A comprehensive review on the framework to valorise lignocellulosic biomass as biorefinery feedstocks

Promoting lignocellulosic biorefinery by machine learning: progress, perspectives and challenges

The lignocellulosic biorefinery involves pretreatment, enzymatic hydrolysis, mixed sugar fermentation, and optional anaerobic digestion. This pipeline could be effectively implemented through machine learning (ML)-guided process optimization and strain modification rather than experimental or experience-based ones. This review takes a holistic perspective on the entire pipeline, discussing how ML could aid lignocellulosic, while other published work has focused on individual modules within the pipeline. This review also explores the model construction and evaluation strategies and highlights the emerging potential of transfer learning and hybrid ML models to address data insufficiency and improve model interpretability. Furthermore, challenges and future prospects of ML in lignocellulosic biorefinery will be elaborated in this review. Integrating ML into lignocellulosic biorefinery offers a promising pathway towards sustainable and competitive biorefinery systems.

Acetic acid production from corn straw via enzymatic degradation using putative acetyl esterase from the metagenome assembled genome

Acetic acid production from corn straw by enzyme catalysis shows its application value in food industry. In this study, a gene encoding for a putative acetyl esterase derived from Sphingobacterium soilsilvae Em02 was discovered in metagenome assembled genome. The gene was expressed in Escherichia coli BL21 to obtain enzyme with a molecular mass of 38.8 kDa. P-Nitrophenyl acetate was used as a substrate to determine the enzyme activity. The enzyme demonstrated optimal activity under conditions of 40 °C and a neutral pH of 7.0. Under optimal conditions, 17.58 mg of acetic acid was obtained using the enzyme from 50 mg corn straw pretreated with amylase. The acetyl esterase derived from Sphingobacterium soilsilvae Em02, demonstrates significant potential for biotechnological applications, particularly in biomass degradation.

Integrated Bioelectrochemical Conversion of Bacillus subtilis-Pretreated Sugar Cane Bagasse: Metabolic Profile Optimization for Enhanced Microbial Fuel Cell Efficiency and Sustainable Biorefinery Applications

Lignocellulose recalcitrance remains a significant economic challenge in modern biomass conversion processes. Microbial strategies offer considerable promise for ecofriendly bioenergy generation. This study presents an advanced integrated approach that combines bacterial treatment with a bioelectrochemical system (BES) to enhance the conversion efficiency of lignocellulosic biomass. Unlike integrated or sequential approaches, a comparative evaluation of two distinct pretreatment strategies, alkaline delignification and biological treatment, was conducted independently to assess their individual effectiveness in sugar cane bagasse (SCB) degradation and their performance in a microbial fuel cell (MFC). Biological treatment with B. subtilis alone yielded superior outcomes in terms of saccharification efficiency, microbial growth, and bioelectricity generation, as evidenced by higher open-circuit potentials in MFC half-cell studies in comparison with alkali delignified SCB. Notably, B. subtilis treatment increased cellulose content by 72% and reduced hemicellulose and lignin by approximately 0.84-fold, indicating effective enzymatic action. Metabolomic profiling identified 2846 metabolites that significantly diverged between the experimental groups. Notably, lignin-derived compounds such as ferulic acid, syringic acid, and p-coumaric acid were detected at elevated levels, confirming enhanced ligninase activity in pretreated SCB. Additionally, the presence of organic acids (e.g., acetic acid), amino acids, and their derivatives, resulting from the breakdown of cellulose, hemicellulose, and lignin, provided essential bioenergy substrates for exoelectrogenic organisms in BESs. This integration led to a maximum power density of 353 ± 5 mW/m2 and a current density of 200 ± 3 mA/m2, demonstrating significant enhancement in performance of MFC. Furthermore, the biotransformation of SCB facilitated the channeling of metabolites into value-added products, increasing the overall efficiency of the biomass valorization. Thus, the rational utilization of SCB underscores its potential for scalable biorefinery applications and its broader implications for sustainable bioenergy production.

Lignocellulosic materials valorization in second generation biorefineries: an opportunity to produce fungal biopigments

Second generation biorefineries play an important role in the production of renewable energy and fuels, utilizing forest and agro-industrial residues and by-products as raw materials. The integration of novel bioproducts, such as: xylitol, β-carotene, xylooligosaccharides, and biopigments into the biorefinery's portfolio can offer economic benefits in the valorization of lignocellulosic materials, particularly cellulosic and hemicellulosic fractions. Fungal biopigments, known for their additional antioxidant and antimicrobial properties, are appealing to consumers and can have applications in various industrial sectors, including food and pharmaceuticals. The use of lignocellulosic materials as carbon and nutrient sources for the growth medium helps to reduce production costs, increasing the competitiveness of fungal biopigments in the market. In addition, the implementation of biopigment production in biorefineries allows the utilization of underutilized fractions, such as hemicellulose, for value-added bioproducts. This study deals with the potential of fungal biopigments production in second generation biorefineries in order to diversify the produced biomolecules together with energy generation. A comprehensive and critical review of the recent literature on this topic has been conducted, covering the major possible raw materials, general aspects of second generation biorefineries, the fungal biopigments and their potential for incorporation into biorefineries.

Surface modification of cellulose nanocrystals for biomedical and personal hygiene applications

The increasing demand for sustainable and effective materials in biomedical and personal hygiene applications has driven the exploration of cellulose nanocrystals (CNCs) derived from biomass. These nanomaterials are highly valued for their exceptional mechanical properties, biocompatibility, and renewable nature. Researchers are exploring CNCs for advancing medical and hygiene products, but surface modification is often needed to maximize their benefits. Techniques such as chemical functionalization, physical coating, and hybridization can significantly enhance CNCs dispersibility, stability, and interaction with biological systems. This versatility makes CNCs suitable for a variety of applications, including drug delivery systems, wound dressings, and personal hygiene products. Despite their advantages, maintaining the inherent properties of CNCs while integrating new functionalities through modification poses a challenge. Understanding the impact of various modification techniques on CNC performance is crucial for optimizing their effectiveness. This review aimed to consolidate current knowledge on the surface modification of biomass-derived CNCs, offering insights into different methods and their implications for biomedical and personal hygiene applications. By highlighting advancements, challenges, and prospects, it served as a crucial resource for advancing the development and application of CNCs in these critical fields.

Biorefinery and Bioremediation Strategies for Efficient Management of Recalcitrant Pollutants Using Termites as an Obscure yet Promising Source of Bacterial Gut Symbionts: A Review

Lignocellulosic biomass (LCB) in the form of agricultural, forestry, and agro-industrial wastes is globally generated in large volumes every year. The chemical components of LCB render them a substrate valuable for biofuel production. It is hard to dissolve LCB resources for biofuel production because the lignin, cellulose, and hemicellulose parts stick together rigidly. This makes the structure complex, hierarchical, and resistant. Owing to these restrictions, the junk production of LCB waste has recently become a significant worldwide environmental problem resulting from inefficient disposal techniques and increased persistence. In addition, burning LCB waste, such as paddy straws, is a widespread practice that causes considerable air pollution and endangers the environment and human existence. Besides environmental pollution from LCB waste, increasing industrialization has resulted in the production of billions of tons of dyeing wastewater from several industries, including textiles, pharmaceuticals, tanneries, and food processing units. The massive use of synthetic dyes in various industries can be detrimental to the environment due to the recalcitrant aromatic structure of synthetic dyes, similar to the polymeric phenol lignin in LCB structure, and their persistent color. Synthetic dyes have been described as possessing carcinogenic and toxic properties that could be harmful to public health. Environmental pollution emanating from LCB wastes and dyeing wastewater is of great concern and should be carefully handled to mitigate its catastrophic effects. An effective strategy to curtail these problems is to learn from analogous systems in nature, such as termites, where woody lignocellulose is digested by wood-feeding termites and humus-recalcitrant aromatic compounds are decomposed by soil-feeding termites. The termite gut system acts as a unique bioresource consisting of distinct bacterial species valued for the processing of lignocellulosic materials and the degradation of synthetic dyes, which can be integrated into modern biorefineries for processing LCB waste and bioremediation applications for the treatment of dyeing wastewaters to help resolve environmental issues arising from LCB waste and dyeing wastewaters. This review paper provides a new strategy for efficient management of recalcitrant pollutants by exploring the potential application of termite gut bacteria in biorefinery and bioremediation processing.

