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Life-Cycle of Waste Image and Description
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The image above illustrates the four main stages of product life-cycles, all of which provide opportunities for GHG emissions and/or offsets. These stages are: raw material acquisition, manufacturing, recycling, and waste management.
Raw Material Acquisition. All products use inputs of raw materials, such as metal ore, petroleum, trees, etc. Extracting and transporting these materials entails the combustion of fossil fuels for energy, which results in emissions of carbon dioxide. These fossil fuels must be extracted themselves, which requires additional energy use.
Manufacture. The processes that transform raw materials into products require the combustion of fossil fuels for energy. Again, energy use produces GHG emissions both directly from the combustion of fossil fuels (mainly in the form of carbon dioxide) and from the upstream energy used to obtain and transport those fossil fuels. In addition, some manufacturing processes release other GHGs, although the type and amount of these emissions are specific to the manufacturing processes for each material.
Recycling. Once a product has been used, it can be recycled into new products. While manufacturing products from recycled inputs still requires energy, fewer raw materials are necessary. GHG emissions are therefore offset by the avoided fossil fuel use for raw material acquisition. In addition, for products that require wood or paper inputs, recycling reduces the need to cut down trees, increasing carbon sequestration in forests.
Waste Management. If a product is not recycled at the end of its useful life, it goes through one of three waste management options: composting, combustion, and landfilling. All three use energy for transporting and managing the waste, but they produce additional GHGs to varying degrees.
Composting – an option for organic materials such as food scraps and yard waste – releases some non-biogenic carbon dioxide associated with transporting and turning the compost. However, some of the carbon contained in organic materials is returned and stored in the soil and therefore not released into the atmosphere.
Combustion releases both carbon dioxide and nitrous oxide (a GHG that is 310 times more potent that carbon dioxide). However, some of the energy released during combustion can be harnessed and used to power other processes, which results in offset GHG emissions from avoided fossil fuel use.
Landfilling, the most common waste management practice, results in the release of methane from the anaerobic decomposition of organic materials. Methane is 21 times more potent a GHG than carbon dioxide. However, landfill methane is also a source of energy, and some landfills capture and use it for energy. In addition, many materials in landfills do not decompose fully, and the carbon that remains is sequestered in the landfill and not released into the atmosphere.
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