The production of biofuels (biogas, ethanol, methanol, biodiesel, and solid fuels, etc.), beginning with cocoa pod husk (CPH), is a way for obtaining a final product from the use of the principal waste product of the cocoa industry. However, there are limitations to the bioconversion of the material due to its structural components (cellulose, hemicellulose, and lignin). Currently, CPH pretreatment methods are considered a good approach towards the improvement of both the degradation process and the production of biogas or ethanol. The present document aims to set out the different methods for pretreating lignocellulosic material, which are: physical (grinding and extrusion, among others); chemical (acids and alkaline); thermochemical (pyrolysis); ionic liquid (salts); and biological (microorganism) to improve biofuel production. The use of CPH as a substrate in bioconversion processes is a viable and promising option, despite the limitations of each pretreatment method.

In this work, we report a green synthesis of zinc oxide (ZnO) nanoparticles using aqueous and ethanolic extracts of Tradescantia spathacea (purple maguey) as bioreducing and stabilizing agents, which are plant extracts not previously employed for metal oxide nanoparticle synthesis. This method provides an efficient, eco-friendly, and reproducible route to obtain ZnO nanoparticles, while minimizing environmental impact compared to conventional chemical approaches. The extracts were prepared following a standardized protocol, and their phytochemical profiles, including total phenolics, flavonoids, and antioxidant capacity, were quantified via UV-Vis spectroscopy to confirm their reducing potential. ZnO nanoparticles were synthesized using zinc acetate dihydrate as a precursor, with variations in pH and precursor concentration in both aqueous and ethanolic media. UV-Vis spectroscopy confirmed nanoparticle formation, while X-ray diffraction (XRD) revealed a hexagonal wurtzite structure with preferential (101) orientation and lattice parameters a = b = 3.244 Å, c = 5.197 Å. Scanning electron microscopy (SEM) showed agglomerated morphologies, and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of phytochemicals such as quercetin, kaempferol, saponins, and terpenes, along with Zn–O bonding, indicating surface functionalization. Zeta potential measurements showed improved dispersion under alkaline conditions, particularly with ethanolic extracts. This study presents a sustainable synthesis strategy with tunable parameters, highlighting the critical influence of precursor concentration and solvent environment on ZnO nanoparticle formation. Notably, aqueous extracts promote ZnO synthesis at low precursor concentrations, while alkaline conditions are essential when using ethanolic extracts. Compared to other green synthesis methods, this strategy offers control and reproducibility and employs a non-toxic, underexplored plant source rich in phytochemicals, potentially enhancing the crystallinity, surface functionality, and application potential of the resulting ZnO nanoparticles. These materials show promise for applications in photocatalysis, in antimicrobial coatings, in UV-blocking formulations, and as functional additives in optoelectronic and environmental remediation technologies.

Currently, residual frying oil has three purposes: it is used again in the preparation of fried foods, mixed with new vegetable oil, which can cause cardiovascular disease in the consumer; it is collected by government institutions, without having an exclusive use; or it is thrown into the drain, causing serious pollution problems to water resources. An alternative is to transform it into biodiesel, through transesterification with methanol, to be used in internal combustion engines, biodiesel-diesel mixtures of 10:90, 15:85 and 20:80 (v/v), according to international regulations in such a way that, in the combustion process, less CO₂ and greenhouse gas emissions are generated. Residual frying oil served as raw material, which was collected, mixed and homogenized to evaluate physicochemical properties before transformation. The biodiesel generated had a density of 0.886 g L⁻¹, an acidity of 0.516%, a viscosity of 7.535 mm² s⁻¹, a flash point of 166.8 °C and an oxidative stability of 49 days at 25 °C. Additionally, the content of functional groups characteristic of biodiesel formation was evaluated by Infrared Spectroscopy. The Biodiesel obtained is of good quality for use in internal combustion engines and agricultural machinery, thus validating its continuous production and complying with the standard values of international regulations.

