Second generation bioethanol production from Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hack

Saccharum (Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hack.), is a rapidly growing, wide ranging high-yield perennial, suitable for second generation bioethanol production. This study evaluated oxalic acid as a pretreatment for bioconversion. Overall sugar yields, sugar degradation products, enzymatic glucan hydrolysis and ethanol production were studied as effects of temperature (150-190 degrees C), reaction time (10-40 min) and oxalic acid concentration 2-8% (w/w). Time and temperature were combined into a single parameter, Severity Factor (SF) [Log(R(0))], and related to oxalic acid using a response surface methodology. Maximum total sugar yield was attained at a SF of 2.93 and 6.79% (w/w) oxalic acid, while maximum formation of sugar degradation products was observed at the highest SF (4.05) and 5% (w/w) oxalic acid. These were also the conditions for maximum simultaneous saccharification and fermentation (SSF) of the residual solids. Commercial cellulases and Saccharomyces cerevisiae attained 89.9% glucan conversion and 17.8 g/l ethanol. Pichia stipitis CBS 6054 fermented hemicellulosic hydrolysates from less severe conditions to ethanol with a yield of 0.35 (g(e)/g(s)). Maximal product yields were 69% of theoretical value and 90% of the SSF conversion efficiency for hydrolysate fermentation and SSF, respectively.