{"id":24539,"date":"2021-06-18T18:30:25","date_gmt":"2021-06-18T13:00:25","guid":{"rendered":"https:\/\/ncertsolutions.guru\/?p=24539"},"modified":"2021-08-07T17:36:32","modified_gmt":"2021-08-07T12:06:32","slug":"ncert-solutions-for-class-7-science-chapter-18","status":"publish","type":"post","link":"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-18\/","title":{"rendered":"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story"},"content":{"rendered":"<p>These <a href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science\/\">NCERT Solutions for Class 7 Science<\/a> Chapter 18 Wastewater Story Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.<\/p>\n<h2>Wastewater Story NCERT Solutions for Class 7 Science Chapter 18<\/h2>\n<h3>Class 7 Science Chapter 18 Wastewater Story Textbook Exercise Questions and Answers<\/h3>\n<p>Question 1.<br \/>\nFill in the blanks:<br \/>\na. Cleaning of water is a process of removing &#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<br \/>\nb. Wastewater released by houses is called &#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<br \/>\nc. Dried &#8230;&#8230;&#8230;&#8230;&#8230;&#8230;. is used as manure.<br \/>\nd. Drains get blocked by &#8230;&#8230;&#8230;&#8230;&#8230;&#8230;. and &#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<br \/>\nAnswer:<br \/>\na. pollutants,<br \/>\nb. sewage,<br \/>\nc. sludge,<br \/>\nd. oils, fats<\/p>\n<p>Question 2.<br \/>\nWhat is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.<br \/>\nAnswer:<br \/>\nWater containing liquid wastes disposed from domestic household activities, industrial activities and agricultural activities is termed as sewage.<\/p>\n<p>The untreated sewage can harm the rivers and seas as the contaminated water pollutes the whole source of water. As the sewage water may contain harmful substances and disease causing organisms, it is dangerous to release the untreated sewage into the water bodies.<\/p>\n<p>Question 3.<br \/>\nWhy should oils and fats be not released in the drain? Explain.<br \/>\nAnswer:<br \/>\nOils and fats can block the drains. In open drains, they block the pores in the soil and thus hamper the filtration by soil. Hence, oils and fats should not be released in the drains.<\/p>\n<p>Question 4.<br \/>\nDescribe the steps involved in getting clarified water from wastewater.<br \/>\nAnswer:<br \/>\nThe following steps are involved in clarifying wastewater:<\/p>\n<ul>\n<li>In the first step, all the physical impurities like stones, plastic bags, cans, etc., are removed by passing the water through bar screens.<\/li>\n<li>Now, water is subjected to sedimentation where impurities are removed by the force of gravity.<\/li>\n<li>Solids settled at the bottom of the sedimentation tank are removed. This is called sludge.<\/li>\n<li>An aerator cleanses the water from other impurities.<\/li>\n<li>Chlorination is done to remove all disease causing bacteria.<\/li>\n<\/ul>\n<p>Question 5.<br \/>\nWhat is sludge? Explain how it is treated.<br \/>\nAnswer:<br \/>\nThe solid waste which settles at the bottom of the sedimentation tank is called sludge. The sludge is further treated by the process of aeration. This helps in growth of bacteria which eat away the human waste. Activated sludge is used as manure.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 6.<br \/>\nUntreated human excreta is a health hazard. Explain.<br \/>\nAnswer:<br \/>\nUntreated human excreta contains many microbes which can cause deadly diseases like cholera, diarrhoea, jaundice and typhoid. The germs of these diseases can easily reach human population through insects and through contaminated food and water. Thus, untreated human excreta is a health hazard.<\/p>\n<p>Question 7.<br \/>\nName two chemicals used to disinfect water.<br \/>\nAnswer:<br \/>\nBleaching powder and chlorine tablets.<\/p>\n<p>Question 8.<br \/>\nExplain the function of bar screens in a wastewater treatment plant.<br \/>\nAnswer:<br \/>\nBar screens are large filters which are placed in the form of vertical screens. Large solid wastes like sticks, pebbles, sand, cans, plastic bottles, plastic bags, etc., are filtered out when the wastewater moves through the bar screens.<\/p>\n<p>Question 9.<br \/>\nExplain the relationship between sanitation and disease.<br \/>\nAnswer:<br \/>\nProper sanitation should be maintained in order to avoid diseases. They are related to each other. By sanitation, proper disposal of sewage and refuse from household and public places is carried out. Implementation of proper sanitation results in a state where we are free from any diseases. Lack of it may lead to various diseases.