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The use of fossil fuels as the main source of energy for most countries has caused several negative environmental impacts, such as global warming and air pollution. Air pollution causes many health problems, causing social and economic negative effects. Worldwide efforts are being made to avoid global warming consequences through the establishment of international agreements that then lead to local policies adapted to the development of each signing nation. In addition, there is a depletion of nonrenewable resources which may be scarce or nonexistent in future generations. The preservation of resources, which is a common goal of the Circular Economy strategy and of sustainable development, is not being accomplished nowadays. In this work, the calculation of indicators and mathematical and statistical analysis were applied to clarify and evidence the trends, provide information for the decision-making process, and increase public awareness. The fact that European countries do not possess abundant reserves of fossil fuels will not change, but the results of this analysis can evolve in the future. In this work, fossil fuel energy consumption, fossil fuel depletion, and their relationship with other variables, such as energy dependence and share of renewable energy in gross final energy consumption, were analyzed for 29 European countries. Furthermore, it was possible to conclude that many European countries still depend heavily on fossil fuels. Significant differences were not found in what concerns gross inland consumption per capita when the Kruskal–Wallis test was applied. It was possible to estimate that by 2050 (considering Jazz scenario) it will only remain approximately 14% of oil proven reserves, 72% of coal proven reserves and 18% of gas proven reserves. Given the small reserves of European countries on fossil fuels, if they need to use them, they will fast disappear.

This work evaluates the possibility of using spent coffee grounds (SCG) for biodiesel production and other applications. An experimental study was conducted with different solvents showing that lipid content up to 6 wt% can be obtained from SCG. Results also show that besides biodiesel production, SCG can be used as fertilizer as it is rich in nitrogen, and as solid fuel with higher heating value (HHV) equivalent to some agriculture and wood residues. The extracted lipids were characterized for their properties of acid value, density at 15 °C, viscosity at 40 °C, iodine number, and HHV, which are negatively influenced by water content and solvents used in lipid extraction. Results suggest that for lipids with high free fatty acids (FFA), the best procedure for conversion to biodiesel would be a two-step process of acid esterification followed by alkaline transesterification, instead of a sole step of direct transesterification with acid catalyst. Biodiesel was characterized for its properties of iodine number, acid value, and ester content. Although these quality parameters were not within the limits of NP EN 14214:2009 standard, SCG lipids can be used for biodiesel, blended with higher-quality vegetable oils before transesterification, or the biodiesel produced from SCG can be blended with higher-quality biodiesel or even with fossil diesel, in order to meet the standard requirements.

Mining and industrial activity are contributing to the increase in heavy metal (HM) pollution in soils. Phytoremediation coupled to selected rhizosphere microbiota is an environmentally friendly technology designed to promote HM bioremediation in soils. In this study, sunflower (Helianthus annuus L.) was used together with Rhizophagus irregularis, an arbuscular mycorrhizal fungi (AMF), and Cupriavidus sp. strain 1C2, a plant growth promoting rhizobacteria (PGPR), as a phytoremediation strategy to remove Zn and Cd from an industrial soil (599 mg Zn kg−1 and 1.2 mg Cd kg−1). The work aimed to understand if it is possible to gradually remediate the tested soil while simultaneously obtaining significant yields of biomass with further energetic values by comparison to the conventional growth of the plant in agricultural (non-contaminated) soil. The H. annuus biomass harvested in the contaminated industrial soil was 17% lower than that grown in the agricultural soil—corresponding to yields of 19, 620, 199 and 52 g m−2 of roots, stems, flowers and seeds. It was possible to remove ca. 0.04 and 0.91% of the Zn and Cd of the industrial soil, respectively, via the HM accumulation on the biomass produced. The survival of applied microbiota was indicated by a high root colonization rate of AMF (about 50% more than in non-inoculated agricultural soil) and identification of strain 1C2 in the rhizosphere at the end of the phytoremediation assay. In this study, a phytoremediation strategy encompassing the application of an energetic crop inoculated with known beneficial microbiota applied to a real contaminated soil was successfully tested, with the production of plant biomass with the potential for upstream energetic valorisation purposes.

