Integrating starchy substrate into cellulosic ethanol production to boost ethanol titers and yields

Starchy grains as current major feedstocks for bioethanol production are competing with food supply; therefore, lignocellulosic biomass was pursued as an alternative feedstock for bioethanol production due to its high availability and low price. Commercial production of second-generation bioethanol from lignocellulosic biomass is still under development as significant challenges of low fermentation efficiency, low ethanol titers, high enzyme cost, and high water usage remain to be addressed. In this research, sugar-rich substrates such as starchy grains were integrated into cellulosic ethanol production, which could boost ethanol titers and ethanol yields. The substrates with various ratios of corn flour and hydrothermal treated corn stover (4:12; 8:8; 12:4; 12:12) were evaluated on the ethanol concentration and ethanol yield via simultaneous saccharification and fermentation. Ethanol concentration and ethanol yield decreased with increasing amounts of treated corn stover in the mixtures. The maximum ethanol concentration (68.7 g/L) was achieved at the corn flour and corn stover ratio of 12:12 using raw starch granular enzyme with the ethanol yield of 86.0%, whereas the maximum ethanol yield was obtained at the corn flour and corn stover ratio of 12:4 as it contained higher amounts of corn flour. All the ethanol concentrations from various mixtures of corn flour and corn stover were higher than 37.9 g/L from the control with 100% of treated corn stover (16%, w/v). Saccharification and fermentation processes were optimized to reduce energy cost and the optimized process was able to complete ethanol fermentation within 48 h.