Including advanced thermochemical technologies in comparative life cycle assessment (LCA) of municipal organic waste management systems: A systematic review

Recently, municipalities worldwide have implemented selective collection systems for the organic fraction of municipal solid waste (OFMSW) to avoid the environmental impacts from landfilling organic matter and to promote resource recovery. Currently, biological methods such as anaerobic digestion (AD) predominate in source-separated OFMSW treatment. However, advanced thermochemical approaches - such as pyrolysis - have recently attracted considerable interest for treating OFMSW. While they offer some advantages over biological treatments, the environmental performance of advanced thermochemical technologies must be thoroughly compared with other available alternatives to guide science-based decision-making. Life cycle assessment (LCA) is a well-established and comprehensive tool to evaluate the environmental sustainability of waste management systems. However, LCA results often vary considerably due to differences in methodological choices and system boundaries. To provide recommendations for future studies and a basis for standardisation, this review aims to identify and critically analyse the most common methodological choices in comparative LCAs of OFMSW management systems that include at least one advanced thermochemical route in their scope. Conducted in accordance with the PRISMA statement, this review examines 19 peer-reviewed articles encompassing 65 distinct technological scenarios. The results show that, in general, advanced thermochemical technologies integrated with AD perform best in terms of global warming potential (GWP), but when considering other impact categories, trade-offs arise. Additionally, we evidence that system boundaries have usually failed to encompass the full complexity of OFMSW management systems. Moreover, the main approaches to solving multifunctionality and modelling environmental credits from co-products are discussed and, in some cases, challenged. Finally, recommendations for future research are given.