Identification and characterization of fermentation inhibitors formed during hydrothermal treatment and following SSF of wheat straw.
A pilot plant for hydrothermal treatment of wheat straw was compared in reactor systems of two steps (first, 80 degrees C; second, 190-205 degrees C) and of three steps (first, 80 degrees C; second, 170-180 degrees C; third, 195 degrees C). Fermentation (SSF) with Sacharomyces cerevisiae of the pretreated fibers and hydrolysate from the two-step system gave higher ethanol yield (64-75%) than that obtained from the three-step system (61-65%), due to higher enzymatic cellulose convertibility. At the optimal conditions (two steps, 195 degrees C for 6 min), 69% of available C6-sugar could be fermented into ethanol with a high hemicellulose recovery (65%). The concentration of furfural obtained during the pretreatment process increased versus temperature from 50 mg/l at 190 degrees C to 1,200 mg/l at 205 degrees C as a result of xylose degradation. S. cerevisiae detoxified the hydrolysates by degradation of several toxic compounds such as 90-99% furfural and 80-100% phenolic aldehydes, which extended the lag phase to 5 h. Acetic acid concentration increased by 0.2-1 g/l during enzymatic hydrolysis and 0-3.4 g/l during fermentation due to hydrolysis of acetyl groups and minor xylose degradation. Formic acid concentration increased by 0.5-1.5 g/l probably due to degradation of furfural. Phenolic aldehydes were oxidized to the corresponding acids during fermentation reducing the inhibition level.
Thomsen
Mette Hedegaard
MH
Biosystems Division, Risø DTU, Technical University of Denmark, POB 49, DK-4000 Roskilde, Denmark. mette.hedegaard.thomsen@risoe.dk
Thygesen
Anders
A
Thomsen
Anne Belinda
AB
D002482:Cellulose / Q000737:chemistry* / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D006868:Hydrolysis; D007218:Industrial Microbiology; D009930:Organic Chemicals / Q000737:chemistry* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature; D014908:Triticum / Q000737:chemistry* / Q000378:metabolism
D009930:Organic Chemicals; D000431:Ethanol; D002482:Cellulose