NCERT Class 7 Science Wastewater Story PDF

13 Wastewater Story All of us use water in our homes and Clean water that is fit make it dirty. for use is unfortunately Dirty! Are you surprised? not available to all. It has Rich in lather, mixed with oil, b...

13 Wastewater Story All of us use water in our homes and Clean water that is fit make it dirty. for use is unfortunately Dirty! Are you surprised? not available to all. It has Rich in lather, mixed with oil, black– been reported that more brown water that goes down the drains than one billion of people from sinks, showers, toilets, laundries have no access to safe is dirty. It is called wastewater. This drinking water. This accounts for a large used water should not be wasted. We number of water-related diseases and must clean it up by removing pollutants. even deaths. People even children walk Have you ever thought where the for several kilometres to collect clean wastewater goes and what happens to it? water. Is it not a serious matter for human dignity? 13.1 WATER, OUR LIFELINE The increasing scarcity of fresh-water Clean water is a basic need of human due to population growth, pollution, being. Let us make a mindmap of the industrial development,mismanagement many uses of clean water. and other factors. Realising the urgency Activity 13.1 of the situation on the World Water Day, on 22 March 2005, the General (We have given one example of the Assembly of the United Nations use of clean water. You can add many proclaimed the period 2005– 2015 as the more.) International Decade for action on “Water for life”. All efforts made during this decade aim to reduce by half the number of people who do not have access to safe drinking water. Clean water There has been perceptible progress put to use in the direction of the aim but still there is a lot to achieve. Cleaning of water is a process of removing pollutants before it enters a water body or is reused. This process of Drinking wastewater treatment is commonly 156 SCIENCE Rationalised 2023-24 known as “Sewage Treatment”. It takes oil, urea (urine), place in several stages. pesticides, herbicides, fruit 13.2 WHAT IS SEWAGE? and vegetable Sewage is wastewater released by homes, waste, etc. industries, hospitals, offices and other Inorganic impurities – Nitrates, users. It also includes rainwater that has Phosphates, run down the street during a storm or metals. heavy rain. The water that washes off Nutrients – Phosphorus roads and rooftops carries harmful and Nitrogen. substances with it. Sewage is a liquid Bacteria – Such as vibrio waste. Most of it is water, which has cholera which dissolved and suspended impurities. causes cholera Activity 13.2 and salmonella paratyphi which Locate an open drain near your home, causes typhoid. school or on the roadside and inspect water flowing through it. Other microbes – Such as Record colour, odour and any other protozones observation. Discuss with your friends which cause and your teacher and fill up the dysentery. following Table 13.1. 13.3 WATER FRESHENS UP — AN We know that sewage is a complex EVENTFUL JOURNEY mixture containing suspended solids, organic and inorganic impurities, In a home or a public building generally nutrients, saprophytes and disease one set of pipes brings clean water and causing bacteria and other microbes. another set of pipes takes away These include the following. wastewater. Imagine that we could see Organic impurities – Human faeces, through the ground. We would see a animal waste, network of big and small pipes, called Table 13.1 Contaminant survey S. No. Type of sewage Point of origin Contaminants Any other remark 1. Sullage water Kitchen 2. Foul waste Toilets 3. Trade waste Industrial and commercial organisations WASTEWATER STORY 157 Rationalised 2023-24 sewers, forming the sewerage. It is like  Cap the jar, shake it well and let the a transport system that carries sewage mixture stand in the sun for two from the point of being produced to the days. point of disposal, i.e. treatment plant.  After two days, shake the mixture Manholes are located at every 50 m and pour a small sample into test to 60 m in the sewerage, at the junction tube. Label this test tube “Before of two or more sewers and at points treatment; Sample 1”. How does it where there is a change in direction. smell?  Use an aerator from an aquarium to Activity 13.3 bubble air through the sample in the Study the sewage route in your home/ glass jar. Allow several hours for school/building. Do the following: aeration; leave the aerator attached  Make a line diagram of the sewage overnight. If you do not have an route. aerator, use a mechanical stirrer or  Walk down the street or survey the a mixer. You may have to stir it campus to find the number of several times.  The next day when aeration is manholes. complete, pour another sample into  If possible, observe open drain and a second test tube. Label it as “After record which living organisms are aeration; Sample 2”. found in and around it.  Fold a piece of filter paper to form a In case you do not have a sewerage cone. Wet the paper with tap water system in your locality, find out how and then insert the cone in a funnel. sewage is being disposed off. Mount the funnel on a support Treatment of polluted water (as you have learnt in Class VI). Perform the following activity. It will help  Place layers of sand, fine gravel and you understand the processes that take finally medium gravel in the funnel (Fig. 13.2). (An actual filtration plant place at the wastewater treatment plant. does not use filter paper, but the sand Activity 13.4 filter is several metres deep).  