The ability of the oleaginous yeast Trichosporon fermentans to efficiently produce lipids when cultivated in dried sweet sorghum was evaluated. First, lipid production was evaluated in synthetic media mimicking the composition of sweet sorghum stalks and optimized based on the nitrogen source and C: N ratio. Under optimum conditions, the lipid production reached 3.66 g/L with 21.91% w/w lipid content by using a mixture of sucrose, glucose and fructose and peptone at C: N ratio 160. Cultivation on pre-saccharified sweet sorghum stalks offered 1.97 g/L, while it was found that sweet sorghum stalks can support yeast growth and lipid production without the need for external nitrogen source addition. At an attempt to increase the carbon source concentration for optimizing lipid production, the Crabtree effect was observed in T. fermentans. To this end, the yeast was evaluated for its potential to produce ethanol under anaerobic conditions in synthetic media and sweet sorghum. The ethanol concentration at 100 g/L glucose was 40.31 g/L, while utilizing sweet sorghum by adding a distinct saccharification step and external nitrogen source offered ethanol concentration equal to 23.5 g/L. To the authors’ knowledge, this is the first time that the Crabtree effect is observed in T. fermentans.

In gas fermentation, a range of chemolithoautotrophs fix single-carbon (C1) gases (CO2 and CO) when H2 or other reductants are available. Microbial electrosynthesis (MES) enables CO2 reduction by generating H2 or reducing equivalents with the sole input of renewable electricity. A combined approach as gas electro-fermentation is attractive for the sustainable production of biofuels and biochemicals utilizing C1 gases. Various platform compounds such as acetate, butyrate, caproate, ethanol, butanol and bioplastics can be produced. However, technological challenges pertaining to the microbe-material interactions such as poor gas-liquid mass transfer, low biomass and biofilm coverage on cathode, low productivities still exist. We are presenting a review on latest developments in MES focusing on the configuration and design of cathodes that can address the challenges and support the gas electro-fermentation. Overall, the opportunities for advancing CO and CO2-based biochemicals and biofuels production in MES with suitable cathode/reactor design are prospected.

High-rate production of acetate and other value-added products from the reduction of CO₂ in microbial electrosynthesis (MES) using acetogens can be achieved with high reducing power where H₂ appears as a key electron mediator. H₂ evolution using metal cathodes can enhance the availability of H₂ to support high-rate microbial reduction of CO₂. Due to the low solubility of H₂, the availability of H₂ remains limited to the bacteria. In this study, we investigated the performances of Sporomusa ovata for CO₂ reduction when dual cathodes were used together in an MES, one was regular carbon cathode, and the other was a titanium mesh that allows higher hydrogen evolution. The dual cathode configuration was investigated in two sets of MES, one set had the usual S. ovata inoculated graphite rod, and another set had a synthetic biofilm-imprinted carbon cloth. Additionally, the headspace gas in MES was recirculated to increase the H₂ availability to the bacteria in suspension. High-rate CO₂ reduction was observed at −0.9 V vs Ag/AgCl with dual cathode configuration as compared to single cathodes. High titers of acetate (up to ∼11 g/L) with maximum instantaneous rates of 0.68–0.7 g/L/d at −0.9 V vs Ag/AgCl were observed, which are higher than the production rates reported in literatures for S. ovata using MES with surface modified cathodes. A high H₂ availability supported the high-rate acetate production from CO₂ with diminished electricity input.

Acetate can be produced from carbon dioxide (CO2) and electricity using bacteria at the cathode of microbial electrosynthesis (MES). This process relies on electrolytically-produced hydrogen (H2). However, the low solubility of H2 can limit the process. Using metal cathodes to generate H2 at a high rate can improve MES. Immobilizing bacteria on the metal cathode can further proliferate the H2 availability to the bacteria. In this study, we investigated the performances of 3D bioprinting of Sporomusa ovata on three metal meshes—copper (Cu), stainless steel (SS), and titanium (Ti), when used individually as a cathode in MES. Bacterial cells were immobilized on the metal using a 3D bioprinter with alginate hydrogel ink. The bioprinted Ti mesh exhibited higher acetate production (53 ± 19 g/m2/d) at −0.8 V vs. Ag/AgCl as compared to other metal cathodes. More than 9 g/L of acetate was achieved with bioprinted Ti, and the least amount was obtained with bioprinted Cu. Although all three metals are known for catalyzing H2 evolution, the lower biocompatibility and chemical stability of Cu hampered its performance. Stable and biocompatible Ti supported the bioprinted S. ovata effectively. Bioprinting of synthetic biofilm on H2-evolving metal cathodes can provide high-performing and robust biocathodes for further application of MES.

