NCERT Solutions Class 7 Science Chapter 13 Wastewater Story

The thirteenth chapter of Class 7 Science, Wastewater Story, is an important exploration into topics crucial for understanding water management and sanitation. This chapter emphasizes key concepts, including Water - Our Lifeline, Clean Water, What is Sewage?, Water Freshens Up – An Eventful Journey, and the workings of a Wastewater Treatment Plant (WWTP). It provides valuable insights into Better Housekeeping Practices to reduce pollution and prevent diseases, alongside discussions on Sanitation and Disease control. Students will also learn about Alternative Arrangements for Sewage Disposal and the importance of Sanitation at Public Places. This chapter is essential for grasping how we manage waste and protect our water resources. For those seeking more detailed guidance, NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story offers comprehensive answers, helping students understand every aspect of this topic.

1.0Download Class 7 Science Chapter 13 Wastewater Story Question Answer

This article provides NCERT-aligned solutions for Class 7 Science Chapter 13, Wastewater Story. Practicing these solutions will help students build a solid foundation in science, enhance their problem-solving skills, and prepare effectively for exams. 

For comprehensive guidance, students can download the expert-curated NCERT Class 7 Science Chapter 13 PDF solution by ALLEN below.

2.0Class 7 Science Chapter 13 Wastewater Story Overview

Before diving into the details of the NCERT Solutions for Class 7 Science Chapter 13, Wastewater Story, let's take a quick look at the main topics and subtopics covered in this chapter of the NCERT Class 7 Science book.

Topics covered in this Chapter

1. Water, Our Lifeline
2. What is Sewage?
3. Water Freshens Up - An Eventful Journey
4. Wastewater Treatment Plant (WWTP)
5. Better Housekeeping Practices
6. Sanitation and Disease
7. Alternative Arrangement for Se

3.0NCERT Questions with Solutions for Class 7 Science Chapter 13 - Detailed Solutions

• Fill in the blanks: (a) Cleaning of water is a process of removing _______. (b) Wastewater released by houses is called _______. (c) Dried _______ is used as manure. (d) Drains get blocked by ______ and_______. Ans. (a) Cleaning of water is a process of removing pollutants. (b) Wastewater released by houses is called sewage. (c) Dried sludge is used as manure. (d) Drains get blocked by cooking oil and fats.
• What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas. Ans. Sewage is the wastewater containing both liquid and solid wastes produced by human activities from homes, industries, hospitals, offices, etc. Sewage contains various contaminants including diseasecausing bacteria and other microbes. If untreated sewage is discharged into rivers or seas, then the water in the rivers or seas would also get contaminated. If this contaminated water is used for drinking, then it can cause diseases such as cholera, typhoid, dysentery, etc. which may lead to death. That is why it is harmful to discharge untreated sewage into rivers or seas.
• Why should oils and fats not be released in the drain? Explain. Ans. Oils and fats harden and block the sewage pipes. In an open drain also, fats block porosity of soil which affects its water filtering efficiency. That is why oils and fats should not be released in the drain.
• Describe the steps involved in getting clarified water from wastewater. Ans. The steps involved in getting clarified water from wastewater are as follows: (i) Use an aerator to bubble air through the wastewater. A mechanical stirrer or a mixer can also be used in place of the aerator. This helps in reducing bad odour of the wastewater. (ii) Then, the water is filtered through the layers of sand, fine gravel and medium gravel. Filtration makes the wastewater clean from various types of pollutants. The water is filtered continuously until it becomes clear. (iii) Then any disinfectant such as chlorine tablet is added to the filtrate and stirred to obtain completely clear water.
• What is sludge? Explain how it is treated. Ans. Semi-solids such as faeces that settle down during wastewater treatment are called sludge. This sludge is removed using a scraper and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas. This biogas is used as a low-cost fuel for heating, cooking, etc. It is also used to produce electricity.
• Untreated human excreta is a health hazard. Explain. Ans. Semi-solids such as faeces that settle down during wastewater treatment are called sludge. This sludge is removed using a scraper and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas. This biogas is used as a low-cost fuel for heating, cooking, etc. It is also used to produce electricity.
• Name two chemicals used to disinfect water. Ans. Two chemicals used to disinfect water are chlorine and ozone.
• Explain the function of bar screens in a wastewater treatment plant. Ans.
  
