Selective Delignification Research Articles

An orientational graphene/bamboo evaporator for efficient solar-powered steam generation and desalination

Solar-powered steam generation and desalination by interfacial solar steam generation (ISSG) are promising techniques for addressing the freshwater shortage. However, the insufficient conversion efficiency and complex pollutant components confine its further extension and application. This study innovatively constructs an orientational graphene/bamboo evaporator (GBE), maintaining a solvent-accessible surface area and reducing vaporization enthalpy by selective delignification and torrefaction. The GBE device features a channel oriented from bamboo, consolidating the parallel architecture with multilayer biofilm filtration that guides efficient bulk-water pumping, steam release, and pollutant interception. The GBE demonstrates full-spectrum optical absorption at 90.5 % and 33.4 s response time while maintaining operational stability across different salt concentrations and natural water environments. The GBE achieved an evaporation rate of 1.53 kg m-2h-1as 4.34 enhancement factor under 1 kW/m−2(−|-) illumination, surpassing microplastics (99.84 %) and tetracycline (99.87 %) desalination. This work provides a high-performance and innovative approach to bamboo evaporator design, offering a viable and alternative method to address freshwater shortage.

Pretreatment of Camellia oleifera shell by ethanolamine-based solvents for selective delignification and enhanced enzymatic saccharification

Fruit shell biomass is an agricultural waste that could be valorised into various value-added chemicals. However, the intertwined structure between lignin and holocellulose limits free sugar generation for further fermentation, requiring efficient pretreatment for selective delignification. We pretreated Camellia oleifera shell by ethanolamine-based solvents (binary deep eutectic solvents and single ethanolamine or its derivatives), and compared pretreatment effectiveness of these solvents. Single ethanolamine was the best among ethanolamine-based solvents, indicating the unnecessity of deep eutectic solvent synthesis. Furthermore, structural characterization confirms that ethanolamine could effectively deconstruct Camellia oleifera shell with the highest delignification (76.46%) and sugar yields (83.73% for glucose and 66.87% for xylose) at 130 °C for 3 h. Additionally, correlation analysis suggests that alkalinity and proton dissociation capacity together determined the delignification capacity of ethanolamine. Our findings serve a potential solution to valorise the waste fruit shell lignocellulose resources.

Application of Aromatic Ring Quaternary Ammonium and Phosphonium Salts–Carboxylic Acids-Based Deep Eutectic Solvent for Enhanced Sugarcane Bagasse Pretreatment, Enzymatic Hydrolysis, and Cellulosic Ethanol Production

Deep eutectic solvents (DESs) with a hydrophobic aromatic ring structure offer a promising pretreatment method for the selective delignification of lignocellulosic biomass, thereby enhancing enzymatic hydrolysis. Further investigation is needed to determine whether the increased presence of aromatic rings in hydrogen bond receptors leads to a more pronounced enhancement of lignin removal. In this study, six DES systems were prepared using lactic acid (LA)/acetic acid (AA)/levulinic acid (LEA) as hydrogen bond donors (HBD), along with two independent hydrogen bond acceptors (HBA) (benzyl triethyl ammonium chloride (TEBAC)/benzyl triphenyl phosphonium chloride (BPP)) to evaluate their ability to break down sugarcane bagasse (SCB). The pretreatment of the SCB (raw material) was carried out with the above DESs at 120 °C for 90 min with a solid–liquid ratio of 1:15. The results indicated that an increase in the number of aromatic rings may result in steric hindrance during DES pretreatment, potentially diminishing the efficacy of delignification. Notably, the use of the TEBAC:LA-based DES under mild operating conditions proved highly efficient in lignin removal, achieving 85.33 ± 0.52% for lignin removal and 98.67 ± 2.84% for cellulose recovery, respectively. The maximum digestibilities of glucan (56.85 ± 0.73%) and xylan (66.41 ± 3.06%) were attained after TEBAC:LA pretreatment. Furthermore, the maximum ethanol concentration and productivity attained from TEBAC:LA-based DES-pretreated SCB were 24.50 g/L and 0.68 g/(L·h), respectively. Finally, the comprehensive structural analyses of SCB, employing X-rays, FT-IR, and SEM techniques, provided valuable insights into the deconstruction process facilitated by different combinations of HBDs and HBAs within the DES pretreatment.

