The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.

By using pig pancreatic lipase (EC 3.1.1.3 or PPL) as a biocatalyst, covalently immobilized on amorphous AlPO 4 support, a new second generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a 2:1 molar ratio. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuels composition, has similar physicochemical properties as conventional biodiesel and also avoids the removal step of the by-product by washing of the biodiesel with water. Immobilization of PPL was achieved by covalent attachment of the ε-amino group of the lysine residues of PPL with the aldehyde groups of p-hydroxybenzaldehyde linked on a hybrid organic-inorganic functionalized AlPO 4 surface. With this procedure, the PPL biocatalyst was strongly fixed to the inorganic support surface (94.3%). Nevertheless, the efficiency of the immobilized enzyme was relatively lower compared to that of the free PPL, but it showed a remarkable stability as well as a great capacity of reutilization (25 reuses) without a significant loss of its initial OPEN ACCESSEnergies 2013, 6 3880 catalytic activity. Therefore, this enzymatic method allows the production of a biodiesel which integrates the glycerol, allows a more efficient fabrication method and minimizes the waste production as compared to the conventional alkali-catalyzed process.

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By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL), covalently immobilized on AlPO4/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.

The aim of this work is to analyze the effect of using diethyl ether (DEE) as an oxygenated additive of straight vegetable oils (SVOs) in triple blends with fossil diesel, to be used in current compression ignition (C.I.) engines, in order to implement the current process of replacing fossil fuels with others of a renewable nature. The use of DEE is considered taking into account the favorable properties for blending with SVO and fossil diesel, such as its very low kinematic viscosity, high oxygen content, low autoignition temperature, broad flammability limits (it works as a cold start aid for engines), and very low values of cloud and pour point. Therefore, DEE can be used as a solvent of vegetable oils to reduce the viscosity of the blends and to improve cold flow properties. Besides, DEE is considered renewable, since it can be easily obtained from bioethanol, which is produced from biomass through a dehydration process. The vegetable oils evaluated in the mixtures with DEE were castor oil, which is inedible, and sunflower oil, used as a standard reference for waste cooking oil. In order to meet European petrodiesel standard EN 590, a study of the more relevant rheological properties of biofuels obtained from the DEE/vegetable oil double blends has been performed. The incorporation of fossil diesel to these double blends gives rise to diesel/DEE/vegetable oil triple blends, which exhibited suitable rheological properties to be able to operate in conventional diesel engines. These blends have been tested in a conventional diesel engine, operating as an electricity generator. The efficiency, consumption and smoke emissions in the engine have been measured. The results reveal that a substitution of fossil diesel up to 40% by volume can be achieved, independently of the SVO employed. Moreover, a significant reduction in the emission levels of pollutants and better cold flow properties has been also obtained with all blends tested.