Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Abstract

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.

Circular Economy of Water: Definition, Strategies and Challenges

“…In practice, Avoid is rarely applicable because it is usually difficult to stop using water. Nevertheless, there are several examples of water-free solutions such as water-free toilets based on vacuum flush, vacuum pumps in industry, dry wash sprays or atmospheric-plasma technologies for clothing [40][41][42][43].…”

Hydrochar: A Promising Step Towards Achieving a Circular Economy and Sustainable Development Goals

“…Similarly, sewage sludge and food waste are increasingly generated in urban areas due to the increasing population, where their use for hydrochar production can yield multiple benefits, as described above (Tasca et al, 2019). In fact, urban-produced wastes are often found to cause air, water, and soil pollution while, at the same time, cities account for 75% of global greenhouse gas emissions (Van Hullebusch et al, 2021). Hence, using these wastes for generating value-added products for various sustainable applications is a prime example of a circular economy in action.…”

Potential for use of Spent Substrate of Pleurotus Mushrooms Grown on Urban Waste as Feed for Dairy Cattle

“…Information is widely available online regarding the efficacy of growing oyster mushrooms on cardboard and SCG, as both products are widely available in urban settings; however, little academic research has been done to support these claims. Given growing awareness on the need for increased urban waste redirection through the circular economy, in which resources are recovered and reapplied in different cycles 21 , this research gap should be rectified. This paper will contribute by growing oyster mushrooms on urban waste substrates (cardboard and coffee) and assessing the suitability of the resulting SMS for use as cattle feed.…”