In this study, a Compacted Biomass with Recycled Ammonia (COBRA) pretreatment was used, utilizing densified corn stover and anhydrous liquid ammonia under mild conditions to increase pretreatment throughput. COBRA was then compared with established Ammonia Fiber Expansion (AFEX) and Extractive Ammonia (EA) pretreatments for sugar conversion and ethanol fermentation. The optimal pretreatment conditions for the COBRA process were determined to be 67 degrees C, with an NH3-to-biomass ratio of 0.8:1, and a duration of 5.5 h. X-ray diffraction analysis confirmed that COBRA effectively converted recalcitrant crystalline cellulose I to the more digestible cellulose III. Using an optimized enzyme cocktail (CTec2:HTec2:Pectinex; 0.6:0.2:0.2) of 15 mg/g glucan, COBRA-pretreated corn stover achieved high sugar yields. Separate hydrolysis and fermentation (SHF) at 6 % glucan loading, yielded 62 g/L glucose and 28 g/L xylose after 96 h of hydrolysis. Subsequent fermentation with S. cerevisiae 424A for 96 h, without nutrient supplementation or detoxification, produced 38.3 g/L ethanol with an 87.6 % metabolic yield. COBRA pretreatment followed by hydrolysis and fermentation produced 216.9 g of ethanol per kg of biomass, compared to AFEX (198.0 g) and EA (235.9 g). While COBRA's ethanol yield was lower than EA, its advantages lie in improved reactor filling ratio (16.7 % vs 4.4 %), milder conditions (67 degrees C vs 120 degrees C, 400 psi vs 1300 psi), and lower ammonia usage (NH3:biomass 0.8:1 vs 6:1). A techno-economic analysis showed that integrating COBRA pretreatment with a localized biomass supply chain system is economically viable for large-scale cellulosic ethanol production.

The development of sustainable pretreatment technologies is essential for improving biomass conversion efficiency in second generation biorefineries. This review provides a comprehensive analysis of ammonia-based pretreatment methods, tracing their evolution from early advancements to recent innovations. It highlights advanced technologies such as Ammonia Fiber Expansion (AFEX), Extractive Ammonia (EA), and Compacted Biomass with Recycled Ammonia (COBRA), alongside other approaches, including dilute ammonia, gaseous, and aqueous methods. These pretreatment methods vary in their effectiveness, particularly in lignin removal and lignin carbohydrate complex modification, with most ammonia preserving cellulose while their impact on hemicellulose and lignin range from minimal alterations to extensive removal. The review also explores the integration of ammonia-based pretreatment with biomass densification strategies, emphasizing their role in improving feedstock logistics while maintaining conversion efficiency. Recent innovations in sustainable ammonia production such as electrochemical synthesis and biomass-based processes are discussed, showcasing opportunities to develop environmentally friendly pretreatment solutions. Additionally, the applications of ammonia-pretreated biomass are examined across three key sectors: biofuel production, leveraging enzymatic hydrolysis and fermentation; animal feed, with enhanced digestibility and nutritional benefits; and biomaterial development, including lipid and protein extraction for value-added products. This review offers a comprehensive understanding of ammonia-based pretreatment technologies and their expanding potential in sustainable biorefining applications.

Crop residues hold promise to alleviate food vs. fuel competition and contribute to biofuel production. However, the impacts of lateral sediment and carbon fluxes caused by residue removal are not fully understood. Here we employ agroecosystem modeling to conservatively estimate lateral sediment and carbon fluxes resulting from partial corn stover removal in the U.S. Midwest. Results show substantial increases in soil erosion resulting from corn stover removal. For example, the area of continuous corn and corn soybean cropping systems exceeding soil erosion tolerance threshold could increase from 1.1 to 13.3% because of 66% corn stover removal. Depending on removal intensity, conservation, and crop rotation, the stover removal-induced increases in eroded soil organic carbon is equivalent to 3.9-12.5 gCO2e MJ-1, which is comparable to other components of the life cycle impacts of corn stover-derived biofuel. Our findings highlight the need to consider the soil erosion and lateral carbon fluxes impacts of corn stover removal in designing supply chains for cellulosic biofuel production.

