Combined liquid hot water with sodium carbonate-oxygen pretreatment to improve enzymatic saccharification of reed

Combined sulfuric acid and choline chloride/glycerol pretreatment for efficiently enhancing enzymatic saccharification of reed stalk

In this study, an efficient combination of pretreatment solvents involving Choline chloride/Glycerol (ChCl/Gly) and H2SO4 was firstly developed to assess the pretreatment performance and determine optimal pretreatment conditions. The results illustrated that the H2SO4-[ChCl/Gly] combination efficiently removed lignin (52.6%) and xylan (80.5%) from the pretreated reed stalk, and subsequent enzymatic hydrolysis yielded 91.1% of glucose. Furthermore, several characterizations were conducted to examine the structural and morphological changes of the reed stalk, revealing apparently enhanced accessibility (128.4 to 522.6 mg/g), reduced lignin surface area (357.9 to 229.5 m2/g), and substantial changes on biomass surface. Based on the aforementioned study, possible mechanisms for the H2SO4-[ChCl/Gly] pretreatment of reed stalks were proposed. The comprehensive understanding of combined H2SO4-[ChCl/Gly] pretreatment system for enhancing the saccharification of the reed stalk was interpreted in this work. Overall, this novel approach could be efficiently applied to pretreat and saccharify reed stalks, empowering the biomass refining industry.

`A critical review on current status and environmental sustainability of pre-treatment methods for bioethanol production from lignocellulose feedstocks

Lignocellulosic biomass resource has been widely used as a natural resource for the synthesis of biofuels and bio-based products through pre-treatment, saccharification and fermentation processes. In this review, we delve into the environmental implications of bioethanol production from the widely utilized lignocellulosic biomass resource. The focus of our study is the critical stage of pre-treatment in the synthesis process, which also includes saccharification and fermentation. By collecting scientific data from the available literature, we conducted a comprehensive life cycle analysis. Our findings revealed substantial differences in the environmental burdens associated with diverse pre-treatment methods used for lignocellulosic biomass. These results highlight the importance of selecting environmentally benign pre-treatment techniques to promote the sustainability of bioethanol production. Future research directions are suggested, emphasizing the optimization of pre-treatment processes to further mitigate their environmental impact.

Increasing the value of Phragmites australis straw in a sustainable integrated agriculture model (SIAM) comprising edible mushroom cultivation and spent mushroom substrate compost

Because of the regular annual harvest, Phragmites australis used in wetland protection produces an abundance of straw, resulting in a large amount of straw waste. As a result, the extra straw should be used in a convenient and efficient manner. A comprehensive analysis of P. australis straw use in Pleurotus cultivation and spent mushroom substrate compost was performed in this study to increase its value. The lignocellulose content in the straw was shown to meet the nutritional requirements of the Pleurotus mushroom. Immediately thereafter, the replacement of bagasse with P. australis proved to be reasonable for Pleurotus eryngii substrate and could generate a profit of ¥17,400 per 10,000 cultivation bags. Substituting P. australis for approximately 20 % to 40 % of bagasse is recommended for Pleurotus ostreatus cultivation and can yield a profit of approximately ¥16,000. Spent mushroom substrate compost was confirmed to increase the organic matter content, and post-compost use of this substrate as a fertilizer could increase economic income by approximately ¥1000 for every 10,000 bags. Overall, this recycling pathway for P. australis resources presents positive ecological and social benefits, and the model is a sustainable and eco-friendly solution for agricultural waste worthy of promotion and further application.

