Improving the urban resource nexus through urban agriculture systems with biowaste utilisation and renewable energy
Keywords: urban agriculture
regional food systems
organic waste
controlled-environment agriculture
biowaste management

The food systems in developed societies face a host of challenges in the early 21st century; increasing urbanisation, supply chain shocks due to extreme climate events and pandemics, high impacts of air freight, nutrient run-off and animal farming, and tremendous amounts of wasted food and nutrients. A transformation to a more sustainable and resilient food system includes, among other pathways, increased consumption of fruits and vegetables, a localisation of food production and the recovery of nutrients in urban organic waste. Urban agriculture thus receives emerging research interest, ranging from community gardens to high-tech indoor farming. Efforts so far have focused on socio-economic aspects and life-cycle assessments of individual case studies or have described the qualitative potential of integrating urban waste streams into urban farming. Significant gaps remain in the literature about the carbon and land intensity of different growing methods when scaled-up and the quantification of productivity and nutrient recovery potentials. On the city and regional level, the design of productive food systems integrated with biowaste management and renewable energy systems has found little attention so far. These gaps are addressed in this thesis through mathematical modelling and geospatial analysis at multiple scales, including the facility, the urban area, a metropolitan area, and the regional level.
The match of supply and demand of a scaled-up urban food production system and their organic waste flow utilisation potential was assessed and compared for two urban areas, Glasgow and Lyon. Potentially convertible land and rooftop space were determined with geospatial processing, and monthly biowaste utilisation in those new farms was optimised based on nutrient requirements and CO2 emission savings. The results showed that high self-sufficiency came with significantly increased CO2 emissions for the productive urban food system in the colder climate due to high demand and carbon intensity of electricity for greenhouses, which also negated the benefits of utilising a large share of the biowaste.
The next project thus investigated the interplay and logistics of local composting treatment combined with low-input local farming for 76 districts in Porto from waste system perspective. Existing fields, convertible greenspaces, and compost island requirements were obtained from geospatial analysis and waste collection pilots and distance scripts informed collection and transport requirements to central facilities. The results showed that more remote districts could benefit both in cost and climate impacts from having their own decentralised biowaste systems, although mainly from collection route reduction rather than a conversion of greenspaces.
Focusing more on the contextual sustainability of high-intensive growing methods, the energy consumption of electrified greenhouses and vertical farm facilities was assessed for ten regions across the globe. A rigorous thermodynamic model for lighting and air conditioning requirements was optimised for minimum specific energy in relation to the outside climate on an hourly basis. The outcomes showed that significant energy reductions can be achieved in greenhouses with optimised climate control, while local climate conditions and design choices still have a strong impact. Vertical farms, or plant factories, had significantly higher energy consumptions, even in extreme climates. The final project applied the learnings from the energy optimisation to a land-use based assessment of regionalised vegetable supply with renewable energy generation for nine city-regions. Potentially available land for energy generation was assessed, and the selection and sizing of solar PV and wind farms were economically optimised for the required electrical load. The results show that although greenhouse production requires oversized renewable energy systems due to higher load fluctuations, its land footprint is lower than that of open-field and vertical farming. The land use relative to existing and available land contextualised this finding, but a full regionalised vegetable supply was feasible and desirable for most of the regions.
The implications from the work are that to achieve increased food self-sufficiency and climate change mitigation, energy-efficient and low-carbon urban agriculture approaches are indispensable. Recommendations for specific urban growing systems are strongly context-dependent and many transferable aspects of relevance to decision-makers have been quantified in this work. Further, the integration of biowaste mainly provides benefits from a holistic waste management perspective and thus a multi-stakeholder approach and commitments will always be required.