Microbial metabolism enables the sustainable synthesis of fuels and chemicals from gaseous substrates (H₂, CO, and CO₂), thus drastically diminishing the carbon load in the atmosphere. Various value-added biochemicals and biofuels, such as acetate, methane, ethanol, butanol, butyrate, caproate, and bioplastics, have been produced during the conversion of syngas or H₂/CO₂, using a variety of microorganisms as biocatalysts. Gas fermentation processes using acetogenic and methanogenic organisms are being extensively investigated. This chapter provides an overview of microbial CO and CO₂ conversion technology, with an emphasis on recent developments and integration with renewable electricity for the generation of H₂ or other forms of electron donors. A discussion on technological challenges in gas fermentation addresses issues, such as poor mass transfer, low microbial biomass, and low productivity. It also presents possible solutions based on the latest advances in bioelectrochemical processes including microbial gas electrofermentation. Finally, the chapter includes a sustainability analysis of the process and includes a brief update on commercially established companies operating gas fermentation systems. Overall, an integrated approach combining gas fermentation and renewable electricity offers an opportunity for the development of CO and CO₂- based biochemical and biofuel production at commercial scale.

Beneficiation of the tailings from Iron Oxide Apatite (IOA) ore has become an important topic in the field of mineral processing as phosphate rock is considered as critical raw material by the European Union. Driven by the strong call for sustainability and green technology, this paper introduces the application of novel and bio-based organosolv lignin particles (OLP) as a reagent for apatite flotation. In the artificial mineral mixture flotation tests, OLP addition or replacement to tall oil fatty acid-based collector (TOFA) was shown to improve flotation kinetics and recovery. In this study, it was demonstrated that one of the widely used commercial TOFA collectors could be replaced with OLP by 70 %. The replacement led to an increase in recovery (+2%) and only a minimal decrease in P grade (−0.3 %) for the rougher-cleaner flotation tests in one of the two feed types tested. The influence of OLP and other reagents on apatite floatability has been investigated through Hallimond tube tests and laboratory scale batch flotation tests as well as zeta potential measurements and spectroscopy tests to further understand the possible mechanism and synergism of reagents in the apatite flotation system.

A shift towards an economically viable biomass biorefinery concept requires the use of all biomass fractions (cellulose, hemicellulose, and lignin) for the production of high added-value products. As lignin is often underutilized, the establishment of lignin valorization routes is highly important. In-house produced organosolv as well as commercial Kraft lignin were used in this study. The aim of the current work was to make a comparative study of thermoplastic biomaterials from two different types of lignins. Native lignins were alkylate with two different alkyl iodides to produce ether-functionalized lignins. Successful etherification was verified by FT-IR spectroscopy, changes in the molecular weight of lignin, as well as ¹³C and ¹H Nuclear Magnetic Resonance (NMR). The thermal stability of etherified lignin samples was considerably improved with the T_2% of organosolv to increase from 143 °C to up to 213 °C and of Kraft lignin from 133 °C to up to 168 °C, and glass transition temperature was observed. The present study shows that etherification of both organosolv and Kraft lignin with alkyl halides can produce lignin thermoplastic biomaterials with low glass transition temperature. The length of the alkyl chain affects thermal stability as well as other thermal properties.

Single cell oils (SCOs) are considered potential raw material for the production of biodiesel. Rhodosporidium sp. and Lipomyces sp. are good candidates for SCO production. Lipid extractability differs according to yeast species and literature on the most suitable method for each oleaginous yeast species is scarce. This work aimed to investigate the efficiency of the most cited strategies for extracting lipids from intact and pretreated cells of Rhodosporidium toruloides and Lipomyces starkeyi. Lipid extractions were conducted using hexane or combinations of chloroform and methanol. The Folch method resulted in the highest lipid yields for both yeasts (42% for R. toruloides and 48% for L. starkeyi). Also, this method eliminates the cell pretreatment step. The Bligh and Dyer method underestimated the lipid content in the tested strains (25% for R. toruloides and 34% for L. starkeyi). Lipid extractability increased after acid pretreatment for the Pedersen, hexane, and Bligh and Dyer methods. For R. toruloides unexpected fatty acid methyl esters (FAME) composition were found for some lipid extraction strategies tested. Therefore, this work provides useful information for analytical and process development aiming at biodiesel production from the SCO of these two yeast species.

The present research investigated the effect of organosolv pretreatment on two species of salt-tolerant Salicornia spp. biomass, Salicornia dolichostachya and Salicornia ramosissima, for increasing biomethane production through anaerobic digestion. The final biomethane yield of de-juiced green fibers of Salicornia spp. from wet fractionation increased by 23–28% after organosolv treatment. The highest methane yield of about 300 mL-CH4/gVS was found after organosolv treatment with 60% v/v ethanol solution at 200 °C for 30 min, or at 180 °C for 30 or 60 min treatment time. Furthermore, the methane production rate increased significantly, reducing the time until 95% of the final methane yield was reached from 20 days to 6–10 days for the organosolv-treated biomass. This research shows that the process of anaerobic digestion of halophyte biomass benefits from cascade processing of Salicornia fibers in a biorefinery framework by sequential wet and organosolv fractionation for full utilization of halophytic biomass.

