Variation of the Ethanol Yield During Very Rapid Batch Fermentation of Sugar-Cane Blackstrap Molasses

Abstract

During rapid ethanol fermentation (2-3 h) of sugar-cane blackstrap molasses, a significant increase in the ethanol yield was frequently observed as fermentation proceeded, eventually leading to yields higher than the theoretical value when the end of the process was approached. In order to explain the above facts, three assumptions were examined: 1. temporary ethanol accumulation within the yeast cells; 2. variation of the dry matter content and/or of the microorganism density during the fermentation; 3. transformation of sugars into undetectable extra-cellular fermentable compounds at the initial stages of the process. Based on the experimental results presented here, the third of the above assumptions seems to explain the observed increase in the ethanol yield

Candida shehatae and Saccharomyces cerevisiae work synergistically to improve ethanol fermentation from sugarcane bagasse and rice straw hydrolysate in immobilized cell bioreactor

“…4, ethanol yield at early stage of fermentation (24-48 h) went beyond the theoretical value (0.51 g/g) for both recycled batch and continuous ethanol. This phenomenon was in good agreement to previous study reporting that during early stage of ethanol fermentation of sugarcane molasses, a significant increase in the ethanol yield was frequently observed as fermentation proceeded, eventually leading to yields higher than the theoretical value [37]. Three assumptions of higher ethanol yield beyond the theoretical value were proposed from this study: (i) temporary ethanol accumulation within the yeast cells and also immobilizing carrier; (ii) variation of the microorganism density and/or the dry matter content during the fermentation; and (iii) transformation of sugars into undetectable extra-cellular fermentable compounds at the initial stages of the process and consecutive conversion of those undetectable fermentable compounds to ethanol at the final stage of fermentation.…”

Parameter oscillation attenuation and mechanism exploration for continuous VHG ethanol fermentation

“…These oscillations were characterized by long oscillation periods and large oscillation amplitudes. For example, the oscillation periods about 50 h for glucose, ethanol and biomass, and the oscillation amplitudes of 20-100 g L À1 for glucose and 50-90 g L À1 for ethanol were reported in the continuous ethanol fermentation with Z. mobilis (McLellan et al, 1999), while much longer oscillation periods of 160 h for sugar, ethanol, and biomass, and larger oscillation amplitudes of 10-70 g L À1 for sugar and 40-70 g L À1 for ethanol were observed in the continuous ethanol fermentation with S. cerevisiae (Borzani, 2001). Our recent studies further indicated that these oscillations negatively affected ethanol fermentation performance with increase in residual sugar and decrease in the ethanol yield which is calculated without the deduction of the residual sugar in the ethanol fermentation industry (Bai et al, 2008); therefore, these oscillations need be attenuated.…”

“…Sustainable parameter oscillations were observed for continuous ethanol fermentations with Zymononos mobilis (Bruce et al, 1991;Daugulis et al, 1997;Ghommidh et al, 1989;Jöbses et al, 1986;Jarzebski, 1992;Lee et al, 1979;McLellan et al, 1999), and Saccharomyces cerevisiae (Bai et al, 2004;Borzani, 2001). These oscillations were characterized by long oscillation periods and large oscillation amplitudes.…”

Influence of the accumulation of phosphate and magnesium ions in the yeast cells on the ethanol productivity in batch ethanol fermentation

“…Gravimetric methods (Cunniff, 1995) were used to measure the concentrations of phosphorus and magnesium in the aqueous phase and in the biomass. The biomass concentrations (dry matter) were measured as by Borzani and Jurkiewicz (1998). Table 1, presenting the results obtained in a typical test, show that both phosphorus and magnesium accumulated in the biomass: at t = 2 h, the phosphorus and magnesium contents of the biomass were, respectively, 145% and 75% higher than the corresponding initial values; at fermentation completion the above percentages were 117% and 65%, respectively.…”