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

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(R) and Celluclast(R) 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 SF process time was shorter (24-38 h) than that for the SHF (approximate to 100 h), leading to significantly increased ethanol productivity for the former process (0.64-1.08 g/l It for SSF; 0.11-0.37 g/l h for SHF). (C) 2003 Elsevier Ltd. All rights reserved.