Engineering oleaginous red yeasts as versatile chassis for the production of oleochemicals and valuable compounds: Current advances and perspectives

Enabling the transition towards a future circular bioeconomy based on industrial biomanufacturing necessitates the development of efficient and versatile microbial platforms for sustainable chemical and fuel production. Recently, there has been growing interest in engineering non-model microbes as superior biomanufacturing platforms due to their broad substrate range and high resistance to stress conditions. Among these non-conventional microbes, red yeasts belonging to the genus Rhodotorula have emerged as promising industrial chassis for the production of specialty chemicals such as oleochemicals, organic acids, fatty acid derivatives, terpenoids, and other valuable compounds. Advancements in genetic and metabolic engineering techniques, coupled with systems biology analysis, have significantly enhanced the production capacity of red yeasts. These developments have also expanded the range of substrates and products that can be utilized or synthesized by these yeast species. This review comprehensively examines the current efforts and recent progress made in red yeast research. It encompasses the exploration of available substrates, systems analysis using multi-omics data, establishment of genome-scale models, development of efficient molecular tools, identification of genetic elements, and engineering approaches for the production of various industrially relevant bioproducts. Furthermore, strategies to improve substrate conversion and product formation both with systematic and synthetic biology approaches are discussed, along with future directions and perspectives in improving red yeasts as more versatile biotechnological chassis in contributing to a circular bioeconomy. The review aims to provide insights and directions for further research in this rapidly evolving field. Ultimately, harnessing the capabilities of red yeasts will play a crucial role in paving the way towards next-generation sustainable bioeconomy.

Utilization of benzoic acid-based green deep eutectic solvents for the fractionation of lignocellulosic biomass

The fractionation of lignocellulose utilizing green solvents is essential for the effective operation of biorefineries. In this study, a deep eutectic solvent (DES) system composed of benzoic acid (BA, hydrogen bond donor) and choline chloride (ChCl, hydrogen bond acceptor) was fabricated and successfully applied to the lignocellulose fractionation. The DES has low toxicity and little pollution. In this system, 67.8 % of lignin and 91.2 % of hemicellulose in poplar were removed, leaving 95.8 % of cellulose intact as solid residue. Due to the removal of the amorphous components, crystallinity of cellulose-rich water-insoluble solid (CIS) substantially increased from 55.6 % to 68.6 %, and CIS was used as feedstock for nanocrystalline cellulose preparation with excellent properties. The results showed that the obtained lignin had similar properties to CEL by GPC, FT-IR, 2D-NMR and TGA. A high-purity lignin rich in G units was recovered with a well-preserved structure, which has β-O-4 linkage content up to 53.01 %, low molecular weight, low polydispersity (1.99). Finally, the hydrolyzate can be used for fermentation. This study demonstrated that BA is suitable for DES design with excellent properties on lignin extraction, and this promising DES enable efficient pretreatment for economically feasible biomass conversion. This ChCl-BA DES facilitates environmentally friendly production of functional materials derived from cellulose and lignin under mild conditions.

Maximizing microbial activity and synergistic interaction to boost biofuel production from lignocellulosic biomass

Addressing global environmental challenges and meeting the escalating energy demands stand as two pivotal issues in the current landscape. Lignocellulosic biomass emerges as a promising renewable bio-energy source capable of fulfilling the world's energy requirements on a large scale. One of the most important steps in lowering reliance on fossil fuel and lessening environmental effect is turning lignocellulosic biomass into biofuel. As carbon-neutral substitutes for traditional fuel, biofuel offer a solution to environmental concerns compared to conventional fuel. Effective utilization of lignocellulosic biomass is imperative for sustainable development. Ongoing research focuses on exploring the potential of various microorganisms and their co-interactions to synthesize diverse biofuels from different starting materials, including lignocellulosic biomass. Co-culture techniques demonstrate resilience to nutrient scarcity and environmental fluctuations. By utilising a variety of carbon sources, microbes can enhance their adaptability to environmental stressors and potentially increase productivity through their symbiotic interactions. Furthermore, compared to single organism involvement, co-interactions allow faster execution of multistep processes. Lignocellulosic biomass serves as a primary substrate for pre-treatment, fermentation, and enzymatic hydrolysis processes. This review primarily delves into the pretreatment, enzymatic hydrolysis process and the biochemical pathways involved in converting lignocellulosic biomass into bioenergy.

CRISPR/Cas9 mediated targeted knock-in of eglA gene to improve endoglucanase activity of Aspergillus fumigatus LMB-35Aa

Bioeconomy goals for using biomass feedstock for biofuels and bio-based production has arisen the demand for fungal strains and enzymes for biomass processing. Despite well-known Trichoderma and Aspergillus commercial strains, continuous bioprospecting has revealed the fungal biodiversity potential for production of biomass degrading enzymes. The strain Aspergillus fumigatus LMB-35Aa has revealed a great potential as source of lignocellulose-degrading enzymes. Nevertheless, genetic improvement should be considered to increase its biotechnological potential. Molecular manipulation based on homologous direct recombination (HDR) in filamentous fungi poses a challenge since its low recombination rate. Currently, CRISPR/Cas9-mediated mutagenesis can enable precise and efficient editing of filamentous fungi genomes. In this study, a CRISPR/Cas9-mediated gene editing strategy for improving endoglucanase activity of A. fumigatus LMB-35Aa strain was successfully used, which constitutes the first report of heterologous cellulase production in filamentous fungi using this technology. For this, eglA gene from A. niger ATCC 10,864 was integrated into conidial melanin pksP gene locus, which facilitated the selection of edited events discerned by the emergence of albino colonies. Heterologous production of the EglA enzyme in a biofilm fermentation system resulted in a 40% improvement in endoglucanase activity of the mutant strain compared to the wild type.

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.

Harnessing recalcitrant lignocellulosic biomass for enhanced biohydrogen production: Recent advances, challenges, and future perspective

Biohydrogen (Bio-H2) is widely recognized as a sustainable and environmentally friendly energy source, devoid of any detrimental impact on the environment. Lignocellulosic biomass (LB) is a readily accessible and plentiful source material that can be effectively employed as a cost-effective and sustainable substrate for Bio-H2 production. Despite the numerous challenges, the ongoing progress in LB pretreatment technology, microbial fermentation, and the integration of molecular biology techniques have the potential to enhance Bio-H2 productivity and yield. Consequently, this technology exhibits efficiency and the capacity to meet the future energy demands associated with the valorization of recalcitrant biomass. To date, several pretreatment approaches have been investigated in order to improve the digestibility of feedstock. Nevertheless, there has been a lack of comprehensive systematic studies examining the effectiveness of pretreatment methods in enhancing Bio-H2 production through dark fermentation. Additionally, there is a dearth of economic feasibility evaluations pertaining to this area of research. Thus, this review has conducted comparative studies on the technological and economic viability of current pretreatment methods. It has also examined the potential of these pretreatments in terms of carbon neutrality and circular economy principles. This review paves the way for a new opportunity to enhance Bio-H2 production with technological approaches.

