The rise of population in urban areas makes it ever more important to promote urban agriculture (UA) that is efficient in terms of water and nutrients. How to meet the irrigation demand of UA is of ...particular concern in urban areas where water sources are often limited. With the aim of determining how to reduce water use for irrigation while maintaining productivity and reducing environmental impacts in UA, this study explores the agronomic performance and environmental life cycle impacts and benefits of three different fertigation management practices used in a rooftop greenhouse for tomato crop in Barcelona: 1) open management (OP); 2) recirculation (RC), in which 30% of the drained, unused water is used to irrigate the crop; and 3) the same recirculated management of RC with a further reduction in fresh water input of 15%(RR). Despite the recirculation and reduction of water and nutrients, all three irrigation management practices resulted in similar yields: 16.2, 17.9, and 16.8·kg·m−2 for OP, RC, and RR, respectively. In terms of water-use efficiency, RR management was the most efficient, requiring 48.7·liters·kg−1 of tomato, followed by RC (52.4·L·kg−1) and OP (75.2·L·kg−1). RR presented an improvement of 7% in water-use efficiency. In terms of environmental performance, RC had the best performance in almost all impact categories during the operational phase, especially in regard to marine and freshwater eutrophication, with 44% and 93% fewer impacts than OP due to the recirculation of nutrients and reduced nutrient loss through leachates. In terms of infrastructure, even though recirculation management requires additional equipment, the materials present better performance in the range from 0.2 to 14% depending on the impact category. This study can support evaluation of agricultural projects in the city, through yields and water consumption presented, incentivizing good practices aligned with the sustainability of UA.
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•Recirculation systems reduce the marine and freshwater eutrophication.•Leachate as irrigation water is an alternative for the reduction of irrigation water and maintains yields.•It is necessary to find ways to fertilizer substitution and irrigation optimization.•Water reduction management can increase in 7% the WUE of the tomato crop.•The operation phase shows improvements in all of the impact categories evaluated.
•We determine the GHG emissions of plastic waste recovery in Spain.•We evaluate quality and market of plastic waste and application of plastic recycled.•We conduct dynamic material flow analysis and ...life cycle assessment.•The highest GHG emissions savings are obtained for mechanical recycling.•Export and low quality of plastic waste reduce the GHG emissions savings.
This paper concentrates on the quantification of greenhouse gas (GHG) emissions of post-consumer plastic waste recovery (material or energy) by considering the influence of the plastic waste quality (high or low), the recycled plastic applications (virgin plastic substitution or non-plastic substitution) and the markets of recovered plastic (regional or global). The aim is to quantify the environmental consequences of different alternatives in order to evaluate opportunities and limitations to select the best and most feasible plastic waste recovery option to decrease the GHG emissions. The methodologies of material flow analysis (MFA) for a time period of thirteen years and consequential life cycle assessment (CLCA) have been integrated. The study focuses on Spain as a representative country for Europe. The results show that to improve resource efficiency and avoid more GHG emissions, the options for plastic waste management are dependent on the quality of the recovered plastic. The results also show that there is an increasing trend of exporting plastic waste for recycling, mainly to China, that reduces the GHG benefits from recycling, suggesting that a new focus should be introduced to take into account the split between local recycling and exporting.
Developing countries, including Brazil, Russia, India, China and South Africa (BRICS), are implementing mitigation strategies for greenhouse gas (GHG) emissions in specific sectors, such as municipal ...solid wastes (MSW), to reduce the impacts of climate change. The purpose of this research was to evaluate different GHG emission mitigation scenarios in MSW management in Brazil, countrywide and at municipal level, to determine the best transition towards eco-efficiency (TEE) relative to the current scenario. Environmental (GHG emissions, using the CO2ZW tool) and economic (operating and investment costs and climate change externalities) indicators were determined and analysed per ton of MSW treated, based on field work and national data. An analysis was made of six scenarios of transitions of MSW management and treatment via wet processes (composting and mechanical biological treatment – MBT), dry routes (recycling and incineration) and disposal in sanitary landfills (DSL). The most eco-efficient scenario for Brazil and the municipalities with the largest populations, such as São Paulo and Sorocaba, corresponded to: 70% composting and 30% DSL for wet MSW and; 70% recycling and 30% DSL for dry MSW. In the smaller municipalities such as Humaitá, Piedade and Santa Cruz do Sul, the best results in TEE were: 42% composting and 58% DSL for wet MSW and; 41% recycling and 59% DSL for dry MSW. The scenarios showing the lowest TEE performance were MBT and incineration, due to the high costs of these technologies in Brazil.
