Biomass pretreatment: Fundamentals toward application

Alkaline and alkaline peroxide pretreatments at mild temperature to enhance enzymatic hydrolysis of rice hulls and straw

The current study explores alkaline and alkaline peroxide pretreatments in order to achieve a method to improve saccharification of agricultural residues for ethanol production. The effects of reagent concentration and pretreatment time at 30°C and atmospheric pressure on biomass dissolution after the pretreatment and enzymatic hydrolysis of the pretreated biomass were investigated. In fact, although all pretreatments tested improved enzymatic hydrolysis of native residues, the best results were not achieved for the highest biomass loss. The maximum conversions to reducing sugars in the hydrolysis stage of 77.5% and 92.6% were obtained for rice hulls and straw pretreated by alkaline peroxide (4%, 24h) and alkaline (1%, 48 h) methods, respectively. For both pretreated residues, the reduction to more than half the recommended enzyme loading allowed obtaining more than 94% the reducing sugars attained with the recommended dose.

Conversion of lignocellulosic biomass to nanocellulose: structure and chemical process

Lignocellulosic biomass is a complex biopolymer that is primary composed of cellulose, hemicellulose, and lignin. The presence of cellulose in biomass is able to depolymerise into nanodimension biomaterial, with exceptional mechanical properties for biocomposites, pharmaceutical carriers, and electronic substrate's application. However, the entangled biomass ultrastructure consists of inherent properties, such as strong lignin layers, low cellulose accessibility to chemicals, and high cellulose crystallinity, which inhibit the digestibility of the biomass for cellulose extraction. This situation offers both challenges and promises for the biomass biorefinery development to utilize the cellulose from lignocellulosic biomass. Thus, multistep biorefinery processes are necessary to ensure the deconstruction of noncellulosic content in lignocellulosic biomass, while maintaining cellulose product for further hydrolysis into nanocellulose material. In this review, we discuss the molecular structure basis for biomass recalcitrance, reengineering process of lignocellulosic biomass into nanocellulose via chemical, and novel catalytic approaches. Furthermore, review on catalyst design to overcome key barriers regarding the natural resistance of biomass will be presented herein.

Pretreatment of Japanese cedar by ionic liquid solutions in combination with acid and metal ion and its application to high solid loading

BACKGROUND

Lignocellulosic biomass from plant biomass, especially softwoods, are well-known to present difficulties during attempts at hydrolysis due to their rigid structure. Pretreatment of lignocellulosic biomass with ionic liquids (ILs) is attractive as this requires to a low input of energy. However, IL pretreatment has the disadvantage of the presence of large amounts of water. Recently, it was reported that a small amount of acid has a positive effect on the degradation of biomass in IL with water. In this study the pretreatment of Japanese cedar, the most abundant softwood in Japan, was investigated using a combination of IL, acid and metal ions.

RESULTS

First, the novel ionic liquid pretreatment was investigated by changing the pretreatment solvent and the anti-solvent. A mixture of IL, acid and ferric oxide (Fe(3+)) ion was most effective for pretreatment, and an acetone-water mixture was also most effective on the precipitation of biomass. These optimized pretreatment combinations attained a higher degree of glucose release from the pretreated biomass. The amount of cellulose was concentrated from to a level of 36 to 84% of the insoluble fraction by the optimized pretreatment. Based on this result, it was assumed that the extraction of the lignin fraction from the biomass into an anti-solvent solution was attained. Finally, this optimized pretreatment was applied to the enzymatic hydrolysis of Japanese cedar at high-solid biomass loading, and 110 g/L of glucose production was attained. In addition, the ethanol fermentation with this hydrolyzed solution by Saccharomyces cerevisiae achieved 50 g/L ethanol production, and this yield reached 90% of the theoretical yield.

CONCLUSIONS

We developed an effective pretreatment protocol by changing to a pretreatment solvent containing IL, acid, metal ion and anti-solvent. The optimized pretreatment has an effect on softwood and separately retrieved lignin as a by-product. The saccharified solution at high-solid biomass loading was converted to ethanol in a high yield. This proposed methodology would boost the performance of the bioconversion of low-cost materials to other chemicals, and would not be limited to only ethanol but also would include other target chemicals.

Characterization of a GHF45 cellulase, AkEG21, from the common sea hare Aplysia kurodai

