Light is the only key factor essential for plant growth, and ultraviolet (UV) rays, the harmful part of solar radiation, have the ability to decrease the metabolic rate in photosynthesis, causing deterioration in their growth. Accurate handling of the ultraviolet light that reaches the crops allows the improvement of different aspects of production, such as the shape and color of the plants, the precocity of the crops, and an improvement in the control of pests and diseases. The present study was carried out with the purpose of studying the responses in terms of germination and growth of four plant species—Glycine max, Triticum aestivum, Helianthus annuus, and Pinus maximartinezii—exposed to different doses of UV-C and UV-B radiation, for evaluation through the standard germination and accelerated aging tests, registering the germination rate (GR) and vigor (V), the number of normal seedlings (NS), and the average lengths of radicle (ALR) and plumule (ALP). Seeds treated with UV-C radiation showed a significant difference (p <0.05) between treatments (doses) and species, both in the standard germination and accelerated aging tests for the ALR and ALP variables. Seeds of G. max showed low sensitivity in both tests, with the dose 43.20 kJ/m²/day. The seeds of H. annuus and P. maximartinezii showed high sensitivity in both tests under UV-C radiation, with the doses 8.64 kJ/m²/day and 0.864 kJ/m²/day, respectively. Both tests under UV-B radiation showed a significant difference (p < 0.01) between species and treatments in the variables NS and ALP, with the minimum dose (T2).

Background: The need for energy sources with low greenhouse gas emissions and sustainable production encourages the search for alternative biomass sources. However, the use of biomass fuels faces the problem of storage, transport and lower energy densities. Low-density values can negatively affect energy density, leading to an increase in transportation and storage costs. Use of pellets as alternative biomass source is a way to reduce the volume of biomass by densification, which improves their energy quality. They are produced by diverse biomass resources and mainly from wood materials. In all cases, it is important to evaluate the fuel characteristics, to determine their suitability on the heating system and handling properties. Methods: The present study determines and compares data from proximate analysis, calorific values, physical and mechanical properties of wood pellets produced from the common tropical species Acacia wrightii, Ebenopsis ebano and Havardia pallens. Data were obtained from pellets produced from each species chips collected from an experimental plantation and analyzed through ANOVA and Kruskal–Wallis test at 0.05 significance level. Results: The results of diameter, length and length/diameter ratio didn’t show statistical differences (p > 0.05) among species. Acacia wrightii showed the highest density (1.2 g/cm³). Values on weight retained and compression test showed statistical differences (p = 0.05) among species. Havardia pallens was more resistant to compression strength than A. wrightii and Ebenopsis ebano. Statistical differences (p < 0.01) were also observed for the volatile matter and calorific value. E. ebano has the lowest volatile matter (72%), highest calorific value (19.6 MJ/kg) as well as the fixed carbon (21%). Discussion: The pellets of the species studied have a high energy density, which makes them suitable for both commercial and industrial heating applications.A pellet with low compression resistance tends to disintegrate easily, due to moisture adsorption. The percentages obtained for the resistance index were higher than 97.5%, showing that the pellets studied are high-quality biofuels. Proximate analysis values also indicate good combustion parameters. Pellets of Acacia wrightii and Ebenopsis ebano are the more favorable raw material sources for energy purposes because of their high density, calorific value, low ash content and they also met majority of the international quality parameters.

Particle size is a physical property that sometimes limits the quality of briquettes, so it is recommended to use different sizes in mixtures for their manufacture. The objective of this research was to evaluate the effect of different particle sizes of sawdust in mixtures on some physical, mechanical, and energetic properties of briquettes made from Pinus durangensis sawdust, as well as set the ranges within the appropriate values found to obtain desired values. Three particle sizes were established (large, medium, and small), and 10 mixtures were prepared using different percentages of each particle classification. The particle density, volumetric swelling, compressive strength, impact resistance index (IRI), and gross calorific value of the briquettes were evaluated. For the determination of optimal mixtures, the surface response methodology was used under a three-factor simplex-lattice model. The particle density values were in the range 0.92 to 1.02 g cm⁻³ and the volumetric swelling was 0.96 to 3.9%. The highest resistance to compression was 37.01 N mm⁻¹, and the IRI was found in the range of 53 to 107%. The gross calorific values were from 19.35 to 21.63 MJ kg⁻¹. The selection of different particle sizes for the mixtures increases the quality of the briquettes.

