Cellulase Loading Research Articles

Stirring the hydrogen and butanol production from Enset fiber via simultaneous saccharification and fermentation (SSF) process

Enset fiber is a promising feedstock for biofuel production with the potential to reduce carbon emissions and improve the sustainability of the energy system. This study aimed to maximize hydrogen and butanol production from Enset fiber through simultaneous saccharification and fermentation (SSF) process in bottles as well as in bioreactor. The SSF process in bottles resulted in a higher butanol concentration of 11.36 g/L with a yield of 0.23 g/g and a productivity of 0.16 g/(L h) at the optimal process parameters of 5% (w/v) substrate loading, 16 FPU/g cellulase loading, and 100 rpm agitation speed from pretreated Enset fiber. Moreover, a comparable result to the bottle experiment was observed in the bioreactor with pH-uncontrolled SSF process, although with a decreased in butanol productivity to 0.095 g/(L h). However, using the pre-hydrolysis simultaneous saccharification and fermentation (PSSF) process in the bioreactor with a 7% (w/v) substrate loading led to the highest butanol concentration of 12.84 g/L with a productivity of 0.104 g/(L h). Furthermore, optimizing the SSF process parameters to favor hydrogen resulted in an increased hydrogen yield of 198.27 mL/g-Enset fiber at atmospheric pressure, an initial pH of 8.0, and 37 °C. In general, stirring the SSF process to shift the product ratio to either hydrogen or butanol was possible by adjusting temperature and pressure. At 37 °C and atmospheric pressure, the process resulted in an e-mol yield of 12% for hydrogen and 38% for butanol. Alternatively, at 30 °C and 0.55 bar overpressure, the process achieved a yield of 6% e-mol of hydrogen and 48% e-mol of butanol. This is the first study to produce hydrogen and butanol from Enset fiber using the SSF process and contributes to the development of a circular bioeconomy.Graphical

Efficient co-production of glucose and carboxylated cellulose nanocrystals from cellulose-rich biomass waste residues via low enzymatic pre-hydrolysis and persulfate oxidation

Carboxylated cellulose nanocrystals (cCNCs) can be prepared directly from biomass in a one-step ammonium persulfate (APS) oxidation. However, the cellulose in the biomass is not fully utilized because APS oxidation degrades the cellulose amorphous regions. In this paper, to improve cellulose utilization rate, a two-step method (enzymatic pre-hydrolysis and APS oxidation) was developed to co-produce fermentable sugar and cCNCs from xylooligosaccharides manufacturing waste residue (XOR) of corncob. Enzymatic pre-hydrolysis produced 26.1 g of glucose per 100 g of XOR with a cellulase loading of 5 FPU/g cellulose in 24 h. Subsequent oxidation produced 22.9 g cCNCs with 0.5 M APS in 8 h. In contrast, the one-step APS method only produced 28.3 g cCNCs per 100 g of XOR. The total cellulose utilization rate by the two-step method increased by 73 % compared to the one-step APS method. Structural characteristics of cCNCs prepared by the two-step method were slightly different from those of the one-step method, but good properties were maintained. Therefore, the co-production method could prepare glucose and cCNCs with stable properties from XOR with a greatly improved cellulose utilization rate.

Integrating ball milling assisted enzymatic hydrolysis of bamboo cellulose for controllable production of xylo-oligosaccharides, monosaccharides and cellulose nanofibrils

Green bioconversion technology has been regarded as a fundamental solution to energy challenges and environmental issues. During bioconversion, a combination of mechanical and enzymatic treatment on lignocellulosic biomass can not only conformity with environmental concepts but also enable efficient conversion. In this study, a ball milling assisted enzymatic treatment was applied for full utilization of bamboo cellulose. In addition to the production of soluble saccharides, the residues that remained after enzymatic hydrolysis were collected for producing high-quality nanocellulose. Ball milling efficiently broke the hydrogen bonding interactions between glucan chains thus promoting the following xylanase and cellulase conversion. The highest Xylo-oligosaccharides (XOS) yield reached 21.6%. Meanwhile, xylanase facilitated cellulase hydrolysis by separation of hemicellulose on cellulose. With a low commercial cellulase loading of 5 FPU/g glucan, a maximum yield of 76.6% glucose and 53.3% xylose was reached. Finally, nanocellulose was extracted from the enzymatic hydrolyzate residue with a minimum width of 3.5 nm and an average size of 294.8 nm. The present study proposed an efficient combination of mechanical treatment assisted enzymatic digestion, which is not only environmentally friendly but also allows for complete bioconversion of bamboo cellulose.