AbstractThis study investigates uncertainties in greenhouse gas (GHG) emission factors related to switchgrass‐based biofuel production in Michigan. Using three life cycle assessment (LCA) databases—US lifecycle inventory (USLCI) database, GREET, and Ecoinvent—each with multiple versions, we recalculated the global warming intensity (GWI) and GHG mitigation potential in a static calculation. Employing Monte Carlo simulations along with local and global sensitivity analyses, we assess uncertainties and pinpoint key parameters influencing GWI. The convergence of results across our previous study, static calculations, and Monte Carlo simulations enhances the credibility of estimated GWI values. Static calculations, validated by Monte Carlo simulations, offer reasonable central tendencies, providing a robust foundation for policy considerations. However, the wider range observed in Monte Carlo simulations underscores the importance of potential variations and uncertainties in real‐world applications. Sensitivity analyses identify biofuel yield, GHG emissions of electricity, and soil organic carbon (SOC) change as pivotal parameters influencing GWI. Decreasing uncertainties in GWI may be achieved by making greater efforts to acquire more precise data on these parameters. Our study emphasizes the significance of considering diverse GHG factors and databases in GWI assessments and stresses the need for accurate electricity fuel mixes, crucial information for refining GWI assessments and informing strategies for sustainable biofuel production.

Lignocellulosic biomass holds a crucial position in the prospective bio-based economy, serving as a sustainable and renewable source for a variety of biobased products. These products play a vital role in displacing fossil fuels and contributing to environmental well-being. However, the inherent recalcitrance of biomass poses a significant obstacle to the efficient access of sugar polymers. Consequently, the bioconversion of lignocellulosic biomass into fermentable sugars remains a prominent challenge in biorefinery processes to produce biofuels and biochemicals. In addressing these challenges, extensive efforts have been dedicated to mitigating biomass recalcitrance through diverse pretreatment methods. One noteworthy process is Ammonia Fiber Expansion (AFEX) pretreatment, characterized by its dry-to-dry nature and minimal water usage. The volatile ammonia, acting as a catalyst in the process, is recyclable. AFEX contributes to cleaning biomass ester linkages and facilitating the opening of cell wall structures, enhancing enzyme accessibility and leading to a fivefold increase in sugar conversion compared to untreated biomass. Over the last decade, AFEX has demonstrated substantial success in augmenting the efficiency of biomass conversion processes. This success has unlocked the potential for sustainable and economically viable biorefineries. This paper offers a comprehensive review of studies focusing on the utilization of AFEX-pretreated biomass in the production of second-generation biofuels, ruminant feed, and additional value-added bioproducts like enzymes, lipids, proteins, and mushrooms. It delves into the details of the AFEX pretreatment process at both laboratory and pilot scales, elucidates the mechanism of action, and underscores the role of AFEX in the biorefinery for developing biofuels and bioproducts, and nutritious ruminant animal feed production. While highlighting the strides made, the paper also addresses current challenges in the commercialization of AFEX pretreatment within biorefineries. Furthermore, it outlines critical considerations that must be addressed to overcome these challenges, ensuring the continued progress and widespread adoption of AFEX in advancing sustainable and economically viable bio-based industries.

