The burning of fossil fuels is an unsustainable activity, which is leading to an increase in greenhouse gases (GHGs) emissions and related global warming. Among sustainable energy sources, microalgae ...represent a promising alternative to fossil fuel and contribute to the achievement of important Sustainable Development Goals (SDGs). In particular, the potential contribution of marine microalgae to sustainable development is large as, among other benefits, they represent a carbon negative energy source and may be applied in many coastal areas around the world. Despite this, significant economic and technological improvements are needed in order to make microalgae biofuels viable on a large scale. This review aims to explore how and to what extent third-generation biofuels (marine microalgae, but also the latest advances in freshwater microalgae) can benefit the realization of these SDGs. From this study we concluded that the production of large-scale marine microalgae biofuels is not yet feasible from the economic perspective at a large scale. However, the cultivation of microalgae in seawater holds great potential for increasing the small to medium viability of this biofuel source. The possibilities for improvement along with the contributions to sustainable development lay the groundwork for continuing to study and apply the potential of sustainable production of microalgae bioenergy.
•Three alternatives are designed to recover nutrients from urban hydroponic crops.•These are direct leachate recirculation, chemical precipitation and membrane filtration.•LCA shows that direct ...leachate recirculation has the best environmental performance.•Chemical precipitation has more impacts than the business-as-usual.•All alternatives avoid eutrophication impacts triggered by nutrient discharge.
In light of global population growth and the increasing food demand in cities, new food production strategies have been developed to promote a more resource-efficient urban agriculture. Greenhouses with hydroponic systems have been proposed as sustainable systems for growing food in urban areas with a better control of plant growth. However, nutrient management in hydroponic agricultural systems is an environmental challenge and its efficiency could be improved from a circular economy standpoint. The goal of this study is to analyze the potential implementation of three nutrient recovery alternatives that promote re-use for urban hydroponics, i.e. direct leachate recirculation (DLR), chemical precipitation (CP) and membrane filtration (MF), and to study their environmental performance through life cycle assessment. The study focuses on the recovery of phosphorus (P), magnesium, potassium and calcium in a hydroponic tomato crop cycle carried out in an integrated rooftop greenhouse (i-RTG), located in the Metropolitan Area of Barcelona. The assessment shows that DLR was the most environmentally friendly option in terms of global warming (5.5 kg CO2 eq. to recover 447 g of P) as opposed to CP and MF, which had 3 and 5 times more impact, respectively. Moreover, all three alternatives showed less eutrophication potential than the baseline scenario, which considered that 447 g of P were discharged into the environment. Meeting the crop’s nutritional requirements through recovered nutrients helped save between 44–52% of global warming impacts with respect to new fertilizers when using DLR and MF. Oppositely, CP showed a 2% impact increase in global warming because this technology was only able to recover P and part of the magnesium. This study informs practitioners and decision-makers about the environmental benefits of applying circular thinking to nutrient management in urban agriculture to promote urban sustainability.
Phosphorus (P) resources are decreasing at an alarming rate due to global fertilizer use and insufficient nutrient recovery strategies. Currently, more circular approaches are promoted, such as ...recovering P from wastewater in the form of struvite. This is especially attractive for urban areas, where there is a growing trend of local crop production and large volumes of wastewater are treated in centralized wastewater treatment plants (WWTPs). This research aims to assess the technical and environmental feasibility of applying a struvite recovery and reuse strategy to meet the P requirements to fertilize the agricultural fields of an urban region. To do so, we analyze the potential P recovery and the environmental impacts of integrating three recovery technologies (REM-NUT®, Ostara® and AirPrex®) in the two biggest WWTPs of the Àrea Metropolitana de Barcelona. The results show that all technologies are able to recover between 5 and 30 times the amount of P required to fertilize the agricultural area of the region annually (36.5 t). As can be expected, including P recovery technologies result in additional impacts per m3 of wastewater due to increased electricity consumption and chemicals required for the struvite precipitation. However, struvite recovery results in less eutrophication potential, especially in the REM-NUT® case, with an average reduction of 5.4 times. On the other hand, Ostara®, that recovers P from the digestate, had the lowest impacts (9 kgCO2eq/kgP), even compared to the production of mineral fertilizer. When we apply our findings to the whole region, we can see that chemical use for struvite precipitation and energy consumption during the wastewater treatment process are the elements with the greatest impact. Thus, choosing the most appropriate technology in the most suitable WWTP is the most efficient strategy to diminish the environmental impacts of the system.