•A tool for CO2emissions calculations from municipal solid waste (MSW) is presented.•The tool can be adapted to other cities, regions and countries.•The operational costs, externalities and total costs for society were analysed.•An analysis through the transition towards eco-efficiency for MSW was established.•The best results were the integration of recycling, composting and landfill.
Buildings and greenhouses consume vast amounts of energy and natural resources for heating and ventilation. It is still unclear how the synergetic effect of combining greenhouses and buildings' ...forced waste airflows could improve both systems' energy efficiency. This study quantified the energy recovery potential of exchanging airflows in a rooftop greenhouse (iRTG) integrated with an office building HVAC system in a Mediterranean climate. Using monitored and calibrated energy model data, the results showed that the iRTG can act as a solar collector and as a sink for a building's low-grade waste heat. The magnitude of harvested thermal energy that could be recirculated into the building by the integrated HVAC system was 205.2 kWh/m2y−1 and was limited by greenhouse low transmissivity (54%). The magnitude of building exhaust air was 198 kWh/m2y−1 at temperatures sufficient to heat and cool the iRTG. Compared to a passive ventilated configuration, the integration of active ventilation strategies doubled the energy benefits. Building ventilation requirements directly determined building and greenhouse waste flows and energy benefits, which increased by 63.1% when air changes per hour moved from 1.59 to 3.16. Overall, this demonstrates that greenhouse and building functionalities could be coupled to contribute to urban circularity and sustainability.
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•A greenhouse integrated within the building HVAC system was investigated.•Real and modelling data was combined to quantify energy co-benefits.•The iRTG recycled 143 kWh/m2·y of sensible heat from building waste heat.•The iRTG solar capacity conveyed 205 kWh/m2·y of sensible heat to the building.•Active strategies doubled the energy benefits compared to passive mechanisms.
Urban agriculture systems, such as rooftop greenhouses, are attractive alternatives for mitigating the impacts of the extensive food supply chains that currently feed cities. In this study, we study ...the opportunity that nutrient recirculation offers to improve the environmental performance of agricultural systems. In particular, we analyze the environmental burdens of a hydroponic closed-loop production system that recovers nutrients and reduces water demand by recirculating the irrigation water leaching from the substrate bags along with nutrients that have not been assimilated by the plant. The closed-loop system is compared to a linear system in which there is no nutrient or water recovery. Based on two green bean crop cycles in a Mediterranean rooftop greenhouse, we analyze the yield, climatic variables and water and nutrient balances, and apply life cycle assessment (LCA) to study the environmental impacts.
The results of this study indicate that closed-loop systems save daily 40% of irrigation water and between 35 and 54% of nutrients. Moreover, leachate reuse leads to reduced eutrophication impacts, but it can entail nutrient deficiencies. However, implementing a closed-loop system requires additional infrastructure causing larger impacts than linear systems in terms of global warming and fossil resource scarcity. The results of the LCA were highly sensitive to the yield, the crop production period and the meteorological conditions. Based on these results, we design improved scenarios, providing recommendations for reducing the impacts of closed-loop systems for more sustainable cities.
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•Closed systems presented 40% in daily water savings.•Large savings were obtained in closed systems in eutrophication impacts.•High sensitivity was found related to yield, climatic conditions and crop length.•High impacts in closed systems came from the materials required, mainly benches.•Room for improvement exists for closed systems.
