d) – (iii)

Check Also

7th Class CBSE Science NCERT Book

Reproduction in Plants: 7 NCERT CBSE Science Chapter 12

Reproduction in Plants 7th Class NCERT CBSE Science Chapter 12 Question: Why is the process of reproduction …

Leave a Reply

Your email address will not be published. Required fields are marked *