Dynamic Model for the Methane Emission from Manure Storage

Abstract

Methane emission from liquid manure is an important source of greenhouse gases from agriculture. Methanogenic bacteria produce methane when manure decomposes in an anaerobic environment. Manure management practice is a dominant factor determining methane emissions. Methane emissions from agricultural sources should be calculated in accordance with the IPCC good practice guidelines, based on emission factors and activity data. Emission factors are based on the volatile solids content, biodegradability and methane conversion factor (MCF), which differs per management system and climate region. Not included in the IPCC models are dynamic factors of storage systems, like storage time, loading and unloading rates, and temperature. A new dynamic model has been developed to include these factors and the effect of the temperature. A slurry pit storage is an accumulation system. Experimental results show that the emission velocity (m3/h) in an accumulation system is linearly increasing with filling time. The relation between emission and filling time is quadratic. The model is used to derive values for the MCF, depending on filling time and temperature. The dynamic model has been applied to a typical dairy and pig farm, with a large effect on the emission figures. The proposed model can be used to improve calculations of national emissions.