Lignin, one of the three main structural biopolymers of lignocellulosic biomass, is the most abundant natural source of aromatics with a great valorization potential towards the production of fuels, chemicals, and polymers. Although kraft lignin and lignosulphonates, as byproducts of the pulp/paper industry, are available in vast amounts, other types of lignins, such as the organosolv or the hydrolysis lignin, are becoming increasingly important, as they are side-streams of new biorefinery processes aiming at the (bio)catalytic valorization of biomass sugars. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis of softwood (spruce) and hardwood (birch) lignins, isolated by a hybrid organosolv–steam explosion biomass pretreatment method in order to investigate the effect of lignin origin/composition on product yields and lignin bio-oil composition. The catalysts studied were conventional microporous ZSM-5 (Zeolite Socony Mobil–5) zeolites and hierarchical ZSM-5 zeolites with intracrystal mesopores (i.e., 9 and 45 nm) or nano-sized ZSM-5 with a high external surface. All ZSM-5 zeolites were active in converting the initially produced via thermal pyrolysis alkoxy-phenols (i.e., of guaiacyl and syringyl/guaiacyl type for spruce and birch lignin, respectively) towards BTX (benzene, toluene, xylene) aromatics, alkyl-phenols and polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes), with the mesoporous ZSM-5 exhibiting higher dealkoxylation reactivity and being significantly more selective towards mono-aromatics compared to the conventional ZSM-5, for both spruce and birch lignin.

Banana production generates significant amounts of agricultural wastes, being fiber extraction one of the most relevant alternatives for their valorization. This process produces banana’s pseudostem pulp (BPP) as a byproduct, which shows an interesting composition for the biorefinery’s biochemical platform, with high polysaccharides (68%) and low lignin contents. This work deals with the enzymatic hydrolysis (EH) of raw and hydrothermally pre-treated BPP, focusing on the production of oligosaccharides (OS). Raw BPP hydrolysis with cellulase at different dosages rendered only 3.2% OS yields (OSY). Pectinase addition has not affected EH performance. On the other hand, EH of hydrothermally pre-treated BPP at 150 °C and 170 °C (P150 and P170) allowed to increase OSY up to 28% (P150, 1 FPU of cellulase/g dry biomass, 12 h), being 72% of the solubilized sugars in the form of cello-oligosaccharides. This last condition was subjected to a multi-stage EH strategy without improvements in OSY. An endo-glucanase was also tested, but obtained OSY were lower than cellulase results. Finally, obtained OS demonstrated to stimulate the growth of two Lactobacilli strains. The results show that BPP pre-treated under mild operational conditions is a good candidate for cello-oligosaccharides production by EH using 1 FPU/g DB of cellulase with a simple strategy.

Plastics usage is rising daily because of increased population, modernization, and industrialization, which produces a lot of plastic garbage. Due to their various chemical structures, long chain polymeric compositions, and thermal/decomposition behavior, it is challenging to recycle these plastic wastes into hydrocarbon fuels. In the current work, domestic plastic waste was pyrolyzed at 473 to 973 K in a fixed bed reactor and compared with the three virgin plastics LDPE (low-density polyethylene), HDPE (high-density polyethylene), and PP (polypropylene), as well as a mixture of the three (virgin mixed plastics). The pyrolysis results showed that maximum liquid hydrocarbons obtained from HDPE, LDPE, PP, mixed plastic, and domestic waste were 64.6 wt.%, 62.2 wt.%, 63.1 wt.%, 68.6 wt.%, and 64.6 wt.% at 773 K, respectively. The composition of liquid fuels was characterized using FTIR and GC-MS, which showed a wide spectrum of hydrocarbons in the C8–C20 range. Furthermore, liquid fuel characteristics such as density, viscosity, fire and flash point, pour point, and calorific value were examined using ASTM standards, and the results were found to be satisfactory. This study provides an innovative method for recycling waste plastics into economical hydrocarbon fuel for use in transportation.

Rapid climate change and forecasted damage from fossil fuel combustion, forced researchers to investigate renewable and clean energy sources for the sustainable development of societies throughout the world. Biomass-based energy is one of the most important renewable energy sources for meeting daily energy needs, which are gaining in popularity daily. Gasification-based bioenergy production is an effective way to replace fossil fuels and reduce CO2 emissions. Even though biomass gasification has been studied extensively, there is still much opportunity for improvement in terms of high-quality syngas generation (high H2/CO ratio) and reduced tar formation. Furthermore, the presence of tar has a considerable impact on syngas quality. Downdraft gasifiers have recently shown a significant potential for producing high-quality syngas with lower tar concentrations. This article presents a comprehensive review on the advancement in biomass downdraft gasification technologies for high-quality synthesis gas. In addition, factors affecting syngas production and composition e.g., equivalency ratio, temperature, particle size, and gasification medium on synthesis gas generation are also comprehensively studied. The up-gradation and various applications of synthesis gas are also discussed in brief in this review article.

