Evaluating the Production of Second-Generation Ethanol by Spathaspora passalidarum Immobilized on Sugarcane Bagasse

Second-generation (2G) ethanol is obtained from the processing of lignocellulosic biomasses, such as sugarcane bagasse. However, several obstacles need to be overcome to make the industrial fermentation of the sugarcane bagasse hydrolysates viable, such as the time and capital expense of the process when compared with first-generation (1G) ethanol (produced by sugary and starchy raw materials), the inhibitors generated, and the process scaling-up. The intrinsic release of inhibitor compounds during the deconstruction of lignocellulosic material into sugars is one of the biggest challenges in the fermentation step. Cell immobilization can be used as a strategy to protect microorganisms from these inhibitory compounds. Immobilization can add costs to the process; therefore, the use of materials already available in the ethanol production is interesting from an economic point of view. In this sense, the objective of this study was to evaluate the immobilization of Spathaspora passalidarum in raw, alkaline, and acid-pretreated sugarcane bagasse. In addition, the fermentation of hemicellulosic hydrolysate (HH) from acid pretreatment of sugarcane bagasse was evaluated by immobilized and the free cells. Fermentation by S. passalidarum immobilized on sugarcane bagasse obtained growth and product yield factor of Y P/S (0.35 g/g) and Y X/S (0.43 g/g), respectively, against Y P/S (0.27 g/g) and Y X/S (0.086 g/g) for the cell-free assay. After 24 h of fermentation, it was possible to reach a productivity of 0.153 g/(L·h) and a yield of 68.37% with immobilized cells, which were also superior to the fermentation with free cells (0.148 g/(L·h) and 54%). Based on the results, it was possible to verify that sugarcane bagasse can be used not only as an effective source of carbon for the production of 2G ethanol, but also as a support for cell immobilization, increasing the productivity of the process.