Enhancement of very high gravity bioethanol production via fed-batch fermentation using sago hampas as a substrate

Very high gravity (VHG) ethanolic fermentation is a promising technology used for producing bioethanol. However, the technology is often associated with the excessive amount of glucose that is entirely supplied in the beginning of the culture causing the fermentation process to be sluggish and therefore inhibits complete utilisation of glucose. The high concentration of glucose in the fermentation medium also elevates the osmotic pressure, which has a destructive effect on yeast cells. This study aims to enhance the production of VHG bioethanol from sago hampas hydrolysate (SHH) via fed-batch fermentation. The fermentations were performed in a 2-L stirred tank bioreactor. Batch fermentation was conducted as a control. Our results showed that the maximum yeast cell concentration achieved was significantly improved by 1.5-fold when the fermentation was carried out in fed-batch mode. The ethanol yield attained in the fed-batch culture represents an enhancement of 22% over that achieved in the batch culture. Moreover, the ethanol productivity achieved in the fed-batch culture was found to be increased by 1.8 times in comparison to the productivity attained in the batch culture. In general, this work provides useful insights into promising techniques for enhancing VHG fermentations in the stirred tank bioreactor employing agricultural residues as feedstocks