Advances in physicochemical pretreatment strategies for lignocellulose biomass and their effectiveness in bioconversion for biofuel production

Biohydrogen production from residual biomass: The potential of wheat, corn, rice, and barley straw - recent advances

This work reviews the potential of wheat, corn, rice, and barley straw for biohydrogen production, highlighting it as a promising solution for sustainable energy. We analyze the physicochemical properties of these straws, which are rich in carbohydrates and lignin, essential components for bioenergy production. Advanced pretreatment approaches, such as ultrasound, torrefaction, and electrohydrolysis, have proven effective in increasing biohydrogen yields. Research and development of fermentation technologies, such as dark fermentation and photofermentation, are crucial to improving process efficiency. Despite environmental and economic advantages, biohydrogen production faces significant challenges, including biomass conversion efficiency and economic viability. The infrastructure for the collection, transportation, and storage of agricultural residues also presents a challenge. This review explores the potential of wheat, corn, rice, and barley straw for biohydrogen production, emphasizing its role in sustainable energy generation. Biohydrogen production from agricultural residues is a viable alternative for the circular economy and environmental sustainability, contributing to waste reduction and climate change mitigation.

A mild and efficient pretreatment strategy for the high-value utilization of cellulose derived from Sargassum spp

Algae are pivotal in biofuel production, with pretreatment serving as a crucial step in the process. Traditional methods predominantly rely on strong acids, bases, or high temperatures, which contradict the principles of green and sustainable development. To overcome these challenges, this study optimized a novel chemical pretreatment method for Sargassum spp. using ultrasound-assisted KMnO₄ and Na₂SO₃ at 20-60 °C. Key parameters, including reagent concentration, temperature, and reaction time, were refined, with optimal conditions established at 40 °C for 4 h. Ultrasound improved reagent permeability, while KMnO₄ and Na₂SO₃ disrupted the biomass structure through redox reactions. The cellulose content in the residual biomass increased from 11.99 wt% to 23.88 wt%, while AIR content decreased to 15.96 wt%. The maximum cellulose enzyme accessibility reached 19.56 mg/g. Compared to conventional methods, the glucose yield from Sargassum spp. hydrolysis increased from 51.62 mg/g to 107.75 mg/g, and ethanol yield from fermentation rose from 24.61 mg/g to 50.90 mg/g. This study presents a simple, cost-effective, efficient, and environmentally friendly pretreatment method for algal biomass, highlighting its significant industrial potential.

Characterization of two GH10 enzymes with ability to hydrolyze pretreated Sorghum bicolor bagasse

In this study, we characterized two novel enzymes of the glycoside hydrolase family 10 (GH10), Xyl10 C and Xyl10E, identified in the termite gut microbiome. The activities of both enzymes were assayed using beechwood xylan, barley β-glucan, and pretreated Sorghum bicolor bagasse (SBB) as substrates. Both enzymes, assessed individually and in combination, showed activity on beechwood xylan and pretreated SBB, whereas Xyl10E also showed activity on barley β-glucan. The composition of pretreated SBB mainly consisted of xylose and arabinose content. Purified Xyl10 C showed optimum xylanase activity in the pH range 7.0-8.0 and at a temperature of 50-60 °C, while Xyl10E was active at a wider pH range (5.0-10.0) and at 50 °C. The residual activities of Xyl10 C and Xyl10E after 8 h of incubation at 40 °C were 85% and 70%, respectively. The enzymatic activity of Xyl10 C increased to 115% in the presence of 5 M NaCl, was only inhibited in the presence of 0.5% sodium dodecyl sulfate (SDS), and decreased with β-mercaptoethanol. The xylanase and glucanase activities of Xyl10E were inhibited only in the presence of MnSO4, NaCl, and SDS. The main hydrolysis enzymatic product of Xyl10 C and Xyl10E on pretreated SBB was xylobiose. In addition, the xylo-oligosaccharides produced by xylanase Xyl10E on pretreated SBB demonstrated promising antioxidant activity. Thus, the hydrolysis products using Xyl10E on pretreated SBB indicate potential for antioxidant activity and other valuable industrial applications. KEY POINTS: • Two novel GH10 xylanases from the termite gut microbiome were characterized. • Xylo-oligosaccharides obtained from sorghum bagasse exhibited antioxidant potential. • Both enzymes and their hydrolysis product have potential to add value to agro-waste.

