Oxidative submerged lime pretreatment and high-solids saccharification of corn stover
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Agriculture↗
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Steam explosion pretreatment coupling high-temperature short-time sterilization facilitating cellulose degradation and sporulation-regulatory gene expression in high-solid fermentation
Steam explosion coupling high-temperature short-time sterilization (SE-HTST) was exploited to modify cellulosic biomass medium properties and promote high-solid fermentation (HSF). Biomass characterization analysis showed that SE-HTST enlarged microstructural pores and cavities in solid media, providing more effective space for microbial growth. Meanwhile, SE-HTST helped to release glucose from the cellulose with 35.8 ± 4.5, 20.0 ± 2.3, and 12.3 ± 5.7 mg glucose/g dry medium at 24, 48, and 72 h of fermentation, which were 3.1, 2.3, and 1.5 times higher than that in medium from conventional thermal sterilization (CTS), respectively. SE-HTST increased the viable cell and spore number of Bacillus subtilis by 1.8 and 1.6 times at 72 h of fermentation compared to CTS. Moreover, the expressions of master transcriptional gene spo0A and the early sigma factors of sigF and sigE genes gradually increased in the SE-HTST medium, showing enhanced sporulation in HSF. Therefore, SE-HTST is an effective strategy for facilitating cellulose degradation, improving glucose nutrients in biomass medium, and promoting sporulation-regulatory gene expression during high-solid fermentation, which enhances the production of microbial ecological agents using B. subtilis significantly.
59 BASIC BIOLOGICAL SCIENCES↗
A high-solid DES pretreatment using never-dried biomass as the starting material: towards high-quality lignin fractionation
This study investigated a high-solid diol deep eutectic solvent (DES) pretreatment using a wet substrate as the starting material. This pretreatment led to a remarkable glucan saccharification of 94.8% with efficient lignin and xylan removal (as high as 63.1% and 73.0%, respectively). Here the chemical structures of the substrates were analyzed comprehensively to reveal the impact of the pretreatment. In addition, over 90% of the removed lignin was recovered from the pretreated liquid, which exhibited a well-preserved β-O-4 structure (46–56/100Ar). The protection mechanism of our DES was investigated by 2D HSQC NMR, GPC, and 31 P NMR analysis. This study emphasized that diol-based DES pretreatment of undried lignocellulosic biomass at a high-solid loading can significantly utilize both carbohydrates and lignin fractions with high saccharification yields and high-quality lignin as a co-product.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Natural deep eutectic solvent mediated extrusion for continuous high-solid pretreatment of lignocellulosic biomass
Several deep eutectic solvents (DESs) have been demonstrated to be highly effective for lignocellulosic biomass pretreatment, combining the advantages of simple synthesis, relatively low chemical cost and better biocompatibility. However, low biomass loading that is usually involved with DES pretreatment hinders its practical use. Here, a twin-screw extruder was used for pretreating biomass sorghum bagasse at solid loadings up to 50%, mediated by a neutral-pH DES, choline chloride : glycerol (ChCl : Gly). This continuous extrusion process led to high glucose and xylose yields of >85% from enzymatic saccharification of the pretreated sorghum. A combination of microscopic, spectroscopic, and X-ray diffraction analyses demonstrate a high degree of defibration and disruption of the biomass cell wall structures; however, little or no change in chemical compositions. Further results from gel permeation chromatographic (GPC) and nuclear magnetic resonance (NMR) spectroscopic analyses indicate that ChCl : Gly-mediated extrusion preserved the basic lignin structural characteristics with no significant differences between extruded biomass at a solid loading of 30% and 50%. This study demonstrates the potential of DES-mediated extrusion as a highly effective continuous high-solid biomass pretreatment technology for industrially relevant applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
BDEM (Discrete-element-simulator for high-solids granular flows) [SWR-22-72]
BDEM is a discrete element method based simulation tool developed specifically for modeling high-solids granular flows that include polydispersity, heat-transfer, moving boundaries and chemistry. Our solver provides facilities for simulating spherical/non-spherical particles with modified contact and friction models in complex dynamic geometries defined using level-sets or triangulated files. The solver is developed on top of NREL's open-source performance portable library, AMReX, providing parallel execution capabilities on current and upcoming high-performance-computing (HPC) architectures. Simulations at the scale of several millions to billion particles have been performed using this software on large scale computing resources. This software can be applied to non-reacting solids dominant flows in silos, hoppers and screw conveyors as well as in high temperature reacting systems such as screw kilns and auger reactors.
