Constructing super large scale cellulosic ethanol plant by decentralizing dry acid pretreatment technology into biomass collection depots

Lytic polysaccharide monooxygenase synergized with lignin-degrading enzymes for efficient lignin degradation

Even though the discovery of lytic polysaccharide monooxygenases (LPMOs) has fundamentally shifted our understanding of biomass degradation, most of the current studies focused on their roles in carbohydrate oxidation. However, no study demonstrated if LPMO could directly participate to the process of lignin degradation in lignin-degrading microbes. This study showed that LPMO could synergize with lignin-degrading enzymes for efficient lignin degradation in white-rot fungi. The transcriptomics analysis of fungi Irpex lacteus and Dichomitus squalens during their lignocellulosic biomass degradation processes surprisingly highlighted that LPMOs co-regulated with lignin-degrading enzymes, indicating their more versatile roles in the redox network. Biochemical analysis further confirmed that the purified LPMO from I. lacteus CD2 could use diverse electron donors to produce H2O2, drive Fenton reaction, and synergize with manganese peroxidase for lignin oxidation. The results thus indicated that LPMO might uniquely leverage the redox network toward dynamic and efficient degradation of different cell wall components.

High solids loading pretreatment: The core of lignocellulose biorefinery as an industrial technology - An overview

Pretreatment is the first and most determinative, yet the least mature step of lignocellulose biorefinery chain. The current stagnation of biorefinery commercialization indicates the barriers of the existing pretreatment technologies are needed to be unlocked. This review focused on one of the core factors, the high lignocellulose solids loading in pretreatment. The high solids loading of pretreatment significantly reduces water input, energy requirement, toxic compound discharge, solid/liquid separation costs, and carbon dioxide emissions, improves the titers of sugars and biproducts to meet the industrial requirements. Meanwhile, lignocellulose feedstock after high solids loading pretreatment is compatible with the existing logistics system for densification, packaging, storage, and transportation. Both the technical-economic analysis and the cellulosic ethanol conversion performance suggest that the solids loading in the pretreatment step need to be further elevated towards an industrial technology and the effective solutions should be proposed to the technical barriers in high solids loading pretreatment operations.

Application and prospect of organic acid pretreatment in lignocellulosic biomass separation: A review

As a clean and efficient method of lignocellulosic biomass separation, organic acid pretreatment has attracted extensive research. Hemicellulose or lignin is selectively isolated and the cellulose structure is preserved. Effective fractionation of lignocellulosic biomass is achieved. The separation characteristics of hemicellulose or lignin by different organic acids were summarized. The organic acids of hemicellulose were separated into hydrogen ionized, autocatalytic and α-hydroxy acids according to the separation mechanism. The separation of lignin depends on the dissolution mechanism and spatial effect of organic acids. In addition, the challenges and prospects of organic acid pretreatment were analyzed. The separation of hemicellulose and enzymatic hydrolysis of cellulose were significantly affected by the polycondensation of lignin, which is effectively inhibited by the addition of green additives such as ketones or alcohols. Lignin separation was improved by developing a deep eutectic solvent treatment based on organic acid pretreatment. This work provides support for efficient cleaning of carbohydrate polymers and lignin to promote global carbon neutrality.

Re-examination of dilute acid hydrolysis of lignocellulose for production of cellulosic ethanol after de-bottlenecking the inhibitor barrier

Dilute acid hydrolysis of lignocellulose biomass had been used for production of cellulosic ethanol since 1940s. The major technical barrier is the acid catalyzed dehydration of monosaccharides to furan aldehydes (furfural and 5-hydroxymethylfurfural), resulting in the high loss of fermentable sugars and significant inhibition on the fermentability of ethanologenic strains. This study re-examined the dilute acid hydrolysis of corn stover and cellulosic ethanol fermentation after a novel biodetoxification approach was introduced to de-bottleneck the inhibitor barrier. The cocktail of sulfuric acid, phosphoric acid and oxalic acid hydrolyzed corn stover to the 51.1g/L of glucose (0.50g/g cellulose) and 18.1g/L of xylose (0.22g/g xylan). The furfural, 5-hydroxymethylfurfural and acetic acid in the corn stover hydrolysate were completely removed by Paecilomyces variotii FN89, leading to the successful ethanol fermentation of 24.2g/L, corresponding to 72.6kg per metric ton of dry corn stover. No wastewater streams, solid wastes and toxic compounds were generated in hydrolysis, biodetoxification and fermentation. The techno-economic evaluations suggest that the cost reduction of replacing cellulase enzyme with cheap acid catalysts compensated the partial ethanol loss of sugar conversion to inhibitors (21.5-89.1%). The re-examination of acid hydrolysis process reveals that a substantial breakthrough in highly active and selective acid catalyst is required for acid hydrolysis to compete with enzymic hydrolysis for cellulosic ethanol fermentation.