<\/p>\n<p>Question 10.<br \/>\nOutline your role as an active citizen in relation to sanitation.<br \/>\nAnswer:<br \/>\nAs an active citizen, we should take care of our personal environmental sanitation. For this, we should follow these steps:<\/p>\n<ul>\n<li>Throwing garbage at designated places and in garbage bins.<\/li>\n<li>Preventing clogging of drains by not releasing oils and fats and solid wastes into the drains.<\/li>\n<li>Using a dustbin to throw trash at public places.<\/li>\n<li>By not spitting at public places.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 11.<br \/>\nHere is a crossword puzzle. Good luck!<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24540\" src=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-1.png?resize=325%2C321&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 1\" width=\"325\" height=\"321\" srcset=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-1.png?w=325&amp;ssl=1 325w, https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-1.png?resize=300%2C296&amp;ssl=1 300w\" sizes=\"(max-width: 325px) 100vw, 325px\" data-recalc-dims=\"1\" \/><br \/>\nAcross:<br \/>\n3. Liquid waste products<br \/>\n4. Solid waste extracted in sewage treatment<br \/>\n6. A word related to hygiene<br \/>\n8. Waste matter discharged from humans<br \/>\nDown:<br \/>\n1. Used water<br \/>\n2. A pipe carrying sewage<br \/>\n5. Micro-organisms which cause cholera<br \/>\n7. A chemical to disinfect water<br \/>\nAnswer:<br \/>\n1. Wastewater<br \/>\n2. Sewer<br \/>\n3. Sewage<br \/>\n4. Sludge<br \/>\n5. Bacteria<br \/>\n6. Sanitation<br \/>\n7. Ozone<br \/>\n8. Excreta<\/p>\n<p>Question 12.<br \/>\nStudy the following statements about ozone:<br \/>\n(a) It is essential for breathing of living organisms.<br \/>\n(b) It is used to disinfect water.<br \/>\n(c) It absorbs ultraviolet rays.<br \/>\n(d) Its proportion in air is about 3%. Which of these statements are correct?<br \/>\n(i) (a), (b) and (c)<br \/>\n(ii) (b) and (c)<br \/>\n(iii) (a) and (d)<br \/>\n(iv) All four<br \/>\nAnswer:<br \/>\n(ii) (b) and (c)<\/p>\n<p><span style=\"color: #0000ff;\">NCERT Extended Learning Activities and Projects<\/span><\/p>\n<p>Question 1.<br \/>\nThen and now: Talk to your grandparents and other elderly people in the neighbourhood. Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief report on the information you collected.<br \/>\nHint:<br \/>\nDo it yourself<\/p>\n<p>Question 2.<br \/>\nVisit a sewage treatment plant.<br \/>\nIt could be as exciting and enriching as a visit to a zoo, a museum or a park. To guide your observation here are a few suggestions.<br \/>\nRecord in your notepad:<br \/>\nPlace &#8230;&#8230;&#8230;&#8230;..<br \/>\nDate &#8230;&#8230;&#8230;&#8230;..<br \/>\nTime &#8230;&#8230;&#8230;&#8230;..<br \/>\nName of the official at the plant &#8230;&#8230;&#8230;&#8230;.. Guide\/<br \/>\nTeacher &#8230;&#8230;&#8230;&#8230;..<br \/>\na. The location of the sewage plant.<br \/>\nb. Treatment capacity.<br \/>\nc. The purpose of screening as the initial process.<br \/>\nd. How is air bubbled through the aeration tank?<br \/>\ne. How safe is the water at the end of the treatment? How is it tested?<br \/>\nf. Where is the water discharged after treatment?<br \/>\ng. What happens to the plant during heavy rains?<br \/>\nh. Is biogas consumed within the plant or sold to the other consumers?<br \/>\ni. What happens to treated sludge?<br \/>\nj. Is there any special effort to protect nearby houses from the plant?<br \/>\nk. Other observations.<br \/>\nHint:<br \/>\nDo it yourself with the help of your teacher.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"color: #0000ff;\">Activity 1<\/span><\/p>\n<p>Objective: To locate an open drain near your home, school or on the road side and inspect water flowing through it.<br \/>\nProcedure: Visit the nearby drain and observe it carefully.<br \/>\nObservations:<\/p>\n<table border=\"2\">\n<tbody>\n<tr>\n<td style=\"text-align: center;\" width=\"29\">S. No.<\/td>\n<td style=\"text-align: center;\" width=\"46\">Type of sewage<\/td>\n<td style=\"text-align: center;\" width=\"69\">Point of origin<\/td>\n<td style=\"text-align: center;\" width=\"74\">Substances which contaminate<\/td>\n<td style=\"text-align: center;\" width=\"61\">Smell<\/td>\n<\/tr>\n<tr>\n<td width=\"29\">1.