Effects of Metal Chloride Salt Pretreatment and Additives on Enzymatic Hydrolysis of Poplar

Metal chloride salt pretreatment was performed to isolate and convert cellulose to glucose from poplar. A glucose yield of 82.0% ± 0.7 was achieved after 0.05 mol/L AlCl3 pretreatment conducted at 180 °C for 20 min, ascribing to the removal of hemicellulose, the alteration of crystallinity, surface morphology, and the retention of the majority of cellulose. Then, the influence of different additives on glucose yield was assessed, generating the highest glucose yield of 88.5 ± 0.06 with the addition of PEG 8000. Meanwhile, a similar glucose yield of 82.8% ± 0.3 could be obtained with PEG 8000 when hydrolysis time was reduced by a quarter and enzyme dosage by three-quarters. It can be seen that AlCl3 pretreatment is a viable and efficient pretreatment method for poplar, while the addition of PEG 8000 can enhance the enzymatic efficiency and reduce cellulase loading, ascribing to the reservation of free enzyme and enzyme activity in the supernatant and the reduction in surface tension, which provide an idea to improve the economics of the enzymatic conversion of poplar.

Biobased lignin-blockers enable efficient production of glucose from lignocelluloses

Enzymatic hydrolysis of cellulose in lignocelluloses exhibits low efficiency due to low cellulose accessibility and adverse lignin effects. By using phenylsulfonic acid pretreatment to improve cellulose accessibility, we have developed several new plant proteins such as corn germ and green rapeseed proteins that extracted from inexpensive defatted meals as lignin-blockers. For pretreated lignocellulosic substrates with high cellulose accessibility, such plant proteins could effectively overcome negative lignin effects and achieve robust cellulose enzymatic conversion (88–97 %) at a low cellulase loading of 5 FPU/g glucan. To reach the same level of cellulose enzymatic conversion, adding corn germ protein could save cellulase loading by 3.6 times as compared to those without lignin-blockers. But these plant proteins showed insignificant promotion effects on substrates with low cellulose accessibility. Overall, this study coupled high cellulose-accessible substrates and efficient lignin-blockers to synergistically improve the profitability of lignocellulosic biorefinery.

Comparison of Alkaline Sulfite Pretreatment and Acid Sulfite Pretreatment with Low Chemical Loading in Saccharification of Poplar.

Sulfite pretreatment is a productive process for lignin dissolution in lignocelluloses and to reduce the hydrophobicity of lignin by sulfonation, thus promoting the hydrolyzability of the substrate. Previously, sulfite pretreatment needs high dosages of chemicals and thus results in the high cost of the pretreatment and the great pressure of environmental pollution. To overcome these problems, it was crucial to research whether alkaline sulfite pretreatment (ALS) and acid sulfite pretreatment (ACS) with low chemical loading could enhance the saccharification of poplar. In this work, the results indicated that with low loading of chemicals in sulfite pretreatment, ALS pretreatment (1.6% Na2SO3 and 0.5% NaOH) at 180°C removed more lignin, resulted in lower hydrophobicity and higher cellulase adsorption capacity of poplar than ACS pretreatment (1.6% Na2SO3 and 0.5% H2SO4) at 180°C. A satisfying glucose yield of 84.9% and a xylose yield of 76.0% were obtained from poplar after ALS pretreatment with 1.6% Na2SO3 and 0.5% NaOH at 180°C for 1h using 10 FPU cellulase/g dry matter, saving sodium sulfite by 60.0% compared to the loading of sulfite in traditional sulfite pretreatment. The strategy developed in this work reduced chemical loading and cellulase loading in alkali sulfite pretreatment for the saccharification of poplar.

