Precise pretreatment of lignocellulose: relating substrate modification with subsequent hydrolysis and fermentation to products and by-products
Open Access
- 11 April 2017
- journal article
- research article
- Published by Springer Science and Business Media LLC in Biotechnology for Biofuels
- Vol. 10 (1), 1-15
- https://doi.org/10.1186/s13068-017-0775-3
Abstract
Pretreatment is a crucial step for valorization of lignocellulosic biomass into valuable products such as H2, ethanol, acids, and methane. As pretreatment can change several decisive factors concurrently, it is difficult to predict its effectiveness. Furthermore, the effectiveness of pretreatments is usually assessed by enzymatic digestibility or merely according to the yield of the target fermentation products. The present study proposed the concept of “precise pretreatment,” distinguished the major decisive factors of lignocellulosic materials by precise pretreatment, and evaluated the complete profile of all fermentation products and by-products. In brief, hemicellulose and lignin were selectively removed from dewaxed rice straw, and the cellulose was further modified to alter the crystalline allomorphs. The subsequent fermentation performance of the selectively pretreated lignocellulose was assessed using the cellulolytic, ethanologenic, and hydrogenetic Clostridium thermocellum through a holistic characterization of the liquid, solid, and gaseous products and residues. The transformation of crystalline cellulose forms from I to II and from I α to I β improved the production of H2 and ethanol by 65 and 29%, respectively. At the same time, the hydrolysis efficiency was merely improved by 10%, revealing that the crystalline forms not only influenced the accessibility of cellulose but also affected the metabolic preferences and flux of the system. The fermentation efficiency was independent of the specific surface area and degree of polymerization. Furthermore, the pretreatments resulted in 43–45% of the carbon in the liquid hydrolysates unexplainable by forming ethanol and acetate products. A tandem pretreatment with peracetic acid and alkali improved ethanol production by 45.5%, but also increased the production of non-ethanolic low-value by-products by 136%, resulting in a huge burden on wastewater treatment requirements. Cellulose allomorphs significantly affected fermentation metabolic pathway, except for hydrolysis efficiency. Furthermore, with the increasing effectiveness of the pretreatment for ethanol production, more non-ethanolic low-value by-products or contaminants were produced, intensifying environmental burden. Therefore, the effectiveness of the pretreatment should not only be determined on the basis of energy auditing and inhibitors generated, but should also be assessed in terms of the environmental benefits of the whole integrated system from a holistic view.Keywords
Funding Information
- National Natural Science Foundation of China (51622809, 51378375, 21177096)
This publication has 53 references indexed in Scilit:
- Increased enzyme binding to substrate is not necessary for more efficient cellulose hydrolysisProceedings of the National Academy of Sciences of the United States of America, 2013
- Hemicelluloses negatively affect lignocellulose crystallinity for high biomass digestibility under NaOH and H2SO4 pretreatments in MiscanthusBiotechnology for Biofuels, 2012
- Clostridium thermocellum ATCC27405 transcriptomic, metabolomic and proteomic profiles after ethanol stressBMC Genomics, 2012
- Real-Time Observation of the Swelling and Hydrolysis of a Single Crystalline Cellulose Fiber Catalyzed by Cellulase 7B from Trichoderma reeseiLangmuir, 2012
- Ionic-Liquid Induced Changes in Cellulose Structure Associated with Enhanced Biomass HydrolysisBiomacromolecules, 2011
- Transcriptomic analysis of Clostridium thermocellumATCC 27405 cellulose fermentationBMC Microbiology, 2011
- Global Gene Expression Patterns in Clostridium thermocellum as Determined by Microarray Analysis of Chemostat Cultures on Cellulose or CellobioseApplied and Environmental Microbiology, 2011
- Clostridium thermocellum cellulosomal genes are regulated by extracytoplasmic polysaccharides via alternative sigma factorsProceedings of the National Academy of Sciences of the United States of America, 2010
- Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis: A reviewBioresource Technology, 2010
- Global View of the Clostridium thermocellum Cellulosome Revealed by Quantitative Proteomic AnalysisJournal of Bacteriology, 2007