A comparison between batch and fed-batch simultaneous saccharification and fermentation of steam pretreated spruce

Cellulolytic and Ethanologenic Evaluation of Heterotermes indicola's Gut-Associated Bacterial Isolates

Cellulose is the basic component of lignocellulosic biomass (LCB) making it a suitable substrate for bioethanol fermentation. Cellulolytic and ethanologenic bacteria possess cellulases that convert cellulose to glucose, which in turn yields ethanol subsequently. Heterotermes indicola is a subterranean termite that causes destructive damage by consuming wooden structures of infrastructure, LCB products, etc. Prospectively, the study envisioned the screening of cellulolytic and ethanologenic bacteria from the termite gut. Twenty six bacterial strains (H1-H26) based on varied colonial morphologies were isolated. Bacterial cellulolytic activity was tested biochemically. Marked gas production in the form of bubbles (0.1-4 cm) in Durham tubes was observed in H3, H7, H13, H15, H17, H21, and H22. Sugar degradation of all isolates was indicated by pink to maroon color development with the tetrazolium salt. Hallow zones (0.42-11 mm) by Congo red staining was exhibited by all strains except H2, H7, H8, and H19. Among the 26 bacterial isolates, 12 strains were identified as efficient cellulolytic bacteria. CMCase activity and ethanol titer of all isolates varied from 1.30 ± 0.03 (H13) to 1.83 ± 0.01 (H21) umol/mL/min and 2.36 ± 0.01 (H25) to 7.00 ± 0.01 (H21) g/L, respectively. Likewise, isolate H21 exhibited an ethanol yield of 0.40 ± 0.10 g/g with 78.38 ± 2.05% fermentation efficiency. Molecular characterization of four strains, Staphylococcus sp. H13, Acinetobacter baumanni H17, Acinetobacter sp. H21, and Acinetobacter nosocomialis H22, were based on the maximum cellulolytic index and the ethanol yield. H. indicola harbor promising and novel bacteria with a natural cellulolytic tendency for efficient bioconversion of LCB to value-added products. Hence, the selected cellulolytic bacteria can become an excellent addition for use in enzyme purification, composting, and production of biofuel at large.

Very High Gravity Bioethanol Revisited: Main Challenges and Advances

Over the last decades, the constant growth of the world-wide industry has been leading to more and more concerns with its direct impact on greenhouse gas (GHG) emissions. Resulting from that, rising efforts have been dedicated to a global transition from an oil-based industry to cleaner biotechnological processes. A specific example refers to the production of bioethanol to substitute the traditional transportation fuels. Bioethanol has been produced for decades now, mainly from energy crops, but more recently, also from lignocellulosic materials. Aiming to improve process economics, the fermentation of very high gravity (VHG) mediums has for long received considerable attention. Nowadays, with the growth of multi-waste valorization frameworks, VHG fermentation could be crucial for bioeconomy development. However, numerous obstacles remain. This work initially presents the main aspects of a VHG process, giving then special emphasis to some of the most important factors that traditionally affect the fermentation organism, such as nutrients depletion, osmotic stress, and ethanol toxicity. Afterwards, some factors that could possibly enable critical improvements in the future on VHG technologies are discussed. Special attention was given to the potential of the development of new fermentation organisms, nutritionally complete culture media, but also on alternative process conditions and configurations.

Consolidated bioprocesses for efficient bioconversion of palm biomass wastes into biodiesel feedstocks by oleaginous fungi and yeasts

