Lakhmir Singh Solutions for Class 7 Science Chapter 18 Wastewater Story - PDF

Very Short Answer Type Questions 

1. Name two organic impurities present in sewage.

Ans: Human faeces and fruits and vegetable waste are two organic impurities present in sewage.

2. Name two inorganic impurities present in sewage.

Ans: Nitrates and phosphates are two inorganic impurities present in sewage.

3. Name two nutrients present in sewage. 

Ans: Nitrogen and potassium are two nutrients present in sewage. 

4. What type of microbes present in sewage cause diseases such as cholera and typhoid?

Ans: Bacteria present in sewage cause diseases such as cholera and typhoid. 

5. Name two diseases which are caused by bacteria present in sewage. 

Ans: Cholera and typhoid are two diseases that are caused by bacteria present in sewage.

6. Name one disease which is caused by microbes (other than bacteria) present in sewage.

Ans: Dysentery is a disease that is caused by microbes (other than bacteria) present in sewage.

7. Write the full form of WWTP.

Ans: The full form of WWTP is a wastewater treatment plant. It is a wastewater treatment plant used to treat industrial waste. 

8. Name two chemicals used to disinfect water.

Ans: Chlorine and ozone are two chemicals used to disinfect water.

9. Name the solid waste extracted during sewage treatment.

Ans: Sludge is solid waste extracted during sewage treatment. 

10. Name two things that can be made from sludge extracted during the treatment of sewage.

Ans: Biogas and manure are two things that can be made from sludge extracted during the treatment of sewage.

11. What is the cause of a large number of diseases in our country? 

Ans: Poor sanitation and contaminated drinking water are the cause of a large number of diseases in our country

12. Name any four water-borne diseases which are caused by drinking contaminated water.

Ans: The four water-borne diseases which are caused by drinking contaminated water are:

• Cholera

• Typhoid

• Dysentery 

• Diarrhoea

13. State whether the following statement is true or false:

Human excreta can be used in biogas plants.

Ans: The statement is true human excreta can be used in biogas plants. 

14. Name any two low-cost, onsite sewage disposal systems for human waste.

Ans: Septic tank and vermicompost unit are two low-cost, onsite sewage disposal systems for human waste.

15. What type of sewage disposal system will be suitable for an isolated cluster of 4 or 5 houses in an area where there is no sewerage? 

Ans: Septic toilets are the type of sewage disposal system suitable for an isolated cluster of 4 or 5 houses in an area where there is no sewerage. 

16. What type of toilets are most suitable for holding an outdoor music festival in a park?

Ans: Chemical toilets are the type of toilets most suitable for holding an outdoor music festival in a park. 

17. What type of toilets are the most suitable for an area where water supply is limited?

Ans: Composting toilets are the type of toilets that are most suitable for an area where water supply is limited. 

18. What type of toilets are used in aeroplanes?

Ans: Vacuum toilets are the type of toilets used in aeroplanes. 

19. At a sewage treatment plant, what type of bacteria work: 

1. in the digester tank,

2. in the aeration tank?

Ans:

1. Anaerobic bacteria work in the digestion tank. 

2. Anaerobic bacteria work in the aeration tank 

20. Fill in the following blanks with suitable words :

1. Wastewater released by houses is called..........

Ans: Wastewater released by houses is called sewage. 

Sewage wastewater is wastewater produced by a community of people. 

2. Cleaning of water is a process of removing ............

Ans: Cleaning of water is a process of removing contaminants. 

Contaminants are toxic or harmful substances. 

3. Dried ...........is used as manure.

Ans: Dried dung is used as manure.

Manure is the organic fertiliser. 

4. Drains get blocked by ............and ...........

Ans: Drains get blocked by sludge and plastics. 

Sludge is the byproduct of wastewater treatment. 

Plastics are non-biodegradable materials. 

5. Untreated human excreta is a ............hazard.

Ans: Untreated human excreta is a health hazard.

Untreated human excreta may cause soil pollution and water pollution.

6. Untreated human excreta may cause .......... pollution and ......... pollution.

Ans: Untreated human excreta may cause soil pollution and water pollution.

Untreated human excreta is a health hazard.

7. Vermi-processing toilets use..........to treat human waste.

Ans: Vermi-processing toilets use earthworms to treat human waste.

Earthworms treat human waste. They turn human waste into a cake of vermin that is used as manure. 

8. All the portable toilets are..............toilets.

Ans: All the portable toilets are chemical toilets.

Chemical toilets are movable and self-contained toilets.

9. Poor sanitation in crowded public places can result in the spread of..........

Ans: Poor sanitation in crowded public places can result in the spread of disease. 

Diseases are the particular state of an abnormal condition. 

Short Answer Type Questions 

21. What is meant by :

1. sewer

2. sewerage?

