Different dissolved oxygen tensions on bioethanol production by Scherffersomyces stipitis


The hardwood spent sulfite liquor (HSSL) is a by-product from acidic sulphite pulping of wood, which can be used to produce bioetanol. The HSSL is composed by both hexoses and pentoses, that must be converted to ethanol to ensure the economic viability of the process. Scherffersomyces stipitis is one of the most efficient yeasts to ferment xylose, which make it one of the best microorganisms to produce bioethanol from HSSL. However, S. stipitis is quite sensitive to the inhibitory compounds found in the HSSL. But, this drawback can be overcome using a strain of S. stipitis that resulted from an adaptation process to HSSL. Nevertheless, to obtain high ethanol productivity this yeast requires specific microaerophilic conditions Consequently, this work aimed to investigate in bioreactor the best dissolved oxygen tension (DOT) to the bioethanol production by S. stipitis adapted to HSSL. Both 50 and 5 % DOT values failed in the bioethanol production. However, the fermentation with two stages, first with a DOT value of 2.5 % and then with a DOT value below 1% allows the bioethanol production. With this strategy was possible a sugars conversion efficiency of 95% and a ethanol productivity of 0,10 g.L-1.h-1 in the second fermentation stage. This indicated that the oxygen limitation directed the matabolism from metabolic respirative and cell growth pathway to fermentative pathway. In conclusion, the adaptation of S. stipitis to HSSL and the aeration control perspective the success of bioethanol production from HSSL.


T. M. Henriques, S. R. Pereira, L. S. Serafim, and A. M. R. B. Xavier

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