We describe a roadmap using three sets of technologies to enable base-load nuclear reactors to replace all fossil fuels in a low-carbon world. The technologies integrate nuclear, wind, solar, hydroelectricity and biomass energy sources. Base-load nuclear reactors with large-scale heat storage enable dispatchable electricity to the grid. The low-cost heat storage enables buying excess wind and solar electricity to charge heat storage for later electricity production while providing assured generating capacity. Nuclear hydrogen production facilities at the scale of global oil refineries produce hydrogen to replace natural gas (gaseous fuel) as a chemical feedstock and heat source. Single sites may have tens of modular reactors produced in a local factory to lower costs by converting to a manufacturing model for reactor construction. Nuclear heat and hydrogen convert cellulosic biomass into drop-in liquid hydrocarbon biofuels to replace fossil-fuel gasoline, diesel, jet fuel, and hydrocarbon feed stocks for the chemical industry. External heat and hydrogen inputs increase the quantities of biofuels that can be produced per unit of cellulosic feedstock, thus assuring sufficient biomass feed stocks to replace all crude oil without major impacts on food and fiber prices. The biofuel production system enables the removal of large quantities of carbon dioxide from the atmosphere that is sequestered as carbon char in the soil while recycling plant nutrients (potassium, phosphorous, etc.) to assure agricultural and forest sustainability.

The feedstock supply chain of a biorefinery is critical in determining the economic and environmental performance of biofuels. This study investigated various feedstock supply chains for a centralized biorefinery based on different objective functions and how the biorefinery responds to supply chain volatility. For the analysis, a hypothetical centralized biorefinery was supplied by switchgrass grown on marginal lands in Michigan. From an economic standpoint, the minimum biofuel selling price is an important metric of the objective function, and the greenhouse gas mitigation potential is a similarly important metric for global warming impact. A trade-off therefore exists between the economic and environmental performance of biofuels under this system configuration. However, when a carbon tax credit is applied to soil organic carbon sequestration in switchgrass production, the metric of the objective function may not be the key factor in establishing a supply chain as long as it is associated with biorefinery capacity as well as economic or environmental values. Year-to-year fluctuations in cellulosic biomass yield (supply chain volatility) might also prevent the biorefinery from operating at full capacity. Cellulosic biomass pellets can serve as an auxiliary feedstock for the centralized cellulosic biorefinery system to minimize the impacts of supply chain volatility.

The isomerization of xylose to xylulose is considered the most promising approach to initiate xylose bioconversion. Here, phylogeny-guided big data mining, rational modification, and ancestral sequence reconstruction strategies were implemented to explore new active xylose isomerases (XIs) for Saccharomyces cerevisiae. Significantly, 13 new active XIs for S. cerevisiae were mined or artificially created. Moreover, the importance of the amino-terminal fragment for maintaining basic XI activity was demonstrated. With the mined XIs, four efficient xylose-utilizing S. cerevisiae were constructed and evolved, among which the strain S. cerevisiae CRD5HS contributed to ethanol titers as high as 85.95 and 94.76 g/liter from pretreated corn stover and corn cob, respectively, without detoxifying or washing pretreated biomass. Potential genetic targets obtained from adaptive laboratory evolution were further analyzed by sequencing the high-performance strains. The combined XI mining methods described here provide practical references for mining other scarce and valuable enzymes.

Abstract Energy crops for biofuel production, especially switchgrass (Panicum virgatum), are of interest from a climate change perspective. Here, we use outputs from a crop growth model and life cycle assessment (LCA) to examine the global warming intensity (GWI; g CO2 MJ−1) and greenhouse gas (GHG) mitigation potential (Mg CO2 year−1) of biofuel systems based on a spatially explicit analysis of switchgrass grown on marginal land (abandoned former cropland) in Michigan, USA. We find that marginal lands in Michigan can annually produce over 0.57 hm3 of liquid biofuel derived from nitrogen‐fertilized switchgrass, mitigating 1.2–1.5 Tg of CO2 year−1. About 96% of these biofuels can meet the Renewable Fuel Standard (60% reduction in lifecycle GHG emissions compared with conventional gasoline; GWI ≤37.2 g CO2 MJ−1). Furthermore, 73%–75% of these biofuels are carbon‐negative (GWI less than zero) due to enhanced soil organic carbon (SOC) sequestration. However, simulations indicate that SOC levels would fail to increase and even decrease on the 11% of lands where SOC stocks >>200 Mg C ha−1, leading to carbon intensities greater than gasoline. Results highlight the strong climate mitigation potential of switchgrass grown on marginal lands as well as the needs to avoid carbon rich soils such as histosols and wetlands and to ensure that productivity will be sufficient to provide net mitigation.