The use of newly isolated fungal cultures for the selective delignification of bamboo culms.

The screening of ligninolytic enzyme-producing fungal species in samples led to the identification of Paracremonium sp. LCB1, Clonostachys compactiuscula LCD1 and C. compactiuscula LCN1. Both these strains produced high levels of hemicellulase and ligninolytic enzyme production over a relatively short fermentation period of 3-5days while exhibiting very low levels of cellulase activity. The results of the tests indicated that co-culturing LCB1 and LCN1 enhanced the ability to degrade lignin, and the ideal degrading circumstances and internal degrading mechanism of combined fungi were examined. The results showed that under conditions of temperature (30°C), pH (5), culture time (40 d), solid-liquid ratio (1:2.5), the pretreatment of bamboo culms with a co-culture of LCB1 and LCN1 resulted in a pronounced 76.37% drop in lignin weight and a high lignin/cellulose loss ratio (>10). Fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the physicochemical properties of these bio-pretreated bamboo culms, further confirming that LCB1 and LCN1 co-culture represents an effective approach to bamboo delignification.

Biological decay by microorganisms in stems from the Upper Triassic Ischigualasto Formation (San Juan Province, Argentina): A striking microbial diversity in Carnian-Norian terrestrial ecosystems

We studied degradation patterns and microorganisms preserved in permineralized stems of Rhexoxylon piatnitzky, Protojuniperoxylon ischigualastense, and Agathoxylon argentinum from the Valle de la Luna Member of the Ischigualasto Formation (Upper Triassic, San Juan, Argentina). All three species show loss of middle lamella, thinning, and whitening of tracheid cell walls, and detachment of the S3 layer, consistent with selective delignification by white rot. This type of rot is the product of lignin and cellulosic degradation by Basidiomycetes and Ascomycetes. Rhexoxylon piatnitzkyi also shows small cavities, more or less circular in outline, on the wall of tracheids. This is known as soft rot and can be produced by some Ascomycetes, the anamorphic phases of diverse fungi, and tunneling bacteria. Additionally, abundant and diverse microorganisms were found. Rhexoxylon piatnitzkyi shows fragments of septate hyphae, evidence of bacterial activity, and structures of unknown affinity. Protojuniperoxylon ischigualastense presents structures common to anamorphic phases of diverse fungi, such as chlamydospores and conidiophores. Lastly, Agathoxylon argentinum bears coiled and septate hyphae, and a fan-shaped mycelium, whose significance is discussed. The microbiological study was complemented by the assessment of sedimentary and taphonomic data of the fossil-bearing beds. A gradual increment in humidity for the Valle de la Luna Member is interpreted, which concludes with a humidity peak in its upper section. This contribution represents the first detailed study of xylophagous and saprophyte micro-communities for the Ischigualasto Formation. The abundance and diversity of microorganisms described illustrate the complexity of wood-inhabiting micro-communities from the Carnian-Norian interval of Argentina.

Low-temperature highly selective water delignification based on geopolymer materials

Delignification pretreatment is the main source of high cost and high pollution in biomass processing. This paper reports on a simple cheap geopolymers-based highly selective and efficient pretreatment process for delignification under low-temperature water-cooking without discharging black liquor. The geopolymer with a SiO2/Al2O3 ratio of 4.4 showed the largest number of acidic sites and highest catalytic activity. Under mild reaction conditions (mGeopolymer/mFiber = 1/4, 90 min and 90 °C), the delignification rates of woody (eucalyptus) and herbaceous (bagasse) biomass increased by up to 38.90% and 62.20%, respectively. Moreover, the low-alkali black liquor produced by the new water delignification process facilitates subsequent water treatment, eliminating the need for alkali recovery. This study confirms the immense application prospects of geopolymers for the highly selective delignification of most biomass fibre. This study will develop a low-temperature water-cooking process for the delignification of papermaking or biomass processing without wastewater discharge.

