Chapter 7 Waste Disposal PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Seven Waste disposal Introduction In Standard Six, you learnt about sources, types and effects of...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Seven Waste disposal Introduction In Standard Six, you learnt about sources, types and effects of waste, LY waste management and some methods of proper waste disposal. In this chapter, you will learn about the concept of waste disposal as one of the methods of waste management, advantages of proper N waste disposal, and steps for disposing waste. In addition, you will learn about the structure of an incinerator and the appropriate places O for its construction. The competencies developed will enable you to use proper methods of waste disposal to conserve the environment. The concept of waste disposal SE Waste disposal is one of the waste management methods that involve the U removal and destruction of waste substances. Waste disposal is done to prevent the effects that the waste cause to the environment, human beings and other living things. There are three types of wastes, namely solid, liquid E and gaseous wastes. Methods of waste disposal are based on the types of wastes. Burning, chemical waste treatments, burying at sea, crushing N and landfilling are among the common methods of waste disposal. LI Think N Possible effects to human beings if wastes are not properly disposed O Advantages of proper waste disposal R There are different advantages of proper waste disposal in our environment. FO These advantages include the following: Prevention of the spread of diseases When wastes accumulate in a given area for a long period, they become a breeding site for different insects such as houseflies and mosquitoes. 80 SCIENCE AND TECHNOLOGY STD 7.indd 80 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Accumulated wastes can also provide breeding sites and habitats for destructive animals such as rats, which destroy cereals and other property. Houseflies spread diseases such as dysentery and cholera, and mosquitoes spread malaria. These diseases can be prevented by destroying wastes which are breeding sites for insects that spread such diseases. Prevention of unpleasant smell When the decomposed wastes are accumulated for a long time, they LY give off unpleasant smell. The smell annoys people who live around that environment. Therefore, proper waste disposal prevents such smell. N Keeping the environment clean When wastes are scattered around, the environment becomes dirty and O unattractive. In contrast, proper waste disposal makes the environment clean and attractive. Prevention of accidents SE When wastes are scattered or accumulated for a long time, they may become hiding places for dangerous organisms like snakes, scorpions, U and centipedes. Wastes such as pieces of metals and broken glasses can cause injuries to human beings. Proper waste disposal prevents accidents such as bites from poisonous organisms and injuries from dangerous E things found in the waste. N Prevention of water pollution Wastes may enter water sources and pollute water. They may contain LI poison or have pathogens that cause diseases to human beings and other living things. Therefore, the people using such water may be infected. N Proper waste disposal reduces the possibility of wastes to contaminate O water sources. Proper use of land R Stored wastes occupy a large area of land if they are not destroyed. This is because some wastes take longer to decompose. Some of the waste FO disposal methods tend to destruct them by compaction or ash formation. After disposing them, the land may be used for other activities. 81 SCIENCE AND TECHNOLOGY STD 7.indd 81 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Generation of electricity Heat produced from an incinerator can be used to generate electricity. The generated heat may also be used to boil water. The steam produced from the boiled water may be used to run electric generators. Electricity is used to run machines and other equipment that simplify work. Warming houses In very cold areas, heat from the incinerator is used to warm water. The warm water is distributed to human settlements through special systems LY of pipes for warming houses. Production of fertiliser N Remains of some burned wastes are used as soil fertiliser. The fertiliser O can be used in agriculture to increase crop yields. Protection of living organisms found in the soil SE Some wastes are toxic to the living things found in the soil. Proper waste disposal eliminates or reduces their effects on living organisms. U Exercise 1 Answer the following questions: 1. What is waste disposal? E 2. List two accidents that may occur when wastes are not properly disposed. N 3. How does waste disposal help to conserve land? LI N Steps for disposing wastes O Discuss with your fellow pupils R Steps to follow during waste disposal FO It is important to follow various steps for effective waste disposal. The following are the steps to follow for effective waste disposal: 82 SCIENCE AND TECHNOLOGY STD 7.indd 82 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Sorting wastes Sorting wastes helps to group wastes based on their nature. It helps to choose proper methods that will be used to destroy or recycle them. Each type of wastes has its specific waste characteristics which differentiate it from others. Therefore, specific methods of disposal are needed for each type of wastes. Waste sorting also helps to avoid explosions and accidents that may occur when wastes composed of different chemicals are kept together. Waste sorting reduces waste disposal costs. During waste disposal, wastes are sorted and kept in groups as follows: LY Combustible wastes: These are dry wastes such as paper, trees, leaves, N and clothes. O Non-combustible