The common sea hare Aplysia kurodai is known to be a good source for the enzymes degrading seaweed polysaccharides. Recently four cellulases, i.e., 95, 66, 45, and 21 kDa enzymes, were isolated from A. kurodai (Tsuji et al., 2013). The former three cellulases were regarded as glycosyl-hydrolase-family 9 (GHF9) enzymes, while the 21 kDa cellulase was suggested to be a GHF45 enzyme. The 21 kDa cellulase was significantly heat stable, and appeared to be advantageous in performing heterogeneous expression and protein-engineering study. In the present study, we determined some enzymatic properties of the 21 kDa cellulase and cloned its cDNA to provide the basis for the protein engineering study of this cellulase. The purified 21 kDa enzyme, termed AkEG21 in the present study, hydrolyzed carboxymethyl cellulose with an optimal pH and temperature at 4.5 and 40°C, respectively. AkEG21 was considerably heat-stable, i.e., it was not inactivated by the incubation at 55°C for 30 min. AkEG21 degraded phosphoric-acid-swollen cellulose producing cellotriose and cellobiose as major end products but hardly degraded oligosaccharides smaller than tetrasaccharide. This indicated that AkEG21 is an endolytic β-1,4-glucanase (EC 3.2.1.4). A cDNA of 1013 bp encoding AkEG21 was amplified by PCR and the amino-acid sequence of 197 residues was deduced. The sequence comprised the initiation Met, the putative signal peptide of 16 residues for secretion and the catalytic domain of 180 residues, which lined from the N-terminus in this order. The sequence of the catalytic domain showed 47–62% amino-acid identities to those of GHF45 cellulases reported in other mollusks. Both the catalytic residues and the N-glycosylation residues known in other GHF45 cellulases were conserved in AkEG21. Phylogenetic analysis for the amino-acid sequences suggested the close relation between AkEG21 and fungal GHF45 cellulases.

Electron beam irradiation enhances the digestibility and fermentation yield of water-soaked lignocellulosic biomass

•

Hydrolysis yield by WEBI is not less than that of a conventional system.

•

Adequate diffusion of the solvent can induce a high-yield of digestibility.

•

Ethanol productivity by WEBI is not less than that of a conventional system.

•

In environmentally friendly WEBI, inhibitory compounds were not detected.

In order to overcome the limitation of commercial electron beam irradiation (EBI), lignocellulosic rice straw (RS) was pretreated using water soaking-based electron beam irradiation (WEBI). This environment-friendly pretreatment, without the formation (or release) of inhibitory compounds (especially hydroxymethylfurfural and furfural), significantly increased the enzymatic hydrolysis and fermentation yields of RS. Specifically, when water-soaked RS (solid:liquid ratio of 100%) was treated with WEBI doses of 1 MeV at 80 kGy, 0.12 mA, the glucose yield after 120 h of hydrolysis was 70.4% of the theoretical maximum. This value was predominantly higher than the 29.5% and 52.1% measured from untreated and EBI-treated RS, respectively. Furthermore, after simultaneous saccharification and fermentation for 48 h, the ethanol concentration, production yield, and productivity were 9.3 g/L, 57.0% of the theoretical maximum, and 0.19 g/L h, respectively. Finally, scanning electron microscopy images revealed that WEBI induced significant ultrastructural changes to the surface of lignocellulosic fibers.

Effects of acid impregnated steam explosion process on xylose recovery and enzymatic conversion of cellulose in corncob

Corncob residue is a cellulose-rich byproduct obtained from industrial xylose production via dilute acid hydrolysis processes. Enzymatic hydrolysis of cellulose in acid hydrolysis residue of corncob (AHRC) is often less efficient without further pretreatment. In this work, the process characteristics of acid impregnated steam explosion were studied in conjunction with a dilute acid process, and their effects on physiochemical changes and enzymatic saccharification of corncob residue were compared. With the acid impregnated steam explosion process, both higher xylose recovery and higher cellulose conversion were obtained. The maximum conversion of cellulose in acid impregnated steam explosion residue of corncob (ASERC) reached 85.3%, which was 1.6 times higher than that of AHRC. Biomass compositional analysis showed similar cellulose and lignin content in ASERC and AHRC. XRD analysis demonstrated comparable crystallinity of ASERC and AHRC. The improved enzymatic hydrolysis efficiency was attributed to higher porosity in ASERC, measured by mercury porosimetry.

Facile pulping of lignocellulosic biomass using choline acetate

Treating ground bagasse or Southern yellow pine in the biodegradable ionic liquid (IL), choline acetate ([Cho][OAc]), at 100°C for 24h led to dissolution of hemicellulose and lignin, while leaving the cellulose pulp undissolved, with a 54.3% (bagasse) or 34.3% (pine) reduction in lignin content. The IL solution of the dissolved biopolymers can be separated from the undissolved particles either by addition of water (20 wt% of IL) followed by filtration or by centrifugation. Hemicellulose (19.0 wt% of original bagasse, 10.2 wt% of original pine, containing 14-18 wt% lignin) and lignin (5.0 wt% of original bagasse, 6.0 wt% of original pine) could be subsequently precipitated. The pulp obtained from [Cho][OAc] treatment can be rapidly dissolved in 1-ethyl-3-methylimidazolium acetate (e.g., 17 h for raw bagasse vs. 7h for pulp), and precipitated as cellulose-rich material (CRM) with a lower lignin content (e.g., 23.6% for raw bagasse vs. 10.6% for CRM).

