Aline Perin Dresch

Strong mineral acids such as sulfuric acid are still mainly used to break down carbohydrates in processes that prepare plant-based waste for further use. However, researchers are increasingly studying the use of organic acids as alternatives. This study aimed to obtain organic compounds by fermenting a hemicellulosic extract rich in simple sugars from the organic acid pretreatment of brewer’ spent grain. Hydrolysis tests using 4.5% oxalic acid for 24 minutes at 125.6°C dissolved over 99% of the hemicellulose, producing 14.9 g/L of xylose and 4.9 g/L of glucose. The production of inhibitory compounds was relatively low (0.05 g/L and 0.12 g/L of 5-hydroxymethylfurfural and furfural, respectively), which is beneficial for the yeast’s performance during the next step. The extract was then fermented by three strains of Saccharomyces cerevisiae : one industrial strain (PE-2) and two genetically modified strains (MP-P5 and JDY-01). Despite the hydrolysate containing around 45 g/L of oxalic acid, which significantly inhibited yeast activity in producing ethanol, for example, the three strains still produced several important volatile organic compounds, including 2-phenylethanol, known for its antimicrobial properties, and 4-hydroxy-2-methylacetophenone, a phenolic compound with antioxidant and antiseptic properties.

Planting conditions and harvest timing significantly influence the morphological composition and quality of elephant grass. The objective of this study was to evaluate the dry matter production and compositional changes of elephant grass in terms of ash, extractives, protein, lignin, cellulose, and hemicellulose contents at different growth stages (60 days, 90 days, 120 days, and 60 days regrowth) to recommend ideal harvest periods for specific applications. During the experimental period, favorable climatic conditions prevailed, with temperatures ranging from 17.3 °C to 32.2 °C and cumulative precipitation totaling 1,178 mm. Ash content decreased from 7.2% at 60 days to 4.8% at 120 days, while lignin content increased significantly from 16.9% to 32.7%, reflecting structural changes with plant maturity. Based on these findings, shorter harvest intervals (e.g., 60 days or 60-day regrowth) are recommended for energy generation and forage production due to the lower ash content and higher biodegradability. In contrast, longer growth periods (e.g., 90-120 days) are preferable for applications requiring higher cellulose, hemicellulose, and lignin fractions in lignocellulosic biorefineries.

Waste treatment and valorization have become crucial for sustainable development towards a circular economy. As an alternative, biochar production is a promising process to convert wastes into a valuable product that presents several potential applications to cope with environmental problems. Biochar in recent years has been the subject of many studies, which have leveraged the number of patents and the industrial interest in this process. Against this background, this overview aimed: (i) to identify the advances in biochar research; (ii) to assess the number of patents on biochar over the years; (iii) to look at the industrial production of biochar worldwide; (iv) to detect the potential for biochar production in Brazil regarding waste biomass availability; and (v) to discuss the potential of biochar in contributing to reach some Sustainable Development Goals (SDGs). The holistic analysis presented here suggests that progress has been made in research, patent development, and industrial implementation of biochar, and that its potential role in achieving certain SDGs is noteworthy. Therefore, this overview can be useful in guiding future research about biochar to improve the knowledge of the different branches in this field.

It is mandatory to make the circular economy a reality, developing ways of transforming waste into valuable products. In this context, investigating the biotechnological potential of different residues is most welcome. This review analyzes how orange waste can be used as biorefinery feedstock to produce different bioproducts using yeasts as the major biocatalysts. In addition to the current orange market, its pectin-rich biomass is described in detail, aiming to elucidate how yeast cells can convert it into ethanol, xylitol, polyphenols, and organic acids (some of them, volatile compounds). Genetic, metabolic, and evolutionary engineering are also analyzed as biotechnological tools to improve the existing processes. Finally, this review also addresses the potential employment of fruit-dwelling yeasts in biorefining pectin-rich biomasses such as orange wastes. All the data presented herein lead to the conclusion that these residues could already be used for noble purposes.