Resource recovery from lignocellulosic wastes via biological technologies: Advancements and prospects

Lignocellulosic wastes were recently considered as biomass resources, however, its conversion to valuable products is still immature although researchers have put lots of effort into this issue. This article reviews the key challenges of the biorefinery utilizing lignocellulosic materials and recent developments to conquer those obstacles. Available biological techniques and processes, from the pretreatments of cellulosic materials to the valorization processes, were emphasized. Biological pretreatments, including hydrolysis using microbial consortia, fungi, enzymes, engineered bacterial/fungal strains, and co-culture systems, could enhance the release of reducing sugar. Resources recovery, including biogases, ethanol, butanol, PHA, etc., from lignocellulosic materials were also discussed, while the influences of composition of lignocellulosic materials and pretreatment options, applications of co-culture system, and integrated treatments with other wastes, were described. In the review, co-culture system and metabolic engineering are emphasized as the promising biological technologies, while perspectives are provided for their future developments.

Formulating a fully converged biorefining chain with zero wastewater generation by recycling stillage liquid to dry acid pretreatment operation

Huge wastewater generation is the major challenge of biorefinery technology for production of cellulosic ethanol. This study designed and verified a method for completely recycling of wastewater stream (the stillage liquid from the beer column) in cellulosic ethanol production by dry biorefining processing. When the stillage liquid was directly recycled to dry acid pretreatment operation, ethanol production gradually reduced after two recycles primarily because the inorganic compounds accumulated by around 139%. To ultimately solve this technical barrier, the stillage liquid was evaporated and condensed into distillated water, then recycled to the pretreatment for complete dry biorefining process. This strategy supported a stable cellulosic ethanol production, and the overall mass and heat balance confirmed that only 65% of the lignin residue consumption was used for wastewater evaporation with 35% surplus for electricity generation. This study provided a fully converged biorefining process with a closed-loop wastewater recycling.

Superior adsorption capacity of functionalised straw adsorbent for dyes and heavy-metal ions

Dyes and heavy-metal ions are common pollutants in printing and dyeing wastewater, and are thus attracting considerable attention. Herein, an eco-friendly straw-based adsorbent, WS-CA-AM, was prepared by grafting with acrylamide (AM) and citric acid (CA) groups to remove representative dyes and heavy metals from aqueous solution. The adsorption capacities of WS-CA-AM for methyl orange (MO) and methylene blue (MB) were 3053.48 and 120.84 mg/g, which were 54 and 3 times those of unmodified straw, respectively. Moreover, the adsorption capacities for MB, MO, Cr₂O₇^2- and Cu²⁺ in the mixed system increased by 210%, 133%, 196% and 151%, respectively, compared with those in the single system. The significant increase in adsorption capacity can be attributed to the collaborative effect through electrostatic attraction. The functional groups and adsorbed pollutants all served as adsorption sites for pollutants. These results indicate that WS-CA-AM is a potential applicant for the removal of dyes and heavy-metal ions from mixed aqueous solution.

Pyrolysis Characteristics and Reaction Mechanisms of Pine Needles

Pyrolysis has been considered as a promising method to utilize biomass by thermal cracking for energy or feedstock. In order to provide guidance for thermochemical process management of pine needle utilization by pyrolysis, the pyrolysis kinetics and reaction mechanism of one typical pine needle are investigated employing thermogravimetric analysis in nitrogen in the present study. Multi kinetics methods including model-free method and model-fitting method are adopted. Results indicate that one peak and three shoulders occur in the reaction rate curves. The maximum reaction rates decrease with the increasing of heating rates, and the average reaction rate of the whole process is 0.0021 K^-1. The pyrolysis process of pine needles in nitrogen may be divided into four stages in the conversion rate range of 0~0.1, 0.1~0.5, 0.5~0.75, and 0.75~1, which may be mainly resulted by the reaction of the extractives, hemicellulose, cellulose, and lignin, respectively. The reaction mechanisms of stages I, II, and III may be regarded as random nucleation and nuclei growth, but the reaction mechanism of stage IV may be chemical reaction. The average value of activation energy and logarithm of the pre-exponential factor for the whole pyrolysis process is 215.99 kJ mol^-1 and 38.75 min^-1, respectively.