Use of Models and Facility-Level Data in Greenhouse Gas Inventories

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Use of Models and Facility-Level Data in Greenhouse Gas Inventories ABSTRACT Measurements of landfill methane emission were performed at 9 solid waste disposal sites in Thailand including 5 managed sanitary landfills (4 deep and 1 shallow landfills), and 4 unmanaged landfill (3 deep and 1 shallow dumpsites). It was found that methane emissions during the rainy season were about 5 - 6 times higher than that during the winter and summer seasons in the case of managed landfill and 2-5 times higher in the case of unmanaged landfill. Comparison of methane emission estimate using the IPCC Waste Model to the actual field measurement from the studied disposal sites with methane correction factors and methane oxidation factors that obtained by error function analysis with default values of half-life parameters. The methane emissions from the first order decay model from the IPCC Waste Model yielded fair results compared to field measurements. The best fitting values of methane correction factor were 0.65, 0.20, 0.15 and 0.1 for deep landfill, shallow landfill, deep dumpsite and shallow dumpsite, respectively. Using these key parameters in case of Thailand, it was estimated that 89.22 Gg of methane were released from solid waste disposal sites into the atmosphere in 2006. Keywords: landfill gas, methane emission, flux chamber, IPCC Waste Model, methane correction factor INTRODUCTION When municipal solid waste (MSW) is buried in a landfill, the biodegradable fractions that decompose via a complex series of microbial and abiotic reactions in anaerobic condition produce landfill gas (LFG) and leachate which amount to significant environmental emissions (Spokas et al., 2006). Most of the organic materials will be degraded over a longer or shorter period of time, ranging in a wide span from less than one year to 100 years or more. The majority of this process will be bio-degradation. Strongly depending on the conditions at the site where the waste is disposed, this biodegradation will be aerobic or anaerobic. The main degradation products are carbon dioxide (CO 2), water and heat for the aerobic process and methane (CH 4) and CO 2 for the anaerobic process. The CH 4 produced and released into the atmosphere contributes to global warming (Frøiland et al., 2002). Moreover, methane is a fairly potent greenhouse gas, with a global warming potential 21 times that of CO 2 (Foster et al., 2007). Landfills account for about 10-19% of annual global CH 4 emissions (Kumar et al., 2004). In 2005, worldwide solid waste disposal sites emitted 747.4 MtCO 2eq (USEPA, 2006). Recently, some models have been introduced to estimate the LFG generation rate of landfills. Among them, the first order decay (FOD) model is generally recognized as being the most widely used approach as it is recommended by the Intergovernmental Panel on Climate Change (IPCC, 2006) in the IPCC Waste Model and by the US Environmental Protection Agency (USEPA, 1998) in Landfill Gas Emission Model (LandGEM) for calculating methane emissions from landfills. Moreover, FOD model had been applied to other developed models such as Palos Verdes Model, Sheldon- Arleta Model, Scholl Canyon Model, First order model Netherlands (TNO), GasSim, European Pollutant Emission Register (EPER) model France (ADEME), EPER model Germany (Umwelt Bundesamt) (Cossu et al., 1996; Scharff and Jacobs, 2006). In the LandGEM, the model rests on two basic parameters, Lo, the methane generation potential (m 3 CH 4/Mg of MSW) and k, the methane generation rate constant (yr -1 ), while the IPCC version rests on decomposable degradable organic carbon, DDOCm, instead of Lo (Sandro et al., 2009). Thailand, one of the developing countries in Asia, experiences increasing urbanization, economic development and rapid growth of population. Problems arising from this development are municipal solid waste (MSW) management and disposal handling (Thailand Environment Monitor, 2003). Many cities and towns face serious environmental hazards and health risks. The country’s MSW generation showed an increasing trend parallel to the development (Visvanathan et al., 2004). The increasing MSW generation along with the high fraction of organic waste and disposal by open dumping is the current scenario in many areas, which lack any precautionary environmental and health measures (Chiemchaisri et al., 2007). As response to this problem, recently, the country’s Pollution Control Department (PCD) aims to replace open dumping with sanitary landfill, which reduces negative environmental impacts. However, the methane gas generation potential due to biological degradation of the organic waste fraction within anaerobic condition in sanitary landfills is higher than in open dumpsites because the former is more anaerobic due to the presence of a top barrier cover that provides favorable conditions for methane production (Chiemchaisri et al., 2007; IPCC, 2006). The design of all landfills in Thailand is based on the anaerobic landfill concept; thus, the main emissions in terms of gas will be of CH 4 and CO 2. IPCC Expert Meeting Report 54 TFI
Use of Models and Facility-Level Data in Greenhouse Gas Inventories The total methane emissions from solid waste sector in Thailand were estimated at 76.51 Gg for the year 1990 by using mass balance method (TEI, 1996). In the year 1994, the total methane emissions were estimated at 19.57 Gg by the Office of Environmental Policy and Planning (OEPP) (OEPP, 2000). The estimation was obtained using a single phase model with theoretical first-order kinetics that takes into consideration the long period of release rather than the instantaneous emissions of methane. By using Landfill Air Emissions Estimation Model (LAEEM), the methane emissions were estimated at 24.77 Gg in 1994 and 92.26 Gg in 2000 (Towprayoon and Masniyon, 1999). This calculation was based on the single phase model and used country default values. Chiemchaisri et al. (2007) estimated methane emissions at 115.4 Gg in 2004 by using LandGEM which is based on the first-order decay reaction. By assuming that upgrading of open dumpsites to landfills will be complete in 15 years from 2005, it is estimated that the national methane emissions from those waste disposal sites will gradually increase to 339 Gg in 2020. Presently, the IPCC Waste Model has been used in many countries as a standard tool for methane emission inventory from waste sector. However, the uncertainty of this model as well as the difference between estimates and real emissions from landfills have rarely been investigated or verified in Asian countries where most Clean Development Mechanism (CDM) projects are focused on. Measurements of methane emission from solid waste disposal sites are, therefore, important to reduce uncertainties in the inventory estimates from this source. The main objective of this study is to achieve an accurate estimation with IPCC Waste Model by optimizing methane correction factor and oxidation factor as well as also develop the country’s default parameters for the emission inventory that can be applied to most developing countries-where the waste degrade under tropical condition. METHODOLOGY Site description Figure 1 Location of study sites Methane emission measurements were performed at 4 managed deep (MD) landfills (waste height ≥ 5m), 1 managed shallow (MS) landfill (waste height < 5m), 3 unmanaged deep (UD) landfills (deep dumpsites) (waste height ≥ 5m) and 1 unmanaged shallow(US) landfill (shallow dumpsite) (waste height < 5m), located in central Thailand. Landfill sites comprise of those at Pattaya (MD1), Mabtapud (MD2), Laemchabang (MD3), Hua-Hin (MD4) and Cha-Am (MS1). Deep dumpsites (waste height ≥ 5m) include those at Samut Prakan (UD1), Nakhon Pathom (UD2) and Nonthaburi (UD3) and a shallow dumpsite (waste height < 5m) locate at Rayong (US1). The location of study sites is shown in Figure 1. The characteristics of study sites are summarized in Table 1. The methane emission measurements were conducted from September to October 2005 for rainy season data, from December 2005 to February 2006 for winter season data and from April to May 2006 for summer season data. The characteristics of waste in these study sites that had been investigated by Pollution Control Department (PCD) of Thailand showed that food waste was the main component at all disposal sites ranging between 60% and 80%, followed by plastic, paper, glass, textile and wood (PCD, 2004). These composition can predict that significant of methane will generate at landfill site in the short time period because most of IPCC Expert Meeting Report 55 TFI
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