Acid hydrolysis pretreatment for extraction of oligosaccharides derived from spent coffee grounds: valorization of a promising biomass

The coffee industry generates approximately 6 million tons of waste annually, primarily spent coffee grounds (SCGs), whose disposal in landfills poses environmental risks. Therefore, new valorization strategies must be implemented to mitigate their environmental impact. In this sense, the objective of this study was to characterize SCGs and to optimize the dilute sulfuric acid pretreatment process for extracting oligosaccharides (OS). Optimal extraction conditions were determined using response surface methodology (RSM) with a Box-Behnken (BB) 33 design that included five central points for improved accuracy. The factors evaluated were temperature (140-190 °C), solid/liquid (S/L) ratio (1:40-1:4 g/mL), reaction time (20-120 min), and sulfuric acid concentration (0-2% v/v). Hemicellulose was identified as the predominant component, consisting mainly of mannose. OS extraction yields varied from 1.65 to 22.40 g per 100 g dry SCGs, depending on the process conditions. The quadratic model yielded an R2 value of 0.91128, indicating that the S/L ratio was the most influential factor, while reaction time had no significant effect. The optimized conditions-S/L ratio of 1:40 (g/mL), reaction time of 20 min, and H₂SO₄ concentration of 1.43% v/v at 168.57 °C-were experimentally validated and showed a margin of error of less than 9%. MALDI-TOF-MS analysis revealed oligosaccharide structures composed of hexose and pentose chains with up to eight sugar units. This study advances the understanding of OS extraction from SCGs via dilute acid pretreatment and provides valuable insight into waste valorization through process optimization and engineering approaches.

Deep eutectic solvent-enabled lignocellulosic biomass valorization: Toward understanding of biomass pretreatment, lignin dissolution, and lignin's antioxidant activity

A comprehensive study was conducted to determine the effects of water and ethylene glycol (EG) on biomass pretreatment using a binary deep eutectic solvent (DES) containing choline chloride and acetic acid (1ChCl3AC) at a mole ratio of 1:3. Different quantities of water and EG were combined with 1ChCl3AC to pretreat wheat straw, miscanthus, eucalyptus, and sorghum stalk at 130 °C for 6 h. The changes in nanopore structure and surface roughness of wet biomass, as well as biomass crystallinity after 1ChCl3AC-based pretreatment were investigated using XRD and small-angle neutron scattering (SANS). Adding a certain amount of water or EG did not reduce the delignification ratio or saccharification rate. Furthermore, SANS was used to explore the interactions between lignin, 1ChCl3AC, and water. The study found that lignin molecules produced various nanostructures through hydrogen bond, π-π, and hydrophobic interactions in 1ChCl3AC and its aqueous solutions. Following pretreatment, lignins were extracted and fractionated with three organic solvents to minimize structural heterogeneity. A collection of lignin antioxidants with varying activities was obtained, and antioxidant activity assessments revealed three distinct interactions amongst binary lignin combinations. The findings of this study add to our understanding of the interplay of 1ChCl3AC, water, EG, and lignin.

Lignocellulosic biomass as promising substrate for polyhydroxyalkanoate production: Advances and perspectives

The depletion of fossil resources, coupled with global warming and adverse environmental impact of traditional petroleum-based plastics, have necessitated the discovery of renewable resources and innovative biodegradable materials. Lignocellulosic biomass (LB) emerges as a highly promising, sustainable and eco-friendly approach for accumulating polyhydroxyalkanoate (PHA), as it completely bypasses the problem of "competition for food". This sustainable and economically efficient feedstock has the potential to lower PHA production costs and facilitate its competitive commercialization, and support the principles of circular bioeconomy. LB predominantly comprises cellulose, hemicellulose, and lignin, which can be converted into high-quality substrates for PHA production by various means. Future efforts should focus on maximizing the value derived from LB. This review highlights the momentous and valuable research breakthroughs in recent years, showcasing the biosynthesis of PHA using low-cost LB as a potential feedstock. The metabolic mechanism and pathways of PHA synthesis by microbes, as well as the key enzymes involved, are summarized, offering insights into improving microbial production capacity and fermentation metabolic engineering. Life cycle assessment and techno-economic analysis for sustainable and economical PHA production are introduced. Technological hurdles such as LB pretreatment, and performance limitations are highlighted for their impact on enhancing the sustainable production and application of PHA. Meanwhile, the development direction of co-substrate fermentation of LB and with other carbon sources, integrated processes development, and co-production strategies were also proposed to reduce the cost of PHA and effectively valorize wastes.

