Solid waste

Solid waste is composed of a broad array of materials discarded by households, businesses, industries, and agriculture. The United States generates more than 11 billion tons (10 billion metric tons) of solid waste each year. The waste is composed of 7.6 billion tons (6.9 billion metric) of industrial nonhazardous waste, 2–3 billion tons (1.8–2.7 billion metric) of oil and gas waste, over 1.4 billion tons (1.3 billion metric) of mining waste, and 195 million tons (177 billion metric) of municipal solid waste .

Not all solid waste is actually solid. Some semi-solid, liquid, and gaseous wastes are included in the definition of solid waste. The Resource Conservation and Recovery Act (RCRA) defines solid waste to include garbage , refuse, sludge from municipal sewage treatment plants, ash from solid waste incinerators, mining waste, waste from construction and demolition, and some hazardous wastes. Since the definition is so broad, it is worth considering what the act excludes from regulations concerning solid waste: untreated sewage, industrial wastewater regulated by the Clean Water Act , irrigation return flows, nuclear materials and by-products, and hazardous wastes in large quantities.

RCRA defines and establishes regulatory authority for hazardous waste and solid waste. According to the act, some hazardous waste may be disposed of in solid waste facilities. These include hazardous wastes discarded from households, such as paint, cleaning solvents, and batteries, and small quantities of hazardous materials discarded by business and industry. Some states have their own definitions of solid waste which may vary somewhat from the federal definition. Federal oversight of solid-waste management is the responsibility of the Environmental Protection Agency (EPA).

Facilities for the disposal of solid waste include municipal and industrial landfills, industrial surface impoundments, and incinerators. Incinerators that recover energy as a by-product of waste combustion are called resource recovery or waste-to-energy facilities. Sewage sludge and agricultural waste may be applied to land surfaces as fertilizers or soil conditioners. Other types of waste management practices include composting , most commonly of separated organic wastes, and recycling . Some solid waste ends up in illegal open dumps.

Three quarters of industrial nonhazardous waste comes from four industries: iron and steel manufacturers, electric utilities , companies making industrial inorganic chemicals , and firms producing plastics and resins. About one-third of industrial nonhazardous waste is managed on the site where it is generated, and the rest is transported to off-site municipal or industrial waste facilities. Although surveys conducted by some states are beginning to fill in the gaps, there is still not enough landfills and surface impoundments for industrial solid wastes. Available data suggest there is limited use of environmental controls at those facilities, but there is insufficient information to determine the extent of pollution they may have caused.

The materials in municipal solid waste (MSW) are discarded from residential, commercial, institutional, and industrial sources. The materials include plastics, paper, glass, metals, wood, food, and yard waste ; the amount of each material is evaluated by weight or volume. The distinction between weight and volume is important when considering such factors as landfill capacity. For example, plastics account for only about 8% of MSW by weight, but more than 21% by volume. Conversely, glass represents about 7% of the weight and only 2% of the volume of MSW.

MSW has recently been the focus of much attention in the United States. Americans generated 4.5 lb (2 kg) per day of MSW in 2000, an increase from 4.3 lb (1.95 kg) per day 1990, 4.0 lb (1.8 kg) per day in 1980, and 2.7 lb (1.2 kg) per day in 1960. This increase has been accompanied by tightening federal regulations concerning the use and construction of landfills. The expense of constructing new landfills to meet these regulations, as well as frequently strong public opposition to new sites for them, have sharply limited the number of disposal options available, and the result is what many consider to be a solid waste disposal crisis. The much-publicized "garbage barge" from Islip, New York, which roamed the oceans from port to port during 1987 looking for a place to unload, has become a symbol of this crisis.

The disposal of MSW is only the most visible aspect of the waste disposal crisis; there are increasingly limited disposal options for all the solid waste generated in America. In response to this crisis, the EPA introduced a waste management hierarchy in 1989. The hierarchy places source reduction and recycling above incineration and landfilling as the preferred options for managing solid waste.