Synergy of ball milling, microwave irradiation, and deep eutectic solvents for a rapid and selective delignification: walnut shells as model for lignin-enriched recalcitrant biomass

The combination of ball milling (BM), microwave irradiation (MI), and deep eutectic solvents (DES) results synergistic for an efficient, selective, and very rapid (10 min) delignification of materials with high lignin content (ca. 50 wt%) such as walnut shells (WS). Lignin is dissolved in the DES, whereas the polysaccharide fractions remain suspended with limited degradation, due to the rapid pretreatment. After ball milling procedure (3 h), biomass loadings in the range of 100–200 g L−1 are selectively delignified in 10 min at 150 °C by using choline chloride:formic acid DES (1:2 molar ratio), rendering lignin yields of 60–80% (ca. ~ 40–60 g lignin L−1). Ball milling, microwave irradiation, and DES systems are much more efficient than ball milling, conventional heating, and DES system. The obtained lignins exhibited similar Fourier-transform infrared spectroscopy (FTIR) profile to that of milled wood lignin (MWL), indicating minimal functional group changes.Graphical abstract

Fenton-reaction-aid selective delignification of lignocellulose by Inonotus obliquus to improve enzymatic saccharification

Aiming at improving the efficiency of recovering sugars from wheat straw by the white rot fungus Inonotus obliquus in solid-state fermentation, two Fenton-reaction-aid systems, i.e., one system containing Fenton reaction pretreatment (FRP) and subsequent Inonotus obliquus culture, one system composed of fungal combined treatment with Fe3O4 nanomaterials (NMs), were developed. FRP and NMs improved the fungal growth and degradation efficiency of wheat straw (WS) by regulating ligninolytic enzyme secretion with manganese peroxidase (MnP) (471.0, 359.8 IU g−1), lignin peroxidase (LiP) (108.0, 48.6 IU g−1), and laccase (Lac) (18.0, 13.4 IU g−1) in the FRP group and NMs group within 15 days. Hemicellulose removal on Day 5 and delignification on Day 10 in FRP group (51.3 % and 20.93 %) and NMs group (40.7 % and 12.60 %) were more severe than the control group (19.2 %, 7.37 %). Sugar yield and conversion rate of 10-day-cultured FRP-WS were 228.4 g kg−1 and 37.2 %, 2.1 and 2.6 times higher than that of 10-day-cultured raw WS. Synergism of Fenton reaction and white-rot fungus quickened fermentation period, promoted degradation selectivity, and then subsequent enzymatic hydrolysis. The Fenton-like system established by NMs and I. obliquus made the synergistic system simpler and represented biocompatible chemistry for developing novel microbial cell factories.

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.

Characterization of Eucalyptus Lignin Fractionation from a MIBK-Based Solvothermal Process

