Methane Oxidation and Generation Rate Measurement at a Landfill Using the AMM Method

摘要

The CH_4 generation rate at the Eastview Landfill was quantified by measuring three individual components: CH_4 collected by the LFG collection system, CH_4 emitted by the landfill, and CH_4 biologically oxidized in the landfill cover. The CH_4 collected by the LFG collection system was measured in a pipe using a flow meter to be 92 g/s (492 m~3/hr). The fugitive CH_4 emission rate was measured using the AMM method to be 5.0 g/s (27 m~3/hr). The rate of CH_4 biologically oxidized in the landfill cover was measured to be 11 g/s (60 m~3/hr), based on the AMM method measured CO_2 emissions. Therefore, the CH_4 generation rate was measured to be 108 g/s (578 m~3/hr). The measurement of biological CH_4 oxidation not only determined the biological CH_4 oxidation rate in terms of a flow rate, but also determined that virtually 100% of the CH_4 flowing through the landfill cover was biologically oxidized. This feature, of determining a biological CH_4 oxidation emission rate under conditions of 100% biological CH_4 oxidation, is not available to the isotope fractionation method of biological CH_4 oxidation determination because no CH_4 would be collected from an emission flux chamber sample of the isotope fractionation method. The use of the AMM method to measure biological CH_4 oxidation is limited to those sites that have a CO_2 emission plume that is distinguishable from background concentrations and that do not have significant other sources of CO_2 emissions contributing to the CO_2 plume that is measured, such as vehicle emissions, compost piles, or very young landfilled waste. The accuracy of the method for measurement of the biological CH_4 oxidation rate is subject to interpretation of the upper and lateral extent of the CO_2 emission plume and the uncertainty could be as much as ±35% based on Figure 3. A potential improvement for further research that may be able to better distinguish CO_2 due to biological oxidation in the landfill cover and CO_2 in the background, would be to measure the relative concentration of the heavier carbon isotope ~(13)C/~(12)C in the plume. The relative concentration of ~(13)C/~(12)C is expected to be different for atmospheric air compared with that of landfill gas emissions or from methane oxidation.