Ans: 

1. Sewer - The sewer is the carrier channel that carries wastewater from its point of source to the treatment plant 

There are three types of modern sewer systems are

•  Sanitary sewers (foul sewers) 

• storm sewers (surface water sewers)

•  combined sewer.

2. Sewerage - The physical facility through which the sewage flows is known as sewerage. A few examples of sewerage are pipes, lift stations, disposal facilities, etc. 

22. Explain the function of the bar screen in a wastewater treatment plant.

Ans:

• A bar screen is a filter that is used to filter large impurities such as plastic, cans, large objects, etc. 

• The wastewater is passed through the bar screen so that large impurities present in the wastewater are removed. 

• It is the first level of filtration of wastewater used by the wastewater treatment plant. 

23. What is sludge? Explain how it is treated.

Ans: Human waste that is produced during the treatment of wastewater is known as sludge. Human faeces is included in this. This is an organic waste that is used to produce biogas and manure. A tool known as a scraper is used to remove the sludge and transfer it to the tank. 

24. Name two useful substances which are produced by the treatment of sewage. State their uses.

Ans: The two useful substances which are produced by the treatment of sewage are biogas and manure. 

Biogas - Biogas can be used as fuel. It contains different types of gases. Biogas is produced by the breakdown of organic matter in the absence of oxygen. 

Manure - Manure is an organic fertiliser. It is obtained by the decomposition of dead plants and animals.

25. What is the purpose of bubbling air into the aeration tank during the treatment of sewage?

Ans:

•  Before reaching the aeration tank, wastewater is mixed with the activated sludge that contains different types of microorganisms i.e. aerobic and anaerobic microorganisms. 

• These microorganisms are capable of degrading the organic waste present in the wastewater.

• The reason for bubbling air into the aeration tank during the treatment of sewage is to provide oxygen to the aerobic bacteria. So that they provide pure water by removing the impurities during the treatment. 

26. Name the various wastes which should not be thrown down the drain. Why?

Ans: 

• The various wastes which should not be thrown down the drain are cooking oil and fat. 

• They hardened the sewage pipes and also blocked them. 

• Fats restrict the flow of water into the soil by blocking the holes in the soil. 

• Pores in the soil are important for filtering water. 

• Oil and fats are insoluble in water. 

27. Why should oils and fats not be released into the drain?

Ans:

• Oils and fats should not be released into the drain because it affects the soil fertility and blocks the sewage pipes. 

• They hardened the sewage pipes and also blocked them. 

• Fats restrict the flow of water into the soil by blocking the holes in the soil. 

• Pores in the soil are important for filtering water. 

• Oil and fats are insoluble in water.

28. What is a vermi-processing toilet? Name the useful by-product obtained from such toilets.

Ans:

• The toilets in which human waste is treated with earthworm are known as Vermi-processing toilets. 

• In this type of toilet low water is used. 

• Vermi-processing toilets provide a good quality of manure. It increases the fertility of the soil. 

• The useful byproduct produced in this process is known as vermin cake. 

29. What will happen if the large amount of waste generated in public places is not disposed of properly?

Ans: If the large amount of waste generated in public places is not disposed of properly following problems occur: 

• Many diseases can be spread due to Improper disposal of human waste. 

• The ecosystem may be affected. 

• It will cause death to many living organisms. 

• Improper disposal of waste contaminates the entire environment. 

30. With the help of an example, outline your role as an active citizen in relation to sanitation.

Ans: An active citizen has many responsibilities in relation to sanitation. 

• Separate the trash as biodegradable and non-biodegradable, and throw them into a separate dustbin. 

• Ensure the proper management of the sewage system.

• Chemicals should not be drained directly into water that harms aquatic life. 

• Leakage problems in the sewerage system should be informed to the municipal cooperation. 

Long Answer Type Questions

31. What is sewage? State the various ways in which we produce sewage in our homes. What is the name of underground pipelines which carry sewage from our homes to the wastewater treatment plants?

Ans: The wastewater that is produced by the group of people is known as sewage.  Sewage is produced in different ways in our houses are:

• Sewage is produced in the kitchen by cleaning vegetables and utensils. 

• Sewage is produced by washing clothes in the houses. 

• Sewage containing rainwater comes from the pipes of buildings and houses. 

• Sewage contains human waste(excreta). 

The underground pipelines which carry sewage from our homes to the wastewater treatment plants are known as a sewer. 

There are three types of modern sewer systems are

• Sanitary sewers (foul sewers) 

• storm sewers (surface water sewers)

•  combined sewer.

32. 

1. Explain why it is harmful to discharge untreated sewage into rivers, lakes, or ground.

2. What is meant by the 'treatment of sewage'? What is its main purpose?

Ans:

1. The liquid that discharges from houses, industries, and agricultural activities is known as sewage. It is harmful to discharge untreated sewage into rivers, lakes, or the ground because it contains harmful chemicals released from the industries. It pollutes the water and harms aquatic life. This water used for cooking and drinking causes diseases like cholera, diarrhoea, etc.