Effect of alkali salt-coupled ball milling pretreatment of wheat straw on improving enzymatic hydrolysis and energy efficiency

Pretreatment of lignocellulosic biomass is crucial in producing fermentable sugars in a sustainable biorefinery. In this study, wheat straw was pretreated with a combination of ball milling (BM) and NaAlO2 particles (NaAlO2-BM) for enzymatic hydrolysis within a short hydrolysis period. The effects of energy consumption on modifications of physicochemical proprieties and energy efficiency were elucidated. NaAlO2-BM pretreatment decreased particle size rapidly to tissue scale in 10 min with energy consumption reduced by 0.5 times compared to BM pretreatment. NaAlO2-BM pretreated for 20 min achieved a glucose yield of 95.4% at a cellulase loading of 10 FPU/g dry substrate for 24 h enzymatic hydrolysis and provided the highest energy efficiency of 0.121 kg glucose/kWh, increasing by 1.1 times than BM pretreatment. Energy consumption showed a positive relationship with cellulose content while it negatively correlated with median particle size, cellulose crystallinity and energy efficiency. The combination of BM and NaAlO2 particles was demonstrated to be a promising pretreatment approach for glucose production and improving energy efficiency during hydrolysis of lignocellulose.

Comparison of organosolv pretreatment of masson pine with different solvents in promoting delignification and enzymatic hydrolysis efficiency

Organosolv pretreatment has been verified to facilitate the enzymatic hydrolysis by efficient delignification. Recently, novel solvents derived from biomass have been applied in lignocellulose pretreatment. However, few studies on the pretreatment of softwood with novel solvents have been reported. In this study, organosolv pretreatments with three green solvents, including γ-valerolacton (GVL), tetrahydrofuran (THF), and 2-methyltetrahydrofuran (2-MTHF), were performed on masson pine, and compared with conventional ethanol (EtOH) pretreatment. The results showed that GVL pretreatment exhibited the best performance for removing lignins from masson pine, achieving a pretty high lignin removal ratio of 87.2 % at 150 °C with 75 mM H2SO4. Correspondingly, the highest glucose yield of 76.8 % was observed in the enzymatic hydrolysis of GVL pretreated masson pine with a relatively low cellulase loading (20 FPU/g glucan). The relations between relative energy difference of the solvent-lignin interactions and both of the lignin removal and enzymatic digestibility of organosolv pretreated substrates were evaluated. Furthermore, the structural features of four organosolv lignins were characterized, including molecular weights, functional groups, inter-unit linkages and aromatic information. The results provide a better understanding of organosolv pretreatment effects on enzymatic digestibility of softwood biomass, and give comprehensive lignin properties for valorization of organosolv lignins from softwood.

Enhancing ethylene glycol and ferric chloride pretreatment of rice straw by low-pressure carbon dioxide to improve enzymatic saccharification

Ethylene glycol and ferric chloride pretreatment assisted by low-pressure carbon dioxide (1 MPa CO2) realized the targeted deconstruction of lignocelluloses at 170 °C for 5 min, achieving 98 % cellulose recovery with removal of 92 % lignin and 90 % hemicellulose. After the pretreatment, the formation of stable platform mono-phenol components would be with the destruction of the lignin-carbohydrate complexes structure, and the surface of rice straw became rough, with a less negative charge and higher specific surface area, while the enzyme adsorption rate increased by 8.1 times. Furthermore, the glucose yield of pretreated straw was remarkably increased by 5.6 times that of the untreated straw, reaching 91 % after hydrolyzed for 48 h. With Tween 80 added in concentrated solid (12 %) hydrolysis at low cellulase loading (3 FPU/g dry substrate), half of the hydrolysis time was shortened than that without Tween 80, with 45 % higher glucose yield.

Extracting high β-O-4 content lignin and by-producing substrate susceptible to enzymatic hydrolysis by a green flow through process

Maleic acid (MA), a solid dicarboxylic acid can be obtained from renewable lignocellulose, was used to extract lignin through flow through (FT) process for the first time. Due to the high boiling point and flash point of MA, the FT process was carried out at atmospheric pressure without VOCs release and explosion risk. 50 wt% MA aqueous solution could extract 60 % lignin from birch wood, and the dilution factor for precipitating lignin was only 3. MA-extracted lignin preserved more than 80 % of βO4 bonds and a monophenol yield (＞30 %) comparable to that of milled wood lignin was obtained by catalytic hydrogenolysis. The recyclability of MA was demonstrated through three rounds of lignin extraction by recovered MA. And the cellulose-rich residue could be efficiently converted into glucose (glucose yield＞90 %) at a low cellulase loading of 10 FPU/g glucan due to the rich carboxyl groups of lignin. In addition, the low corrosiveness of MA and the mild operating conditions make the process have strong industrial application prospects.

