Multi-criteria assessment of biomethane production from waste and residual feedstocks of Emilia-Romagna (Italy)

Sammanfattning: Biomethane can be produced by anaerobic digestion of residues or wastes and it can be used as a renewable fuel for transport. It is associated with reduced GHG emissions, offsetting of fossil fuels and of mineral fertilizers, waste management and nutrient recycling in agriculture. Six suitable feedstocks for the production of biomethane are compared through a multi-criteria assessment designed by the Linköping University and applied to the context of Emilia-Romagna region in Italy. The aim of this work is to provide decision-making support on the choice between feedstocks by identifying opportunity, technical feasibility and environmental sustainability of producing biomethane out of them. Feedstocks availability, current uses and accessibility in relation to the case study are assessed. In addition, technical aspects such as suitability for anaerobic digestion, biomethane yields and digestate quality, are complemented by a life cycle assessment including climate impact and energy balance for each feedstock. The results suggest that there are strengths and weaknesses for every feedstock and that the choice depends on the objective to be achieved and on the specific conditions. In a nutshell, the agricultural feedstocks considered (cow manure and wheat straw) and the agro-industrial (milk and cheese industry by-products and wine industry by-products) respectively have very high and medium theoretical availability and poor or satisfactory suitability for production of biomethane and biofertilizer through single-feedstocks digestion. Organic municipal solid waste (OMSW) and pig slaughterhouse wastes (PSW) have low theoretical availability but are well suitable for the production of biomethane. PSW is also well suitable as biofertilizer. From an environmental point of view, PSW and OMSW are associated to the best performances and liquid manure to the worst if the assessment is done according to the RED guidelines. By applying a system expansion to the environmental assessment different outcomes were obtained and the sensitivity of the parameters chosen was studied through sensitivity analysis. To conclude, the production of biomethane from the selected feedstocks can relevantly contribute to the regional targets for the transport sector and the methodology of this assessment is useful to deal holistically with the feedstock-choice while providing decision-oriented information.