Organosolv lignin nanoparticles have been recently evaluated for their use in mineral froth flotation as a flotation reagent, and as a result, the recovery of the target minerals was improved and the selectivity of the process was increased. However, the mechanism of lignin activity in mineral froth flotation is not known. Therefore, this study is the first step in understanding the interaction of organosolv lignin with the mineral surface. As such, the organosolv lignin was characterized by GPC and 31P NMR, where the structural differences between the birch and spruce lignins were determined. The molecular size and lignol unit composition were evaluated. Subsequently, the morphology and size of the organosolv lignin particles were examined for all 4 produced types: BN, BM, SN, and SM. The ? potential was measured in the pH range of 2-11. All particles had a high negative charge, which indicated good stability of the dispersion in the alkali range. The stability of their colloidal dispersion was observed under increasing concentrations of mono- and divalent cations, and electrostatic repulsion was identified as the main stabilization mechanism. Finally, QCM-D was used to study the interaction of the lignin particles with the mineral surfaces of chalcopyrite, pyrite, and galena, which gave insight into the possible mechanism during the flotation process.

Flotation is a key step during mineral separation. Xanthates are the most commonly used collectors for recovering Cu, Ni, and Zn from sulphide ores. However, xanthates are fossil-based and toxic for the environment. The aim of this study was to evaluate the use of lignin nanoparticles and microparticles as sustainable and environmentally friendly collectors. Lignin particles demonstrated good selectivity toward Cu (chalcopyrite), with total recoveries exceeding 80% and grades of up to 8.6% w/w from a Cu-Ni ore in rougher flotation tests. When floating Zn-Pb-Cu ore, lignin nanoparticles could reduce the use of xanthates by 50%. Moreover, they outperformed xanthates alone, achieving total recoveries of up to 91%, 85%, and 98% for Cu, Pb, and Zn, respectively. These results prove the potential of lignin as a flotation collector.

The rising demand for surfactants by the pharmaceuticals and cosmetic industries has generated vast amounts of petroleum-based synthetic surfactants, which are often toxic and non-degradable. Owing to their low toxicity, stability in extreme conditions, and biodegradability, biosurfactants could represent a sustainable alternative. The present study aimed to maximize the production of rhamnolipids (RL) from Pseudomonas aeruginosa by optimizing glucose concentration, temperature, and C/N and C/P ratios. After 96 h of cultivation at 37 °C, the final RL concentration was 4.18 ± 0.19 g/L with a final yield of 0.214 ± 0.010 g/gglucose when pure glucose was used as a carbon source. At present, the main obstacle towards commercialization of RL production is economic sustainability, due to the high cost of downstream processes and media components. For this reason, a renewable source such as wood hydrolysates (from birch and spruce woodchips) was examined here as a possible source of glucose for RL production. Both hydrolysates proved to be adequate, resulting in 2.34 ± 0.17 and 2.31 ± 0.10 g/L of RL, respectively, and corresponding yields of 0.081 ± 0.006 and 0.089 ± 0.004 g/gsugar after 96 h. These results demonstrate the potential of using renewable biomass for the production of biosurfactants and, to the best of our knowledge, they constitute the first report on the use of wood hydrolysates for RL production.

Biofuels are essential for transitioning to a sustainable society. This switch can be achieved by introducing novel feedstocks and technologies for efficient and economically feasible biofuel production. Second-generation biofuels are particularly advantageous, as they are produced from nonedible lignocellulosic biomass derived primarily from agricultural byproducts. Ciona intestinalis, a marine filter feeder, is cultivated to produce fish feed from the invertebrate’s inner tissue body. This process generates also vast amounts of a renewable side stream, namely the tunicate’s external cellulose-rich tunic. The aim of the present study was to evaluate the potential of the C. intestinalis tunic as a novel feedstock for bioethanol production. For this purpose, organosolv fractionation of the tunic was optimized to increase cellulose content. Enzymatic saccharification of the pretreated biomass was assessed to identify the most promising materials, which were subsequently utilized as carbon source in fermentation trials. Under optimal conditions, a titer of 38.7 g/L of ethanol, with a yield of 78.3% of the maximum theoretical, was achieved. To the best of our knowledge, this is the first report whereby organosolv pretreated tunic biomass is valorized toward bioethanol production; the current work paves the way for incorporating tunicates in bioconversion processes for the generation of biofuels and other biobased chemicals.

Background

One of the sustainable development goals focuses on the biomass-based production as a replacement for fossil-based commodities. A novel feedstock with vast potentials is tunicate biomass, which can be pretreated and fermented in a similar way to lignocellulose. Ciona intestinalis is a marine filter feeder that is cultivated to produce fish feed. While the inner tissue body is used for feed production, the surrounding tunic remains as a cellulose-rich by-product, which can be further separated into outer and inner tunic. Ethanol production from organosolv-pretreated whole-tunic biomass was recently validated. The aim of the present study was to evaluate the potential of organosolv pretreated outer-tunic biomass for the production of biofuels and cellobiose that is a disaccharide with prebiotic potential.

Results

As a result, 41.4 g/L of ethanol by Saccharomyces cerevisiae, corresponding to a 90.2% theoretical yield, was achieved under the optimal conditions when the tunicate biomass was pretreated at 195 °C for 60 min at a liquid-to-solid ratio of 50. In addition, cellobiose production by enzymatic hydrolysis of the pretreated tunicate biomass was demonstrated with a maximum conversion yield of 49.7 wt. %.

