Biological pretreatment of lignocellulosic biomass--An overview

Comparison of enzymatic saccharification and lignin structure of masson pine and poplar pretreated by p-Toluenesulfonic acid

p-Toluenesulfonic acid (p-TsOH) with the hydrotropic and recyclable properties is widely used for rapid remove of lignin from lignocelluloses at low temperature (<100 °C). In this work, both softwood masson pine and hardwood poplar were pretreated with p-TsOH under different conditions and then subjected to enzymatic hydrolysis to compare the effect of p-TsOH pretreatment on their saccharification and lignin structure. Results showed p-TsOH has sensitive selectivity to lignin structure during pretreatment. Around 95% of lignin in poplar can be dissolved at 80 °C within 30 min, while for masson pine, the delignification is only 50%. Following enzymatic hydrolysis with cellulase loading of 20 FPU/g-cellulose for 72 h, the highest sugar yield of pretreated poplar and masson pine is 92.13% and 29.46%, respectively, which indicates that p-TsOH pretreatment alone works well with hardwoods (poplar). Structural analysis of removed lignin implies that p-TsOH mainly results in the cleavage of β-aryl ether bonds of lignin side chains, and the aromatic structure of lignin keeps intact. p-TsOH pretreatment shows the key advantages of low cost and rapid delignification for highly enzymatic saccharification, and provides a promising and green pathway for the development of low cost and sustainable bio-based products for developing a bio-based economy.

The Effect of Mechanocatalytic Pretreatment on the Structure and Depolymerization of Willow

In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. The milling parameters, such as the rotation speed of the mill, the catalyst-to-willow ratio, and the milling time influenced the amount of sugars in the hydrolysate and the composition of the sugar solution produced. Changes were observed in the surface of the willow particles as well as changes in the crystalline structure. Glucose and xylose yields increased after 15 min of milling and reached their maximum level after 45 min of milling with the 0.5 mmol/g sulfuric acid load.

Recent advances in the pretreatment of microalgal and lignocellulosic biomass: A comprehensive review

Microalgal and lignocellulosic biomass is the most sumptuous renewable bioresource raw material existing on earth. Recently, the bioconversion of biomass into biofuels have received significant attention replacing fossil fuels. Pretreatment of biomass is a critical process in the conversion due to the nature and structure of the biomass cell wall that is complex. Although green technologies for biofuel production are advancing, the productivity and yield from these techniques are low. Over the past years, various pretreatment techniques have been developed and successfully employed to improve the technology. This paper presents an in-depth review of the recent advancement of pretreatment methods focusing on microalgal and lignocellulosic biomass. The technological approaches involving physical, chemical, biological and other latest pretreatment methods are reviewed.

Biomolecules from municipal and food industry wastes: An overview

Biological wastes generated from food and fruit processing industries, municipal markets, and water treatment facilities are a major cause of concern for Health Departments and Environmentalists around the world. Conventional means of managing these wastes such as transportation, treatment, and disposal, are proving uneconomical. The need is to develop green and sustainable technologies to circumvent this ever-growing and persistent problem. In this article, the potential of diverse microbes to metabolize complex organic rich biowastes into a variety of bioactive compounds with diverse biotechnological applications have been presented. An integrated strategy has been proposed that can be commercially exploited for the recovery of value-adding products ranging from bioactive compounds, chemical building blocks, energy rich chemicals, biopolymers and materials, which results in a self-sustaining circular bioeconomy with nearly zero waste generation and complete degradation.

Towards the Properties of Different Biomass-Derived Proteins via Various Extraction Methods

This study selected three representative protein-rich biomass-brewer's spent grain (BSG), pasture grass (PG), and cyanobacteria (Arthrospira platensis; AP) for protein extraction with different extraction methods (alkaline treatment, aqueous extraction, and subcritical water extraction). The yield, purity, molecular weight, oil-water interfacial tension, and thermal stability of the obtained proteins derived from different biomass and extraction methods were comprehensively characterized and compared. In the view of protein yield and purity, alkaline treatment was found optimal for BSG (21.4 and 60.2 wt.%, respectively) and AP (55.5 and 68.8 wt.%, respectively). With the decreased oil-water interfacial tension, the proteins from all biomass showed the potential to be emulsifier. BSG and AP protein obtained with chemical treatment presented excellent thermal stability. As a novel method, subcritical water extraction is promising in recovering protein from all three biomass with the comparable yield and purity as alkaline treatment. Furthermore, the hydrolyzed protein with lower molecular weight by subcritical water could promote its functions of foaming and emulsifying.