Pretreatment of sugarcane bagasse with acid catalyzed ethylene glycol-water to improve the cellulose enzymatic conversion

In this work, HCl catalyzed ethylene glycol-water pretreatment (HCl/EG-H₂O) of sugarcane bagasse (SCB) was explored with response surface methodology (RSM) and single factor analysis, which aim to investigate the influence of pretreatment variable on pretreated solid cellulose enzymatic conversion. The result showed that HCl/EG-H₂O pretreatment could selectively extract ∼89.9 % xylan and ∼61.2 % lignin in SCB, meanwhile maintain a relatively high cellulose retention (∼86.8 %). Pretreatment of SCB at 120 °C for 60 min with 1.00 % HCl and 90 % EG obtained the pretreated solid having maximum cellulose enzymatic conversion of 88.7 % under 10 FPU/g enzyme dosage, this enhancement of cellulose enzymatic conversion mainly attributed to structure change of SCB in pretreatment. The adding of enzymatic additives into the hydrolysis process could not only improve hydrolysis efficiency but also lower the enzyme dosage. Besides, the linear relationship between substrate characteristic parameters (such cellulose content, lignin removal rate etc.) and cellulose conversion were observed.

Emerging challenges for the agro-industrial food waste utilization: A review on food waste biorefinery

Modernization and industrialization has undoubtedly revolutionized the food and agro-industrial sector leading to the drastic increase in their productivity and marketing thereby accelerating the amount of agro-industrial food waste generated. In the past few decades the potential of these agro-industrial food waste to serve as bio refineries for the extraction of commercially viable products like organic acids, biochemical and biofuels was largely discussed and explored over the conventional method of disposing in landfills. The sustainable development of such strategies largely depends on understanding the techno economic challenges and planning for future strategies to overcome these hurdles. This review work presents a comprehensive outlook on the complex nature of agro-industrial food waste and pretreatment methods for their valorization into commercially viable products along with the challenges in the commercialization of food waste bio refineries that need critical attention to popularize the concept of circular bio economy.

A Combination Method of Liquid Hot Water and Phosphotungstic Acid Pretreatment for Improving the Enzymatic Saccharification Efficiency of Rice Straw

Chemical pretreatment can significantly improve the enzymatic hydrolysis efficiency of lignocellulosic biomass, thereby improving the yield of sugar materials for the production of cellulosic ethanol, but commonly used acid–base catalysts are difficult to recover and reuse. In this work, a combination method of liquid hot water (LHW) and phosphotungstic acid (PTA) pretreatment was performed to improve the saccharification efficiency of rice straw, and we attempted to evaluate the reuse effect of PTA catalysts. The rice straw was first treated with LHW at 180 °C for 90 min, and then treated with 20 mM PTA at 130 °C for 60 min. After pretreatment, the cellulose hydrolysis efficiency and glucose recovery of the rice straw increased by 201.85% and 164.25%, respectively. Glucose accounted for 96.8% of the total reducing sugar in the final enzymatic hydrolysate. After each PTA pretreatment, approximately 70.8–73.2% of the PTA catalyst could be recycled. Moreover, the catalytic activity of the PTA catalyst that had been used five times did not decrease. The improved enzymatic saccharification efficiency was attributed to the removal of 89.24% hemicellulose and 21.33% lignin from the lignocellulosic substrate. The two-step LHW-PTA pretreatment could pretreat biomass in the field of cellulosic ethanol production.

Integral Analysis of Liquid-Hot-Water Pretreatment of Wheat Straw: Evaluation of the Production of Sugars, Degradation Products, and Lignin

Developing sustainable biorefineries is an urgent matter to support the transition to a sustainable society. Lignocellulosic biomass (LCB) is a crucial renewable feedstock for this purpose, and its complete valorization is essential for the sustainability of biorefineries. However, it is improbable that a single pretreatment will extract both sugars and lignin from LCB. Therefore, a combination of pretreatments must be applied. Liquid-hot-water (LHW) is highlighted as a pretreatment for hemicellulose hydrolysis, conventionally analyzed only in terms of sugars and degradation products. However, lignin is also hydrolyzed in the process. The objective of this work was to evaluate LHW at different conditions for sugars, degradation products, and lignin. We performed LHW at 160, 180, and 200 °C for 30, 60, and 90 min using wheat straw and characterized the extract for sugars, degradation products (furfural, hydroxymethylfurfural, and acetic acid), and lignin. Three conditions allowed reaching similar total sugar concentrations (~12 g/L): 160 °C for 90 min, 180 °C for 30 min, and 180 °C for 60 min. Among these, LHW performed at 160 °C for 90 min allowed the lowest concentration of degradation products (0.2, 0.01, and 1.4 g/L for furfural, hydroxymethylfurfural, and acetic acid, respectively) and lignin hydrolysis (2.2 g/L). These values indicate the potential use of the obtained sugars as a fermentation substrate while leaving the lignin in the solid phase for a following stage focused on its extraction and valorization.

