Municipal solid waste, 2015-2016
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Municipal solid waste is commonly referred to as garbage or trash. These wastes include durable goods such as furniture and tires, as well as nondurable goods like plastic cups, newspapers, milk cartons, and food or yard waste, including 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 to focus on sewage management, given the problems associated with 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 are usually able to reduce the volume of trash to less than half its original volume if the garbage were not compacted. Garbage collection typically occurs once a week, given the relatively short time it takes for food waste to decompose. Recycling, the process by which used materials, such as waste, are transformed into new materials, was adopted in part to reduce the amount of solid waste collected from individuals and businesses. Some municipalities have transfer stations, which are facilities where trash is collected from multiple collection vehicles and then transferred to a more permanent facility using a larger vehicle.[2][4][5]
After municipal solid waste is collected, some municipalities modify the form of the waste to facilitate easier treatment and final disposal. This modification reduces the total weight and volume of the trash. Some facilities also recover heat energy from some waste to be recycled or reused.[2][4][5]
Treatment and disposal
Incineration is a standard method for reducing solid waste. Most incinerators can reduce waste volume by more than 90 percent, resulting in the production of glass, ash, and metal residues. The furnaces, constructed 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 remains after incineration, including fine particles such as dust and soot, is transferred via an 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 to decompose. Microbes interact with organic waste to break it down, resulting in compost that can be used as mulch or to improve soil conditions.[2][4][5]
Land disposal is also a standard method for disposing of waste. Sanitary landfills, which are sites designed to prevent waste from affecting public health or the environment, serve as storage facilities for solid waste, which is buried underground. One requirement for sanitary landfills is that buried waste must not come into contact with groundwater or surface water. New landfills often require a barrier at the bottom to keep waste from groundwater. Additionally, parts of the landfill must have impermeable covers to prevent rain or surface runoff from contacting 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
