Life Cycle Assessment of biogas production by monofermentation of energy crops and injection into the natural gas grid

The use of renewable energy is a possible solution to reduce the contribution to climate change of human activities. Nevertheless, there is much controversy about the non-climate related environmental impacts of renewable energy as compared to fossil energy. The aim of this study is to assess a new technology of biomethane production by monofermentation of cultivated crops. Based on the results of an attributional Life Cycle Assessment (LCA), the contribution to climate change of biomethane production and injection into the grid is 30–40% (500a time horizon) or 10–20% (100a) lower than the contribution of natural gas importation. The reduction depends mainly on the biogas yield, the amount of readily available nitrogen in the digestate and the type of agricultural practices. Nevertheless, the natural gas definitively generates far lower ecosystem quality and human health damages than the biomethane production. Farming activities have the most important contribution to the damages mainly because of land occupation and the use of fertilizer. The main improvement opportunities highlighted are: the increase of biogas yield, the choice of good agricultural practices and the cultivation of winter or summer crops exclusively. Future research should include the emission and sequestration of CO2 from soil. The ripple effects related to the total increase of farming area and the consequences of farming activities on the food production chain should be addressed as well. To this aim, the switch to consequential LCA is a critical challenge, from both the methodological and application point of view, to support decision-making.