Consolidated bioprocesses for bioconversion of lignocellulosic biomass into biodiesel feedstocks were developed. Palm empty fruit bunch (EFB) was biologically pretreated coupling with fungal lipid production (121.4 ± 2.7 mg/g-EFB) by lignocellulolytic oleaginous fungi prior to lipid production by oleaginous yeasts. In subsequent separate hydrolysis and fermentation (SHF) of fungal pretreated EFB (FPEFB), the oleaginous yeast with the maximum lipid yield of 37.0 ± 0.1 mg/g-FPEFB was screened. While a higher lipid yield of 47.9 ± 1.5 mg/g-FPEFB was achieved in simultaneous saccharification and fermentation (SSF) with less enzyme requirement. Fed-batch SSF of non-sterile FPEFB was proven as a practical and efficient strategy to increase lipid yield up to 53.4 ± 0.5 mg/g-FPEFB. Total lipid yield by both fungi and yeast was 165.0 ± 4.4 mg/g-EFB. Interestingly, the consolidated bioprocesses of enzyme and lipid production also achieved comparable total lipid yield of 149.3 ± 6.6 mg/g-EFB. These strategies may contribute greatly to cost-effective and sustainable bioconversion of lignocellulosic biomass into biodiesel feedstocks.

Techno-Economic Implications of Fed-Batch Enzymatic Hydrolysis

Fed-batch enzymatic hydrolysis has the potential to improve the overall process of converting cellulosic biomass into ethanol. This paper utilizes a process simulation approach to identify and quantify techno-economic differences between batch and fed-batch enzymatic hydrolysis in cellulosic ethanol production. The entire process of converting corn stover into ethanol was simulated using SuperPro Designer simulation software. The analysis was conducted for a plant capacity of 2000 metric tons of dry biomass per day. A literature review was used to identify baseline parameters for the process. The sensitivity of the ethanol production cost to changes in sugar conversion efficiency, plant capacity, biomass cost, power cost, labor cost, and enzyme cost was evaluated using the process simulation. For the base scenario, the ethanol unit production cost was approximately $0.10/gallon lower for fed-batch hydrolysis. The greatest differences were seen in facilities costs, labor costs, and capital costs. Using a fed-batch operation decreased facilities costs by 41%, labor costs by 21%, and capital costs by 15%. The sensitivity analysis found that cost of biomass had the greatest effect on ethanol production cost, and in general, the results support the proposition that fed-batch enzymatic hydrolysis does improve the techno-economics of cellulosic ethanol production.

Sequential chemical and enzymatic pretreatment of palm empty fruit bunches for Candida pelliculosa bioethanol production

Second-generation bioethanol production process was developed using pretreated empty fruit bunches (EFB). Consecutive acid/alkali EFB pretreatment was performed, first with HCl and then with NaOH with final washing steps for phenolic compounds elimination. Scanning electron microscopy images showed that EFB chemical treatments indeed attacked the cellulose fibers and removed the silica from surface pores. The optimization of enzymatic hydrolysis of EFB's cellulosic fraction was performed with 0.5%-4% v/v of Cellic® CTec2/Novozymes, different EFB concentrations (5%-15%, w/v), and hydrolysis time (6-72 H). Optimization essays were carried out in Erlenmeyer flasks and also in a 1 L stirred tank reactor. After enzymatic hydrolysis, a hydrolysate with 66 g/L of glucose was achieved with 2.2% (v/v) Cellic® CTec2, 15% (m/v) acid/alkaline pretreated EFB after 39 H of hydrolysis. A gain of 11.2% was then obtained in the 1 L stirred tank promoted by the agitation (72.2 g/L glucose). The hydrolysate was employed in bioethanol production by a new isolate Candida pelliculosa CCT 7734 in a separate hydrolysis and fermentation process reaching 16.6 and 23.0 g/L of bioethanol through batch and fed-batch operation, respectively. An integrated biorefinery process was developed for EFB processing chain.

Comparison of ethanol yield from pretreated lignocellulo-starch biomass under fed-batch SHF or SSF modes