In this study, the effects of sulfuric acid on cellulose yield, lignin removal, and lignin recovery in solvothermal fractionation of eucalyptus (EC) were studied. An acid concentration of 0.04 M sulfuric acid (H2SO4), temperature of 180 °C and residence time of 30 min resulted in maximum lignin removal from the solid phase, at 87.7 %. Lignin recovery in the organic phase under optimum conditions was 84.6 %. It should be noted that H2SO4 was the best catalyst in the optimal solvothermal process, and it increased the cellulose yield to 95.2 % in the solid phase. Additionally, the physicochemical and structural properties of the extracted lignin were analyzed using FTIR, TGA, elemental analysis, GPC, and Py-GCMS methods. Thermal degradation analysis showed that recovered lignin is primarily composed of syringyl, guaiacyl and p-hydroxyphenyl units cross-linked by C–C, inter-unit α-O-4, β-O-4 linkages. The weight average molecular weight (Mw) analysis of recovered lignin demonstrated a low molecular weight for recovered lignin (2.19 g/mol). However, the main phenolic derivatives in the extracted lignin obtained from EC were S-units (i.e., syringol, 4-methylsyringol, 4-vinylsyringol). In addition, G-units (4-vinylguaiacol, 4-methylguaiacol, phenol, 2-methylphenol, and 4-methylphenol) were obtained after release from H-units. Py-GCMS analysis showed the predominance of G-units (32.8 %) over S-units (57.4 %). This work demonstrated the potential of fractionated lignin in the production of valuable chemicals in biorefineries.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Eucalyptus was fractionated with solvothermal process with different conditions&#x0D; The maximum lignin removal of 87.7 % was achieved in the presence of catalyst of 0.04 M&#x0D; Organosolv fractionation enabled an extensive and selective delignification&#x0D; The structural changes of lignin were characterized comprehensively&#x0D; &#x0D; GRAPHICAL ABSTRACT

Insight into the negative effects of lignin on enzymatic hydrolysis of cellulose for biofuel production via selective oxidative delignification and inhibitive actions of phenolic model compounds

Oxidative pretreatment of wheat straw with sodium chloride has been used for selective delignification to obtain ideal samples to understand the negative effects of lignin on cellulose accessibility of lignocellulosic biomass. Strong interactive effects has been found between hemicellulose and lignin. To achieve a high enzymatic glucan conversion (EGC) (>80% with 20 FPU/g solid) in the case of high xylan content (25–30%), a moderate degree of delignification (56.3%) with relatively low lignin content (11.9%) is necessary; while in the case of low xylan content (2.6–3.9%), slight removal of lignin by oxidative treatment can well increase cellulose digestibility with a final EGC reaching 90% even that the residual lignin content is as high as 30.9%. Delignification greatly modifies substrate surface morphology with deformation, fracture of cell wall layers and even disappearance of middle lamella. Oxidation also modifies the functional groups and surface properties of lignin, leading to reduction in the inhibitive effects. Phenolic hydroxyl group (Ph-OH) in p-hydroxyphenyl unit has been found to show the strongest inhibition to filter paper activity of cellulase cocktail. Ph-OH exerts stronger inhibition to β-glucosidase than to the endo- and exo-glucanases. Hydrogen bonding and electrostatic interaction are primarily responsible for the inhibitive action of Ph-OH.

Isolation and Screening of Microorganisms for the Effective Pretreatment of Lignocellulosic Agricultural Wastes.

Lignocellulosic waste is the most abundant biorenewable biomass on earth, and its hydrolysis releases highly valued reducing sugars. However, the presence of lignin in the biopolymeric structure makes it highly resistant to solubilization thereby hindering the hydrolysis of cellulose and hemicellulose. Microorganisms are known for their potential complex enzymes that play a dominant role in lignocellulose conversion. Therefore, the current study was designed to isolate and screen potential microorganisms for their selective delignification ability for the pretreatment of lignocellulosic biomass. An extensive isolation and screening procedure yielded 36 desired isolates (22 bacteria, 7 basidiomycete fungi, and 7 filamentous fungi). Submerged cultivation of these desired microorganisms revealed 4 bacteria and 10 fungi with potent lignocellulolytic enzyme activities. The potent isolates were identified as Pleurotus, Trichoderma, Talaromyces, Bacillus, and Chryseobacterium spp. confirmed by morphological and molecular identification. The efficiency of these strains was determined through enzyme activities, and the degraded substrates were analyzed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). Among all isolated microbes, Pleurotus spp. were found to have high laccase activity. The cellulose-decomposing and selective delignification strains were subjected to solid-state fermentation (SSF). SSF of field waste corn stalks as a single-carbon source provides Pleurotus spp. better condition for the secretion of ligninolytic enzymes. These isolated ligninolytic enzymes producing microorganisms may be used for the effective pretreatment of lignocellulosic agricultural wastes for the production of high value-added natural products by fermentation.