Hydrothermal co-hydrolysis of corncob/sugarcane bagasse/Broussonetia papyrifera blends: Kinetics, thermodynamics and fermentation

Biorefinery of biomass blends can achieve sustainable development of biofuel production. Herein, three lignocellulosic wastes with significant differences in chemical composition-namely corncob (CC), sugarcane bagasse (SB), and Broussonetia papyrifera (BP)-were selected to investigate their hydrothermal co-hydrolysis kinetics and thermodynamics of different biomass blends. Activation energies of hemicellulose decomposition (Ea₁, 90.59 kJ/mol) for CC/SB were lower than those for CC (126.12 kJ/mol) and CC/SB/BP (153.62 kJ/mol). BP (having a high content of nitrogen sources) loading weakened the acidic autohydrolysis of CC/SB hemicellulose, but yielded stable products as indicated by the negative entropy value for CC/SB/BP hydrolysis. Cumulative feedback inhibition occurred among different biomass, and it could be minimized by controlling the blending ratio. The highest total xylose yield was 83.64% for CC/SB with a mass ratio of 2:1. Moreover, biomass blend of CC/SB/BP enabled complete utilization of hexose, pentose and amino acids by co-production of ethanol and microalga biomass.

Bioethanol production from pistachio (pistacia vera L.) shells applying ozone pretreatment and subsequent enzymatic hydrolysis

Pistachio (pistacia vera L.) is a lignocellulosic raw material. One of the most pistachio produced three countries in the World is Turkey and Şanlıurfa is the city that most pistachio production in Turkey. As a result of this production, a large amount of pistachio waste is generated. Therefore, this study was conducted considering the abundant pistachio waste and furthermore, the effects of ozone and combined (ozone and hot water) pretreatments for bioethanol production from pistachio shells were investigated. Initially, the ozone and combined pretreatments were applied to the pistachio shells. It has been observed that applying the combined pretreatment provides better lignin removal than only ozone pretreatment and on the other hand, the ozone pretreatment provides better lignin removal than the hot water pretreatment. Scanning electron microscopy (SEM) images of pretreated and untreated pistachio shells were compared. Enzyme activity was measured, and 30-60 FPU enzyme loading was applied in an enzymatic hydrolysis. The enzymatic hydrolysis was applied to obtain fermentable sugar from the pistachio shells after pretreatments. As a result of enzymatic hydrolysis, 2.34-8.24 g/L reducing sugar was obtained. On the other hand, 1.21-2.33 g/L ethanol concentration was obtained end of the fermentation process. Fermentation efficiency was calculated between 42% and 55%. As a result, this study showed that combined pretreatment was more effective than the single pretreatment in the ethanol production process.

Cellulose-assisted construction of high surface area Z-scheme C-doped g-C3N4/WO3 for improved tetracycline degradation

The preparation of heteroatom doping heterojunction photocatalysts with nontoxic carbonaceous materials and simple method still remains a challenge. Herein, ternary Z-scheme C-doped graphitic carbon nitride/tungsten oxide (C-doped g-C₃N₄/WO₃) was successfully fabricated via the hydrothermal impregnation with cellulose nanocrystal, high-temperature calcination, and electrostatic self-assembly with WO₃ nanocuboids in turns. Benefiting from the porous structure, high specific areas (57.20 m² g^-1), C-substitution, and the formation of Z-scheme heterojunction, the resulting photocatalyst exhibited narrower band-gap, enhanced visible-light absorption and separation of charge carrier, faster interfacial charge transfer, good oxidation/reduction capacities, and thus improved the photocatalytic activity performance. As such, this investigation will provide an effective route for not only incorporating semiconductors and heteroatoms into g-C₃N₄ but also developing more heterojunction with markedly improved photocatalytic performance.

