Municipal solid waste, 2015-2016
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Municipal solid waste is commonly known as garbage or trash. These wastes include durable goods such as furniture and tires as well as nondurable goods such as plastic cups, newspapers, milk cartons and food or yard waste, such as uneaten food, branches, and leaves. The definition of municipal solid waste excludes waste from industrial sources, such as hazardous pollution like mercury or sulfur dioxide. [1][2][3]
Background
During the late 19th and early 20th centuries, local governments began focusing on sewage management given the problems greater urbanization and the need to dispose of more waste from a growing population. In the late 19th century, cities in the United States began using watertight garbage cans and vehicles to collect and transport trash to landfills. By the early 20th century, 15 percent of major U.S. cities were using incinerators to destroy their trash, though other large cities continued disposing trash in water or on land.[2]
Throughout the 20th century, new technologies emerged to manage solid waste, such as compactor trucks (commonly known as garbage trucks), garbage grinders, and pneumatic collection systems (a system used to transport waste at high speed through underground tubes to a station for compaction and sealing in containers). By the 1950s, municipalities adopted sanitary landfills, which are sites where waste is isolated and buried either underground or in large piles.[2]
Management and disposal
Collection
Solid waste is typically collected by compactor trucks, which usually are able to reduce the volume of trash to less than half of its volume if the garbage were not compacted. Garbage collection typically occurs once a week given the relatively short time that food waste decomposes. Recycling, the process in which used materials like waste are used to create new materials, was adopted partly in order to reduce the amount solid waste collected from individuals and businesses. Some municipalities contain transfer stations, which are facilities where trash is received from several collection vehicles to be transferred to a more permanent facility via a larger vehicle.[2][4][5]
After municipal solid waste is collected, some municipalities modify the form of the waste to make treatment and final disposal easier. This modification reduces the trash's total weight and volume. Some facilities also recover heat energy from some waste to be recycled or reused.[2][4][5]
Treatment and disposal
Incineration is a common and effective way to reduce solid waste. Most incinerators can reduce waste volume by more than 90 percent, resulting in glass, ash, and metal residues. The furnaces, which are built with bricks that can withstand high temperatures, burn the waste under controlled conditions. Combined with oxygen, the combustible parts of the waste release carbon dioxide, heat, and water vapor. What is left after incineration, including fine particles like dust and soot, is transferred via airstream and filtered through various technologies before the air is released outside. Another method to treat waste is known as composting, in which organic parts of garbage are allowed decompose. Microbes interact with the organic waste to break it down, resulting in compost, which can be used as mulch or a way to improve soil conditions.[2][4][5]
Land disposal is also a common method for disposing of waste. Sanitary landfills, which are sites designed to keep waste from affecting public health or the environment, act as storing sites for solid waste, which is buried underground. One requirement for sanitary landfills is that buried waste cannot come near groundwater or surface water. New landfills are often required to a barrier at the bottom to keep waste from groundwater. Additionally, parts of the landfill must have impermeable covers to keep rain or surface runoff away from buried waste. These barriers can be made of plastic, clay soil, or a combination thereof.[2][4][5]
Waste to energy generation
Municipal solid waste can be used to produce energy at plants and landfills. Materials like paper, cardboard, food, grass, leaves, and wood are known as biomass, a renewable form of energy made from organic, biological, non-fossil materials. Plants that generate energy from waste, known as waste-to-energy plants, burn the organic materials to make steam to generate electricity. To generate electricity, waste-to-energy plants have combustion chambers to burn the fuel in the waste to produce heat. The heat is then used to turn water into steam in a boiler. At high pressure, the steam turns turbine blades to produce electricity. In 2013, the United States had 80 waste-to-energy plants generating electricity or producing steam. These plants burned 30 million tons of municipal solid waste to generate electricity in 2013.[6]
See also
Footnotes
- ↑ U.S. Environmental Protection Agency, "Municipal Solid Waste," accessed March 11, 2015
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Encyclopedia Britannica, "Solid-waste management," accessed December 20, 2016
- ↑ University of Michigan, "Municipal Solid Waste," accessed December 20, 2016
- ↑ 4.0 4.1 4.2 4.3 United Nations, "Waste Management," accessed December, 20, 2016
- ↑ 5.0 5.1 5.2 5.3 United Nations Environment Program, "Municipal Solid Waste Management," accessed December 20, 2016
- ↑ U.S. Energy Information Administration, "Waste-to-Energy (Municipal Solid Waste)," accessed December 20, 2016