<\/td>\n<td width=\"46\">Sludge water<\/td>\n<td width=\"69\">Kitchen<\/td>\n<td width=\"74\">Fruits and vegetable waste, oil<\/td>\n<td width=\"61\">No smell<\/td>\n<\/tr>\n<tr>\n<td width=\"29\">2.<\/td>\n<td width=\"46\">Foul waste<\/td>\n<td width=\"69\">Toilets<\/td>\n<td width=\"74\">Human feces, urine<\/td>\n<td width=\"61\">Unpleasant smell<\/td>\n<\/tr>\n<tr>\n<td width=\"29\">3.<\/td>\n<td width=\"46\">Trade waste<\/td>\n<td width=\"69\">Industrial and commercial organisations<\/td>\n<td width=\"74\">Nitrates, phosphates of metals<\/td>\n<td width=\"61\">Unpleasant smell<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Conclusion: The open drain water is dirty and has a foul smell. Many organic impurities are found there such as human faeces, animal wastes, fruit and vegetable wastes, etc.<\/p>\n<p>Wastewater Treatment Plant (WWTP) or Sewage Treatment Plant: These are large plants where wastewater is cleaned before being sent to the nearest water bodies or being reused. The sewage treatment involves physical, chemical and biological processes to remove impurities from the wastewater. This is done in the following steps:<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24541\" src=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-2.png?resize=431%2C372&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 2\" width=\"431\" height=\"372\" srcset=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-2.png?w=431&amp;ssl=1 431w, https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-2.png?resize=300%2C259&amp;ssl=1 300w\" sizes=\"(max-width: 431px) 100vw, 431px\" data-recalc-dims=\"1\" \/><br \/>\ni. Wastewater is passed through bar screens to remove large objects such as rags, cans, plastic packets, polythene, etc.<\/p>\n<p>ii. Sand and Grit removal tank: The speed of incoming wastewater in this tank is decreased to allow sand, grit, pebbles, etc., to sediment and settle down.<\/p>\n<p>iii. The water then goes into a large tank sloping in the middle where solids, like faeces, settle at the bottom and are removed with a scraper. This solid is called the sludge.<br \/>\nA skimmer removes the floatable solids like oil and grease. Water so cleared is called the clarified water.<\/p>\n<p>iv. Anaerobic bacteria: Bacteria which can grow and multiply in absence of free oxygen are called anaerobic bacteria. The sludge is transferred to a separate tank for decomposition by anaerobic bacteria.<\/p>\n<p>The gas produced by the decomposition of sludge by the anaerobic bacteria is known as biogas. The biogas produced during decomposition can be used as fuel or used to produce electricity.<\/p>\n<p>v. Role of aerobic bacteria: The clarified water also needs to be cleaned further. Hence, it is moved to an aerator that pumps air into it. This allows aerobic bacteria to grow in this water. Bacteria which require free oxygen for their growth and multiplication are called aerobic bacteria. The aerobic bacteria consume organic wastes, soaps, food waste and other elements that remain in the clarified water.<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24542\" src=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-3.png?resize=320%2C282&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 3\" width=\"320\" height=\"282\" srcset=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-3.png?w=320&amp;ssl=1 320w, https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-3.png?resize=300%2C264&amp;ssl=1 300w\" sizes=\"(max-width: 320px) 100vw, 320px\" data-recalc-dims=\"1\" \/><\/p>\n<p>vi. Activated sludge: After several hours of decomposition in the tank, the microbes settle down at the bottom as activated sludge. It contains about 97% water. The water is then removed from the top by sand drying beds or machines. The treated water with very low amount of suspended matter is discharged into water bodies where it is further cleaned by nature. Water can also be disinfected with chemicals like chlorine UV radiations and ozone before releasing it into the distribution system.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"color: #0000ff;\">Activity 2<\/span><\/p>\n<p>Objective: To treat a sample of polluted water and make it clean.<br \/>\nMaterials Required: Funnel, a glass jar, filter paper, funnel stand, soil, grass pieces, orange peels, detergent, ink, strainer and beaker.