wastes: These include ceramics, remains of household utensils, pieces of glass and metals. SE Hazardous wastes: Some wastes can be harmful to the environment, human beings and other living things. These wastes need special attention during disposal. They also have long term effects to the environment. Examples of hazardous wastes are expired medicines, used batteries, U radioactive wastes, and scrap metals. E Non-hazardous wastes: These are wastes that have no evidence of causing harm to the environment, human beings and other living things. N Examples of non-hazardous wastes are paper and wooden materials. LI Harmful wastes during disposal: Some wastes can cause harmful effects during disposal. Some of these wastes emit toxic gases that can affect N people living around the environment. For example, wastes containing nitric acid can produce nitrogen dioxide when burnt. The resulting gas is O toxic; when inhaled, it can cause health problems. Therefore, such types of wastes are separated to apply proper disposal methods. To comply R with hazardous waste disposal laws, experts are normally involved. FO Non-harmful wastes during disposal: These are wastes that have been approved to be harmless to the environment, human beings and other living things. Examples of such wastes include food remains, paper, plant leaves, grasses and worn out clothes. These wastes can be collected and 83 SCIENCE AND TECHNOLOGY STD 7.indd 83 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE buried to decompose and produce manure that can be used in agriculture to increase crop yields. Wastes sorting can be done using special containers that are differentiated by their colours as shown in Figure 1. The colours of the containers and the types of wastes placed in are usually as follows: (a) A blue-coloured container is used to keep wastes originating from paper such as boxes; (b) A yellow-coloured container is used to keep wastes of metallic origins LY such as iron; (c) An orange-coloured container is used to keep wastes originating N from plastic such as plastic bottles; (d) A grey-coloured container is used to keep glass based wastes, such O as broken glass cups; (e) A red-coloured container is used to store electronic wastes such as broken cell phones, chargers, and batteries; and SE (f) A green-coloured container is used to keep organic wastes like food remains. U E PAPER METALLIC PLASTIC N WASTE WASTE WASTE LI N O GLASS ELECTRONIC ORGANIC WASTE WASTE WASTE R FO Figure 1: Different containers for keeping wastes 84 SCIENCE AND TECHNOLOGY STD 7.indd 84 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Selecting an appropriate area for waste disposal During waste disposal, it is important to choose a suitable area where the disposal will not cause harm to human beings and the environment. For example, waste disposal by burning should be carefully done far away from human settlements. Selecting proper methods of waste disposal The selection of proper methods of waste disposal depends on the LY types of wastes, disposal costs, and the laws governing the disposal of wastes in that place. Different methods can be used to dispose wastes. These include crushing and landfilling, burning, chemical treatment, and N incineration. These methods of waste disposal are described below: O Crushing or grinding wastes and landfilling: This method is used to dispose solid wastes that cannot be easily destroyed by burning. Wastes SE that can be destroyed by this method include substandard and expired products. Examples of these products are radio, television, electrical goods, and canned foods. These products are crushed or ground as U shown in Figure 2 and buried in a special area. E N LI N O R FO Figure 2: Waste disposal by crushing or grinding 85 SCIENCE AND TECHNOLOGY STD 7.indd 85 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Burning of wastes: Fire is used to destroy solid wastes that can be burnt easily. The burning method has several advantages: it is cheap; it kills destructive insects found in the waste; and it prevents spreading of pathogens. However, the method has many disadvantages. First, waste burning degrades soil fertility since it also kills organisms responsible for waste decomposition and soil fertility. Second, the smoke released during burning annoys people, and it affects the respiratory system, and third, mismanaged burning of wastes can burn houses, forests and grazing areas. Lastly, some wastes produce toxic chemicals when burnt, hence affecting LY health of humans and other organisms. Chemical treatment: This method is normally used to dispose dangerous N chemical wastes, such as cosmetics. This method involves experts due to their legal requirements. For example, when different chemicals used O at school expire, the school management should report to the relevant authority for disposing them. Normally, acidic wastes are treated using alkali to make them harmless to the environment, human beings and other living things. SE Incineration: In this method, wastes are destroyed using high temperature U from a heat source. The method is used to destroy solid wastes such as hospital bandages used in dressing wounds in hospitals. E Exercise 2 Answer the following questions: N 1. Mention the types of wastes that can be destroyed by the chemical LI treatment method. 