Bioconversion of hemicellulosic fraction of wheat straw biomass to bioethanol by Scheffersomyces stipitis : A k L a-based scale-up study

The potent utilization of hemicellulosic fraction, which comprises one-third of carbohydrates in lignocellulosic biomass (LCB), is vital to strengthen the bioethanol production from it. Most studies on bioethanol production from LCB focused on cellulosic fraction only, or very low ethanol productivity is reported from hemicellulosic fraction. The present study investigated a process to convert the hemicellulosic fraction of wheat straw biomass to bioethanol effectively using Scheffersomyces stipitis. This work aimed to develop and demonstrate a systematic approach for scaling up the fermentation process, keeping the volumetric oxygen transfer coefficient (kLa) nearly constant in different scale bioreactors. It was found that 99.11 +/- 0.13% of synthetic xylose and 99.04 +/- 0.10% of lignocellulosic xylose were converted to bioethanol with a yield and productivity of 0.4706 +/- 0.0022 g/g and 1.5325 +/- 0.0020 g/Lh; 0.4290 +/- 0.0030 g/g and 0.7399 +/- 0.0043 g/Lh, respectively at an optimum kLa of 0.5776 (0.5735, 0.5817) min-1 and 0.6924 (0.6887, 0.6961) min-1, respectively in a 0.5 L bioreactor. After that, these optimum kLa were validated in 1 L and 5 L bioreactors. The successful kLa validation revealed that the hemicellulosic fraction of lignocellulosic biomass could also be well utilized for bioethanol production.