Efficient pretreatment of lignocellulosic biomass with high recovery of solid lignin and fermentable sugars using Fenton reaction in a mixed solvent

Microwave-assisted extraction of cellulose and aromatic compounds from rose petals based on deep eutectic solvent

High-value utilization of agricultural wastes such as rose petals promotes the development of the dual carbon economy. In this study, rose petals were pretreated by microwave-assisted deep eutectic solvent (DES). Choline chloride-ethylene glycol (ChCl-EG) was used as the basis for the addition of P-toluenesulfonic acid (TsOH) or Ferric chloride (FeCl3). Forming ternary DESs, as well as designing quaternary DESs with a synergistic effect. The effects of different types of multicomponent DES on treating anthocyanins, cellulose, and lignin in rose flowers were explored. The results showed that the highest anthocyanin extraction of 173.71 mg/g and the highest lignin removal of 40.80 % could be achieved after tetrad DES pretreatment when the molar ratio was ChCl:EG:TsOH:FeCl3 = 1:2:0.3:0.3. The interaction energy between anthocyanins and DES was calculated using density functional theory (DFT), and the maximum was -543.14 kcal/mol. This study demonstrated that DES pretreatment can provide novel insights for the utilization of roses in high-value.

Catalytic Degradation of Lignin over Sulfonyl-Chloride-Modified Lignin-Based Porous Carbon-Supported Metal Phthalocyanine: Effect of Catalyst Concentrations

A sulfonyl-chloride-modified lignin-based porous carbon-supported metal phthalocyanine catalyst was prepared and used to replace the traditional Fenton's reagent for lignin degradation. The catalyst underwent a detailed characterization analysis in terms of functional group distributions, surface area, morphological structure, via FT-IR, XPS, BET, and SEM. The catalyst possessed a specific surface area of 638.98 m2/g and a pore volume of 0.291 cm3/g. The prepared catalyst was studied for its ability of oxidative degradation of lignin under different reaction conditions. By optimizing the reaction conditions, a maximum liquid product yield of 38.94% was obtained at 135 °C with 3.5 wt% of catalyst and 15 × 10-2 mol/L H2O2; at the same time, a maximum phenols selectivity of 32.58% was achieved. The compositions and properties of liquid products obtained from lignin degradation using different catalyst concentrations were studied comparatively via GC-MS, FT-IR, 1H-NMR, and EA. Furthermore, the structure changes of solid residues are also discussed.

Streptomyces spp. as biocatalyst sources in pulp and paper and textile industries: Biodegradation, bioconversion and valorization of waste

Complex polymers represent a challenge for remediating environmental pollution and an opportunity for microbial-catalysed conversion to generate valorized chemicals. Members of the genus Streptomyces are of interest because of their potential use in biotechnological applications. Their versatility makes them excellent sources of biocatalysts for environmentally responsible bioconversion, as they have a broad substrate range and are active over a wide range of pH and temperature. Most Streptomyces studies have focused on the isolation of strains, recombinant work and enzyme characterization for evaluating their potential for biotechnological application. This review discusses reports of Streptomyces-based technologies for use in the textile and pulp-milling industry and describes the challenges and recent advances aimed at achieving better biodegradation methods featuring these microbial catalysts. The principal points to be discussed are (1) Streptomyces' enzymes for use in dye decolorization and lignocellulosic biodegradation, (2) biotechnological processes for textile and pulp and paper waste treatment and (3) challenges and advances for textile and pulp and paper effluent treatment.

Preparation of Cellulose Nanofibers from Corn Stalks by Fenton Reaction: A New Insight into the Mechanism by an Experimental and Theoretical Study

Agricultural biomass wastes are an abundant feedstock for biorefineries. However, most of these wastes are not treated in the right way. Here, corn stalks (CSs) were assigned as the raw material to produce cellulose nanofibers (CNFs) via in situ Fenton oxidation treatment. In order to probe the formation mechanism of an in situ Fenton reactor, the bonding interaction of hydrated Fe²⁺ ions and fiber has been systemically studied based on adsorption experiments, IR spectroscopy, density functional theory (DFT) calculations, and Raman spectroscopy. The results indicate that the coordination of the hydrated Fe²⁺ ion to the fiber generates a quasi-octahedral-coordinated sphere around the Fe center. The Jahn-Teller distortion effect of the Fe center promotes the Fe-O₂H₂ bonding interaction via reduction of the energy gap of the d_z² orbital of the Fe center and π_2py/π_2pz orbitals of the H₂O₂ molecule. The oxidation treatment of the pretreated CS by the in situ Fenton process shows the formation of a new carboxyl group on the fiber surface. The scanning electron microscopy image shows that the Fenton-treated fiber was scattered into the nanosized CNFs with a diameter of up to 50 nm. Both experimental and theoretical studies show that the pseudo-first-order kinetic reaction could describe the in situ Fenton kinetics well. Moreover, the proposed catalytic cycle shows that the large thermodynamic barrier is the cleavage of the O-O bond of H₂O₂ to generate the ^•OH radical, and the whole catalytic cycle is found to be spontaneous at room temperature.