<br \/>\nProcedure:<\/p>\n<ul>\n<li>Fill a glass jar three-fourths with tap water. Add a little of soil, some dirty organic matter such as grass pieces and orange peels, a small amount of detergent and a few drops of ink to it. Cap the glass jar, shake it well and keep it in the sun for at least two days.<\/li>\n<li>Shake the contents of the glass jar well and pour the content over a strainer kept over a beaker. The large pieces of grass and orange peels will not pass through the holes of strainer and hence get removed. The remaining part of the polluted water will collect in the beaker kept below the strainer.<\/li>\n<li>Allow the polluted water to stand in the beaker for some time. The solid fine soil present in the polluted water will settle down at the bottom of the beaker.<\/li>\n<li>Transfer the polluted water from this beaker into another beaker by decantation. Pass air into this polluted water for several hours by using an aerator.<\/li>\n<li>When the aeration is complete, we will find that the foul smell from polluted water has almost disappeared. Filter the aerated water through the layer of sand, fine gravel and medium gravel arranged on a filter paper in a funnel. Collect the clean water as a filtrate in a beaker kept below the funnel.<\/li>\n<li>Add a small piece of chlorine tablet to the clean water collected in the beaker. Mix well until the water is clear and colourless. This is the clean and clear safe water obtained by the treatment of polluted water.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-24543\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-4.png?resize=340%2C243&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 4\" width=\"340\" height=\"243\" srcset=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-4.png?w=340&amp;ssl=1 340w, https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-4.png?resize=300%2C214&amp;ssl=1 300w\" sizes=\"(max-width: 340px) 100vw, 340px\" data-recalc-dims=\"1\" \/><br \/>\nObservation:<\/p>\n<table border=\"2\">\n<tbody>\n<tr>\n<td width=\"27\">\n<p style=\"text-align: center;\">S. No.<\/p>\n<\/td>\n<td style=\"text-align: center;\" width=\"64\">State<\/td>\n<td style=\"text-align: center;\" width=\"56\">Colour<\/td>\n<td style=\"text-align: center;\" width=\"72\">Transparency<\/td>\n<td style=\"text-align: center;\" width=\"61\">Smell<\/td>\n<\/tr>\n<tr>\n<td width=\"27\">1.<\/td>\n<td width=\"64\">Raw sample (before treatment)<\/td>\n<td width=\"56\">Greyish<\/td>\n<td width=\"72\">Almost opaque<\/td>\n<td width=\"61\">Foul smell<\/td>\n<\/tr>\n<tr>\n<td width=\"27\">2.<\/td>\n<td width=\"64\">After aeration<\/td>\n<td width=\"56\">Greyish<\/td>\n<td width=\"72\">Almost opaque<\/td>\n<td width=\"61\">Unpleasant smell<\/td>\n<\/tr>\n<tr>\n<td width=\"27\">3.<\/td>\n<td width=\"64\">After filtration<\/td>\n<td width=\"56\">Almost colourless<\/td>\n<td width=\"72\">Almost transparent<\/td>\n<td width=\"61\">No smell<\/td>\n<\/tr>\n<tr>\n<td width=\"27\">4.<\/td>\n<td width=\"64\">After chlorination<\/td>\n<td width=\"56\">colourless<\/td>\n<td width=\"72\">Transparent<\/td>\n<td width=\"61\">Odourless<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Conclusion: With this treatment, we can clean polluted water. This treated water does not give foul smell and it is safe to use.<\/p>\n<p>Sanitation: Sanitation refers to the health and hygienic conditions of people related to the disposal of sewage, human excreta and provision of clean drinking water. Poor sanitation and polluted drinking water can lead to many diseases. Hence, a sanitation system aims to provide a clean environment for us so that we can stay away from diseases. Improper sanitation can give rise to different diseases that arise from contaminated water such as typhoid, dysentery, hepatitis, polio, cholera and meningitis. The human excreta is a health hazard and can lead to soil and water pollution. It can pollute the surface water and groundwater. Hence, people should never defecate in open areas.<\/p>\n<p>Alternative Arrangement for Sewage Disposal:<br \/>\ni. In the absence of a sewerage system, arrangements for onsite sewage disposal can be made. For example, septic tanks are built in which human excreta are collected. In due course of time, the human excreta gets decomposed into compost.<br \/>\nii. Composting pits can be made to dump waste and to make manure from them. Sewage can be collected into biogas plants to produce useful biogas.<\/p>\n<p>Chemical toilets are new discoveries. They do not require much water for the disposal of human excreta and are environment friendly. Such toilets are ideal for the trains.