BIOETHANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS HYDROLYSATE BY CO-FERMENTATION

Abstract

Kans grass biomass is one of the most promising lignocellulosic biomass available throughout the year in large quantities. Kans grass biomass have up to 60% fermentable sugars in the form of glucose and xylose entrapped as cellulose (glucose polymer) and hemi-cellulose (xylose polymer). These sugars can be extracted from Kans grass biomass by acid hydrolysis process in the form of glucose rich fraction and xylose rich fraction. Zymomonas mobilis (bacteria) is used for glucose fermentation whereas Pichia stipitis (yeast) was used for xylose fermentation. However, the concentration of glucose and xylose obtained in hydrolysate by acid hydrolysis process can vary which in turn effects the fermentation process. So, the effect of initial glucose and xylose concentration on growth pattern and ethanol productivity of Zymomonas mobilis and Pichia stipitis, respectively, was studied using synthetic sugars at flask level. The microorganisms were grown to determined optimum as well as inhibitory concentration of sugars and kinetic parameters were determined. The optimum glucose and xylose concentration was found to be 160 g/L and 60 g/L for Zymomonas mobilis and Pichia stipitis, respectively. 100 g/L glucose resulted into maximum ethanol productivity of 2.06 g/L/h after 24 h of fermentation with maximum ethanol production of 49.63 g/L while 60 g/L xylose resulted into maximum ethanol productivity of 2.06 g/L/h after 24 h of fermentation with maximum ethanol production of 49.63 g/L. Inhibitory glucose concentration for Zymomonas mobilis was 400 g/L and for Pichia stipitis, it was 100 g/L xylose. At these sugar concentrations, either the growth of microorganisms slows down or arrested. The studies were also tried on bioreactor to verify the scalability of processes and its suitability for lignocellulosic biomass hydrolysate.