Additive manufacturing in cities: Closing circular resource loops

Cities are the core of social interactions and resource consumption in our current times. However, urban systems are still largely based on linear activities in which resources are discarded after usage. Current practices around waste reduce possibilities of circularity, mainly due to low percentages of sorting and recycling practices in high- and middle-income countries and landfill practices in middle- and low-income countries. This resulted in a continuous increase in urban waste and negative environmental impact over the last decades. The development of circular practices and innovations, such as additive manufacturing, is crucial to modify the current supply chain and return valuable discarded materials to urban industries. Additive manufacturing is a novel technology based on the creation of objects layer by layer involving the use of a diverse range of materials. Several materials such as plastics, metal or concrete, for example, can be transformed into functional products for cities. Based on a literature review, this paper showcases the potential of urban waste for 3D printing with a main focus on recycling practices at the end of the supply chain. This paper aims to examine the current knowledge, regulations, and practices in circularity and additive manufacturing in the urban context, to identify opportunities and practices for material recovery applications, and showcase applications for additive manufacturing at the last stage of the supply chain. Furthermore, it identifies the needs for further research that could support the implementation and diffusion of additive manufacturing in society.