Polyhydroxyalkanoate (PHA) biosynthesis from directly valorized ragi husk and sesame oil cake by Bacillus megaterium strain Ti3: Statistical optimization and characterization

Polyhydroxyalkanoates (PHAs) signify the most promising biological substitute to petrochemical plastics. Renewable and inexpensive agro-industrial by-products can be used as potent fermentation feedstocks for sustainable PHA biosynthesis. This study aimed at using a wild type B. megaterium strain Ti3 innate hydrolytic enzyme/s for eco-friendly valorization of 16 lignocellulosic agrowastes to PHA without pretreatments. Initial hydrolytic screening PHA concentration of (0.04-0.17 g/L), highlighted the strain's metabolic versatility. Pareto ranking of Taguchi orthogonal array (TOA) established ragi husk (RH), sesame oil cake (SOC) and KH₂PO₄ as the most influential factors (p < 0.05). The optimized and validated Response surface methodology (RSM) model (R², 0.979; desirability, 1) resulted in 3.8 and 3.6 fold increased PHA production, 4.3 and 3.25 fold increased PHA productivity. A positive correlation (r², 0.5-0.97) was observed amid the producer innate hydrolytic enzymes (lipase, amylase and cellulase) and PHA production. The PHA was characterized by ¹H and ¹³C NMR, GPC, TGA. The polymer was identified as a scl-mcl copolyester with 92% 3HB (3-hydroxybutyrate) and 8% 3HHp (3-hydroxyheptanoate) monomers by NMR. This the first report on B. megaterium self-enzyme reliant non-food agrowastes bioconversion to PHA with 3HHp (3-hydroxyheptanoate) monomers excluding precursor addition, commercial enzymes, pure carbon and nitrogen sources.

Enhancement of the anti-inflammatory properties of grape pomace treated by Trametes versicolor

The application of solid-state fermentation for the production of value-added products from the agro- and food-industry residues has been recently investigated greatly.

Microwave support of the alcoholic fermentation process of cyanobacteria Arthrospira platensis

The search for a balance between the energy-related challenges of the future and providing nutritional security has resulted in the development of a market for biofuels of successive generations. The larger their portion in biofuel production, the less the prices of agricultural products will increase. The use of algae, cyanobacteria and aquatic plants in the production of liquid fuels is an alternative. The aim of this study was to determine the effect of thermal hydrolysis on degradation of polysaccharides contained in biomass of cyanobacteria Arthrospira platensis and to assess the effectiveness of ethanol production from preconditioned biomass. The study is aimed at the selection of the most advantageous parameters of thermochemical hydrolysis to reach the experiment variant with the best effects, degree of polysaccharide degradation and effectiveness of alcohol fermentation. The experiment was divided into two stages; in stage I, the possibility of obtaining fermentable sugars by hydrothermal and chemical treatment of the substrate was tested. Stage II involved an assessment of the effectiveness of the pretreatment methods to produce bioethanol in alcohol fermentation. Yeast used in industrial ethanol production-Saccharomyces cerevisiae As4-was used in the alcohol fermentation. The results have shown that the temperature of 150 °C was the most beneficial for the process of thermohydrolysis, and the mash in the microwave-heated sample contained the highest concentration of alcohol (0.97 g/l), which is 98% more than in the control mash and 37% more than in the conventionally heated sample.

Multi-perspective analyses of rice straw modification by Pleurotus ostreatus and effects on biomethane production

Multi-perspective analyses were carried out to investigate the effect of rice straw modification for 45 days by P. ostreatus on biomethane of production. The results showed that rice straw modified for 25 days achieved the highest biomethane yield of 269 mL·g^-1 VS, which was a 26.9% improvement compared with non-modified rice straw. The multi-perspective analyses demonstrated that the improvement resulted from fungal enzymatic reactions, which led to changes in the physicochemical properties of rice straw. The porosity, surface area, acetyl group abundance, degree of polymerization, and lignin degradation selectivity of rice straw modified for 25 days were optimal for enzyme adsorption. Compared with non-modified rice straw, the adsorption of cellulase and xylanase on rice straw modified for 25 days was increased by 18.8% and 58.1%, respectively, which facilitated biomethane production. The study indicated that P. ostreatus is effective for improving biomethane production from rice straw.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Brassinosteroid overproduction improves lignocellulose quantity and quality to maximize bioethanol yield under green-like biomass process in transgenic poplar

BACKGROUND

As a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals. However, lignocellulose recalcitrance particularly in wood plants, basically causes a costly bioethanol production unacceptable for commercial marketing with potential secondary pollution to the environment. Therefore, it becomes important to reduce lignocellulose recalcitrance by genetic modification of plant cell walls, and meanwhile to establish advanced biomass process technology in woody plants. Brassinosteroids, plant-specific steroid hormones, are considered to participate in plant growth and development for biomass production, but little has been reported about brassinosteroids roles in plant cell wall assembly and modification. In this study, we generated transgenic poplar plant that overexpressed DEETIOLATED2 gene for brassinosteroids overproduction. We then detected cell wall feature alteration and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments.