<\/p>\n<p>Sanitation at Public Places: There are numerous places in our country which are very busy such as airports, railway stations and bus depots. Many times, large gatherings such as fairs and festivals are also organised where a large number of people visit. This results in the generation of large amounts of waste and if the waste is not treated properly, it can lead to several diseases and even an epidemic. Hence, we should all become aware and contribute to maintaining sanitation not only in our homes but also at public places. If we adopt certain practices at public places we can help in maintaining their sanitation, for instance:<\/p>\n<ul>\n<li>We should not throw garbage in public places and always use the dustbins.<\/li>\n<li>We should not spit around in a public place.<\/li>\n<li>We should wash our hands thoroughly before eating anything at a public place.<\/li>\n<\/ul>\n<h3>Class 7 Science Chapter 18 Wastewater Story Additional Important Questions and Answers<\/h3>\n<p><span style=\"color: #0000ff;\">Very Short Answer Type Questions<\/span><\/p>\n<p>Question 1.<br \/>\nWhich day is celebrated as World Water Day?<br \/>\nAnswer:<br \/>\n22 March.<\/p>\n<p>Question 2.<br \/>\nWhat is sewerage?<br \/>\nAnswer:<br \/>\nIt is like a transport system that carries sewage from the point of being produced to the point of disposal, i.e., treatment plant.<\/p>\n<p>Question 3.<br \/>\nWhat are the harmful effects of drinking contaminated water?<br \/>\nAnswer:<br \/>\nContaminated drinking water is the cause of a large number of diseases such as cholera, typhoid, polio, meningitis, hepatitis and dysentery.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 4.<br \/>\nWhat is cleaning of water?<br \/>\nAnswer:<br \/>\nCleaning of water is a process of removing pollutants before it enters a water body or is reused. This process of wastewater treatment is commonly known as \u2018Sewage Treatment\u201d.<\/p>\n<p>Question 5.<br \/>\nWhy chemicals should not be thrown down the drain?<br \/>\nAnswer:<br \/>\nChemicals should not be thrown down the drain because chemicals like paints, solvents, insecticides, motor oil and medicines may kill microbes that help purify water.<\/p>\n<p>Question 6.<br \/>\nName two nutrients present in the sewage?<br \/>\nAnswer:<br \/>\nNitrogen and phosphorus.<\/p>\n<p>Question 7.<br \/>\nName the solid waste extracted during sewage treatment.<br \/>\nAnswer:<br \/>\nSludge.<\/p>\n<p>Question 8.<br \/>\nName any two things that can be made from the sludge extracted during treatment of sewage.<br \/>\nAnswer:<br \/>\nBiogas and manure.<\/p>\n<p>Question 9.<br \/>\nWrite the examples of on site sewage disposal systems.<br \/>\nAnswer:<br \/>\nSeptic tanks, chemical toilets, composting pits, etc.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 10.<br \/>\nName the toilet in which human excreta is treated by earthworms.<br \/>\nAnswer:<br \/>\nVermi-processing toilet.<\/p>\n<p>Question 11.<br \/>\nWhat is the use of dried sludge?<br \/>\nAnswer:<br \/>\nDried sludge is used as manure, thus returning organic matter and nutrients to the soil.<\/p>\n<p>Question 12.<br \/>\nHow can we improve the sanitation?<br \/>\nAnswer:<br \/>\nTo improve sanitation, low cost onsite sewage disposal systems must be encouraged.<\/p>\n<p>Question 13.<br \/>\nWhy are ozone and chlorine used in water purification?<br \/>\nAnswer:<br \/>\nOzone and chlorine are used to kill the bacteria, etc., present in the clarified water.<\/p>\n<p>Question 14.<br \/>\nHow are floatable solids removed from the wastewater?<br \/>\nAnswer:<br \/>\nA skimmer is used to remove floatable impurities.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 15.<br \/>\nWhich microorganism decomposes the sludge?<br \/>\nAnswer:<br \/>\nAnaerobic bacteria decompose the sludge.<\/p>\n<p><span style=\"color: #0000ff;\">Short Answer Type Questions<\/span><\/p>\n<p>Question 1.<br \/>\nDefine community hygiene? How can it be effectively maintained?<br \/>\nAnswer:<br \/>\nCommunity hygiene means maintenance, protection and improvement of health of the whole community. It can be maintained by:<\/p>\n<ul>\n<li>Provision of clean and safe drinking water.<\/li>\n<li>Maintaining green open space.<\/li>\n<li>Maintaining proper sanitation.<\/li>\n<li>Maintaining clean air.<\/li>\n<\/ul>\n<p>Question 2.<br \/>\nWhat are the problems arising due to open drains and other unsanitary conditions?