2. 
   

• Treatment of sewage is the process of removing waste, pollutants, impurities, and harmful chemicals from the wastewater. 

• The purpose of this sewage treatment is to make water harmless and remove pollutants.  

• After this treatment water is now suitable to dispose into the river, ponds, etc. 

33. Draw a labelled sketch of a wastewater treatment plant. Describe the various steps involved in getting clear water from wastewater. Which fuel can be extracted during this process?

Ans: The steps in which sewage treatment plant work are :

• Bar screen: It removes the large impurities. 

• Grit and sand removal tank: After passing through the bar screen, wastewater is passed through the grit and sand removal tank. In this tank sand and grit settle down at the bottom of the tank. 

• First sedimentation tank: Now wastewater passes through the first sedimentation tank, in this tank large organic impurities settle down at the bottom of the tank. 

• Aeration tank: After the first sedimentation tank, wastewater passes through the aeration tank. 

• Second sedimentation tank: In this tank, microorganisms settle down that are used in the aeration tank, and at last activated sludge is formed.

• The first sedimentation tank gives most of the sludge that is used to obtain the biogas fuel. A large amount of sludge is settled down at the sloping bottom of the first sedimentation tank.

Wastewater Treatment Plant

34. Explain the relationship between sanitation and disease. State the various ways in which you can contribute to maintaining sanitation in public places.

Ans:

•  The relation between sanitation and disease is that poor sanitation causes diseases. 

• Many diseases are caused by poor sanitation and contaminated drinking water.

• Poor sanitation leads to the growth of mosquitoes, flies, etc that cause many diseases like typhoid, dengue, dysentery, etc

• So it is necessary to make our environment clean and have good sanitation. 

The various ways in which you can contribute to maintaining sanitation in public places are:

• Separate the trash as biodegradable and non-biodegradable, and throw them into the separate dustbin. 

• Ensure the proper management of the sewage system.

• Chemicals should not be drained directly into water that harms aquatic life. 

• Leakage problems in the sewerage system should be informed to the municipal cooperation. 

Sewage System

35. What is a septic tank? Describe the septic tank-based toilet with the help of a labelled diagram. Where are septic tank toilets used?

Ans: 

• An underground chamber made up of plastic used to carry the domestic wastewater for treatment is known as a septic tank. 

• The tank has two pipes, one is an inlet pipe and the other is an outlet pipe for entering and outgoing wastewater. 

• The toilet based on the septic tank has a toilet seat connected to the tank, and human excreta is collected with the help of an inlet pipe. The solid form of excreta remains at the bottom and the liquid form remains above it. 

• The liquid flows outside with the help of an outlet pipe. Most of the solid sludge is decomposed by aerobic bacteria. 

• Septic toilets are suitable for places that do not have any sewage system. 

Multiple Choice Questions 

36. Which of the following statements about ozone are correct?

1. It is essential for the breathing of living organisms

2. It is used to disinfect water

3. It absorbs ultraviolet rays 

4. Its proportion in the air is about 3 

1. A and B

2. B and C

3. A and C

4. B and D

Ans: Option (b) B and C are correct. 

Ozone is used to purify the water and also absorbs ultraviolet rays. 

37. Which of the following is not an inorganic impurity present in sewage?

1. nitrate

2. phosphate

3. urea

4. metal salt

Ans: Option (c) urea is correct.

Urea is an inorganic fertiliser. It is not an inorganic impurity present in sewage. 

38. Which of the following organisms produce biogas from sludge in the digester tank of a wastewater treatment plant?

1. anaerobic bacteria

2.  fungi

3. aerobic bacteria

4. protozoa

Ans: Option (a) aerobic bacteria is correct.

Aerobic bacteria are those that require oxygen for their survival. 

39. Which of the following can be used to disinfect the clean water in a sewage treatment plant before releasing it into the distribution system?

1. Iodine

2. Ozone

3. Oxygen

4. Chlorine

1. A and B

2. B and C

3. B and D

4. Only D

Ans: Option (c)  B and D are correct.

Ozone and chlorine can be used to disinfect the clean water in a sewage treatment plant before releasing it into the distribution system

40. Which of the following is not a water-borne disease?

1. cholera

2. tuberculosis

3. typhoid 

4. dysentery

Ans: Option (b) tuberculosis is correct.

Tuberculosis is a disease caused by bacteria. It attacks the kidney, spine, and brain. 

41. One of the following types of trees is said to help in purifying wastewater quite rapidly when planted all along the sewage ponds. These are:

1. eucalyptus trees

2. ficus trees

3. neem tree

4. peepal trees

Ans: Option (a) eucalyptus trees are correct.