RESULTS

Compared with wild type, the PtoDET2 overexpressed transgenic plants contained much higher brassinosteroids levels. The transgenic poplar also exhibited significantly enhanced plant growth rate and biomass yield by increasing xylem development and cell wall polymer deposition. Meanwhile, the transgenic plants showed significantly improved lignocellulose features such as reduced cellulose crystalline index and degree of polymerization values and decreased hemicellulose xylose/arabinose ratio for raised biomass porosity and accessibility, which led to integrated enhancement on biomass enzymatic saccharification and bioethanol yield under various chemical pretreatments. In contrast, the CRISPR/Cas9-generated mutation of PtoDET2 showed significantly lower brassinosteroids level for reduced biomass saccharification and bioethanol yield, compared to the wild type. Notably, the optimal green-like pretreatment could even achieve the highest bioethanol yield by effective lignin extraction in the transgenic plant. Hence, this study proposed a mechanistic model elucidating how brassinosteroid regulates cell wall modification for reduced lignocellulose recalcitrance and increased biomass porosity and accessibility for high bioethanol production.

CONCLUSIONS

This study has demonstrated a powerful strategy to enhance cellulosic bioethanol production by regulating brassinosteroid biosynthesis for reducing lignocellulose recalcitrance in the transgenic poplar plants. It has also provided a green-like process for biomass pretreatment and enzymatic saccharification in poplar and beyond.

Structural Motifs of Wheat Straw Lignin Differ in Susceptibility to Degradation by the White-Rot Fungus Ceriporiopsis subvermispora

The white-rot fungus Ceriporiopsis subvermispora delignifies plant biomass extensively and selectively and, therefore, has great biotechnological potential. We previously demonstrated that after 7 weeks of fungal growth on wheat straw 70% w/w of lignin was removed and established the underlying degradation mechanisms via selectively extracted diagnostic substructures. In this work, we fractionated the residual (more intact) lignin and comprehensively characterized the obtained isolates to determine the susceptibility of wheat straw lignin's structural motifs to fungal degradation. Using 13C IS pyrolysis gas chromatography-mass spectrometry (py-GC-MS), heteronuclear single quantum coherence (HSQC) and 31P NMR spectroscopy, and size-exclusion chromatography (SEC) analyses, it was shown that β-O-4' ethers and the more condensed phenylcoumarans and resinols were equally susceptible to fungal breakdown. Interestingly, for β-O-4' ether substructures, marked cleavage preferences could be observed: β-O-4'-syringyl substructures were degraded more frequently than their β-O-4'-guaiacyl and β-O-4'-tricin analogues. Furthermore, diastereochemistry (threo > erythro) and γ-acylation (γ-OH > γ-acyl) influenced cleavage susceptibility. These results indicate that electron density of the 4'-O-coupled ring and local steric hindrance are important determinants of oxidative β-O-4' ether degradation. Our findings provide novel insight into the delignification mechanisms of C. subvermispora and contribute to improving the valorization of lignocellulosic biomass.

Application of industrial amylolytic yeast strains for the production of bioethanol from broken rice

Amylolytic Saccharomyces cerevisiae derivatives of Ethanol Red™ Version 1 (ER T12) and M2n (M2n T1) were assessed through enzyme assays, hydrolysis trials, electron microscopy and fermentation studies using broken rice. The heterologous enzymes hydrolysed broken rice at a similar rate compared to commercial granular starch-hydrolysing enzyme cocktail. During the fermentation of 20% dw/v broken rice, the amylolytic strains converted rice starch to ethanol in a single step and yielded high ethanol titers. The best-performing strain (ER T12) produced 93% of the theoretical ethanol yield after 96 h of consolidated bioprocessing (CBP) fermentation at 32 °C. Furthermore, the addition of commercial enzyme cocktail (10% of the recommended dosage) in combination with ER T12 did not significantly improve the maximum ethanol concentration, confirming the superior ability of ER T12 to hydrolyse raw starch. The ER T12 strain was therefore identified as an ideal candidate for the CBP of starch-rich waste streams.

Thermotolerant cellulolytic Clostridiaceae and Lachnospiraceae rich consortium enhanced biogas production from oil palm empty fruit bunches by solid-state anaerobic digestion

Thermotolerant cellulolytic consortium for improvement biogas production from oil palm empty fruit bunches (EFB) by prehydrolysis and bioaugmentation strategies was investigated via solid-state anaerobic digestion (SS-AD). The prehydrolysis EFB with Clostridiaceae and Lachnospiraceae rich consortium have maximum methane yield of 252 and 349 ml CH₄ g^-1 VS with total EFB degradation efficiency of 62% and 86%, respectively. Clostridiaceae and Lachnospiraceae rich consortium augmentation in biogas reactor have maximum methane yield of 217 and 85.2 ml CH₄ g^-1 VS with degradation efficiency of 42% and 16%, respectively. The best improvement of biogas production was achieved by prehydrolysis EFB with Lachnospiraceae rich consortium with maximum methane production of 113 m³ CH₄ tonne^-1 EFB. While, Clostridiaceae rich consortium was suitable for augmentation in biogas reactor with maximum methane production of 70.6 m³ CH₄ tonne^-1 EFB. Application of thermotolerant cellulolytic consortium into the SS-AD systems could enhance biogas production of 3-11 times.