Xylooligosaccharides: A comprehensive review of production, purification, characterization, and quantification

Xylooligosaccharides (XOS), short-chain polymers with prebiotic properties, have gained significant commercial attention over the past few decades due to their potential as nutraceutical components. Derived from lignocellulosic biomass (LCB), XOS serve as health promoting compounds with applications across multiple sectors, including food pharmaceutical and cosmetic. This comprehensive review provides an overview of XOS production, purification, characterization, and quantification, highlighting their derivation from various sources such as agricultural waste, agro-economical forest residues, and nutrient-dense energy crops. The production of XOS involves enzymatic hydrolysis, acid hydrolysis, and steam explosion, each offering distinct advantages and limitations in terms of cost-effectiveness and scalability for industrial applications. Methods for purification including chromatographic techniques, membrane filtration, capillary electrophoresis (CE) and enzyme-linked immunosorbent assay (ELISA) are evaluated based on their efficiency and feasibility. Characterization techniques such as nuclear magnetic resonance (NMR) spectroscopy, high-performance liquid chromatography (HPLC), and mass spectrometry (MS) provide detailed insight into XOS structure and composition. Conclusively, XOS are promising biological macromolecules with significant industrial and scientific interest due to their diverse applications and potential for cos-effective large-scale production.

Revisiting alkali pretreatment to transform lignocellulose fermentation with integration of bioprocessible lignin

This study emphasized the synergistic production of bioprocessible lignin and carbohydrates during a sequential liquid hot water and alkali pretreatment of lignocellulose, facilitating their subsequent individual fermentation. Increasing the dose of alkaline lignin from 0 to 8 g/L inhibited cell growth in anaerobic digestion, with varying levels of inhibition observed in the following order: hydrolytic bacteria < acidogens < acetogens. Alkali pretreatment was adapted to maximize yields of bioprocessible lignin liquor without compromising utilization of the carbohydrates. Increasing the NaOH dose from 50 to 200 mg/g-feedstock monotonically improved lignin yields, but further increases in alkali loading led to a decline in lignin recovery. Volatile fatty acids production from anaerobic digestion of the carbohydrate moiety consistently increased with higher NaOH doses. The optimal conditions for maximizing lignin yields were determined to be 105 °C for 30 min, with NaOH loading in the range of 150-200 mg/g-feedstock, resulting in approximately 80 % lignin recovery, of which 35 % was biologically utilizable. Liquid hot water treatment prior to alkali pretreatment was confirmed as necessary to preserve carbohydrates of 0.1 g/g-feedstock at a low temperature of 70 °C. These findings are crucial for economically producing bioprocessible lignin without carbohydrate loss, a key step towards achieving full lignocellulose valorization.

Nanocellulose separation from barley straw via ultrasound-assisted choline chloride - Formic acid deep eutectic solvent pretreatment and high-intensity ultrasonication

The present study aims at investigating the application of ultrasound assisted choline chloride (ChCl) - formic acid (FA) deep eutectic solvent (DES) pretreatment of Barley straw. In addition, the efficiency of a wet grinding followed by high intensity ultrasound (HIUS) treatment for production of cellulose nanofibers (CNF) has been evaluated. The DES (using ChCl: FA at 1:9 M ratio) treatment at 45 kHz ultrasound frequency and 3 h of treatment duration resulted in 84.68 ± 1.02 % and 82.96 ± 0.79 % of lignin and hemicellulose solubilisation, respectively. The purification of DES treated solid residue resulted in cellulose with more than 90 % purity. Further, 10 min of wet grinding followed by 40 min of HIUS treatment resulted in more than 80 % nano-fibrillation efficiency. The produced CNF had diameters less than 100 nm in number size distribution and type I cellulose structure. This study confirmed that the developed process offers a sustainable method for producing nanocellulose from agricultural waste.

