Bioethanol is the most commonly used biofuel. It is an alternative to replace fossil fuels in renewable energy; it can be produced from lignocellulosic feedstock using a biotechnological process. Their participation of microorganisms is crucial in the bioconversion process of fermentation for ethanol production and can involve bacteria, fungi, and yeasts. However, when working within bioethanol processes from lignocellulose feedstock, microorganisms face some challenges, such as high temperature, high solids content, and the ability to ferment sugars for high ethanol concentration. Such challenges will depend on operative strategies, such as simultaneous saccharification and fermentation, separate hydrolysis and fermentation, semi-simultaneous saccharification and fermentation, and consolidated bioprocessing; these are the most common configurations. This review presents different trends of the microbial role, biochemical application, and fermentation operative strategies for bioethanol production of the second generation.

Sweet sorghum bagasse (SSB) provides a raw material rich in polysaccharides that can be converted into biofuel and other high-value-added bioproducts under the biorefinery concept. The aim of this study was to evaluate the effect of hydrothermal pretreatment on the availability of SSB fermentable sugars for bioethanol production, considering the energy balance of the process. For this, the biomass was subjected to one process, pre-saccharification simultaneous and fermentation (PSSF). Previously, the temperature, time, and particle size effect were determined, as well as the enzymatic load for the more significant release of monomeric sugars. It was observed that the increase in the pretreatment severity, defined by the severity factor [log(R_o)], resulted in a more significant release of sugar and energy consumption. In the PSSF, bioethanol production was 22.17 g/L, with a total energy consumption of 2.46 MJ/g of processed biomass, of which 79.14% was by concept of electricity.

The proliferation of Sargassum biomass in various coastal areas has led to environmental and socio-economic problems. However, due to their unique composition, these biomasses offer versatile applications, prompting research into their potential in third-generation biorefineries. In this study, the hydrothermal processing of Sargassum sp. was evaluated under specific conditions at 190 °C/50 min and 150 °C/30 min. The resulting hydrolysates (liquid phase) were used as alternative culture media for cultivation. Nine treatments for the cultivation of Arthrospira platensis were assessed, varying the concentration of hydrothermal hydrolysates (HH) at 190 °C/50 min: T1 (5% v/v), T2 (10% v/v), and T3 (15% v/v). T4 (5% v/v), T5 (10% v/v), and T6 (15% v/v), maintaining the same HH conditions, and with the addition of 0.7 g/L NaNO₃; and treatments T7, T8, and T9 had concentrations of 5%, 10%, and 15% of HH, respectively, at 150 °C/30 min with the addition of 0.7 g/L NaNO₃, respectively. Each treatment was inoculated with 15% (v/v) of A. platensis. Growth kinetics were performed by sampling every three days for 24 days. Quantification of soluble proteins was performed for the best conditions of biomass production. The microalgae demonstrated the ability to grow under mixotrophic medium conditions and to utilize the available carbon sources in the culture medium. Treatment 4 has the highest biomass, with an Xmax (g/L) of 1.94 ± 0.06 and a protein production of 24.17 ± 0.86% (w/w). Therefore, this microalgal biomass can be used in the food matrix according to the biorefinery concept.

Micro-macro algal biomass contains important components such as pigments, carbohydrates, lipids and protein, and these aquatic biomasses are gaining wide attention as an alternative in the production of high added value compounds with specific properties for applications in the food, medical and energy industries according to the concept of biorefineries. These high added value compounds must be extracted from algal biomass using innovative extraction methods. Furthermore, the biorefinery concept requires processes that allow efficient utilization of all components of the biomass. The extraction step in a biorefinery is often based on microwave, or ultrasound. Therefore, in this chapter, a review on the main advances in the extraction processes of compounds from aquatic biomass is presented.