Exploitation of lignocellulosic-based biomass biorefinery: A critical review of renewable bioresource, sustainability and economic views

Urbanization has driven the demand for fossil fuels, however, the overly exploited resource has caused severe damage on environmental pollution. Biorefining using abundant lignocellulosic biomass is an emerging strategy to replace traditional fossil fuels. Value-added lignin biomass reduces the waste pollution in the environment and provides a green path of conversion to obtain renewable resources. The technology is designed to produce biofuels, biomaterials and value-added products from lignocellulosic biomass. In the biorefinery process, the pretreatment step is required to reduce the recalcitrant structure of lignocellulose biomass and improve the enzymatic digestion. There is still a gap in the full and deep understanding of the biorefinery process including the pretreatment process, thus it is necessary to provide optimized and adapted biorefinery solutions to cope with the conversion process in different biorefineries to further provide efficiency in industrial applications. Current research progress on value-added applications of lignocellulosic biomass still stagnates at the biofuel phase, and there is a lack of comprehensive discussion of emerging potential applications. This review article explores the advantages, disadvantages and properties of pretreatment methods including physical, chemical, physico-chemical and biological pretreatment methods. Value-added bioproducts produced from lignocellulosic biomass were comprehensively evaluated in terms of encompassing biochemical products , cosmetics, pharmaceuticals, potent functional materials from cellulose and lignin, waste management alternatives, multifunctional carbon materials and eco-friendly products. This review article critically identifies research-related to sustainability of lignocellulosic biomass to promote the development of green chemistry and to facilitate the refinement of high-value, environmentally-friendly materials. In addition, to align commercialized practice of lignocellulosic biomass application towards the 21st century, this paper provides a comprehensive analysis of lignocellulosic biomass biorefining and the utilization of biorefinery green technologies is further analyzed as being considered sustainable, including having potential benefits in terms of environmental, economic and social impacts. This facilitates sustainability options for biorefinery processes by providing policy makers with intuitive evaluation and guidance.

A high throughput screening process and quick isolation of novel lignin-degrading microbes from large number of natural biomasses

High throughput screening approaches can significantly speed up the identification of novel enzymes from natural microbial consortiums. A two-step high throughput screening process was proposed and explored to screen lignin-degrading microorganisms. By employing this modified culture enrichment method and screening based on enzyme activity, a total of 82 bacterial and 46 fungal strains were isolated from fifty decayed wood samples (100 liquid cultures) collected from the banks of the Ottawa River in Canada. Among them, ten bacterial and five fungal strains were selected and identified based on their high laccase activities by 16S rDNA and ITS gene sequencing, respectively. The study identified bacterial strains from various genera including Serratia, Enterobacter, Raoultella, and Bacillus, along with fungal counterparts including Mucor, Trametes, Conifera and Aspergillus. Moreover, Aspergillus sydowii (AORF21), Mucor sp. (AORF43), Trametes versicolor (AORF3) and Enterobacter sp. (AORB55) exhibited xylanase and β- glucanase activities in addition to laccase production. The proposed approach allowed for the quick identification of promising consortia and enhanced the chance of isolating desired strains based on desired enzyme activities. This method is not limited to lignocellulose and lignin-degrading microorganisms but can be applied to identify novel microbial strains and enzymes from different natural samples.

Enhancement of biogas production rate from bioplastics by alkaline pretreatment

The effect of alkali-based pretreatment on the methanization of bioplastics was investigated. The tested bioplastics included PHB [poly(3-hydroxybutyrate)], PHBH [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)], PHBV [poly(3-hydroxybutyrate-co-3-hydroxyvalerate], PLA (polylactic acid), and a PLA/PCL [poly(caprolactone)] 80/20 blend. Prior to methanization tests, the powdered polymers (500-1000 μm) at a concentration of 50 g/L were subjected to alkaline pretreatment using NaOH 1 M for PLA and PLA/PCL, and NaOH 2 M for PHB-based materials. Following 7 days of pretreatment, the amount of solubilized carbon for PLA and its blend accounted for 92-98% of the total initial carbon, while lower carbon recoveries were recorded for most PHB-based materials (80-93%), as revealed by dissolved total organic carbon analysis. The pretreated bioplastics were then tested for biogas production by means of mesophilic biochemical methane potential tests. Compared to unpretreated PHBs, methanization rates of pretreated PHBs were accelerated by a factor of 2.7 to 9.1 with comparable (430 NmL CH₄/g material feed) or slightly lower (15% in the case of PHBH) methane yields, despite featuring a 1.4-2.3 times longer lag phases. Both materials, PLA and the PLA/PCL blend, were only extensively digested when pretreated, yielding about 360-380 NmL CH₄ per gram of material fed. Unpretreated PLA-based materials showed nearly zero methanization under the timeframe and experimental conditions tested. Overall, the results suggested that alkaline pretreatment can help to enhance the methanization kinetics of bioplastics.

3D printed polylactide scaffolding for laccase immobilization to improve enzyme stability and estrogen removal from wastewater

This study reports a biocatalytic system of immobilized laccase and 3D printed open-structure biopolymer scaffoldings. The scaffoldings were computer-designed and 3D printed using polylactide (PLA) filament. The immobilization of laccase onto the 3D printed PLA scaffolds were optimized with regard to pH, enzyme concentration, and immobilization time. Laccase immobilization resulted in a small reduction in reactivity (in terms of Michaelis constant and maximum reaction rate) but led to significant improvement in chemical and thermal stability. After 20 days of storage, the immobilized and free laccase showed 80% and 35% retention of the initial enzymatic activity, respectively. The immobilized laccase on 3D printed PLA scaffolds achieved 10% improvement in the removal of estrogens from real wastewater as compared to free laccase and showed the significant reusability potential. Results here are promising but also highlight the need for further study to improve enzymatic activity and reusability.

Development of a phosphorous-based biorefinery process for producing lignocellulosic functional materials from coconut wastes

This work aimed to develop a phosphorous-based biorefinery process for obtaining phosphorylated lignocellulosic fractions in a one-pot protocol from coconut fiber. Natural coconut fiber (NCF) was mixed with 85 % m/m H₃PO₄ at 70 °C for 1 h to yield the modified coconut fiber (MCF), aqueous phase (AP), and coconut fiber lignin (CFL). MCF was characterized by its TAPPI, FTIR, SEM, EDX, TGA, WCA, and P content. AP was characterized regarding its pH, conductivity, glucose, furfural, HMF, total sugars and ASL contents. CFL structure was evaluated by FTIR, ¹H, ³¹P and ¹H-¹³C HSQC NMR, TGA and P content and was compared to that of milled wood lignin (MWL). It was observed that MCF and CFL were phosphorylated during the pulping (0.54 and 0.23 % wt., respectively), while AP has shown high sugar levels, low inhibitor content, and some remaining phosphorous. The phosphorylation of MCF and CFL also showed an enhancement of their thermal and thermo-oxidative properties. The results show that a platform of functional materials such as biosorbents, biofuels, flame retardants, and biocomposites can be created through an eco-friendly, simple, fast, and novel biorefinery process.

