7 wastewater story


Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

7 wastewater story

  1. 1. 18 Wastewater StoryAll of us use water in our homes and Clean water that is fitmake it dirty. for use is unfortunately Dirty! Are you surprised? not available to all. It Rich in lather, mixed with oil, black– has been reported thatbrown water that goes down the drains more than one billion offrom sinks, showers, toilets, laundries our fellow human beingsis dirty. It is called wastewater This wastewater. have no access to safe drinking water.used water should not be wasted. We This accounts for a large number ofmust clean it up by removing pollutants. water-related diseases and even deaths.Have you ever thought where the Women and girls walk for severalwastewater goes and what happens to it? kilometres to collect clean water, as you read in Chapter 16. Is it not a serious18.1 WATER, OUR LIFELINE matter for human dignity?Clean water is a basic need of human You have studied in Chapter 16being. Let us make a mindmap of the about the increasing scarcity of fresh-many uses of clean water. water due to population growth,Activity 18.1 pollution, industrial development, mismanagement and other factors. (We have given one example of the Realising the urgency of the situationuse of clean water. You can add many on the World Water Day, on 22 Marchmore.) 2005, the General Assembly of the United Nations proclaimed the period 2005 – 2015 as the International Decade for action on “Water for life”. All efforts made during this decade aim to reduce Clean water by half the number of people who do put to use not have access to safe drinking water. Cleaning of water is a process of removing pollutants before it enters a water body or is reused. This process of wastewater treatment is commonly Drinking known as “Sewage Treatment”. It takes place in several stages.220 SCIENCE
  2. 2. 18.2 WHAT IS SEWAGE? pesticides,Sewage is wastewater released by homes, herbicides, fruitindustries, hospitals, offices and other and vegetableusers. It also includes rainwater that has waste, etc.run down the street during a storm or Inorganic impurities – Nitrates,heavy rain. The water that washes off Phosphates,roads and rooftops carries harmful metals.substances with it. Sewage is a liquid waste. Nutrients – PhosphorusMost of it is water, which has dissolved and Nitrogen.and suspended impurities. These Bacteria – Such as whichimpurities are called contaminants contaminants. cause cholera and typhoid.Activity 18.2 Other microbes – Such as whichLocate an open drain near your home, cause dysentery.school or on the roadside and inspect 18.3 WATER FRESHENS UP — ANwater flowing through it. EVENTFUL JOURNEY Record colour, odour and any otherobservation. Discuss with your friends In a home or a public building generally one set of pipes brings clean water andand your teacher and fill up thefollowing Table 18.1. another set of pipes takes away We know that sewage is a complex wastewater. Imagine that we could see through the ground. We would see amixture containing suspended solids,organic and inorganic impurities, network of big and small pipes, called sewers forming the sewerage It is like sewers, sewerage.nutrients, saprotrophic and disease a transport system that carries sewagecausing bacteria and other microbes.Organic impurities – Human faeces, from the point of being produced to the animal waste, point of disposal, i.e. treatment plant. Manholes are located at every 50 m oil, urea (urine), to 60 m in the sewerage, at the junction Table 18.1 Contaminant survey S. No. Type of sewage Point of origin Substances which Any other contaminate remark 1. Sullage water Kitchen 2. Foul waste Toilets 3. Trade waste Industrial and commercial organisationsWASTEWATER STORY 221
  3. 3. of two or more sewers and at points treatment; Sample 1”. How does it 1”where there is a change in direction. smell? Use an aerator from an aquarium toActivity 18.3 bubble air through the sample in theStudy the sewage route in your home/ glass jar. Allow several hours forschool/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. manholes. The next day when aeration is Follow an open drain and find out complete, pour another sample into where it ends and which living a second test tube. Label it as “After organisms are found in and aeration; Sample 2” 2”. 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 watersystem in your locality, find out how and then insert the cone in a funnel.sewage is being disposed off. Mount the funnel on a supportTreatment of polluted water (as you have learnt in Class VI). Place layers of sand, fine gravel andPerform the following activity. It will help finally medium gravel in the funnelyou understand the processes that take (Fig. 18.2). (An actual filtration plantplace at the wastewater treatment plant. does not use filter paper, but the sandActivity 18.4 filter is several metres deep). Pour the remaining aerated liquidDivide yourself into groups to perform through the filter into the beakers.the activity. Record observations at each Do not allow the liquid to spill overstage: 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”. Cap the jar, shake it well and let the Pour another sample of the filtered mixture stand in the sun for two water into a fourth test tube. Add a days. small piece of a chlorine tablet. Mix After two days, shake the mixture well until the water is clear. Label the and pour a small sample into test test tube “Chlorinated; Sample 4” 4”. tube. Label this test tube “Before222 SCIENCE
  4. 4. Fig. 18.2 Filtration process Fig. 18.3 Bar screen Observe carefully the samples in all 2. Water then goes to a grit and sand the test tubes. Do not taste Just taste! removal tank. The speed of the smell them! incoming wastewater is decreased to Now answer the following questions: allow sand, grit and pebbles to settle(a) What changes did you observe in the down (Fig. 18.4). 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?18.4 WASTEWATER TREATMENT PLANT (WWTP) Fig. 18.4 Grit and sand removal tankTreatment of wastewater involvesphysical, chemical, and biological 3. The water is then allowed to settle inprocesses, which remove physical, a large tank which is sloped towardschemical and biological matter that the middle. Solids like faeces settlecontaminates the wastewater. at the bottom and are removed with1. Wastewater is passed through bar a scraper. This is the sludge A sludge. screens. Large objects like rags, skimmer removes the floatable solids sticks, cans, plastic packets, napkins like oil and grease. Water so cleared are removed (Fig. 18.3). is called clarified water (Fig. 18.5).WASTEWATER STORY 223
