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.

Due to its unique physicochemical properties, Pullulan is an exopolysaccharide with many applications in the food, biomedical, and pharmaceutical industries. Aiming to reduce its production cost, an interesting alternative is to consider other possibilities of raw materials, including the production of this biopolymer in a lignocellulosic biorefinery concept. Xylose is the main sugar of hemicellulosic hydrolysates obtained from different biomasses, and it is a sugar still not extensively exploited regarding its potential for pullulan production. This study aimed to evaluate the production of pullulan from sugarcane bagasse hemicellulosic hydrolysate by cultivating Aureobasidium pullulans ATCC 42023 in a bubble column reactor. The hemicellulosic hydrolysate was obtained through dilute acid treatment carried out in a stirred tank reactor before being detoxified to remove microbial growth inhibitors. The maximum concentration of 28.62 ± 1.43 g/L of pullulan was obtained after 120 h of fermentation in a bubble column reactor in batch mode. Analysis of spectroscopic properties through FTIR of the obtained pullulan revealed α-(1→6)-linked maltosyl units, similar to those of commercial samples of the biopolymer. XRD analysis showed that the prepared pullulan is amorphous, and a homogeneous morphology with a smooth surface of the pullulan was observed in SEM analysis. This study showed the potential of the production of pullulan from sugarcane bagasse hemicellulosic hydrolysate in a bubble column bioreactor, an alternative strategy for the industrial production of this biopolymer.

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.