  Bar screen: In a wastewater treatment plant, bar screen removes large solid objects from water. The wastewater is allowed to pass through bar screen so that large solid objects such as rags, napkins, sticks, cans, plastic bags, polythene, etc. present in wastewater can be removed.
• Explain the relationship between sanitation and diseases. Ans. Sanitation and disease are related to each other as lack of sanitation can cause diseases. In our country, a large number of people even today do not have sewerage facilities and thus defecate in open fields, railway tracks, etc. The untreated human excreta thus pollute soil and water sources including the underground water. When this contaminated water is used for drinking, it can cause diseases such as cholera, typhoid, hepatitis, dysentery, etc. which may even lead to death. Therefore, lack of sanitation results in drinking of contaminated water can cause health problems.
• Outline your role as an active citizen in relation to sanitation. Ans. A citizen has many responsibilities regarding sanitation. Among other things, an active citizen should do the following with regard to maintaining proper sanitation: (i) Ensure that his surroundings (both inside and outside home) are clean. (ii) Ensure that the sewerage system in his house is properly managed. (iii) If he notices some leakage or other problem in the sewerage system, he should report it to the municipality.
• Crossword puzzle
  

Across

• Liquid waste products
• Solid waste extracted in sewage treatment.
• A word related to hygiene
• Waste matter discharged from human body.

Down

• Used water
• A pipe carrying sewage
• Micro-organism which causes cholera
• A chemical to disinfect water.
  
• Study the following statements about ozone: (a) It is essential for breathing of living organisms. (b) It is used to disinfect water. (c) It absorbs ultraviolet rays. (d) Its proportion in air is about $3\%$. Which of these statements is correct? (i) (a), (b) and (c) (ii) (b) and (c) (iii) (a) and (d) (iv) All four Ans. (ii) (b) and (c)

Exercise-01

Multiple choice questions

• Which of the following processes are used in the purification of water in a municipal water treatment system? (1) Sedimentation, sublimation and filtration (2) Evaporation and filtration (3) Sedimentation and distillation (4) Sedimentation, filtration and chlorination
• Chlorine is used in municipal water treatment plant to (1) change the taste of water (2) prevent evaporation (3) kill the harmful micro-organisms (4) prevent sedimentation
• The last step in waste water treatment is a _____ process. (1) biological (2) mechanical (3) chemical (4) physical
• Stagnant water in blocked drains is (1) a good place for breeding flies and mosquitoes (2) very good for agricultural purposes (3) used to generate electricity (4) all of the above
• What will happen if drainage is not proper to dispose off sewage? (1) We will get pure water (2) Diseases will spread (3) Water will get polluted (4) Both (2) and (3)
• Which of the following is the quality of wastewater? (1) Dirty look (2) Foul smell (3) Bad taste (4) All of these
• Which of the following is used in vermiprocessing toilets? (1) Cockroach (2) Earthworm (3) Bacteria (4) None of these
• All of us can contribute in maintaining sanitation at public places by (1) not throwing litter anywhere (2) adopting good sanitation practices (3) influencing others to keep our surroundings clean (4) All of these
• The full form of WWTP is (1) World wide transport programme (2) Waste water treatment plant (3) World workers talent programme (4) none of these
• Which of the following is the step of waste water treatment? (1) Chlorination (2) Aeration (3) Sedimentation (4) All of these
• Why should cooking oil, ghee and fat not be poured down the drains? (1) These will block the pipes and reduce the flow of water. (2) These will burst the pipes. (3) These will add harmful chemicals in drains. (4) These will add microbes in the drains.
• Which statement defines aeration? (1) To expose air to circulating water (2) To expose water to circulating air (3) A method of disinfecting water (4) A method of disinfecting air
• This is a by-product of sewage treatment and can be decomposes to produce biogas. (1) Sewage (2) Sludge (3) Sewer (4) Scum
• The chemical which is used to kill the harmful micro-organisms present in water is (1) carbon (2) ozone (3) chlorine (4) both (2) and (3)
• Which of the following is not a waterborne disease? (1) Heat attack (2) Cholera (3) Dysentery (4) Hepatitis
• Match column-I with Column-II and select the correct option.

