Una perspectiva d'economia circular a l'agricultura urbana: un anàlisi ambiental

• Autores: Martí Rufí Salís
• Directores de la Tesis: Xavier Gabarrell Durany (dir. tes.), Gara Villalba Méndez (codir. tes.), Anna Petit Boix (codir. tes.)
• Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2020
• Idioma: español
• ISBN: 9788449098208
• Tribunal Calificador de la Tesis: Damiá Barceló Culleres (presid.), Joan Marull López (secret.), Matthew Eckelman (voc.)
• Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología Ambientales por la Universidad Autónoma de Barcelona
• Materias:
  • Ciencias agrarias
    • Horticultura
      • Técnicas de cultivo
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • Food supply to ever-growing urban areas follows a linear tendency: cities consume a vast amount of imported food while generating waste and environmental impacts in different fronts. Urban agriculture (UA) has stood out as a practice to mitigate the volume of the imported flow, generating benefits in all three dimensions of sustainability and an excellent opportunity for the restoration of flows. The young concept of a circular economy (CE) can contribute to this mitigation by minimizing waste flows and take advantage of strategies to recover resources while exploiting synergies between urban systems, contributing to an improvement of the urban metabolism. However, the application of CE principles in UA systems should be strictly monitored in terms of environmental performance to avoid a clash between CE and sustainability goals. To avoid this, the present thesis aims to evaluate the environmental performance of applying circular strategies in UA systems. We use the Life Cycle Assessment (LCA) combined with other complementary methods and tools: nutrient balances, analysis of climatic variables, geographical information systems or a circularity assessment through the material circularity indicator (MCI).

    We first analyze the environmental performance of 25 cycles of 7 different crops in a hydroponic rooftop greenhouse to determine which should be the targets to optimize within the inventory and define the best year-round crop combinations. The results show that the fertilizers and their related emissions to water are the item with the biggest room for improvement. To avoid nutrient depletion, we evaluate the application of three possible nutrient recovery strategies: membrane filtration, chemical precipitation and direct leachate recirculation, finding that the latter had the best environmental performance. Considering this, we evaluate with different approaches the performance of two different recirculation strategies: the recirculation of leachates in the same crop and the recirculation of leachates in a parallel crop in what is known as a cascade system. The results of the analysis outline the potentials and limitations of both systems, concluding that the ultimate configuration would include a cascade system in which the receiving crop reuses the nutrients that leaches.

    Phosphorus (P) is a scarce and valuable resource due to the anthropogenic demand to produce fertilizers. The synergy between urban systems can contribute to enlarge the utility of P resources at the urban level. In this sense, we analyze the recovery of struvite in urban wastewater treatment plants and its application in UA systems with two different approaches: experimentally to test its potential and limitations in hydroponic systems, and with a regional perspective that treats a metropolitan area like a self-sufficient entity. The results show how the use of struvite can produce higher yields than mineral fertilizers while diminishing P losses. The regional perspective showed how the area under study is able to recover enough P to feed all the agriculture of the region, although parameters like the choice of the wastewater treatment plant or the recovery technology are important to avoid additional environmental impacts.

    Finally, we gather all the recovery strategies and evaluate their environmental performance and degree of circularity to prioritize circular strategies in UA systems. After solving detected limitations of the assessment through indicator development, we find that nutrient recirculation, the use of struvite or recycled materials are the best strategies to improve both the circularity and environmental performance of the system.

    Considering the findings of the thesis, different future research lines were defined: standardization of circular economy metrics and concepts or integration of different perspectives in the assessment of UA systems.