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•Scenarios of struvite recovery and reuse are quantified for an urban region.•Some WWTPs should be modified to recover P, like the inclusion of EBPR.•Agricultural P demand of Barcelona region is met with only one WWTP.•Eutrophication potential of WWTPs is mitigated through P recovery technologies.•Impacts of electricity and chemical use of WWTPs as the target to optimize
•The solar energy potential of underutilized urban rooftops in Peru was analyzed.•A model was elaborated for medium-sized Peruvian cities with GIS.•Life Cycle Assessment was used to compute ...environmental impacts.•Results demonstrate that self-sufficiency in electricity production is attainable.•Substantial climate change mitigation could be accomplished with this layout.
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Urban environments in Latin America must begin decarbonizing their activities to avoid increasing greenhouse gases (GHGs) emissions rates due to their reliance on fossil fuel-based energy to support economic growth. In this context, cities in Latin America have high potential to convert sunlight into energy. Hence, the main objective of this study was to determine the potential of electricity self-sufficiency production and mitigation of GHG emissions in three medium-sized cities in Peru through the revalorization of underutilized rooftop areas in urban environments. Each city represented a distinct natural area of Peru: Pacific coast, Andean region and Amazon basin. More specifically, photovoltaic solar systems were the technology selected for implementation in these rooftop areas. Data on incident solar energy, temperature and energy consumption were collected. Thereafter, ArcGis10.3 was used to quantify the total usable area in the cities. A series of correction factors, including tilt, orientation or roof profiles were applied to attain an accurate value of usable area. Finally, Life Cycle Assessment was the methodology chosen to calculate the reduction of environmental impacts as compared to the current context of using electricity from the regional grids. Results showed that the cities assessed have the potential to obtain their entire current electricity demand for residential, commercial and public lighting purposes, augmenting energy security and resilience to intermittent natural disasters, with the support of decentralized storage systems. This approach would also translate into substantial reductions in terms of GHG emissions. Annual reductions in GHG emissions ranged from 112ton CO2eq in the city of Ayacucho to over 523kton CO2eq in Pucallpa, showing that cities in the Amazon basin would be the ones that benefit the most in terms of climate change mitigation.
A paradigm shift is needed in wastewater treatment plants (WWTPs) to progress from traditional pollutant removal to resource recovery. However, whether this transformation produces overall ...environmental benefits will depend on the efficient and sustainable use of resources by emerging technologies. Given that many of these technologies are still being tested at the pilot scale, there is a lack of environmental assessments quantifying their impacts and benefits. In particular, an integrated approach to energy and nutrient recovery can elucidate the potential configurations for WWTPs. In this study, we conduct a life cycle assessment (LCA) of emergent wastewater treatment technologies aimed at increasing resource circularity in WWTPs. We focus on increasing energy self-sufficiency through biogas upgrades and a more radical circular approach aimed at nutrient recovery. Based on a case-study WWTP, we compare its current configuration with (1) implementing autotrophic nitrogen removal in the mainstream and deriving most of the organic matter for biogas production, which increases the quality and quantity of biogas available for energy production; (2) implementing struvite recovery through enhanced biological phosphorus removal (EBPR) as a radical approach to phosphorus management, offering an alternative to mineral fertilizer; and (3) a combination of both approaches. The results show that incremental changes in biogas production are insufficient for compensating for the environmental investment in infrastructure, although autotrophic nitrogen removal is beneficial for increasing the quality of the effluent. Combined phosphorus and energy recovery reduce the environmental impacts from the avoided use of fertilizers and phosphorus and the nitrogen release into water bodies. An integrated approach to resource management in WWTPs is thus desirable and creates new opportunities toward the implementation of circular strategies with low environmental impact in cities.
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•Rethinking wastewater treatment is key to recover energy and resources in cities.•Increased biogas production, nitrogen removal and struvite recovery are studied.•Radical upgrades through nutrient recovery decrease the plant's environmental impacts.
