Hemicellulose biorefineries: a review on biomass pretreatments

Biomass pretreatment (BP) plays a crucial role in a lignocellulose feedstock-based biorefinery (LCFBR) for processing of three major output streams (cellulose, hemicelluloses and lignin) into chemicals and biofuels. BP includes processing of lignocellulosic material (LCM) under aqueous, dilute acid or alkaline media to obtain a cellulosic fraction, which is then fermented to produce bioethanol. Hemicellulose is usually treated as a secondary stream due to lack of efficient fermentation of hemicellulosic sugars to ethanol. This review provides BPs assuming that hemicellulose stream should be integrated in LCFBR as a primary fraction for converting into value-added compounds other than bioethanol. Different LCM treatments are analyzed foreseeing bio-based products possible to obtain from hemicellulose path

Hydrothermal processing of corn residues:process optimisation and products characterisation

Hydrothermal processing was used as pre-treatment method for the selective solubilisation of hemicellulose from corn residues (leaves and stalks). The raw material was treated at a liquidto- solid ratio of 10 g/g, under non-isothermal conditions (150-240ºC) and the effect of treatment on the composition of both liquid and solid phases was evaluated. The yields of solid residue and soluble products, e.g., oligosaccharides, monosaccharides, acetic acid and degradation compounds, such as furfural, hydroxymethylfurfural are presented and interpreted using the severity factor (log R0). The operational conditions leading to the maximum recovery of XOS (53% of initial (arabino)xylan) and for highest glucan content of the solid residue (64%) were established for log R0 of 3.75 and 4.21, respectively. Under the severest condition 95% of xylan was selectively solubilised and 90% of initial glucan was recovered on the solid residue, making it very attractive for further processing in a biorefinery framework

Fermentation of biomass-derived syngas to ethanol and acetate by clostridium ljungdahlii

In the biochemical pathway of lignocellulosics conversion into fuels, a significant portion of biomass cannot be hydrolysed to fermentable sugars and remains as waste substrate that, due to its recalcitrance, is not converted to ethanol by microorganisms. In terms of product yield, this residual biomass represents renewable feedstock that is being wasted, which contradicts the target of 100% feedstock utilisation. The gasification of this biomass constitutes an alternative to circumvent this problem, as the produced synthesis gas (syngas) can be used as substrate for microorganisms that are able to convert CO, CO2 and H2 into important bulk chemicals and biofuels, such as ethanol, acetate and butanol [1,2]. Thus, syngas fermentation to ethanol and acetate can be regarded as a possible process to increase the overall product yield from lignocellulosic feedstock. Some advantages of fuels and chemicals production through syngas fermentation over metal catalyst conversion are the possibility of utilisation of the whole biomass regardless its quality, the independence of a fixed H2:CO ratio for the bioconversion process, a higher specificity of the microbial biocatalyst over chemical catalysts, and the bioreactor operation at ambient conditions [3]. However, syngas fermentation also presents several limitations, such as low yields and poor solubility of the gaseous substrate in the liquid phase. The objective of the present study was to evaluate C. ljungdahlii as microbial catalyst capable of fermenting syngas produced by gasification of spent solids obtained after lignocellulosic biomass saccharification and fermentation into ethanol. The heterotrophic and autotrophic growth of C. ljungdahlii were compared. Parameters such as bacterial growth, acetate and ethanol production, substrate consumption, and bioconversion yields were evaluated. In order to overcome the problem of gas diffusion in the liquid phase, fermentations were conducted at different total pressure

Simplex optimization and mathematical modeling of wheat straw dilute acid hydrolysisand

Wheat straw is an interesting biorefinery raw material, due to its abundance, chemical composition, and cost. Among the different pretreatments suitable for its processing, dilute acid hydrolysis still presents some benefits due to its simplicity. Nevertheless, it requires a careful optimization to avoid excessive by-products formation and catalyst spending. An attractive and simple optimization approach is the Sequential Simplex Method, an iterative procedure that enables to rapidly screen a large area ofoperational conditions and effectively encircle the optimal. In this work, dilute acid hydrolysis of wheat straw was optimized to selectively hydrolyze the hemicellulose fraction and obtain a pentose-rich fermentable hydrolyzate. The influence oftime (up to 180 min), and sulfuric acid concentration (up to 4%, w/w) were studied. The hydrolyzates obtained in the optimized conditions mainly contain free sugars (total content higher than 46 giL). The main potential microbial inhibitors found were acetic acid, furfural, and HMF, in concentrations lower than 4.8,1.7 and 0.3 giL, respectively. Empirical models describing the influence ofthe studied variables on sugars and by-products formation were validated for the entire domain. Sulfuric acid concentration was found to be the most influential variable, although both variables are statistically significant for xylose recovery. Interaction effects play a significant (negative) role. Data was also modeled based on the combined severity parameter (CS) and the results of these two approaches are compared and discussed. These hydrolyzates were easily utilized by Debaryomyces hansenii, a natural pentose assimilating yeast

Prebiotic xylo-oligosaccharides as high-value co-products on an integrated biorefinery approach from lignocellulosic feedstock