Alkaline post-incubation improves the saccharification of poplar after hydrogen peroxide\u2013acetic acid pretreatment

BackgroundHydrogen peroxide–acetic acid (HPAA) is widely used in pretreatment of lignocellulose because it has a good capability in selective delignification. However, high concentration (more than 60%) of HPAA increases the cost of pretreatment and the risk of explosion. In this work, alkaline post-incubation was employed to decrease the HPAA loading and improve the saccharification of poplar.ResultsPretreatment with 100% HPAA removed 91.0% lignin and retained 89.9% glucan in poplar. After poplar was pretreated by 100% HPAA at 60 °C for 2 h, the glucan conversion in enzymatic hydrolysis by cellulase increased to 90.1%. Alkaline incubation reduced the total lignin, surface lignin, and acetyl group of HPAA-pretreated poplar. More than 92% acetyl groups of HPAA-pretreated poplar were removed by alkaline incubation with 1.0% NaOH at 50 °C for 1 h. After incubation of 60% HPAA-pretreated poplar with 1.0% NaOH, the glucan conversion enhanced to 95.0%. About 40% HPAA loading in pretreatment was reduced by alkaline incubation without the decrease of glucose yield.ConclusionsAlkaline post-incubation had strong ability on the deacetylation and delignification of HPAA-pretreated poplar, exhibiting a strong promotion on the enzymatic hydrolysis yield. This report represented alkaline incubation reduced the HPAA loading, improved pretreatment safety, exhibiting excellent potential application in saccharification of poplar.

Selective delignification of poplar wood with a newly isolated white-rot basidiomycete Peniophora incarnata T-7 by submerged fermentation to enhance saccharification

BackgroundPretreatment is a critical step required for efficient conversion of woody biomass into biofuels and platform chemicals. Fungal pretreatment is regarded as one of the most promising technology for woody biomass conversion but remains challenging for industrial application. The exploration of potential fungus strain with high efficient delignification and less processing time for woody biomass pretreatment will be valuable for development of biorefinery industry. Here, a newly isolated white-rot basidiomycete Peniophora incarnate T-7 was employed for poplar wood pretreatment.ResultsThe chemical component analysis showed that cellulose, hemicellulose and lignin from poplar wood declined by 16%, 48% and 70%, respectively, after 7 days submerged fermentation by P. incarnate T-7. Enzymatic saccharification analysis revealed that the maximum yields of glucose and xylose from 7 days of P. incarnate T-7 treated poplar wood reached 33.4% and 27.6%, respectively, both of which were enhanced by sevenfold relative to the untreated group. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD) and pyrolysis gas chromatography–mass spectrometry (Py-GC/MS) characterization confirmed that lignocellulosic structure of poplar wood was largely broken by P. incarnate T-7, including delignification and de-crystalline of cellulose. Meanwhile, lignin component of poplar wood was selectively degraded by P. incarnate T-7, and G-type unit of lignin was preferentially attacked by the strain. Furthermore, quantitative proteomic analysis revealed that a considerable amount of lignocellulolytic enzymes were detected in the secretory proteins of P. incarnate T-7, especially with high abundance of lignin-degrading enzymes and hemicellulases. Combination of quantitative proteomic with transcriptomic analysis results showed that most of those lignocellulolytic enzymes were highly upregulated on poplar wood substrate compared to glucose substrate.ConclusionsThis study showed that P. incarnate T-7 could selectively delignify poplar wood by submerged fermentation with short time of 7 days, which greatly improved its enzymatic saccharification efficiency. Our results suggested that P. incarnate T-7 might be a promising candidate for industrial woody biomass pretreatment.

