Continuous ethanol production in a nonconventional five-stage system operating with yeast cell recycling at elevated temperatures

Abstract

Three ranges of increasing temperatures (35-43, 37-45, 39-47 degrees C) were sequentially applied to a five-stage system continuously operated with cell recycling so that differences of 2 degrees C (between one reactor to the next) and 8 degrees C (between the first reactor at the highest temperature and the fifth at the lowest temperature) were kept among the reactors for each temperature range. The entire system was fed through the first reactor. The lowest values of biomass and viability were obtained for reactor R(3) located in the middle of the system. The highest yield of biomass was obtained in the effluent when the system was operated at 35-43 degrees C. This nonconventional system was set up to simulate the local fluctuations in temperature and nutrient concentrations that occur in different regions of the medium in an industrial bioreactor for fuel ethanol production mainly in tropical climates. Minimized cell death and continuous sugar utilization were observed at temperatures normally considered too high for Saccharomyces cerevisiae fermentations.

Enrichment of a continuous culture of Saccharomyces cerevisiae with the yeast Issatchenkia orientalis in the production of ethanol at increasing temperatures

“…To study the eVects of increasing temperatures, a continuous fermentation system made up of Wve reactors linked in series was used [19]. This system was continuously fed (F feeding = 0.12 l h ¡1 = F out ) with sterilized sugar-cane syrup containing 15% diluted sugar-cane syrup at pH 4.5.…”

“…A total of 15 samples (three samples from each reactor) were collected from the Wve mini-reactors of the fermentation system [19] after 60 days of operation as described above. The samples were diluted and plated on YPD medium containing 0.035 g l ¡1 Rose Bengal and 0.192% (v/v) propionic acid to inhibit fungal proliferation as recommended by Booth [5].…”

“…Yeast cells showing morphological alterations were eventually observed during the operation of a continuous fermentation system used in the present work to produce ethanol at high temperatures [19]. In this case, it was deemed necessary to know whether the observed elongated cells resulted from morphological alterations of the cells of S. cerevisiae or from a slow proliferation of the other thermotolerant yeasts still remaining in the sugar-cane syrup due to an insuYcient sterilization.…”

Advanced Biorefineries for the Production of Fuel Ethanol

“…In the fermentation of molasses it is important to use a thermotolerant strain of Saccharomyces cerevisiae, since considerable heat is generated in the process. The maximal growth of S. cerevisiae is attained at 34-37 C, whilst at temperatures above 44 C the ethanol production is reduced and the residual sugar content is increased (Laluce et al, 2002). Notably, molasses is often contaminated by Leuconostoc mesenteroides, a bacterium that forms dextran chains from sucrose, thus necessitating treatment with dextranase (Jim enez, 2005).…”

RESEARCH PAPER Structural changes of corn starch during fuel ethanol production from corn flour

“…ambient temperature and acidity suitable for both processes, poses a serious problem. For most strains of distiller's yeast, the optimal growth temperature is 30-32EC, whereas in the SSF process, the temperature of the medium is 35-37EC, which is higher than the tolerance limit of distiller's yeast (Mensonides et al, 2002;Laluce et al, 2002).…”