2. Using examples, explain the meaning of hazardous wastes. N 3. Explain the advantages of sorting and segregating wastes into their respective groups before disposing. O 4. Explain the advantages and disadvantages of burning wastes. R An incinerator FO An incinerator is a furnace or special unit for burning wastes at high temperatures. The sizes of incinerators differ depending on the uses and quantities of wastes to be burnt. Incinerators are used in different places such as schools, hospitals and industries. The materials for constructing 86 SCIENCE AND TECHNOLOGY STD 7.indd 86 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE an incinerator depend on the intended use of the incerator. Some of the incinerators are made in industries using steel which cannot melt easily. A simple incinerator is constructed using an iron steel bar or iron ore, cement, coarse aggregates and sand. This incinerator is used to burn wastes such as paper, sanitary pads, and cotton. The structure of an incinerator The incinerator has three main parts, which are the air inlet and ash vent, the combustion chamber and the chimney, as shown in Figure 3. LY N Chimney O SE Combustion chamber U Air inlet and ash vent E N LI Figure 3: An incinerator N Air inlet and ash vent: This is the lower part of the incinerator which O allows air in. The oxygen gas contained in the air helps to burn wastes placed in the incinerator. This part is also used to remove ashes after the waste is burnt. R FO The combustion chamber: This is the middle part of the incinerator found above the air inlet and ash vent. The wastes to be destroyed are placed in this part. This part is large enough to allow turning of wastes to ensure efficient burning. Gases produced in this chamber are released via the 87 SCIENCE AND TECHNOLOGY STD 7.indd 87 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE chimney. The door in this area is always closed to prevent the emission of smoke and gas. The chimney: This part is directed upwards and normally connected to a long pipe to emit smoke. The pipe helps to release smoke high in the atmosphere where it is blown by wind. Therefore, it protects people around the incinerator from the effects of smoke. Places for building an incinerator LY Before building an incinerator, it is important to evaluate the area. An incinerator should be built away from human settlements, but it should be easily accessible. This will help to prevent smoke and unpleasant smell. N The incinerator should also be built by considering the wind direction so O that the smoke should not be blown towards human settlements. The incinerator should not be constructed near combustible materials. It should be constructed away from electric lines to avoid the possibility of SE accidents. The incinerator should also be built away from water sources to avoid water pollution. U Exercise 3 Answer the following questions: E 1. What is an incinerator? 2. List four places where an incinerator is used. N 3. Describe the roles of each main part of an incinerator. LI Activity: Constructing a model of an incinerator N O Materials: clay soil, sticks, rope or threads, water, machete and a picture of an incinerator Procedure R 1. Mix clay soil to form clay lump. FO 2. Cut a piece of rope that is enough to tie sticks. 3. Use the rope and sticks to construct a model with the shape as shown in Figure 3. 88 SCIENCE AND TECHNOLOGY STD 7.indd 88 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Spread clay on the model. 5. Allow the model to air-dry. Question Can the model you have constructed be used as an incinerator? Why? Exercise 4 LY Answer all questions in sections A, B and C. Section A N Choose the most correct answer and write its letter in the box provided. 1. Which of the following is not among the criteria to be considered O when constructing an incinerator? (a) To be far from human settlements SE (b) Being in an area with a lot of wastes (c) Being far from combustible materials (d) Easily accessible U 2. If an incinerator is constructed near combustible materials, it __________. (a) will cause fast burning of wastes E (b) will cause a lot of smoke during burning N (c) produces more ashes (d) may cause fire accidents LI 3. Identifying the types of wastes during sorting will help __________. (a) to decide on the methods of disposal N (b) to determine the quantity of waste O (c) to decide how to arrange them (d) to reduce waste smell R 4. Generation of electricity using an incinerator requires __________. (a) water to run machines that generate electricity FO (b) boiled water to run machines that generate electricity (c) steam to run machines that generate electricity (d) oxygen gas to run electricity generating machines 89 SCIENCE AND TECHNOLOGY STD 7.indd 89 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B 5. Write TRUE for a correct statement and FALSE for an incorrect statement in the space provided. (a) Burning of waste is not the only method of waste disposal. __________ (b) The state of the waste is an important criterion for selecting the disposal method. __________ (c) The size of an incinerator depends only on the financial capacity LY of the user. __________ (d) Disposing toxic and non-toxic wastes does not involve experts. __________ N (e) All household wastes are disposed by incineration. __________ O Section C 6. List three methods of waste disposal. SE 7. Explain the characteristics of a suitable area to construct an incinerator. 8. Briefly explain what will happen if an incinerator is constructed without the following: (a) a chimney U (b) an ash vent 9. What is the importance of turning wastes during burning? 10. Explain the disadvantages of constructing an incinerator near human E settlements. N 11. Why is it necessary to use an incinerator to dispose wastes? 12. Is it possible to generate electricity from incinerators in Tanzania? LI Explain. 13. Why do incinerators vary in sizes? N O Vocabulary Chimney a vertical pipe which conducts smoke and combustion gases up from a fire or furnace R Electrical generators machines used in generating electricity FO Organic waste is any material that is easily decomposed. It comes from either a plant or an animal Segregation separating things from others. 90 SCIENCE AND TECHNOLOGY STD 7.indd 90 26/07/2021 12:00