(1) A-(iii), B-(ii), C-(i), D-(iv) (2) A-(iii), B-(i), C-(iv), D-(ii) (3) A-(ii), B-(iii), C-(i), D-(iv) (4) A-(i), B-(iv), C-(ii), D-(iii)

• Untreated human excreta is health hazard. It results in (1) pollution of soil and water (2) contamination of ground water and surface water (3) spread of water-borne disease (4) all of these
• Which of the following options includes organic impurities present in the sewage? (1) Phosphates and nitrates (2) Urea and faeces (3) Fruit and vegetable waste (4) Both (2) and (3)
• Which of the following statements is false? (1) Potable water is fit for drinking. (2) Biogas is obtained by action of aerobic on organic wastes. (3) Aeration tanks contain aerobic bacteria. (4) Both (2) and (3)
• We can help in waste management by (1) not littering anywhere (2) reducing the amount of garbage produced (3) by creating awareness among people (4) all of these

True or False

• Sewage consists mainly of human excreta.
• Micro-organisms decompose the organic matter present in sewage.
• Chlorination is done to remove the foul smell of water.
• Suspended matter present in sewage which settles in settling tanks is called sludge.
• Dried sludge is used as manure.
• Domestic wastewater does not contain micro-organisms.
• After proper sewage treatment, wastewater can be used for agriculture.
• In a city, there should be separate pipes for disposing sewage and storm water.
• The first step in the treatment of wastewater is to pass the wastewater through grit and sand removal tanks.
• If drainage is not proper, diseases can spread due to pollution of surface water and ground water.

Fill in the blanks

• The sewage is carried by ______ pipes or ______.
• Dried _____ is used as manure.
• Chlorination is done during _______ treatment.
• Wastewater released by houses is called _____.
• In secondary treatment, sewage water is treated with _______.
• The activated sludge is about ______water. _______ is the solid matter that settles at the bottom of the settling tank.
• Raw sewage is a _______ hazard.
• Drains get blocked by _____ and _______.
• _______ trees release pure water vapour into the atmosphere.

Match the column

Crossword puzzle

Across

• A process used for treating sludge, in which the sludge is burnt into ashes is
• Waste water containing suspended impurities are called
• Light floatable waste that rises at the top during waste water treatment is called
• Grit and sand removal tank are
• Discharge of liquid waste from an industry is called

Down

• Wastes that settles at the bottom in the primary treatment of waste water is called
• Major constituent of biogas
• Digestion process of organic matter in the sludge, from this process which gas is produced.

Answer Key

Multiple choice questions

True or False

• True
• True
• False
• True
• True
• False
• True
• True
• False
• True

Fill in the blanks

• drainage, sewers
• sludge
• tertiary
• sewage
• anaerobic bacteria
• $97\%$
• Sludge
• health
• plastics, household waste 10. Eucalyptus

Match the column

• (1) $\to \mathrm{d}$; (2) $\to \mathrm{a}$; (3) $\to \mathrm{b}$; (4) $\to \mathrm{c}$

Crossword puzzle

Exercise-02

Very short answer type questions

• Define sewage.
• What happens when drinking water supplies get mixed with sewage?
• Define the term 'wastewater'.
• What is the reason behind increasing scarcity of freshwater?
• Which period was proclaimed as the International Decade for action on "water for life" by the United Nations?
• What is meant by sewerage?
• Define the term 'contaminants'.
• Why should sewage be treated before being discharged in a water body?
• How are cholera and typhoid caused?
• Which removes the floatable solid like oil and greases?
• What is incineration?
• What is a septic tank? Where is it used?
• Define the term 'sludge'.
• What is meant by vermi-composting toilet?
• Name the two by-products of wastewater treatment.
• Through which water pollution and soil pollution may be caused?
• Why are bacteria used in sewage treatment?
• What could be done in our homes to maintain sanitation?
• From where does sewage water come out?
• From where does foul waste come out?
• What is the function of screens in a wastewater treatment plant?
• Which disposal systems are being encouraged to improve sanitation now a days?
• Which process of wastewater treatment is commonly known as "sewage treatment"?
• Why most of the diseases are caused by using open drain system?
• Which sludge is used as a manure?

Short answer type questions

• What is meant by wastewater treatment plant?
• Why should paints, solvents and insecticides not be released in the drain? Explain.
• (a) Which is a source of water for wells, tube wells, springs and many rivers? (b) Which emits foul smell?
• (a) What is meant by cleaning of water? (b) How hepatitis is caused?
• Why should we plant eucalyptus trees all along sewage ponds?
• (a) Through which, dirty water is drained? (b) Which drains carry water to sewer system?
• Explain the term effluent.
• What is decomposed by the anaerobic bacteria when it is transferred to a separate tank? Explain this process.
• What is domestic waste water? What should be done to it?
• What are manholes? How it is useful in cities?

