4 minute read

Waste Management

Municipal Solid Waste

Municipal solid waste (MSW) is what most people think of as garbage, refuse, or trash. It is generated by households, businesses (other than heavy industry), and institutions, such as schools and hospitals. However, MSW does not include toilet wastes or other liquid wastes from these sources, which are commonly handled through public sewage treatment systems.

The first humans did not worry much about waste management. They simply left their garbage where it dropped. However, as permanent communities developed, people began to dispose their waste in designated dumping areas. The use of such "open dumps" for garbage is still common in many parts of the world. Open dumps have major disadvantages, however, especially in A household hazardous waste disposal day sponsored by the city of Livonia, Michigan. Residents are asked to bring toxic materials, such as paint, petroleum products, insecticides, and antifreeze, to a central location where they are combined and placed in barrels for disposal. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission.
heavily populated areas. Toxic chemicals can filter down through a dump and contaminate groundwater. The liquid that filters through a dump or landfill is called leachate. Dumps may also generate methane, a flammable and explosive gas produced when organic wastes decompose under anaerobic (oxygen-poor) conditions.

The landfill, also known as the "sanitary landfill," was invented in England in the 1920s. At a landfill, the garbage is compacted and covered at the end of every day with several inches of soil. Landfilling became common in the United States in the 1940s. By the late 1950s, it was the dominant method for disposing municipal solid waste in the nation.

Early landfills had significant problems with leachate and methane, but those have largely been resolved at facilities built since about the early 1970s. Well-engineered landfills are lined with several feet of clay and with thick plastic sheets. Leachate is collected at the bottom, drained through pipes, and processed. Methane gas is also safely piped out of many landfills.

The dumping of waste does not just take place on land. Ocean dumping, in which barges carry garbage out to sea, was once used as a disposal method by some United States coastal cities and is still practiced by some nations. Sewage sludge, or waste material from sewage treatment, was dumped at sea in huge quantities by New York City as recently as 1992, but this is now prohibited in the United States Also called biosolids, sewage sludge is not generally considered solid waste, but it is sometimes composted with organic municipal solid waste.

Burning has a long history in municipal solid waste management. Some American cities began to burn their garbage in the late nineteenth century in devices called cremators. These were not very efficient, however, and cities went back to dumping and other methods. In the 1930s and 1940s, many cities built new types of more-efficient garbage burners known as incinerators. The early incinerators were rather dirty in terms of their emissions of air pollutants, and beginning in the 1950s they were gradually shut down.

However, beginning in the 1970s waste burning enjoyed another revival. These newer incinerators, many of which are still in operation, are called "resource recovery" or "waste-to-energy" plants. In addition to burning garbage, they produce heat or electricity that can be used in nearby buildings or residences, or sold to a utility. Many local governments became interested in waste-to-energy plants following the energy crisis in 1973. However, since the mid-1980s, it became difficult to find locations to build these facilities, mainly because of public opposition focused on air-quality issues.

Another problem with incineration is that it generates ash, which must be landfilled. Incinerators usually reduce the volume of garbage by 70–90%. The remainder of the incinerated MSW comes out as ash that often contains high concentrations of toxic substances.

Municipal solid waste will likely always be landfilled or burned to some extent. In the past 25 years, however, non-disposal methods such as waste prevention and recycling have become more common. Because of public concerns and the high costs of landfilling and burning (especially to build new facilities), local governments want to reduce the amount of waste that must be disposed in these ways.

Even the earliest civilizations recycled some items before they became garbage. For example, broken pottery was often ground up and used to make new pottery. Recycling has taken many forms. One unusual type of recycling was common in large United States cities from about 1900 to 1930. This involved so-called reduction plants, where food waste, dead horses, and other dead animals were cooked in large vats to produce grease and fertilizer. A more familiar, and certainly less unappealing, type of recycling took place during World War II, when all scrap metal was fervently collected to help the war effort. Modern-day recycling has had two recent "booms," from about 1969 to 1974, and from the late 1980s until the present.

Reuse and repair are the earliest forms of waste prevention, which is also known as waste reduction. When tools, clothes and other necessities were scarce, people naturally repaired them again and again. When they were beyond repair, people tried to find other uses for them. People are again realizing the value of reuse, and are increasingly doing this with furniture, clothing, and disused building materials. In fact, some of these reuse activities are becoming quite fashionable.

Refillable soft drink bottles are another example of reuse. These are still the norm in many countries, but have become increasingly rare in the United States. One form of waste prevention, called source reduction, is a reduction in the quantity or the toxicity of the material used for a product or packaging.

Additional topics

Science EncyclopediaScience & Philosophy: Verbena Family (Verbenaceae) - Tropical Hardwoods In The Verbena Family to WelfarismWaste Management - History Of Waste Management, Municipal Solid Waste, Agricultural, Mining, And Industrial Waste, Hazardous Waste