Utilization of bamboo as biorefinery feedstock: Co-production of xylo-oligosaccharide with succinic acid and lactic acid

Herein, we investigated the possibility of co-producing xylo-oligosaccharides (XOSs) from bamboo, as value-added products, along with succinic and lactic acids, as platform chemicals. Xylan was extracted from bamboo using the alkali method under mild conditions. From xylan, XOSs were produced by partial enzymatic hydrolysis at a conversion rate of 83.9%, and all reaction conditions resulted in similar degrees of polymerization. Hydrogen peroxide-acetic acid (HPAC) pretreatment effectively removed lignin from NaOH-treated bamboo, and the enzymatic hydrolytic yield of NaOH and HPAC-treated bamboo was 84.3% of the theoretical yield. The production of succinic and lactic acids from the hydrolysate resulted in conversion rates of approximately 63.2% and 91.3% of the theoretical yield using Corynebacterium glutamicum Δldh and Actinobacillus succinogenes, respectively, under facultative anaerobic conditions. This study demonstrates that bamboo has a high potential to produce value-added products using a biorefinery process and is an alternative resource for compounds typically derived from petroleum.

Effects of thermal and physical modification on functional properties of organosolv lignin from sugarcane bagasse and its application in cosmeceutical products

Organosolv lignin is an emerging bio-additive for creating functional properties in various products with its advantages in high-purity, sulfur-free, biocompatibility, and solubility in green solvents. In this study, effects of thermal and physical modification on alterations of functional properties and particle size distribution of isolated organosolv lignin from sugarcane bagasse (OLB) were studied. Thermal treatment of OLB at increasing temperatures from 170 to 230°C in 70%w/w aqueous ethanol led to alteration of phenolic hydroxyl content, while ultrasonication resulted in homogeneous size distribution of the modified OLB according to laser diffraction and scanning electron micrograph. The highest ultraviolet light absorbance and antioxidant activities were obtained at 190°C treatment which were correlated to the highest phenolic group content. Application of the modified OLB at 3% w/w in a base cream formulation resulted in enhancement of the anti-UV activity to exceed SPF 50 with increasing antioxidant activity in the product. The work provides basis on modification of organosolv lignin for application as a potent functional additive in cosmeceutical products.

Effect of pretreatment strategies on halophyte Atriplex crassifolia to improve saccharification using thermostable cellulases

Bioethanol is believed to be an influential revolutionary gift of biotechnology, owing to its elevating global demand and massive production. Pakistan is home to a rich diversity of halophytic flora, convertible into bounteous volumes of bioethanol. On the other hand, the accessibility to the cellulosic part of biomass is a major bottleneck in the successful application of biorefinery processes. The most common pre-treatment procedures existent include physicochemical and chemical approaches, which are not environmentally benign. To overcome these problems, biological pre-treatment has gained importance but the drawback is the low yield of the extracted monosaccharides. The current research was aimed at exploring the best pre-treatment method for the bioconversion of halophyte Atriplex crassifolia into saccharides using three thermostable cellulases. Atriplex crassifolia was subjected to acid, alkali and microwave pre-treatments, followed by compositional analysis of the pre-treated substrates. Maximum delignification i.e. 56.6% was observed in the substrate pre-treated using 3% HCl. Enzymatic saccharification using thermostable cellulases also validated the results where the highest saccharification yield i.e. 39.5% was observed for the sample pre-treated using same. Maximum enzymatic hydrolysis of 52.7% was obtained for 0.40 g of the pre-treated halophyte Atriplex crassifolia where Endo-1,4- β -glucanase (300U), Exo-1,4- β -glucanase (400U) and β -1,4-glucosidase (1000U) were simultaneously added and incubated for 6 h at 75°C. The reducing sugar slurry obtained after optimization of saccharification was utilized as glucose in submerged fermentation for bioethanol production. The fermentation medium was inoculated with Saccharomyces cerevisiae, incubated at 30°C and 180 rpm for 96 h. Ethanol production was estimated using potassium dichromate method. Maximum production of bioethanol i.e. 16.33% was noted at 72 h. It can be concluded from the study that Atriplex crassifolia owing to its high cellulosic content after pre-treatment using dilute acid method, yields substantial amount of reducing sugars and high saccharification rates when subjected to enzymatic hydrolysis using thermostable cellulases, under optimized reaction conditions. Hence, the halophyte Atriplex crassifolia is a beneficial substrate that can be utilized to extract fermentable saccharides for bioethanol production.

Impact of nanomaterials on sustainable pretreatment of lignocellulosic biomass for biofuels production: An advanced approach

Biomass to biofuels production technology appears to be one of the most sustainable strategies among various renewable energy resources. Herein, pretreatment is an unavoidable and key step to increase free cellulose availability and digestibility to produce green fuels. Various existing pretreatment technologies of lignocellulosics biomasses (LCBs) face distinct challenges e.g., energy consuming, cost intensive, may lead partial removal of lignin, complex inhibitors production as well as may cause environmental pollutions. These, limitations may be overcome with the application of nanomaterials, employed as nanocatalysts during the pretreatment process of LCBs. In this prospect, the present review focuses and summarizes results of numerous studies and exploring the utilizations of magnetic, carbon based nanostructure, and nanophotocatalysts mediated pretreatment processes along with their possible mechanisms to improve the biofuels production compared to conventional chemical based pretreatment approaches. Furthermore, different aspects of nanomaterials based pretreatment methods with their shortcomings and future prospects have been discussed.

Rapid and massive fractionation of hemicelluloses for purifying cellulose at room temperature by tetramethylammonium hydroxide

The fractionation of hemicelluloses is a promising method to improve the comprehensive utilization of lignocellulosic biomass. However, the effective fractionation of hemicelluloses is always limited by the structural complexity and easy degradability. In this study, tetramethylammonium hydroxide (TMAH) was developed to fractionate hemicelluloses from poplar holocellulose with high molecular weights and high yields at room temperature. Approximately 90% of hemicelluloses could be dissolved at room temperature in 1 h, and the yield was up to 81.9%. Compared with the fractionation using NaOH solution, the hemicelluloses isolated by TMAH solvent showed a more complete structure and higher purity. Meanwhile, the retention rate of cellulose after treatment with TMAH was up to 90.2%, and the crystal structure of cellulose in the residues was practically unchanged. Moreover, the TMAH solvent could be recycled to fractionate hemicelluloses. The work provides an elegant and significantly efficient method towards hemicelluloses fractionation and cellulose purification.

Innovative strategies in algal biomass pretreatment for biohydrogen production

Biohydrogen is one of the cleanest renewable energies with a high calorific value. Algal biomass can be utilized as a sustainable feedstock for biohydrogen production via dark fermentation. However, the recovery of fermentable sugar from algal biomass is challenging because of the diversity and complex cell wall composition and therefore, requires an additional pretreatment step. However, most of the conventional pretreatment strategies suffer from limited technological feasibility and poor economic viability. In this context, this review aims to present the structural complexities of the cell wall of algae and highlight the innovative approaches such as the use of hybrid technologies, biosurfactants, nanoparticles, and genetic engineering approaches for the hydrolysis of algal biomass and improved biohydrogen production. Additionally, a comprehensive discussion of the comparative evaluation of various pretreatment methods, and the techno-economic and life cycle assessment of algal biohydrogen production is also presented in this review.

