Search

BackgroundPretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars. Furthermore, lignocellulosic biomass must typically be reduced in size to increase the pretreatment effectiveness and realize high sugar yields. However, biomass size reduction is a very energy-intensive operation and contributes significantly to the overall capital cost.ResultsIn this study, the effect of particle size reduction and biomass presoaking on the deconstruction of Alamo switchgrass was examined prior to pretreatment by dilute sulfuric acid (DSA) and Co-solvent Enhanced Lignocellulosic Fractionation (CELF) at pretreatment conditions optimized for maximum sugar release by each pretreatment coupled with subsequent enzymatic hydrolysis. Sugar yields by enzymatic hydrolysis were measured over a range of enzyme loadings. In general, DSA successfully solubilized hemicellulose, while CELF removed nearly 80% of Klason lignin from switchgrass in addition to the majority of hemicellulose. Presoaking and particle size reduction did not have a significant impact on biomass compositions after pretreatment for both DSA and CELF. However, presoaking for 4 h slightly increased sugar yields by enzymatic hydrolysis of DSA-pretreated switchgrass compared to unsoaked samples, whereas sugar yields from enzymatic hydrolysis of CELF solids continued to increase substantially for up to 18 h of presoaking time. Of particular importance, DSA required particle size reduction by knife milling to

[This corrects the article DOI: 10.1186/s13068-019-1353-7.].

Low- and middle-income countries have tremendous potential for renewable energy production, including production of renewable carbon from locally prolific crops. In this work, bamboo endemic to West Africa (Bambusa vulgaris) was studied as a feedstock for the production of renewable sugars as the gateway to the local production of biofuels and bio-based chemical products. The effectiveness of delignification and amorphization pretreatments was evaluated, with the observation that quantitative (97 ± 4%) sugar yields could be obtained with a rapid initial hydrolysis rate (82 ± 4 mg g−1 h−1) but only when amorphization was performed following delignification. Experimental measurements and further characterization using 13C solid state nuclear magnetic resonance (NMR) helped establish the importance of amorphization and delignification and explained why the order of these treatments determined their effectiveness. The economics of the bamboo-based process were compared with those projected for corn stover, selected as a well-studied benchmark crop. Because of the higher bamboo growth rate compared with corn stover and the effectiveness of the pretreatment, the projected net present value (NPV) of the bamboo biorefinery was positive ($190 MM, U.S.), whereas the corn biorefinery projected to negative NPV (−$430 MM, U.S.). A socially sustainable framework for deployment of a bamboo biorefinery in a low- or middle-income economy was then proposed, guided by the principle of local ownership and stakeholder buy-in. The findings presented here motivate further investment in development of bamboo cultivation and conversion to sugars as a rapid route to decarbonization of low- and middle-income economies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]