Potential Nutrient Conversion Using Nature-Based Solutions in Cities and Utilization Concepts to Create Circular Urban Food Systems

Abstract

The present food system is characterized by a linear flow of resources from rural areas into cities, where most food is consumed and essential nutrients discharged as wastewater. Limited water and phosphorus resources and large carbon footprints of chemical fertilizers drive increased recovery of water and nutrients for reuse in agriculture. Alongside end-of-pipe technologies at conventional wastewater treatment plants, nature-based solutions provide a robust and low-energy alternative solution. This paper assesses the potential of treatment processes using NBS to close water and nutrient cycles in the urban food system. A Substance Flow Analysis approach is used to quantify the recoverable urban nutrient (nitrogen, phosphorus, potassium) budget contained in household wastewater and biodegradable kitchen waste, using the city of Vienna, Austria, as an example. The developed model reflects the metabolization of water and nutrients by treatment wetlands and biogas digesters into fertigation water and fertilizer. It differentiates between specific crop nutrient requirements and yields, and by greenhouse and outdoor farming conditions in a temperate climate. Results indicate that, using NBS, the wastewater and kitchen waste from 77,250 persons could fully cover the nitrogen and phosphorus fertilizer demand of the entire vegetable production in Vienna, which currently supplies one-third of Vienna’s vegetable consumption. Additional people connected to the system can supply significant excess nutrients to produce other crops within and beyond the city. The model can inform selection and design of NBS for nutrient recovery and reuse, and support integrated planning regarding use of secondary nutrient sources and optimization of secondary nutrient utilization.

A Unique Perspective of Materials, Practices and Structures Within the Food, Energy and Water Nexus of Australian Urban Alternative Food Networks

“…One consideration for large-scale urban wastewater management not considered in Australian studies was the use of nature-based solutions such as treatment wetlands. Such a non-chemical treatment method would implicate significant reductions in energy use to treat wastewater and allow for both nutrient and water recycling [35]. Such a system has been suggested for achieving circularity within the energy-water-environment nexus within Qatar [36] and Vienna, Austria [35], however seems more suited to decentralised management systems, not common in Australia, despite their purported benefits to circular urban and peri-urban greening initiatives.…”

“…Such a non-chemical treatment method would implicate significant reductions in energy use to treat wastewater and allow for both nutrient and water recycling [35]. Such a system has been suggested for achieving circularity within the energy-water-environment nexus within Qatar [36] and Vienna, Austria [35], however seems more suited to decentralised management systems, not common in Australia, despite their purported benefits to circular urban and peri-urban greening initiatives. Nevertheless, urban greening including for UA has been achieved in Adelaide via chemical wastewater treatments [13].…”

Capture of CO2 and Water While Driving for Use in the Food and Agricultural Systems

“…The way food is produced has become a controversial issue across the world. Limited water and phosphorus resources and the large carbon footprints of chemical fertilizers drive increased recovery of water and nutrients for reuse in agriculture [1]. Furthermore, the environmental impact of today's global food production system is enormous, being responsible for 25% of all the greenhouse gas emissions with most of the absolute emissions coming from cattle rearing and the horticultural industry [2][3][4].…”

Towards a Cross-Sectoral View of Nature-Based Solutions for Enabling Circular Cities

“…As an example, the built environment did not select S_u for "remediation, treatment, and recovery" (#21-25 and S3-S10). This is of interest as those S_u can be identified as key technologies for onsite resource recovery and need to be integrated in the buildings to support circularity [16,24]. On the other hand, resource recovery did not select "vertical greening systems and green roofs" (# [13][14][15][16][17][18][19][20].…”

“…This can be explained by the applied criteria, specifically, the primary focus on nutrient recovery and usage within the city, including quantity and quality, and not on water circularity. Vertical greening systems and green roofs represent very effective NBSs for closing the water cycle at the building scale [24][25][26][27]. Both vertical greening systems and green roofs are suitable to be implemented in buildings across district and neighborhood scales, thus contributing to UCC 7 "building system recovery".…”