Biofuels produced from waste biomass are the best alternative to fossil fuels; however, considering that bioethanol production occurs due to fermentation, the yield should be improved during this stage by incorporating microorganisms that can increase yields in the conversion of carbohydrates present in the residue to ethanol. Therefore, native yeasts were isolated and identified from natural fermentation of coffee cherries (Coffea arabica) from Chiapas, Mexico, and then, evaluated the yield of ethanol. First, a morphological study was conducted in which yeast-like microorganisms were isolated from plates with a YPDA culture medium, taking into account their texture, surface, margin, elevation, and color. In total, 15 isolates with macroscopic and microscopic characteristics typical of yeasts were obtained. Subsequently, biochemical tests were conducted to evaluate the fermentative capacity of the strains; simple sugars such as glucose, fructose, sucrose, lactose, and xylose were tested in a liquid medium composed of 0.3% yeast extract, 0.5% peptone, and 2% simple sugar. The mixture was incubated for 48 h at room temperature. The strains fermented with the aforementioned sugars were subjected to a qualitative iodoform test to confirm the presence of ethanol in the medium, identifying the best M2A and M2B strains with yields of 3.7 and 18 g/L, respectively. The M2A strain corresponded to Wikerhamomyces anomalus, and the M2B strain corresponded to Pichia kudriavzevii. To summarize, native yeasts represent a biological alternative to the production of bioethanol, which guarantees the conversion of the sugars present in the substrate to ethanol. Key words: Bioethanol; fermentation of coffee cherry; native yeasts; non-Saccharomyces; residue.

Introduction: The production of biogas by the anaerobic decomposition of biomass guarantees an efficient and safe reduction of environmental pollution resulting from treating organic wastes, positioning it as a promising technology for the future. The anaerobic digestion process carried out in this research project utilized pumpkin peel, tamarind peel, and corn cob leaves as substrates. Cow, sheep, and poultry fecal wastes were also analyzed as microbial inocula for biogas production. This research focused on evaluating the physical, chemical, and bromatological parameters of the aforementioned organic waste to determine the optimal parameters that define the stages of biogas production. This study is proposed because Mexico is the main generator of this waste, and lacks studies on its proper management. Methods: The anaerobic digestion experiments were carried out in batch biodigesters with a capacity of 1.8 L at 36 ± 2 °C for a retention time of 30 days, using the methods of the Mexican Standards for Environmental Protection for the determination of humidity, ash, pH, Total Volatile Solids (TVS), Total Solids (TS), chemical oxygen demand, carbon, and nitrogen. Results: Among the obtained results, the carbon/nitrogen ratio of the tamarind husk and corn cob leaves residues indicated a positive effect on biogas production in treatments mixtures 1 and 8, with values of 21.87 and 24.34, respectively, considered as values within the optimal range of 20:1 to 30:1, these values constitute the ideal availability of energy and nitrogen for cell replication of biogas producing methanogenic bacteria. These treatments were influenced by the Specific Methanogenic Activity (SMA) of the cattle manure inoculum, which had an organic matter biodegradability value of 0.58 grams of Chemical Oxygen Demand de Methane entre grams Total Volatile Solids for a day (COD-CH₄/g TVS/day). This value supports the efficient assimilation of the carbon/nitrogen ratio based on the mentioned values. On the other hand, determining the TVS/TS ratio yielded percentages of 60%, 92%, and 95% in pumpkin peel, tamarind husk, and corn cob husks, respectively. Discussion: Comparing the results with other studies, the optimal TVS/TS ratio should be greater than 50%; therefore, the results indicate that the substrates contain sufficient assimilable organic matter for anaerobic microorganisms and could produce biogas. Similarly, many scientific studies indicate that calculating the Specific Methanogenic Activity can not only determine the degree of biodegradability of substrates but also estimate possible pH changes in the medium, in addition to determining the maximum load of organic matter applied to any other type of anaerobic inoculum outside of this research work. Conclusion: Under these conditions, the treatments obtained a cumulative biogas yield of 3645 and 4250 milliliters of methane, respectively. This research contributes to improving the quality of biogas through the management of standardized waste.