Conclusions

The utilisation of tunicate biomass offers an eco-friendly and sustainable alternative for value-added biofuels and chemicals. The cultivation of tunicate biomass in shallow coastal sea improves the quality of the water and ensures sustainable production of fish feed. Moreover, there is no competition for arable land, which leaves the latter available for food and feed production.

The aim of this study was to assess the effect of hot water extraction followed by organosolv pretreatment on the enzymatic hydrolysability of spruce bark biomass. To this end, samples were pretreated at five different temperatures in the presence or not of acid catalyst. The cellulose content of pre-treated biomass reached 49.6% w/w. During the enzymatic hydrolysis trials with 3% w/w dry solids, the final hydrolysis yield reached up to 70.1%, which corresponded to the release of 7.8 g/L of glucose. Whereas, the final hydrolysis yield obtained during the high-gravity enzymatic hydrolysis reached up to 43.5%. The concentration of released glucose was in range of 33.3 – 40.0 g/L with a hemicellulose sugars in a range of 5.5 – 6.6 g/L. These values are suitable for downstream bioconversion processes and represent a significant improvement over existing steam pretreatment methods.

This study was conducted to investigate the feasibility of microalgal biomass production and nutrient removal from recirculating aquaculture systems (RAS) water (RASW) with low phosphate concentration. For this purpose, Nannochloropsis oculata, Pavlova gyrans, Tetraselmis suecica, Phaeodactylum tricornutum, and their consortium were cultivated in RASW and RASW supplemented with vitamins (+V). Among them, N. oculata showed the maximum biomass production of 0.4 g/L in RASW. Vitamins supplementation significantly increased the growth of T. suecica from 0.16 g/L in RASW to 0.33 g/L in RASW + V. Additionally, T. suecica showed the highest nitrate (NO3–N) removal efficiency of 80.88 ± 2.08 % in RASW and 83.82 ± 2.08 % in RASW + V. Accordingly, T. suecica was selected for scaling up study of microalgal cultivation in RASW and RASW supplemented with nitrate (RASW + N) in 4-L airlift photobioreactors. Nitrate supplementation enhanced the growth of T. suecica up to 2.2-fold (day 15). The fatty acid nutritional indices in T. suecica cultivated in RASW and RASW + N showed optimal polyunsaturated fatty acids (PUFAs)/saturated fatty acid (SFAs), omega-6 fatty acid (n-6)/omega-3 fatty acid (n-3), indices of atherogenicity (IA), and thrombogenicity (IT)). Overall, the findings of this study revealed that despite low phosphate concentration, marine microalgae can grow in RASW and relatively reduce the concentration of nitrate. Furthermore, the microalgal biomass cultivated in RASW consisting of pigments and optimal fatty acid nutritional profile can be used as fish feed, thus contributing to a circular bioeconomy.

Bioelectrochemical systems (BES) are emerging as potential technologies that can remediate acid mine drainage (AMD) by cathodic reduction of sulfates to metal sulfides. This study evaluated bioelectrochemical remediation of sulfate rich AMD at two applied cathode potentials; BES-1: −1.0 V and BES-2: −0.8 V. Sulfate reducing bacteria were selectively enriched to be used as biocatalyst in BES. Initially, lactate was fed as carbon source and switched to chemolithoautotrophy with only CO2-fed conditions. Both BESs were operated at 3±0.2 g/l of sulfate with synthetic AMD (SAMD) fed first, and gradually changed to 50% AMD from mining site with 50% SAMD. Sulfate reduction was relatively higher with BES-1: 82% than BES-2: 76% coupled with sulfidogenesis. Interestingly, acetogenesis (BES-1: 2.12±0.2 g/l, BES-2: 1.9±0.2 g/l) was also noticed with high reduction currents (BES-1&2: >-70 mA). Microbiome community analysis revealed the dominant presence of sulfate reducers, acetogens, syntrophic bacteria and Methanobacterium, probing microbial synergy aiding sulfate reduction. An added advantage was the iron-sulfide (FeS) particles formation on cathode, which might have contributed to increased reduction currents. This study reveals insights into microbial synergy for autotrophic sulfate reduction within mixed microbiome communities along with the impact of FeS particles as conducive facilitator for electron transfer in BES, thereby enhancing electrosynthetic acetate production.

Background: Future biorefineries will focus on converting low value waste streams to chemical products that are derived from petroleum or refined sugars. Feedstock pretreatment in a simple, cost effective, agnostic manner is a major challenge.

Methods: In this work, beechwood sawdust was delignified via an organosolv process, assisted by homogeneous inorganic acid catalysis. Mixtures of water and several organic solvents were evaluated for their performance. Specifically, ethanol (EtOH), acetone (AC), and methyl- isobutyl- ketone (MIBK) were tested with or without the use of homogeneous acid catalysis employing sulfuric, phosphoric, and oxalic acids under relatively mild temperature of 175 °C for one hour.

Results: Delignification degrees (DD) higher than 90% were achieved, where both AC and EtOH proved to be suitable solvents for this process. Both oxalic and especially phosphoric acid proved to be good alternative catalysts for replacing sulfuric acid. High gravity simultaneous saccharification and fermentation with an enzyme loading of 8.4 mg/g_solids at 20 wt.% initial solids content reached an ethanol yield of 8.0 w/v%.