Understanding of promoting enzymatic hydrolysis of combined hydrothermal and deep eutectic solvent pretreated poplars by Tween 80

In this study, lignin blockers including non-catalytic protein and surfactants were employed to promote enzymatic digestibility of pretreated poplars. Among them, Tween 80 exhibited the most pronounced facilitation, improving the glucose yield from 26.6% to 99.6% at a low enzyme loading (10 FPU/g glucan), and readily reduced the required cellulase loading by 75%. The underlying mechanism for this remarkable improvement on glucose yields by Tween 80 was elucidated. The impacts of Tween 80 on the enzyme-lignin interaction were explored by quartz crystal microbalance analysis, revealing that the binding rate of Tween 80 on lignin surfaces was 3-fold higher than that of enzyme. More importantly, Tween 80 remarkably decreased the binding capacity and binding rate of enzyme on lignins. Furthermore, the substrate properties dominating the increase in glucose yields with Tween 80 were explored. The results facilitate to understand the underlying mechanism of the promotion of surfactants on enzymatic hydrolysis.

Enhancing α-etherification of lignin in Eucalyptus diol pretreatment to improve lignin monomer production

In this work, α-etherification of lignin in diol pretreatment was selectively enhanced at mild temperature for lignin isolation and subsequent valorisation. More than 90 % of lignin was removed from Eucalyptus at 120 °C in diol (ethylene glycol and 1,4-butanediol) pretreatment, resulting in >90 % cellulose conversion in 24 h at 7.5 FPU/g glucan cellulase loading. Subsequent catalytic transfer hydrogenolysis of the isolated lignins with Ru/C in ethanol gave 15 % monomer yield on native lignin basis, 5 times of that from the technical ethanol process (170 °C). HSQC NMR analysis revealed that diol pretreated lignin (120 °C) contained ∼23 % α-etherified β–O–4 interunit bonds, indicating that lignin degradation (i.e. cleavage of β–O–4 bonds) was suppressed via etherification by grafting a hydroxyl group at the α position of lignin. This finding was consistent with the isolated lignin (120 °C) had less number of phenolic OH and higher molecular weight via31P NMR and GPC analysis. 31P NMR analysis also revealed that diol isolated lignin contained more number of aliphatic OH than ethanol-isolated lignin, which increased lignin solubility and maintained the high yield (>80 %) of isolated lignin from Eucalyptus at 120 °C as expected. In summary, diol pretreatment of woody biomass can effectively isolate more lignin for hydrogenolysis to valued-added monomers without compromising the isolated yield of lignin and hydrolysis yield of remained cellulose.

Optimization of Pretreatment Conditions and Enzymatic Hydrolysis of Corn Cobs for Production of Microbial Lipids by Trichosporon oleaginosus

Microbial lipids produced from lignocellulosic biomass are sustainable alternative feedstock for biodiesel production. In this study, corn cobs were used as a carbon source for lipid production and growth of oleaginous yeast Trichosporon oleaginosus. Lignocellulosic biomass was subjected to alkali and acid pretreatment using sulfuric acid and sodium hydroxide under different temperatures, catalyst concentrations and treatment times. Pretreatment of corn cobs was followed by cellulase hydrolysis. Hydrolysis of alkali pretreated (2% NaOH at 50 °C for 6 h, 1% NaOH at 50 °C for 16 h, 2% NaOH at 121 °C for 1 h, 1% NaOH at 121 °C for 2 h) and acid pretreated (1% H2SO4 120 °C for 20 min, and 2% H2SO4 120 °C for 10 min) corn cobs resulted in more than 80% of the theoretical yield of glucose. The effect of substrate (5, 10, 15 and 20%, g g−1) and cellulase loading (15 and 30 Filter Paper Units per gram of glucan, FPU g−1) on fermentable sugar yield was also studied. The maximal glucose concentration of 81.64 g L−1 was obtained from alkali-pretreated corn cobs (2% NaOH at 50 °C for 6 h) at 20% substrate loading and 30 FPU of Cellic CTec2 g−1 of glucan. Enzymatic hydrolysates of pretreated biomasses and filtrates of lignocellulosic slurries obtained after pretreatment were used for growth and lipid synthesis by T. oleaginosus. The highest lipid concentration of 18.97 g L−1 was obtained on hydrolysate of alkali-pretreated corn cobs (with 1% NaOH at 50 °C for 16 h) using a 15% (g g−1) substrate loading and 15 FPU g−1 of cellulase loading. Significant lipid accumulation was also achieved using undetoxified filtrates of pretreated slurries as substrates. Results showed that pretreated corn cobs and undetoxified filtrates are suitable carbon sources for the growth and efficient accumulation of lipids in T. oleaginosus.