Fractionation of hemp hurds by organosolv pretreatment and its effect on production of lignin and sugars

Fractionation of hemp hurds into its three main components, cellulose, hemicellulose, and lignin, was carried out using organosolv pretreatment. The effect of processing parameters, such as temperature, catalyst concentration, reaction time, and methanol (MeOH) concentration, on the dissolution and recovery of hemicellulose and lignin was determined. More than 75% of total hemicellulose and 75% of total lignin was removed in a single step with low amounts of degradation products under the following conditions: 165 °C, 3% H2 SO4 , 20 min reaction time, and 45% MeOH. Enzymatic hydrolysis of the residual pretreated biomass yielded up to 60% of cellulose-to-glucose conversion. The maximum recovery of the main components was obtained at a combined severity factor value of around one. Characterization of pretreated biomass and isolated lignin was carried out with FTIR and 2D (13) C-(1) H correlation HSQC NMR spectroscopy, the latter technique providing detailed structural information about the obtained methanol organosolv lignin (MOSL). Results suggested that xylopyranoside is the major carbohydrate associated with hemp lignin. The chemical properties of MOSL samples in terms of their phenolic group content and antioxidant capacity were also investigated. The results showed that MOSL samples have a high phenolic group content and antioxidant capacity relative to Klason lignin.

Pretreatment methods for bioethanol production

Lignocellulosic biomass, such as wood, grass, agricultural, and forest residues, are potential resources for the production of bioethanol. The current biochemical process of converting biomass to bioethanol typically consists of three main steps: pretreatment, enzymatic hydrolysis, and fermentation. For this process, pretreatment is probably the most crucial step since it has a large impact on the efficiency of the overall bioconversion. The aim of pretreatment is to disrupt recalcitrant structures of cellulosic biomass to make cellulose more accessible to the enzymes that convert carbohydrate polymers into fermentable sugars. This paper reviews several leading acidic, neutral, and alkaline pretreatments technologies. Different pretreatment methods, including dilute acid pretreatment (DAP), steam explosion pretreatment (SEP), organosolv, liquid hot water (LHW), ammonia fiber expansion (AFEX), soaking in aqueous ammonia (SAA), sodium hydroxide/lime pretreatments, and ozonolysis are intensively introduced and discussed. In this minireview, the key points are focused on the structural changes primarily in cellulose, hemicellulose, and lignin during the above leading pretreatment technologies.

Comparison of hydrophilic variation and bioethanol production of furfural residues after delignification pretreatment

Furfural residue (FR) is a waste lignocellulosic material with enormous potential for bioethanol production. In this study, bioethanol production from FR after delignification was compared. Hydrophilic variation was measured by conductometric titration to detect the relationship between hydrophilicity and bioethanol production. It was found that ethanol yield increased as delignification enhanced, and it reached up to 75.6% of theoretical yield for samples with 8.7% lignin. The amount of by-products decreased as delignification increased. New inflection points appeared in conductometric titration curves of samples that were partially delignified, but they vanished in the curves of the highly delignified samples. Total charges and carboxyl levels increased after slight delignification, and they decreased upon further delignification. These phenomena suggested some new hydrophilic groups were formed during pretreated delignification, which would be beneficial to enzymatic hydrolysis. However, some newly formed groups may act as toxicant to the yeast during simultaneous saccharification and fermentation.

Complementary substrate-selectivity of metabolic adaptive convergence in the lignocellulolytic performance by Dichomitus squalens

The lignocellulolytic platform of the wood-decaying organism Dichomitus squalens is important for production of biodegradable elements; however, the system has not yet been fully characterized. In this study, using statistical target optimization, we analysed substrate selectivity based on a variety of D. squalens metabolic pathways using combined omics tools. As compared with the alkali-lignin (AL) programme, the rice straw (RS) programme has the advantage of multilayered signalling to regulate cellulolytic-related genes or to connect their pathways. The spontaneous instability of the AL programme was accelerated by harsh starvation as compared with that of the RS programme. Therefore, the AL programme converged on cellular maintenance much easier and more rapidly. However, regardless of external substrate/concentration type, the compensatory pattern of the major targets (especially peroxidases and growth regulators) was similar, functioning to maintain cellular homeostasis. Interestingly, ligninolytic-mediated targets under non-kaleidoscopic conditions were induced by a substrate-input-control, and especially this mechanism had an important effect on the early stages of the biodegradation process. This optimized target analysis could be used to understand lignocellulolytic network and to improve downstream efficiency.

Isolation of high quality lignin as a by-product from ammonia percolation pretreatment of poplar wood

A two-step process combining percolation-mode ammonia pretreatment of poplar sawdust with mild organosolv purification of the extracted lignin produced high quality, high purity lignin in up to 31% yield and 50% recovery. The uncondensed fraction of the isolated lignin was up to 34%, close to that the native lignin (40%). Less lignin was recovered after pretreatment in batch mode, apparently due to condensation during the longer residence time of the solubilised lignin at elevated temperature. The lignin recovery was directly correlated with its molecular weight and its nitrogen content. Low nitrogen incorporation, observed at high ammonia concentration, may be explained by limited homolytic cleavage of β-O-4 bonds. Ammonia concentrations from 15% to 25% (w/w) gave similar results in terms of lignin structure, yield and recovery.

