Comparison of different detoxification methods for steam-exploded poplar wood as a substrate for the bioproduction of ethanol in SHF and SSF

Abstract

Different methods of detoxification were investigated for overcoming the toxicity problem in ethanol fermentation of steam-exploded (SE) poplar wood. The adopted severity parameter for biomass pretreatment was log R 0=4.13. Biomass detoxification procedures include: calcium hydroxide overliming, water rinsing, water–ethyl acetate two-phase contacting and in situ detoxification with high level yeast inocula. The detoxified substrates (100 g DW/l) were hydrolysed with a blend of Novozym ® and Celluclast ® cellulase (0.06 g/g DW). The glucose hydrolysate was bioconverted to ethanol with separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), using Saccharomyces cerevisiae. The glucose formed varied from 25.0 to 49.4 g/l and the saccharification yield from 43.9 to 88.4%, depending on the detoxification methods. The highest ethanol yield (92% of theoretical value) was obtained with overliming in SHF (10 g/l yeast). The SSF process time was shorter (24–38 h) than that for the SHF (≈100 h), leading to significantly increased ethanol productivity for the former process (0.64–1.08 g/l h for SSF; 0.11–0.37 g/l h for SHF).