(Municipal Solid Waste Power Plant)
Municipal solid waste (MSW) is one of three major waste-to-energy technologies (the others are anaerobic digestion and biomass) (1). The term MSW describes the stream of solid waste collected through households and apartments, commercial establishments, industries and institutions. Medical wastes from hospitals and radioactive and toxic garbage must be treated separately(2). In the United States, the Environmental Protection Agency (EPA) regulates household, industrial, manufacturing and commercial solid and hazardous wastes under the Resource Conservation and Recovery ACT (RCRA). (3)
Municipal solid waste can be used to generate electricity as well as an alternative method of waste disposal. No new fuel sources are required other than waste. MSW is considered as a renewable resource, because some of the content is food and paper. Several MSW-to-electricity technology have been developed which make the electricity generation processing of MSW more environmental friendly and more economical than before. There are two commonly MSW-to-electricity technology, which refers to mass burn and pyrolysis(4).
Mass burn is the combustion of unprocessed or minimally processed refuse. After shredding MSW and removal of the non-combustible materials, bulky items and metal from refuse. The shredded MSW is combusted directly in MSW plants that is pretty much the same way as fossil fuels.The heat generated in the high temperature combustion can be converted to high-temperature steam, which turns a steam turbine to generate electricity. In the incineration, pathogenic organisms and corrosive organic would be completely eliminated. Pyrolysis is the decomposition process of organic items which cannot be directly combusted. The process produces a mixture of combustible gases (primarily methane) liquids and solid residues.
Burning MSW can generate energy while reducing the volume of waste by up to 90 percent(5), which is very significant beneficial to environment. However there is a wide variation of environmental impacts associated with power generation, mainly are ash disposal and the air polluting emissions. The emission involves carbon dioxide, nitrogen oxides and trace amount of toxic pollutants, such as mercury compounds and dioxins. The high amount of carbon dioxide produced is a contributor to global climate change. If MSW containing batteries and tires are burned, toxic materials can be released into the air. The combined ash and air pollution accounts typically 20 % to 25 % of the incoming refuse weight(6). The ash pollution can be reduced by avoiding the hazardous sources to enter the combustion process.
2 Nonhazardous Waste U.S. Environmental Protection Agency, Municipal Solid Waste
4 Environmental and Energy Study Institute Issue Brief
6 Municipal Solid Waste U.S. Energy Information Administration