Abstract
Urban residual flows contain significant amounts of valuable nutrients, which, if recovered, could serve as input for the own city needs or those of its immediate surroundings. In this study, the possibilities for decentralized recovery of nutrient rich residual flows in Santiago, Chile, are studied by means of a case study considering technical and socio-economic criteria. In particular, we calculate circularity indicators for organic matter (OM), nitrogen (N), and phosphorus (P) and cost–benefits of household and community on-site technological alternatives. Kitchen waste (KW) and garden residues (GR) as well as urine were considered as system inputs whereas urban agriculture, municipality green, or peri-urban agriculture were the considered destinations for nutrients recovered. The technologies studied were anaerobic digestion, vermicomposting, and composting, while urine storage and struvite precipitation were considered for nutrient recovery from urine. Material flow analysis was used to visualize the inputs and outputs of the baseline situation (the traditional urban waste management system), and of the different household and municipality resource recovery scenarios (the decentralized valorization systems). Our findings show that decentralized valorization of KW and GR are a clear win–win policy, since they can not only produce important environmental benefits for the city in the long run, but also important cost savings considering the landfill fees and residues transportation of the current centralized waste management system.
Highlights
Urban metabolism refers to the accounting of energy and material fluxes of a city or any inhabited core; the concept serves as a framework for analyzing its inputs and outputs, often focusing on energy, water, and nutrients flows
It is usually the aim to understand current linear resource management strategies in the cities characterized by high resource demand and polluting discharges of waste streams, and propose alternative closed-loop systems where resources are efficiently used within urban boundaries with a restorative perspective [1,2]
On the supply side, these nutrients need to be brought to the agricultural sector and/or urban agriculture (UA) where food consumed in the city is being produced, causing negative impacts, resource depletion and indirect energy consumption [3,4,5,6]
Summary
Urban metabolism refers to the accounting of energy and material fluxes of a city or any inhabited core; the concept serves as a framework for analyzing its inputs and outputs, often focusing on energy, water, and nutrients flows. Of particular interest are nutrient transformations, as cities can substantially impact ecosystem cycles through the fluxes of elements such as carbon (C), nitrogen (N), and phosphorus (P). The city, as an organism, intakes those elements via food inputs coming mostly from external agricultural sources, which, after consumed, transform partially into unwanted by-products i.e., solid waste or human excreta [1]. On the supply side, these nutrients need to be brought to the agricultural sector and/or urban agriculture (UA) where food consumed in the city is being produced, causing negative impacts, resource depletion (i.e., phosphorus) and indirect energy consumption (i.e., artificial nitrogen fertilizer production) [3,4,5,6]
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