Abstract
The immobilization of S. passalidarum in calcium alginate beads for second-generation ethanol production (2G ethanol) was evaluated in a medium that simulated a hemicellulosic hydrolysate of sugarcane bagasse pretreated with diluted sulfuric acid in terms of sugar composition. Three sets of sequential batch fermentations (SBF) were carried out with free cells or immobilized cells in high (HSC) and moderate (MSC) initial sugar concentration (120 and 70 g/L, respectively). SBF were characterized by five consecutive batches performed in shaker, at 30 °C and 110 rpm. Better results were observed for the SBF with immobilized cells in MSC medium when compared to HSC (Y’P/S of 0.27 ± 0.02 and 0.19 ± 0.03 g/g, respectively), in the second batch cycle. The value for YP/S in MSC was similar to the obtained with free cells (0.30 ± 0.02 to 0.33 ± 0.02 g/g). However, QP was lower for MSC with immobilized cells, reaching 0.81 ± 0.04 g/L.h in the second batch, while for free cells the QP varied from 1.06 ± 0.02 to 1.16 ± 0.22 g/L.h. A technique for determining the concentration of immobilized cells in the alginate beads was applied, which made it possible to determine the specific rates for the SBF performed. According to the results obtained, it was possible to demonstrate that S. passalidarum can be immobilized in calcium alginate and reused through SBF, with performance similar to free cells, which can be a good strategy for fermentation of hemicellulosic hydrolysates.
Highlights
In the last decades, the use of renewable energy sources has been given emphasis, considering the environmental problems related to the exploration and use of fossil fuels, in addition to the uncertainties and volatilities in the price of oil and the restriction factors in the emissions of carbon dioxide
According to the results obtained, it was possible to demonstrate that S. passalidarum can be immobilized in calcium alginate and reuse through sequential batch fermentations (SBF), with performance similar to free cells, which can be a good strategy for fermentation of hemicellulosic hydrolysates
The cell concentration for the immobilized cells is presented as total cells in the fermentations, which corresponds to the sum of the immobilized cells inside the calcium alginate beads and the cells suspended in the medium
Summary
The use of renewable energy sources has been given emphasis, considering the environmental problems related to the exploration and use of fossil fuels, in addition to the uncertainties and volatilities in the price of oil and the restriction factors in the emissions of carbon dioxide. Pre-treatment can result in the formation of toxic compounds such as acetic acid, furfural, hydroxymethylfurfural and phenolic compounds, which are inhibitors for fermentation [2, 4, 5] These compounds act in different ways in cell metabolism by decreasing the energy for multiplication and production, causing interference in enzyme activity, damaging the cell membrane and resulting in the death of microorganisms [6,7,8,9]
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