Cellulosic Ethanol Production Using a Dual Functional Novel Yeast.

Reducing the cost of cellulosic ethanol production, especially for cellulose hydrolytic enzymes, is vital to growing a sustainable and efficient cellulosic ethanol industry and bio-based economy. Using an ethanologenic yeast able to produce hydrolytic enzymes, such as Clavispora NRRL Y-50464, is one solution. NRRL Y-50464 is fast-growing and robust, and tolerates inhibitory compounds 2-furaldehyde (furfural) and 5-hydroxymethyl-2-furaldehyde (HMF) associated with lignocellulose-to-fuel conversion. It produces three forms of β-glucosidase isozymes, BGL1, BGL2, and BGL3, and ferment cellobiose as the sole carbon source. These β-glucosidases exhibited desirable enzyme kinetic parameters and high levels of enzyme-specific activity toward cellobiose and many oligosaccharide substrates. They tolerate the product inhibition of glucose and ethanol, and are stable to temperature and pH conditions. These characteristics are desirable for more efficient cellulosic ethanol production by simultaneous saccharification and fermentation. NRRL Y-50464 provided the highest cellulosic ethanol titers and conversion rates at lower cellulase loadings, using either pure cellulose or agricultural residues, as so far reported in the literature. This review summarizes NRRL Y-50464 performance on cellulosic ethanol production from refined cellulose, rice straw, and corn stover processed in various ways, in the presence or absence of furfural and HMF. This dual functional yeast has potential to serve as a prototype for the development of next-generation biocatalysts. Perspectives on continued strain development and process engineering improvements for more efficient cellulosic ethanol production from lignocellulosic materials are also discussed.

Highly selective delignification of poplar by hydrogen peroxide-ethyl acetate pretreatment at room temperature

Highly selective delignification of lignocellulose with green solvent at mild conditions is a challenge. Previously, hydrogen peroxide-acetic acid (HPAA) was used as a green solvent in pretreatment exhibits excellent selective delignification capacity at a low reaction temperature (<80 °C). However, the release of oxygen can increase the pressure of the hydrogen peroxide-acetic acid (HPAA) pretreatment system and the risk of explosion. To overcome this problem, a novel hydrogen peroxide-ethyl acetate (HPEA) pretreatment was developed to remove poplar lignin, aiming at improving the pretreatment safety and saccharification efficiency. After HPEA pretreatment at room temperature for three days, 97.2% of poplar lignin was removed and 92.1% of original carbohydrate was retained. The glucose and xylose yields of HPEA-pretreated poplar reached 90.6% and 81.5% by a cellulase loading of 5 FPU/g dry matter, respectively. Compared with HPAA pretreatment, HPEA pretreatment reduced more than 93% of pressure in pretreatment system and largely increased pretreatment safety. The results indicates that HPEA pretreatment exhibited stronger delignification capacity, high carbohydrate retention, high safety, and strong enhancement of digestibility of poplar. This work provides a safe pretreatment to selectively remove lignin at mild conditions for efficient saccharification of poplar.

Facile Cellulase Immobilisation on Bioinspired Silica.

