Welcome dear students! Today we are going to learn about Wastewater Story from Class 7 Science. All of us use water in our homes and make it dirty. Dirty! Are you surprised? Rich in lather, mixed with oil, black-brown water that goes down the drains from sinks, showers, toilets, laundries is dirty. It is called wastewater. This used water should not be wasted. We must clean it up by removing pollutants. Have you ever thought where the wastewater goes and what happens to it? Clean water is a basic need of human being. Let us make a mindmap of the many uses of clean water. Activity 13.1 gives one example of the use of clean water: Drinking. You can add many more uses to your mindmap. Clean water that is fit for use is unfortunately not available to all. It has been reported that more than one billion of people have no access to safe drinking water. This accounts for a large number of water-related diseases and even deaths. People even children walk for several kilometres to collect clean water. Is it not a serious matter for human dignity? The increasing scarcity of fresh-water is due to population growth, pollution, industrial development, mismanagement and other factors. Realising the urgency of the situation on the World Water Day, on 22 March 2005, the General Assembly of the United Nations proclaimed the period 2005 to 2015 as the 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. There has been perceptible progress 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 wastewater treatment is commonly known as Sewage Treatment. It takes place in several stages. [CHECKPOINT]
Now let us move to section 13.2 to understand what sewage is. Sewage is wastewater released by homes, industries, hospitals, offices and other users. It also includes rainwater that has run down the street during a storm or heavy rain. The water that washes off roads and rooftops carries harmful substances with it. Sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities. Activity 13.2 asks you to locate an open drain near your home, school or on the roadside and inspect water flowing through it. Record colour, odour and any other observation. Discuss with your friends and your teacher and fill up Table 13.1, the Contaminant survey. The table classifies sewage into three types. First is Sullage water, originating from the Kitchen. Second is Foul waste, originating from Toilets. Third is Trade waste, originating from Industrial and commercial organisations. We know that sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes and disease causing bacteria and other microbes. Organic impurities include human faeces, animal waste, oil, urea which is urine, pesticides, herbicides, fruit and vegetable waste. Inorganic impurities consist of Nitrates, Phosphates, and metals. Nutrients are Phosphorus and Nitrogen. Bacteria include vibrio cholera which causes cholera and salmonella paratyphi which causes typhoid. Other microbes include protozoa which cause dysentery. [CHECKPOINT]
Next, we will explore how water freshens up on its eventful journey in section 13.3. In a home or a public building generally one set of pipes brings clean water and another set of pipes takes away wastewater. Imagine that we could see through the ground. We would see a network of big and small pipes, called sewers, forming the sewerage. It is like a transport system that carries sewage from the point of being produced to the point of disposal, that is, the treatment plant. Manholes are located at every 50 m to 60 m in the sewerage, at the junction of two or more sewers and at points where there is a change in direction. Activity 13.3 asks you to study the sewage route in your home, school or building. Make a line diagram of the sewage route. Walk down the street or survey the campus to find the number of manholes. If possible, observe an open drain and record which living organisms are found in and around it. In case you do not have a sewerage system in your locality, find out how sewage is being disposed off. Now let us perform Activity 13.4 to understand the processes at a wastewater treatment plant. Divide yourselves into groups to perform the activity and record observations at each stage. Fill a large glass jar three-fourths full of water. Add some dirty organic matter such as grass pieces or orange peels, a small amount of detergent, and a few drops of an ink or any colour. Cap the jar, shake it well and let the mixture stand in the sun for two days. After two days, shake the mixture and pour a small sample into a test tube. Label this test tube Before treatment, Sample 1. How does it smell? Use an aerator from an aquarium to bubble air through the sample in the glass jar. Allow several hours for aeration; leave the aerator attached overnight. If you do not have an aerator, use a mechanical stirrer or a mixer. You may have to stir it several times. The next day when aeration is complete, pour another sample into a second test tube. Label it as After aeration, Sample 2. Fold a piece of filter paper to form a cone. Wet the paper with tap water and then insert the cone in a funnel. Mount the funnel on a support. Place layers of sand, fine gravel and finally medium gravel in the funnel, as shown in Figure 13.2, Filtration process. Pour the remaining aerated liquid through the filter into the beakers. Do not allow the liquid to spill over the filter. If the filtered liquid is not clear, filter it a few times till you get clear water. Pour a sample of the filtered water into a third test tube labelled Filtered, Sample 3. 