Conclusions: Efficient delignification combining common volatile solvents and mild acid catalysis allowed for the production of ethanol at high concentration in an efficient manner

Biomass fractionation, as an alternative to biomass pretreatment, has gained increasing research attention over the past few years as it provides separate streams of cellulose, hemicellulose, and lignin. These streams can be used separately and can provide a solution for improving the economics of emerging biorefinery technologies. The sugar streams are commonly used in microbial conversions, whereas during recent years lignin has been recognized as a valuable compound as it is the only renewable and abundant source of aromatic chemicals. Successfully converting lignin into valuable chemicals and products is key in achieving both environmental and economic sustainability of future biorefineries. In this work, lignin retrieved from beechwood sawdust delignification pretreatment via an organosolv process was depolymerized with thermal and catalytic pyrolysis. ZSM-5 commercial catalyst was used in situ to upgrade the lignin bio-oil vapors. Lignins retrieved from different modes of organosolv pretreatment were tested in order to evaluate the effect that upstream pretreatment has on the lignin fraction. Both thermal and catalytic pyrolysis yielded oils rich in phenols and aromatic hydrocarbons. Use of ZSM-5 catalyst assisted in overall deoxygenation of the bio-oils and enhanced aromatic hydrocarbons production. The oxygen content of the bio-oils was reduced at the expense of their yield. Organosolv lignins were successfully depolymerized towards phenols and aromatic hydrocarbons via thermal and catalytic pyrolysis. Hence, lignin pyrolysis can be an effective manner for lignin upgrading towards high added value products

Environmental pollution, greenhouse gas emissions, depletion of fossil fuels, and a growing population have sparked a search for new and renewable energy sources such as biodiesel. The use of waste or residues as substrates for microbial growth can favor the implementation of a biorefinery concept with reduced environmental footprint. Cyanobacteria constitute microorganisms with enhanced ability to use industrial effluents, wastewaters, forest residues for growth, and concomitant production of added-value compounds. In this study, a recently isolated cyanobacterium strain of Pseudanabaena sp. was cultivated on hydrolysates from pretreated forest biomass (silver birch and Norway spruce), and the production of biodiesel-grade lipids was assessed. Optimizing carbon source concentration and the (C/N) carbon-to-nitrogen ratio resulted in 66.45% w/w lipid content when microalgae were grown on glucose, compared to 62.95% and 63.79% w/w when grown on spruce and birch hydrolysate, respectively. Importantly, the lipid profile was suitable for the production of high-quality biodiesel. The present study demonstrates how this new cyanobacterial strain could be used as a biofactory, converting residual resources into green biofuel.

BackgroundGrowing evidence points to a link between specific fatty acids ingested through the diet and human health. Chain length, saturation degree, and position of double bonds in fatty acids determine their effect in humans. Omega-3 and omega-6 fatty acids have been recognized for their contribution to the prevention and/or treatment of diabetes, cancer, visual impairment, cardiovascular diseases, as well as neurological and musculoskeletal disorders.

Scope and approachHumans cannot synthesize these fatty acids in sufficient amounts and need to absorb them through the diet. Oleaginous microalgae constitute a promising, sustainable source of such fatty acids, as they can accumulate up to 85% of lipids on a cell dry weight basis.

Key findings and conclusionsThe present review summarizes the potential of oleaginous microalgae as a convenient, economical, and sustainable source of polyunsaturated fatty acids, and explores their beneficial role in human health. The growing prevalence of cardiovascular diseases and changing dietary preferences are driving the increasing demand for microbial omega-3 fatty acids. Following the COVID-19 pandemic, the importance of a healthy immune system has further strengthened the market for omega-3 fatty acids.

The tunicate species Ciona intestinalis is a fast-growing marine invertebrate animal that contains cellulose in its outer part - the tunic. The high crystallinity and microfibril aspect ratio of tunicate cellulose make it an excellent starting material for the isolation of nanocellulose. In the present work, tunic from C. intestinalis was subjected to organosolv pretreatment followed by bleaching and acid-hydrolysis steps for the isolation of nanocrystals. Applying an intermediate enzymatic treatment step with a lytic polysaccharide monooxygenase (LPMO) from the thermophilic fungus Thermothelomyces thermophila was proved to facilitate the isolation of nanocellulose and to improve the overall process yield, even when the bleaching step was omitted. LPMOs are able to oxidatively cleave the glycosidic bonds of a polysaccharide substrate, either at the C1 and/or C4 position, with the former leading to introduction of carboxylate moieties. X-ray photoelectron spectroscopy analysis showed a significant increase in the atomic percentage of the C═O/O-C-O and O-C═O bonds upon the addition of LPMO, while the obtained nanocrystals exhibited higher thermal stability compared to the untreated ones. Moreover, an enzymatic post-treatment with LPMOs was performed to additionally functionalize the cellulose nanocrystals. Our results demonstrate that LPMOs are promising candidates for the enzymatic modification of cellulose fibers, including the preparation of oxidized-nanocellulose, and offer great perspectives for the production of novel biobased nanomaterials. ©