Long answer type questions

• Explain why sewage is harmful to discharge untreated sewage into rivers and seas.
• What should be done to maintain sanitation and avoid water pollution?
• (a) Why a proper drainage system is very important? (b) Why there a change is observed in the appearance of the liquid after aeration?
• (a) Name the diseases that spread due to pollution of groundwater. (b) Why is it possible to have safe disposal of excreta by low cost methods?
• Why do some organisations offer hygienic onsite human waste disposal technology?

Multiple choice questions

• Option (4) Sedimentation, filtration and chlorination
  
• Option (3) Chlorine is used as disinfectant to kill the harmful micro-organisms.
• Option (3) Tertiary process: This is basically a chemical process in which chemicals are used to remove phosphorus and nitrogen from the water.
• Option (1) Stagnant water in blocked drains is a good place for breeding flies and mosquitoes.
• Option (4) Diseases will spread, water will get polluted.
• Option (4) All of these.
• Option (2) A vermi-processing toilet is a type of toilet in which human excreta is treated by earthworms.
• Option (4) All of us can contribute in maintaining sanitation at public places. We should not scatter litter anywhere.
• Option (2) Full form is waste water treatment plant.
• Option (4) All of these.
• Option (1) Cooking oil and fats should not be poured down in the drains. They can harden and block the pipes.
• Option (2) Aeration is to expose water to circulating air. This results in the growth of aerobic bacteria which consume organic matter.
• Option (2) Sludge and biogas are the by-products of sewage treatment.
• Option (4) Ozone and chlorine are the common disinfectants used to kill the harmful micro-organisms present in water.
• Option (1) Contaminated drinking water results in the spread of water-borne diseases such as cholera, typhoid, polio, meningitis, hepatitis, dysentery, etc. Heart attack is not a water-borne disease.
• Option (1) A-(iii), B-(ii), C-(i), D-(iv)
• Option (4) Untreated human excreta is a health hazard. It causes water pollution and soil pollution.
• Option (4) Sewage is a complex mixture containing suspended solids, organic and inorganic impurities.
• Option (2) The sludge collected from sedimentation tank is transferred to separate tanks called digesters.
• Option (4) All of these.

True or False

• True Sewage consists mainly of human excreta.
• True Micro-organisms decompose the organic matter present in sewage.
• False Chlorine is added to kill remains bacteria which disinfects the water.
• True Sludge: Solid wastes that settles at the bottom in the primary treatment of wastewater is called the sludge. A process used for treating sludge, in which the sludge is burnt into ashes is called incineration.
• True Dried sludge is used as manure.
• False Domestic wastewater contains dirt, detergents, soaps, fruit and vegetables waste, faeces, urine etc. Micro-organisms are present in domestic wastewater.
• True
• True
• False The first step in the treatment of wastewater is to pass the wastewater through bar screens.
• True

Exercise-02 Solution

Very short answer type questions

• Sewage: Waste water containing suspended impurities is called sewage.
• Water will get polluted when get mixed with sewage and will result in various diseases.
• The dirty water which is produced in kitchens, bathrooms, while washing cars or your bicycles and industrial wastes is called wastewater. Wastewater is used water.
• All the wastewater that is released from various sources like industries, homes, offices, hospitals etc. forms the sewage which contains suspended impurities and pollutes freshwater too.
• General Assembly of the United Nations on 22 March, 2005 declared the period 2005-2015 as the International Decade for action on 'Water for life.'
• A channel of pipe, which carries away sewage, is called sewerage.
• All the wastewater that is released from various source forms the sewage which contains suspended impurities. These impurities are called contaminants.
• Sewage should be treated before being discharge in a water body because there would be lots of impurities present in it.
• When people drink dirty water with impurities, cholera and typhoid caused.
• A skimmer removes the floatable solids like oil and greases.
• A process used for treating sludge, in which the sludge is burnt into ashes is called incineration.
• A septic tank consists of a concrete or metal tank with an outlet submerged in the ground. It is used in low cost onsite sewage disposal system.
• Sludge: Solids wastes that settles at the bottom in the primary treatment of wastewater is called the sludge.
• Vermi-composting toilet is a design of a toilet in which humans' excreta is treated by earthworms.
• Methane and dried sludge are the two products of wastewater treatment.
• Through chemicals of various industries, water pollution and soil pollution may be caused.
• In biological process, bacteria is used to broken down the sludge, forming biogas
• To maintain sanitation in our homes, wastes should be disposed off properly and not thrown anywhere.
• From drain pipes, sewage water comes out.
• Waste water released from toilets is termed as foul waste.
• The sewage is passed through screens of vertical bars to remove larger impurities such as a metal cans, plastic bags, cloth pieces, etc.
• Biogas plants and vermi composition toilets are being encouraged to improve sanitation now a days.
• Primary process of wastewater treatment is commonly known as "sewage treatment".
• Due to impurities and waster present in open drain system, mosquitos and flies find these open drain systems as breeding place and cause various diseases.
• Dried sludge is used as manure.