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 test tube Chlorinated, Sample 4. Observe carefully the samples in all the test tubes. Do not taste! Just smell them! Now answer the following questions. What changes did you observe in the appearance of the liquid after aeration? Did aeration change the odour? What was removed by the sand filter? Did chlorine remove the colour? Did chlorine have an odour? Was it worse than that of the wastewater? [CHECKPOINT]
Now we move to the Wastewater Treatment Plant, or WWTP, in section 13.4. Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater. Step 1: Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed, as shown in Figure 13.3, Bar screen. Step 2: Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down, as shown in Figure 13.4, Grit and sand removal tank. Step 3: The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water, as shown in Figure 13.5, Water clarifier. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity. Step 4: Air 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 clarified water, as shown in Figure 13.6, Aerator. 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 percent 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 chlorine and ozone before releasing it into the distribution system. [CHECKPOINT]
Let us become an active citizen. Waste generation is a natural part of human activity. But we can limit the type of waste and quantity of waste produced. Often we have been repelled by offensive smell. The sight of open drains is disgusting. The situation worsens in the rainy season when the drains start overflowing. We have to wade through the mud pools on the roads. Most unhygienic and unsanitary conditions prevail. Flies, mosquitoes and other insects breed in it. You can be an enlightened citizen and approach the municipality or the gram panchayat. Insist that the open drains be covered. If the sewage of any particular house makes the neighbourhood dirty, you should request them to be more considerate about others health. Do not add to the load of WWTP. Paheli wonders how! Here is a special note for you. The water in a river is cleaned naturally by processes that are 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 atmosphere. Now let us look at better housekeeping practices in section 13.5. 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 water. Throw oil and fats in the dustbin. Chemicals like paints, solvents, insecticides, motor oil, medicines may kill microbes that help purify water. So do not throw them down the drain. Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin, as shown in Figure 13.7, Do not throw everything in the sink. These wastes choke the drains. They do not allow free flow of oxygen. This hampers the degradation process. 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. Let us learn about the 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. [CHECKPOINT]
Next, we will discuss sanitation and disease in section 13.6. Poor sanitation and contaminated drinking water is the cause of a large number of diseases. Let us look at our own country. A vast number of our people are still without sewerage facilities. Where do they relieve themselves? A very large fraction of our people defecates in the open, on dry riverbeds, on railway tracks, near fields and many a time directly in water. Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery. Bhoojo wants to know how sewage is disposed of in an aeroplane. To improve sanitation, low cost onsite sewage disposal systems are being encouraged in section 13.7. 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. Let us look at sanitation at public places in section 13.8. In our country fairs are organised periodically. A large number of people participate in them. In the same way railway stations, bus depots, airports, hospitals are very busy places. Thousands of people visit them daily. Large amount of waste is generated here. It must be disposed of properly otherwise epidemics could break out. The government has laid down certain standards of sanitation but, unfortunately, they are not strictly enforced. However, all of us can contribute in maintaining sanitation at public places. We should not scatter litter anywhere. If there is no dustbin in sight, we should carry the litter home and throw it in the dustbin. [CHECKPOINT]
To conclude this chapter, we all have a role to play in keeping our environment clean and healthy. You must realise your responsibility in maintaining the water sources in a healthy state. Adopting good sanitation practices should be our way of life. As an agent of change your individual initiative will make a great difference. Influence others with your energy, ideas and optimism. A lot can be done if people work together. There is great power in collective action. Mahatma Gandhi said: No one need to wait for anyone else to adopt a humane and enlightened course of action. Let us quickly review the keywords: Aeration, Aerobic bacteria, Anaerobic bacteria, Biogas, Contaminant, Sanitation, Sewage, Sewer, Sewerage, Sludge, Wastewater. And here is 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. [CHECKPOINT]