Rural farms constitute a vital component of a country’s agricultural landscape, traditionally reliant on energy installations known for their reliability yet notorious for their energy-intensive and inefficient characteristics. While the smart farm concept, integrating renewable energy sources and resource management technologies, has seen widespread adoption in domestic and industrial sectors, rural farms have been slower to embrace these innovations. This study presents a groundbreaking solution, deployed on a rural farm in Portugal, resulting in an impressive 83.24% reduction in energy consumption sourced from the grid. Notably, this achievement translates to a substantial reduction in CO2 emissions, aligning with the growing need for environmentally sustainable farming practices. The technical intricacies of this pioneering solution are comprehensively described and juxtaposed with other scientific case studies, offering valuable insights for replication. This initiative represents a vital first step towards the integration or combination of conventional farming with photovoltaic energy production, exemplified by agrivoltaic systems. In conclusion, this research showcases the potential for rural farms to significantly enhance energy efficiency and financial viability, thereby contributing to a more sustainable and cost-effective agricultural sector. These findings serve as a model for similar endeavors, paving the way for a greener and more economically viable future for rural farming practices.

This article presents and describes the LCA4Power tool, developed in this work to assess the potential environmental impacts, as, for example, the contribution to global warming, of electricity generation in continental Portugal, not considering the Madeira and Azores archipelagos. Based on a life cycle perspective, the tool considers the life cycles of various available technologies for producing electricity, on a cradle-to-gate perspective, excluding distribution and final use. It was implemented in MS Excel™ using emission factors obtained from the literature and other sources, instead of raw life cycle inventory data. The current version of the tool includes wind and hydroelectric power as renewable energy sources, and thermal and combined heat and power generation from fossil fuels as non-renewable energy sources. The combination of the aforementioned electricity generation technologies is responsible for more than 90% of the electricity generated in continental Portugal. Results were validated comparing the tool’s predictions with data from other LCA studies of electricity production, showing a good agreement, in particular for the greenhouse gas emissions. As added value, this tool provides a user-friendly way of simulating the potential environmental impacts of different endogenous energy mixes in Portugal, thus support decision making and communication. Future developments of the tool will include other technologies for electricity generation and its application to support decision making through the analysis of future scenarios for electricity generation in Portugal.

Difficulties and cost of suspended microalgal biomass harvest and processing can be overcome by cultivating microalgae as biofilms. In the present work, a new photoautotrophic biofilm photobioreactor, the rotating flat plate photobioreactor (RFPPB), was developed aiming at a cost-effective production of Chlorella vulgaris (SAG 211-12), a strain not frequently referred in the literature but promising for biofuel production. Protocols were developed for evaluating initial adhesion to different materials and testing the conditions for biofilm formation. Polyvinyl chloride substrate promoted higher adhesion and biofilm production, followed by polypropylene, polyethylene, and stainless steel. The new RFPPB was tested, aiming at optimizing incident light utilization, minimizing footprint area and simplifying biomass harvesting. Tests show that the photobioreactor is robust, promotes biofilm development, and has simple operation, small footprint, and easy biomass harvest. Biomass production (dry weight) under non-optimized conditions was 3.35 g m−2, and areal productivity was 2.99 g m−2 day−1. Lipid content was 10.3% (dw), with high PUFA content. These results are promising and can be improved by optimizing some operational parameters, together with evaluation of long-term photobioreactor maximum productivity.