Pour the remaining aerated liquid Divide yourself into groups to perform through the filter into the beakers. the activity. Record observations at each Do not allow the liquid to spill over stage: the filter. If the filtered liquid is not  Fill a large glass jar 3/4 full of water. clear, filter it a few times till you get Add some dirty organic matter such clear water. as grass pieces or orange peels, a  Pour a sample of the filtered water small amount of detergent, and a few into a third test tube labelled drops of an ink or any colour. “Filtered; Sample 3”. 158 SCIENCE Rationalised 2023-24  1. Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed (Fig. 13.3). Fig. 13.2 Filtration process  Pour another sample of the filtered water into a fourth test tube. Add a small piece of a chlorine tablet. Mix well until the water is clear. Label the Fig. 13.3 Bar screen test tube “Chlorinated; Sample 4”. 2. Water then goes to a grit and sand  Observe carefully the samples in all removal tank. The speed of the the test tubes. Do not taste! Just incoming wastewater is decreased to smell them! allow sand, grit and pebbles to settle Now answer the following questions: down (Fig. 13.4). (a) What changes did you observe in the appearance of the liquid after aeration? (b) Did aeration change the odour? (c) What was removed by the sand filter? (d) Did chlorine remove the colour? (e) Did chlorine have an odour? Was it worse than that of the wastewater? 13.4 WASTEWATER TREATMENT PLANT (WWTP) Fig. 13.4 Grit and sand removal tank Treatment of wastewater involves physical, chemical, and biological 3. The water is then allowed to settle in processes, which remove physical, a large tank which is sloped towards chemical and biological matter that the middle. Solids like faeces settle contaminates the wastewater. at the bottom and are removed with WASTEWATER STORY 159 Rationalised 2023-24  After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil. The treated water has a very low level of organic material and suspended Fig. 13.5 Water clarifer matter. It is discharged into a sea, a river or into the ground. Nature cleans it up a scraper. This is the sludge. A further. Sometimes it may be necessary skimmer removes the floatable solids to disinfect water with chemicals like like oil and grease. Water so cleared chlorine and ozone before releasing it is called clarified water (Fig. 13.5). into the distribution system. The sludge is transferred to a separate tank where it is decomposed Become an active citizen by the anaerobic bacteria. The biogas Waste generation is a natural part of produced in the process can be used as human activity. But we can limit the fuel or can be used to produce electricity. 4. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted The water in a river is cleaned matter still remaining in clarified naturally by processes that are water (Fig. 13.6). similar to those adopted in a wastewater treatment plant. Did you know ? It has been suggested that we should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the Fig. 13.6 Aerator atmosphere. 160 SCIENCE Rationalised 2023-24 type of waste and quantity of waste  Chemicals like paints, solvents, produced. Often we have been repelled insecticides, motor oil, medicines by offensive smell. The sight of open may kill microbes that help purify drains is disgusting. The situation water. So do not throw them down worsens in the rainy season when the the drain. drains start overflowing. We have to  Used tealeaves, solid food remains, wade through the mud pools on the soft toys, cotton, sanitary towels, etc. roads. Most unhygienic and unsanitary should also be thrown in the dustbin conditions prevail. Flies, mosquitoes and (Fig. 13.7). These wastes choke the other insects breed in it. drains. They do not allow free flow You can be an enlightened citizen of oxygen. This hampers the and approach the municipality or the degradation process. gram panchayat. Insist that the open drains be covered. If the sewage of any particular house makes the neighbourhood dirty, you should Don’t add to the load of WWTP. Paheli wonders how! request them to be more considerate about others’ health. 13.5 BETTER HOUSEKEEPING PRACTICES One of the ways to minimise or eliminate waste and pollutants at their source is to see what you are releasing down the drain.  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 Fig. 13.7 Do not throw everything in the sink water. Throw oil and fats in the dustbin. WASTEWATER STORY 161 Rationalised 2023-24  In the year 2016, the Government of India has initiated a new mission known as “Swachh Bharat” under which a lot of drives such as proper sewage disposal and providing toilets for everyone have been started. Vermi-processing toilet A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, low water-use toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes — a resource much needed for soil. 13.6 SANITATION AND DISEASE 13.7 ALTERNATIVE ARRANGEMENT Poor sanitation and contaminated FOR SEWAGE DISPOSAL drinking water is the cause of a large To improve sanitation, low cost onsite number of diseases. sewage disposal systems are being Let us look at our own country. A encouraged. Examples are septic tanks, vast number of our people are still chemical toilets, composting pits. Septic without sewerage facilities. Where do tanks are suitable for places where there they relieve themselves? is no sewerage system, for hospitals, A very large fraction of our people isolated buildings or a cluster of 4 to 5 defecates in the open, on dry riverbeds, houses. on railway tracks, near fields and many Some organisations offer hygienic a time directly in water. Untreated on-site human waste disposal human excreta is a health hazard. It technology. These toilets do not require may cause water pollution and soil scavenging. Excreta from the