Biotechnological production of ethanol from renewable resources by Neurospora crassa: an alternative to conventional yeast fermentations?

Microbial production of ethanol might be a potential route to replace oil and chemical feedstocks. Bioethanol is by far the most common biofuel in use worldwide. Lignocellulosic biomass is the most promising renewable resource for fuel bioethanol production. Bioconversion of lignocellulosics to ethanol consists of four major unit operations: pretreatment, hydrolysis, fermentation, and product separation/distillation. Conventional bioethanol processes for lignocellulosics apply commercial fungal cellulase enzymes for biomass hydrolysis, followed by yeast fermentation of resulting glucose to ethanol. The fungus Neurospora crassa has been used extensively for genetic, biochemical, and molecular studies as a model organism. However, the strain's potential in biotechnological applications has not been widely investigated and discussed. The fungus N. crassa has the ability to synthesize and secrete all three enzyme types involved in cellulose hydrolysis as well as various enzymes for hemicellulose degradation. In addition, N. crassa has been reported to convert to ethanol hexose and pentose sugars, cellulose polymers, and agro-industrial residues. The combination of these characteristics makes N. crassa a promising alternative candidate for biotechnological production of ethanol from renewable resources. This review consists of an overview of the ethanol process from lignocellulosic biomass, followed by cellulases and hemicellulases production, ethanol fermentations of sugars and lignocellulosics, and industrial application potential of N. crassa.     

Variation in Cell Wall Composition and Accessibility in Relation to Biofuel Potential of Short Rotation Coppice Willows

Short rotation coppice (SRC) willow is currently emerging as an important dedicated lignocellulosic energy crop in the UK. However, investigation into the variation between species and genotypes in their suitability for liquid transport biofuel processing has been limited. To address this, four traits relevant to biofuel processing (composition, enzymatic saccharification, response to pretreatment and projected ethanol yields) were studied in 35 genotypes of willow including Europe’s leading SRC willow cultivars. Large, genotype-specific variation was observed for all four traits. Significant positive correlations were identified between the accessibility of glucan to enzymatic saccharification before and after pretreatment as well as glucose release and xylose release via acid hydrolysis during pretreatment. Of particular interest is that the lignin content of the biomass did not correlate with accessibility of glucan to enzymatic saccharification. The genotype-specific variations identified have implications for SRC willow breeding and for potential reductions in both the net energy expenditure and environmental impact of the lignocellulosic biofuel process chain. The large range of projected ethanol yields demonstrate the importance of feedstock selection based on an ideotype encompassing the performance of both field biomass growth and ease of conversion.     

Evaluation of pretreatment methods for lignocellulosic ethanol production from energy cane variety L 79-1002

Approximately half of the 80 billion tons of crop produced annually around the world remains as residue that could serve as a renewable resource to produce valuable products such as ethanol and butanol. Ethanol produced from lignocellulosic biomass is a promising renewable alternative to diminishing oil and gas liquid fuels. Sugarcane is an important industry in Louisiana. The recently released variety of “energy cane” has great potential to sustain a competitive sugarcane industry. It has been demonstrated that fuel-grade ethanol can be produced from post harvest sugarcane residue in the past, but optimized ethanol production was not achieved. Optimization of the fermentation process requires efficient pretreatment to release cellulose and hemicellulose from lignocellulosic complex of plant fiber. Determining optimal pretreatment techniques for fermentation is essential for the success of lignocellulosic ethanol production process. The purpose of this study was to evaluate three pretreatment methods for the energy cane variety L 79-1002 for maximum lignocellulosic ethanol production. The pretreatments include alkaline pretreatment, dilute acid hydrolysis, and solid-state fungal pretreatment process using brown rot and white rot fungi. Pretreated biomass was enzymatically saccharified and subjected to fermentation using a recombinant Escherichia coli FBR5. The results revealed that all pretreatment processes produced ethanol. However, the best result was observed in dilute acid hydrolysis followed by alkaline pretreatment and solid-state fungal pretreatment.     