Microbial dynamics for lignocellulosic waste bioconversion and its importance with modern circular economy, challenges and future perspectives

An extensive use of microbial dynamics for utilizing the lignocellulosic wastes has been attributed to their efficiency in bioenergy and bioproducts development as a cost effective high nutritional value. The integration of lignocellulosic waste into the circular economy can scaleup the sustainable bioproducts and bioenergy development. In this review paper, the aim is to describe the existing research efforts on organic lignocellulosic waste, cellulase producing microbes, their potential enzyme, modern circular economy with associated challenges and future perspectives. Presently, it has been reviewed that microbial cellulases have provided treasure bioproducts visions into industrial bioproducts marvels unveiled through lignocellulosic waste cutting-edge microbial explorations. Furthermore, the review focused on new insights of the growing circular economy of lignocellulosic waste used for many bioproducts and bioenergy dealings and explored the emergent lignocellulosic biorefinery approaches which could then be applied to review industrial-scale sustainable economic models for upgraded bioproducts and other production associated problems.

A Review on Anaerobic Digestion of Lignocellulosic Wastes: Pretreatments and Operational Conditions

Anaerobic digestion (AD) has become extremely popular in the last years to treat and valorize organic wastes both at laboratory and industrial scales, for a wide range of highly produced organic wastes: municipal wastes, wastewater sludge, manure, agrowastes, food industry residuals, etc. Although the principles of AD are well known, it is very important to highlight that knowing the biochemical composition of waste is crucial in order to know its anaerobic biodegradability, which makes an AD process economically feasible. In this paper, we review the main principles of AD, moving to the specific features of lignocellulosic wastes, especially regarding the pretreatments that can enhance the biogas production of such wastes. The main point to consider is that lignocellulosic wastes are present in any organic wastes, and sometimes are the major fraction. Therefore, improving their AD could cause a boost in the development in this technology. The conclusions are that there is no unique strategy to improve the anaerobic biodegradability of lignocellulosic wastes, but pretreatments and codigestion both have an important role on this issue.

Genetically encoded biosensors for lignocellulose valorization

Modern society is hugely dependent on finite oil reserves for the supply of fuels and chemicals. Moving our dependence away from these unsustainable oil-based feedstocks to renewable ones is, therefore, a critical factor towards the development of a low carbon bioeconomy. Lignin derived from biomass feedstocks offers great potential as a renewable source of aromatic compounds if methods for its effective valorization can be developed. Synthetic biology and metabolic engineering offer the potential to synergistically enable the development of cell factories with novel biosynthetic routes to valuable chemicals from these sustainable sources. Pathway design and optimization is, however, a major bottleneck due to the lack of high-throughput methods capable of screening large libraries of genetic variants and the metabolic burden associated with bioproduction. Genetically encoded biosensors can provide a solution by transducing the target metabolite concentration into detectable signals to provide high-throughput phenotypic read-outs and allow dynamic pathway regulation. The development and application of biosensors in the discovery and engineering of efficient biocatalytic processes for the degradation, conversion, and valorization of lignin are paving the way towards a sustainable and economically viable biorefinery.

Nature's recyclers: anaerobic microbial communities drive crude biomass deconstruction

Microbial communities within anaerobic ecosystems have evolved to degrade and recycle carbon throughout the earth. A number of strains have been isolated from anaerobic microbial communities, which are rich in carbohydrate active enzymes (CAZymes) to liberate fermentable sugars from crude plant biomass (lignocellulose). However, natural anaerobic communities host a wealth of microbial diversity that has yet to be harnessed for biotechnological applications to hydrolyze crude biomass into sugars and value-added products. This review highlights recent advances in 'omics' techniques to sequence anaerobic microbial genomes, decipher microbial membership, and characterize CAZyme diversity in anaerobic microbiomes. With a focus on the herbivore rumen, we further discuss methods to discover new CAZymes, including those found within multi-enzyme fungal cellulosomes. Emerging techniques to characterize the interwoven metabolism and spatial interactions between anaerobes are also reviewed, which will prove critical to developing a predictive understanding of anaerobic communities to guide in microbiome engineering.

Comparing impacts of physicochemical properties and hydrolytic inhibitors on enzymatic hydrolysis of sugarcane bagasse

An autohydrolysis pretreatment with different conditions was applied to sugarcane bagasse to compare the impacts of the physicochemical properties and hydrolytic inhibitors on its enzymatic hydrolysis. The results indicate that the autohydrolysis conditions significantly affected the physicochemical properties and inhibitors, which further affected the enzymatic hydrolysis. The inhibitor amount, pore size, and crystallinity degree increased with increasing autohydrolysis severity. Furthermore, the enzymatic hydrolysis was enhanced with increasing severity owing to the removal of hemicellulose and lignin. The physicochemical obstruction impeded the enzymatic hydrolysis more than the inhibitors. The multivariate correlated component regression analysis enabled an evaluation of the correlations between the physicochemical properties (and inhibitors) and enzymatic hydrolysis for the first time. According to the results, an autohydrolysis with a severity of 4.01 is an ideal pretreatment for sugarcane bagasse for sugar production.