Biomass densification allows economic long-distance hauling and enables mega-biorefineries that benefit from economies of scale. COBRA-LE pretreatment uses densified biomass to achieve near-theoretical conversion of carbohydrates and usable lignin.

Biofuels, Bioproducts and BiorefiningVolume 16, Issue 4 p. 927-928 Editorial The Society of Chemical Industry (SCI) at 140 years and Biofuels, Bioproducts and Biorefining. Bruce E. Dale, Corresponding Author Bruce E. Dale University Distinguished Professor bdale@egr.msu.edu Michigan State UniversityCorrespondence to: E-mail: bdale@egr.msu.eduSearch for more papers by this author Bruce E. Dale, Corresponding Author Bruce E. Dale University Distinguished Professor bdale@egr.msu.edu Michigan State UniversityCorrespondence to: E-mail: bdale@egr.msu.eduSearch for more papers by this author First published: 14 July 2022 https://doi.org/10.1002/bbb.2399Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue4July/August 2022Pages 927-928 RelatedInformation

We describe a roadmap, based on a series of workshops and studies, to use base-load nuclear reactors to replace fossil fuels in a low-carbon world that integrates nuclear, wind, solar, hydro-electricity and biomass energy sources.Nuclear reactors with large-scale heat storage enable variable electricity to the grid with nuclear plants that both buy and sell electricity.The low-cost heat storage and assured generating capacity enables efficient use of largescale wind and solar.Nuclear hydrogen production facilities at the scale of global oil refineries produce hydrogen to replace natural gas as a heat source.Nuclear heat and hydrogen convert plant biomass into drop-in hydrocarbon biofuels to replace gasoline, diesel, jet fuel and hydrocarbon feed stocks for the chemical industry.The external heat and hydrogen greatly increases the quantities of biofuels that can be produced per unit of feedstock.The system can produce variable quantities of biofuels and sequestered carbon dioxide that enables negative carbon dioxide emissions and increases revenue if there is a market for removing carbon dioxide from the atmosphere.

In this study, the potential integration of steam explosion (StEx) and ammonia fiber expansion (AFEX) with existing sugar/ethanol mills to form decentralized pre-processing depots was explored. Both StEx and AFEX pretreatment facilitated the production of sugarcane bagasse (SCB) and cane leaf matter (CLM) pellets with significantly higher bulk density, mechanical durability, and hydrophobicity relative to their untreated biomass pellet controls. However, ethanol production from standalone StEx and AFEX-treated SCB and CLM pellets required enzyme dosages greater than 21 mg/g glucan to achieve enzymatic hydrolysis sugar yields of 75% and ethanol titres greater than 40 g.L-1. Coupling AFEX-treated SCB or CLM pellets with a room temperature CIIIIactivation step using liquid ammonia lowered enzyme dosage requirements by more than 50% without affecting ethanol titers and production yields (greater than300 L per Mg residual dry matter raw dry biomass (RDM)). In contrast, treating StEx-treated pellets with CIIII-activation using liquid ammonia did not result in similar enzyme dosage reductions, due to pseudo-lignin formation, leading to enzyme deactivation and/or lignin blockage that retarded enzymatic hydrolysis at low enzyme dosages. A gross energy conversion assessment revealed that low enzyme dosage (3-4 mg enzyme/g RDM) ethanol and electricity co-production from AFEX and CIIII-activated SCB and CLM can recover up to 73% of the energy in the untreated biomass, compared to 54% recovered by StEx and CIIII-activation. The results from this work suggest that StEx or AFEX based pre-processing depots can produce dense and mechanically durable biomass pellets. The AFEX-treated pellets can be easily upgraded using a room temperature CIIII-activation step at the biorefinery to significantly reduce bioconversion enzymes.