Quantitative proteomic analysis of lignocellulolytic enzymes by Phanerochaete chrysosporium on different lignocellulosic biomass

Lignocellulosic biomass from agricultural crop residues and forest waste represents an abundant renewable resource for bioenergy and future biofuel. The current bottleneck of lignocellulosic biofuel production is the hydrolysis of biomass to sugar. To understand the enzymatic hydrolysis of complex biomasses, in this report, lignocellulolytic enzymes secretion by Phanerochaete chrysosporium cultivated in different natural lignocellulosic biomass such as corn stover, hay, sawdust, sugarcane baggase, wheat bran and wood chips were quantitatively analyzed with the iTRAQ technique using LC-MS/MS. A diverse groups of enzymes, including cellulases, glycoside hydrolases, hemicellulases, lignin degrading enzymes, peroxidases, esterases, lipases, chitinases, peptidases, protein translocating transporter and hypothetical proteins were quantified, of which several were novel lignocellulosic biomass hydrolyzing enzymes. The quantitative expression and regulation of lignocellulolytic enzymes by P. chrysosporium were dependent on the nature and complexity of lignocellulosic biomass as well as physical size of the biomass. The iTRAQ data revealed oxidative and hydrolytic lignin degrading mechanism of P. chrysosporium. Numerous proteins presumed to be involved in natural lignocellulosic biomass transformation and degradation were expressed and produced in variable quantities in response to different agricultural and forest wastes.     

A thermophilic ionic liquid-tolerant cellulase cocktail for the production of cellulosic biofuels

Generation of biofuels from sugars in lignocellulosic biomass is a promising alternative to liquid fossil fuels, but efficient and inexpensive bioprocessing configurations must be developed to make this technology commercially viable. One of the major barriers to commercialization is the recalcitrance of plant cell wall polysaccharides to enzymatic hydrolysis. Biomass pretreatment with ionic liquids (ILs) enables efficient saccharification of biomass, but residual ILs inhibit both saccharification and microbial fuel production, requiring extensive washing after IL pretreatment. Pretreatment itself can also produce biomass-derived inhibitory compounds that reduce microbial fuel production. Therefore, there are multiple points in the process from biomass to biofuel production that must be interrogated and optimized to maximize fuel production. Here, we report the development of an IL-tolerant cellulase cocktail by combining thermophilic bacterial glycoside hydrolases produced by a mixed consortia with recombinant glycoside hydrolases. This enzymatic cocktail saccharifies IL-pretreated biomass at higher temperatures and in the presence of much higher IL concentrations than commercial fungal cocktails. Sugars obtained from saccharification of IL-pretreated switchgrass using this cocktail can be converted into biodiesel (fatty acid ethyl-esters or FAEEs) by a metabolically engineered strain of E. coli. During these studies, we found that this biodiesel-producing E. coli strain was sensitive to ILs and inhibitors released by saccharification. This cocktail will enable the development of novel biomass to biofuel bioprocessing configurations that may overcome some of the barriers to production of inexpensive cellulosic biofuels.     

Biodelignification of lignocellulose substrates: An intrinsic and sustainable pretreatment strategy for clean energy production

Lignocellulosic biomass (LB) is a promising sugar feedstock for biofuels and other high-value chemical commodities. The recalcitrance of LB, however, impedes carbohydrate accessibility and its conversion into commercially significant products. Two important factors for the overall economization of biofuel production is LB pretreatment to liberate fermentable sugars followed by conversion into ethanol. Sustainable biofuel production must overcome issues such as minimizing water and energy usage, reducing chemical usage and process intensification. Amongst available pretreatment methods, microorganism-mediated pretreatments are the safest, green, and sustainable. Native biodelignifying agents such as Phanerochaete chrysosporium, Pycnoporous cinnabarinus, Ceriporiopsis subvermispora and Cyathus stercoreus can remove lignin, making the remaining substrates amenable for saccharification. The development of a robust, integrated bioprocessing (IBP) approach for economic ethanol production would incorporate all essential steps including pretreatment, cellulase production, enzyme hydrolysis and fermentation of the released sugars into ethanol. IBP represents an inexpensive, environmentally friendly, low energy and low capital approach for second-generation ethanol production. This paper reviews the advancements in microbial-assisted pretreatment for the delignification of lignocellulosic substrates, system metabolic engineering for biorefineries and highlights the possibilities of process integration for sustainable and economic ethanol production.     

