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.Graphical
Highlights
The present-day food system is characterized by a one-directional flow of resources from rural areas into cities
A Substance Flow Analysis approach is used to quantify the recoverable urban nutrient budget contained in household wastewater and biodegradable kitchen waste, using the city of Vienna, Austria, as an example
This study quantified the recoverable nutrient budget contained in household wastewater and MOW, with the example of the city of Vienna, Austria
Summary
The present-day food system is characterized by a one-directional flow of resources from rural areas into cities. Cities consume 75% of natural resources, produce 50% of global waste, and 60–80% of greenhouse gas emissions [13], a large proportion of which are directly associated with the urban food system [14]. The nutrients contained in the consumed food are discharged via urban sanitation systems, and largely removed by treatment processes and lost to potential reuse, with recovery technologies being adopted only slowly [26]. Given the ongoing tendency of growing population in cities, water and nutrient recovery from urban wastewater bears large and growing potential to sustain food supply in cities and the overall transition to a circular economy [4]. Instead of collecting and removing potential water and nutrient resources, sanitation systems could be redesigned to contribute to resilient food systems and cities
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