Assessment of the chemical composition of buriti (Mauritia flexuosa Liliopsida) and cassava (Manihot esculenta Crantz) residues and their possible application in the bioproduction of coconut aroma (6 pentyl-α-pyrone)

This work aimed to define strategies to increase the bioproduction of 6 pentyl-α-pyrone (bioaroma). As first strategy, fermentations were carried out in the solid state, with agro-industrial residues: Mauritia flexuosa Liliopsida. and Manihot esculenta Crantz in isolation, conducting them with different nutrient solutions having Trichoderma harzianum as a fermenting fungus. Physicochemical characterizations, centesimal composition, lignocellulosic and mineral content and antimicrobial activity were required. Fermentations were conducted under different humidification conditions (water, nutrient solution without additives and nutrient solutions with glucose or sucrose) for 9 days. Bioaroma was quantified by gas chromatography, assisted by solid-phase microextraction. The results showed the low production of this compound in fermentations conducted with sweet cassava (around 6 ppm (w/w)). The low bioproduction with sweet cassava residues can probably be related to its starch-rich composition, homogeneous substrate, and low concentration of nutrients. Already using buriti, the absence of aroma production was detected. Probably the presence of silicon and high lignin content in buriti minimized the fungal activity, making it difficult to obtain the aroma of interest. Given the characteristics presented by the waste, a new strategy was chosen: mixing waste in a 1:1 ratio. This fermentation resulted in the production of 156.24 ppm (w/w) of aroma using the nutrient solution added with glucose. This combination, therefore, promoted more favorable environment for the process, possibly due to the presence of fermentable sugars from sweet cassava and fatty acids from the buriti peel, thus proving the possibility of an increase of around 2500% in the bioproduction of coconut aroma.

Unlocking the potential of Algerian lignocellulosic biomass: exploring indigenous microbial diversity for enhanced enzyme and sugar production

Nowadays, natural resources like lignocellulosic biomass are gaining more and more attention. This study was conducted to analyse chemical composition of dried and ground samples (500 μm) of various Algerian bioresources including alfa stems (AS), dry palms (DP), olive pomace (OP), pinecones (PC), and tomato waste (TW). AS exhibited the lowest lignin content (3.60 ± 0.60%), but the highest cellulose (58.30 ± 2.06%), and hemicellulose (20.00 ± 3.07%) levels. DP, OP, and PC had around 30% cellulose, and 10% hemicellulose. OP had the highest lignin content (29.00 ± 6.40%), while TW contained (15.70 ± 2.67% cellulose, 13.70 ± 0.002% hemicellulose, and 17.90 ± 4.00% lignin). Among 91 isolated microorganisms, nine were selected for cellulase, xylanase, and/or laccase production. The ability of Bacillus mojavensis to produce laccase and cellulase, as well as B. safensis to produce cellulase and xylanase, is being reported for the first time. In submerged conditions, TW was the most suitable substrate for enzyme production. In this conditions, T. versicolor K1 was the only strain able to produce laccase (4,170 ± 556 U/L). Additionally, Coniocheata hoffmannii P4 exhibited the highest cellulase activity (907.62 ± 26.22 U/L), and B. mojavensis Y3 the highest xylanase activity (612.73 ± 12.73 U/L). T. versicolor K1 culture showed reducing sugars accumulation of 18.87% compared to initial concentrations. Sucrose was the predominant sugar detected by HPLC analysis (13.44 ± 0.02 g/L). Our findings suggest that T. versicolor K1 holds promise for laccase production, while TW represents a suitable substrate for sucrose production.

Composition of Lignocellulose Hydrolysate in Different Biorefinery Strategies: Nutrients and Inhibitors

The hydrolysis and biotransformation of lignocellulose, i.e., biorefinery, can provide human beings with biofuels, bio-based chemicals, and materials, and is an important technology to solve the fossil energy crisis and promote global sustainable development. Biorefinery involves steps such as pretreatment, saccharification, and fermentation, and researchers have developed a variety of biorefinery strategies to optimize the process and reduce process costs in recent years. Lignocellulosic hydrolysates are platforms that connect the saccharification process and downstream fermentation. The hydrolysate composition is closely related to biomass raw materials, the pretreatment process, and the choice of biorefining strategies, and provides not only nutrients but also possible inhibitors for downstream fermentation. In this review, we summarized the effects of each stage of lignocellulosic biorefinery on nutrients and possible inhibitors, analyzed the huge differences in nutrient retention and inhibitor generation among various biorefinery strategies, and emphasized that all steps in lignocellulose biorefinery need to be considered comprehensively to achieve maximum nutrient retention and optimal control of inhibitors at low cost, to provide a reference for the development of biomass energy and chemicals.