A review of biological delignification and detoxification methods for lignocellulosic bioethanol production

Future biorefineries will integrate biomass conversion processes to produce fuels, power, heat and value-added chemicals. Due to its low price and wide distribution, lignocellulosic biomass is expected to play an important role toward this goal. Regarding renewable biofuel production, bioethanol from lignocellulosic feedstocks is considered the most feasible option for fossil fuels replacement since these raw materials do not compete with food or feed crops. In the overall process, lignin, the natural barrier of the lignocellulosic biomass, represents an important limiting factor in biomass digestibility. In order to reduce the recalcitrant structure of lignocellulose, biological pretreatments have been promoted as sustainable and environmentally friendly alternatives to traditional physico-chemical technologies, which are expensive and pollute the environment. These approaches include the use of diverse white-rot fungi and/or ligninolytic enzymes, which disrupt lignin polymers and facilitate the bioconversion of the sugar fraction into ethanol. As there is still no suitable biological pretreatment technology ready to scale up in an industrial context, white-rot fungi and/or ligninolytic enzymes have also been proposed to overcome, in a separated or in situ biodetoxification step, the effect of the inhibitors produced by non-biological pretreatments. The present work reviews the latest studies regarding the application of different microorganisms or enzymes as useful and environmentally friendly delignification and detoxification technologies for lignocellulosic biofuel production. This review also points out the main challenges and possible ways to make these technologies a reality for the bioethanol industry.     

Recent trends in ionic liquid (IL) tolerant enzymes and microorganisms for biomass conversion

Second generation biofuel production depends on lignocellulosic (LC) biomass transformation into simple sugars and their subsequent fermentation into alcohols. However, the main obstacle in this process is the efficient breakdown of the recalcitrant cellulose to sugar monomers. Hence, efficient feedstock pretreatment and hydrolysis are necessary to produce a cost effective biofuel. Recently, ionic liquids (ILs) have been recognized as a promising solvent able to dissolve different biomass feedstocks, providing higher sugar yields. However, most of the hydrolytic enzymes and microorganisms are inactivated, completely or partially, in the presence of even low concentrations of IL, making necessary the discovery of novel hydrolytic enzymes and fermentative microorganisms that are tolerant to ILs. In this review, the current state and the challenges of using ILs as a pretreatment of LC biomass was evaluated, underlining the advances in the discovery and identification of new IL-tolerant enzymes and microorganisms that could improve the bioprocessing of biomass to fuels and chemicals.     

Consolidated Pretreatment and Hydrolysis of Plant Biomass Expressing Cell Wall Degrading Enzymes

Significant amounts of cell wall degrading (CWD) enzymes are required to degrade lignocellulosic biomass into its component sugars. One strategy for reducing exogenous enzyme production requirements is to produce the CWD enzymes in planta. For this work, various CWD enzymes were expressed in maize (Zea mays). Following growth and dry down of the plants, harvested maize stover was tested to determine the impact of the expressed enzymes on the production of glucose and xylose using different exogenous enzyme loadings. In this study, a consolidated pretreatment and hydrolysis process consisting of a moderate chemical pretreatment at temperatures below 75°C followed by enzymatic hydrolysis using an in-house enzyme cocktail was used to evaluate engineered transgenic feedstocks. The carbohydrate compositional analysis showed no significant difference in the amounts of glucan and xylan between the transgenic maize plants expressing CWD enzyme(s) and the control plants. Hydrolysis results demonstrated that transgenic plants expressing CWD enzymes achieved up to 141% higher glucose yield and 172% higher xylose yield over the control plants from enzymatic hydrolysis under the experimental conditions. The hydrolytic performance of a specific xylanase (XynA) expressing transgenic event (XynA.2015.05) was heritable in the next generation, and the improved properties can be achieved even with a 25% reduction in exogenous enzyme loading. Simultaneous saccharification and fermentation of biomass hydrolysates from two different transgenic maize lines with yeast (Saccharomyces cerevisiae D5A) converted 65% of the biomass glucan into ethanol, versus only a 42% ethanol yield with hydrolysates from control plants, corresponding to a 55% improvement in ethanol production.     

