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solid waste,discarded materials other than fluids. In the United States in 1996, nearly 210 million tons—about 4.3 lb. (2 kg) per person daily (up from 2.7 lb./1.2 kg in 1960)—were collected and disposed of by municipalities. In that year, municipal garbage included 12.4 million tons of glass and about 80 million tons of paper and paperboard (by far the largest constituent); in addition enormous tonnages of food residues, yard trimmings, textiles, plastics, and sludge formed in sewage treatment were produced. Although the amount of the increase has been slowed somewhat by recyclingrecycling,
the process of recovering and reusing waste products—from household use, manufacturing, agriculture, and business—and thereby reducing their burden on the environment.
..... Click the link for more information. and composting programs and improvements in packaging, the amount of solid waste continues to increase annually. Moreover, the most common disposal methods pollute land, water, or air to some degree (see pollutionpollution,
contamination of the environment as a result of human activities. The term pollution refers primarily to the fouling of air, water, and land by wastes (see air pollution; water pollution; solid waste).
..... Click the link for more information. ). Management of solid waste therefore presents an increasingly acute problem.
See also environmentalismenvironmentalism,
movement to protect the quality and continuity of life through conservation of natural resources, prevention of pollution, and control of land use. The philosophical foundations for environmentalism in the United States were established by Thomas Jefferson,
..... Click the link for more information. ; radioactive wasteradioactive waste,
material containing the unusable radioactive byproducts of the scientific, military, and industrial applications of nuclear energy. Since its radioactivity presents a serious health hazard (see radiation sickness), disposing of such material is a great problem.
..... Click the link for more information. .
Approximately 62% of municipal waste is placed in landfills. If the waste is dumped untreated, it can promote the proliferation of rats, flies, and other vermin, encourage growth of disease-carrying organisms, contaminate surface and underground water, scar the land, and preempt open space. An alternative method of solid waste disposal is the sanitary landfill, first employed in Fresno, Calif., in 1937: waste is spread in thin layers, each tamped compactly and covered by a layer of earth. While more expensive than open dumping, the sanitary landfill eliminates health hazards and permits reclamation of the site for construction, recreation, or other purposes. The chief drawbacks are that feasible locations are relatively rare and costly and that sites must be insulated from water resources to avoid polluting them (see water pollutionwater pollution,
contamination of water resources by harmful wastes; see also sewerage, water supply, pollution, and environmentalism. Industrial Pollution
..... Click the link for more information. ). Both open dump and sanitary landfill disposal depend on the natural degradability of wastes for an ultimate return to normal earth conditions. Decay, however, takes time; buried paper, for example, can persist as long as 60 years. Many plastics and synthetic textiles do not degrade at all.
To reduce the bulk of solid waste burning of paper, plastic, and other components is often resorted to, either in open dumps or incinerators. Fly ash, noxious gases, and chemical contaminants can thus be released into the air (see air pollutionair pollution,
contamination of the air by noxious gases and minute particles of solid and liquid matter (particulates) in concentrations that endanger health. The major sources of air pollution are transportation engines, power and heat generation, industrial processes, and the
..... Click the link for more information. ). However, new techniques for "scrubbing" pollutants from incinerator stacks are being developed. Incineration of typical garbage reduces its weight and volume by as much as 80%. Approximately 15.9% of municipal solid waste is combusted.
Recycling of solid wastes is an option that many municipalities have explored in recent years. It not only facilitates disposal but conserves energy, cuts pollution, and preserves natural resources. To make cans from recovered aluminum, for example, requires 10% of the energy needed to make them from virgin ore. At the same time ore is saved, and the pollution resulting from mining and processing are avoided. Making steel bars from scrap requires 74% less energy and 50% less water, while reducing air-polluting emissions by 85% and mining wastes by 95%.
Similarly, sludge from treated sewage can be used for fertilizer, but it has been less costly to dump it at sea or on open land (see seweragesewerage,
system for the removal and disposal of chiefly liquid wastes and of rainwater, which are collectively called sewage. The average person in the industrialized world produces between 60 and 140 gallons of sewage per day.
..... Click the link for more information. ). Dumped sludge has killed marine life and threatened beaches along the Eastern seaboard; elsewhere in the United States it is a growing nuisance. Between 1975 and 1985 the amount of sludge dumped in U.S. coastal waters increased by 60%; the effects of dumping and illegal dumping are still felt despite the fact that it has been illegal since the beginning of 1992. Recycling and composting take care of approximately 2.7% of municipal solid waste.
The federal government now provides assistance to localities in developing new means of recovering materials and energy from solid waste, and encourages private industry to seek similar goals. One technique being tried involves intensified combustion of wastes to produce heat for generating power. A second promising approach is pyrolysis, the thermal decomposition of wastes in controlled amounts of oxygen to produce valuable petrochemicals; the residue is an inert char of little bulk. Another method of reducing solid wastes is to replace polystyrene packaging with less bulky wrapping made largely of paper. Wider application of such processes is being advocated not only to diminish pollution of the environment by solid waste, but also to conserve natural resources.