A novel endo-1,4-β-xylanase from Alicyclobacillus mali FL18: Biochemical characterization and its synergistic action with β-xylosidase in hemicellulose deconstruction

A novel endo-1,4-β-xylanase-encoding gene was identified in Alicyclobacillus mali FL18 and the recombinant protein, named AmXyn, was purified and biochemically characterized. The monomeric enzyme worked optimally at pH 6.6 and 80 °C on beechwood xylan with a specific activity of 440.00 ± 0.02 U/mg and a good catalytic efficiency (kcat/KM = 91.89 s-1mLmg-1). In addition, the enzyme did not display any activity on cellulose, suggesting a possible application in paper biobleaching processes. To develop an enzymatic mixture for xylan degradation, the association between AmXyn and the previously characterized β-xylosidase AmβXyl, deriving from the same microorganism, was assessed. The two enzymes had similar temperature and pH optima and showed the highest degree of synergy when AmXyn and AmβXyl were added sequentially to beechwood xylan, making this mixture cost-competitive and suitable for industrial use. Therefore, this enzymatic cocktail was also employed for the hydrolysis of wheat bran residue. TLC and HPAEC-PAD analyses revealed a high conversion rate to xylose (91.56 %), placing AmXyn and AmβXyl among the most promising biocatalysts for the saccharification of agricultural waste.

Extrusion puffing as a pretreatment method to change the surface structure, physicochemical properties and in vitro protein digestibility of distillers dried grains with solubles

BACKGROUND

Distillers dried grains with solubles (DDGS) are rich in nutrition, and they are potential protein feed raw material. However, the existence of cellulose, hemicellulose and lignin hinders animals' digestion and absorption of DDGS. Making full use of unconventional feed resources such as DDGS can alleviate the shortage of feed resources to a certain extent. This research investigated the effects of twin-screw extrusion on the macromolecular composition, physical and chemical properties, surface structure and in vitro protein digestibility (IVPD) of DDGS.

RESULTS

The findings showed that extrusion puffing significantly increased the protein solubility, bulk density, water holding capacity, and swelling capacity, while significantly decreased hemicellulose and crude protein content, particle size and zeta potential of DDGS. The structure damage of DDGS induced by the extrusion was characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FITR) spectroscopy and X-ray diffraction (XRD) analysis. Interestingly, no random coil was observed in the analysis of the secondary structure, and extrusion promoted the transformation of α-helix and β-turn to β-sheet, which led to significant increases in protein solubility and IVPD of DDGS (P < 0.05). Additionally, correlation analysis revealed that IVPD and PS had a positive relationship.

CONCLUSION

Extrusion puffing was an ideal pretreatment method for DDGS modification to improve in vitro protein digestibility. © 2023 Society of Chemical Industry.

Efficient hemicellulose removal from lignocellulose by induced electric field-aided dilute acid pretreatment

This study evaluated the effectiveness of induced electric field (IEF) as a novel electrotechnology to assist dilute acid pretreatment of wheat straw (WS) at atmospheric pressure and low temperature (90 °C). The effects of acid concentration and duration on cellulose recovery, hemicellulose and lignin removal were investigated. Meanwhile, the differences between IEF pretreatment and hydrothermal pretreatment were compared by quantitative and qualitative analysis. The optimal pretreatment condition was acid concentration 1 % with the period of 5 h. Under the parameters, the hemicellulose removal of WS after IEF pretreatment was up to 73.6 %, and the enzymatic efficiency was 55.8 %. In addition, the irregular surface morphology, diminished functional groups associated with hemicellulose, increased specific surface area and pore volume, as well as improved thermal stability of the residual WS support the remarkable effect of IEF pretreatment. The feasibility of IEF pretreatment is might be due to the fact that the magneto-induced electric field promotes ionization of H+ and formation of hydrated hydrogen ions, increasing the acidity of the medium. Secondly, electroporation disrupts the anti-degradation structure of WS and increases the accessibility of cellulose to cellulases. It indicated that IEF is a green and efficient strategy for assisting the separation of hemicellulose from lignocellulose.

