Environmental performance of biogas produced from industrial residues including competition with animal feed - life-cycle calculations according to different methodologies and standards

摘要

Today incentives for an increased use of biofuels exist, one being the EU Renewable Energy Directive (RED). In this article the environmental performance of biogas systems using industrial residues from biofuel and food industries as substrates are analysed using a life-cycle perspective. These substrates are interesting since they do not compete directly with agricultural land for food production. The environmental performance is calculated using both the method described in the ISO-standard for life cycle assessment and the method presented in the EU RED. Furthermore, two perspectives are included, one where the residues are not utilised for other purposes today and one where the residues are utilised as animal feed, here presented as systems expansion. The results show that biogas from all residues investigated leads to a reduction of greenhouse gas (GHG) emissions compared to fossil fuels. When system expansion is applied, however, the benefit will be significantly smaller since the alternative utilisation of the substrates as animal feed is considered and included in the system. This might also lead to an indirect land-use competition since additional protein feed crops must be cultivated. Thus, all residues studied are well suited for biogas production if there is no demand for them as animal feed today. Otherwise, it is often more efficient to grow dedicated biogas crops directly. Similar to other studies of bio-based systems the results also show that emissions related to acidification and eutro-phication will be higher compared to a fossil fuel based system. A conclusion is that the calculation method in RED has a limited systems perspective, which could lead to a sub optimisation of the utilisation of industrial waste from a GHG perspective depending on the current alternative utilisation of the residues.