The ethanol yields from lignocellulo-starch biomass (peels of sweet potato, elephant foot yam, tannia, greater yam and beet root) by fed-batch separate hydrolysis and fermentation (F-SHF) and simultaneous saccharification and fermentation (F-SSF) using Saccharomyces cerevisiae were compared. Fed-batch saccharification of steam or dilute sulphuric acid pretreated biomass enhanced the reducing sugar yield which resulted in high RS consumption, volumetric ethanol productivity and ethanol yield during the first 24 h fermentation under F-SHF mode, while continuous production and utilization of reducing sugars occurred up to 72 h in F-SSF. Dilute sulphuric acid pretreated residues under F-SHF gave higher ethanol yield (34-43 g/L) and productivity (274-346 ml/kg dry biomass) than steam pretreatment (27-36 g/L and 223-295 ml/kg respectively), while F-SSF was superior for steam pretreated peels of sweet potato, elephant foot yam and tannia giving ethanol yields from 281 to 302 ml/kg. Glucose and xylose were present in all the hydrolysates with a preponderance of glucose and fermentation resulted in significant reduction in glucose levels in both F-SHF and F-SSF. Higher levels of total soluble phenolics and hydroxymethyl furfural were observed in the hydrolysates from dilute sulphuric acid pretreatment and yeast assimilated/detoxified part of the inhibitors, while only trivial amounts of furfural were present due to the low xylose content in the hydrolysates. Continuous formation led to higher accumulation of inhibitors in F-SSF despite supplementation with the detoxification mix comprising Tween 20, polyethylene glycol and sodium borohydride. F-SHF of dilute sulphuric acid pretreated biomass could be considered as a comparatively advantageous process where only one time feeding of enzyme cocktail and yeast was adopted compared to multiple feeds of enzymes and yeast along with other additives such as detoxification mix or nutrient solution in F-SSF.

Comparison of One-Stage Batch and Fed-Batch Enzymatic Hydrolysis of Pretreated Hardwood for the Production of Biosugar

Fed-batch method has shown a great promise in debottlenecking the high-solid enzymatic hydrolysis for the commercialization of cellulosic biosugar conversion for biofuel/biochemical production. To further improve enzymatic hydrolysis efficiency at high solid loading, fed-batch methods of green liquor-pretreated hardwood were performed to evaluate their effects on sugar recovery by comparing with one-stage batch method in this study. Among all the explored conditions, the fed-batch at 15% consistency gave higher sugar recovery on green liquor-pretreated hardwood compared to that of one-stage batch. By using general linear model analysis, the percentage of enzymatic sugar recovery in fed-batch consistency method (increasing consistency from the initial 10.7 to 15% at intervals of 24 and 48 h) was higher than that of batch hydrolysis at higher density of 15% consistency. Under that best fed-batch condition, the total sugar recovery of pretreated hardwood in enzymatic hydrolysate reached approximately 48.41% at Cellic® enzyme loading of 5 filter-paper unit (FPU)/g and 58.83% at Cellic® enzyme loading of 10 FPU/g with a hydrolysis time of 96 h.

An integrated process to produce bio-ethanol and xylooligosaccharides rich in xylobiose and xylotriose from high ash content waste wheat straw

A bio-refinery process of wheat straw pulping solid residue (waste wheat straw, WWS) was established by combining prewashing and liquid hot water pretreatment (LHWP). The results showed that employing a prewashing step prior to the LHWP remarkably improved enzymatic glucose yields from 39.7% to 76.6%. Moreover, after 96h simultaneous saccharification and fermentation (SSF), identical ethanol yields of 0.41g/g-cellulose were obtained despite varied solid loadings (5-30%). Beyond ethanol, enzymatic post-hydrolysis of the prehydrolyzate effectively increased xylobiose and xylotriose yields from 15mg/g-WWS and 14mg/g-WWS to 53mg/g-WWS and 20mg/g-WWS, respectively. For mass balance, about 10.9tons raw WWS will be consumed to produce 1ton ethanol, in addition to producing 614.8kg xylooligosaccharides (XOS) containing 334.3kg xylobiose and 124.8kg xylotriose. The results demonstrated that the integrated process for the WWS bio-refinery is promising, based on value-adding co-production in addition to robust ethanol yields.