The treatment of nitrogen-deficient agriculture wastewater, arising from the vegetable and fruit processing, is a significant problem that limits the efficiency of its biological treatment. This study evaluates the effectiveness of the symbiotic co-culture of Azospirillum brasilense and Scenedesmus sp., under two nitrogen levels (8.23 mg L−1 and 41.17 mg L−1) and mixing systems (aeration and magnetic stirring), aiming to simultaneously use the N-deficient media for their growth while producing biomass for biofuels. Microalgae growth and biomass composition, in terms of protein, carbohydrate and fatty acid contents, were evaluated at the end of the exponential growth phase (15 days after inoculation). Results show that the symbiotic co-culture of microalgae-bacteria can be effectively performed on nitrogen-deficient media and has the potential to enhance microalgae colony size and the fatty acid content of biomass for biofuels. The highest biomass concentration (103 ± 2 mg·L−1) was obtained under aeration, with low nitrogen concentration, in the presence of A. brasilense. In particular, aeration contributed to, on average, a higher fatty acid content (48 ± 7% dry weight (DW)) and higher colony size (164 ± 21 µm2) than mechanical stirring (with 39 ± 2% DW and 134 ± 21 µm2, respectively) because aeration contribute to better mass transfer of gases in the culture. Also, co-culturing contributed in average, to higher colony size (155 ± 21 µm2) than without A. brasilense (143 ± 21 µm2). Moreover, using nitrogen deficient wastewater as the culture media can contribute to decrease nitrogen and energy inputs. Additionally, A. brasilense is approved and already extensively used in agriculture and wastewater treatment, without known environmental or health issues, simplifying the biomass processing for the desired application.

The production of municipal waste is increasing all over the world. Although a significant part of the waste is collected as commingled waste, much of it is recyclable if disposed of properly. Thus, separate deposition and collection plays an extremely important role today, more than ever, not only in terms of preventing pollution but also from the point of view of recycling as a driver of circular economy and of efficient use of resources. This work is focused on the development of compaction equipment to be applied to containers, which allows a more efficient approach to the process of collecting waste for recycling. As a management option, recycling depends on collective behavior which is based on individual acts. Therefore, individual use of plastic/metal compaction systems can help meet recycling targets, even as a complement to conventional bins. Thus, herein a proposal is presented for a plastic/metal collection station with a built-in compaction element that allows for the compacting of the separated waste, individually, in an easily accessible drawer. Sorting and compacting waste before collection will result in a reduction of the number of collection/transport stops, which will also translate into higher energy efficiency, cost savings, optimization of the transported tons/km ratio, and profitability.

While in general, with a few exceptions, the natural CH4 cycle is balanced, the anthropogenic disturbances have typically led to increase the CH4 emissions. [...]better understanding of mechanisms that control CH4 cycle in nature can be used to engineer better systems in human-built environments. Mimicking natural processes in laboratory/pilot-scale bioreactors that are designed to optimize specific operational conditions to regulate such communication may lead to successful implementation of technology to effectively utilize the waste materials e.g., municipal solid waste, food waste, industrial organics and wastewaters, or low-grade coals with/without the aid of external carbon/electron sources to produce CH4 as bio-energy, as shown by Yang et al. Marina G. Kalyuzhnaya1, Deepak Kumaresan2, Kirsten Heimann3, Nidia S. Caetano4, Chettiyappan Visvanathan5 and Obulisamy Parthiba Karthikeyan6,7* * 1Department of Biology, San Diego State University, San Diego, CA, United States * 2School of Biological Sciences, Queen's University of Belfast, Belfast, United Kingdom * 3Centre for Marine Bioproducts Development, College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia * 4Department of Chemical Engineering, Instituto Superior de Engenharia Do Porto, Porto, Portugal * 5Department of Energy, Environment, and Climate, School of Environment, Resources and Development, Asian Institute of Technology, Pathumthani, Thailand * 6Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, United States * 7Department of Engineering Technology, College of Technology, University of Houston, Houston, TX, United States

Several microalgae species have been exploited due to their great biotechnological potential for the production of a range of biomolecules that can be applied in a large variety of industrial sectors. However, the major challenge of biotechnological processes is to make them economically viable, through the production of commercially valuable compounds. Most of these compounds are accumulated inside the cells, requiring efficient technologies for their extraction, recovery and purification. Recent improvements approaching physicochemical treatments (e.g., supercritical fluid extraction, ultrasound-assisted extraction, pulsed electric fields, among others) and processes without solvents are seeking to establish sustainable and scalable technologies to obtain target products from microalgae with high efficiency and purity. This article reviews the currently available approaches reported in literature, highlighting some examples covering recent granted patents for the microalgae’s components extraction, recovery and purification, at small and large scales, in accordance with the worldwide trend of transition to bio-based products.