Bioconversion of Lignocellulose into Bioethanol: Process Intensification and Mechanism Research

Biofuels produced from lignocellulosic biomass can significantly reduce the energy dependency on fossil fuels and the resulting effects on environment. In this respect, cellulosic ethanol as an alternative fuel has the potential to become a viable energy source in the near future. Over the past few decades, tremendous effort has been undertaken to make cellulosic ethanol cost competitive with conventional fossil fuels. The pretreatment step is always necessary to deconstruct the recalcitrant structures and to make cellulose more accessible to enzymes. A large number of pretreatment technologies involving physical, chemical, biological, and combined approaches have been developed and tested at the pilot scale. Furthermore, various strategies and methods, including multi-enzyme complex, non-catalytic additives, enzyme recycling, high solids operation, design of novel bioreactors, and strain improvement have also been implemented to improve the efficiency of subsequent enzymatic hydrolysis and fermentation. These technologies provide significant opportunities for lower total cost, thus making large-scale production of cellulosic ethanol possible. Meanwhile, many researchers have focused on the key factors that limit cellulose hydrolysis, and analyzing the reaction mechanisms of cellulase. This review describes the most recent advances on process intensification and mechanism research of pretreatment, enzymatic hydrolysis, and fermentation during the production of cellulosic ethanol.     

Uncertainty in techno-economic estimates of cellulosic ethanol production due to experimental measurement uncertainty

ABSTRACT: BACKGROUND: Cost-effective production of lignocellulosic biofuels remains a major financial and technical challenge at the industrial scale. A critical tool in biofuels process development is the techno-economic (TE) model, which calculates biofuel production costs using a process model and an economic model. The process model solves mass and energy balances for each unit, and the economic model estimates capital and operating costs from the process model based on economic assumptions. The process model inputs include experimental data on the feedstock composition and intermediate product yields for each unit. These experimental yield data are calculated from primary measurements. Uncertainty in these primary measurements is propagated to the calculated yields, to the process model, and ultimately to the economic model. Thus, outputs of the TE model have a minimum uncertainty associated with the uncertainty in the primary measurements. RESULTS: We calculate the uncertainty in the Minimum Ethanol Selling Price (MESP) estimate for lignocellulosic ethanol production via a biochemical conversion process: dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis and co-fermentation of the resulting sugars to ethanol. We perform a sensitivity analysis on the TE model and identify the feedstock composition and conversion yields from three unit operations (xylose from pretreatment, glucose from enzymatic hydrolysis, and ethanol from fermentation) as the most important variables. The uncertainty in the pretreatment xylose yield arises from multiple measurements, whereas the glucose and ethanol yields from enzymatic hydrolysis and fermentation, respectively, are dominated by a single measurement: the fraction of insoluble solids (fIS) in the biomass slurries. CONCLUSIONS: We calculate a $0.15/gal uncertainty in MESP from the TE model due to uncertainties in primary measurements. This result sets a lower bound on the error bars of the TE model predictions. This analysis highlights the primary measurements that merit further development to reduce the uncertainty associated with their use in TE models. While we develop and apply this mathematical framework to a specific biorefinery scenario here, this analysis can be readily adapted to other types of biorefining processes and provides a general framework for propagating uncertainty due to analytical measurements through a TE model.     