Urban planning has been focusing its attention on urban rooftop agriculture as an innovative way to produce local and reliable food in unused spaces in cities. However, there is a lack of ...quantitative data on soilless urban home gardens and their contribution to self-sufficiency. The aim of the present study is to provide quantitative agronomic and environmental data on an actual soilless urban garden to estimate its degree of self-sufficiency and sustainability. For this purpose, an 18 m
soilless polyculture rooftop urban home garden in the city center of Barcelona was analyzed. From 2015 to 2017, 22 different crops were grown to feed 2 people in an open-air soilless system, and a life cycle assessment was performed. A total productivity of 10.6 kg/m
/year was achieved, meaning that 5.3 m
would be needed to fulfill the yearly vegetable requirements of an average citizen (in terms of weight). Considering the vegetable market basket of Catalonia, an 8.2 m
soilless garden would be needed to cover 62% of the market basket for one person. The top 5 most productive crops were tomato, chard, lettuce, pepper and eggplant, accounting for 85.5% of the total production. The water consumption was 3.7 L/m
/day, and 3.3 kg/year/m
of waste was generated. A high degree of self-sufficiency was achieved, although adjustments could be made to adapt the production to the market basket. The environmental assessment showed that the fertilizers and their associated leachates accounted for the highest environmental impacts in all the studied impact categories. Overall, 0.6 kg CO
eq. was generated per kg of vegetables produced. The quantitative data provided by the present study offer a reference from which urban planners and researchers can project future implementations of rooftop urban agriculture (UA) on a large scale.
Soilless crop production is a viable way to promote vertical agriculture in urban areas, but it relies extensively on the use of mineral fertilizer. Thus, the benefits of fresher, local food and ...avoiding the transportation and packaging associated with food import could be counteracted by an increase in nutrient-rich wastewater, which could contribute to freshwater and marine eutrophication. The present study aimed to explore the use of mineral fertilizer substitutes in soilless agriculture.
Phaseolus vulgaris
(common bean) was fertilized with a combination of slow-releasing fertilizer struvite (a source of N, P, and Mg), which is a byproduct of wastewater treatment plants, and inoculation with Rhizobium (a N
2
-fixing soil bacteria). The experiment included three bean-production lines: (A) 2 g/plant of struvite and rhizobial inoculation; (B) 5 g/plant of struvite and rhizobial inoculation, both irrigated with a Mg-, P-, and N-free nutrient solution; and (C) a control treatment that consisted of irrigation with a full nutrient solution and no inoculation. Plant growth, development, yields, and nutrient contents were determined at 35, 62, and 84 days after transplanting as well as biological N
2
fixation, which was determined using the
15
N natural abundance method. Treatments A and B resulted in lower total yields per plant than the control C treatment (e.g., 59.35 ± 26.4 g plant
–1
for A, 74.2 ± 23.0 g plant
–1
for B, and 147.71 ± 45.3 g plant
–1
for C). For A and B, the nodulation and N
2
fixation capacities appeared to increase with the amount of initially available struvite, but, over time, deficient levels of Mg were reached as well as nearly deficient levels of P, which could explain the lower yields. Nevertheless, we conclude that the combination of struvite and N
2
-fixing bacteria covered the N needs of plants throughout the growth cycle. However, further studies are needed to determine the optimal struvite quantities for vertical agriculture systems that can meet the P and Mg requirements throughout the lifetime of the plants.
Purpose
Rooftop greenhouses (RTGs) are agricultural systems that can improve the food supply chain by producing vegetables in unused urban spaces. However, to date, environmental assessments of RTGs ...have only focused on specific crops, without considering the impacts resulting from seasonality, combinations of crops and nonoperational time. We analyze vegetable production in an RTG over 4 years to determine the crop combinations that minimize yearly environmental impacts while diversifying food supply.
