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The development of biomass pretreatment approaches that, next to (hemi)cellulose valorization, aim at the conversion of lignin to chemicals is essential for the long-term success of a biorefinery. Herein, we discuss a dithionite-assisted organosolv fractionation (DAOF) of lignocellulose in n-butanol and water to produce cellulosic pulp and mono-/oligo-aromatics. The present study frames the technicalities of this biorefinery process and relates them to the features of the obtained product streams. Via the extensive characterization of the solid pulp (by acid hydrolysis-HPLC, ATR-FTIR, XRD, SEM and enzymatic hydrolysis-HPLC), of lignin derivatives (by GPC, GC-MS/FID, 1H-13C HSQC NMR, and ICP-AES) and of carbohydrate derivatives (by HPLC) we comprehensively identify and quantify the different products of interest. These results were used for inspecting the economic feasibility of DAOF. The adoption of a dithionite loading of 16.7% w/wbiomass and of an equivolumetric mixture of n-butanol and water, which led to a high yield of monophenolics (~20%, based on acid insoluble lignin, for the treatment of birch sawdust), was identified as the most profitable process configuration. Furthermore, the treatment of various lignocellulosic feedstocks was explored, which showed that DAOF is particularly effective for processing hardwood and herbaceous biomass. Overall, this study provides a comprehensive view of the development of an effective dithionite-assisted organosolv fractionation method for the sustainable upgrading of lignocellulosic biomass.

Lignin is the most abundant source of renewable aromatics on Earth, but its tendency to undergo irreversible condensation reactions during lignocellulose pretreatment hampers its valorization in current biorefinery schemes. A strategy for circumventing this issue is the so-called reductive catalytic fractionation (RCF), which relies on the use of redox catalysts and hydrogen gas to promote the reductive cleavage of lignin and to prevent lignin condensation, ultimately yielding low-molecular weight phenolics, along with a delignified (hemi)cellulose fraction. Some limitations must be overcome to improve the potential of RCF. The treatment of biomass feedstocks alternative to the widely explored virgin wood is important for extending the range of applications of this method. In addition, the recurrent adoption of high pressures of hydrogen gas poses safety and equipment constraints. This dissertation reports on research undertaken to investigate the RCF of wheat straw, an inexpensive and abundantly available agricultural residue, with a focus on the study of hydrogen-free process configurations. Moreover, an innovative dithionite-assisted organosolv fractionation (DAOF) method for the reductive depolymerization of lignin within biomass pretreatment is developed, based on the use of sodium dithionite as a reducing agent, instead of hydrogen gas and redox catalysts. Overall, this dissertation shows that RCF and DAOF represent promising approaches for the sustainable production of light aromatics via the reductive depolymerization of lignin., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2022

The development of biomass pretreatment approaches that, next to (hemi)cellulose valorization, aim at the conversion of lignin to chemicals is essential for the long-term success of a biorefinery. Herein, we discuss a dithionite-assisted organosolv fractionation (DAOF) of lignocellulose in n-butanol and water to produce cellulosic pulp and mono-/oligo-aromatics. The study frames the technicalities of this biorefinery process and relates them to the features of the obtained product streams. We comprehensively identify and quantify all products of interest: solid pulp (acid hydrolysis-HPLC, ATR-FTIR, XRD, SEM, enzymatic hydrolysis-HPLC), lignin derivatives (GPC, GC–MS/FID, 1H–13C HSQC NMR, ICP-AES), and carbohydrate derivatives (HPLC). These results were used for inspecting the economic feasibility of DAOF. In the best process configuration, a high yield of monophenolics was reached (∼20 wt%, based on acid insoluble lignin in birch sawdust). Various other lignocellulosic feedstocks were also explored, showing that DAOF is particularly effective on hardwood and herbaceous biomass. Overall, this study demonstrates that DAOF is a viable fractionation method for the sustainable upgrading of lignocellulosic biomass.

The reductive catalytic fractionation (RCF) is a promising method for the development of “lignin-first” biorefineries. Apart from the widely investigated virgin woody biomass, it is essential to explore the potential of waste biomass feedstocks. Herein, the RCF of wheat straw is examined to produce lignin mono-/oligomers along with a processable carbohydrate pulp. The use of different catalysts (Ru/C and Ru/Al2O3) and catalyst loadings (0–20% w/wbiomass) revealed the superior performance of Ru/C, which resulted in the largest yield of phenolic monomers (up to ∼25 wt % of initial acid-insoluble lignin) and in the lowest formation of high-molecular-weight fragments in the extracted lignin oil. Furthermore, the operating temperature was shown to substantially affect both lignin extraction–depolymerization and polysaccharides preservation–processability. For a reaction time of 3 h, an increase of the temperature from 200 to 250 °C resulted in a >2-fold boost of the yields of lignin oil and monophenolics, while the recovery of polysaccharides decreased by about 30 wt % (with ∼20% lower enzymatic digestibility). An economic assessment highlighted that the high-temperature treatment becomes the most profitable configuration as the market price of lignin products increases. Overall, this work provides insight into the adoption of the RCF for the upgrading of lignocellulose from inexpensive and widely available wheat straw biomass.