Cellulases are enzymes with great potential for converting biomass to biofuels for sustainable energy. However, their commercial use is limited by their costs and low reusability. Therefore, the scientific and industrial sectors are focusing on finding better strategies to reuse enzymes and improve their performance. In this work, cellulase from Aspergillus niger was immobilised through in situ entrapment and adsorption on bio-inspired silica (BIS) supports. To the best of our knowledge, this green effect strategy has never been applied for cellulase into BIS. In situ entrapment was performed during support synthesis, applying a one-pot approach at mild conditions (room temperature, pH 7, and water solvent), while adsorption was performed after support formation. The loading efficiency was investigated on different immobilisation systems by Bradford assay and FTIR. Bovine serum albumin (BSA) was chosen as a control to optimize cellulase loading. The residual activity of cellulase was analysed by the dinitro salicylic acid (DNS) method. Activity of 90% was observed for the entrapped enzyme, while activity of ~55% was observed for the adsorbed enzyme. Moreover, the supported enzyme systems were recycled five times to evaluate their reuse potential. The thermal and pH stability tests suggested that both entrapment and adsorption strategies can increase enzyme activity. The results highlight that the entrapment in BIS is a potentially useful strategy to easily immobilise enzymes, while preserving their stability and recycle potential.

Polystyrene sulfonate is effective for enhancing biomass enzymatic saccharification under green liquor pretreatment in bioenergy poplar

BackgroundWater-soluble lignin (particularly lignosulfonate, LS) has been well documented for its significance on enzymatic saccharification of lignocellulose, though the promotion mechanism has not been fully understood. Much attention has been paid to natural lignin or its derivatives. The disadvantage of using natural lignin-based polymers as promoting agents lies in the difficulty in tailor-incorporating functional groups due to their complex 3D structures. To further improve our understanding on the promotion mechanism of water-soluble lignin in the bioconversion of lignocellulose and to pursue better alternatives with different skeleton structures other than natural lignin, herein we reported a synthetic soluble linear aromatic polymer, sodium polystyrene sulfonate (PSS), to mimic LS for enhancing the efficiency of enzymatic saccharification.ResultsThe role of PSS in enzymatic saccharification of pure cellulose and green liquor-pretreated poplar (GL-P) was explored by analyzing substrate enzymatic digestibility (SED) under different addition dosages and various pH media, along with LS for comparison. At the cellulase loading of 13.3 FPU/g-glucan, the glucose yield of GL-P increased from 53% for the control to 81.5% with PSS addition of 0.1 g/g-substrate. It outperformed LS with the addition of 0.2 g/g-substrate by 6.3%. In the pH range from 4.5 to 6, PSS showed a positive effect on lignocellulose saccharification with the optimum pH at 4.8, where the most pronounced SED of GL-P was achieved. The underlying mechanism was unveiled by measuring zeta potential and using Quartz Crystal Microbalance (QCM) and Multi-parametric Surface Plasmon Resonance (MP-SPR). The results confirmed that the complexes of cellulase and PSS were conjugated and the negatively supercharged complexes reduced non-productive binding effectively along with the improved saccharification efficiency. The thickness of PSS required to block the binding sites of cellulase film was less than half of that of LS, and the PSS adlayer on cellulase film is also more hydrated and with a much lower shear modulus than LS adlayer.ConclusionsPSS as LS analogue is effective for enhancing the biomass enzymatic saccharification of GL-pretreated poplar. PSS exhibited a severer inhibition on the enzymatic saccharification of pure cellulose, while a more positive effect on bioconversion of lignocellulose (GL-P) than LS. In addition, a much lower dosage is required by PSS. The dynamic enzymatic hydrolysis indicated PSS could prolong the processive activity of cellulase. The valid data stemmed from QCM and SPR expressed that PSS bound to cellulases and the as-formed complexes reduced the non-productive adsorption of cellulase onto substrate lignin more efficiently than LS due to its flexible skeleton and highly hydrated structure. Therefore, PSS is a promising alternative promoting agent for lignocellulose saccharification. From another perspective, the synthetic lignin mimics with controllable structures enable us to reach an in-depth understanding of the promotion mechanism of soluble lignins on enzymatic saccharification.

Efficient saccharification of wheat straw pretreated by solid particle-assisted ball milling with waste washing liquor recycling

Wheat straw was pretreated using ball milling (BM) promoted by solid particles (NaOH, NaCl, citric acid). NaOH showed the best synergistic interaction effect, due to the breakage of β-1,4-glycosidic bonds among cellulose molecules by the alkali solid particles induced by BM. NaOH-BM pretreatment decreased the straw crystallinity from 46% to 21.4% and its average particle size from 398.3 to 50.6 μm in 1 h. After 4 h milling, the reducing-end concentration of cellulose increased by 3.8 times from 12.5 to 60.2 μM, with glucose yield increased by 2.1 times from 26.6% to 82.4% for 72 h enzymatic hydrolysis at cellulase loading of 15 FPU/g dry substrate. The pretreatment washing liquor was recycled for the re-treatment of partially pretreated biomass at 121 °C for 30 min, resulting in 99.4% glucose yield by enzymatic hydrolysis. BM assisted with alkali particles was an effective approach for improving biomass enzymatic saccharification.

