Repeated-batch operation of surface-aerated fermentor for bioethanol production from the hydrolysate of seaweed Sargassum sagamianum.

In this study, we investigated the feasibility of sustainable long-term bioethanol production from the hydrolysate of a brown seaweed, Sargassum sagamianum. Because the hydrolysate was prepared as a liquid solution using a hightemperature liquefying system, a repeated-batch operation was utilized as the operational strategy for bioethanol production. Additionally, we used surface aeration to improve bioethanol production from the hydrolysate containing C5 monosaccharides such as xylose. In this study, the C5 monosaccharide-utilizable yeast strain Pichia stipitis was used for bioethanol production. Therefore, based on this repeated-batch flask culture, we designed a surface-aerated repeated-batch fermentor culture, in which the aeration was finely controlled at 100 ml/min and delivered into the headspace of a 2.5-l fermentor. When the medium was replaced every 48 h, bioethanol was continuously produced for 200 h under repeated-batch fermentor culture, where the level of bioethanol production was about 9~10 (g/l). Additionally, the bioethanol yield based on the reducing sugar was about 0.386, which was the average value throughout four consecutive cultures and was about 74.5% of the theoretical value. In addition, the bioethanol yield based on quantitative TLC analyses of glucose and xylose was about 0.431, which was the average value throughout four consecutive cultures and was about 84.3% of theoretical value. Consequently, throughout this repeated-batch operation, we demonstrated that it was actually feasible to produce bioethanol from the hydrolysate of seaweed S. sagamianum. In addition, the approach described here is a practical strategy for commercial bioethanol production from seaweed, particularly for finely controlling aeration through surface aeration.