Anaerobic digestion is a well-established technology for the sustainable production of biogas. However, to be used as a substitute for natural gas or as vehicle fuel, it is necessary to remove carbon dioxide (CO₂) and other contaminants from biogas that can compromise the useful life of combustion engines. Upgraded biogas is known as biomethane (>95% methane content). This work reviews the different technologies used for upgrading biogas, emphasizing microalgae–nanoparticle systems, representing a more sustainable and environmentally friendly system. Parameters affecting these systems performance are discussed, and the trends and areas of opportunity for subsequent work are evaluated through a bibliometric analysis.

Ethanol production from corn and sugarcane is well established; however, reliance on these feedstocks raises concerns related to food security, highlighting the need to explore alternative raw materials such as cassava. This study evaluates bioethanol production from different cassava root fractions—peeled cassava, starch, and peel—assessed individually within a unified experimental framework. Chemical hydrolysis using HCl or H₂SO₄ was employed as a cost-effective alternative to enzymatic saccharification. Hydrolysis efficiencies above 95% were achieved for both cassava and starch, regardless of the acid used, although HCl promoted higher glucose release in all samples. Chemical hydrolysis induced noticeable increases in surface roughness and porosity across all fractions. Fermentation efficiencies for cassava (93.1 ± 1.1% vs. 77.8 ± 4.9%) and peel (85.7 ± 2.8% vs. 69.8 ± 7.4%) were higher when HCl was used during hydrolysis, whereas starch showed no significant differences between acids. In contrast, the highest ethanol yields on a dry raw material basis were obtained from cassava hydrolyzed with H₂SO₄ (up to 0.37 ± 0.002 g/g), corresponding to a 73% ethanol recovery efficiency. The highest volumetric ethanol production rates were achieved with HCl hydrolysates, reaching up to 1.85 g/L/h for peel-derived hydrolysates.