Lipid bioproduction from delignified native grass (Cyperus distans) hydrolysate by Yarrowia lipolytica

In the present study, native grass (Cyperus distans) was utilized for the production of lipid using Yarrowia lipolytica MTCC 9519. Initially, pretreatment methods using hydrothermal and alkaline delignification were performed to obtain cellulose rich liquid fractions. Delignified native grass biomass was enzymatically hydrolyzed to convert non fermentable sugars in to fermentable sugars. The growth of Y. lipolytica MTCC 9519 by utilizing pretreated native grass hydrolysate was evaluated. The yield and concentration of total reducing sugars after enzyme hydrolysis were found to be 378 ± 35 mg/g of pretreated biomass and 28.64 g/L ± 1.25 g/L, respectively. When pretreated, delignified native grass hydrolysate was used with (NH₄)₂SO₄ (30C/N ratio) and sodium n-octanoate (0.4% w/w), the dry cell weight and lipid accumulation of Y. lipolytica MTCC 9519 reached about 19.88 ± 1.54 g/L and 53.62% (w/w) respectively after 96 h. Thus, native grass could become a promising substrate for biolipid production.

Generation of highly amenable cellulose-Iβ 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.

Comprehensive analysis of important parameters of choline chloride-based deep eutectic solvent pretreatment of lignocellulosic biomass

Choline chloride based deep eutectic solvents have showed great potential in lignocellulosic biomass pretreatment. In this study, for DES pretreatment with different hydrogen bond donners of different raw materials under different reaction conditions, multivariate analysis methods including principal component analysis and partial least squares analysis were used for reveal the pretreatment mechanism by evaluating the inner relationships among 42 key process factors. Furthermore, based on molecular simulation, the detailed relationships between key variables were further analyzed. Meanwhile, four-dimensional color graphs were used to intuitively reveal the synergistic influence of multivariate conditions variables on pretreatment effect to obtain better economic benefits and energy consumption indicators for DES pretreatment. The results showed that HBD hydrophilic ability, HBD polarity, HBD acidity, HBD ability to form hydrogen bonds, molar ratio of HBD to choline chloride and pretreatment severity had great influence on the Choline chloride based deep eutectic solvents pretreatment effect.

Mild O2-aided alkaline pretreatment effectively improves fractionated efficiency and enzymatic digestibility of Napier grass stem towards a sustainable biorefinery

Napier grass is a promising energy source on account of its strong adaptability and high productivity. Herein, an O₂-aided alkaline pretreatment with mild operating conditions was developed to modify Napier grass stem structure for improving its fractionated efficiency and enzymatic digestibility. Compared with the conventional alkaline pretreatment, it could be proceeded at lower temperature (80 °C) and dilute NaOH solution (1%) to remove over 80% lignin and retain 92% cellulose. The recovered lignin possessed typical structures of native lignin and well-preserved molecular weight, anticipating feasible potential in preparation of biomaterials or aromatic chemicals. Coupled with the enzymatic hydrolysis managements of solid remain and hydrolysate after the pretreatment, the recovery yields of glucose and xylose based on the raw material feeds reached 89.7% and 90.2%, respectively. This contribution demonstrates a highly-reliable strategy to fractionate Napier grass stem for maximizing fermentation sugar production and valorizing lignin toward sustainable biorefinery processes.