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

The inherent recalcitrance of lignocellulosic biomass is a significant barrier to efficient lignocellulosic biorefinery owing to its complex structure and the presence of inhibitory components, primarily lignin. Efficient biomass pretreatment strategies are crucial for fragmentation of lignocellulosic biocomponents, increasing the surface area and solubility of cellulose fibers, and removing or extracting lignin. Conventional pretreatment methods have several disadvantages, such as high operational costs, equipment corrosion, and the generation of toxic byproducts and effluents. In recent years, many emerging single-step, multi-step, and/or combined physicochemical pretreatment regimes have been developed, which are simpler in operation, more economical, and environmentally friendly. Furthermore, many of these combined physicochemical methods improve biomass bioaccessibility and effectively fractionate ∼96 % of lignocellulosic biocomponents into cellulose, hemicellulose, and lignin, thereby allowing for highly efficient lignocellulose bioconversion. This review critically discusses the emerging physicochemical pretreatment methods for efficient lignocellulose bioconversion for biofuel production to address the global energy crisis.

A comprehensive review on the biological conversion of lignocellulosic biomass into hydrogen: Pretreatment strategy, technology advances and perspectives

The globe has dependent on energy generation and utilization for many years; conversely, ecological concerns constrained the world to view hydrogen as an alternative for economic development. Lignocellulosic biomass is broadly accessible as a low-cost renewable feedstock and nonreactive nature; it has received a lot of consideration as a global energy source and the most attractive alternative to replace fossil natural substances for energy production. Pretreatment of lignocellulosic biomass is essential to advance its fragmentation and lower the lignin content for sustainable energy generation. This review's goal is to provide the different pretreatment strategies for enlarging the solubility and surface area of lignocellulosic biomass. The biological conversion of lignocellulosic biomass to hydrogen was reviewed and operational conditions and enhancing methods were discussed. This review summarizes the working conditions, parameters, yield percentages, techno-economic analysis, challenges, and future recommendations on the direct conversion of biomass to hydrogen.

Processing of Biomass Prior to Hydrogen Fermentation and Post-Fermentative Broth Management

Using bioconversion and simultaneous value-added product generation requires purification of the gaseous and the liquid streams before, during, and after the bioconversion process. The effect of diversified process parameters on the efficiency of biohydrogen generation via biological processes is a broad object of research. Biomass-based raw materials are often applied in investigations regarding biohydrogen generation using dark fermentation and photo fermentation microorganisms. The literature lacks information regarding model mixtures of lignocellulose and starch-based biomass, while the research is carried out based on a single type of raw material. The utilization of lignocellulosic and starch biomasses as the substrates for bioconversion processes requires the decomposition of lignocellulosic polymers into hexoses and pentoses. Among the components of lignocelluloses, mainly lignin is responsible for biomass recalcitrance. The natural carbohydrate-lignin shields must be disrupted to enable lignin removal before biomass hydrolysis and fermentation. The matrix of chemical compounds resulting from this kind of pretreatment may significantly affect the efficiency of biotransformation processes. Therefore, the actual state of knowledge on the factors affecting the culture of dark fermentation and photo fermentation microorganisms and their adaptation to fermentation of hydrolysates obtained from biomass requires to be monitored and a state of the art regarding this topic shall become a contribution to the field of bioconversion processes and the management of liquid streams after fermentation. The future research direction should be recognized as striving to simplification of the procedure, applying the assumptions of the circular economy and the responsible generation of liquid and gas streams that can be used and purified without large energy expenditure. The optimization of pre-treatment steps is crucial for the latter stages of the procedure.

Thermophilic biohydrogen production strategy using agro industrial wastes: Current update, challenges, and sustainable solutions

Continuously increasing wastes management issues and the high demand of fuels to fulfill the current societal requirements is not satisfactory. In addition, severe environmental pollution caused by generated wastes and the massive consumption of fossil fuels are the main causes of global warming. In this scenario, production of hydrogen from organic wastes is a potential and one of the most feasible alternatives to resolve these issues. However, sensitivity of H₂ production at higher temperature and lack of potential substrates are the main issues which are strongly associated with such kinds of biofuels. Therefore, the present review is targeted towards the evaluation and enhancement of thermophilic biohydrogen production using organic, cellulosic wastes as promising bioresources. This review discusses about the current status, development in the area of thermophilic biohydrogen production wherein organic wastes as key substrate are being employed. The combinations of suitable organic and cellulose rich substrates, thermo-tolerant microbes, high enzymes stability may support to enhance the biohydrogen production, significantly. Further, various factors which may significantly contribute to enhance biohydrogen production have been discussed thoroughly in reference to the thermophilic biohydrogen production technology. Additionally, existing obstacles such as unfavorable thermophilic biohydrogen pathways, inefficiency of thermophilic microbiomes, genetic modifications, enzymes stability have been discussed in context to the possible limitations of thermophilic biohydrogen production strategy. Structural and functional microbiome analysis, fermentation pathway modifications via genetic engineering and the application of nanotechnology to enhance the thermophilic biohydrogen production have been discussed as the future prospective.

Synthesis of a biobased resin and its screening as an alternative adsorbent for organic and inorganic micropollutant removal

The sol-gel route was used to synthesize a biophenolic resin from a blend of Kraft black liquor and condensed tannin. The biobased resin has an amorphous structure and diversified surface functional groups. The biomaterial thermal stability was improved by Kraft black liquor, which increased the fixed carbon yield by 19.78% in an oxidant medium and 9.07% in an inert medium. Moreover, the presence of fixed carbon and char is positively related to the material flame retardant property. Additionally, impedance measurements were used to understand the physical phenomena occurring at the polymeric matrix's interface and the material's final properties. The biobased resin characterization and the considerable increase in the presence of micropollutants in surface and water bodies suggest the new biomaterial application in the adsorption process. Thus, its adsorption capacity toward several organic and inorganic micropollutants and its effectiveness in complex water matrices were evaluated. Methylene blue was used as a model compound to assess the influence of the resin composition on the adsorption capacity, and the type H isotherm indicates the high affinity of the biobased resin toward the micropollutant. The adsorption occurs in multilayer by intermolecular interaction and electrostatic forces. The amount of Kraft black liquor favored the adsorption, and the adsorption capacity was greater than 1250 mg g-1. When inorganic compounds were evaluated, the carboxyl and phenol groups favor the biomaterial affinity toward metal ions. Cu2+ and Ni2+ were completely removed from the contaminated water, and the adsorption capacity of the other inorganic compounds was: Pb2+ (36.97 mg g-1), Al3+ (22.17 mg g-1), Ba2+ (12.76 mg g-1), Ag1+ (33.85 mg g-1), and Fe2+ (19.44 mg g-1). In contrast, the adsorption capacity of the organic micropollutants was: 2,4-D (3.09 mg g-1), diuron (5.89 mg g-1), atrazine (2.71 mg g-1), diclofenac (2.04 mg g-1), caffeine (5.79 mg g-1), acetaminophen (4.80 mg g-1), methylene Blue (106.66 mg g-1), and methyl orange (30.48 mg g-1). The results pointed that the adsorption efficiency of organic micropollutants increases with the distribution coefficient (logD), indicating the biobased resin affinity toward more lipophilic compounds and ionized species.

