Verification of methodologies and estimation of IPCC model parameters for solid waste landfills

Abstract

Solid waste landfill is one of the major anthropogenic methane source around world contributing 3 to 4 % of the annual anthropogenic GHG emissions (IPCC, 2001). Landfill is the 3rd largest methane emission source accounting for 21% of methane emissions in Korea (GIR, 2014). However, uncertainty of landfill gas emission estimate is still high. In case of United States of America, uncertainty of greenhouse gas (GHG) emission estimates from landfills has been estimated from -52 to 44% while total emission uncertainty is between -2 and 5% (US EPA, 2012). The objective of this study are to suggest developing method for each emission factors in IPCC reference model for solid waste landfill sector. Also DOC, DOCF, F and OX is developed following suggested methods. Moisture content analysis, organic matter content analysis and element analysis have been conducted for papers, food wastes and woods. Evaluating TOC content by multiplying TC content and VS content has significant error. The error has been derived from the difference of carbon content between organic fraction and inorganic fraction of the wastes. DOC for food wastes and woods were evaluated as 10.46 % and 43.66 % by wet waste basis with uncertainties of 3.65 % and 33.55 %, respectively. The key factor of high uncertainty of DOC for woods were the uncertainty of moisture content. High uncertainty of moisture content is resulted in low moisture containing waste and vice versa. Biochemical methane potential test have been conducted for papers, food wastes and woods to develop DOCF. Biogas conversion rate was most proper index. Mass balance approach is not recommended due to low carbon recovery rate. Biogas conversion rate has advantages on low uncertainty than methane conversion rate. DOCF for papers, food wastes and woods were evaluated as 0.568, 0.696 and 0.462 with uncertainties of 2.72 %. 9.38% and 10.23 %, respectively. Criteria determining landfill type have been developed to apply MCF. Field investigation and landfill gas monitoring has been conducted in five landfills to develop criteria. Operation conditions were most important in categorizing landfill types. Five semi-aerobically designed landfills satisfied systems for semi-aerobic landfill in IPCC guidelines. However, the end of leachate collection pipes were closed of submerged that introduction of fresh air is prohibited. CH4/CO2 ratio can be the index to categorize landfill type. In semi-aerobic landfills, CH4/CO2 ratio at LFG in vent pipes need to be smaller than 1.0 considering other references. To develop F, landfill gas at landfill gas collection pipes and vent pipes have been monitored. By the carbon mass balance model, CH4 concentration at vent pipes or LFG collection pipes corresponds to the value MCF×F. Also, the LFG at vent pipes or LFG collection pipes contains fresh air. According to LFG collection data at two SLC landfills, temporal changes can be neglected and handled as one dataset. MCF×F can be developed using CH4/CO2 ratio. MCF×F were evaluated as 0.527 to 0.607 in seven landfills with uncertainties lower than 5%. Landfill gas emission from landfill surface has been monitored in ten landfills. Flux chamber was used to measure CH4 fluxes. Bilinear model is applied for spatial interpolation. Surface methane emission estimate utilizing mean value of CH4 fluxes measured from flux chamber made significant bias due to heterogeneity of landfills. The 20 % of total area contributed more than 65 % of total surface methane emissions. Identifying the hot spots before the flux measurement is required. The required number of flux chamber measurements depend on size of landfill has been made based on reproducibility test. The required number of samples suggested in US EPA guidelines is expected to have 20 % error in the emission estimate. Fluxes of CH4 and CO2 are monitored in four landfills using closed flux chamber to evaluate OX. Evaluating OX with mean or median value of fluxes measured by flux chambers have chances to over- or under-estimate. Due to heterogeneity of landfill gas emissions spatial interpolation model need to be applied to the flux from surface. OX is evaluated as 0.42 to 0.88 in four landfills.