  5. 5. 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 matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like Fig. 18.5 Water clarifer chlorine and ozone before releasing it into the distribution system. The sludge is transferred to aseparate tank where it is decomposed Become an active citizenby the anaerobic bacteria. The biogas Waste generation is a natural part ofproduced in the process can be used as human activity. But we can limit thefuel or can be used to produce electricity. type of waste and quantity of waste4. Air is pumped into the clarified water produced. Often we have been repelled to help aerobic bacteria to grow. by offensive smell. The sight of open Bacteria consume human waste, drains is disgusting. The situation food waste, soaps and other unwanted matter still remaining in clarified water (Fig. 18.6). After several hours, the suspendedmicrobes settle at the bottom of the tank The water in a river is cleanedas activated sludge. The water is then naturally by processes that areremoved from the top. 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. 18.6 Aerator atmosphere.224 SCIENCE
  6. 6. worsens in the rainy season when the Used tealeaves, solid food remains,drains start overflowing. We have to soft toys, cotton, sanitary towels, etc.wade through the mud pools on the should also be thrown in the dustbinroads. Most unhygienic and unsanitary (Fig. 18.7). These wastes choke theconditions prevail. Flies, mosquitoes andother insects breed in it. You can be an enlightened citizenand approach the municipality or thegram panchayat. Insist that the opendrains be covered. If the sewage ofany particular house makes theneighbourhood dirty, you should Don’t add to the load of WWTP. Paheli wonders how!request them to be more considerateabout others’ health.18.6 BETTER HOUSE KEEPING P RACTICESOne of the ways to minimise or eliminatewaste and pollutants at their source isto see what you are releasing down thedrain. Cooking oil and fats should not be thrown down the drain. They can Fig. 18.7 Do not throw every thing in the sink harden and block the pipes. In an drains. They do not allow free flow open drain the fats clog the soil pores of oxygen. This hampers the reducing its effectiveness in filtering degradation process. water. Throw oil and fats in the dustbin. 18.7 SANITATION AND DISEASE Chemicals like paints, solvents, Poor sanitation and contaminated insecticides, motor oil, medicines drinking water is the cause of a large may kill microbes that help purify number of diseases. water. So do not throw them down Let us look at our own country. A the drain. vast number of our people are stillWASTEWATER STORY 225
  7. 7. 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.without sewerage facilities. Where do isolated buildings or a cluster of 4 to 5they relieve themselves? houses. A very large fraction of our people Some organisations offer hygienicdefecates in the open, on dry riverbeds, on-site human waste disposalon railway tracks, near fields and many technology. These toilets do not requirea time directly in water. Untreated scavenging. Excreta from the toilet seatshuman excreta is a health hazard. It flow through covered drains into amay cause water pollution and soil biogas plant. The biogas produced ispollution. Both the surface water and used as a source of energy.groundwater get polluted. Groundwater 18.9 SANITATION AT PUBLIC PLACESis a source of water for wells, tubewells,springs and many rivers as you learnt In our country fairs are organisedin Chapter 16. Thus, it becomes the periodically. A large number of peoplemost common route for water borne participate in them. In the same waydiseases. They include cholera, typhoid, railway stations, bus depots, airports,polio, meningitis, hepatitis and hospitals are very busy places.dysentery. Thousands of people visit them daily. Large amount of waste is generated18.8 ALTERNATIVE ARRANGEMENT FOR here. It must be disposed of properly SEWAGE DISPOSAL otherwise epidemics could break out.To improve sanitation, low cost onsite The government has laid downsewage disposal systems are being certain standards of sanitation but,encouraged. Examples are septic tanks, unfortunately, they are not strictlychemical toilets, composting pits. Septic enforced.tanks are suitable for places where there However, all of us can contribute inis no sewerage system, for hospitals, maintaining sanitation at public places. We should not scatter litter anywhere. Bhoojo wants to know how If there is no dustbin in sight, we should sewage is disposed of in an carry the litter home and throw it in the aeroplane. dustbin.226 SCIENCE
  8. 8. Conclusion Influence others with your energy, ideasWe all have a role to play in keeping our and optimism. A lot can be done if peopleenvironment clean and healthy. You work together. There is great power inmust realise your responsibility in collective action.maintaining the water sources in a Mahatma Gandhi said:healthy state. Adopting good sanitation “No one need to wait for anyone elsepractices should be our way of life. As to adopt a humane and enlightenedan agent of change your individual course of action.”initiative will make a great difference. 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 227
  9. 9. 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!228 SCIENCE
  10. 10. 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 229
  11. 11. (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/ World Water Day - Themes and Importance: http://www.worldwaterday.org/ Through the ages Development of Sanitation: http://www.sewerhistory.org/ 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 children.” — 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.230 SCIENCE