Maximising Bioethanol Production from Banana Stem Hydrolysate

In recent years, various initiatives have been made to use low-cost renewable agricultural resources for biofuel production. Amongst these, banana waste has emerged as an alternative substrate for bioethanol production due to its abundance and rich carbohydrate content. This study explores the fermentable sugars in banana stem hydrolysate (BSH), which were utilised for bioethanol fermentation by Saccharomyces cerevisiae. The work was divided into preliminary investigations of BSH as a fermentation medium, optimisation of nitrogen sources used in bioethanol fermentation using BSH-based media, and scale-up of bioethanol fermentation from shake flasks to a 2 L bioreactor. Initially, BSH was prepared based on our novel 4-cycle enzymatic hydrolysis. Our results showed that the ethanol yield obtained using banana hydrolysate was 0.152, which was 1.43 folds higher than the ethanol yield produced using commercial glucose (0.106 g/g). Among the four nitrogen sources investigated (yeast extract, ammonium sulphate, urea, and peptone) 3 g/L yeast extract was found to result in the highest ethanol yield, which was 3.27 folds higher than that of the fermentation without the supplementation of nitrogen source. Scaling up the fermentation process from a shake flask to a 2 L bioreactor resulted in a specific growth rate, while maintaining a comparable bioethanol yield. In summary, this study proposes a novel approach to valorising bioethanol production from banana stems, suggesting that this technique could also be applied for bioproductions employing other types of agricultural waste.