The potential of urban agriculture in combination with organic waste valorization: Assessment of resource flows and emissions for two european cities

Abstract

Abstract Large scale urban agriculture (UA) has been considered as a potential contributor to the sustainability and the resilience of the food system. However, its synergy with the tackling of another main challenge in cities, namely the management of organic wastes, has previously not been extensively explored. The aim of this work is to understand the potential of an integrated food-energy-water-waste system in terms of food production, resource circularity and carbon footprint, in comparison with the current food and waste management systems in cities and an UA system without integration with waste management. Employing spatial analysis and a breadth of process parameters and city-specific data, the monthly material and energy flows were simulated and optimized for two European cities, Glasgow and Lyon. The results indicate a strong dependency of food self-sufficiency, waste assimilation and carbon footprint on the ratio between high-intensity greenhouse growing and urban gardening. For a chosen greenhouse to garden ratio of 1:4, the production of a large share of fruit, vegetable and fish supplied with nutrients from waste products and water from rainwater harvesting is theoretically possible, and the integrated UA systems could assimilate 51.7% and 16.9% of food waste in Glasgow and Lyon, respectively. From a food production perspective, co-located waste valorization could reduce the carbon footprint of the UA system by 7.8% for Glasgow and 12.6% for Lyon. However, overall emissions for the integrated UA system are 75.1% (Glasgow) and 4.3% (Lyon) higher than the current system, primarily due to high heating and lighting requirements for greenhouses in winter, even more so in Glasgow which is colder and with a carbon-intensive electricity grid. However, if a UA system is already in place, the decentralized valorization in combination with UA could provide significant emission reduction benefits compared to existing waste-to-energy schemes, in particular for insect rearing in combination with aquaponics. The outcome may inspire urban policy makers and stakeholders to consider the propagation of urban agriculture in symbiosis with decentralized manage waste strategies, in particular in areas with a low-carbon electricity grid, as a move towards self-sustaining cities and a more circular economy overall.