Understanding the effects of regionally available residues, wastes, and purpose-grown energy crops on anaerobic microbes and corresponding digestion performance is important for designing and implementing suitable anaerobic digestion systems to manage them appropriately and to use them for bioenergy generation. This study analyzed and compared dynamic changes in anaerobic microbes and digestion performance using mixtures of six different materials (citrus pulp, olive pomace, cattle manure, poultry litter, whey, and corn silage) generated from Mediterranean agro-industry. The results indicate that the feedstock mixture (FM3) with low citrus pulp (26% dry matter) and high olive pomace (18% dry matter) reached stable methane production of 210 mL methane/g volatile solids (VS) loading within 30 days after the start up. In contrast, the feedstock mixture (FM1) with high citrus pulp (44% dry matter) and low olive pomace (0% dry matter) required a longer time of at least 70 days to achieve a good methane production of 209 mL methane/g VS loading. The microbial community analysis and corresponding non-metric dimensionless scaling (NMDS) analysis revealed dynamic relationships between microbial community, feedstock mixture, and digestion time. The feedstock mixtures with low citrus pulp content (FM2 and FM3) facilitated the accumulation of Archaea (i.e., Methanosarcinaceae), which led their digestion to reach stable methane production quicker than the digestion of FM1. This study provided useful information to valorize agricultural residues and wastes for bioenergy production in the Mediterranean region. (c) 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Novel Immunological and Mass Spectrometry Methods for Comprehensive Analysis of Recalcitrant Oligosaccharides in AFEX Pretreated Corn Stover. Lignocellulosic biomass is a sustainable alternative to fossil fuel and is extensively used for developing bio-based technologies to produce products such as food, feed, fuel, and chemicals. The key to these technologies is to develop cost competitive processes to convert complex carbohydrates present in plant cell wall to simple sugars such as glucose, xylose, and arabinose. Since lignocellulosic biomass is highly recalcitrant, it must undergo a combination of thermochemical treatment such as Ammonia Fiber Expansion (AFEX), dilute acid (DA), Ionic Liquid (IL) and biological treatment such as enzyme hydrolysis and microbial fermentation to produce desired products. However, when using commercial fungal enzymes during hydrolysis, only 75–85% of the soluble sugars generated are monomeric sugars, while the remaining 15–25% are soluble recalcitrant oligosaccharides that cannot be easily utilized by microorganisms. Previously, we successfully separated and purified the soluble recalcitrant oligosaccharides using a combination of charcoal and celite-based separation followed by size exclusion chromatography and studies their inhibitory properties on enzymes. We discovered that the oligosaccharides with higher degree of polymerization (DP) containing methylated uronic acid substitutions were more recalcitrant towards commercial enzyme mixtures than lower DP and neutral oligosaccharides. Here, we report the use of several complementary techniques that include glycome profiling using plant biomass glycan specific monoclonal antibodies (mAbs) to characterize sugar linkages in plant cell walls and enzymatic hydrolysate, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) using structurally-informative diagnostic peaks offered by negative ion post-secondary decay spectra, gas chromatography followed by mass spectrometry (GC–MS) to characterize oligosaccharide sugar linkages with and without derivatization. Since oligosaccharides (DP 4–20) are small, it is challenging to mobilize these molecules for mAbs binding and characterization. To overcome this problem, we have applied a new biotin-coupling based oligosaccharide immobilization method that successfully tagged most of the low DP soluble oligosaccharides on to a micro-plate surface followed by specific linkage analysis using mAbs in a high-throughput system. This new approach will help develop more advanced versions of future high throughput glycome profiling methods that can be used to separate and characterize oligosaccharides present in biomarkers for diagnostic applications.