Eucalyptus trees are a type of trees that are said to help in purifying wastewater quite rapidly when planted all along the sewage ponds.

42. Which of the following are used for the safe disposal of human excreta in those areas where sewerage systems do not exist and water supply is limited or not available at all?

1. chemical toilets

2. vacuum toilets

3. septic tank toilet 

4. composting toilets

Ans: Option (d) composting toilets is correct.

Composting toilets are used where water supply is limited or not available at all.

43. Vacuum toilets are usually used in:

1. superfast trains

2. cinema halls

3. aeroplanes 

4. large ships

Ans: Option (c) of aeroplanes is correct.

Vacuum toilets are the type of toilet that use the minimum amount of water. 

Questions Based on High Order Thinking Skills (HOTS)

44. A sewage treatment plant involves the following steps in its working :

1. Aeration tank, Grit and sand removal tank, Second sedimentation tank, Bar screen, First sedimentation tank

2. Arrange all the above steps in the correct order in which they occur in the sewage treatment plant.

Which step gives most of the sludge which is used for obtaining biogas fuel?

Ans:

1. The steps in which sewage treatment plant work are :

• Bar screen: It removes the large impurities. 

• Grit and sand removal tank: After passing through the bar screen, wastewater is passed through the grit and sand removal tank. In this tank sand and grit settle down at the bottom of the tank. 

• First sedimentation tank: Now wastewater passes through the first sedimentation tank, in this tank large organic impurities settle down at the bottom of the tank. 

• Aeration tank: After the first sedimentation tank, wastewater passes through the aeration tank. 

• Second sedimentation tank: In this tank, microorganisms settle down that are used in the aeration tank, and at last activated sludge is formed.

2. The first sedimentation tank gives most of the sludge that is used to obtain the biogas fuel. A large amount of sludge is settled down at the sloping bottom of the first sedimentation tank. 

45. Some of the alternative sewage disposal systems for human waste are given below:

Chemical toilets, Composting toilets, Vacuum toilets, Septic tank toilets, Vermi-processing toilets.

1. Which of these toilets provides high-quality manure?

2. Which of these toilets are used in aeroplanes?

3. Which of these toilets are used at outdoor gatherings like marriages?

4. Which of these toilets are used where water supply is limited or not available at all?

5. Which of these toilets is most likely to contaminate water from a hand pump installed nearby?

Ans: 

1. Vermi-processing toilets provide a good quality of manure. In this type of toilet human waste is treated with earthworms. 

2. Vacuum toilets are used in aeroplanes. 

3. Chemical toilets are used at outdoor gatherings like marriage. 

4. Composting toilets are used where water supply is limited or not available at all. 

5. Septic tank toilets are most likely to contaminate water from a hand pump installed nearby. 

Importance of Lakhmir Singh Class 7 Science Chapter 18 Wastewater Story

This chapter holds immense significance in developing a conceptual foundation related to pollution, wastewater management, and its various aspects. Students will learn the definitions and descriptions of wastewater and the processes involved in treating it.

It will explain what wastewater is and how it is formed from different sources. The contaminants and impurities of wastewater will also be explained along with their sources. Students will become aware of how wastewater can harm the environment if not treated before release.

They will also learn how different impurities are treated and wastewater is made safer to release in nature for automatic recycling. They will find out how certain impurities emerge in water and how they affect the natural factors of the ecosystem.

This chapter will explain how wastewater can cause various diseases. The source of waterborne diseases will also be explained in this chapter with proper description. Students will learn how to get rid of such diseases. They will also understand the importance of safe water for drinking and other household uses.

This chapter will proceed to explain what sewage is and how wastewater management is done in big cities. Villages and suburban areas are not the prime contributors of wastewater. Industrial areas and urban development are the prime sources of sewage water.

Thus, Chapter 18 Class 7 Science is of utmost importance as it makes students aware of how urban growth can affect the natural sources of water. They will also learn the necessary measures to take and save such sources.

Benefits of Lakhmir Singh Class 7 Science Chapter 18 Wastewater Story Solutions

• These solutions will be the ideal study material for the students to practice the exercise questions. They will learn how to answer the fundamental questions by using the concepts explained in this chapter.

• They will also be able to use the Lakhmir Singh Class 7 Science Chapter 18 question answers for evaluation of their preparation. By answering the questions and comparing them to these solutions, they will figure out which part of this chapter needs more focus.

• Resolving doubts will become a lot easier with these solutions, as there is no need to wait when you can do it on your own.

Download Lakhmir Singh Class 7 Science Chapter 18 Solutions PDF

Why wait then? Get the free PDF version of these solutions for free from Vedantu. Find out how the experts have framed the answers to the questions and develop your answering skills. Learn the concepts and principles of this chapter properly by following the Ch 18 Class 7 Solutions to score more in the exams