toilet seats pollution. Both the surface water and flow through covered drains into a groundwater get polluted. Groundwater biogas plant. The biogas produced is is a source of water for wells, tubewells, springs and many rivers. Thus, it used as a source of energy. becomes the most common route for 13.8 SANITATION AT PUBLIC PLACES water borne diseases. They include In our country fairs are organised cholera, typhoid, polio, meningitis, periodically. A large number of people hepatitis and dysentery. participate in them. In the same way railway stations, bus depots, airports, Bhoojo wants to know how hospitals are very busy places. sewage is disposed of in an Thousands of people visit them daily. aeroplane. Large amount of waste is generated 162 SCIENCE Rationalised 2023-24 here. It must be disposed of properly must realise your responsibility in otherwise epidemics could break out. maintaining the water sources in a The government has laid down healthy state. Adopting good sanitation certain standards of sanitation but, practices should be our way of life. As unfortunately, they are not strictly an agent of change your individual enforced. initiative will make a great difference. However, all of us can contribute in Influence others with your energy, ideas maintaining sanitation at public places. and optimism. A lot can be done if people We should not scatter litter anywhere. work together. There is great power in If there is no dustbin in sight, we should collective action. carry the litter home and throw it in the dustbin. Mahatma Gandhi said: Conclusion “No one need to wait for anyone else to adopt a humane and enlightened We all have a role to play in keeping our course of action.” environment clean and healthy. You Keywords Aeration Contaminant Sewerage Aerobic bacteria Sanitation Sludge Anaerobic bacteria Sewage Wastewater Biogas Sewer What you have learnt Used water is wastewater. Wastewater could be reused. Wastewater is generated in homes, industries, agricultural fields and in other human activities. This is called sewage. Sewage is a liquid waste which causes water and soil pollution. Wastewater is treated in a sewage treatment plant. Treatment plants reduce pollutants in wastewater to a level where nature can take care of it. Where underground sewerage systems and refuse disposal systems are not available, the low cost on-site sanitation system can be adopted. By-products of wastewater treatment are sludge and biogas. Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases. We should not defecate in the open. It is possible to have safe disposal of excreta by low cost methods. WASTEWATER STORY 163 Rationalised 2023-24  Exercises 1. 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 ____________. 2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas. 3. Why should oils and fats be not released in the drain? Explain. 4. Describe the steps involved in getting clarified water from wastewater. 5. What is sludge? Explain how it is treated. 6. Untreated human excreta is a health hazard. Explain. 7. Name two chemicals used to disinfect water. 8. Explain the function of bar screens in a wastewater treatment plant. 9. Explain the relationship between sanitation and disease. 10. Outline your role as an active citizen in relation to sanitation. 11. Here is a crossword puzzle: Good luck! 164 SCIENCE Rationalised 2023-24  Across 3. Liquid waste products 4. Solid waste extracted in sewage treatment 6. A word related to hygiene 8. Waste matter discharged from human body Down 1. Used water 2. A pipe carrying sewage 5. Micro-organisms which causes cholera 7. A chemical to disinfect water 12. 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 are correct? (i) (a), (b) and (c) (ii) (b) and (c) (iii) (a) and (d) (iv) All four Extended Learning — Activities and Projects 1. Construct a crossword puzzle of your own using the keywords. 2. Then and now: Talk to your grand parents 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. 3. Visit a sewage treatment plant. It 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. Record in your notepad: Place ___________ Date ___________ Time ___________ Name of the official at the plant __________ Guide/Teacher ___________ WASTEWATER STORY 165 Rationalised 2023-24  (a) The location of the sewage plant. (b) Treatment capacity. (c) The purpose of screening as the initial process. (d) How is air bubbled through the aeration tank? (e) How safe is the water at the end of the treatment? How is it tested? (f ) Where is the water discharged after treatment? (g) What happens to the plant during heavy rains? (h) Is biogas consumed within the plant or sold to other consumers? (i) What happens to the treated sludge? (j) Is there any special effort to protect nearby houses from the plant? (k) Other observations. For more information, consult: Millennium Development Goals: http://www.un.org/millenniumgoals/ “Water for Life” International Decade for Action: http://www.un.org/waterforlifedecade/ http://www.cep.unep.org/pubs/Techreports/tr43en/Household% 20systems.htm “By providing clean water and sanitation to the poorest people on the planet, we can reduce poverty and suffering and ensure education for all chil- dren.” — UNICEF An early engineering feat: Indus valley civilisation One of the ancient civilisations, Harappa and Mohenjodaro had perhaps the world’s first urban sanitation system. Within the city individual houses, or groups of houses, obtained water from wells. There was a separate room for bathing, and wastewater was directed to the covered drains which lined the major streets. The oldest toilet made of bricks is about 4500 years old. 166 SCIENCE Rationalised 2023-24 CK Rationalised 2023-24 CK Notes Rationalised 2023-24