Abstract
A combination of thermochemical pretreatment and biological digestion technologies is usually required to overcome lignocellulosic recalcitrance and accomplish effective biomass deconstruction. This study is aimed at understanding switchgrass breakdown by hydrothermal, dilute acid, dilute alkali, and co-solvent enhanced lignocellulosic fractionation (CELF) pretreatments followed by application of traditional fungal enzymatic hydrolysis (EH) and Clostridium thermocellum consolidated bioprocessing (CBP) to the resulting solids. Unpretreated and pretreated switchgrass and their EH and CBP residues were characterized by a suite of analytical techniques to understand structural changes that occurred during deconstruction. CELF pretreated solids showed the highest accessibility and digestibility by both EH and CBP followed by dilute alkali and then dilute acid/hydrothermal pretreated solids. Lignin removal from biomass had a more positive impact on substrate accessibility and digestibility than did xylan removal, while xyloglucan removal by pretreatment appeared essential for cellulose digestion by fungal enzymes. The extent of CBP digestion of cellulose and non-cellulosic glycans was larger than that by EH. Unlike dilute alkali pretreatment, cellulose crystallinity increased for acid-based pretreatments in the following order: hydrothermal, dilute acid, and CELF. Acid-based pretreatments also substantially reduced cellulose degree of polymerization. All thermochemical and biological digestion approaches increased syringyl to guaiacyl lignin (S/G) ratio and reduced β-O-4 lignin interunit linkage and hydroxycinnamates content from levels in unpretreated switchgrass. The substantial increase in S/G ratio after hydrothermal and dilute alkali preatreatments suggested that high temperatures or alkali removed a large portion of G lignin from switchgrass.
| Original language | English |
|---|---|
| Pages (from-to) | 7924-7945 |
| Number of pages | 22 |
| Journal | Green Chemistry |
| Volume | 22 |
| Issue number | 22 |
| DOIs | |
| State | Published - Nov 21 2020 |
Funding
We would like to thank Professor Lee Lynd’s laboratory group at Dartmouth College, Hanover, NH, USA. Prof. Lynd’s laboratory provided Clostridium thermocellum DSM 1313 strain used in this work. We would like to acknowledge the Ford Motor Company for funding the Chair in Environmental Engineering that facilitates projects such as this one. We thank the Center for Environmental Research and Technology (CE-CERT) of the Bourns College of Engineering at University of California, Riverside, CA for providing the facilities used to complete this work. We further also thank the Joint Institute of Advanced Materials (JIAM), University of Tennessee, Knoxville for use of the SEM. We are grateful for funding by the Office of Biological and Environmental Research in the Department of Energy (DOE) Office of Science through the BioEnergy Science Center (BESC) (Contract DE-PS02-06ER64304), Genomic Science Program (Contract FWP ERKP752) and Center for Bioenergy Innovation (CBI) at Oak Ridge National Laboratory. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract DE-AC05-00OR22725. The United States Government and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.
| Funders | Funder number |
|---|---|
| BioEnergy Science Center | DE-PS02-06ER64304, FWP ERKP752 |
| Office of Biological and Environmental Research in the Department of Energy | |
| U. S. Department of Energy | DE-AC05-00OR22725 |
| U.S. Department of Energy | |
| Ford Motor Company | |
| Office of Science | |
| Oak Ridge National Laboratory | |
| Center for Bioenergy Innovation |