Biological pretreatment of corn stover with Phlebia brevispora NRRL‐13108 for enhanced enzymatic hydrolysis and efficient ethanol production

Biological pretreatment of lignocellulosic biomass by white‐rot fungus can represent a low‐cost and eco‐friendly alternative to harsh physical, chemical, or physico‐chemical pretreatment methods to facilitate enzymatic hydrolysis. In this work, solid‐state cultivation of corn stover with Phlebia brevispora NRRL‐13018 was optimized with respect to duration, moisture content and inoculum size. Changes in composition of pretreated corn stover and its susceptibility to enzymatic hydrolysis were analyzed. About 84% moisture and 42 days incubation at 28°C were found to be optimal for pretreatment with respect to enzymatic saccharification. Inoculum size had little effect compared to moisture level. Ergosterol data shows continued growth of the fungus studied up to 57 days. No furfural and hydroxymethyl furfural were produced. The total sugar yield was 442 ± 5 mg/g of pretreated corn stover. About 36 ± 0.6 g ethanol was produced from 150 g pretreated stover per L by fed‐batch simultaneous saccharification and fermentation (SSF) using mixed sugar utilizing ethanologenic recombinant Eschericia coli FBR5 strain. The ethanol yields were 32.0 ± 0.2 and 38.0 ± 0.2 g from 200 g pretreated corn stover per L by fed‐batch SSF using Saccharomyces cerevisiae D5A and xylose utilizing recombinant S. cerevisiae YRH400 strain, respectively. This research demonstrates that P. brevispora NRRL‐13018 has potential to be used for biological pretreatment of lignocellulosic biomass. This is the first report on the production of ethanol from P. brevispora pretreated corn stover. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:365–374, 2017     

Room temperature ionic liquids as emerging solvents for the pretreatment of lignocellulosic biomass

Room temperature ionic liquids (RTILs) are emerging as attractive and green solvents for lignocellulosic biomass pretreatment. The unique solvating properties of RTILs foster the disruption of the 3D network structure of lignin, cellulose, and hemicellulose, which allows high yields of fermentable sugars to be produced in subsequent enzymatic hydrolysis. In the current review, we summarize the physicochemical properties of RTILs that make them effective solvents for lignocellulose pretreatment including mechanisms of interaction between lignocellulosic biomass subcomponents and RTILs. We also highlight several recent strategies that exploit RTILs and generate high yields of fermentable sugars suitable for downstream biofuel production, and address new opportunities for use of lignocellulosic components, including lignin. Finally, we address some of the challenges that remain before large-scale use of RTILs may be achieved.     

Interspecific evolutionary relationships of alpha-glucuronidase in the genus Aspergillus

The increased availability and production of lignocellulosic agroindustrial wastes has originated proposals for their use as raw material to obtain biofuels (ethanol and biodiesel) or derived products. However, for biomass generated from lignocellulosic residues to be successfully degraded, in most cases it requires a physical (thermal), chemical, or enzymatic pretreatment before the application of microbial or enzymatic fermentation technologies (biocatalysis). In the context of enzymatic technologies, fungi have demonstrated to produce enzymes capable of degrading polysaccharides like cellulose, hemicelluloses and pectin. Because of this ability for degrading lignocellulosic material, researchers are making efforts to isolate and identify fungal enzymes that could have a better activity for the degradation of plant cell walls and agroindustrial biomass. We performed an in silico analysis of alpha-glucoronidase in 82 accessions of the genus Aspergillus. The constructed dendrograms of amino acid sequences defined the formation of 6 groups (I, II, III, IV, V, and VI), which demonstrates the high diversity of the enzyme. Despite this ample divergence between enzyme groups, our 3D structure modeling showed both conservation and differences in amino acid residues participating in enzyme–substrate binding, which indicates the possibility that some enzymes are functionally specialized for the specific degradation of a substrate depending on the genetics of each species in the genus and the condition of the habitat where they evolved. The identification of alpha-glucuronidase isoenzymes would allow future use of genetic engineering and biocatalysis technologies aimed at specific production of the enzyme for its use in biotransformation.     

