Assessment of GHG emissions of biomethane from energy cereal crops in Umbria, Italy

Biomethane from energy crops is a renewable energy carrier and therefore it potentially contributes to climate change mitigation. However, significant greenhouse gas (GHG) emissions resulting from cultivation and processing must be considered. Among those, the production and use of nitrogen fertilizers, the resulting nitrous oxide (N2O) emissions, the methane emissions from digestate storage and the energy consumption of the biogas plant are crucial factors. In the present paper an integrated life cycle assessment (LCA) of GHG emissions from biomethane production is carried out, taking into account own measurements and experience data from a modern biogas plant located in Umbria, Italy. The study is also focused on the electricity consumption of the biogas plant, assessing the specific absorption power of each machinery. The analysis is based on the methodology defined by the European Union Renewable Energy Directive 2009/28/EC (RED). The main result is that the biomethane chain exceeds the minimum value of GHG saving (35%) mainly due to the open storage of digestate. However by varying the system, using heat and electricity from a biogas CHP plant and covering digestate storage tank, a reduction of 68.9% could be obtained.