Selective fungal pretreatment favored pyrolysis products of wheat straw based on pyrolytic polygeneration system

A novel wheat straw valorization strategy was developed in which selective fungal pretreatment was applied to promote pyrolytic polygeneration from wheat straw using a fixed-bed reactor. Selective delignification of wheat straw by Pleurotus ostreatus was confirmed. Kinetic analysis based on a modified three-parallel-reaction model indicated that thermally resistant lignin structures were converted to easily degradable structures during fungal pretreatment, facilitating the pyrolysis of wheat straw. The effects of the selective fungal pretreatment on the profiles of pyrolytic products (bio-oil, biogas and biochar) were clearly illustrated. After selective fungal pretreatment, the bio-oil yield increased by 51.09%, and the yields of some high value-added products, such as isosorbide, greatly increased. Moreover, the biochar produced by pyrolysis from the selective fungus-treated wheat straw had characteristics for the adsorption of dyes and pollutants. Therefore, selective delignification by fungal pretreatment increased the thermochemical conversion efficiency during pyrolytic polygeneration from wheat straw.

Generation of highly amenable cellulose-I\u03b2 via selective delignification of rice straw using a reusable cyclic ether-assisted deep eutectic solvent system

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. The enzymatic hydrolysis of cellulose is necessary for generating monomeric sugars, which are then fermented into ethanol. In our study, a combination of a deep eutectic (DE) mixture (of 2-aminoethanol and tetra-n-butyl ammonium bromide) and a cyclic ether (tetrahydrofuran) was used for selective delignification of rice straw (RS) under mild conditions (100 °C). Pretreatment with DE-THF solvent system caused ~ 46% delignification whereas cellulose (~ 91%) and hemicellulose (~ 67%) recoveries remained higher. The new solvent system could be reused upto 10 subsequent cycles with the same effectivity. Interestingly, the DE-THF pretreated cellulose showed remarkable enzymatic hydrolysability, despite an increase in its crystallinity to 72.3%. Contrary to conventional pretreatments, we report for the first time that the enzymatic hydrolysis of pretreated cellulose is enhanced by the removal of lignin during DE-THF pretreatment, notwithstanding an increase in its crystallinity. The current study paves way for the development of newer strategies for biomass depolymerization with DES based solvents.

Scalable aesthetic transparent wood for energy efficient buildings

Nowadays, energy-saving building materials are important for reducing indoor energy consumption by enabling better thermal insulation, promoting effective sunlight harvesting and offering comfortable indoor lighting. Here, we demonstrate a novel scalable aesthetic transparent wood (called aesthetic wood hereafter) with combined aesthetic features (e.g. intact wood patterns), excellent optical properties (an average transmittance of ~ 80% and a haze of ~ 93%), good UV-blocking ability, and low thermal conductivity (0.24 W m−1K−1) based on a process of spatially selective delignification and epoxy infiltration. Moreover, the rapid fabrication process and mechanical robustness (a high longitudinal tensile strength of 91.95 MPa and toughness of 2.73 MJ m−3) of the aesthetic wood facilitate good scale-up capability (320 mm × 170 mm × 0.6 mm) while saving large amounts of time and energy. The aesthetic wood holds great potential in energy-efficient building applications, such as glass ceilings, rooftops, transparent decorations, and indoor panels.