Mushroom spent straw: a potential substrate for an ethanol-based biorefinery

Rice straw (RS) is an important lignocellulosic biomass with nearly 800 million dry tons produced annually worldwide. RS has immense potential as a lignocellulosic feedstock for making renewable fuels and chemicals in a biorefinery. However, because of its natural recalcitrance, RS needs thermochemical treatment prior to further biological processing. Ammonia fiber expansion (AFEX) is a leading biomass pretreatment process utilizing concentrated/liquefied ammonia to pretreat lignocellulosic biomass at moderate temperatures (70–140°C). Previous research has shown improved cellulose and hemicellulose conversions upon AFEX treatment of RS at 2:1 ammonia to biomass (w/w) loading, 40% moisture (dwb) and 90°C. However, there is still scope for further improvement. Fungal pretreatment of lignocellulosics is an important biological pretreatment method that has not received much attention in the past. A few reasons for ignoring fungal-based pretreatments are substantial loss in cellulose and hemicellulose content and longer pretreatment times that reduce overall productivity. However, the sugar loss can be minimized through use of white-rot fungi (e.g. Pleutorus ostreatus) over a much shorter duration of pretreatment time. It was found that mushroom spent RS prior to AFEX allowed reduction in thermochemical treatment severity, while resulting in 15% higher glucan conversions than RS pretreated with AFEX alone. In this work, we report the effect of fungal conditioning of RS followed by AFEX pretreatment and enzymatic hydrolysis. The recovery of other byproducts from the fungal conditioning process such as fungal enzymes and mushrooms are also discussed. JIMB-2008: BioEnergy—Special issue.     

Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis

Production of ethanol by bioconversion of lignocellulosic biomass has attracted much interest in recent years. However, the pretreatment process for increasing the enzymatic digestibility of cellulose has become a key step in commercialized production of cellulosic ethanol. During the last decades, many pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. From the point of view for integrated utilization of lignocellulosic biomass, organosolv pretreatment provides a pathway for biorefining of biomass. This review presents the progress of organosolv pretreatment of lignocellulosic biomass in recent decades, especially on alcohol, organic acid, organic peracid and acetone pretreatments, and corresponding action mechanisms. Evaluation and prospect of organosolv pretreatment were performed. Finally, some recommendations for future investigation of this pretreatment method were given.     

An effective chemical pretreatment method for lignocellulosic biomass with substituted imidazoles

Lignocellulosic biomass is the most abundant naturally renewable organic resource for biofuel production. Because of its recalcitrance to enzymatic degradation, pretreatment is a crucial step before hydrolysis of the feedstock. A variety of pretreatment methods have been developed and intensively studied to achieve optimal yield without imposing significant adverse impact on the environment. Herein, we present a novel chemical pretreatment method using substituted heterocycles with low temperature and short residence time requirements. 1‐Methylimidazole (MI) is a precursor to some imidazolium‐based ionic liquids. In this study, its potential utilization as a biomass pretreatment agent is being investigated for the first time. At mild conditions, such as 25°C for 5 min at ambient pressure, a substantial increase in the hydrolysis rate throughout the entire course of conversion for cellulose substrate was obtained. Furthermore, the pretreatment effectiveness of MI on both untreated and steam‐exploded lignocellulosic biomass including loblolly pine, switchgrass, and sugarcane bagasse has been studied and MI was found to be an efficient delignifier. Remarkable rate enhancement was also observed for the non‐woody lignocellulosic substrates after a short period of MI pretreatment at ambient conditions. The mechanism of MI pretreatment is explored through analysis of cellulose physical properties including crystallinity index, degree of polymerization, accessibility, and lignin dissolution quantification. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:25–34, 2015     