Screening method for Enzyme-based liquefaction of corn stover pellets at high solids

Liquefaction of high solid loadings of unpretreated corn stover pellets has been demonstrated with rheology of the resulting slurries enabling mixing and movement within biorefinery bioreactors. However, some forms of pelleted stover do not readily liquefy, so it is important to screen out lots of unsuitable pellets before processing is initiated. This work reports a laboratory assay that rapidly assesses whether pellets have the potential for enzyme-based liquefaction at high solids loadings. Twenty-eight pelleted corn stover (harvested at the same time and location) were analyzed using 20 mL enzyme solutions (3 FPU cellulase/ g biomass) at 30 % w/v solids loading. Imaging together with measurement of reducing sugars were performed over 24-hours. Some samples formed concentrated slurries of 300 mg/mL (dry basis) in the small-scale assay, which was later confirmed in an agitated bioreactor. Also, the laboratory assay showed potential for optimizing enzyme formulations that could be employed for slurry formation.

Lignocellulose biohydrogen towards net zero emission: A review on recent developments

This review mainly determines novel and advance physical, chemical, physico-chemical, microbiological and nanotechnology-based pretreatment techniques in lignocellulosic biomass pretreatment for bio-H2 production. Further, aim of this review is to gain the knowledge on the lignocellulosic biomass pretreatment and its priority on the efficacy of bio-H2 and positive findings. The influence of various pretreatment techniques on the structure of lignocellulosic biomass have presented with the pros and cons, especially about the cellulose digestibility and the interference by generation of inhibitory compounds in the bio-enzymatic technique as such compounds is toxic. The result implies that the stepwise pretreatment technique only can ensure eventually the lignocellulosic biomass materials fermentation to yield bio-H2. Though, the mentioned pretreatment steps are still a challenge to procure cost-effective large-scale conversion of lignocellulosic biomass into fermentable sugars along with low inhibitory concentration.

Carbohydrate active enzyme system in rumen fungi: a review

Hydrolysis and dehydration reactions of carbohydrates, which are used as energy raw materials by all living things in nature, are controlled by Carbohydrate Active Enzyme (CAZy) systems. These enzymes are also used in different industrial areas today. There are different types of microorganisms that have the CAZy system and are used in the industrial sector. Apart from current organisms, there are also rumen fungi within the group of candidate microorganisms with the CAZy system. It has been reported that xylanase (EC3.2.1.8 and EC3.2.1.37) enzyme, a member of the glycoside hydrolase enzyme family obtained from Trichoderma sp. and used especially in areas such as bread, paper, and feed industry, is more synthesized in rumen fungi such as Orpinomyces sp. and Neocallimastix sp. Therefore, this study reviews Neocallimastixsp., Orpinomyces sp., Caecomyces sp., Piromyces sp., and Anaeromyces sp., registered in the CAZy and Mycocosm database for rumen fungi to have both CAZy enzyme activity and to be an alternative microorganism in the industry. Furthermore the CAZy enzyme activities of the strains are investigated. The review shows thatNeocallimax sp. and Orpinomyces sp. areconsidered as candidate microorganisms.

Sugarcane bagasse into value-added products: a review

Strategic valorization of readily available sugarcane bagasse (SB) is very important for waste management and sustainable biorefinery. Conventional SB pretreatment methods are ineffective to meet the requirement for industrial adaptation. Several past studies have highlighted different pretreatment procedures which are lacking environmentally benign characteristics and effective SB bioconversion. This article provides an in-depth review of a variety of environmentally acceptable thermochemical and biological pretreatment techniques for SB. Advancements in the conversion processes such as pyrolysis, liquefaction, gasification, cogeneration, lignin conversion, and cellulose conversion via fermentation processes are critically reviewed for the formation of an extensive array of industrially relevant products such as biofuels, bioelectricity, bioplastics, bio adsorbents, and organic acids. This article would provide comprehensive insights into several crucial aspects of thermochemical and biological conversion processes, including systematic perceptions and scientific developments for value-added products from SB valorization. Moreover, it would lead to determining efficient pretreatment and/or conversion processes for sustainable development of industrial-scale sugarcane-based biorefinery.

A consolidated review of commercial-scale high-value products from lignocellulosic biomass

For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.

A Systematic Review on Waste as Sustainable Feedstock for Bioactive Molecules—Extraction as Isolation Technology

In today’s linear economy, waste streams, environmental pollution, and social–economic differences are increasing with population growth. The need to develop towards a circular economy is obvious, especially since waste streams are composed of valuable compounds. Waste is a heterogeneous and complex matrix, the selective isolation of, for example, polyphenolic compounds, is challenging due to its energy efficiency and at least partially its selectivity. Extraction is handled as an emerging technology in biorefinery approaches. Conventional solid liquid extraction with organic solvents is hazardous and environmentally unfriendly. New extraction methods and green solvents open a wider scope of applications. This research focuses on the question of whether these methods and solvents are suitable to replace their organic counterparts and on the definition of parameters to optimize the processes. This review deals with the process development of agro-food industrial waste streams for biorefineries. It gives a short overview of the classification of waste streams and focuses on the extraction methods and important process parameters for the isolation of secondary metabolites.

Enzymatic Conversion of Different Qualities of Refined Softwood Hemicellulose Recovered from Spent Sulfite Liquor

Spent sulfite liquor (SSL) from softwood processing is rich in hemicellulose (acetyl galactoglucomannan, AcGGM), lignin, and lignin-derived compounds. We investigated the effect of sequential AcGGM purification on the enzymatic bioconversion of AcGGM. SSL was processed through three consecutive purification steps (membrane filtration, precipitation, and adsorption) to obtain AcGGM with increasing purity. Significant reduction (~99%) in lignin content and modest loss (~18%) of polysaccharides was observed during purification from the least pure preparation (UFR), obtained by membrane filtration, compared to the purest preparation (AD), obtained by adsorption. AcGGM (~14.5 kDa) was the major polysaccharide in the preparations; its enzymatic hydrolysis was assessed by reducing sugar and high-performance anion-exchange chromatography analysis. The hydrolysis of the UFR preparation with Viscozyme L or Trichoderma reesei β-mannanase TrMan5A (1 mg/mL) resulted in less than ~50% bioconversion of AcGGM. The AcGGM in the AD preparation was hydrolyzed to a higher degree (~67% with TrMan5A and 80% with Viscozyme L) and showed the highest conversion rate. This indicates that SSL contains enzyme-inhibitory compounds (e.g., lignin and lignin-derived compounds such as lignosulfonates) which were successfully removed.

A Cleaner Delignification of Urban Leaf Waste Biomass for Bioethanol Production, Optimised by Experimental Design

This work is focused on optimising a low-temperature delignification as holocellulose purification pretreatment of Platanus acerifolia leaf waste for second-bioethanol production. Delignification was accomplished by acid-oxidative digestion using green reagents: acetic acid and 30% hydrogen peroxide 1:1. The effect of reaction time (30–90 min), temperature (60–90 °C), and solid loading (5–15 g solid/20 g liquid) on delignification and solid fraction yield were studied. The process parameters were optimised using the Box–Behnken experimental design. The highest attained lignin removal efficiency was larger than 80%. The optimised conditions of delignification, while maximising holocellulose yield, pointed to using the minimum temperature of the examined range. Analysis of variance on the solid fraction yield and the lignin removal suggested a linear model with a negative influence of the temperature on the yield. Furthermore, a negative effect of the solid loading and low effect of temperature and time was found on the degree of delignification. Then the temperature range was extended back to 60 °C, providing 71% holocellulose yield and 70% while improving energy efficiency by working at a lower temperature. Successful lignin removal was confirmed using confocal laser scanning microscopy. As evaluated by scanning electron microscopy, the solid structure presented an increased exposition of the cellulose fibre structure.

