Bioconversion of sugarcane bagasse and dry spent yeast to ethanol through a sequential process consisting of solid-state fermentation, hydrolysis, and submerged fermentation

Sequential process of solid-state cultivation with fungal consortium and ethanol fermentation by Saccharomyces cerevisiae from sugarcane bagasse

Solid-state cultivation (SSC) is the microbial growth on solid supports, producing a nutrient-rich solution by cell enzymes that may be further used as a generic microbial medium. "Second-generation" ethanol is obtained by fermentation from mainly the acid hydrolysates of lignocellulosic wastes, generating several microbial growth inhibitors. Thus, this research aimed at evaluating the feasibility of ethanol fermentation from sugarcane bagasse hydrolysate after SSC with vinasse as the impregnating solution by a consortium of A. niger and T. reesei as opposed to the conventional method of acid hydrolysis. Fermentation of the hydrolysate from SSC leading to the yield of 0.40 g g^-1, i.e., about 78% of maximum stoichiometric indicating that the nonconventional process allowed the use of two by-products from sugarcane processing in addition to ethanol production from glucose release.

Potential Role of Sequential Solid-State and Submerged-Liquid Fermentations in a Circular Bioeconomy

An efficient processing of organic solid residues will be pivotal in the development of the circular bioeconomy. Due to their composition, such residues comprise a great biochemical conversion potential through fermentations. Generally, the carbohydrates and proteins present in the organic wastes cannot be directly metabolized by microorganisms. Thus, before fermentation, enzymes are used in a hydrolysis step to release digestible sugars and nitrogen. Although enzymes can be efficiently produced from organic solid residues in solid-state fermentations (SsF), challenges in the development and scale-up of SsF technologies, especially bioreactors, have hindered a wider application of such systems. Therefore, most of the commercial enzymes are produced in submerged-liquid fermentations (SmF) from expensive simple sugars. Instead of independently evaluating SsF and SmF, the review covers the option of combining them in a sequential process in which, enzymes are firstly produced in SsF and then used for hydrolysis, yielding a suitable medium for SmF. The article reviews experimental work that has demonstrated the feasibility of the process and underlines the benefits that such combination has. Finally, a discussion is included which highlights that, unlike typically perceived, SsF should not be considered a counterpart of SmF but, in contrast, the main advantages of each type of fermentation are accentuated in a synergistic sequential SsF-SmF.

Consequence analysis due to possible ethanol leaks in sugarcane biorefineries

This study simulated and evaluated the consequences of possible ethanol leaks in a hypothetical sugarcane biorefinery, considering climatic factors in the region of the State of São Paulo-BR. The Gaussian model was used to obtain the results of the hypothetical scenarios. From these values, an empirical mathematical model was established to describe the behavior of the system within the investigated experimental domain. The results obtained the modeling values of the hypothetical scenarios, the statistical treatment for the two responses-a range, slight damage (R1), and a range, high damage (R2), the joint analyses of variables R1 and R2, and the risk classification of catastrophic events. The consequence analysis allowed the calculation and plotting of graphs, such as the areas of thermal radiation range. Among the variables addressed in the study, the diameter of the leakage hole was the most noticeable in the range of thermal radiation. Therefore, it is relevant to make simulations to prevent hazardous material leakages by applying the exact characteristics of the plant to conduct the procedure.