Recycling diverts waste already created away from incinerators and landfills. Source reduction, in contrast, decreases the amount of waste created. It is considered the best waste management option, and the EPA defines it as reducing the quantity and toxicity of waste through the design, manufacture, and use of products. Source reduction measures include reducing packaging in products, reusing materials instead of throwing them away, and designing products to be long lasting. Individuals can practice waste reduction by the goods they choose to buy and how they use these products once they bring them home. Many businesses and industries have established procedures for waste reduction, and some have reduced waste toxicity by using less toxic materials in products and packaging. Source reduction can be part of an overall industrial pollution prevention and waste minimization strategy, including recapturing process wastes for reuse rather than disposal.

Some solid wastes are potentially threatening to the environment if thrown away but can be valuable resources if reused or recycled. Used motor oil is one example. It contains heavy metals and other hazardous substances that can contaminate groundwater , surface water, and soils. One gallon (3.8 L) of used oil can contaminate 1 million gal (3.8 million L) of water, but these problems can be avoided and energy saved if used oil is rerefined into motor oil or reprocessed for use as industrial fuel. Much progress remains to be made in this area: of the 200 million gal (757 million L) of used oil generated annually by people who change their own oil, only 10% is recycled.

Another solid waste with recycling potential are used tires, which take up a large amount of space in landfills and cause uneven settling. Tire stockpiles and open dumps can be breeding grounds for mosquitoes, and are hazardous if ignited, emitting noxious fumes that are difficult to extinguish. Instead of being thrown away, tires can be shredded and recycled into objects such as hoses and doormats; they can also be mixed in road-paving materials or used as fuel in suitable facilities. Whole tires can be retreaded and reused on automobiles, or simply used for such purposes as artificial reef construction. Other solid wastes with potential for increased recycling include construction and demolition wastes (building materials), household appliances, and waste wood.

The EPA recommends implementation of this waste management hierarchy through integrated waste management. The agency has encouraged businesses and communities to develop systems where components in the hierarchy complement each other. For example, removing recyclables before burning waste for energy recovery not only provides all the benefits of recycling, but it reduces the amount of residual ash. Removing recyclable materials that are difficult to burn, such as glass, increases the Btu value of waste, thereby improving the efficiency of energy recovery.

Some state and local governments have chosen to conserve landfill space or reduce the toxicity of waste by instituting bans on the burial or burning of certain materials. The most commonly banned materials are automotive batteries, tires, motor oil, yard waste, and appliances. Where such bans exist, there is usually a complementary system in place for either recycling the banned materials or reusing them in some way. Programs such as these usually compost yard waste and institute separate collections for hazardous waste.

Perhaps because of the solid waste disposal crisis, there have been recent changes in solid waste management practices. About 55.3% of MSW was buried in landfills in 2000, down from 67% in 1990 and 81% in 1980. Recovery of materials for recycling and composting also increased, with 64 million tons of material diverted away from landfills and incinerators in 1999, up from 34 million tons in 1990.

See also Refuse-derived fuel; Sludge treatment and disposal; Solid waste incineration; Solid waste landfilling; Solid waste recycling and recovery; Solid waste volume reduction; Source separation

[Teresa C. Donkin and Douglas Smith ]

RESOURCES

BOOKS

Blumberg, L., and R. Grottleib. War on Waste—Can America Win Its Battle With Garbage? Covelo, CA: Island Press, 1988.

Neal, H. A., and J. R. Schubel. Solid Waste Management and the Environment: The Mounting Garbage and Trash Crisis. Englewood Cliffs, NJ: Prentice-Hall, 1987.

Robinson, W. D., ed. The Solid Waste Handbook. New York: Wiley, 1986.

Underwood, J. D., and A. Hershkowitz. Facts About U. S. Garbage Management: Problems and Practices. New York: INFORM, 1989.

PERIODICALS

Glenn, J. "The State of Garbage in America." Biocycle (May 1992).

OTHER

U.S. Environmental Protection Agency. Characterization of Municipal Solid Waste in the United States: 1992 Update (Executive Summary). Washington, DC: U. S. Government Printing Office, July 1992.

U.S. Environmental Protection Agency. Solid Waste Disposal in the United States. Washington, DC: U.S. Government Printing Office, 1989.