Sitaraman, Hariswaran↗
The role of binding modules in enzymatic poly(ethylene terephthalate) hydrolysis at high-solids loadings
In nature, enzymes that deconstruct biological polymers, such as cellulose and chitin, often exhibit multi-domain architectures, comprising a catalytic domain and a non-catalytic binding module; the latter serves to increase the enzyme concentration at the substrate surface. This multi-domain architecture has been shown to improve the hydrolysis of poly(ethylene terephthalate) (PET) using engineered cutinase enzymes. Here, we examine the role of accessory binding modules at industrially relevant PET solids loadings necessary for cost-effective enzymatic recycling. Using a thermostable variant of leaf compost cutinase (LCC), we produced synthetic fusion constructs of LCC with five type A carbohydrate-binding modules (CBMs). At solids loadings below 10 wt%, the CBMs improve aromatic monomer yield from PET, but above this threshold, conversion extents up to 97% are reached with no added benefits from the presence of CBM fusions. This suggests that fusion constructs with the herein studied CBMs are not necessary for industrial enzymatic PET recycling.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Conversion of High-Solids Hydrothermally Pretreated Bioenergy Sorghum to Lipids and Ethanol Using Yeast Cultures
Glucose and xylose are the major sugars in cellulosic hydrolysates. The cellulosic sugars can be used for the production of biofuels and value-added bioproducts. In this study, lipid and ethanol were produced from bioenergy sorghum syrups using engineered yeasts. Here, bioenergy sorghum was hydrothermally pretreated at 50% solids loading in a continuous reactor system and mechanically refined sequentially using a burr mill to improve biomass accessibility for hydrolysis. Fed-batch enzymatic hydrolysis was conducted with 50% w/v solids loading to achieve 230 g/L sugar concentration. Different strains of Rhodosporidium toruloides were used to ferment sugars into lipids, and the highest lipid yield of 9.2 g/L was observed. The lipid yield was improved to 19.0 g/l by implementing a two-stage culture where once the sugars were exhausted in the first stage, the yeast was introduced into fresh hydrolysate without adding nitrogen. For ethanol production, the engineered Saccharomyces cerevisiae SR8ΔADH6 was utilized to coferment glucose and xylose. Additionally, the effects of nutrient media (YP, YNB/urea, and urea), cellulosic sugar concentration, and sulfite addition were investigated to optimize the ethanol yield from sorghum syrups. The optimal ethanol yield at 73.3% was obtained from the YNB/urea culture consisting of 34 g glucose/L and 17 g xylose/L.
09 BIOMASS FUELS↗
Data for Conversion of High-Solids Hydrothermally Pretreated Bioenergy Sorghum to Lipids and Ethanol Using Yeast Cultures
Glucose and xylose are the major sugars present in cellulosic hydrolysates. The cellulosic sugars can be used for the production of platform chemicals. In this study, productions of lipid and ethanol by yeasts were compared for concentrated bioenergy sorghum syrup. Bioenergy sorghum was hydrothermally pretreated at 50% w/w solids in a continuous industrial reactor and sequentially mechanically refined using a burr mill to improve biomass accessibility for hydrolysis. Fed-batch enzymatic hydrolysis was conducted with 50% w/v solids loading and cellulase cocktail (50 FPU/g biomass) to achieve 230 g/L sugar concentration. Various strains of Rhodosporidium toruloides were evaluated for converting sugars into lipids, and strain Y-6987 had the highest lipid titer (9.2 g/L). The lipid titer was improved to 19.0 g/L by implementing a two-stage culture scheme, where the first stage was optimized for yeast growth and the second for lipid production. For ethanol production, the engineered Saccharomyces cerevisiae SR8ΔADH6 was used to coferment glucose and xylose. Ethanol fermentation was optimized for media nutrients (YP, YNB/urea, and urea), cellulosic sugar concentration, and sulfite conditioning to maximize the ethanol concentration from sorghum syrups. Fermentation of 70% v/v concentrated hydrolysate conditioned with sulfite produces 50.1 g/L ethanol from 141 g/L of sugars.
Conversion↗
Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review
We report enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs “high-solid effects”, ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.
