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Title: Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol

Abstract

Simultaneous saccharification and fermentation (SSF) of solid biomass can reduce the complexity and improve the economics of lignocellulosic ethanol production by consolidating process steps and reducing end-product inhibition of enzymes compared with separate hydrolysis and fermentation (SHF). However, a long-standing limitation of SSF has been too low ethanol yields at the high-solids loading of biomass needed during fermentation to realize sufficiently high ethanol titers favorable for more economical ethanol recovery. Here, we illustrate how competing factors that limit ethanol yields during high-solids fermentations are overcome by integrating newly developed cosolvent-enhanced lignocellulosic fractionation (CELF) pretreatment with SSF. First, fed-batch glucose fermentations by Saccharomyces cerevisiae D 5 A revealed that this strain, which has been favored for SSF, can produce ethanol at titers of up to 86 g⋅L −1 . Then, optimizing SSF of CELF-pretreated corn stover achieved unprecedented ethanol titers of 79.2, 81.3, and 85.6 g⋅L −1 in batch shake flask, corresponding to ethanol yields of 90.5%, 86.1%, and 80.8% at solids loadings of 20.0 wt %, 21.5 wt %, and 23.0 wt %, respectively. Ethanol yields remained at over 90% despite reducing enzyme loading to only 10 mg protein⋅g glucan −1 [∼6.5 filter paper units (FPU)], revealing that the enduringmore » factors limiting further ethanol production were reduced cell viability and glucose uptake by D 5 A and not loss of enzyme activity or mixing issues, thereby demonstrating an SSF-based process that was limited by a strain’s metabolic capabilities and tolerance to ethanol.« less

Authors:
; ORCiD logo; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1399640
Grant/Contract Number:  
PS02-06ER64304
Resource Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 44; Journal ID: ISSN 0027-8424
Publisher:
Proceedings of the National Academy of Sciences
Country of Publication:
United States
Language:
English

Citation Formats

Nguyen, Thanh Yen, Cai, Charles M., Kumar, Rajeev, and Wyman, Charles E. Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol. United States: N. p., 2017. Web. doi:10.1073/pnas.1704652114.
Nguyen, Thanh Yen, Cai, Charles M., Kumar, Rajeev, & Wyman, Charles E. Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol. United States. doi:10.1073/pnas.1704652114.
Nguyen, Thanh Yen, Cai, Charles M., Kumar, Rajeev, and Wyman, Charles E. Mon . "Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol". United States. doi:10.1073/pnas.1704652114.
@article{osti_1399640,
title = {Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol},
author = {Nguyen, Thanh Yen and Cai, Charles M. and Kumar, Rajeev and Wyman, Charles E.},
abstractNote = {Simultaneous saccharification and fermentation (SSF) of solid biomass can reduce the complexity and improve the economics of lignocellulosic ethanol production by consolidating process steps and reducing end-product inhibition of enzymes compared with separate hydrolysis and fermentation (SHF). However, a long-standing limitation of SSF has been too low ethanol yields at the high-solids loading of biomass needed during fermentation to realize sufficiently high ethanol titers favorable for more economical ethanol recovery. Here, we illustrate how competing factors that limit ethanol yields during high-solids fermentations are overcome by integrating newly developed cosolvent-enhanced lignocellulosic fractionation (CELF) pretreatment with SSF. First, fed-batch glucose fermentations by Saccharomyces cerevisiae D 5 A revealed that this strain, which has been favored for SSF, can produce ethanol at titers of up to 86 g⋅L −1 . Then, optimizing SSF of CELF-pretreated corn stover achieved unprecedented ethanol titers of 79.2, 81.3, and 85.6 g⋅L −1 in batch shake flask, corresponding to ethanol yields of 90.5%, 86.1%, and 80.8% at solids loadings of 20.0 wt %, 21.5 wt %, and 23.0 wt %, respectively. Ethanol yields remained at over 90% despite reducing enzyme loading to only 10 mg protein⋅g glucan −1 [∼6.5 filter paper units (FPU)], revealing that the enduring factors limiting further ethanol production were reduced cell viability and glucose uptake by D 5 A and not loss of enzyme activity or mixing issues, thereby demonstrating an SSF-based process that was limited by a strain’s metabolic capabilities and tolerance to ethanol.},
doi = {10.1073/pnas.1704652114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 44,
volume = 114,
place = {United States},
year = {2017},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1073/pnas.1704652114

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Cited by: 12 works
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