Abstract
The aim of the present study was to compare bioethanol production from wet exploded corn stover (WECS) and loblolly pine (WELP) hydrolyzed with in-house and commercial enzymes and fermented separately (SHF) and simultaneously (SSF). In-house enzymes produced from Trichoderma reesei, RUT-C30 and a novel fungal strain, Aspergillus saccharolyticus were loaded as 5 and 15 FPU/g glucan and supplemented with 10 and 30 CBU/g glucan, respectively. For hydrolysis and fermentation, slurries of WECS and WELP at 5 and 10% (w/w) solids loading (SL) were utilized. Saccharomyces cerevisae was used for ethanol fermentation at 33°C. Maximally, 15.6 g/L and 13.4 g/L (corresponding to theoretical ethanol yield of 76% and 67%, respectively) were achieved in SSF process from WECS and WELP, respectively at 5% SL and 15 FPU/g glucan loading of in-house enzymes. Ethanol concentrations in all cases were higher for SSF compared to SHF under same conditions. A cross comparison of SSF with commercial enzymes (Celluclast 1.5 L + Novozym 188) showed highest ethanol concentration of 17.3 g/L and 15.4 g/L (corresponding to theoretical ethanol yield of 84% and 77%, respectively) from WECS and WELP, respectively at 5% SL and 15 FPU/g glucan. These findings demonstrated that in-house enzymes were comparable to commercial enzymes as these fungi produced other lignocellulolytic enzymes beyond cellulase and hence enhanced the overall enzyme activity.
Highlights
The cost and hydrolytic efficiency of lignocellulolytic enzymes are critical parameters in bioethanol production (Himmel et al 1999; Lynd et al 2005; Galbe and Zacchi 2002; Kovács et al 2009)
In this study, cellulolytic enzymes were produced inhouse using T. reesei Rut C30 and A. saccharolyticus to reduce the cost of enzymatic hydrolysis and still keep high hydrolysis efficiency
Our results showed that we had all the necessary cellulolytic activities by combining the two selected fungal species
Summary
The cost and hydrolytic efficiency of lignocellulolytic enzymes are critical parameters in bioethanol production (Himmel et al 1999; Lynd et al 2005; Galbe and Zacchi 2002; Kovács et al 2009). Hydrolysis of sugars followed by fermentation step is called separate hydrolysis and fermentation (SHF). As an alternative these hydrolysis and fermentation steps can be merged together in one process known as simultaneous saccharification and fermentation (SSF). In SSF, temperature is not optimal for cellulases and, the rate of hydrolysis is slow, but hydrolysis products can be consumed as they are formed due to fermentation, avoiding the inhibition seen with SHF (Ballesteros et al 2004; Olsson et al 2006). Ethanol in the fermentation broth prevents significant microbial contamination. Another advantage of SSF is that the process integration of hydrolysis and fermentation in one reactor reduces the overall capital cost
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