Oxidative pretreatment of lignocellulosic biomass for enzymatic hydrolysis: Progress and challenges

Deconstruction of cell wall structure is important for biorefining of lignocellulose to produce various biofuels and chemicals. Oxidative delignification is an effective way to increase the enzymatic digestibility of cellulose. In this work, the current research progress on conventional oxidative pretreatment including wet oxidation, alkaline hydrogen peroxide, organic peracids, Fenton oxidation, and ozone oxidation were reviewed. Some recently developed novel technologies for coupling pretreatment and direct biomass-to-electricity conversion with recyclable oxidants were also introduced. The primary mechanism of oxidative pretreatment to enhance cellulose digestibility is delignification, especially in alkaline medium, thus eliminating the physical blocking and non-productive adsorption of enzymes by lignin. However, the cost of oxidative delignification as a pretreatment is still too expensive to be applied at large scale at present. Efforts should be made particularly to reduce the cost of oxidants, or explore valuable products to obtain more revenue.

Inhibitor formation and detoxification during lignocellulose biorefinery: A review

For lignocellulose biorefinery, pretreatment is needed to maximize the cellulose accessibility, frequently generating excess inhibitory substances to decline the efficiency of the subsequent fermentation processes. This mini-review updates the current research efforts to detoxify the adverse impacts of generated inhibitors on the performance of biomass biorefinery. The lignocellulose pretreatment processes are first reviewed. The generation of inhibitors, furans, furfural, phenols, formic acid, and acetic acid, from the lignocellulose, with their action mechanisms, are listed. Then the detoxification processes are reviewed, from which the biological detoxification processes are noted as promising and worth further study. The challenges and prospects for applying biological detoxification in lignocellulose biorefinery are outlined. Integrated studies considering the entire biorefinery should be performed on a case-by-case basis.

Novel Two-Step Process in Cellulose Depolymerization: Hematite-Mediated Photocatalysis by Lytic Polysaccharide Monooxygenase and Fenton Reaction

To transform cellulose from biomass into fermentable sugars for biofuel production requires efficient enzymatic degradation of cellulosic feedstocks. The recently discovered family of oxidative enzymes, lytic polysaccharide monooxygenase (LPMO), has a high potential for industrial biorefinery, but its energy efficiency and scalability still have room for improvement. Hematite (α-Fe₂O₃) can act as a photocatalyst by providing electrons to LPMO-catalyzed reactions, is low cost, and is found abundantly on the Earth's surface. Here, we designed a composite enzymatic photocatalysis-Fenton reaction system based on nano-α-Fe₂O₃. The feasibility of using α-Fe₂O₃ nanoparticles as a composite catalyst to facilitate LPMO-catalyzed cellulose oxidative degradation in water was tested. Furthermore, a light-induced Fenton reaction was integrated to increase the liquefaction yield of cellulose. The innovative approach finalized the cellulose degradation process with a total liquefaction yield of 93%. Nevertheless, the complex chemical reactions and products involved in this system require further investigation.

Xylitol production by Pseudomonas gessardii VXlt-16 from sugarcane bagasse hydrolysate and cost analysis

Xylitol is a well-known sugar alcohol with exponentially rising market demand due to its diverse industrial applications. Organic agro-industrial residues (OAIR) are economic alternative for the cost-effective production of commodity products along with addressing environmental pollution. The present study aimed to design a process for xylitol production from OAIR via microbial fermentation with Pseudomonas gessardii VXlt-16. Parametric analysis with Taguchi orthogonal array approach resulted in a conversion factor of 0.64 g xylitol/g xylose available in untreated sugarcane bagasse hydrolysate (SBH). At bench scale, the product yield increased to 71.98/100 g (0.66 g/L h). 48.49 g of xylitol crystals of high purity (94.56%) were recovered after detoxification with 2% activated carbon. Cost analysis identified downstream operations as one of the cost-intensive parts that can be countered by adsorbent recycling. Spent carbon, regenerated with acetic acid washing can be reused for six cycles effectively and reduced downstream cost by about ≈32%. The strategy would become useful in the cost-effective production of several biomass-dependent products like proteins, enzymes, organic acids, as well.

