Societal Impact Statement Agricultural industrialisation has led to levels of nutrients in the environment that are well above safe operating limits, yet fertiliser use is necessary to feed a growing population. The recovery of nutrients from human urine in large, developed cities may offset some of the ecological and economic impacts associated with fertiliser production, as well as lessen environmental impacts associated with wastewater. Achieving a circular economy of nutrients faces several challenges, many of which require transdisciplinary solutions. Here we summarise some of the key challenges and highlight potential solutions at all stages from collection at the source to application to plants.

Summary The utilisation of nitrogen (N) and phosphorus (P) in agriculture has surpassed the safe-operating thresholds for biogeochemical cycles, necessitating the adoption of more efficient nutrient management strategies to restore this balance. The predominant source of N and P supplementation globally stems from the application of synthetic fertilisers. This study explores the potential of nutrient recovery and recycling from human urine as a viable alternative at sub-global and regional levels. Such an approach could significantly reduce energy consumption associated with fertiliser production and transportation, as well as the demand for precursor materials. Additionally, it would mitigate the risk of eutrophication resulting from the release of excess N and P into the environment via untreated or inadequately treated wastewater. By integrating waste material utilisation within the nexus of social and ecological systems, this strategy may enhance socio-ecological resilience, particularly in urban areas. Here, economies of scale could facilitate the successful implementation of urine diversion and conversion initiatives, offering a sustainable solution for nutrient management in densely populated regions.