Urban agriculture (UA) is a means for cities to become more resilient in terms of food sovereignty while shortening the distance between production and consumption. However, intensive soilless UA ...still depends on the use of fertilizers, which relies on depleting non-renewable resources such as phosphorous (P) and causes both local and global impact for its production and application. With the aim to reduce such impacts and encourage a more efficient use of nutrients, this study assesses the feasibility of using struvite precipitated from an urban wastewater treatment plant as the unique source of P fertilizer. To do so, we apply various quantities of struvite (ranging from 1 to 20 g/plant) to the substrate of a hydroponic Phaseolus vulgaris crop and determine the yield, water flows and P balances. The results show that treatments with more than 5 g of struvite per plant produced a higher yield (maximum of 181.41 g/plant) than the control (134.6 g/plant) with mineral fertilizer (KPO4H2). On the other hand, P concentration in all plant organs was always lower when using struvite than when using chemical fertilizer. Finally, the fact that different amounts of struvite remained undissolved in all treatments denotes the importance to balance between a correct P supply to the plant and a decrease of P lost through the leachates, based on the amount of struvite and the irrigated water. The findings of this study show that it is feasible for UA to efficiently use locally recovered nutrients such as P to produce local food.
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•Struvite is tested in hydroponic production of Phaseolus vulgaris.•Yield, water fluxes, and P balances are analysed.•More yield is produced by plants with more than 5 g of struvite.•Slow release by struvite decreases the leached P.
Defining sustainable cities is not straightforward. The main issues involved in urban sustainability are buildings, energy, food, green areas and landscape, mobility, urban planning, water and waste; ...and their improvement is promoted through different strategies. However, a quantitative method, such as life cycle thinking (LCT), is essential to evaluating these strategies. This paper reviews LCT studies related to urban issues to identify the main research gaps in the evaluation of these improvement strategies. The review identifies the main sustainability strategies associated with each urban issue and compiles articles that deal with these strategies through LCT, including environmental life cycle assessment (LCA), life cycle costing (LCC), social LCA (S-LCA) and life cycle sustainability assessment (LCSA), as well as integrated analyses with combined tools. Water, waste and buildings are the urban issues that accounted for a larger amount of studies. In contrast, a limited number of papers assessed urban planning and energy (excluding energy in buildings). Strong interrelations among urban issues were identified, most of them including water. In terms of methods, 79% of the studies exclusively applied life cycle tools (i.e., LCA, LCC, S-LCA or LCSA). Within this group, the environmental dimension was the focus of 84% of the papers. Single environmental indicators (e.g., global warming) were common in 20% of the analyses, highlighting the need to integrate more impact categories to prevent trade-offs. In the field of social and sustainability assessment, there is a need for methodological advances that foster their application in urban areas. Further research should cover the thematic and methodological gaps identified in this paper, such as developing models that assess complex urban issues, generating comprehensive LCT studies and promoting multi-indicators. Life cycle tools might benefit from revising the methodology with stakeholders to optimize the understanding and communication of life cycle results for policy- and decision-making processes.
•We identified strategies promoted to achieve urban sustainability.•Based on urban issues, we reviewed the life cycle studies conducted for each strategy.•Water, waste and buildings were widely covered from a life cycle standpoint.•Urban planning and energy still need to be included in these assessments.•There is a lack of social studies and more methodological advancements are needed.
Waste management on small islands does not hold any straightforward solutions. The numerous difficulties include limited space availability, restricted recycling and resale opportunities and impacts ...on the local environment that become magnified particularly when the island is small-sized, densely populated and tourist dependent.
The well-documented impact on the local environment includes resource loss, damage to the marine and local environment and continuous nuisances created by littering, trucks and treatment facilities. However, waste management can leave its mark beyond the local borders. The generation and treatment of waste is in fact gaining attention in its connection with greenhouse gas emissions (GHG). Although in the past GHG emissions were mainly associated with energy generation, today it is frequently acknowledged that improved waste management can also mitigate these emissions.
This research paper analysis the flows involved in the management of municipal waste (MW) from an island perspective. Focusing on the island of Malta, which consists of 316 km2 and sustains a population density of 1327 people/km2, a Material Flow Analysis together with a carbon footprint is presented for 2012. The same analysis is then made for three prospective scenarios proposed in the Waste Management Plan for the Maltese Islands 2014–2020 using projected 2018 data.
