The replacement of fossil-based products with renewable alternatives is today a major research topic. Biofuels, such as second-generation ethanol, offer a promising way to overcome dependence on fossil fuels. However, second-generation biorefineries still face bottlenecks that hinder their economic sustainability. These include challenges in pretreatment (formation of inhibitors and high costs of chemicals) and hydrolysis (high enzyme costs and low solid content) and maximizing the utilization of biomass components. To achieve economic sustainability, biorefineries can adopt approaches such as integrating first and second generation (1G and 2G) technologies, using different production alternatives, or diversifying the product portfolio. This last alternative could include the simultaneous production of biomaterials, building blocks, and others from all fractions of the materials, favoring biorefinery profitability. Techno-economic assessment plays a crucial role in assessing the economic feasibility of these approaches and provides important information about the process. This article discusses how product diversification in cellulosic biorefineries enhances their economic sustainability, based on simulation techniques and techno-economic analysis, with a comprehensive and critical review of current possibilities and future trends. The information discussed can inform stakeholders about investing in 2G ethanol biorefineries, including strategies, associated risks, and profitability, allowing better planning of different options of future ventures.

Corncobs are a plentiful lignocellulosic material that can be utilized for energy production as well as the generation of other high-value products. Within the modern concept of biorefineries, we present processes conducted in a column reactor for the valorization of corncobs as a substrate for ethanol and xylitol production. In the first step, corncobs were subjected to acid hydrolysis, resulting in a hemicellulosic hydrolysate rich in xylose sugars intended for xylitol production by Candida tropicalis UFMGBX12-a. The Y_P/S (yield coefficient of product to substrate) and Q_P (productivity) values were approximately 0.2 g/g and 0.15 g/L·h, respectively, for the assays conducted in the column reactor. Next, the remaining solid portion of cellulignin was used for ethanol production through semi-simultaneous saccharification and fermentation process by Scheffersomyces parashehatae UFMG-HM 52.2. This approach involved an intensified successive process consisting of alkaline pretreatment of cellulignin, followed by enzymatic hydrolysis and fermentative processes conducted in the same reactor without biomass transfer. After obtaining the enzymatic hydrolysate, a Q_P value of 0.4 g/L·h for ethanol production was observed in the fermentation process conducted in the column reactor. The results demonstrate the potential of corncobs as a carbon source for biomolecules production, utilizing a process conducive to scale-up.

This study evaluated innovative approaches for the enzymatic hydrolysis of lignocellulosic biomass. More specifically, assays were performed to evaluate the supplementation of the commercial cellulolytic cocktail Cellic^® CTec2 (CC2) with LPMO (GcLPMO9B), H₂O₂, or cello-oligosaccharide dehydrogenase (CelDH) FgCelDH7C in order to boost the LPMO action and improve the saccharification efficiency of biomass into monosaccharides. The enzymatic hydrolysis was carried out using sugarcane bagasse pretreated by hydrodynamic cavitation-assisted oxidative process, 10% (w/w) solid loading, and 30 FPU CC2/g dry biomass. The results were compared in terms of sugars release and revealed an important influence of the supplementations at the initial 6 h of hydrolysis. While the addition of CelDH led to a steady increase in glucose production to reach 101.1 mg of glucose/g DM, accounting for the highest value achieved after 72 h of hydrolysis, boosting the LPMOs activity by the supplementation of pure LPMOs or the LPMO co-substrate H₂O₂ were also effective to improve the cellulose conversion, increasing the initial reaction rate of the hydrolysis. These results revealed that LPMOs play an important role on enzymatic hydrolysis of cellulose and boosting their action can help to improve the reaction rate and increase the hydrolysis yield. LPMOs-CelDH oxidative pairs represent a novel potent combination for use in the enzymatic hydrolysis of lignocellulose biomass. Finally, the strategies presented in this study are promising approaches for application in lignocellulosic biorefineries, especially using sugarcane bagasse as a feedstock.

This study explored innovative approaches to produce ethanol and xylitol from sugarcane bagasse using a hydrodynamic cavitation-assisted photo-Fenton process as the pretreatment, and yeast co-culture for hydrolysate fermentation. Pretreatment conditions were optimized (20 mg/L of iron sulfate, pH 5.0, and reaction time of 14 min) resulting in glucan and xylan hydrolysis yields of 96% and 89%, respectively. The hydrolysate produced under these conditions was fermented using a co-culture of Saccharomyces cerevisiae IR2 (an ethanol-producing strain) and Candida tropicalis UFMGBX12 (a xylitol-producing strain). Optimal co-culture conditions consisted of using an inoculum concentration of 1.5 g/L for each yeast strain. After 36 h of fermentation, ethanol and xylitol concentrations reached 20 g/L and 13 g/L, respectively. These results demonstrate the potential of combining hydrodynamic cavitation-assisted photo-Fenton pretreatment with co-culture fermentation to simultaneously produce ethanol and xylitol. This strategy presents a promising approach for enhancing the efficiency of lignocellulosic biorefineries.

The rising demand for renewable and sustainable oleochemicals underscores the necessity of producing yeast oil from lignocellulosic hydrolysates. We isolated two oleaginous yeast strains of Candida maltosa (UFV-1 and UFV-2) able to assimilate xylose and tolerate hemicellulosic hydrolysate inhibitors (acetic acid, furfural, hydroxymethylfurfural and formic acid). To optimize growth and lipid production by C. maltosa in malt bagasse hemicellulosic hydrolysate, we applied a central composite rotational design with response surface methodology, evaluating initial pH and yeast extract:peptone ratio (P:YE). The maximum lipid responses were recorded in: (P:YE = 1.0:0.0 g/L, pH = 6.0) for UFV-1 and (P:YE = 0.58:0.42 g/L, pH = 6.5) for UFV-2. Biomass and lipid production were higher in the detoxified hydrolysate than in the non-detoxified hydrolysate. Biomass titers increased from 9.12 to 17.0 g/L and from 10.5 to 12.9 g/L for UFV-1 and UFV-2, respectively; whilst the lipid titers increased from 0.84 to 3.14 g/L and 0.91 to 1.58 g/L for UFV-1 and UFV-2, respectively. Importantly, the levels of 16:0, 18:0, 10:0 fatty acids increased in the detoxified medium. Cultivation of the UFV-1 strain from detoxified hydrolysate in a benchtop bioreactor improved biomass formation, achieving a lipid productivity of 0.29 ± 0.02 g/L h, highlighting its potential to produce oil from hemicellulosic hydrolysates in biorefineries. Graphic abstract