Municipal solid waste (MSW) is often considered to be a "renewable" energy source because its composition is largely waste food, paper, and other materials formed from biogenic carbon. Although plastics are also a component of MSW and are produced primarily from petroleum feedstocks, they make up less than 12% of the 251 million tons of total MSW mass in the U.S. . Energy recovery using MSW directly is achieved through combustion of the waste in waste-to-energy (WTE) plants. Emission levels from these units are generally lower on a per-kWh basis than coal plants due to more stringent emissions reduction requirements for WTE plants.5 Even so, the energy generation potential from MSW is limited: even if all the MSW in the U.S. were to be disposed of in WTE facilities, the total impact on national electricity production would be about 2% of total electricity generation.
The environmental impacts of these plants can be significantly lower than those of land filling, the other major MSW disposal option. This is particularly true if landfills do not capture methane generated by waste decomposition. For both MSW landfills and disposal of WTE combustion residues, appropriate landfill design and maintenance is needed to ensure protection of water supplies from potential leaching of metals and other materials from the landfill into ground and
5 A plant with a spray dryer and fabric filter is estimated to emit 0.46 lb CO, 0.062 lb PM, 0.55 lb SO2, and .021 lb HCl per ton of waste combusted. Uncontrolled NOx emissions are estimated at 3.6 lb per ton of waste, which can be reduced by 40% using non-selective catalytic reduction. Hg emissions are limited to 0.08 mg/dscm and dioxin/furan emissions to 13 ng/dscm under the 1995 rule for new municipal waste combustors.
surface water. It should also be noted that collection and use of landfill gas as an energy source can both reduce net GHG emissions by conversion of methane to CO2 (much of it from renewable rather than fossil carbon) and by displacing other, often fossil, energy consumption. Methane can also be recovered from wastes other than MSW, such as waste water treatment solids and agricultural wastes. For all of these sources, use of the methane reduces fugitive emissions of methane and displaces CO2 from fossil fuels, providing a multiple benefit.
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