Anthropogenic activities linked to our consumer society have led to the current environmental crisis. Mankind must move away from the sole use of non-renewable fossil resources and promote sustainable production of biobased chemicals and biofuels. The utilization of low-cost organic feedstocks, such as food wastes or agro-industrial residues are promising alternative to fossil resources in order to produce value added bio-based molecules. Mixed microbial fermentations can transform such feedstocks to short and medium chain carboxylates. These molecules have potential application in the pharmaceutical, chemical and biofuel sector. This study investigated the influence of the supplementation of H2 and CO2, in addition to the reducing equivalents and carbon fed by brewer’s spent grains, on the production of medium chain carboxylic acids by a mixed microbial culture. The fermentations were operated in triplicates for 21 days in batch mode under N2, H2, CO2 or H2/CO2 atmospheres, respectively. H2 promoted the MCCAs production, CO2 inhibited the global fermentation and the mixture H2/CO2 was the only condition that exhibited a second elongation phase. This second elongation phase led to an increase in MCCAs production by 211% and 385%, as compared to respectively the H2 reference and the N2 control conditions. A longer-term batch mode fermentation of 63 days under H2/CO2 atmosphere confirmed the fermentation profile and exhibited a MCCAs maximum concentration of 16.5±2.8 kgDCO/m3ML (11.6±1.8kg/m3ML) at day 42. Considering the sampling and refill of the mixed liquor, in order to keep a constant volume, a total MCCAs production of 25.6±4.0kgCOD/m³ML was achieved. Overall, this study demonstrated that H2 alone promotes the MCCAs production, CO2 alone inhibits the whole fermentation process, but when added together, H2 and CO2 chain elongation restarts.

info:eu-repo/semantics/nonPublished

Carbohydrate active enzymes play an important role in biorefining. They are key players in the deconstruction of polysaccharides, with applications for the production of bio-molecules and renewable fuels from lignocellulosic biomass. In the context of bioprospecting for such new enzymes, the aim of this PhD thesis was to characterize the carbohydrate hydrolytic potential of lignocellulose-degrading microbiomes. Using metagenomics, metatranscriptomics and downstream bioinformatic analyses, I investigated the polysaccharide deconstruction potential of bacteria extracted from anaerobic bioreactors fed with sugar beet pulp, as well as from the gut of termites exposed to a miscanthus diet. I enlightened the genomic redundancy of the carbohydrate hydrolysis function of the anaerobic bioreactor microbiome, i.e. the metagenomic potential was maintained while the operational conditions (pH) and composition of the bacterial community evolved. In the case of the termite gut microbiome exposed to miscanthus, an up regulation of carbohydrate active enzymes involved in lignocellulosic biomass deconstruction was observed. With the intention of confirming the in-silico predictions of the substrate specificity of selected carbohydrate active enzymes, I developed a complete in-vitro workflow, from DNA isolation to heterologous expression of the proteins and activity detection. This work led to the discovery of new carbohydrate active enzymes and related gene clusters, which bring additional knowledge towards the strategy employed by bacteria to deconstruct lignocellulosic biomass. Additionally, these nature-optimised enzymatic cocktails might be mimicked and new specific enzymes be introduced in the precision biorefining pre-treatments of lignocellulosic biomass., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2020

Miscanthus sp. biomass could satisfy future biorefinery value chains. However, its use is largely untapped due to high recalcitrance. The termite and its gut microbiome are considered the most efficient lignocellulose degrading system in nature. Here, we investigate at holobiont level the dynamic adaptation of Cortaritermes sp. to imposed Miscanthus diet, with a long-term objective of overcoming lignocellulose recalcitrance. We use an integrative omics approach combined with enzymatic characterisation of carbohydrate active enzymes from termite gut Fibrobacteres and Spirochaetae. Modified gene expression profiles of gut bacteria suggest a shift towards utilisation of cellulose and arabinoxylan, two main components of Miscanthus lignocellulose. Low identity of reconstructed microbial genomes to closely related species supports the hypothesis of a strong phylogenetic relationship between host and its gut microbiome. This study provides a framework for better understanding the complex lignocellulose degradation by the higher termite gut system and paves a road towards its future bioprospecting.