Ethanol production from sweet sorghum juice under very high gravity conditions: Batch, repeated-batch and scale up fermentation

Abstract

Batch ethanol fermentations from sweet sorghum juice by Saccharomyces cerevisiae NP 01 were carried out in a 500 ml air-locked Erlenmeyer flask under very high gravity (VHG) and static conditions. The maximum ethanol production efficiency was obtained when 9 g l -1 of yeast extract was supplemented to the juice. The ethanol concentration (P), productivity (Qp) and yield (Yp/s) were 120.24 ± 1.35 g l -1, 3.01 ± 0.08 g l -1 h -1 and 0.49 ± 0.01, respectively. Scale up ethanol fermentation in a 5-litre bioreactor at an agitation rate of 100 rev min -1 revealed that P, Qp and Yp/s were 139.51 ± 0.11 g l -1 , 3.49 ± 0.00 g l -1 h -1 and 0.49 ± 0.01, respectively, whereas lower P (119.53 ± 0.20 g l -1 ) and Qp (2.13 ± 0.01 g l -1 h -1 ) were obtained in a 50-litre bioreactor. In the repeated-batch fermentation in the 5-litre bioreactor with fill and drain volume of 50% of the working volume, lower P and Qp were observed in the subsequent batches. P in batch 2 to 8 ranged from 103.37 ± 0.28 to 109.53 ± 1.06 g l -1.

Dried Spent Yeast and Its Hydrolysate as Nitrogen Supplements for Single Batch and Repeated-Batch Ethanol Fermentation from Sweet Sorghum Juice

“…Lower ethanol concentration and productivity in batches 2 to 20 might be due to lower yeast cell concentrations in the fermentation broth compared with those in the first batch. These results were similar to those of Ariyajarearnwong et al [21], Chen et al [36] and Nuangpeng et al [28]. They demonstrated that the initial cell concentration affected ethanol concentration and productivity in repeated-batch fermentation using free yeast cells.…”

“…Then, they were mixed thoroughly to obtain the final total sugar concentration of 280 g·L of yeast extract [8,28] were also prepared as the control treatments. For repeated-batch ethanol fermentation, the concentrated juice was diluted with distilled water to the desired total sugar concentration and used as the EP medium.…”

“…Since our previous studies showed that the ethanol concentrations under 3 and 6 g·L −1 of yeast extract supplementation were lower than that of 9 g·L −1 [28], ethanol fermentation from the juice with and without yeast extract (9 g·L −1 ) supplementation was used as control treatments [8,28]. In addition, repeated-batch ethanol fermentation using the "fill and drain" technique under the optimum nutrient supplementation conditions was also investigated.…”

Optimization of Agitation and Aeration for Very High Gravity Ethanol Fermentation from Sweet Sorghum Juice by Saccharomyces cerevisiae Using an Orthogonal Array Design

“…It is found to have protective effects either on growth and fermentation or cell viability, which stimulate the fermentation rate and ethanol production [12,23]. Laopaiboon et al [23] and Nuanpeng et al [24] showed that 9 g L −1 of yeast extract promoted batch ethanol production from sweet sorghum juice containing 280 g L −1 of total sugar and sugar utilization was almost complete under the agitation rate of 100 rpm without aeration. However, a very high initial yeast cell concentration (1 × 10 8 cells mL −1 ) was required.…”

Sorghum as a Multifunctional Crop for the Production of Fuel Ethanol: Current Status and Future Trends

“…Besides sugar and nitrogen content, fermentation performance of sweet sorghum juice can also be affected with processing parameters and bioreactor configuration. Nuanpeng et al (2011) observed in a repeated-batch study that very high gravity (VHG) fermentation is a good alternative to produce high ethanol concentrations from sweet sorghum juice when an adequate level of yeast cell concentration, nitrogen, and agitation are used. On the other hand, Laopaiboon et al (2007) reported better results in fed-batch fermentation compared to batch configuration, in terms of ethanol concentration and product yield but not in productivity (measured as grams of ethanol generated/L/hr).…”