Enhanced enzymatic hydrolysis of poplar cellulosic residue fractionated by a magnetic carbon-based solid-acid catalyst in the γ-valerolactone–water system

The conventional pretreatment method of poplar comprises multiple steps, including different procedures for fractionating hemicellulose and lignin separately. In our study, hemicellulose and lignin were removed simultaneously by a one-step method. In the γ-valerolactone (GVL)–water environment, the cellulose retention, hemicellulose removal, and lignin removal rates of 84.94%, 89.08%, and 72.28%, respectively, were achieved over a magnetic carbon-based solid acid (MMCSA) catalyst, under best conditions (160 °C, 30 min, 2 g of poplar, 2 g of MMCSA, 35 mL of GVL, and 15 mL of water). The pretreatment of fresh poplar in the reused MMCSA–GVL–water environment showed similar fractionation results as the first time. Scanning electron microscopy characterization of the cellulosic residue revealed the presence of noticeable structural fragmentation. Brunauer–Emmett–Teller characterization showed that the total pore volume of the residue was 2.13 times that of the raw material. The above features of the residue confirmed the high enzymatic hydrolysis potential of the pretreated residue. The enzymatic hydrolysis efficiency of the poplar residue was 67% at a cellulase loading of 20 FPU/g cellulose in dry matter, and it increased to 77.02% at 40 FPU/g cellulose in dry matter. Interestingly, the addition of Tween 80 did not improve the enzymatic hydrolysis efficiency at high cellulase loadings (30 and 40 FPU/g cellulose in dry matter) compared to the case at low cellulase loadings. The relative mechanisms were also analyzed. In this study, a one-step pretreatment method comprising the MMCSA–GVL system for the catalytic depolymerization of poplar wood was developed. The system was verified to be very effective for the subsequent enzymatic hydrolysis of the residues.

The advanced performance of microbial consortium for simultaneous utilization of glucose and xylose to produce lactic acid directly from dilute sulfuric acid pretreated corn stover

BackgroundLignocellulosic feedstocks have attracted much attention as a potential carbon source for lactic acid (LA) production because of their ready availability, sustainability, and renewability. However, there are at least two major technical challenges to producing LA from lignocellulose. Inhibitors derived from lignocellulose pretreatment have a negative impact on the growth of cells producing LA. Furthermore, pentose sugars produced from the pretreatment are difficultly utilized by most LA producers, which is known as the carbon catabolite repression (CCR) effect. This complex feedstock can be utilized by a robust microbial consortium with high bioconversion efficiency.ResultsIn this study, a thermophilic consortium DUT50 producing LA was enriched and employed to improve corn stover (CS) utilization. Enterococcus was the dominant family in the consortium DUT50, accounting for 93.66% of the total abundance, with Lactobacillus, Bacillus, Lactococcus, and Trichococcus accounted for the remaining 2.68%. This consortium could be resistant to inhibitors concentration up to 9.74 g/L (2.88 g/L acetic acid, 2.46 g/L furfural, 2.20 g/L 5-HMF, and 2.20 g/L vanillin derived from pretreatment of CS), and simultaneously metabolizes hexose and pentose without CCR effect. Based on the promising consortium features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid pretreated corn stover, in which solid–liquid separation and detoxification were avoided. The key influencing factors were investigated and optimized, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v), which is the highest LA production from non-detoxified acid pretreated corn stover via the SSCF process without wastewater generation reported to date. The simultaneous metabolism of hexose and pentose revealed collaboration between Enterococcus in the consortium, whereas xylose may be efficiently metabolized by Lactobacillus and Bacillus with low abundance via the pentose phosphate pathway.ConclusionsThe experimental results demonstrated the potential advantage of symbiosis in microbial consortia used for LA production from lignocellulosic biomass.