Mass burn

Mass burn refers to the incineration of unsorted municipal waste in a Municipal Waste Combustor (MWC) or other incinerator designated to burn only waste from municipalities. This waste management method avoids the expensive and unpleasant task of sorting through the garbage for unburnable materials. All waste received at the facility is shredded into small pieces and fed into the incinerator. Steam produced in the incinerator's boiler can be used to generate electricity or to heat nearby buildings. The residual ash and unburnable materials, representing about 10-20 percent of the original volume of waste, are taken to a landfill for disposal. Mass burn incineration also has several drawbacks. Since the waste is unsorted, it often generates more polluting emissions than sorted waste, and it is more likely to corrode burner grates and chimneys. The residual ash and unburned materials may be toxic and require special treatment.

The Environmental Protection Agency (EPA) establishes standards for the burning of municipal waste. A MWC is designed so that it cannot burn continuously 24 hours a day. Waste cannot be fed to the unit nor can ash be removed while combustion is occurring. As a result, burning occurs in batches or spurts. A large MWC plant has a capacity greater than 250 tons per day. A very large MWC plant has a capacity of about 1,100 tons per day.

Municipal solid waste includes household, commercial or retail, and institutional waste. Household waste includes material discarded by single and multiple residential dwellings, hotels, motels, and other similar permanent or temporary housing establishments. Commercial or retail waste includes material discarded by stores, offices, restaurants, warehouses, and nonmanufacturing activities at industrial facilities. Institutional waste includes material discarded by schools, hospitals, and nonmanufacturing activities at prisons, government facilities, and other similar establishments.

Household, commercial or retail, and institutional wastes do not include sewage, wood pallets, construction and demolition wastes, industrial process or manufacturing wastes, or motor vehicles (including motor vehicle parts or vehicle fluff). Municipal solid waste also does not include solely segregated medical wastes. However, any mixture of segregated medical wastes and other wastes which contains more than 30 percent medical waste discards is considered to be acceptable as municipal solid waste.

The Code of Federal Regulations (CFR) specifically defines a Municipal Waste Combustor (MWC) unit as any device that combusts solid, liquid or gasified municipal solid waste including but not limited to field-erected incinerators (with or without heat recovery), modular incinerators (starved air or excess air), boilers (steam generating units), furnaces (whether suspension-fired, grate-fired, mass-fired or fluidized bed-fired), and gasification/combustion units. This does not include combustion units, engines or other devices that combust landfill gases collected by landfill gas collection systems.

According to the CFR, terms connected with a MWC must be clearly defined. MWC acid gases are defined as all acid gases emitted in the exhaust gases from MWC units including sulfur dioxide and hydrogen chloride gases. MWC organics are defined as organic compounds emitted in the exhaust gases from MWC units including total tetra- (4) through octa- (8) chlorinated di-benzo-p-dioxins and dibenzofurans. This class of chlorinated chemicals (where chlorine gas binds with certain organic matter, especially carbon atoms) includes dioxin or TCDD.

EPA also identifies some of following as potential discharges from a MWC: hydrogen chloride, sulfur dioxide, refuse-derived fuel (RDF), nitrogen oxides , and carbon monoxide . The amounts of these emissions discharged are closely monitored. EPA sets allowable standards and compliance schedules for each emission . These standards are legally enforceable regulations.

EPA also sets standards for facility operations. These standards include guidelines for monitoring, for handling ash, for reporting and recordkeeping, for operating the MWC unit within acceptable standards, for maintaining proper combustion air supply levels, and for start-up, shutdown and malfunction of the unit. Compliance and performance testing guidelines are also included in the CFR. These standards and guidelines apply to MWCs constructed, modified, or reconstructed after December 20, 1989. The Code pertaining to MWC is updated periodically. The latest update was issued in February 1991.

However, there are many older MWC units that still burn municipal wastes. These are not as technologically sophisticated or as rigorously monitored as are the newer incinerators. Emissions tests are not as stringent or comprehensive for these older units. They are listed as Sub Part E under the 1971 Code (amended in 1974). These MWC units were constructed, modified, or reconstructed before December 20, 1989, and burn up to 50 tons per day.

See also Fly ash; Hazardous waste; Scrubbers; Solid waste; Solid waste incineration

[Liane Clorfene Casten ]

RESOURCES

BOOKS

Clarke, M. J. Burning Garbage in the U.S.: Practice vs. State of the Art. New York: INFORM, 1991.

Denison, R. Recycling and Incineration: Evaluating the Choices. Covelo, CA: Island Press, 1990.

PERIODICALS

Griffin, R. D. "Garbage Crisis." CQ Researcher 2 (March 20, 1992): 243–248.

"So Much Smoke? Incineration." The Economist 326 (February 13, 1993): A26–27.