title: Hybrid SSF/SHF Processing of SO2Pretreated Wheat Straw-Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time.
abstract: Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO2as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO2(based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.
authors.affiliation: Department of Chemical Engineering, Lund University, Box 124, 221 00, Lund, SE, Sweden.|Novozymes A/S, Krogshoejvej 36, 2880, Bagsvaerd, SE, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Cassells
authors.affiliation: C5 Ligno Technologies in Lund AB, P.O. Box 124, 221 00, Lund, SE, Sweden.|Hansa Medical AB, P.O. Box 785, -220 07, Lund, SE, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Karhumaa
authors.affiliation: C5 Ligno Technologies in Lund AB, P.O. Box 124, 221 00, Lund, SE, Sweden.|National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: V
authors.initials: V
authors.lastname: Sànchez I Nogué
authors.affiliation: Department of Chemical Engineering, Lund University, Box 124, 221 00, Lund, SE, Sweden. gunnar.liden@chemeng.lth.se.
authors.forename: G
authors.initials: G
authors.lastname: Lidén
mesh_terms: D000431:Ethanol / Q000302:isolation & purification / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology; D006868:Hydrolysis; D010936:Plant Extracts / Q000737:chemistry; D018547:Plant Stems / Q000737:chemistry* / Q000382:microbiology*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013227:Steam; D013458:Sulfur Dioxide / Q000737:chemistry; D014908:Triticum / Q000737:chemistry* / Q000382:microbiology*; D014994:Xylose / Q000737:chemistry / Q000378:metabolism
chemical_list: D010936:Plant Extracts; D013227:Steam; D013458:Sulfur Dioxide; D000431:Ethanol; D014994:Xylose
keywords: Bioethanol; In situ detoxification; SSF; Xylose fermentation; Yeast inoculum size