Liberation of fermentable sugars from soybean hull biomass using ionic liquid 1‐butyl‐3‐methylimidazolium acetate and their bioconversion to ethanol

Optimized hydrolysis of lignocellulosic waste biomass is essential to achieve the liberation of sugars to be used in fermentation process. Ionic liquids (ILs), a new class of solvents, have been tested in the pretreatment of cellulosic materials to improve the subsequent enzymatic hydrolysis of the biomass. Optimized application of ILs on biomass is important to advance the use of this technology. In this research, we investigated the effects of using 1‐butyl‐3‐methylimidazolium acetate ([bmim][Ac]) on the decomposition of soybean hull, an abundant cellulosic industrial waste. Reaction aspects of temperature, incubation time, IL concentration, and solid load were optimized before carrying out the enzymatic hydrolysis of this residue to liberate fermentable glucose. Optimal conditions were found to be 75°C, 165 min incubation time, 57% (mass fraction) of [bmim][Ac], and 12.5% solid loading. Pretreated soybean hull lost its crystallinity, which eased enzymatic hydrolysis, confirmed by Fourier Transform Infrared analysis. The enzymatic hydrolysis of the biomass using an enzyme complex from Penicillium echinulatum liberated 92% of glucose from the cellulose matrix. The hydrolysate was free of any toxic compounds, such as hydroxymethylfurfural and furfural. The obtained hydrolysate was tested for fermentation using Candida shehatae HM 52.2, which was able to convert glucose to ethanol at yields of 0.31. These results suggest the possible use of ILs for the pretreatment of some lignocellulosic waste materials, avoiding the formation of toxic compounds, to be used in second‐generation ethanol production and other fermentation processes. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:312–320, 2016     

木质纤维素预处理技术研究进展

详细评述了木质纤维素的预处理工艺研究进展,特别是浓酸低温水解-酸回收工艺、稀酸二阶段水解工艺、金属离子在稀酸水解过程中的助催化作用以及水蒸汽爆裂、氨纤维爆裂、CO2爆裂、酶催化水解等方法的研究进展情况。木质纤维素原料预处理技术发展为发酵生产乙醇技术的研究开发奠定了坚实基础。     

Scale-up and integration of alkaline hydrogen peroxide pretreatment, enzymatic hydrolysis, and ethanolic fermentation

Alkaline hydrogen peroxide (AHP) has several attractive features as a pretreatment in the lignocellulosic biomass‐to‐ethanol pipeline. Here, the feasibility of scaling‐up the AHP process and integrating it with enzymatic hydrolysis and fermentation was studied. Corn stover (1 kg) was subjected to AHP pretreatment, hydrolyzed enzymatically, and the resulting sugars fermented to ethanol. The AHP pretreatment was performed at 0.125 g H₂O₂/g biomass, 22°C, and atmospheric pressure for 48 h with periodic pH readjustment. The enzymatic hydrolysis was performed in the same reactor following pH neutralization of the biomass slurry and without washing. After 48 h, glucose and xylose yields were 75% and 71% of the theoretical maximum. Sterility was maintained during pretreatment and enzymatic hydrolysis without the use of antibiotics. During fermentation using a glucose‐ and xylose‐utilizing strain of Saccharomyces cerevisiae, all of the Glc and 67% of the Xyl were consumed in 120 h. The final ethanol titer was 13.7 g/L. Treatment of the enzymatic hydrolysate with activated carbon prior to fermentation had little effect on Glc fermentation but markedly improved utilization of Xyl, presumably due to the removal of soluble aromatic inhibitors. The results indicate that AHP is readily scalable and can be integrated with enzyme hydrolysis and fermentation. Compared to other leading pretreatments for lignocellulosic biomass, AHP has potential advantages with regard to capital costs, process simplicity, feedstock handling, and compatibility with enzymatic deconstruction and fermentation. Biotechnol. Bioeng. 2012; 109:922–931. © 2011 Wiley Periodicals, Inc.