One of the greatest challenges facing society in the 21st century is to reconcile the growing energy demand for industrial and transport needs with sustainability. The ethanol fuel, which can be obtained from different raw materials by biotechnological processes, has been considered as a possible alternative to petroleum based fuels. Among the materials that can be used for ethanol production, the lignocellulosic biomass should be highlighted, especially agro-industrial residues. Rice straw is one of the most abundant lignocellulosic residues of agricultural activity in the world, each kilogram of harvested cereal is accompanied by the production of 1 to 1.5 kg of straw. Due to their high content of cellulose and hemicellulose, which can be readily hydrolysed to fermentable sugars, this residue is a potential feedstock for fuel ethanol production of second generation. Enzymatic hydrolysis of the cellulose fraction is favored when the product (glucose) is removed from the medium, thereby decreasing the inhibition of cellulases. The simultaneous saccharification and fermentation (SSF), in which glucose released in the hydrolysis can be readily fermented to ethanol, reduces the enzyme inhibition and promote the productivity of the process. However, it should be employed efficiently fermentative microorganisms in the same temperature range of cellulases (45 to 50° C), which limits the use of conventional yeast such as Saccharomyces cerevisiae, which does not present thermotolerant features. From this context, and in order to contribute to the development of research of ethanol production by SSF, the present work intends to study this process strategy from rice straw under different pre-treatments, employing a thermotolerant yeast previously selected in our laboratories (Kluyveromyces marxianus NRRL Y-6860). With regard to pre-treatment, in addition to the methods widely studied in literature (acid and alkaline), is being proposed the employment of advanced oxidative processes (AOPs), which still not widely used in the literature. In the optimized pretreatment conditions, it will be used a non-conventional reactor, a vertical ball mill (VBM) with glass spheres, in order to combine a physical treatment of biomass with the step of simultaneous saccharification and fermentation. In this step, the SSF will be also evaluated in fed batch configuration, aiming to study the process in higher solid concentration. It is hoped that this reactor configuration will increase the cellulose accessibility to enzymatic hydrolysis, and, therefore, that the fermentative parameters will be improved. In exploratory tests performed with VBM reactor, using dilute-acid pretreated rice straw as substrate, the results showed a 25% increase in enzymatic hydrolysis yield when compared to the results obtained in shake flasks. These results indicate that the use of this reactor can contribute significantly to progress in this area.
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