<br \/>\nAnswer:<br \/>\nOpen drains and unsanitary conditions produce bad smell. It becomes an idle place of breeding for mosquitoes, flies and other harmful insects. These insects spread many harmful diseases and other health hazards.<\/p>\n<p>Question 3.<br \/>\nHow kitchen waste blocks the drain?<br \/>\nAnswer:<br \/>\nCooking oils that drain from kitchen into the pipes, hardens and blocks the pipes. The oil in open drains clogs the soil pores thereby preventing the filtration process and its effectiveness. It further hampers the degradation process.<\/p>\n<p>Question 4.<br \/>\nHow bar screen and grit and sand removal tank help in clarification of water?<br \/>\nAnswer:<br \/>\nWhen wastewater is passed through bar screens, it separates big and large objects like rags, sticks, cans, plastic packets, napkins, etc. In grit and sand removal tank, other solid impurities like pebbles, sand, etc., are removed.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 5.<br \/>\nWhat is vermi-processing toilet?<br \/>\nAnswer:<br \/>\nVermi-processing toilet is a new toilet system developed in India. In this system, human excreta is treated by earthworms for safe processing of human waste. The operation of this toilet is very simple and hygienic. It has the potential to reduce freshwater use and improve sanitation levels.<\/p>\n<p>Question 6.<br \/>\nWhat is the need to chlorinate any water supply? Name two other methods which help to do the same.<br \/>\nAnswer:<br \/>\nFor making water safe for drinking, chlorination can be done. In this process, chlorine tablets, bleaching powder or alum is added to water to prevent it from diseases. Filtration or sedimentation can also be done in order to make the water safe for drinking.<\/p>\n<p>Question 7.<br \/>\nWhy is air pumped into the clarified water?<br \/>\nAnswer:<br \/>\nAir is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in the clarified water.<\/p>\n<p>Question 8.<br \/>\nWhy should eucalyptus trees be planted along sewage ponds?<br \/>\nAnswer:<br \/>\nIt has been suggested that we should plant eucalyptus trees all along the sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.<\/p>\n<p>Question 9.<br \/>\nWhy are bacteria important in sewage treatment?<br \/>\nAnswer:<br \/>\nBacteria are important in sewage treatment because, they consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. Also, they help in the decomposition of solid sludge to make useful things like biogas.<\/p>\n<p>Question 10.<br \/>\nSuggest some alternative arrangements for sewage disposal.<br \/>\nAnswer:<br \/>\nTo improve sanitation, low cost onsite sewage disposal systems are being encouraged. Examples are septic tanks, chemical toilets, composting pits. Septic tanks are suitable for places where there is no sewerage system, for hospitals, isolated buildings or a cluster of 4 to 5 houses. Some organisations offer hygienic on-site 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.<\/p>\n<p><span style=\"color: #0000ff;\">Long Answer Type Questions<\/span><\/p>\n<p>Question 1.<br \/>\nWhat are the different types of inorganic and organic impurities generally present in sewage?<br \/>\nAnswer:<br \/>\nWastewater is composed primarily of natural organic substances which are by-products of human, animal and plant processes. The primary inorganic elements in domestic wastewater are nitrogen, phosphorous, ammonia and carbon. These elements are released with the growth of bacteria in standing water. The bacteria consume the oxygen present in water and as a result, living organisms in the water start to die.<\/p>\n<p>We know that sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.<\/p>\n<table border=\"2\">\n<tbody>\n<tr>\n<td width=\"123\">Organic impurities<\/td>\n<td width=\"158\">Human faeces, animal waste oil, urea (urine)<\/td>\n<\/tr>\n<tr>\n<td width=\"123\">Inorganic impurities<\/td>\n<td width=\"158\">Nitrates, phosphates, metals<\/td>\n<\/tr>\n<tr>\n<td width=\"123\">Nutrients<\/td>\n<td width=\"158\">Phosphorus and nitrogen<\/td>\n<\/tr>\n<tr>\n<td width=\"123\">Bacteria<\/td>\n<td width=\"158\">Such as which cause cholera and typhoid<\/td>\n<\/tr>\n<tr>\n<td width=\"123\">Other microbes<\/td>\n<td width=\"158\">Such as which cause dysentery<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 2.<br \/>\nList some ways to minimise or eliminate waste and pollutants at their source.<br \/>\nAnswer:<br \/>\nOne of me ways to minimise or eliminate waste and pollutants at their source is to see what you are releasing down the drain. Other ways may include:<\/p>\n<ul>\n<li>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.