Anatomical characterization of wood decay patterns in Hevea brasiliensis and Pinus merkusii caused by white-rot fungi: Polyporus arcularius and Pycnoporus sanguineus

Biological pulping is an environmentally friendly process for making pulp and paper whereby the wood raw material is pre-treated with selective delignifying white-rot fungi. Therefore, the purpose of this study is to determine the decay patterns of white-rot fungi Polyporus arcularius and Pycnoporus sanguineus, as well as its ability to decay Hevea brasiliensis (as hardwood) and Pinus merkusii (as softwood) by observing the anatomical characteristics. Fungal attack testing on wood was carried out by the Kolle-flask method with a variation of 6, 9, and 12 weeks incubation time. The structure of wood cells was analyzed using wood incision method, followed by a combination of safranin-picro aniline blue and safranin-astra blue, and maceration method. The results showed that H. brasiliensis wood has a higher percentage of weight loss than P. merkusii wood. Wood attacked by P. sanguineus showed a higher weight loss compared to the P. arcularius. The decay pattern of P. sanguineus infected wood was concluded as selective delignification in P. merkusii and simultaneous delignification in H. brasiliensis while those infected with P. arcularius both performed simultaneous delignification. In the early stages of decay, selective delignification is characterized by the formation of intercellular space due to degradation of lignin in the middle lamella, while simultaneous delignification is characterized by cell wall thinning. The anatomical structure of H. brasiliensis attacked by the white-rot fungi showed differences with P.merkusii, whereby the ray cells of P.merkusii wood was more degraded than in H. brasiliensis.

A comparison of different oxidative pretreatments on polysaccharide hydrolyzability and cell wall structure for interpreting the greatly improved enzymatic digestibility of sugarcane bagasse by delignification

In order to confirm the contribution of delignification to the increase in lignocellulosic cellulose digestibility, several laboratory oxidative pretreatments under mild conditions, including alkaline-hydrogen peroxide (AP), two-step alkaline/peracetic acid (APAA) and sodium chlorite (SC) pretreatments were employed to achieve selective delignification of sugarcane bagasse and retained most of the hemicelluloses (xylan) in the pretreated solids. Four commercial cellulase cocktails were used to test the enzymatic hydrolyzability of pretreated substrates. Results revealed that delignification indeed could greatly improve the final (120 h) cellulose hydrolysis with relatively high final (120 h) glucan conversion (> 90%) by different cellulase cocktails even if the substrates still had a high hemicelluloses content. However, the xylan conversion seemed to be more greatly dependent on the pretreatments and cellulase cocktails used. AP and APAA pretreatments resulted in the disappearance of middle lamella and liberation of cellulose fibers with significant etching, deformation and fracture of cell wall structure. SC pretreatment greatly modified the sugar bagasse surface morphology to make the surface much coarser. The cell wall also underwent serious fracture and deformation with some middle lamella disappearing. However, no significant alteration on the structure of pure cellulose was observed by SC oxidative pretreatment of filter paper. Oxidative pretreatment might also modify lignin structure and surface properties thus greatly reducing the non-specific adsorption of enzymes. The obtained results strongly support the conclusion that delignification under mild pretreatment condition can be very helpful to improve the enzymatic hydrolysis of lignocellulosic cellulose by commercial cellulase cocktails even if the substrates has a high hemicelluloses content.

Bio-pulping: An energy saving and environment-friendly approach

AbstractPretreatment of wood or other raw material with white-rot fungi (WRF) prior to pulping is known as biopulping. Lignin and hemicelluloses are removed selectively during early growth of WRF that produces enriched cellulose, known as selective delignification. Biopulping is considered as environment-friendly and cost-effective approach for delignification of lignocellulosic raw materials. The delignification efficiency of WRF during biopulping is directly related to ligninolytic enzymes production that is influence by several factors such as fungal strain, nature of raw material, oxygen availability, moisture content, pH, temperature, source of nitrogen, presence of Mn++and Cu++ions. The WRF, especiallyCeriporiopsis subvermispora,Trametes versicolorandPhanerochaete chrysosporium, have been used dominantly for the purpose of biopulping. It is an energy saving process that also improves brightness of pulp and strength properties including tensile index, burst index and folding endurance of paper. Significant decrease in kappa number has also been attained by fungal pretreatment of raw materials. Biological pretreatment of raw material also reduces the requirement of pulping chemicals.