Short answer type questions

• A wastewater treatment plant is a facility that treats wastewater from industrial source. There are basically three processes involved in treating wastewater: primary, secondary, and tertiary.
• Chemicals like paints, insecticides and medicines should not be thrown in the drains. These things may kill microbes that help to decompose biowaste.
• (a) For wells, tube wells, springs and many rivers, rain water and ground water are the sources. (b) Sewage emits foul smell.
• (a) To remove impurities from dirty water and disinfect that water by various cleaning process, is called cleaning of water. (b) Intake of dirty water, cause injury to liver, this is how hepatitis caused.
• Eucalyptus trees are planted all along sewage pond because these trees absorb the surplus waste water rapidly and release pure water vapour into the atmosphere.
• (a) Through drain pipes, dirty water is drained. (b) A channel of pipelines, carries out sewage from our houses. The sewage leaves our houses through drain pipes and flows to the sewer mains of the city.
• Effluent - Discharge of liquid waste from industries.
• Organic matter in the sludge is broken down with the help of bacteria and due to this process biogas is produced.
  
• Domestic waste water carries used water from houses and apartments. It is also called sanitary sewage.
• A manhole is a hole, usually with a cover through which a person may enter a sewer/drain to fix the faulty pipe.

Long answer type questions

• Clean water is a basic need of all of us. It is needed for several purposes - for drinking, cooking food, bathing, washing clothes, growing crops and even for industries. Unfortunately, clean water is not available for use. As a result, people suffer from a number of water related diseases like typhoid, cholera and dysentery. Even deaths may take place. Also sewage has various impurities in it like chemical, bacterias etc. and if we'll discharge this untreated sewage into rivers and seas, it will pollute the water of these resources. Some people use that polluted water directly without treating it and it will be harmful.
• To maintain sanitation and avoid water pollution following steps should be taken- (i) Wastes should be disposed off properly and not thrown away anywhere. (ii) Proper toilet facilities should be provided to rural people. (iii) Chemical wastes from the factories should be properly treated before being released into water. (iv) Sewage from cities should not be discharged directly into rivers. It must be treated and made harmless before release. (v) Ensure that there are no leaking sewage pipes. (vi) Ensure that there are no stagnant water in ponds and lakes. (vii)As individuals, in homes the following precautions should be taken:

• Chemicals like paints, insecticides and medicines should not be thrown in the drains. These things may kill microbes that help to decompose biowaste.
• Used food remains, tea leaves, cotton sanitary towels should not be thrown in the drains. These waste choke the drains and do not allow free flow of oxygen. This slows down the degradation process. Such wastes should be thrown in the dustbin.
• Cooking oil and fats should not be thrown down the drain. These items on hardening block the pipes. Oil and fats should be thrown in the dustbin.

• (a) A proper drainage system is very important to treat dirty water and remove impurities from it, so that before releasing into waterbodies there will be no harmful impurities left. (b) The colour of liquid is change after aeration. Air is pumped into clarified water to allow the growth of aerobic bacteria. These bacteria consume human waste, food waste, soap which clean the water change its colour also.
• (a) Typhoid, cholera, hepatitis and dysentery etc. are the diseases that spread due to pollution of ground water. (b) Using biogas plants, it is possible to have safe disposal of excreta by low cost methods. In this method, human and animal excreta flow through covered drains into biogas plants. Microorganisms break down the materials present in the waste and produce biogas. This biogas is then used to produce electricity.
• Sulabh International is an organization that is working towards promoting environmental sanitation, and waste management in India. Since 1970, innovations have been done in erecting two - pit flush toilets and safe methods of human waste disposal technology generating non - conventional sources of energy like biogas and fertilisers. In October 2007, Sulabh designed a system of cheap toilets that recycles human wastes into biogas and fertilisers. For this, the founder of sulabh, Dr. Bindeshwar Pathak, has even been awarded to Stockholm Water Prize of 2009.