With the use of STAN 2.5 (SubSTance Flow ANalysis), a tabled down analysis of the collection, treatment and disposal/export flows involved in the management of Municipal Waste in Malta is presented. The flows are then translated into a carbon footprint analysis using CO2ZW® (a carbon footprint tool for waste management). The objective is to emphasize the relationship between GHG remove GHG and replace with Greenhouse Gas emissions and existing waste management flows and how this relationship changes when different collection, treatment and disposal options are selected. The research’s ultimate aim is therefore to underline the importance of placing climate concerns in waste management policies.
The results note that, in terms of carbon emissions, Malta stands to benefit from the introduction of a second Mechanical Biological Treatment plant since carbon emissions will experience an extensive reduction from the 2012 estimates. However, further reduction of carbon emissions should be accompanied by the increase of dry material recycling, separate organic collection and an analysis of the current collection system particularly route optimisation.
Summary
To support effective urban policies aimed at decreasing the environmental impacts of cities, it is important to develop robust tools for accounting those impacts. Environmentally extended ...input‐output analysis (EEIOA) is among the most used tools for this purpose, allowing the quantification of both direct and indirect impacts. Life cycle assessment (LCA) is also a holistic and comprehensive tool that accounts for direct and indirect impacts—but its application to cities is still very recent. This study aims at applying EEIOA and LCA to the municipality of Aveiro (Portugal) in order to compare the outcomes of the two tools in terms of total impacts (climate change and fossil fuel depletion) and hotspots (sectors/products contributing most to the impacts), to identify limitations and advantages of the tools when applied to Aveiro, and to illustrate how LCA can be applied to cities. The total impacts estimated with LCA and EEIOA were similar and the hotspots were also the same: transports, food, construction, and electricity. However, the relative contribution of some sectors was very different in the two tools due to methodological differences mainly in system boundaries, type of activities or products considered in each sector, and geographical coverage of impact data. This study concludes that the analyzed tools can provide complementary results to support decision making concerning urban planning and management.
•Conventional and Passivhaus proposals for a university building’s renovation are compared.•The energy renovation achieved high energy savings for both proposals, between 60% and 80%.•The Passivhaus ...proposal is 30% better than the conventional one considering the total lifespan of the building.•The use of cork as an insulation material for envelope renovation is assessed.•Cork does not fit the requirements for competing with common non-renewable insulation materials.
The need to improve the energy efficiency of buildings has introduced the concept of nearly zero-energy buildings into European energy policies. Moreover, a percentage of the building stock will have to be renovated annually to attain high energy performance. Conventional passive interventions in buildings are focused on increasing the insulation of the building envelope to increase its energy efficiency during the operating phase. Often, however, intervention practices imply the incorporation of embodied energy into the building materials and increase the associated environmental impacts.
This paper presents and evaluates a comparison of two different proposals for a real-world building renovation. The first proposal was a conventional project for energy renovation, while the second was a low-energy building proposal (following the Passivhaus standard). This study analysed the proposals using an integrated life cycle and thermal dynamic simulation assessment to identify the adequacy of each renovation alternative regarding the post-renovation energy performance of the building, including an evaluation of the introduction of a renewable insulation material into the low-energy building proposal, specifically a specific cork solution. The most significant conclusion was the convenience of the renovation, achieving energy savings of 60% and 80% for the conventional and Passivhaus renovations (ENERPHIT), respectively. The former supposed less embodied energy and environmental impacts but also generated less energy savings. The latter increased the embodied impacts in the building, mainly for the large amount of insulation material. The environmental implications of both proposals can be compensated for within a reasonable period of time, over 2 years in the majority of alternatives and impact categories. However, the ENERPHIT project was 30% better than the conventional proposal when the total lifespan of the building was considered. The introduction of cork did not fit the requirements for competing with the common non-renewable insulation materials because it did not imply better environmental performance in buildings, but cork insulation solutions currently present ample room for improvement.
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