Self-fusion and fusion cell isolation of transformants derived from white rot fungus Phanerochaete sordida YK-624 by simple visual method

In order to develop a simple method for crossing two transformants, we first attempted to elucidate the fusion type (self-compatibility or -incompatible) of Phanerochaete sordida YK-624. Two transformants expressing green or red fluorescent protein derived from an auxotrophic mutant were constructed. Each recombinant protein fluoresced by expression as a fused protein with glyceraldehyde-3-phosphate dehydrogenase. On co-culture of both transformants, a number of sequential hyphal cells emitting dual fluorescence were formed at the contact areas of both hyphae. Some of the single cells isolated as protoplasts and chlamydospore from the co-cultures also expressed these fluorescent proteins. These results suggest that P. sordida YK-624 possesses a self-compatible fusion system. In addition, transformant strains with different fluorescence derived from this fungus can readily undergo self-fusion and nuclear interchange events by confrontational and mixed cultivation, and we developed a simple method that allows fused cells to be isolated as chlamydospores.

Insight into Pretreatment Methods of Lignocellulosic Biomass to Increase Biogas Yield: Current State, Challenges, and Opportunities

Lignocellulosic biomass is recalcitrant due to its heterogeneous structure, which is one of the major limitations for its use as a feedstock for methane production. Although different pretreatment methods are being used, intermediaries formed are known to show adverse effect on microorganisms involved in methane formation. This review, apart from highlighting the efficiency and limitations of the different pretreatment methods from engineering, chemical, and biochemical point of views, will discuss the strategies to increase the carbon recovery in the form of methane by way of amending pretreatments to lower inhibitory effects on microbial groups and by optimizing process conditions.

High-solid pretreatment of rice straw at cold temperature using NaOH/Urea for enhanced enzymatic conversion and hydrogen production

A high-solid loading pretreatment using NaOH/Urea solution at -12 °C was proposed to pretreat rice straw (RS) for enhanced saccharify and hydrogen production. Results shown NaOH/Urea pretreatment exhibited excellent pretreatment performance at solid loading ranged from 10% to 100% (w/v) with an average reducing sugar conversion of 80.22% was obtained which was 31.89% higher than that untreated RS. Upon fermentation of 100% solid loading pretreated hydrolysate, the H₂ yield of 72.5 mL/g-pretreated RS was calculated based on substrate consumption, which enabled 49.5% higher reducing sugar transfer to H₂ through material balance. FTIR and XRD analysis further demonstrated that the cold NaOH/Urea pretreatment at 100% (w/v) could effectively disrupt the lignin structure and decrease the cellulose crystallinity. The present study suggested a high solid loading pretreatment with NaOH/Urea at cold temperature could be a valuable alternative for better techno-economic of the lignocelluloses - to - sugars - to H₂ routes.

Conversion of depolymerized sugars and aromatics from engineered feedstocks by two oleaginous red yeasts

One of the requirements for efficient biological conversion of lignocellulose to bioproducts is the compatibility of biological catalysts with the processes employed to solubilize and depolymerize the lignocellulosic components. The red yeasts Rhodosporidium toruloides and Rhodotorula mucilaginosa were evaluated for their ability to assimilate sugars and aromatic compounds extracted from two engineered lines of Arabidopsis thaliana with modified lignin or the wild-type using ionic liquid, acid or alkaline pretreatments. Differential amounts of monomeric sugars, organic acids and, in the case of the engineered lines, either 4-hydroxybenzoic or protocatechuic acid were additionally released from the biomass and found to be tolerated and consumed by both microorganisms. Genetically-engineered strains of the two red yeasts successfully converted the depolymerized products into the biofuel precursor bisabolene when cultivated on hydrolysates or synthetic media containing specific sugars, acids and aromatics found in the hydrolysates.

Pretreatment Efficiency Using Autoclave High-Pressure Steam and Ultrasonication in Sugar Production from Liquid Hydrolysates and Access to the Residual Solid Fractions of Wheat Bran and Oat Hulls

The objective of this study was to evaluate the combination of physical and chemical pretreatments of wheat bran (WB) and oat hulls (OH) to obtain fermentable sugars and a residual solid fraction with increased susceptibility to enzymatic hydrolysis. High-pressure steam in an autoclave and ultrasonication were employed as pretreatments, and for both processes, WB and OH were treated with sulfuric acid (H₂SO₄), neutral medium (H₂O) and sodium hydroxide (NaOH). Autoclave high-pressure steam in an acid medium was the most effective for the release of sugars (total sugars, xylose and glucose) from liquid hydrolysates and for the modification of the residual solid fraction. The cellulose content of the WB residual solid fraction increased from 7.19 to 39.17%, the lignin fraction of WB decreased from 6.40 to 3.21%, the cellulose content of OH increased from 31.16 to 61.53%, and lignin fraction of OH decreased from 18.12 to 7.24%, resulting in materials more susceptible to enzymatic hydrolysis.

