is derived from a well-understood chemical reaction (i.e., nitric acid oxidation), and only a small number of adipic acid plants exist.

WASTE

The waste sector is not a significant source of greenhouse gas emissions, accounting for only about 3 percent of the total from Annex I countries (UNFCCC, 2008) and about 4 percent of the total from non-Annex I countries (UNFCCC, 2005). This sector covers the greenhouse gas emissions from solid waste disposal, biological treatment of solid waste, burning of waste, and wastewater treatment and discharge (IPCC, 2006). Waste sector reporting includes neither the greenhouse gas emissions resulting from the use of waste material as fuel nor the CO2 emissions resulting from the decomposition or burning of organic biomass. These emissions are accounted for under the energy sector and the agriculture, forestry, and other land-use sector, respectively.

Methane

The primary greenhouse gas emitted from the waste sector is CH4, which accounts for about 90 percent of the total (in terms of waste sector CO2 equivalents) in Annex I countries.3 The degradation of organic material under anaerobic conditions at solid waste disposal sites (SWDS) is the principal source of CH4 emissions. The potential of SWDS to generate CH4 depends on the degradable organic carbon (DOC) content of the waste, which is a function of the amount and composition of the waste disposed, and on the waste management practices. Methane emissions from SWDS are calculated using the First Order Decay method, which assumes that the rate of CH4 production is directly proportional to the amount of DOC remaining in the waste. The quantity of CH4 that is oxidized in the landfill’s top layer and/or is recovered and combusted is then subtracted from the calculated emissions value.

The key source of uncertainty in estimates of CH4 from SWDS is the activity data relating to the quantities and composition of the waste disposed (several decades of historical data are required), although some of the emission factors can also be highly uncertain. For many countries, data on waste amounts and composition (particularly historical data) are not available and default activity data must be used. The major uncertainties in the emission factors include the DOC values assigned to different waste types (e.g., municipal) and materials (e.g., paper, food), the fraction of DOC that is ultimately degraded and released from SWDS, and the half-life of the DOC, which is difficult to measure in real solid waste disposal sites. Also highly uncertain are the emission factors used to determine the fraction of CH4 that is oxidized in the landfill’s top layer, which depends on whether the SWDS is managed or unmanaged and also varies considerably with conditions at the site.

The other significant source of CH4 emissions within the waste sector is the anaerobic treatment or disposal of wastewater. The CH4 emitted from wastewater handling depends on the amount of degradable organic material, measured by biological oxygen demand in domestic wastewater and chemical oxygen demand in industrial wastewater. The Intergovernmental Panel on Climate Change (IPCC) provides a means of estimating the quantity of domestic wastewater generated as well as default values for biological oxygen demand for selected regions and countries. Similarly, the IPCC provides default values for quantities of industrial wastewater generated and the chemical oxygen demand for various industry types. Reliable estimates of the quantity of CH4 released from wastewater discharge are particularly difficult to obtain for developing countries due to uncertainties in the fraction of domestic wastewater that is removed by sewers (as opposed to being treated in latrines), the fraction of sewers that are open, and the degree to which these open sewers are anaerobic (IPCC, 2006).

Carbon Dioxide

Carbon dioxide is a relatively minor source of greenhouse gas emissions from the waste sector, accounting for about 4 percent of total emissions (in terms of CO2 equivalents) from the sector for Annex I Parties.4 The predominant source of these emissions,



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