<\/li>\n<li>Chemicals like paints, solvents, insecticides, motor oil and medicines may kill the microbes that help purify water. So we should not throw them into the drain.<\/li>\n<li>Used tea-leaves, solid food remains, soft toys, cotton, sanitary towels, etc., should also be thrown in the dustbin as these wastes choke the drains. They do not allow free flow of oxygen which hampers the degradation process.<\/li>\n<\/ul>\n<p>Question 3.<br \/>\nWrite some consequences of the malfunctioning of sewage.<br \/>\nAnswer:<\/p>\n<ul>\n<li>Rupture or, blockage or leakage of sewerage lines.<\/li>\n<li>Sewerage may overflow on the roads and streets, creating poor sanitary conditions.<\/li>\n<li>It may upset the ecological balance in lakes and rivers.<\/li>\n<li>Water may become unfit for drinking and other domestic uses.<\/li>\n<li>The place may stink and become breeding ground for mosquitoes, flies, etc.<\/li>\n<\/ul>\n<p>Question 4.<br \/>\nWhat is a septic tank? How does it function?<br \/>\nAnswer:<br \/>\nSeptic tank is a low cost on-site sewage disposal system. Septic tanks are suitable where there is no sewerage system for hospitals, isolated buildings or a cluster of four to five houses. Septic tank needs cleaning every four to six months.<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24544\" src=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-5.png?resize=427%2C266&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 5\" width=\"427\" height=\"266\" srcset=\"https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-5.png?w=427&amp;ssl=1 427w, https:\/\/i2.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-5.png?resize=300%2C187&amp;ssl=1 300w\" sizes=\"(max-width: 427px) 100vw, 427px\" data-recalc-dims=\"1\" \/><\/p>\n<p>Septic tanks serve three functions:<br \/>\na. Removal of solids: As sewage enters the septic tank, its rate of flow is reduced so that the larger solids sink to the bottom and soaps, grease and smaller solids rise to the surface. These solids are retained in the tank and the clarified effluent with suspended and dissolved solids is discharged.<\/p>\n<p>b. Bacterial Action: The solids and the liquids in the tank are partially decomposed by bacteria and other natural processes. These bacteria are called anaerobic because they thrive in the absence of free oxygen. This decomposition of sewage under anaerobic conditions is termed \u201cseptic,\u201d hence the name of the system (and the cause of the odour).<\/p>\n<p>c. Sludge and scum storage: Sludge is the accumulation of solids at the bottom of the tank, while scum is a partially submerged mat of floating solids that may form at or near the surface. Space must exist in the tank to store these residues during the intervals between pumping. Otherwise, the sludge and scum will eventually be scoured from the tank and will clog the leaching field and receiving soil.<\/p>\n<p>The final Stage of Disposal:<br \/>\nThe treated effluent from the septic tank is discharged to the leach field where it percolates through suitable \u201cseptic stone\u201d and finally into the subsoil for further purification.<\/p>\n<p><span style=\"color: #0000ff;\">Picture-Based Questions<\/span><\/p>\n<p>Question 1.<br \/>\nObserve the diagram shown below and answer the following questions.<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24545\" src=\"https:\/\/i0.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-6.png?resize=149%2C203&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 6\" width=\"149\" height=\"203\" data-recalc-dims=\"1\" \/><br \/>\na. What does it depict?<br \/>\nb. Which layers are used in the funnel?<br \/>\nAnswer:<br \/>\na. It depicts purification of polluted water by filtration.<br \/>\nb. Layers of sand, silt and gravel are used in the funnel.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone\" src=\"https:\/\/i1.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/01\/NCERT-Solutions-Guru.png?resize=170%2C17&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" width=\"170\" height=\"17\" data-recalc-dims=\"1\" \/><\/p>\n<p>Question 2.<br \/>\nIdentify the diagram shown below.<br \/>\n<img loading=\"lazy\" class=\"alignnone size-full wp-image-24546\" src=\"https:\/\/i0.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-7.png?resize=351%2C244&#038;ssl=1\" alt=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story 7\" width=\"351\" height=\"244\" srcset=\"https:\/\/i0.