Enhanced bioethanol production by fed-batch simultaneous saccharification and co-fermentation at high solid loading of Fenton reaction and sodium hydroxide sequentially pretreated sugarcane bagasse

A study on the fed-batch simultaneous saccharification and co-fermentation (SSCF) of Fenton reaction combined with NaOH pretreated sugarcane bagasse (SCB) at a high solid loading of 10-30% (w/v) was investigated. Enzyme feeding mode, substrate feeding mode and combination of both were compared with the batch mode under respective solid loadings. Ethanol concentrations of above 80g/L were obtained in batch and enzyme feeding modes at a solid loading of 30% (w/v). Enzyme feeding mode was found to increase ethanol productivity and reduce enzyme loading to a value of 1.23g/L/h and 9FPU/g substrate, respectively. The present study provides an economically feasible process for high concentration bioethanol production.

Integrating enzyme fermentation in lignocellulosic ethanol production: life-cycle assessment and techno-economic analysis

BACKGROUND

Cellulase enzymes have been reported to contribute with a significant share of the total costs and greenhouse gas emissions of lignocellulosic ethanol production today. A potential future alternative to purchasing enzymes from an off-site manufacturer is to integrate enzyme and ethanol production, using microorganisms and part of the lignocellulosic material as feedstock for enzymes. This study modelled two such integrated process designs for ethanol from logging residues from spruce production, and compared it to an off-site case based on existing data regarding purchased enzymes. Greenhouse gas emissions and primary energy balances were studied in a life-cycle assessment, and cost performance in a techno-economic analysis.

RESULTS

The base case scenario suggests that greenhouse gas emissions per MJ of ethanol could be significantly lower in the integrated cases than in the off-site case. However, the difference between the integrated and off-site cases is reduced with alternative assumptions regarding enzyme dosage and the environmental impact of the purchased enzymes. The comparison of primary energy balances did not show any significant difference between the cases. The minimum ethanol selling price, to reach break-even costs, was from 0.568 to 0.622 EUR L^-1 for the integrated cases, as compared to 0.581 EUR L^-1 for the off-site case.

CONCLUSIONS

An integrated process design could reduce greenhouse gas emissions from lignocellulose-based ethanol production, and the cost of an integrated process could be comparable to purchasing enzymes produced off-site. This study focused on the environmental and economic assessment of an integrated process, and in order to strengthen the comparison to the off-site case, more detailed and updated data regarding industrial off-site enzyme production are especially important.

Evaluation of a pilot-scaled paddle dryer for the production of ethanol from lignocellulose including inhibitor removal and high-solids enzymatic hydrolysis

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The use of a paddle dryer system in the bioethanol process from straw is proposed.

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Paddle dryer was employed to detoxify a pretreated substrate by steam explosion.

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Paddle dryer is resulted an efficient system to improve enzymatic hydrolysis.

The advantage of using paddle dryers (PD) in the production of sugars and 2nd generation ethanol from pretreated wheat straw was investigated. This machinery was employed in order to detoxify steam-exploded substrates and to mix different slurries in the hydrolysis step. The obtained hydrolysate was fermented by the yeast Saccharomyces cerevisiae. Acetic acid and furfural were reduced up to 11 and 26 fold respectively in the detoxified substrate. When fermentation was carried out at low solid suspension, the use of PD was as effective as water extraction in detoxifying exploded biomass, giving ethanol yields of 90% at 0.05 solid/liquid ratio (S/L) and 80% at 0.10 S/L. Moreover, by using PD the cellulose conversion yield was significantly improved in the hydrolysis step: when operating at higher S/L (0.4), the hydrolysis efficiency was twice the one achieved by using a bioreactor with a Rushton stirrer.

Integrated bioethanol and protein production from brown seaweed Laminaria digitata

A wild-growing glucose-rich (i.e. 56.7% glucose content) brown seaweed species Laminaria digitata, collected from the North Coast of Denmark in August 2012, was used as the feedstock for an integrated bioethanol and protein production. Glutamic acid and aspartic acid are the two most abundant amino acids in the algal protein, both with proportional content of 10% in crude protein. Only minor pretreatment of milling was used on the biomass to facilitate the subsequent enzymatic hydrolysis and fermentation. The Separate Hydrolysis and Fermentation (SHF) resulted in obviously higher ethanol yield than the Simultaneous Saccharification and Fermentation (SSF). High conversion rate at maximum of 84.1% glucose recovery by enzymatic hydrolysis and overall ethanol yield at maximum of 77.7% theoretical were achieved. Protein content in the solid residues after fermentation was enriched by 2.7 fold, with similar distributions of amino acids, due to the hydrolysis of polymers in the seaweed cell wall matrix.