Economic and environmental assessment of syrup production. Colombian case

This work presents a techno-economic and environmental assessment of the glucose syrups production from sugarcane bagasse, plantain husk, cassava husk, mango peel, rice husk and corncobs. According to the economic analysis, the corncob had both, the lowest production cost (2.48USD/kg syrup) and the highest yield (0.61kgofsugars/kg of wet agroindustrial waste) due to its high content in cellulose and hemicellulose. This analysis also revealed that a heat integration strategy is necessary since the utilities consumption represent an important factor in the production cost. According to the results, the pretreatment section requires more energy in the syrup production in comparison with the requirements of other sections such as production and sugar concentration. The environmental assessment revealed that the solid wastes such as furfural and hydroxymethylfurfural affected the environmental development of the process for all the agroindustrial wastes, being the rice husk the residue with the lowest environmental impact.

Enhancing volatile fatty acid (VFA) and bio-methane production from lawn grass with pretreatment

The bioconversion of fiber-based carbohydrates during anaerobic digestion (AD) is impeded due to the recalcitrant nature of the plant cell wall. Pretreatment of lignocellulose materials under mild conditions are needed to improve the digestibility at minimum cost. This study investigated the effects of different pretreatments, including ozone, soaking aqueous ammonia (SAA), combined ozone and SAA (OSAA), and size reduction to enhance volatile fatty acid (VFA) and bio-methane production when lawn grass was used as substrate. To study VFA production, methanogenesis was selectively inhibited by sodium 2-bromoethanesulfonate to decouple the relation between VFA and bio-methane. The enzymatic hydrolysis of SAA (residence time 24h at 50°C) and OSAA (10 min ozonation and 6h of SAA) in pretreatment of lawn grass sample resulted in 86.71% and 89.63% sugar recovery, respectively. The specific methane yields of the control, ozone, SAA, OSAA, and size-reduced grass samples were 402.5, 358.8, 481.0, 462.6, and 358.3 ml CH4/g volatile solid (VS), respectively.

Current challenges in commercially producing biofuels from lignocellulosic biomass

Biofuels that are produced from biobased materials are a good alternative to petroleum based fuels. They offer several benefits to society and the environment. Producing second generation biofuels is even more challenging than producing first generation biofuels due the complexity of the biomass and issues related to producing, harvesting, and transporting less dense biomass to centralized biorefineries. In addition to this logistic challenge, other challenges with respect to processing steps in converting biomass to liquid transportation fuel like pretreatment, hydrolysis, microbial fermentation, and fuel separation still exist and are discussed in this review. The possible coproducts that could be produced in the biorefinery and their importance to reduce the processing cost of biofuel are discussed. About $1 billion was spent in the year 2012 by the government agencies in US to meet the mandate to replace 30% existing liquid transportation fuels by 2022 which is 36 billion gallons/year. Other countries in the world have set their own targets to replace petroleum fuel by biofuels. Because of the challenges listed in this review and lack of government policies to create the demand for biofuels, it may take more time for the lignocellulosic biofuels to hit the market place than previously projected.

The optimized CO2-added ammonia explosion pretreatment for bioethanol production from rice straw

A CO₂-added ammonia explosion pretreatment was performed for bioethanol production from rice straw. The pretreatment conditions, such as ammonia concentration, CO₂ loading level, residence time, and temperature were optimized using response surface methodology. The response for optimization was defined as the glucose conversion rate. The optimized pretreatment conditions resulting in maximal glucose yield (93.6 %) were determined as 14.3 % of ammonia concentration, 2.2 MPa of CO₂ loading level, 165.1 °C of temperature, and 69.8 min of residence time. Scanning electron microscopy analysis showed that pretreatment of rice straw strongly increased the surface area and pore size, thus increasing enzymatic accessibility for enzymatic saccharification. Finally, an ethanol yield of 97 % was achieved via simultaneous saccharification and fermentation. Thus, the present study suggests that CO₂-added ammonia pretreatment is an appropriate process for bioethanol production from rice straw.

Characterization of pilot-scale dilute acid pretreatment performance using deacetylated corn stover

BACKGROUND

Dilute acid pretreatment is a promising process technology for the deconstruction of low-lignin lignocellulosic biomass, capable of producing high yields of hemicellulosic sugars and enhancing enzymatic yields of glucose as part of a biomass-to-biofuels process. However, while it has been extensively studied, most work has historically been conducted at relatively high acid concentrations of 1 - 4% (weight/weight). Reducing the effective acid loading in pretreatment has the potential to reduce chemical costs both for pretreatment and subsequent neutralization. Additionally, if acid loadings are sufficiently low, capital requirements associated with reactor construction may be significantly reduced due to the relaxation of requirements for exotic alloys. Despite these benefits, past efforts have had difficulty obtaining high process yields at low acid loadings without supplementation of additional unit operations, such as mechanical refining.

