Environmental impacts of dry anaerobic biorefineries in a Life Cycle Assessment (LCA) approach

The organic fraction of municipal solid waste (OFMSW) represents the 34% of European waste and the overall share is going to increase since separate collection will be implemented across the member states. There is still lack of studies on environmental impacts of dry anaerobic biorefineries applying innovative solvents to produce biopolymers (e.g., polyhydroxyalkanoates – PHA) from the OFMSW. A comparative Life Cycle Assessment (LCA) analysis was applied to assess the environmental impacts of a conventional management strategy to recover biomethane and compost from the OFMSW with a dry anaerobic biorefinery recovering biomethane, fertilizers and PHAs. Four approaches to recover PHAs were included in the study, comprising two innovative and environmentally sustainable extraction methods (i.e., solvent extraction with ethyl acetate (EA) and ionic liquids (ILs)). The inventory data were derived from an Italian case study plant, while the data for modelling the PHA selection/accumulation and PHA extraction processes were retrieved from the literature. The comparison revealed that, at the current technological readiness level (TRL), the conventional management strategy has better environmental performances than the novel approach producing PHAs. For example, biomethane recovery, for which a substitution with natural gas was assumed, showed the highest avoided impacts for abiotic depletion of fossil fuel (65.5%), global warming (57.4%) and ozone layer depletion (65.4%) categories. PHA recovery scenarios showed high environmental impacts in all categories linked to natural resource depletion. PHA extraction with EA proved to be the most environmentally sustainable and promising technique towards an industrial application.