Cities face the challenges of supplying food and managing organic municipal solid waste (OMSW) sustainably amid increasing urbanization rates. Urban agriculture (UA) can help with this effort by producing local crops that are fertilized with nutrients recovered from compost generated from OMSW. This research aims to determine the potential of OMSW compost to supply the nitrogen-phosphorus-potassium (NPK) demand of UA and the environmental benefits of replacing mineral fertilizer from a life cycle perspective. The Metropolitan Area of Barcelona (AMB) serves as the case study given its commitment to reuse biowaste according to the Revised Waste Framework Directive and to promote UA as a signing member of the Milan Urban Food Policy Pact. Based on crop requirements and farmer surveys, we find that the annual NPK demands of the agricultural fields of the AMB that cover 5,500 ha and produce 70,000 tons of crops are approximately 769, 113, and 592 tons of NPK, respectively. Spatial material flow analysis and life cycle assessment were applied to found that the current waste management system can potentially substitute 8 % of the total NPK demanded by UA with compost, reduce the impacts by up to 39 % and yield savings in global warming of 130 %. The more ambitious future scenario of 2025 can potentially substitute 21 % of the total NPK demand and reduce environmental impacts up to 1,049 %, depending on the category considered. Avoiding processing of mixed OMSW, mineral fertilizer replacement and cogeneration of electricity from biogas are the major contributors to these environmental savings.

With the latest IPCC report, dramatic global climate action must be taken immediately to limit global warming to 1.5 °C, or face more frequent and extreme weather events with catastrophic implications. Cities must invest in climate resilience development; however, government policies are only effective if they are supported by the society in which they serve. As such, this study aims to characterize the social perception of climate resilience development, in particular the implementation of sustainable urban rooftop strategies, to support policy makers and enable individual action. This was accomplished through the analysis of 1,100 answered surveys in Cerdanyola del Vallès (Spain), to assess one’s willingness to pay (WTP) and willingness to implement (WTI) rooftop strategies according to: 1. socio-demographical characteristics; 2. social perceptions and beliefs; and 3. surrounding land use and land cover, and vulnerabilities identified through temperature and normalized difference vegetation index (NDVI) maps. The results of this study found age played a significant role in predictability, with 18-39-year-olds being the most willing to pay and implement the various rooftop scenarios. However, our results uncovered societal inequality as those 85+ were the second group most interested in rooftop agriculture but the most financially restricted. Belief in the viability of rooftop strategies increased respondents WTP and WTI while having access to ones’ rooftop increased willingness to partake in rooftop food cultivation and enhance rooftop greenery. A new finding presented by this study is the quantifiable impact that urban greenery plays on increasing survey respondents WTP and WTI.

This paper studies the potential application of a novel biogas upgrading technology called alkaline with regeneration (AwR). This technology uses an alkaline solution, along with carbon mineralization, to remove and store CO₂ from biogas in order to create biomethane, a substitute of natural gas. Three different applications of biogas were explored for their potential economic benefits along three different biogas generation capabilities of landfills in Spain (250Nm³/h, 1000Nm³/h and 5000Nm³/h). The scenarios include upgrading biogas using AwR and injecting the biomethane into the natural gas grid, or selling the gas as a vehicle fuel. The third reference scenario assessed directly burning the biogas for the production of electricity. The latter showed an annual profit of 0.2-5 million €₂₀₁₂ while upgrading the biogas to obtain biomethane showed an annual loss of 3-50 million €₂₀₁₂. This was due to the operational costs involved in AwR, namely the cost of NaOH (principal reagent) and the treatment of wastewater. Increasing revenue can help obtain an annual profit. In order to break-even it would be necessary to raise CO₂ credits to 99€₂₀₁₂/t or, through feed in tariffs, increase the price of the sale of biomethane to 0.25€₂₀₁₂/kWh.