A process for energy-efficient high-solids fed-batch enzymatic liquefaction of cellulosic biomass

The enzymatic hydrolysis of cellulosic biomass is a key step in the biochemical production of fuels and chemicals. Economically feasible large-scale implementation of the process requires operation at high solids loadings, i.e., biomass concentrations >15% (w/w). At increasing solids loadings, however, biomass forms a high viscosity slurry that becomes increasingly challenging to mix and severely mass transfer limited, which limits further addition of solids. To overcome these limitations, we developed a fed-batch process controlled by the yield stress and its changes during liquefaction of the reaction mixture. The process control relies on an in-line, non-invasive magnetic resonance imaging (MRI) rheometer to monitor real-time evolution of yield stress during liquefaction. Additionally, we demonstrate that timing of enzyme addition relative to biomass addition influences process efficiency, and the upper limit of solids loading is ultimately limited by end-product inhibition as soluble glucose and cellobiose accumulate in the liquid phase.

The addition of accessory enzymes enhances the hydrolytic performance of cellulase enzymes at high solid loadings

The pretreatment process used and the nature of the biomass feedstock will influence the role that accessory enzymes can play in synergistically interacting with cellulases to effectively deconstruct the substrate. The work reported here assessed the possible boosting effects of the xylanase and lytic polysaccharide monooxygenase (AA9, formerly known as GH61) on the hydrolytic potential of cellulase enzyme mixtures during hydrolysis of steam pretreated poplar and corn stover at high (10-20% w/v) substrate concentrations. A higher proportion of xylanase was required when the substrate had a relatively high xylan content and at high substrate concentrations. In contrast, a relatively small amount of AA9 (about 2 mg/g cellulose) was enough, regardless of the nature or concentration of the substrate. The overall protein loading required to achieve effective hydrolysis of high concentrations of pretreated biomass substrates could be substantially reduced by optimizing the ratio of enzymes in the "cellulase" mixture.

Fed-batch saccharification and ethanol fermentation of Jerusalem artichoke stalks by an inulinase producing Saccharomyces cerevisiae MK01

Biorefinery of Jerusalem artichoke to produce ethanol as biofuel value-added product inulin.

Influence of bark on fuel ethanol production from steam-pretreated spruce

BACKGROUND

Bark and bark-containing forest residues have the potential for utilization as raw material for lignocellulosic ethanol production due to their abundance and low cost. However, the different physical properties and chemical composition of bark compared to the conventionally used wood chips may influence the spruce-to-ethanol bioconversion process. This study assesses the impact of bark on the overall bioconversion in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), utilizing steam-pretreated spruce bark and wood mixtures.

RESULTS

Mixtures of different proportions of spruce bark and wood chips were subjected to SO2-catalyzed steam pretreatment at 210°C for five minutes, which has been shown to be effective for the pretreatment of spruce wood chips. The final ethanol concentration was the highest without bark and decreased significantly with increasing proportions of bark in both process configurations. However, this decrease cannot be attributed solely to the lower availability of the carbohydrates in mixtures containing bark, as the ethanol yield also decreased, from 85 to 59% in SSF and from 84 to 51% in SHF, as the mass fraction of bark was increased from 0 to 100%.

CONCLUSIONS

The results show that it was significantly more difficult to hydrolyse spruce bark to monomeric sugars than wood chips. Bark had an adverse effect on the whole bioconversion process due to its lower enzymatic hydrolyzability. On the other hand, bark inclusion had no detrimental effect on the fermentability of steam-pretreated spruce wood and bark mixtures. It was also observed that lower amounts of inhibitory degradation products were formed during the steam pretreatment of spruce bark than during the steam pretreatment of wood chips.