Furfural wastewater pretreatment of corn stalk for whole slurry anaerobic co-digestion to improve methane production

Previous studies showed that excellent anaerobic digestion performance could be achieved using acid pretreatment, whereas the development of acid pretreatment was limited by high cost of acid consumption and severe operation. The aim of this study consisted in expanding the possibilities of low-cost acid pretreatment method for anaerobic digestion. For this, the feasibility of substituting conventional acid pretreatment with furfural wastewater was verified, and the whole slurry anaerobic digestion was performed to improve the production of methane. The furfural wastewater was used to pretreat crop stalk at different ambient temperatures (20, 35, 50°C) for different time periods (0, 3, 6, 9days). Subsequently, all treated and untreated crop stalk were digested at 35°C for 25days. According to experimental data showed that the dissimilar degradability of compositions for crop stalk was due to furfural wastewater pretreatment, and the reducing sugar content, volatile fatty acid content, pH during pretreatment phase, and their initial maximum & minimum values in anaerobic digestion phase were changed, which made a significant difference in methane production. The highest total methane production of anaerobic digestion (196.68mL/g VS) was achieved by the treatment at 35°C for 6days, which was 59.28% higher than untreated crop stalk (123.48mL/g VS). On the whole, the results showed that furfural wastewater pretreatment followed by the whole slurry anaerobic co-digestion was feasible and could contribute to application value for anaerobic digestion industry while providing an effective way for the treatment of furfural wastewater.

Pretreatment of Miscanthus with biomass-degrading bacteria for increasing delignification and enzymatic hydrolysability

Biomass recalcitrance is still a main challenge for the production of biofuels and high-value products. Here, an alternative Miscanthus pretreatment method by using lignin-degrading bacteria was developed. Six efficient Miscanthus-degrading bacteria were first cultured to produce laccase by using 0.5% Miscanthus biomass as carbon source. After 1-5 days of incubation, the maximum laccase activities induced by Miscanthus in the six strains were ranged from 103 to 8091 U l-1 . Then, the crude enzymes were directly diluted by equal volumes of citrate buffer and added Miscanthus biomass to a solid concentration at 4% (w/v). The results showed that all bacterial pretreatments significantly decreased the lignin content, especially in the presence of two laccase mediators (ABTS and HBT). The lignin removal directly correlated with increases in total sugar and glucose yields after enzymatic hydrolysis. When ABTS was used as a mediator, the best lignin-degrading bacteria (Pseudomonas sp. AS1) can remove up to 50.1% lignin of Miscanthus by obtaining 2.2-fold glucose yield, compared with that of untreated biomass. Therefore, this study provided an effective Miscanthus pretreatment method by using lignin-degrading bacteria, which may be potentially used in improving enzymatic hydrolysability of biomass.

Choosing Physical, Physicochemical and Chemical Methods of Pre-Treating Lignocellulosic Wastes to Repurpose into Solid Fuels

Various methods of physical, chemical and combined physicochemical pre-treatments for lignocellulosic biomass waste valorisation to value-added feedstock/solid fuels for downstream processes in chemical industries have been reviewed. The relevant literature was scrutinized for lignocellulosic waste applicability in advanced thermochemical treatments for either energy or liquid fuels. By altering the overall naturally occurring bio-polymeric matrix of lignocellulosic biomass waste, individual components such as cellulose, hemicellulose and lignin can be accessed for numerous downstream processes such as pyrolysis, gasification and catalytic upgrading to value-added products such as low carbon energy. Assessing the appropriate lignocellulosic pre-treatment technology is critical to suit the downstream process of both small- and large-scale operations. The cost to operate the process (temperature, pressure or energy constraints), the physical and chemical structure of the feedstock after pre-treatment (decomposition/degradation, removal of inorganic components or organic solubilization) or the ability to scale up the pre-treating process must be considered so that the true value in the use of bio-renewable waste can be revealed.

Solid State Fermentation of Brewers’ Spent Grains for Improved Nutritional Profile Using Bacillus subtilis WX-17

Brewers’ spent grains (BSG) are underutilized food waste materials produced in large quantities from the brewing industry. In this study, solid state fermentation of BSG using Bacillus subtilis WX-17 was carried out to improve the nutritional value of BSG. Fermenting BSG with the strain WX-17, isolated from commercial natto, significantly enhanced the nutritional content in BSG compared to unfermented BSG, as determined by the marked difference in the level of metabolites. In total, 35 metabolites showed significant difference, which could be categorized into amino acids, fatty acids, carbohydrates, and tricarboxylic acid cycle intermediates. Pathway analysis revealed that glycolysis was upregulated, as indicated by the drop in the level of carbohydrate compounds. This shifted the metabolic flux particularly towards the amino acid pathway, leading to a 2-fold increase in the total amount of amino acid from 0.859 ± 0.05 to 1.894 ± 0.1 mg per g of BSG after fermentation. Also, the total amount of unsaturated fatty acid increased by 1.7 times and the total antioxidant quantity remarkably increased by 5.8 times after fermentation. This study demonstrates that novel fermentation processes can value-add food by-products, and valorized food waste could potentially be used for food-related applications. In addition, the study revealed the metabolic changes and mechanisms behind the microbial solid state fermentation of BSG.