The present work proposes the production of prebiotic xylo-oligosaccharides (XOS) as high-value co-products of the Lignocellulose Feedstock Biorefinery concept, foreseeing potential applications on food, feed and nutraceutical industries. Autohydrolysis was used to selectively solubilise the hemicellulosic fraction of several xylan-rich, widely available, agricultural, agro-industrial and forestry by-products: corn cobs, brewery’s spent grain and Eucalyptus wood chips. The soluble hemicellulose-rich and the solid cellulose- and lignin-rich fractions were separated, and the crude XOS-rich hydrolysates were further purified by gel filtration chromatography. Selected fractions of purified XOS within the desired ranges of polymerization degree were characterised and their prebiotic potential was investigated in in vitro fermentations by bifidobacteria, lactobacilli and intestinal inocula. Parameters such as bacterial growth and XOS consumption were evaluated and compared with commercially available xylo-oligosaccharides. The differences observed were considered of relevance for the formulation of symbiotic preparations and the future design of targeted, tailor-made prebiotic xylo-oligosaccharides

Single-cell oil production by engineered Ashbya gossypii from non-detoxified lignocellulosic biomass hydrolysate

In this work, microbial lipid production from non-detoxified Eucalyptus bark hydrolysate (EBH) with oleaginous xylose-utilizing Ashbya gossypii strains was explored. The best producing strain from a set of engineered strains was identified in synthetic media mimicking the composition of the non-detoxified EBH (SM), the lipid profile was characterized, and yeast extract and corn steep liquor (CSL) were pinpointed as supplements enabling a good balance between lipid accumulation, biomass production, and autolysis by A. gossypii. The potential of the engineered A. gossypii A877 strain to produce lipids was further validated and optimized with minimally processed inhibitor-containing hydrolysate and high sugar concentration, and scaled up in a 2 L bioreactor. Lipid production from non-detoxified EBH supplemented with CSL reached a lipid titer of 1.42 g/L, paving the way for sustainable single-cell oil production within the concept of circular economy and placing lipids as an alternative by-product within microbial biorefineries.This study was supported by Compete 2020, Portugal 2020, and Lisboa 2020 through MoveToLowC (POCI-01-0247-FEDER-046117) and by the Portuguese Foundation for Science and Technology (FCT) through the strategic funding of UIDB/04469/2020 and project ESSEntial (PTDC/BII-BTI/1858/2021). The authors gratefully acknowledge RAIZ (Forest and Paper Research Institute) for providing the Eucalyptus bark material, and Novozymes A/S for supplying Cellic® CTec3 HS. The technical assistance of STEX company (Aveiro, Portugal) on the operation of pilot-scale infrastructure of steam explosion and enzymatic hydrolysis is also acknowledged.info:eu-repo/semantics/publishedVersio

The pros and cons of the dedicated upgrade of the hemicellulosic sugar stream in a biorefinery framework

The challenge of the future integrated biorefineries is the full economically utilization of all biomass components with the simultaneously production of fuels and chemicals, preferably of added-value. This can only be achieved by the selective fractionation of the lignocellulosic biomass into its polymeric components, thus increasing their individual upgradeability to enhance the process economics. To reach this goal, the fractionation methods used are of crucial importance. Yet, many of the most widely accepted biochemical biorefineries potential lay-outs, are mainly concerned with cellulose hydrolysis and fermentation and the hemicellulosic fractions are, at best, clamped with cellulose, averting its differential upgrade. Therefore, a change in perspective by which the fractionation processes, as well as the overall biorefinery lay-out, are thought and evaluated is needed. The objective of this work is to review, compare and discuss the main advantages and bottlenecks of the currently available biomass pre-treatment technologies, particularly those leading to the selective fractionation of hemicelluloses. The advantages and disadvantages of the methods will be analysed foreseeing the added-value products possible to obtain from the hemicellulose path, and the most relevant factors which influence both product yield and consistency. Actually, the chemical composition and structural diversity of hemicelluloses constitutes an opportunity for the production of many chemicals, which has not yet been fully exploited. The integration of potential added-value products, e.g. oligosaccharides, polyols, and enzymes in a biorefinery framework will also be presented and discussed based on data for the upgrade of agro-food industrial residues and by-products. Examples will compare the use of mild processes for the selective recovery of hemicelluloses such autohydrolysis and dilute acid hydrolysis of brewery's spent grain, wheat straw, and eucalypt wood and the biotechnological processing of the hydrolysates. It is foreseen that hemicellulose-derived chemicals will become an ever more relevant category of products, as they hold a promise of economic benefit for the biorefineries