RESULTS

Recently, we optimized the dilute acid pretreatment of deacetylated corn stover at low acid loadings in a 1-ton per day horizontal pretreatment reactor. This effort included more than 25 pilot-scale pretreatment experiments executed at reactor temperatures ranging from 150 - 170°C, residence times of 10 - 20 minutes and hydrolyzer sulfuric acid concentrations between 0.15 - 0.30% (weight/weight). In addition to characterizing the process yields achieved across the reaction space, the optimization identified a pretreatment reaction condition that achieved total xylose yields from pretreatment of 73.5% ± 1.5% with greater than 97% xylan component balance closure across a series of five runs at the same condition. Feedstock reactivity at this reaction condition after bench-scale high solids enzymatic hydrolysis was 77%, prior to the inclusion of any additional conversion that may occur during subsequent fermentation.

CONCLUSIONS

This study effectively characterized a range of pretreatment reaction conditions using deacetylated corn stover at low acid loadings and identified an optimum reaction condition was selected and used in a series of integrated pilot scale cellulosic ethanol production campaigns. Additionally, several issues exist to be considered in future pretreatment experiments in continuous reactor systems, including the formation of char within the reactor, as well as practical issues with feeding herbaceous feedstock into pressurized systems.

Screening of ecologically diverse fungi for their potential to pretreat lignocellulosic bioenergy feedstock

A widespread and hitherto by far underexploited potential among ecologically diverse fungi to pretreat wheat straw and digestate from maize silage in the future perspective of using such lignocellulosic feedstock for fermentative bioenergy production was inferred from a screening of nine freshwater ascomycetes, 76 isolates from constructed wetlands, nine peatland isolates and ten basidiomycetes. Wheat straw pretreatment was most efficient with three ascomycetes belonging to the genera Acephala (peatland isolate) and Stachybotrys (constructed wetland isolates) and two white-rot fungi (Hypholoma fasciculare and Stropharia rugosoannulata) as it increased the amounts of water-extractable total sugars by more than 50 % and sometimes up to 150 % above the untreated control. The ascomycetes delignified wheat straw at rates (lignin losses between about 31 and 40 % of the initial content) coming close to those observed with white-rot fungi (about 40 to 57 % lignin removal). Overall, fungal delignification was indicated as a major process facilitating the digestibility of wheat straw. Digestate was generally more resistant to fungal decomposition than wheat straw. Nevertheless, certain ascomycetes delignified this substrate to extents sometimes even exceeding delignification by basidiomycetes. Total sugar amounts of about 20 to 60 % above the control value were obtained with the most efficient fungi (one ascomycete of the genus Phoma, the unspecific wood-rot basidiomycete Agrocybe aegerita and one unidentified constructed wetland isolate). This was accompanied by lignin losses of about 47 to 56 % of the initial content. Overall, digestate delignification was implied to be less decisive for high yields of fermentable sugars than wheat straw delignification.

Fibrous Agricultural Biomass as a Potential Source for Bioconversion to Vanillic Acid

This study was conducted to assess the potential of six fibrous agricultural residues, namely, oil palm empty fruit bunch fiber (OPEFBF), coconut coir fiber (CCF), pineapple peel (PP), pineapple crown leaves (PCL), kenaf bast fiber (KBF), and kenaf core fiber (KCF), as a source of ferulic acid and phenolic compounds for bioconversion into vanillic acid. The raw samples were pretreated with organosolv (NaOH-glycerol) and alkaline treatment (NaOH), to produce phenol-rich black liquor. The finding showed that the highest amount of phenolic compounds and ferulic acid was produced from CCF and PP, respectively. This study also found that organosolv treatment was the superior method for phenolic compound extraction, whereas alkaline treatment was the selective method for lignin extraction. Vanillic acid production byAspergillus nigerI-1472 was only observed when the fermentation broth was fed with liquors from PP and PCL, possibly due to the higher levels of ferulic acid in those samples.

Organosolv pretreatment of Sitka spruce wood: conversion of hemicelluloses to ethyl glycosides

A range of Organosolv pretreatments, using ethanol:water mixtures with dilute sulphuric acid, were applied to Sitka spruce sawdust with the aim of generating useful co-products as well as improving saccharification yield. The most efficient of the pretreatment conditions, resulting in subsequent saccharification yields of up to 86%, converted a large part of the hemicellulose sugars to their ethyl glycosides as identified by GC/MS. These conditions also reduced conversion of pentoses to furfural, the ethyl glycosides being more stable to dehydration than the parent pentoses. Through comparison with the behaviour of model compounds under the same reaction conditions it was shown that the anomeric composition of the products was consistent with a predominant transglycosylation reaction mechanism, rather than hydrolysis followed by glycosylation. The ethyl glycosides have potential as intermediates in the sustainable production of high-value chemicals.