Methods
The system under study consists of an integrated RTG (i-RTG) with a hydroponic system in Barcelona, in the Mediterranean region. By using life cycle assessment (LCA), we evaluate the environmental performance of 25 different crop cycles and 7 species cultivated during the period 2015–2018. Three functional units are used: 1 kg of edible fresh production, 1 unit of economic value (€) in the wholesale market and 1 kcal of nutritional value. The system boundaries consider two subsystems: infrastructure (greenhouse structure, rainwater harvesting system and auxiliary equipment) and operation (fertilizers and their emissions into water and substrate). In addition, we perform an eco-efficiency analysis, considering the carbon footprint of the crop cycles and their value at the wholesale market during their harvesting periods.
Results and discussion
Spring tomato cycles exert the lowest impacts in all categories, considering all three functional units, due to the high yields obtained. In contrast, spinach and arugula have the highest impacts. Regarding relative impact, the greenhouse structure presented a large impact, while fertilizer production had notable relative contributions in tomato cycles. Moreover, nitrogen and phosphorus emissions from fertigation are the main causes of freshwater and marine eutrophication. By combining the most eco-efficient cycles, we can see that growing two consecutive tomato cycles is the best alternative with the functional unit of yield (0.49 kg CO
2
eq./kg), whereas a long spring tomato cycle combined with bean and lettuce cycles in the autumn/winter is the best scenario when using market (0.70 kg CO
2
eq./€) and nutritional value (3.18·10
−3
kg CO
2
/ kcal).
Conclusions
This study shows that increasing the diversity of the system leads to better environmental performance of greenhouse urban agriculture if suitable crops are selected for the autumn/winter season. The functional unit involving the economic value and the eco-efficiency analysis are useful to demonstrate the capability of the growing system to produce added-value vegetables under harsher conditions while categorizing and classifying the crops to select the most suitable combinations based on economic and environmental parameters.
The industrial symbiosis in eco-industrial parks requires intense broker involvement to be implemented. However, market changes and technological advancement could undermine the level of symbiosis ...during operations. In this research, the existing symbiosis indicators were identified and classified using a systematic literature review. The results demonstrated the necessity to achieve indicators sufficiently simple that brokers are enabled in confronting the monitoring and promotion of symbiosis. In this paper, an industrial symbiosis indicator is introduced that detects the variation of symbiosis over time and that provides a dynamic perspective of the eco-industrial parks. This indicator can be used in the underpinning of decisions and the provision of continuous improvement. It was evaluated in several theoretical scenarios created from real data. The three scenarios are: absence of symbiosis, presence of symbiosis, and perfect symbiosis. The results demonstrate consistency between the values of the indicator and changes in the scenarios. The industrial symbiosis indicator proposed was able to detect variations in symbiosis with simple measures, and could support managers in encouraging companies to actively engage in effort for more advanced levels of symbiosis. The concept of “environment impact momentum”, proposed and applied in this research, is a theoretical construct that could support a new class of indicators capable of identifying the dynamic behavior of eco-industrial parks.
•Indicators for industrial symbiosis are analyzed.•The capacity to measure the dynamic perspective is a research gap.•The paper introduces the concept of Environmental Impact Momentum (EIM).•Applying the EIM concept, the paper introduces an indicator called ISI.•The ISI was able to detect trends in variation of symbiosis with simple measures.
This study evaluates direct and indirect environmental impacts associated with the consumption of goods and services by the households living in the municipality of Aveiro (Portugal) using ...environmentally extended input output (IO) analysis. The environmental impacts addressed are greenhouse gas (GHG) emissions and fossil fuel consumption. A methodology adapted to the specificities of the data available is proposed. This methodology relies on the Portuguese economic IO table, on GHG emission and fossil fuel consumption intensities, and on national household expenditure data downscaled to the urban level. This methodology could also be applied to other municipalities or cities for which data on local household expenditures are missing. This study also identifies the sectors with the largest impacts in order to prioritise strategies for reducing the impacts to move the municipality towards more sustainable consumption.
The estimated total GHG emissions in 2005 amounted to 26 kg CO2-eq./cap/day and the total fossil fuel consumption was 7.3 koe/cap/day. The sectors that contributed most for both indicators are “land transport and transport by pipelines”, “food, beverages and tobacco”, “construction” and “production, collection and distribution of electricity”. Therefore, improvement measures are proposed for these sectors in order to more effectively decrease the environmental impacts related with GHG emissions and fossil energy consumption of the municipality.
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