Overcoming challenges in lignocellulosic biomass pretreatment for second-generation (2G) sugar production: emerging role of nano, biotechnological and promising approaches

Production of green chemicals and biofuels in biorefineries is the potential alternative for petrochemicals and gasoline in transitioning of petro-economy into bioeconomy. However, an efficient biomass pretreatment process must be considered for the successful deployment of biorefineries, mainly for use of lignocellulosic raw materials. However, biomass recalcitrance plays a key role in its saccharification to obtain considerable sugar which can be converted into ethanol or other biochemicals. In the last few decades, several pretreatment methods have been developed, but their feasibility at large-scale operations remains as a persistent bottleneck in biorefineries. Pretreatment methods such as hydrodynamic cavitation, ionic liquids, and supercritical fluids have shown promising results in terms of either lignin or hemicellulose removal, thus making remaining carbohydrate fraction amenable to the enzymatic hydrolysis for clean and high amount of fermentable sugar production. However, their techno-economic feasibility at industrial scale has not been yet studied in detail. Besides, nanotechnological-based technologies could play an important role in the economically viable 2G sugar production in future. Considering these facts, in the present review, we have discussed the existing promising pretreatment methods for lignocellulosic biomass and their challenges, besides this strategic role of nano and biotechnological approaches towards the viability and sustainability of biorefineries is also discussed.

Optimization of dilute sulfuric acid, aqueous ammonia, and steam explosion as the pretreatments steps for distillers' dried grains with solubles as a potential fermentation feedstock

Distillers' dried grains with solubles (DDGS) is the by-product of bioethanol production from starch-rich grains through dry-mill fermentation. In this study, dilute sulfuric acid hydrolysis, aqueous ammonia, and steam explosion as the pre-treatment methods were optimized. The central composite response surface methodology (RSM) design was used for optimization of dilute acid pretreatment, aqueous ammonia pretreatment. The steam explosion trials were evaluated. The results show that the dilute acid pretreatment at 121 °C is the most effective way of obtaining simple fermentable sugars (0.382 g/g DDGS). The levels of furfural and HMF was also 5.2 mg/g DDGS) and 1.6 mg/g DDGS, respectively, in the dilute sulfuric acid pretreated DDGS. On the other hand, maximum sugar yield for ammonia pretreatment was 0.129 g/g DDGS and 0.055 g/g DDGS for the steam pretreatment, while no significant amounts of furfural and HMF were observed for these two pretreatment methods.

Harvesting of intact microalgae in single and sequential conditioning steps by chemical and biological based - flocculants: Effect on harvesting efficiency, water recovery and algal cell morphology

Quick algae harvesting methodologies relating optimum flocculent dose (D_Opt.), percentage harvesting efficiency (%HE) and percentage water recovery (%W_Recovery) to the in-situ hydrodynamic properties of water-algae systems are presented. Flocculation of three microalgae in single and sequential steps, using chemical (polymer and ferric chloride) and biological (egg shells) flocculants, was studied. Zeta potential and pH analysis were completed to further understand the flocculation mechanism. Polymer at D_Opt. of 7.0 g/kgDS resulted in W_Recovery of 90% and %HE of 96.7%. Lower %HE (92.1), %W_Recovery (79) and noticeable algal cells deformation was observed for ferric chloride at D_Opt. of 7.0 g/kg DS. Bio-flocculant conserved algal structure and resulted in %HE of 96.2 and %W_Recovery of 90 at D_Opt. of 5.4 g/kgDS. Significant % HE of 99.8, %W_Recovery of 99.8%, and up to 95% reduction in D_Opt. were achieved in sequential flocculation. The results established the effectiveness and suitability of sequential/ bio-flocculation for algae harvesting.

Effect of Novel Pretreatment of Steam Explosion Associated with Ammonium Sulfite Process on Enzymatic Hydrolysis of Corn Straw

Effective pretreatment process to improve enzymatic saccharification and decrease inhibitors generation is a key operation involved in the lignocellulosic bioconversion. The pretreatment of steam explosion associated with ammonium sulfite (SEAS) process was carried out to investigate the effect on enzymatic hydrolysis and fermentation production as a combinatorial pretreatment. Results showed that after pretreatment (1.0 MPa, 30 min, 20%w/w ammonium sulfite added), the phenolic inhibitors derived from lignin significantly removed (37.8%), which transformed to chemical humic acid (humic acid and fulvic acid) mostly. Sugar conversion (glucan (77.8%) and xylan (73.3%)) and ethanol concentration (40.8 g/L) of combinatorial pretreated samples were increased by 24.7% and 33.8%, respectively, compared with steam explosion (SE) pretreated samples. FT-IR and elemental analysis results indicated that the lignin structure changed and aromatization degree increased after SEAS pretreatment. In addition, the ratio of C/N decreased and compost maturity degree increased with the holding time. The effect on the growth of wheat seedlings of soluble fulvic acid solution from combinatorial pretreatment was investigated, where below 1% (w/w) concentration did contribute to growth. Therefore, one-step chemical pretreatment process could be provided for inhibitors removal, enzymatic saccharification increase, and chemical humic acid formation as well.