Now let us solve the exercises completely. Question 1 asks to fill in the blanks. The answers are: Cleaning of water is a process of removing pollutants. Wastewater released by houses is called sewage. Dried sludge is used as manure. Drains get blocked by cooking oil and fats and solid wastes like used tealeaves and sanitary towels. Question 2 asks what sewage is and why it is harmful to discharge untreated sewage into rivers or seas. Sewage is wastewater released by homes, industries, hospitals, offices and other users, including storm rainwater. It is harmful because it contains dissolved and suspended impurities, organic and inorganic pollutants, nutrients, and disease causing bacteria. Discharging it untreated pollutes water bodies, kills aquatic life, and spreads waterborne diseases. Question 3 asks why oils and fats should not be released in 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. Question 4 asks to describe the steps involved in getting clarified water from wastewater. First, wastewater passes through bar screens to remove large objects. Second, it enters a grit and sand removal tank where speed is decreased to settle sand, grit and pebbles. Third, it enters a large sloped tank where solids settle as sludge and floatable solids like oil and grease are skimmed off, leaving clarified water. Question 5 asks what sludge is and how it is treated. Sludge is the solid waste like faeces that settles at the bottom of the settling tank. It is transferred to a separate tank where it is decomposed by anaerobic bacteria to produce biogas. The remaining water is removed by sand drying beds or machines, and the dried sludge is used as manure. [CHECKPOINT]
Question 6 asks why untreated human excreta is a health hazard. It causes water pollution and soil pollution. Both surface water and groundwater get polluted. Since groundwater is a source for wells, tubewells, springs and rivers, it becomes the most common route for water borne diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery. Question 7 asks to name two chemicals used to disinfect water. The two chemicals are chlorine and ozone. Question 8 asks to explain the function of bar screens in a wastewater treatment plant. Bar screens remove large objects like rags, sticks, cans, plastic packets, and napkins from the incoming wastewater to prevent damage to pumps and blockages in later stages. Question 9 asks to explain the relationship between sanitation and disease. Poor sanitation and contaminated drinking water is the direct cause of a large number of diseases. Open defecation and untreated sewage pollute water sources, creating breeding grounds for pathogens that cause cholera, typhoid, dysentery, and other illnesses. Good sanitation breaks this cycle. Question 10 asks to outline your role as an active citizen in relation to sanitation. You should limit waste generation, never throw oil, fats, chemicals, or solid waste down drains, insist on covering open drains, report unhygienic conditions to local authorities, avoid scattering litter, carry waste home if no bin is available, and promote awareness about the Swachh Bharat mission. Question 11 is a crossword puzzle. The answers are: Across 3 is Sewage, Across 4 is Sludge, Across 6 is Hygiene, Across 8 is Excreta. Down 1 is Wastewater, Down 2 is Sewer, Down 5 is Bacteria, Down 7 is Chlorine. Question 12 asks which statements about ozone are correct. The statements are: It is essential for breathing of living organisms, It is used to disinfect water, It absorbs ultraviolet rays, Its proportion in air is about 3 percent. The correct option is (ii) (b) and (c), because ozone is used to disinfect water and absorbs ultraviolet rays, but it is not essential for breathing and its proportion in air is much less than 3 percent. [CHECKPOINT]
For extended learning, you are encouraged to construct your own crossword puzzle using the keywords, talk to elderly people about past sewage disposal systems to prepare a brief report, and visit a local sewage treatment plant to observe its location, capacity, screening process, aeration method, water safety testing, discharge point, biogas usage, sludge treatment, and protective measures for nearby houses. You can also explore the Millennium Development Goals and the Water for Life International Decade for Action online. Remember that providing clean water and sanitation to the poorest people on the planet can reduce poverty and suffering and ensure education for all children. An early engineering feat from the Indus valley civilisation shows that Harappa and Mohenjodaro had perhaps the world first urban sanitation system, with houses obtaining water from wells, separate bathing rooms, and wastewater directed to covered drains lining major streets. The oldest toilet made of bricks is about 4500 years old. Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]