The Fractionation of Corn Stalk Components by Hydrothermal Treatment Followed by Ultrasonic Ethanol Extraction

The fractionation of components of lignocellulosic biomass is important to be able to take advantage of biomass resources. The hydrothermal–ethanol method has significant advantages for fraction separation. The first step of hydrothermal treatment can separate hemicellulose efficiently, but hydrothermal treatment affects the efficiency of ethanol treatment to delignify lignin. In this study, the efficiency of lignin removal was improved by an ultrasonic-assisted second-step ethanol treatment. The effects of ultrasonic time, ultrasonic temperature, and ultrasonic power on the ultrasonic ethanol treatment of hydrothermal straw were investigated. The separated lignin was characterized by solid product composition analysis, FT-IR, and XRD. The hydrolysate was characterized by GC-MS to investigate the advantage on the products obtained by ethanol treatment. The results showed that an appropriate sonication time (15 min) could improve the delignification efficiency. A proper sonication temperature (180 °C) can improve the lignin removal efficiency with a better retention of cellulose. However, a high sonication power 70% (840 W) favored the retention of cellulose and lignin removal.

Recent advances in metabolic engineering of microorganisms for advancing lignocellulose-derived biofuels

Combating climate change and ensuring energy supply to a rapidly growing global population has highlighted the need to replace petroleum fuels with clean, and sustainable renewable fuels. Biofuels offer a solution to safeguard energy security with reduced ecological footprint and process economics. Over the past years, lignocellulosic biomass has become the most preferred raw material for the production of biofuels, such as fuel, alcohol, biodiesel, and biohydrogen. However, the cost-effective conversion of lignocellulose into biofuels remains an unsolved challenge at the industrial scale. Recently, intensive efforts have been made in lignocellulose feedstock and microbial engineering to address this problem. By improving the biological pathways leading to the polysaccharide, lignin, and lipid biosynthesis, limited success has been achieved, and still needs to improve sustainable biofuel production. Impressive success is being achieved by the retouring metabolic pathways of different microbial hosts. Several robust phenotypes, mostly from bacteria and yeast domains, have been successfully constructed with improved substrate spectrum, product yield and sturdiness against hydrolysate toxins. Cyanobacteria is also being explored for metabolic advancement in recent years, however, it also remained underdeveloped to generate commercialized biofuels. The bacterium Escherichia coli and yeast Saccharomyces cerevisiae strains are also being engineered to have cell surfaces displaying hydrolytic enzymes, which holds much promise for near-term scale-up and biorefinery use. Looking forward, future advances to achieve economically feasible production of lignocellulosic-based biofuels with special focus on designing more efficient metabolic pathways coupled with screening, and engineering of novel enzymes.

Bioaugmentation combined with biochar to enhance thermophilic hydrogen production from sugarcane bagasse

In this study, Thermoanaerobacterium thermosaccharolyticum MJ2 and biochar were used to enhance thermophilic hydrogen production from sugarcane bagasse. MJ2 bioaugmentation notably increased the hydrogen production by 95.31%, which was further significantly improved by 158.10% by adding biochar. The addition of biochar promoted the degradation of substrate, improved the activities of hydrogenase and electron transfer system, and stimulated microbial growth and metabolism. Microbial community analysis showed that the relative abundance of Thermoanaerobacterium was significantly increased by bioaugmentation and further enriched by biochar. PICRUSt analysis showed that MJ2 combined with biochar promoted metabolic pathways related to substrate degradation and microbial metabolism. This study provides a novel enhancement method for hydrogen production of the cellulolytic microbial consortium by exogenous hydrogen-producing microorganism combined with biochar and deepens the understanding of its functional mechanism.

Superheated Steam Torrefaction of Biomass Residues with Valorisation of Platform Chemicals Part—2: Economic Assessment and Commercialisation Opportunities

Up to now biorefinery concepts can hardly compete with the conventional production of fossil-based chemicals. On one hand, conventional chemical production has been optimised over many decades in terms of energy, yield and costs. Biorefineries, on the other hand, do not have the benefit of long-term experience and therefore have a huge potential for optimisation. This study deals with the economic evaluation of a newly developed biorefinery concept based on superheated steam (SHS) torrefaction of biomass residues with recovery of valuable platform chemicals. Two variants of the biorefinery were economically investigated. One variant supplies various platform chemicals and torrefied biomass. The second variant supplies thermal energy for external consumers in addition to platform chemicals. The results show that both variants can be operated profitably if the focus of the platform chemicals produced is on high quality and thus on the higher-priced segment. The economic analysis gives clear indications of the most important financial influencing parameters. The economic impact of integration into existing industrial structures is positive. With the analysis, a viable business model can be developed. Based on the results of the present study, an open-innovation platform is recommended for the further development and commercialisation of the novel biorefinery.

Effect of Fenton pretreatment and bacterial inoculation on cellulose-degrading genes and fungal communities during rice straw composting

The aims of this article were to study the effect of Fenton pretreatment and bacterial inoculation on cellulose-degrading genes and fungal communities during rice straw composting. The rice straw was pretreated by Fenton reactions and functional bacterial agents were then inoculated during the cooling phase of composting. Three treatment groups were carried out, the control (CK), Fenton pretreatment (FeW) and Fenton pretreatment and bacterial inoculation (FeWI). The results indicated that Fenton pretreatment and bacterial inoculation changed the fungal communities composition and increased fungal diversity, leading to changes in the cellulose-degrading genes. In addition, a network analysis showed that in the FeWI treatment, the fungi from modules 1, 5 and 8 were core hosts of the cellulose-degrading genes driving the cellulosic degradation. Moreover, Fenton pretreatment and bacterial inoculation changed the core module fungal communities and strengthened the correlation between the core fungi and the cellulose-degrading genes, thereby promoting cellulosic degradation. Based on redundancy and structural equation model analyses, the NH₄⁺-N, TOC, pH and Shannon index were important factors influencing the variations in the cellulose-degrading genes. This study provides a foundation for cellulosic degradation during cellulosic waste composting.

Immobilization-Stabilization of β-Glucosidase for Implementation of Intensified Hydrolysis of Cellobiose in Continuous Flow Reactors

Cellulose saccharification to glucose is an operation of paramount importance in the bioenergy sector and the chemical and food industries, while glucose is a critical platform chemical in the integrated biorefinery. Among the cellulose degrading enzymes, β-glucosidases are responsible for cellobiose hydrolysis, the final step in cellulose saccharification, which is usually the critical bottleneck for the whole cellulose saccharification process. The design of very active and stable β-glucosidase-based biocatalysts is a key strategy to implement an efficient saccharification process. Enzyme immobilization and reaction engineering are two fundamental tools for its understanding and implementation. Here, we have designed an immobilized-stabilized solid-supported β-glucosidase based on the glyoxyl immobilization chemistry applied in porous solid particles. The biocatalyst was stable at operational temperature and highly active, which allowed us to implement 25 °C as working temperature with a catalyst productivity of 109 mmol/min/gsupport. Cellobiose degradation was implemented in discontinuous stirred tank reactors, following which a simplified kinetic model was applied to assess the process limitations due to substrate and product inhibition. Finally, the reactive process was driven in a continuous flow fixed-bed reactor, achieving reaction intensification under mild operation conditions, reaching full cellobiose conversion of 34 g/L in a reaction time span of 20 min.