Depolymerization of lignocellulose of oil palm empty fruit bunch by thermophilic microorganisms from tropical climate

Previous studies on screening of lignin-degrading bacteria mainly focused on the ligninolytic ability of the isolated bacteria for the utilization of lignin monomers. In this study, we focused on the depolymerization of alkali lignin to prove the ability of the isolated thermophilic bacterial strains to utilize and depolymerize more than a monomer of alkali lignin within 7 days of incubation. Indigenous thermophilic bacterial isolates from the palm oil plantation were used to evaluate the depolymerization and utilization of alkali lignin. The confirmation of the bacterium-mediated depolymerization of oil palm empty fruit bunch was achieved through the removal of silica bodies, as observed with scanning electron microscopy. Stenotrophomonas sp. S2 and Bacillus subtilis S11Y were able to reduce approximately 50% and 20% of alkali lignin at 7 days of incubation without the requirement for additional carbon sources.

Chaetomium globosporum: A novel laccase producing fungus for improving the hydrolyzability of lignocellulosic biomass

Rapid economic growth and urbanization is imposing an unseen pressure on energy sector to fulfill the increasing energy demand. Non edible horticultural residues viz. wheat and pearl millet straw have the potential to become an economical resource for waste to energy conversion. However, maximum hydrolyzability of the crop residues is a prerequisite for efficient conversion of complex organic materials into biofuels. In the present study, mycological treatment of wheat and pearl millet straw was accomplished by employing Chaetomium globosporum. The straw samples were exposed to mycological treatment for 14, 28 and 42 days. The improvement in hydrolyzability of straw was assessed by estimating the increase in reducing sugar release. The competence of Chaetomium globosporum for treating the straw samples was evaluated by measuring the % lignin removal after treatment. Furthermore, the structural and morphological changes in the straw samples after mycological treatment were examined by using scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction analysis. The results revealed 124 and 91% increase in reducing sugar release along with 43 and 41% removal of lignin for wheat and pearl millet straw respectively. Significant differences were also observed in in the structure, crystallanity and surface morphology.

Fungal bioaugmentation of anaerobic digesters fed with lignocellulosic biomass: What to expect from anaerobic fungus Orpinomyces sp

Energy-efficient biogas reactors are often designed and operated mimicking natural microbial ecosystems such as the digestive tracts of ruminants. Anaerobic fungi play a crucial role in the degradation of lignocellulose-rich fiber thanks to their high cellulolytic activity. Fungal bioaugmentation is therefore at the heart of our understanding of enhancing anaerobic digestion (AD). The efficiency of bioaugmentation with anaerobic fungus Orpinomyces sp. was evaluated in lignocellulose-based AD configurations. Fungal bioaugmentation increased the methane yield by 15-33% during anaerobic co-digestion of cow manure and selected cereal crops/straws. Harvesting stage of the crops was a decisive parameter to influence methane production together with fungal bioaugmentation. A more efficient fermentation process in the bioaugmented digesters was distinguished by relatively-higher abundance of Synergistetes, which was mainly represented by the genus Anaerobaculum. On the contrary, the composition of the methanogenic archaea did not change, and the majority of methanogens was assigned to Methanosarcina.

Symposium review: Technologies for improving fiber utilization

The forage lignocellulosic complex is one of the greatest limitations to utilization of the nutrients and energy in fiber. Consequently, several technologies have been developed to increase forage fiber utilization by dairy cows. Physical or mechanical processing techniques reduce forage particle size and gut fill and thereby increase intake. Such techniques increase the surface area for microbial colonization and may increase fiber utilization. Genetic technologies such as brown midrib mutants (BMR) with less lignin have been among the most repeatable and practical strategies to increase fiber utilization. Newer BMR corn hybrids are better yielding than the early hybrids and recent brachytic dwarf BMR sorghum hybrids avoid lodging problems of early hybrids. Several alkalis have been effective at increasing fiber digestibility. Among these, ammoniation has the added benefit of increasing the nitrogen concentration of the forage. However, few of these have been widely adopted due to the cost and the caustic nature of the chemicals. Urea treatment is more benign but requires sufficient urease and moisture for efficacy. Ammonia-fiber expansion technology uses high temperature, moisture, and pressure to degrade lignocellulose to a greater extent than ammoniation alone, but it occurs in reactors and is therefore not currently usable on farms. Biological technologies for increasing fiber utilization such as application of exogenous fibrolytic enzymes, live yeasts, and yeast culture have had equivocal effects on forage fiber digestion in individual studies, but recent meta-analyses indicate that their overall effects are positive. Nonhydrolytic expansin-like proteins act in synergy with fibrolytic enzymes to increase fiber digestion beyond that achieved by the enzyme alone due to their ability to expand cellulose microfibrils allowing greater enzyme penetration of the cell wall matrix. White-rot fungi are perhaps the biological agents with the greatest potential for lignocellulose deconstruction, but they require aerobic conditions and several strains degrade easily digestible carbohydrates. Less ruminant nutrition research has been conducted on brown rot fungi that deconstruct lignocellulose by generating highly destructive hydroxyl radicals via the Fenton reaction. More research is needed to increase the repeatability, efficacy, cost effectiveness, and on-farm applicability of technologies for increasing fiber utilization.