Multi-scale structural and chemical analysis of sugarcane bagasse in the process of sequential acid-base pretreatment and ethanol production by Scheffersomyces shehatae and Saccharomyces cerevisiae

BACKGROUND

Heavy usage of gasoline, burgeoning fuel prices, and environmental issues have paved the way for the exploration of cellulosic ethanol. Cellulosic ethanol production technologies are emerging and require continued technological advancements. One of the most challenging issues is the pretreatment of lignocellulosic biomass for the desired sugars yields after enzymatic hydrolysis. We hypothesized that consecutive dilute sulfuric acid-dilute sodium hydroxide pretreatment would overcome the native recalcitrance of sugarcane bagasse (SB) by enhancing cellulase accessibility of the embedded cellulosic microfibrils.

RESULTS

SB hemicellulosic hydrolysate after concentration by vacuum evaporation and detoxification showed 30.89 g/l xylose along with other products (0.32 g/l glucose, 2.31 g/l arabinose, and 1.26 g/l acetic acid). The recovered cellulignin was subsequently delignified by sodium hydroxide mediated pretreatment. The acid-base pretreated material released 48.50 g/l total reducing sugars (0.91 g sugars/g cellulose amount in SB) after enzymatic hydrolysis. Ultra-structural mapping of acid-base pretreated and enzyme hydrolyzed SB by microscopic analysis (scanning electron microcopy (SEM), transmitted light microscopy (TLM), and spectroscopic analysis (X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy) elucidated the molecular changes in hemicellulose, cellulose, and lignin components of bagasse. The detoxified hemicellulosic hydrolysate was fermented by Scheffersomyces shehatae (syn. Candida shehatae UFMG HM 52.2) and resulted in 9.11 g/l ethanol production (yield 0.38 g/g) after 48 hours of fermentation. Enzymatic hydrolysate when fermented by Saccharomyces cerevisiae 174 revealed 8.13 g/l ethanol (yield 0.22 g/g) after 72 hours of fermentation.

CONCLUSIONS

Multi-scale structural studies of SB after sequential acid-base pretreatment and enzymatic hydrolysis showed marked changes in hemicellulose and lignin removal at molecular level. The cellulosic material showed high saccharification efficiency after enzymatic hydrolysis. Hemicellulosic and cellulosic hydrolysates revealed moderate ethanol production by S. shehatae and S. cerevisiae under batch fermentation conditions.

One-pot pretreatment, saccharification and ethanol fermentation of lignocellulose based on acid–base mixture pretreatment

One-pot pretreatment, saccharification and ethanol fermentation of lignocellulose, which is based on acid–base mixture pretreament, will greatly reduces the overall processing costs not only for the production of cellulosic ethanol but also for the lignocellulose-based biorefinery.

Evaluation of hydrothermal treatment in enhancing rice straw compost stability and maturity

In order to evaluate the hydrothermal treatment (HTT) in enhancing compost stability and maturity of lignocellulosic agricultural residues, a bin-scale (90 L) composting of rice straw with and without "HTT" was performed. The rice straw compost product with "HTT" after 6 weeks of composting can be considered stable and adequate for field application as expressed by pH of 8.4, "EC value" of 2.96 dS m(-1), C/N ratio of 12.5, microbial activity of <8.05 mg CO2 g(-1) OM d(-1), NH4(+)-N content of 93.75 mg kg(-1) DM and finally, by "GI" of >83%. However, compost may prove phytotoxic if used as growing media for EC sensitive plants. As for rice straw compost product without "HTT", the high microbial activity (>12.28 mg CO2 g(-1) OM d(-1)) even after 14 weeks of composting suggests that the residue has not stabilized yet and is far away from stability and maturity, although a higher GI (>100%) was observed.

Dissolution of wet wood biomass without heating

Tetrabutylphosphonium hydroxide containing water made a wet wood disk swollen and extracted polysaccharides without heating.

Experimental Study on Calcium Hydroxide-Assisted Delignification of Hydrothermally Treated Sweet Sorghum Bagasse

The hydrothermally treated sweet sorghum bagasse (SSB) powder was treated using Ca(OH)2to extract the lignin from it. Changes in chemical composition of SSB and the formation of sugars and hydrolytic products were studied. The optimum conditions of 10% (g/g substrate) Ca(OH)2and 106.3 min of isothermal treatment residence time at 394 K resulted in 69.67 ± 1.26% of the lignin extracted from the hydrothermally treated SSB powder, producing a solid residue containing 68.29 ± 0.31% residual cellulose and 13.26 ± 0.32% residual lignin in it. The Ca(OH)2concentration and isothermal treatment residence time were significant in the responses observed. Treatment using Ca(OH)2is one of the potential processes for the on-farm processing of lignocellulosic materials.

Identification and characterization of core cellulolytic enzymes from Talaromyces cellulolyticus (formerly Acremonium cellulolyticus) critical for hydrolysis of lignocellulosic biomass

BACKGROUND

Enzymatic hydrolysis of pretreated lignocellulosic biomass is an essential process for the production of fermentable sugars for industrial use. A better understanding of fungal cellulase systems will provide clues for maximizing the hydrolysis of target biomass. Talaromyces cellulolyticus is a promising fungus for cellulase production and efficient biomass hydrolysis. Several cellulolytic enzymes purified from T. cellulolyticus were characterized in earlier studies, but the core enzymes critical for hydrolysis of lignocellulosic biomass remain unknown.

