Nonisothermal Simultaneous Saccharification and Fermentation for Direct Conversion of Lignocellulosic Biomass to Ethanol

Abstract

The enzymatic reaction in the simultaneous saccharification and fermentation (SSF) is operated at a temperature much lower than its optimum level. This forces the enzyme activity to be far below its potential, consequently raising the enzyme requirement. To alleviate this problem, a nonisothermal simultaneous saccharification and fermentation process (NSSF) was investigated. The NSSF is devised so that saccharification and fermentation occur simultaneously, yet in two separate reactors that are maintained at different temperatures. Lignocellulosic biomass is retained inside a column reactor and hydrolyzed at the optimum temperature for the enzymatic reaction (50°C). The effluent from the column reactor is recirculated through a fermenter, which runs at its optimum temperature (20–30°C). The cellulase enzyme activity is increased by a factor of 2–3 when the hydrolysis temperature is raised from 30 to 50°C The NSSF process has improved the enzymatic reaction in the SSF to the extent that it reduces the overall enzyme requirement by 30–40%. The effect of temperature on β-glucosidase activity was the most significant among the individual cellulase compounds. Both ethanol yield and productivity in the NSSF are substantially higher than those in the SSF at the enzyme loading of 5 IFPU/g glucan. With 10 IFPU/g glucan, improvement in productivity was more discernible for the NSSF. The terminal yield attainable in 4 d with the SSF was reachable in 40 h with the NSSF.

Author to whom all correspondence and reprint requests should be addressed. E-mail: yylee@eng.auburn.edu