Amphipathic lignin derivatives to accelerate simultaneous saccharification and fermentation of unbleached softwood pulp for bioethanol production

Amphipathic lignin derivatives (A-LDs) were already demonstrated to improve enzymatic saccharification of lignocellulose. Based on this knowledge, two kinds of A-LDs prepared from black liquor of soda pulping of Japanese cedar were applied to a fed-batch simultaneous saccharification and fermentation (SSF) process for unbleached soda pulp of Japanese cedar to produce bioethanol. Both lignin derivatives slightly accelerated yeast fermentation of glucose but not inhibited it. In addition, ethanol yields based on the theoretical maximum ethanol production in the fed-batch SSF process was increased from 49% without A-LDs to 64% in the presence of A-LDs.

Optimization of fed-batch enzymatic hydrolysis from alkali-pretreated sugarcane bagasse for high-concentration sugar production

Fed-batch enzymatic hydrolysis process from alkali-pretreated sugarcane bagasse was investigated to increase solids loading, produce high-concentration fermentable sugar and finally to reduce the cost of the production process. The optimal initial solids loading, feeding time and quantities were examined. The hydrolysis system was initiated with 12% (w/v) solids loading in flasks, where 7% fresh solids were fed consecutively at 6h, 12h, 24h to get a final solids loading of 33%. All the requested cellulase loading (10 FPU/g substrate) was added completely at the beginning of hydrolysis reaction. After 120 h of hydrolysis, the maximal concentrations of cellobiose, glucose and xylose obtained were 9.376 g/L, 129.50 g/L, 56.03 g/L, respectively. The final total glucan conversion rate attained to 60% from this fed-batch process.

Combined substrate, enzyme and yeast feed in simultaneous saccharification and fermentation allow bioethanol production from pretreated spruce biomass at high solids loadings

BACKGROUND

Economically feasible cellulosic ethanol production requires that the process can be operated at high solid loadings, which currently imparts technical challenges including inefficient mixing leading to heat and mass transfer limitations and high concentrations of inhibitory compounds hindering microbial activity during simultaneous saccharification and fermentation (SSF) process. Consequently, there is a need to develop cost effective processes overcoming the challenges when working at high solid loadings.

RESULTS

In this study we have modified the yeast cultivation procedure and designed a SSF process to address some of the challenges at high water insoluble solids (WIS) content. The slurry of non-detoxified pretreated spruce when used in a batch SSF at 19% (w/w) WIS was found to be inhibitory to Saccharomyces cerevisiae Thermosacc that produced 2 g l-1 of ethanol. In order to reduce the inhibitory effect, the non-washed solid fraction containing reduced amount of inhibitors compared to the slurry was used in the SSF. Further, the cells were cultivated in the liquid fraction of pretreated spruce in a continuous culture wherein the outflow of cell suspension was used as cell feed to the SSF reactor in order to maintain the metabolic state of the cell. Enhanced cell viability was observed with cell, enzyme and substrate feed in a SSF producing 40 g l-1 ethanol after 96 h corresponding to 53% of theoretical yield based on available hexose sugars compared to 28 g l-1 ethanol in SSF with enzyme and substrate feed but no cell feed resulting in 37% of theoretical yield at a high solids loading of 20% (w/w) WIS content. The fed-batch SSF also significantly eased the mixing, which is usually challenging in batch SSF at high solids loading.

CONCLUSIONS

A simple modification of the cell cultivation procedure together with a combination of yeast, enzyme and substrate feed in a fed-batch SSF process, made it possible to operate at high solids loadings in a conventional bioreactor. The proposed process strategy significantly increased the yeast cell viability and overall ethanol yield. It was also possible to obtain 4% (w/v) ethanol concentration, which is a minimum requirement for an economical distillation process.