Ação concertada das renováveis participação portuguesa

CIES2020 - XVII Congresso Ibérico e XIII Congresso Ibero-americano de Energia SolarRESUMO: A Ação Concertada das Renováveis (CA-RES) é uma iniciativa conjunta de 27 Estados-Membros da EU, da Noruega, da Islândia e da Comissão Europeia (DG ENER, EASME), coordenada pela Agência Austríaca de Energia com vista a apoiar a implementação da Diretiva Europeia de Energias Renováveis. O projeto foi cofinanciado pelo Programa Horizonte 2020 da União Europeia e corresponde ao item B.2.2. “Coordination of Renewable Energy policies development and implementation through concerted actions with Member States” of the HORIZON 2020 WORK PROGRAMME 2014–2015 10. Secure, clean and efficient energy. A terceira fase da Ação Concertada (CA-RES 3) apoia a transposição da Diretiva das Energias Renováveis 2009/28/CE e a sua reformulação na nova Diretiva 2018/2001/UE (RED II). Os objetivos da Concerted Action estando diretamente relacionados com a transposição e implementação da Diretiva RES permitem também fomentar sinergias e criar novas oportunidades para explorar abordagens comuns em áreas específicas das energias Renováveis.ABSTRACT: The Concerted Action for Renewables (CA-RES) is a joint initiative of 27 Member States from the EU, Norway, Iceland and the European Commission (DG ENER, EASME), coordinated by the Austrian Energy Agency to support implementation European Renewable Energy Directive. The project was co-financed by the Horizon 2020 Program of the European Union and corresponds to item B.2.2. “Coordination of Renewable Energy policies development and implementation through concerted actions with Member States” of the HORIZON 2020 WORK PROGRAMME 2014–2015 10. Secure, clean and efficient energy. The third phase of Concerted Action (CA-RES 3) supports the transposition of the Renewable Energy Directive 2009/28 / EC and its reformulation in the new Directive 2018/2001 / EU (RED II). Concerted Action's objectives, being directly related to the transposition and implementation of the RES Directive, also allow to foster synergies and create new opportunities to explore common approaches in specific areas of Renewable Energies.info:eu-repo/semantics/publishedVersio

Engineered Ashbya gossypii for single-cell oil production from non-detoxified Eucalyptus bark hydrolysate

[Excerpt] Ashbya gossypii is a filamentous fungus industrially used for riboflavin production, a bioprocess in which downstream product recovery is facilitated by the ability of this fungus to undergo autolysis during the late stationary phase of growth or at low temperature [1]. In addition to riboflavin, engineered A. gossypii strains are capable of producing other compounds of interest for the food and feed industry, among which Single-Cell Oils (SCOs) from media containing mixed formulations of detoxified corn-cob hydrolysate, sugarcane molasses or crude glycerol [2]. [...]This work was supported by Compete 2020, Portugal 2020 and Lisboa 2020 through MoveToLowC (POCI-01-0247-FEDER-046117) and by FCT through the strategic funding of UIDB/04469/2020 and project ESSEntial (PTDC/BII-BTI/1858/2021).info:eu-repo/semantics/publishedVersio

Biomass and microbial lipids production by Yarrowia lipolytica W29 from eucalyptus bark hydrolysate

Using lignocellulosic biomass hydrolysate as a renewable and abundant feedstock for microbial lipids production is a sustainable and economic high-potential approach. This study investigated the potential of the oleaginous yeast Yarrowia lipolytica to produce lipids-rich biomass from eucalyptus bark hydrolysate (EBH) obtained by enzymatic hydrolysis of the biomass pretreated by steam explosion. The effect of EBH concentration (undiluted and 1:3 v/v diluted) and medium supplementation (CSL and KH2PO4) was evaluated in Erlenmeyer flasks and lab-scale stirred tank bioreactor, respectively. Additionally, the effect of volumetric oxygen transfer coefficient (kLa) and mode of operation (batch and two-stage repeated batch) was also assessed in the bioreactor. Under the best experimental conditions (undiluted EBH, 2gL1 CSL, 1.8gL1(NH4)2SO4, and kLa of 66 h1), Y. lipolytica W29 grown in batch cultures accumulated 26 % (w/w) of intracellular lipids, corresponding to 5.6gL1 of concentration. Lipids of Y. lipolytica were highly unsaturated and mainly composed of oleic acid (48 %), followed by palmitoleic (20 %), linoleic (17 %) and palmitic acids (14 %). This composition of Y. lipolytica lipids suggests their potential use as feedstock for biodiesel (a renewable biofuel). This work demonstrated the robust features of Y. lipolytica W29 as a potential lipids production platform to implement lignocellulose-based biorefineries.This study was supported by the Move2LowC project (POCI-01- 0247-FEDER-046117), cofinanced by Programa Operacional Competitividade e Internacionalizaçao, Programa Operacional Regional de Lisboa, Portugal 2020 and the European Union, through the European Regional Development Fund. It was also supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit (DOI 10.54499/UIDB/04469/2020) and the Doctoral grant (2021.05799. BD). The authors gratefully acknowledge RAIZ (Forest and Paper Research Institute) for providing the eucalyptus bark material, and Novozymes A/S for supplying Cellic® CTec3 HS. The technical assistance of STEX company (Aveiro, Portugal) on the operation of pilot scale infrastructure of steam explosion and enzymatic hydrolysis is also acknowledged.info:eu-repo/semantics/publishedVersio