RESULTS

Six cellulolytic enzymes critical for the hydrolysis of crystalline cellulose were purified from T. cellulolyticus culture supernatant using an enzyme assay based on synergistic hydrolysis of Avicel. The purified enzymes were identified by their substrate specificities and analyses of trypsin-digested peptide fragments and were classified into the following glycosyl hydrolase (GH) families: GH3 (β-glucosidase, Bgl3A), GH5 (endoglucanase, Cel5A), GH6 (cellobiohydrolase II, Cel6A), GH7 (cellobiohydrolase I and endoglucanase, Cel7A and Cel7B, respectively), and GH10 (xylanase, Xyl10A). Hydrolysis of dilute acid-pretreated corn stover (PCS) with mixtures of the purified enzymes showed that Cel5A, Cel7B, and Xyl10A each had synergistic effects with a mixture of Cel6A and Cel7A. Cel5A seemed to be more effective in the synergistic hydrolysis of the PCS than Cel7B. The ratio of Cel5A, Cel6A, Cel7A, and Xyl10A was statistically optimized for the hydrolysis of PCS glucan in the presence of Bgl3A. The resultant mixture achieved higher PCS glucan hydrolysis at lower enzyme loading than a culture filtrate from T. cellulolyticus or a commercial enzyme preparation, demonstrating that the five enzymes play a role as core enzymes in the hydrolysis of PCS glucan.

CONCLUSIONS

Core cellulolytic enzymes in the T. cellulolyticus cellulase system were identified to Cel5A, Cel6A, Cel7A, Xyl10A, and Bgl3A and characterized. The optimized mixture of these five enzymes was highly effective for the hydrolysis of PCS glucan, providing a foundation for future improvement of the T. cellulolyticus cellulase system.

Quantitative determination of methylene blue in environmental samples by solid-phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry: a green approach

Industrial effluents with dyes may have appreciably high chemical oxygen demand and suspended solids, posing adverse effects to both humans and aquatic life; therefore, quantitative monitoring of these effluents is essential.

Plant biomass recalcitrance: effect of hemicellulose composition on nanoscale forces that control cell wall strength

Efficient conversion of lignocellulosic biomass to second-generation biofuels and valuable chemicals requires decomposition of resilient plant cell wall structure. Cell wall recalcitrance varies among plant species and even phenotypes, depending on the chemical composition of the noncellulosic matrix. Changing the amount and composition of branches attached to the hemicellulose backbone can significantly alter the cell wall strength and microstructure. We address the effect of hemicellulose composition on primary cell wall assembly forces by using the 3D-RISM-KH molecular theory of solvation, which provides statistical-mechanical sampling and molecular picture of hemicellulose arrangement around cellulose. We show that hemicellulose branches of arabinose, glucuronic acid, and especially glucuronate strengthen the primary cell wall by strongly coordinating to hydrogen bond donor sites on the cellulose surface. We reveal molecular forces maintaining the cell wall structure and provide directions for genetic modulation of plants and pretreatment design to render biomass more amenable to processing.

A novel cost-effective technology to convert sucrose and homocelluloses in sweet sorghum stalks into ethanol

BACKGROUND

Sweet sorghum is regarded as a very promising energy crop for ethanol production because it not only supplies grain and sugar, but also offers lignocellulosic resource. Cost-competitive ethanol production requires bioconversion of all carbohydrates in stalks including of both sucrose and lignocellulose hydrolyzed into fermentable sugars. However, it is still a main challenge to reduce ethanol production cost and improve feasibility of industrial application. An integration of the different operations within the whole process is a potential solution.

RESULTS

An integrated process combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment was presented in this work. Soluble sugars in sweet sorghum stalks were firstly converted into ethanol by ASSF using crushed stalks directly. Then, the operation combining ethanol distillation and alkaline pretreatment was performed in one distillation-reactor simultaneously. The corresponding investigation indicated that the addition of alkali did not affect the ethanol recovery. The effect of three alkalis, NaOH, KOH and Ca(OH)2 on pretreatment were investigated. The results indicated the delignification of lignocellulose by NaOH and KOH was more significant than that by Ca(OH)2, and the highest removal of xylan was caused by NaOH. Moreover, an optimized alkali loading of 10% (w/w DM) NaOH was determined. Under this favorable pretreatment condition, enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was investigated. 92.0% of glucan and 53.3% of xylan conversion were obtained at enzyme loading of 10 FPU/g glucan. The fermentation of hydrolyzed slurry was performed using an engineered stain, Zymomonas mobilis TSH-01. A mass balance of the overall process was calculated, and 91.9 kg was achieved from one tonne of fresh sweet sorghum stalk.

CONCLUSIONS

A low energy-consumption integrated technology for ethanol production from sweet sorghum stalks was presented in this work. Energy consumption for raw materials preparation and pretreatment were reduced or avoided in our process. Based on this technology, the recalcitrance of lignocellulose was destructed via a cost-efficient process and all sugars in sweet sorghum stalks lignocellulose were hydrolysed into fermentable sugars. Bioconversion of fermentable sugars released from sweet sorghum bagasse into different products except ethanol, such as butanol, biogas, and chemicals was feasible to operate under low energy-consumption conditions.

