Uncertainty in methane emission measurements from anaerobic digestion
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Abstract
This thesis seeks to examine the measurement of methane (CH4) emissions for the purposes of informing and improving greenhouse gas mitigation strategies. In a case study, a data set of CH4 concentration measurements over five years of study at a commercial dairy farm were used to evaluate the impact of introducing an anaerobic digestion biogas system. The long term trend in ambient concentrations indicated that the biogas system was producing substantial fugitive emissions. Fugitive CH4 emissions significantly increased following changes in feedstock management, and were estimated to represent as much as 26% of the total captured biogas at the site. In a lab study, a prototype open-path spectrometer measuring CH4 was analysed with respect to instrument error. Error (bias) was seen to exceed expected values at room temperature. Bias decreased approximately linearly with path temperature. Observed relationships of instrument error with measured concentration and path temperature are reported in detail.