Lignin-degrading enzyme production was enhanced by the novel transcription factor Ptf6 in synergistic microbial co-culture

Synergistic microbial co-culture has been an efficient and energy-saving strategy to produce lignin-degrading enzymes (LDEs), including laccase, manganese peroxidase, and versatile peroxidase. However, the regulatory mechanism of microbial co-culture is still unclear. Herein, the extracellular LDE activities of four white-rot fungi were significantly increased by 88-544% over monoculture levels when co-cultured with Rhodotorula mucilaginosa. Ptf6 was demonstrated from the 9 million Y1H clone library to be a shared GATA transcription factor in the four fungi, and could directly bind to the laccase gene promoter. Ptf6 exists in two alternatively spliced isoforms under monoculture, namely Ptf6-α (1078 amino acids) containing Cys2/Cys2-type zinc finger and Ptf6-β (963 amino acids) lacking the complete domain. Ptf6 responded to co-culture by up-regulation of both its own transcripts and the proportion of Ptf6-α. Ptf6-α positively activated the production of most LDE isoenzymes and bound to four GATA motifs on the LDEs' promoter with different affinities. Moreover, Ptf6-regulation mechanism can be applicable to a variety of microbial co-culture systems. This study lays a theoretical foundation for further improving LDEs production and providing an efficient way to enhance the effects of biological and enzymatic pretreatment for lignocellulosic biomass conversion.

Crop byproducts supplemented in livestock feeds reduced greenhouse gas emissions

Crop byproducts can be supplemented in livestock feeds to improve the utilization of resources and reduce greenhouse gas (GHG) emissions. We explored the mitigation potential of GHG emissions by supplementing crop byproducts in feeds based on a typical intensive dairy farm in China. Results showed that GHG emissions associated with production of forage were significantly decreased by 25.60 % when no GHG emissions were allocated to crop byproducts, and enteric methane emission was significantly decreased by 13.46 % on the basis of CO2 eq, g/kg fat and protein corrected milk. The supplementation did not affect lactation performance, rumen microbiota and microbial enzymes at the gene level. Metabolomics analysis revealed changes in amino acid catabolism of rumen fluid, which were probably responsible for more propionate production. In conclusion, supplementing crop byproducts in feeds can be a potential strategy to reduce GHG emissions of livestock.

Engineering Saccharomyces cerevisiae for application in integrated bioprocessing biorefineries

After decades of research and development, no organism - natural or engineered - has been described that can produce commodity products through direct microbial conversion to meet industry demands in terms of rates and yields. Variation in lignocellulosic biomass (LCB) feedstocks, the lack of a widely applicable pretreatment method, and the limited economic value of energy products further complicates second-generation biofuel production. Nevertheless, the emergence of advanced genomic editing tools and a more comprehensive understanding of yeast metabolic systems offer promising avenues for the creation of yeast strains tailored to LCB biorefineries. Here, we discuss recent advances toward developing yeast strains that could convert different LCB fractions into a series of economically viable commodity products in a biorefinery.

Computer-Aided Reconstruction and Application of Bacillus halodurans S7 Xylanase with Heat and Alkali Resistance

β-1,4-Endoxylanase is the most critical hydrolase for xylan degradation during lignocellulosic biomass utilization. However, its poor stability and activity in hot and alkaline environments hinder its widespread application. In this study, BhS7Xyl from Bacillus halodurans S7 was improved using a computer-aided design through isothermal compressibility (βT) perturbation engineering and by combining three thermostability prediction algorithms (ICPE-TPA). The best variant with remarkable improvement in specific activity, heat resistance (70 °C), and alkaline resistance (both pH 9.0 and 70 °C), R69F/E137M/E145L, exhibited a 4.9-fold increase by wild-type in specific activity (1368.6 U/mg), a 39.4-fold increase in temperature half-life (458.1 min), and a 57.6-fold increase in pH half-life (383.1 min). Furthermore, R69F/E137M/E145L was applied to the hydrolysis of agricultural waste (corncob and hardwood pulp) to efficiently obtain a higher yield of high-value xylooligosaccharides. Overall, the ICPE-TPA strategy has the potential to improve the functional performance of enzymes under extreme conditions for the high-value utilization of lignocellulosic biomass.