The main objective of this study focused on the sustainable production of cellobiose and other cellulose-derived oligosaccharides from non-edible sources, more specifically, from forest residues. For this purpose, a fine-tuning of the performance of the commercially available enzyme mixture Celluclast^® was conducted towards the optimization of cellobiose production. By enzyme reaction engineering (pH, multi-stage hydrolysis with buffer exchange, addition of β-glucosidase inhibitor), a cellobiose-rich product with a high cellobiose to glucose ratio (37.4) was achieved by utilizing organosolv-pretreated birch biomass. In this way, controlled enzymatic hydrolysis combined with efficient downstream processing, including product recovery and purification through ultrafiltration and nanofiltration, can potentially support the sustainable production of food-grade oligosaccharides from forest biomass. The potential of the hydrolysis product to support the growth of two Lactobacilli probiotic strains as a sole carbon source was also demonstrated

Background

Production of value-added materials from lignocellulosic biomass residues is an emerging sector that has attracted much attention as it offers numerous benefits from an environmental and economical point of view. Non-digestible oligosaccharides represent a group of carbohydrates that are resistant to gastrointestinal digestion, and therefore, they are considered as potential prebiotic candidates. Such oligosaccharides can derive from the biomass cellulose fraction through a controlled enzymatic hydrolysis that eliminates the yield of monomers.

Results

In the present study, hydrolysis of organosolv-pretreated forest residues (birch and spruce) was tested in the presence of four cellulases (EG5, CBH7, CBH6, EG7) and one accessory enzyme (LPMO). The optimal enzyme combinations were comprised of 20% EG5, 43% CBH7, 22% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of birch and 35% EG5, 45% CBH7, 10% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of spruce, leading to 22.3% and 19.1 wt% cellulose conversion into cellobiose, respectively. Enzymatic hydrolysis was applied on scale-up reactions, and the produced oligosaccharides (consisted of > 90% cellobiose) were recovered and separated from glucose through nanofiltration at optimized temperature (50 °C) and pressure (10 bar) conditions, yielding a final product with cellobiose-to-glucose ratio of 21.1 (birch) and 20.2 (spruce). Cellobiose-rich hydrolysates were tested as fermentative substrates for different lactic acid bacteria. It was shown that they can efficiently stimulate the growth of two Lactobacilli strains.

Conclusions

Controlled enzymatic hydrolysis with processive cellulases, combined with product recovery and purification, as well as enzyme recycling can potentially support the sustainable production of food-grade oligosaccharides from forest biomass.

Non-digestible oligosaccharides (NDOs) are likely prebiotic candidates that have been related to the prevention of intestinal infections and other disorders for both humans and animals. Lignocellulosic biomass is the largest carbon source in the biosphere, therefore cello-oligosacharides (COS), especially cellobiose, are potentially the most widely available choice of NDOs. Production of COS and cellobiose with enzymes offers numerous benefits over acid-catalyzed processes, as it is milder, environmentally friendly and produces fewer by-products. Cellobiohydrolases (CBHs) and a class of endoglucanases (EGs), namely processive EGs, are key enzymes for the production of COS, as they have higher preference toward glycosidic bonds near the end of cellulose chains and are able to release soluble products. In this work, we describe the heterologous expression and characterization of two CBHs from the filamentous fungus Thermothelomyces thermophila, as well as their synergism with proccessive EGs for cellobiose release from organosolv pretreated spruce and birch. The properties, inhibition kinetics and substrate specific activities for each enzyme are described in detail. The results show that a combination of EGs belonging to Glycosyl hydrolase families 5, 6 and 9, with a CBHI and CBHII in appropriate proportions, can enhance the production of COS from forest materials, underpinning the potential of these biocatalysts in the production of NDOs.

Even though the main components of all lignocellulosic feedstocks include cellulose, hemicellulose, as well as the protective lignin matrix, there are some differences in structure, such as in hardwoods and softwoods, which may influence the degradability of the materials. Under this view, various types of biomass might require a minimal set of enzymes that has to be tailor-made. Partially defined complex mixtures that are currently commercially used are not adapted to efficiently degrade different materials, so novel enzyme mixtures have to be customized. Development of these cocktails requires better knowledge about the specific activities involved, in order to optimize hydrolysis. The role of filamentous fungus Myceliophthora thermophila and its complete enzymatic repertoire for the bioconversion of complex carbohydrates has been widely proven. In this study, four core cellulases (MtCBH7, MtCBH6, MtEG5, and MtEG7), in the presence of other four “accessory” enzymes (mannanase, lytic polyssacharide monooxygenase MtGH61, xylanase, MtFae1a) and β-glucosidase MtBGL3, were tested as a nine-component cocktail against one model substrate (phosphoric acid swollen cellulose) and four hydrothermally pretreated natural substrates (wheat straw as an agricultural waste, birch, and spruce biomass, as forest residues). Synergistic interactions among different enzymes were determined using a suitable design of experiments methodology. The results suggest that for the hydrolysis of the pure substrate (PASC), high proportions of MtEG7 are needed for efficient yields. MtCBH7 and MtEG7 are enzymes of major importance during the hydrolysis of pretreated wheat straw, while MtCBH7 plays a crucial role in case of spruce. Cellobiohydrolases MtCBH6 and MtCBH7 act in combination and are key enzymes for the hydrolysis of the hardwood (birch). Optimum combinations were predicted from suitable statistical models which were able to further increase hydrolysis yields, suggesting that tailor-made enzyme mixtures targeted toward a particular residual biomass can help maximize hydrolysis yields. The present work demonstrates the change from “one cocktail for all” to “tailor-made cocktails” that are needed for the efficient saccharification of targeted feed stocks prior to the production of biobased products through the biorefinery concept.