Smart sustainable biorefineries for lignocellulosic biomass

Lignocellulosic biomass (LCB) is considered as a sustainable feedstock for a biorefinery to generate biofuels and other bio-chemicals. However, commercialization is one of the challenges that limits cost-effective operation of conventional LCB biorefinery. This article highlights some studies on the sustainability of LCB in terms of cost-competitiveness and environmental impact reduction. In addition, the development of computational intelligence methods such as Artificial Intelligence (AI) as a tool to aid the improvement of LCB biorefinery in terms of optimization, prediction, classification, and decision support systems. Lastly, this review examines the possible research gaps on the production and valorization in a smart sustainable biorefinery towards circular economy.

Recent advances in lignocellulosic biomass for biofuels and value-added bioproducts - A critical review

Lignocellulosic biomass is a highly renewable, economical, and carbon-neutral feedstock containing sugar-rich moieties that can be processed to produce second-generation biofuels and bio-sourced compounds. However, due to their heterogeneous multi-scale structure, the lignocellulosic materials have major limitations to valorization and exhibit recalcitrance to saccharification or hydrolysis by enzymes. In this context, this review focuses on the latest methods available and state-of-the-art technologies in the pretreatment of lignocellulosic biomass, which aids the disintegration of the complex materials into monomeric units. In addition, this review deals with the genetic engineering techniques to develop advanced strategies for fermentation processes or microbial cell factories to generate desired products in native or modified hosts. Further, it also intends to bridge the gap in developing various economically feasible lignocellulosic products and chemicals using biorefining technologies.

Lignocellulose biomass bioconversion during composting: Mechanism of action of lignocellulase, pretreatment methods and future perspectives

Composting is a biodegradation and transformation process that converts lignocellulosic biomass into value-added products, such as humic substances (HSs). However, the recalcitrant nature of lignocellulose hinders the utilization of cellulose and hemicellulose, decreasing the bioconversion efficiency of lignocellulose. Pretreatment is an essential step to disrupt the structure of lignocellulosic biomass. Many pretreatment methods for composting may cause microbial inactivation and death. Thus, the pretreatment methods suitable for composting can promote the degradation and transformation of lignocellulosic biomass. Therefore, this review summarizes the pretreatment methods suitable for composting. Microbial consortium pretreatment, Fenton pretreatment and surfactant-assisted pretreatment for composting may improve the bioconversion process. Microbial consortium pretreatment is a cost-effective pretreatment method to enhance HSs yields during composting. On the other hand, the efficiency of enzyme production during composting is very important for the degradation of lignocellulose, whose action mechanism is unknown. Therefore, this review describes the mechanism of action of lignocellulase, the predominant microbes producing lignocellulase and their related genes. Finally, optimizing pretreatment conditions and increasing enzymatic hydrolysis to improve the quality of composts by controlling suitable microenvironmental factors and core target microbial activities as a research focus in the bioconversion of lignocellulose during composting in the future.

Treatment and bioresources utilization of traditional Chinese medicinal herb residues: Recent technological advances and industrial prospect

Traditional Chinese medicine (TCM) has wide application and important functions in curing many diseases, but a great number of herb residues are usually generated after its manufacture and usage. Without proper and timely treatment, these traditional Chinese medicinal herb (TCMH) residues will cause some environmental pollution. In addition to treatment, bioresources utilization of TCMH residues is also important for its great potential as a suitable feedstock for the production of energy, materials, and chemicals. In this situation, advanced and well-designed solid waste management is important to make the TCM industry environmentally friendly and economically attractive. In this review article, the recent progress focusing on various methods for TCMH residues treatment and bioresources utilization are introduced in detail. In particular, the technologies for thermochemical conversion and biochemical conversion of TCMH residues are mainly focused on in order to show how to fulfill effective and efficient bioresources utilization. Besides, some other technologies which are suitable for the treatment and bioresources utilization of TCMH residues are presented as well. Finally, some industrial prospects are given from the economic, operational, and environmental aspects for the further development of treatment and bioresources utilization of TCMH residues. Overall, this work can provide some systematical and comprehensive information for the development of technologies that help sustainably manage the herb residues generated in the TCM industry.

Efficient production of xylooligosaccharides rich in xylobiose and xylotriose from poplar by hydrothermal pretreatment coupled with post-enzymatic hydrolysis

A promising approach for production of value-added xylooligosaccharides (XOS) from poplar was developed by combining hydrothermal pretreatment and endo-xylanase post-hydrolysis. Results showed that the 35.4% XOS (DP 2-6) and 17.6% low DP xylans (DP > 6) were obtained at the identified optimal condition (170 °C, 50 min) for hydrothermal pretreatment. Structural features of low DP xylans generated during the hydrothermal pretreatment were examined, revealing that low DP xylans are mainly comprised of 4-O-methylglucuronic xylan and are involved in lignin carbohydrate complexes. Moreover, higher pretreatment intensity promoted the cleavage of side-chain substituents including arabinose and glucuronic acid groups. The subsequent endo-xylanase hydrolysis of the pretreatment liquor hydrolyzed low DP xylans, contributing to a significant improvement in xylobiose and xylotriose proportions. This combined strategy resulted in a XOS with conversion yield of 44.6% containing 78.7% xylobiose and xylotriose starting from the initial xylan in raw poplar.

Application of free and immobilized novel bifunctional biocatalyst in biotransformation of recalcitrant lignocellulosic biomass

Herein, an innovative, green, and practical biocatalyst was developed using conjugation of a novel bifunctional mannanase/xylanase biocatalyst (PersiManXyn1) to the modified cellulose nanocrystals (CNCs). Firstly, PersiManXyn1 was multi-stage in-silico screened from rumen macrobiota, and then cloned, expressed, and purified. Next, CNCs were synthesized from sugar beet pulp using enzymatic and acid hydrolysis processes, and then Fe₃O₄ NPs were anchored on their surface to produce magnetic CNCs (MCNCs). This hybrid was modified by dopamine providing DA/MCNCs nano-carrier. The bifunctional PersiManXyn1 demonstrated the superior hydrolysis activity on corn cob compared with the monofunctional xylanase enzyme (PersiXyn2). Moreover, the immobilization of PersiManXyn1 on the nano-carrier resulted in an improvement of the thermal stability, kinetic parameters (K_cat), and storage stability of the enzyme. Incorporation of the Fe₃O₄ NPs on the CNCs made magnetic nano-carrier with high magnetization value (25.8 emu/g) which exhibited rapid response toward the external magnetic fields. Hence, the immobilized biocatalyst could be easily separated from the products by a magnet, and reused up to 8 cycles with maintaining more than 50% of its original activity. The immobilized PersiManXyn1 generated 22.2%, 38.7%, and 35.1% more reducing sugars after 168 h hydrolysis of the sugar beet pulp, coffee waste, and rice straw, respectively, compared to the free enzyme. Based on the results, immobilization of the bifunctional PersiManXyn1 exhibited the superb performance of the enzyme to improve the conversion of the lignocellulosic wastes into high value products and develop the cost-competition biomass operations.