Metabolic engineering of Paenibacillus polymyxa for effective production of 2,3-butanediol from poplar hydrolysate

2,3-Butanediol is an essential renewable fuel. The synthesis of 2,3-butanediol using Paenibacillus polymyxa has attracted increasing attention. In this study, the glucose-derived 2,3-butanediol pathway and its related genes were identified in P. polymyxa using combined transcriptome and metabolome analyses. The functions of two distinct genes ldh1 and ldh3 encoding lactate dehydrogenase, the gene bdh encoding butanediol dehydrogenase, and the spore-forming genes spo0A and spoIIE were studied and directly knocked out or overexpressed in the genome sequence to improve the production of 2,3-butanediol. A raw hydrolysate of poplar wood containing 27 g/L glucose and 15 g/L xylose was used to produce 2,3-butanediol with a maximum yield of 0.465 g/g and 93 % of the maximum theoretical value, and the total production of 2,3-butanediol and ethanol reached 21.7 g/L. This study provides a new scheme for engineered P. polymyxa to produce renewable fuels using raw poplar wood hydrolysates.

Optimization of biogas production from straw wastes by different pretreatments: Progress, challenges, and prospects

Lignocellulosic biomass (LCB) presents a promising feedstock for carbon management due to enormous potential for achieving carbon neutrality and delivering substantial environmental and economic benefit. Bioenergy derived from LCB accounts for about 10.3 % of the global total energy supply. The generation of bioenergy through anaerobic digestion (AD) in combination with carbon capture and storage, particularly for methane production, provides a cost-effective solution to mitigate greenhouse gas emissions, while concurrently facilitating bioenergy production and the recovery of high-value products during LCB conversion. However, the inherent recalcitrant polymer crystal structure of lignocellulose impedes the accessibility of anaerobic bacteria, necessitating lignocellulosic residue pretreatment before AD or microbial chain elongation. This paper seeks to explore recent advances in pretreatment methods for LCB biogas production, including pulsed electric field (PEF), electron beam irradiation (EBI), freezing-thawing pretreatment, microaerobic pretreatment, and nanomaterials-based pretreatment, and provide a comprehensive overview of the performance, benefits, and drawbacks of the traditional and improved treatment methods. In particular, physical-chemical pretreatment emerges as a flexible and effective option for methane production from straw wastes. The burgeoning field of nanomaterials has provoked progress in the development of artificial enzyme mimetics and enzyme immobilization techniques, compensating for the intrinsic defect of natural enzyme. However, various complex factors, such as economic effectiveness, environmental impact, and operational feasibility, influence the implementation of LCB pretreatment processes. Techno-economic analysis (TEA), life cycle assessment (LCA), and artificial intelligence technologies provide efficient means for evaluating and selecting pretreatment methods. This paper addresses current issues and development priorities for the achievement of the appropriate and sustainable utilization of LCB in light of evolving economic and environmentally friendly social development demands, thereby providing theoretical basis and technical guidance for improving LCB biogas production of AD systems.

Innovative parallel synthesis of 5-nonanone and furfural from lignocellulosic biomass accompanied by deep economic analysis

An integrated strategy is developed to utilize all three primary components (cellulose, hemicellulose, and lignin) of lignocellulosic biomass for the coproduction of hydrocarbon fuel (5-nonanone) and bio-chemicals (furfural and high purity lignin). After biomass fractionation, (1) 5-nonanone is produced with high yield of 89% using cellulose-derived γ-valerolactone (GVL), which can potentially serve as a platform molecule for the production of liquid hydrocarbon fuels for the transportation sector; (2) furfural, a valuable platform chemical, is produced using hemicellulose; and (3) production of high-purity lignin, which can be used to produce carbon foams or battery anodes. Separation subsystems are designed to effectively recover the solvents for reuse in the conversion processes, which ultimately improves the economic feasibility of the integrated process, resulting in achieving lower minimum selling price (MSP) of $5.47 GGE-1 for 5-nonanone compared to market price. Heat pump is introduced to perform heat integration, which reduces utility requirements more than 85%. Finally, a wide range of techno-economic analysis is performed to highlight the major cost and technological drivers of the integrated process.

