Material flow analysis to assess strategies for aluminum and steel recovery from urban waste: A case study from Austria

The recycling of metals is essential due to their increasing demand, high economic value, and large environmental burden associated with their primary production. It is therefore important to consider waste streams like municipal solid waste as a resource for the recovery of metals. Particularly in cities, municipal solid waste is available in large quantities due to increasing urbanization. This study used the case of Vienna to investigate the status quo of aluminum and steel flows in urban waste by material flow analysis. Furthermore, strategies to recover metals at different access points (separate collection, sorting of mixed municipal solid waste, and recovery from waste incineration bottom ash) were defined and assessed according to their potential to increase the amounts of metals recovered for recycling. In 2022, 796,400 t of municipal solid waste were generated in the city of Vienna, comprising 8,300 t of aluminum and 16,200 t of steel. From these, 63% of the aluminum and 99% of the steel were recovered for recycling. By combining measures to implement a deposit system for aluminum beverage cans and to improve the recovery of metals from mixed municipal solid waste and waste incineration bottom ashes, the recovery rates can be increased to 91% for aluminum and 99.9% for steel. However, the study assessed mass-based recovery rates without considering oxide content or alloy composition of the recovered metals. Future studies should expand their scope to include the recycling process and investigate how the access points influence the quality of recycled metals. • Mass-based evaluation of aluminum and steel recovery from municipal solid waste • Currently, 61% of aluminum and 99% of steel are recovered for recycling • Aluminum recovery rates could reach up to 91% through integrated recovery strategies • Significant quantities of metals are retrieved via incineration bottom ash treatment • Metal quality varies depending on recovery stage—pre- or post-incineration