Integrating phosphotungstic acid-assisted prerefining with cellulase treatment for enhancing the reactivity of kraft-based dissolving pulp

Viscosity control and reactivity enhancement are of practical importance for high-quality dissolving pulp manufacturing. In this work, we demonstrate a two-step activating process consisting of a phosphotungstic acid (PTA)-assisted prerefining (PTA/R pretreatment), followed by cellulase treatment for this purpose. The cellulase adsorption can increase from 29.1% to 49.7% as a result of PTA/R pretreatment (8000 r at 90 °C). The viscosity of the resultant pulp decreases from 665 to 430 mL/g, while its Fock reactivity increases from 31.5% to 74.4% under a low-loading cellulase treatment (0.5 mg cellulase /g odp), which mainly due to the fact that the PTA/R pretreatment can increase fiber accessibility and viscosity control, thus facilitating cellulase adsorption and reaction efficiency. Moreover, PTA also shows a high recyclability/ reusability (more than 86%) during the PTA/R pretreatment. Therefore, the new proposed two-step activating process provides a green, and efficient pathway for large-scale manufacturing of high-quality dissolving pulp.

The hydrothermal-alkaline/oxygen two-step pretreatment combined with the addition of surfactants reduced the amount of cellulase for enzymatic hydrolysis of reed

This study aimed to provide a low cost feasible pretreatment and enzymatic hydrolysis (EH) method for the effective dissolution of xylan and the high glucan digestibility of reed with a low enzyme loading. The combination of polyethylene glycol (PEG) 3000-enhanced EH and hydrothermal-alkaline/oxygen pretreatment was studied. Process conditions were optimized through response surface methodology. Three models of glucan conversion rate, pretreated solids yield and lignin removal rate were established, and their determination coefficient (R²) values were 0.9218, 0.7939, and 0.8156, respectively. The models and experiments were reliable and significant. The optimal conditions favored 94.5% xylan dissolution rate and 95.6% glucan digestibility by using a cellulase loading of 3 filter paper units (FPU)/g-pretreated solids, which obviously enhanced 30.7% of the glucan conversion rate. This method was applicable due to effective xylan dissolution, lignin removal, and EH with PEG 3000 addition, which can help saved 85% cellulase loading.

Recent developments in the application of kraft pulping alkaline chemicals for lignocellulosic pretreatment: Potential beneficiation of green liquor dregs waste

Lignocellulosic waste has offered a cost-effective and food security-wise substrate for the generation of biofuels and value-added products. However, its recalcitrant properties necessitate pretreatment. Of the various pretreatment methods, alkaline techniques have gained prominence as efficient catalysts. The kraft pulping industry represents a major hub for the generation of white, black and green liquor alkaline solutions during the paper making process. Despite its well-known significance in the kraft pulping process, green liquor (GL) has been widely applied for lignocellulosic pretreatment. Recently, green liquor dregs (GLD), an alkaline waste generated from the kraft pulping industry has piqued interest. Therefore, this review outlines the general flow of the kraft pulping process and the alkaline chemicals derived. In addition, the extensively studied GL for lignocellulosic pretreatment is discussed. Subsequently, the potential beneficiation of GLD for lignocellulosic pretreatment is presented. Furthermore, the challenges and prospects of lignocellulosic pretreatments are highlighted.

A Two-Step Ferric Chloride and Dilute Alkaline Pretreatment for Enhancing Enzymatic Hydrolysis and Fermentable Sugar Recovery from Miscanthus sinensis

A two-step process was proposed to enhance enzymatic hydrolysis of Miscanthus sinensis based on a comparative study of acid/alkaline pretreatments. Ferric chloride pretreatment (FP) effectively removed hemicellulose and recovered soluble sugars, but the enzymatic hydrolysis was not efficient. Dilute alkaline pretreatment (ALP) resulted in much better delignification and stronger morphological changes of the sample, making it more accessible to enzymes. While ALP obtained the highest sugar yield during enzymatic hydrolysis, the soluble sugar recovery from the pretreatment stage was still limited. Furthermore, a two-step ferric chloride and dilute alkaline pretreatment (F-ALP) has been successfully developed by effectively recovering soluble sugars in the first FP step and further removing lignin of the FP sample in the second ALP step to improve its enzymatic hydrolysis. As a result, the two-step process yielded the highest total sugar recovery (418.8 mg/g raw stalk) through the whole process.