Selective separation of hemicellulose from poplar by hydrothermal pretreatment with ferric chloride and pH buffer

As an environmentally friendly lignocellulosic biomass separation technology, hydrothermal pretreatment (HP) has a strong application prospect. However, the low separation efficiency is a main factor limiting its application. In this study, the poplar components were separated using HP with ferric chloride and pH buffer (HFB). The optimal conditions were ferric chloride concentration of 0.10 M, reaction temperature of 150 °C, reaction time of 15 min and pH 1.9. The separation of hemicellulose was increased 34.03 % to 77.02 %. The pH buffering resulted in the highest cellulose and lignin retention yields compared to ferric chloride pretreatment (FC). The high efficiency separation of hemicellulose via HFB pretreatment inhibited the degradation of xylose. The hydrolysate was effectively reused for five times. The fiber crystallinity index reached 60.05 %, and the highest C/O ratio was obtained. The results provide theoretical support for improving the efficiency of HP and promoting its application.

Enhanced fermentable sugar production in lignocellulosic biorefinery by exploring a novel corn stover and configuring high-solid pretreatment conditions

This study aimed to produce enhanced fermentable sugars from a novel stover system through the bioprocessing of its soluble sugars and insoluble carbohydrates. The pretreatment conditions were optimized for this high sugar-containing stover (HSS) to control inhibitor formation and obtain enhanced fermentable sugar concentrations. The optimum temperature, acid loading, and reaction time for the pretreatment were 155 °C, 0.5%, and 30 min, respectively, providing up to 97.15% sugar yield and 76.51 g/L total sugars at 10% solid-load. Sugar concentration further increased to 126.9 g/L at 20% solid-load, generating 3.89 g/L acetate, 0.92 g/L 5-hydroxymethyl furfural, 0.82 g/L furfural, and 3.75 g/L total phenolics as inhibitors. To determine the effects of soluble sugars in HSS on fermentable sugar yield and inhibitor formation, sugar-removed HSS was further studied under the optimum conditions. Although prior removal of sugars exhibited a reduction in inhibitor generation, it also decreased total fermentable sugar production to 115.45 g/L.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Development of lignocellulosic biorefineries for the sustainable production of biofuels: Towards circular bioeconomy

The idea of environment friendly and affordable renewable energy resources has prompted the industry to focus on the set up of biorefineries for sustainable bioeconomy. Lignocellulosic biomass (LCB) is considered as an abundantly available renewable feedstock for the production of biofuels which can potentially reduce the dependence on petrochemical refineries. By utilizing various conversion technologies, an integrated biorefinery platform of LCB can be created, embracing the idea of the 'circular bioeconomy'. The development of effective pretreatment methods and biocatalytic systems by various bioengineering and machine learning approaches could reduce the bioprocessing costs, thereby making biomass-based biorefinery more sustainable. This review summarizes the development and advances in the lignocellulosic biorefineries from the LCB to the final product stage using various different state-of-the-art approaches for the progress of circular bioeconomy. The life cycle assessment which generates knowledge on the environmental impacts related to biofuel production chains is also summarized.

Strategies of pretreatment of feedstocks for optimized bioethanol production: distinct and integrated approaches

Bioethanol is recognized as a valuable substitute for renewable energy sources to meet the fuel and energy demand of the nation, considered an environmentally friendly resource obtained from agricultural residues such as sugarcane bagasse, rice straw, husk, wheat straw and corn stover. The energy demand is sustained using lignocellulosic biomass to produce bioethanol. Lignocellulosic biomass (LCBs) is the point of attention in replacing the dependence on fossil fuels. The recalcitrant structure of the lignocellulosic biomass is disrupted using effective pretreatment techniques that separate complex interlinked structures among cellulose, hemicellulose, and lignin. Pretreatment of biomass involves various physical, chemical, biological, and physiochemical protocols which are of importance, dependent upon their individual or combined dissolution effect. Physical pretreatment involves a reduction in the size of the biomass using mechanical, extrusion, irradiation, and sonification methods while chemical pretreatment involves the breaking of various bonds present in the LCB structure. This can be obtained by using an acidic, alkaline, ionic liquid, and organosolvent methods. Biological pretreatment is considered an environment-friendly and safe process involving various bacterial and fungal microorganisms. Distinct pretreatment methods, when combined and utilized in synchronization lead to more effective disruption of LCB, making biomass more accessible for further processing. These could be utilized in terms of their effectiveness for a particular type of cellulosic fiber and are namely steam explosion, liquid hot water, ammonia fibre explosion, CO2 explosion, and wet air oxidation methods. The present review encircles various distinct and integrated pretreatment processes developed till now and their advancement according to the current trend and future aspects to make lignocellulosic biomass available for further hydrolysis and fermentation.