45 multi-scale, multi-phase, enzymatic reaction↗
One-pot generation of lignin microspheres and digestible substrate with a polyol-DES pretreatment in high solid loading
Previous lignin microspheres (LMS) preparation needs multiple steps with very low yield and high cost. Herein, we developed a high-solid deep eutectic solvent (DES) pretreatment for an effective lignin fractionation and enzymatic saccharification of moso bamboo under mild temperature (110 °C) with high-solid loading. Lignin was significantly removed from the plant cell wall, and cellulose properties (e.g., crystallinity and degree of polymerization) were also altered during the pretreatment. As a result, the enzymatic digestibility of the pretreated bamboo was dramatically increased. Uniform micro-spherical lignin was directly produced from the pretreatment system, and its particle size could be regulated by controlling the solid loadings and pretreatment temperatures. The lignin microspheres formation mechanism was investigated by analyzing the lignin's size distribution, molecular weight distribution, chemical structure, and hydrophobicity. The DES showed excellent recyclability, and the recycled DES could still remove 42.78% lignin even after 7th circulation associated with 100% glucan saccharification. Further, the mass balance based on 1000 g biomass showed that 196.28 g LMS was directly recovered, which exhibited a high RhB adsorption. Besides, 404.91 g glucose and 36.67 g xylose were obtained after the enzymatic saccharification process. Specifically, GAPI analysis exhibited a near total green and yellow portions of the pictogram, indicating our DES process was green enough to make this biorefinery sustainable. Overall, the proposed DES generated synergistic productions of digestible solid and LMS which could contribute to establish a green and sustainable biorefinery sequence with diverse outputs in one pot.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
High Solids Performance Testing in a Scaled TSCR System
The Tank Side Cesium Removal (TSCR) project is a technology demonstration that will pretreat Hanford tank waste supernatant in support of the Direct Feed Low-Activity Waste (DFLAW) mission. The TSCR system employs two key separation technologies: dead-end filtration (DEF) and ion exchange (IX) using crystalline silicotitanate (CST) media. DEF will be used to remove undissolved solids from tank waste to protect the functionality of the IX columns and the IX system will remove Cs-137 from tank waste. The separation technologies (DEF and IX) used in TSCR are technically mature and have also been successfully deployed at the Savannah River site in a similar facility known as the Tank Closure Cesium Removal (TCCR) system. While testing with simulants and real waste has been successfully performed under conditions expected during the initial operation of TSCR, test data is absent for assessing off normal high solids loading that may be in the TSCR waste feed. Normal TSCR treatment operations are expected to handle wastes with solids content on the order of 200 ppm, and off normal solids loading could be much larger than the nominal level. The testing program described in this report was conducted to understand the consequence of operating the TSCR system at elevated solids loadings up to the high-solids limit of 15,000 ppm [i.e., 1.5-wt%] identified in the TSCR design basis. Although the system is not required to make throughput above the nominal solids loading, the testing was intended to provide important information related to potential off normal operations. At off normal levels near the high-solids limit, there are potential implications for TSCR performance in the areas of throughput, DEF pressure drop, filter backflush frequency, and IX column pressure drop. In addition, intrusion of solids into the IX column was postulated to impact the Cs-137 loading behavior by promoting channeling or flow maldistribution in the column; since the magnitude of the postulated effect was unknown, assessing it was also of interest. The testing was performed using representative waste simulants and a prototypic, integrated TSCR system designed and assembled specifically to conduct the high solids performance assessment. Overall, the scaled TSCR testing demonstrated that full-scale unit operations can succeed in fulfilling their processing objectives in the presence of solids up to 3,000 ppm, but there are potential performance challenges to filtration operations at solids loadings as low as ~500 ppm. The severity of the challenge is likely to be dependent on the type and size distribution of solids, of which the current testing only examined a single type and size distribution. To provide some flexibility for future full-scale operations, the results of the testing suggest two possible risk reduction strategies that can be implemented without any changes in TSCR design or configuration. One option would be to enact an administrative limit on the solids loading to protect TSCR from feeds that are likely to require a high DEF swap frequency. Another option is to permit operation of the DEFs at differential pressures greater than 2 psid before swapping filters. The selection of a higher differential pressure target is not anticipated to adversely impact DEF backflushing efficacy and would reduce both swap frequency and the amount of waste sent to AP-108.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Maximizing long-term biohydrogen production with Clostridium thermocellum for high solids conversion of lignocellulosic biomass
Biological hydrogen production from lignocellulosic biomass sustainably couples organic waste reduction with renewable energy generation. Efficient conversion is challenged by the structural complexity of lignocellulose and resulting recalcitrance to enzymatic degradation. Clostridium thermocellum natively breaks down biomass with highly effective hemi-/cellulases systems (i.e., cellulosomes) and generates hydrogen in anaerobic cultivation, creating a compelling platform for lignocellulosic biohydrogen production. Achieving commercially viable production rates requires balancing high biomass loading and throughput against uniform mixing conditions required for enzyme dispersion, pH and temperature control, and efficient hydrogen and metabolite removal in continuous operation. To address these barriers to process intensification, we implemented novel reactor and process designs for high-solids lignocellulosic biomass fermentations using the C. thermocellum KJC19-9 strain, genetically engineered for co-utilization of cellulose and hemicellulose sugars (i.e., xylose). Via computational fluid dynamics (CFD) modeling and experimental validation, we achieved a >50% improvement in biohydrogen production with an improved anchor-type impeller morphology, coupled to a threefold reduction in agitation rate. To further reduce rheological constraints and accumulation of toxic metabolites, we then transitioned the process to sequencing fed-batch operation. The resulting process generated 24.87 L H 2 L −1 from 160 g L −1 of deacetylated and mechanically refined (DMR)-pretreated corn stover biomass over 16 days while solubilizing >95% of influent cellulose and hemicellulose, setting a new performance benchmark for continuous production of biohydrogen from lignocellulose.