The current global energy crisis has generated growing interest in looking for alternatives to traditional fossil fuels, presenting lignocellulosic materials as a promising resource for sustainable energy production. In this paper, the calorific values and chemical composition of the trunks, branches, twigs and leaves of five timber species of the semi-arid land of Mexico (Helietta parvifolia (Gray) Benth., Ebenopsis ebano (Berl.) Barneby, Acacia berlandieri (Benth.), Havardia pallens (Benth.) Britton & Rose and Acacia wrightii (Benth.)) were determined according to international standards. The results highlighted the calorific value ranges of 17.56 to 18.61 MJ kg⁻¹ in trunks, 17.15 to 18.45 MJ kg⁻¹ in branches, 17.29 to 17.92 MJ kg⁻¹ in twigs, and 17.35to 19.36 MJ kg⁻¹ in leaves. The pH presented an acidic trend (3.95–5.64). The content of mineral elements varied in trunks (1.09%–2.29%), branches (0.86%–2.75%), twigs (4.26%–6.76%) and leaves (5.77%–11.79%), showing the higher proportion in Ca (57.03%–95.53%), followed by K (0.95%–19.21%) and Mg (0.88%–13.47%). The highest amount of extractives was obtained in the methanolic solvent (3.96%–17.03%). The lignin recorded values of 28.78%–35.84% for trunks, 17.14%–31.39% for branches and 20.61%–29.92% for twigs. Lignin showed a moderately strong correlation (r = 0.66) with calorific value, but the best mathematical model was registered with the calorific value depending on the pH and lignin (R² = 58.86%).

Pecan nut (Carya illinoensis) pericarp is usually considered as a waste, with no or low value applications. Its potential as a densified solid biofuel has been evaluated, searching for alternatives to generating quality renewable energy and reducing polluting emissions in the atmosphere, based on particle size, that is an important feedstock property. Therefore, agro-industrial residues from the pecan nut harvest were collected, milled and sieved to four different granulometry: 1.6 mm (N° 12), 0.84 mm (N° 20), 0.42 mm (N° 40), and 0.25 mm (N° 60), used as raw material for biofuel briquette production. The carbon and oxygen functional groups in the base material were investigated by Fourier transform infrared spectroscopy (FTIR) and proximate analyses were performed following international standards, for determining the moisture content, volatile materials, fixed carbon, ash content, and calorific value. For the biofuel briquettes made from base material of different particle sizes, the physical characteristics (density, hardness, swelling, and impact resistance index) and energy potential (calorific value) were determined to define their quality as a biofuel. The physical transformation of the pecan pericarp wastes into briquettes improved its quality as a solid biofuel, with calorific values from around 17.00 MJ/kg for the base material to around 18.00 MJ/kg for briquettes, regardless of particle size. Briquettes from sieve number 40 had the highest density (1.25 g/cm³). Briquettes from sieve number 60 (finest particles) presented the greater hardness (99.85). The greatest susceptibility to swelling (0.31) was registered for briquettes with the largest particle size (sieve number 20). The IRI was 200 for all treatments.

The need for biomass as an alternative source for energy purposes points toward oil palm fruit residues (Elaeis guineensis Jacq.) as an attractive solution. Oil palm industry residue, such as oil palm empty fruit bunch (EFB) composites and mesocarp fiber (PMF), have a high gross calorific value and could help countries meet their energy demands. However, information concerning physical, mechanical, and energy characteristics of agro-pellets made from mixtures of oil palm residue with pine sawdust, is not available. In this research, oil palm residues were mixed at ratios of 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 with pine sawdust, and were chemically analyzed. Agro-pellets from mixtures were tested on their physical and mechanical properties, and the relationship of these properties with the chemical composition of oil palm residue mixtures was determined. Normality distribution tests of the variables were performed using the Kolmogorov–Smirnov test. Normal variables were analyzed through one-way ANOVA tests. When differences were found, they were validated using the Tukey’s honestly significant difference (HSD) test and were considered statistically significant at p ≤ 0.05. Data not normally distributed were analyzed by the Kruskal–Wallis test. Bulk density, particle density, and gross calorific value of agro-pellets (from mixing 80:20 oil palm residues with pine sawdust) were statistically higher (p < 0.05) to agro-pellets of 100% oil palm residues. Adding pine sawdust to oil palm residues increases some mechanical agro-pellet properties. Addition of pine sawdust to oil palm residues acts to increase some mechanical properties of agro-pellets.