Bioethanol Production from Dilute-acid Pre-treated Wheat Straw Liquor Hydrolysate by Genetically Engineered Saccharomyces cerevisiae

Abstract

Sustainable recycling of lignocellulosic biomass includes utilization of all carbohydrates present in its hydrolysates. Since wheat straw is a xylose-rich raw material, utilization of xylose from obtained liquid part (liquor) of hydrolysates improves overall bioprocess efficiency. In this work, dilute acid pre-treatment of wheat straw was performed in high-pressure reactor at different temperatures (160 °C – 200 °C), residence times (1 min – 10 min), and acids (H2SO4 and H3PO4) concentrations. During dilute acid pre- treatment, hemicellulose is degraded to pentose sugars that cannot be used by industrial ethanol- producing yeasts. Therefore, genetically engineered Saccharomyces cerevisiae strain that can utilize xylose was used. Fermentations were performed on different xylose-rich liquor wheat straw hydrolysates in shake-flasks and in horizontal rotating tubular bioreactor. The efficiency of fermentations carried out in shake flasks using xylose- rich liquor wheat straw hydrolysates were in the range of 19.61 – 74.51 %. However, the maximum bioprocess efficiency (88.24 %) was observed during fermentation in the HRTB on the liquor wheat straw hydrolysate obtained by pre- treatment with 2 % w/w phosphoric acid.