Optimization of NaOH-catalyzed steam pretreatment of empty fruit bunch

BACKGROUND

Empty fruit bunch (EFB) has many advantages, including its abundance, the fact that it does not require collection, and its year-round availability as a feedstock for bioethanol production. But before the significant costs incurred in ethanol production from lignocellulosic biomass can be reduced, an efficient sugar fractionation technology has to be developed. To that end, in the present study, an NaOH-catalyzed steam pretreatment process was applied in order to produce ethanol from EFB more efficiently.

RESULTS

The EFB pretreatment conditions were optimized by application of certain pretreatment variables such as, the NaOH concentrations in the soaking step and, in the steam step, the temperature and time. The optimal conditions were determined by response surface methodology (RSM) to be 3% NaOH for soaking and 160°C, 11 min 20 sec for steam pretreatment. Under these conditions, the overall glucan recovery and enzymatic digestibility were both high: the glucan and xylan yields were 93% and 78%, respectively, and the enzymatic digestibility was 88.8% for 72 h using 40 FPU/g glucan. After simultaneous saccharification and fermentation (SSF), the maximum ethanol yield and concentration were 0.88 and 29.4 g/l respectively.

CONCLUSIONS

Delignification (>85%) of EFB was an important factor in enzymatic hydrolysis using CTec2. NaOH-catalyzed steam pretreatment, which can remove lignin efficiently and requires only a short reaction time, was proven to be an effective pretreatment technology for EFB. The ethanol yield obtained by SSF, the key parameter determining the economics of ethanol, was 18% (w/w), equivalent to 88% of the theoretical maximum yield, which is a better result than have been reported in the relevant previous studies.

Isolation of Bacillus sp. strains capable of decomposing alkali lignin and their application in combination with lactic acid bacteria for enhancing cellulase performance

Effective biological pretreatment method for enhancing cellulase performance was investigated. Two alkali lignin-degrading bacteria were isolated from forest soils in Japan and named CS-1 and CS-2. 16S rDNA sequence analysis indicated that CS-1 and CS-2 were Bacillus sp. Strains CS-1 and CS-2 displayed alkali lignin degradation capability. With initial concentrations of 0.05-2.0 g L(-1), at least 61% alkali lignin could be degraded within 48 h. High laccase activities were observed in crude enzyme extracts from the isolated strains. This result indicated that alkali lignin degradation was correlated with laccase activities. Judging from the net yields of sugars after enzymatic hydrolysis, the most effective pretreatment method for enhancing cellulase performance was a two-step processing procedure (pretreatment using Bacillus sp. CS-1 followed by lactic acid bacteria) at 68.6%. These results suggest that the two-step pretreatment procedure is effective at accelerating cellulase performance.

Correlation between hemicelluloses-removal-induced hydrophilicity variation and the bioconversion efficiency of lignocelluloses

In order to establish the correlation between hemicelluloses removal and bioconversion efficiency of cellulose, fractionation process with increasing NaOH concentration selectively released the hemicellulosic polymers with increasing molecular weight and decreasing degree of substitution. Not only the initial hydrolysis rates also the concentrations of glucose and ethanol were significantly enhanced from 5.93 and 8.39 g/L to the range of 8.67-9.60 g/L and 11.53-13.71 g/L after alkaline treatment, respectively. However, the maximum conversions of cellulose to glucose (61.9%) and ethanol (64.6%) were achieved as 33.0% hemicelluloses was still remained. Excluding the negligible effect on the crystal transformation of cellulose, the improvement of bioconversion efficiency was resulted from the synergetical effects of surface exposure, multi-layers collapse and the hydrophilic property of the cellulosic substrate. It is critical task to balance these factors by the partial removal of hemicellulosic component, not complete.

An overview of key pretreatment processes employed for bioconversion of lignocellulosic biomass into biofuels and value added products

The hunt for alternative sources of energy generation that are inexpensive, ecofriendly, renewable and can replace fossil fuels is on, owing to the increasing demands of energy. One approach in this direction is the conversion of plant residues into biofuels wherein lignocellulose, which forms the structural framework of plants consisting of cellulose, hemicellulose and lignin, is first broken down and hydrolyzed into simple fermentable sugars, which upon fermentation form biofuels such as ethanol. A major bottleneck is to disarray lignin which is present as a protective covering and makes cellulose and hemicellulose recalcitrant to enzymatic hydrolysis. A number of biomass deconstruction or pretreatment processes (physical, chemical and biological) have been used to break the structural framework of plants and depolymerize lignin. This review surveys and discusses some major pretreatment processes pertaining to the pretreatment of plant biomass, which are used for the production of biofuels and other value added products. The emphasis is given on processes that provide maximum amount of sugars, which are subsequently used for the production of biofuels.