Integrated pretreatment of banana agrowastes: Structural characterization and enhancement of enzymatic hydrolysis of cellulose obtained from banana peduncle

An integrated treatment coupling alkali, steam explosion and ammonia/chlorine-free bleaching with sequential mild acid pretreatment were performed to isolate and characterize cellulose from banana agrowastes followed by optimized enzymatic hydrolysis to glucose. The cellulose yield, compositional, microstructural, and morphological analysis initially obtained from three post-harvest banana agrowastes (peel, pseudostem, and peduncle) were surveyed. Isolation parameters for banana peduncle agrowastes, the most efficient precursor, were reconfigured for acid hydrolysis by applying an orthogonal L₉ array of Taguchi design. Effects of solution-to-pulp ratio, acid concentration, temperature, and reaction time on physicochemical parameters were assessed resulting in ~81% cellulose recovery. Subsequently, cellulase driven enzymatic conversion to glucose was modelled using response surface methodology (RSM), where the mutual influences of incubation time, enzyme concentration, substrate concentration, and surfactant concentration were investigated. Artificial Neural Network (ANN) modelling further improved upon RSM optimizations ensuing ~97% optimized glucose yield, verified experimentally.

Rewiring the microbial metabolic network for efficient utilization of mixed carbon sources

Carbon sources represent the most dominant cost factor in the industrial biomanufacturing of products. Thus, it has attracted much attention to seek cheap and renewable feedstocks, such as lignocellulose, crude glycerol, methanol, and carbon dioxide, for biosynthesis of value-added compounds. Co-utilization of these carbon sources by microorganisms not only can reduce the production cost but also serves as a promising approach to improve the carbon yield. However, co-utilization of mixed carbon sources usually suffers from a low utilization rate. In the past few years, the development of metabolic engineering strategies to enhance carbon source co-utilization efficiency by inactivation of carbon catabolite repression has made significant progress. In this article, we provide informative and comprehensive insights into the co-utilization of two or more carbon sources including glucose, xylose, arabinose, glycerol, and C1 compounds, and we put our focus on parallel utilization, synergetic utilization, and complementary utilization of different carbon sources. Our goal is not only to summarize strategies of co-utilization of carbon sources, but also to discuss how to improve the carbon yield and the titer of target products.

Combination of hydrothermal and chemi-mechanical pretreatments to enhance enzymatic hydrolysis of poplar branches and insights on cellulase adsorption

An integration of different pretreatments is important to overcome recalcitrance and realize efficient bioconversion of lignocellulosic biomass. This study aims at the effects of combination of hydrothermal pretreatment and different chemi-mechanical pretreatments on enzymatic hydrolysis, and understanding the enzymes adsorption mechanism. The combination of hydrothermal and chemi-mechanical pretreatments effectively improved the enzymatic hydrolysis of poplar substrates, in which the enzymatic hydrolysis of substrates pretreated by hydrothermal pretreatment + Fenton pretreatment + mechanical refining (HFM) was the highest (92.39% of glucose conversion yield, and 20.88 g/L of glucose concentration). The substrates' main characteristics were obviously changed after combined pretreatments, such as swelling ability and specific surface area of substrates were increased. The Langmuir adsorption model (R² > 0.98) and pseudo second-order adsorption kinetic model (R²≈1) were well suitable to describe the adsorption of enzymes on substrates, meanwhile the adsorption mechanism was summarized.

Improving enzymatic hydrolysis of mechanically refined poplar branches with assistance of hydrothermal and Fenton pretreatment

The combination of different pretreatment methods can effectively overcome recalcitrance of lignocellulosic biomass to ensure its highly efficient conversion into bio-based products. In this study, the combined pretreatments of chemical methods (hydrothermal treatment and Fenton treatment) with mechanical refining were used to improve the enzymatic hydrolysis efficiency of poplar branches. The results indicated that hydrothermal pretreatment and Fenton pretreatment can effectively improve the enzymatic hydrolysis of poplar substrates, e.g., the maximum glucose conversion yield and glucose concentration reached 92.4% and 20.8 g/L, respectively. The pre-hydrolysates contained some valuable components such as monosaccharides, oligosaccharides, acetic acid, furfural, and hydroxymethylfurfural. The main characteristics (specific surface area, water retention value, fines content, and surface lignin concentration) of poplar substrates were obviously changed by the combined pretreatment, which benefit the enzymatic hydrolysis.

Chelator-mediated biomimetic degradation of cellulose and chitin

Non-enzymatic degradation of wood via a chelator-mediated Fenton (CMF) system is the primary method for initial attack in brown rot fungal decomposition of wood, the most common type of fungal degradation of terrestrial carbon biomass on the planet. In this study, the degradation of thin films of cellulose and chitin by a CMF system was investigated and compared to enzymatic hydrolysis. The kinetics of the rapid cellulose and chitin deconstruction and the morphologies of the degraded cellulose and chitin surfaces were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM), respectively. The QCM-D results quantitatively indicated that ~90 wt% of the regenerated cellulose or chitin was capable of being deconstructed by CMF action alone. While enzymatic degradation was consistent with stripping of layers from the surface of the cellulose or chitin films, the CMF process exhibited a pronounced two stage process with a rapid initial depolymerization throughout the films. The initial degradation rates for both model surfaces by the CMF system were faster than enzyme action. This research suggests that the CMF process should be applicable for the deconstruction of a wide variety of polysaccharides over Fenton chemistry alone.