The present work investigates the suitability of pretreated corn stover (CS) to serve as feedstock for high gravity (HG) ethanol production at solids-content of 24 wt%. Steam explosion, with and without the addition of H2SO4, and organosolv pretreated CS samples underwent a liquefaction/saccharification step followed by simultaneous saccharification and fermentation (SSF). Maximum ethanol concentration of ca. 76 g/L (78.3% ethanol yield) was obtained from steam exploded CS (SECS) with 0.2% H2SO4. Organosolv pretreated CS (OCS) also resulted in high ethanol concentration of ca. 65 g/L (62.3% ethanol yield). Moreover, methane production through anaerobic digestion (AD) was conducted from fermentation residues and resulted in maximum methane yields of ca. 120 and 69 mL/g volatile solids (VS) for SECS and OCS samples, respectively. The results indicated that the implementation of a liquefaction/saccharification step before SSF employing a liquefaction reactor seemed to handle HG conditions adequately.

Different concentrations (0.1 and 1 M K⁺/Na⁺) of salt solutions (K₂CO₃, Na₂CO₃, NaOH and NaCl) were used to impregnate alkali in sawdust. After devolatilization, char samples were gasified at different temperatures (750–900 °C) under CO₂ in a macro-thermogravimetric analyzer for gasification kinetics. Morphologically, three classes of chars could be identified. Chars experiencing the highest catalytic influence were in Class-2 (0.5 M K₂CO₃ and 1 M NaOH) with a swollen and molten surface. In contrast, Class-1 (wood char like) and Class-3 (with salt deposits) chars showed moderate and low catalytic effect on gasification reactivity respectively. It is believed to be related to char surface swelling and alkali salt used. At 850 °C or below, the reactivity increased linearly (Class-1 and Class-3 Char) with initial alkali content up to 2200 mmol alkali/kg of char (except for NaCl). The same reaction rate was maintained until 3600 mmol/kg of char of alkali loading (Class-2) and then decreased. However, no trend was observed at 900 °C due to drastic change in reactivity of the samples, probably due to alkali transformation. Among the salts, K₂CO₃ (0.5 M) was found to be the most suitable for catalytic gasification due to its high catalytic activity in combination with relatively low carbon leaching.

Based on char gasification experiments in an isothermal thermogravimetric analyzer, a suitable concentration of alkali salt (K2CO3) was chosen for impregnation due to almost five-fold increase in gasification reactivity and relatively low amount of carbon leaching during impregnation. Furthermore, an optimum method for wet alkali impregnation was proposed based on the several tests performed by varying temperature and time. To study the catalytic effect on tar and soot yield, untreated and impregnated woody biomass were gasified under entrained flow condition between 900 oC and 1200 oC. Impregnation leads to 70% lower tar yield from gasification around 1000 oC and 1100 oC. The lowest amount of soot was detected for the same temperature range whereas the soot yield was one order of magnitude higher for untreated biomass. For tar, this influence became insignificant at a higher temperature (1200 oC). This defines the suitable temperature range for alkali catalyzed gasification without the loss of catalytic activity.

Oleaginous yeasts have attracted increasing scientific interest as single cell oil (SCO) producers. SCO can be used as a fossil-free fuel substitute, but also as a source of rarely found odd-chain fatty acids (OCFAs), such as C15, C17, and C25 fatty acids which have a wide range of nutritional and biological applications. Volatile fatty acids (VFAs) have gained interest as sustainable carbon source for yeasts. This study aims to improve current knowledge on yeast species that yield high amounts of SCO using VFAs as a carbon source. Specifically, the growth of the promising yeasts Cryptococcus curvatus and Rhodotorula toruloides was evaluated on individual VFAs, such as acetic, propionic, and butyric acid. C. curvatus proved to be more tolerant in higher concentrations of VFAs (up to 60 g/L), while butyric acid favored biomass and lipid conversion (0.65 and 0.23 g/gsubstrate, respectively). For R. toruloides, butyric acid favored biomass conversion (0.48 g/gsubstrate), but lipid conversion was favored using acetic acid, instead (0.14 g/gsubstrate). Propionic acid induced the formation of OCFAs, which yielded higher amounts for C. curvatus (up to 2.17 g/L). VFAs derived from the anaerobic digestion of brewer’s spent grain were tested as a cost-competitive carbon source and illustrated the significance of the combination of different VFAs in the quality of the produced SCO, by improving the biodiesel properties and OCFAs production.