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-7.png?w=351&amp;ssl=1 351w, https:\/\/i0.wp.com\/ncertsolutions.guru\/wp-content\/uploads\/2021\/06\/NCERT-Solutions-for-Class-7-Science-Chapter-18-Wastewater-Story-7.png?resize=300%2C209&amp;ssl=1 300w\" sizes=\"(max-width: 351px) 100vw, 351px\" data-recalc-dims=\"1\" \/><br \/>\nAnswer:<br \/>\nSewage treatment plant<\/p>\n<h4><strong>NCERT Solutions for Class 7 Science<\/strong><\/h4>\n<ul>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-1\/\">Class 7 Science Chapter 1 Nutrition in Plants<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 2 Nutrition in Animals\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-2\/\">Class 7 Science Chapter 2 Nutrition in Animals<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-3\/\">Class 7 Science Chapter 3 Fibre to Fabric<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 4 Heat\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-4\/\">Class 7 Science Chapter 4 Heat<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-5\/\">Class 7 Science Chapter 5 Acids, Bases and Salts<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-6\/\">Class 7 Science Chapter 6 Physical and Chemical Changes<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-7\/\">Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 8 Winds, Storms and Cyclones\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-8\/\">Class 7 Science Chapter 8 Winds, Storms and Cyclones<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 9 Soil\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-9\/\">Class 7 Science Chapter 9 Soil<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 10 Respiration in Organisms\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-10\/\">Class 7 Science Chapter 10 Respiration in Organisms<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 11 Transportation in Animals and Plants\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-11\/\">Class 7 Science Chapter 11 Transportation in Animals and Plants<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 12 Reproduction in Plants\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-12\/\">Class 7 Science Chapter 12 Reproduction in Plants<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 13 Motion and Time\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-13\/\">Class 7 Science Chapter 13 Motion and Time<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-14\/\">Class 7 Science Chapter 14 Electric Current and its Effects<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 15 Light\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-15\/\">Class 7 Science Chapter 15 Light<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-16\/\">Class 7 Science Chapter 16 Water: A Precious Resource<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-17\/\">Class 7 Science Chapter 17 Forests: Our Lifeline<\/a><\/li>\n<li><a title=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-18\/\">Class 7 Science Chapter 18 Wastewater Story<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>These NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams. Wastewater Story NCERT Solutions for Class 7 Science Chapter 18 Class 7 Science Chapter 18 Wastewater Story Textbook Exercise Questions and Answers Question 1. Fill &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-18\/\"> <span class=\"screen-reader-text\">NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story<\/span> Read More &raquo;<\/a><\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[9],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v16.7 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story - NCERT Solutions<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/ncertsolutions.guru\/ncert-solutions-for-class-7-science-chapter-18\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story - NCERT Solutions\" \/>\n<meta property=\"og:description\" content=\"These NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams. Wastewater Story NCERT Solutions for Class 7 Science Chapter 18 Class 7 Science Chapter 18 Wastewater Story Textbook Exercise Questions and Answers Question 1. 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Wastewater Story NCERT Solutions for Class 7 Science Chapter 18 Class 7 Science Chapter 18 Wastewater Story Textbook Exercise Questions and Answers Question 1. 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