• Energy Research

In the current energy conjunction, with an expected growth of energy consumption in a context of fossil fuel depletion, more focus is being placed on renewable energy sources (RES) for electricity generation. One of the most appealing alternatives is biomass, which can be efficiently used to generate electricity as well as heat with the application of cogeneration technologies that enhance the efficiency of the entire energy conversion process. The Mediterranean basin is a region with a recognized potential for electricity and heat production using primary forest biomass and sub-products from sawmills, among which highlight wood chips for their easiness to be obtained, processed and dried as well as for their good and stable burning or gasification behavior. However, in order to efficiently use the available resources, that is, minimizing logistical requirements to reduce the energy necessary for the electricity generation process, the biomass found in Mediterranean forests can only be used at micro- and small-scale levels to be compatible with sustainable forestry practices. This article is aimed to describe the different technological alternatives to convert wood chips into electricity and heat and it also reviews and compares the current performances in terms of efficiency of these technologies at the micro- and small-scale levels. Peer Reviewed

In the current energy conjunction, with an expected growth of energy consumption in a context of fossil fuel depletion, more focus is being placed on renewable energy sources (RES) for electricity generation. One of the most appealing alternatives is biomass, which can be efficiently used to generate electricity as well as heat with the application of cogeneration technologies that enhance the efficiency of the entire energy conversion process. The Mediterranean basin is a region with a recognized potential for electricity and heat production using primary forest biomass and sub-products from sawmills, among which highlight wood chips for their easiness to be obtained, processed and dried as well as for their good and stable burning or gasification behavior. However, in order to efficiently use the available resources, that is, minimizing logistical requirements to reduce the energy necessary for the electricity generation process, the biomass found in Mediterranean forests can only be used at micro- and small-scale levels to be compatible with sustainable forestry practices. This article is aimed to describe the different technological alternatives to convert wood chips into electricity and heat and it also reviews and compares the current performances in terms of efficiency of these technologies at the micro- and small-scale levels. Peer Reviewed

Abstract Straight vegetable oils may be used as fuel in existing diesel engines. However, some precautions should be taken into account because some of their physicochemical properties must be adjusted through temperature control to ensure enhanced combustion, thus avoiding premature aging of the engine. Although it is well known that surface tension plays a prevalent role in the fuel atomization process which affects the combustion quality, there is lack of published information about its variation with temperature when dealing with straight vegetable oils to be used as fuel in unmodified diesel engines. In this work, the surface tension of several vegetable oils is studied in a wide temperature interval. The optimal range of temperatures at which each vegetable oil should operate to adjust its properties to those of automotive diesel and biodiesel is found. Moreover, an empirical relationship between the dependence between surface tension and density is presented. Therefore, by means of this relationship, just measuring the density of a given oil, its surface tension can be directly deduced.

Abstract Straight vegetable oils may be used as fuel in existing diesel engines. However, some precautions should be taken into account because some of their physicochemical properties must be adjusted through temperature control to ensure enhanced combustion, thus avoiding premature aging of the engine. Although it is well known that surface tension plays a prevalent role in the fuel atomization process which affects the combustion quality, there is lack of published information about its variation with temperature when dealing with straight vegetable oils to be used as fuel in unmodified diesel engines. In this work, the surface tension of several vegetable oils is studied in a wide temperature interval. The optimal range of temperatures at which each vegetable oil should operate to adjust its properties to those of automotive diesel and biodiesel is found. Moreover, an empirical relationship between the dependence between surface tension and density is presented. Therefore, by means of this relationship, just measuring the density of a given oil, its surface tension can be directly deduced.

Given global coffee consumption, substantial quantities of spent coffee grounds (SCGs) are generated annually as a by-product of brewing coffee. SCG, although rich in bioactive compounds, is nowadays disposed of. The objective of this study is to compare, for the first time and from the same SCG, the efficiency of ethanol–water mixtures and acetone–water mixtures for the recovery of total polyphenols, chlorogenic acid, and caffeine. Acetone at 20% (m/m) was the most convenient solvent to extract all three bioactive compounds simultaneously, yielding 4.37 mg of GAE/g SCG for total polyphenols, chlorogenic acid (0.832 mg 5-CQA/g SCG), and caffeine (1.47 mg/g SCG). Additionally, this study aims to address some challenges associated with the industrial-scale utilization of SCG as a raw material, encompassing factors such as pre-treatment conditions (natural drying and oven drying), storage duration, and the kinetics of the extraction process. No significant difference was observed between the natural drying and oven drying of SCG. In terms of storage duration, it is advisable to process the SCG within less than 3–4 months of storage time. A significant decline of 82% and 70% in chlorogenic acid (5-CQA) and caffeine contents, respectively, was observed after eight months of storage. Furthermore, the kinetic study for the recovery of total polyphenols revealed that the optimal extraction times were 10 min for acetone at 20% and 40 min for water, with a yield increase of 28% and 34%, respectively. What is remarkable from the present study is the approach considered, using the simplest operating conditions (minimal time and solvent-to-solid ratio, and ambient temperature); hence, at an industrial scale, energy and resource consumption and equipment dimensions can be together reduced, leading to a more industrially sustainable extraction process.

Given global coffee consumption, substantial quantities of spent coffee grounds (SCGs) are generated annually as a by-product of brewing coffee. SCG, although rich in bioactive compounds, is nowadays disposed of. The objective of this study is to compare, for the first time and from the same SCG, the efficiency of ethanol–water mixtures and acetone–water mixtures for the recovery of total polyphenols, chlorogenic acid, and caffeine. Acetone at 20% (m/m) was the most convenient solvent to extract all three bioactive compounds simultaneously, yielding 4.37 mg of GAE/g SCG for total polyphenols, chlorogenic acid (0.832 mg 5-CQA/g SCG), and caffeine (1.47 mg/g SCG). Additionally, this study aims to address some challenges associated with the industrial-scale utilization of SCG as a raw material, encompassing factors such as pre-treatment conditions (natural drying and oven drying), storage duration, and the kinetics of the extraction process. No significant difference was observed between the natural drying and oven drying of SCG. In terms of storage duration, it is advisable to process the SCG within less than 3–4 months of storage time. A significant decline of 82% and 70% in chlorogenic acid (5-CQA) and caffeine contents, respectively, was observed after eight months of storage. Furthermore, the kinetic study for the recovery of total polyphenols revealed that the optimal extraction times were 10 min for acetone at 20% and 40 min for water, with a yield increase of 28% and 34%, respectively. What is remarkable from the present study is the approach considered, using the simplest operating conditions (minimal time and solvent-to-solid ratio, and ambient temperature); hence, at an industrial scale, energy and resource consumption and equipment dimensions can be together reduced, leading to a more industrially sustainable extraction process.

Current food consumption patterns must be revised in order to improve their sustainability. The nutritional, environmental, and economic consequences of these dietary patterns must be taken into consideration when diet guidelines are proposed. This study applied a systematic optimization methodology to define sustainable dietary patterns complying with nutritional, environmental, and economic issues. The methodology was based on a multi-objective optimization model that considered a distance-to-target approach. Although the three simultaneous objectives (maximal nutritional contribution, minimal greenhouse gas emissions, and minimal costs) could be divergent, the proposed model identified the optimal intake of each food product to achieve the maximal level of nutritional, environmental, and economic diets. This model was applied to six different eating patterns within the Spanish context: one based on current food consumption and five alternative diets. The results revealed that dietary patterns with improved nutritional profiles and reduced environmental impacts could be defined without additional costs just by increasing the consumption of vegetables, fruits, and legumes, while reducing the intake of meat and fish.