08 HYDROGEN↗
Time-temperature-stress superposition of PBX 9502 compressive creep data for lifetime predictions
The plastic-bonded explosive (PBX) 9502 is a viscoelastic, high-solids loaded polymer bound composite comprised of 95 weight% (wt%) TATB explosive crystals and 5 wt% FK-800 polymer binder. The uniaxial quasi-static mechanical properties have been studied and characterized extensively over 25+ years, including creep. Creep is the strain evolution over time as a result of an asymmetric load typically at temperatures above ambient. Creep measurements to failure can take excessively long periods of time depending on various factors including applied stress, temperature, and loading rate that render a single test to failure impossible. Using the principles of time-temperature-stress superposition (TTSSP), short-term creep tests at various applied stresses and temperatures can be used for long-term creep predictions. The TTSSP model shifts short-term test data using two factors, one for temperature and stress, creating a master curve at a reference test condition. The master curve can be shifted to predict the creep response at any desired test condition. PBX 9502 compression specimens were tested at three temperatures and various applied stresses. This work discusses the TTSSP analysis of PBX 9502 compressive creep data to create a single comprehensive master curve.
36 MATERIALS SCIENCE↗
Impact of temperature and concentration on flow behaviour of reconstituted lactose and protein–rich dairy powders
To help with designing the drying process, this study investigated the flow behaviour of lactose and protein-rich reconstituted dairy powders at 25°C and 50°C. Lactose-rich samples, 50% dried whey (DW) and 60% whey protein concentrate (WPC35) did not follow the Herschel–Bulkley model because of presence of lactose crystals. Reconstituted 50% skim milk powder (SMP) and protein-rich dairy powders exhibited shear-thinning behaviour (n < 0.3). With increasing concentration, whey protein concentrate/isolate (WPC80/WPI) and micellar casein concentrate high-solid dispersions exhibited more shear-thinning behaviour (n < 0.4). Furthermore, understanding shear-thinning behaviour of lactose-rich and protein-rich reconstituted dairy powders will provide basis for optimising drying parameters.
36 MATERIALS SCIENCE↗
Time-Temperature-Stress Superposition of PBX 9502 Compressive Creep Data for Lifetime Predictions
The plastic-bonded explosive (PBX) 9502 is a viscoelastic, high-solids loaded polymer bound composite comprised of 95 weight% (wt%) TATB explosive crystals and 5 wt% FK-800 polymer binder. The uniaxial quasi-static mechanical properties have been studied and characterized extensively over 25+ years, including creep. Creep is the strain evolution over time as a result of an asymmetric load typically at temperatures above ambient. Creep measurements to failure can take excessively long periods of time depending on various factors including applied stress, temperature, and loading rate that render a single test to failure impossible. Using the principles of time-temperature-stress superposition (TTSSP), short-term creep tests at various applied stresses and temperatures can be used for long-term creep predictions. The TTSSP model shifts short-term test data using two factors, one for temperature and stress, creating a master curve at a reference test condition. The master curve can be shifted to predict the creep response at any desired test condition. PBX 9502 compression specimens were tested at three temperatures and various applied stresses. This work discusses the TTSSP analysis of PBX 9502 compressive creep data to create a single comprehensive master curve.
36 MATERIALS SCIENCE↗