Evolutionary engineering of a glycerol-3-phosphate dehydrogenase-negative, acetate-reducing Saccharomyces cerevisiae strain enables anaerobic growth at high glucose concentrations

Glycerol production by Saccharomyces cerevisiae, which is required for redox-cofactor balancing in anaerobic cultures, causes yield reduction in industrial bioethanol production. Recently, glycerol formation in anaerobic S. cerevisiae cultures was eliminated by expressing Escherichia coli (acetylating) acetaldehyde dehydrogenase (encoded by mhpF) and simultaneously deleting the GPD1 and GPD2 genes encoding glycerol-3-phosphate dehydrogenase, thus coupling NADH reoxidation to reduction of acetate to ethanol. Gpd^– strains are, however, sensitive to high sugar concentrations, which complicates industrial implementation of this metabolic engineering concept. In this study, laboratory evolution was used to improve osmotolerance of a Gpd^–mhpF-expressing S. cerevisiae strain. Serial batch cultivation at increasing osmotic pressure enabled isolation of an evolved strain that grew anaerobically at 1 M glucose, at a specific growth rate of 0.12 h⁻¹. The evolved strain produced glycerol at low concentrations (0.64 ± 0.33 g l⁻¹). However, these glycerol concentrations were below 10% of those observed with a Gpd⁺ reference strain. Consequently, the ethanol yield on sugar increased from 79% of the theoretical maximum in the reference strain to 92% for the evolved strains. Genetic analysis indicated that osmotolerance under aerobic conditions required a single dominant chromosomal mutation, and one further mutation in the plasmid-borne mhpF gene for anaerobic growth.

Batch and multi-step fed-batch enzymatic saccharification of Formiline-pretreated sugarcane bagasse at high solid loadings for high sugar and ethanol titers

Formiline pretreatment pertains to a biomass fractionation process. In the present work, Formiline-pretreated sugarcane bagasse was hydrolyzed with cellulases by batch and multi-step fed-batch processes at 20% solid loading. For wet pulp, after 144 h incubation with cellulase loading of 10 FPU/g dry solid, fed-batch process obtained ~150 g/L glucose and ~80% glucan conversion, while batch process obtained ~130 g/L glucose with corresponding ~70% glucan conversion. Solid loading could be further increased to 30% for the acetone-dried pulp. By fed-batch hydrolysis of the dried pulp in pH 4.8 buffer solution, glucose concentration could be 247.3±1.6 g/L with corresponding 86.1±0.6% glucan conversion. The enzymatic hydrolyzates could be well converted to ethanol by a subsequent fermentation using Saccharomices cerevisiae with ethanol titer of 60-70 g/L. Batch and fed-batch SSF indicated that Formiline-pretreated substrate showed excellent fermentability. The final ethanol concentration was 80 g/L with corresponding 82.7% of theoretical yield.

Increase in ethanol production from sugarcane bagasse based on combined pretreatments and fed-batch enzymatic hydrolysis

Enzymatic hydrolysis of pretreated sugarcane bagasse was performed to investigate the production of ethanol. The sugarcane bagasse was pretreated in a process combining steam explosion and alkaline delignification. The lignin content decreased to 83%. Fed-batch enzymatic hydrolyses was initiated with 8% (w/v) solids loading, and 10 FPU/g cellulose. Then, 1% solids were fed at 12, 24 or 48 h intervals. After 120 h, the hydrolysates were fermented with Saccharomyces cerevisiae UFPEDA 1238, and a fourfold increase in ethanol production was reached when fed-batch hydrolysis with a 12-h addition period was used for the steam pretreated and delignified bagasse.

Cellulase production by Penicillium funiculosum and its application in the hydrolysis of sugar cane bagasse for second generation ethanol production by fed batch operation

This study aimed to produce a cellulase blend and to evaluate its application in a simultaneous saccharification and fermentation (SSF) process for second generation ethanol production from sugar cane bagasse. The sugar cane bagasse was subjected to pretreatments (diluted acid and alkaline), as for disorganizing the ligocellulosic complex, and making the cellulose component more amenable to enzymatic hydrolysis. The residual solid fraction was named sugar cane bagasse partially delignified cellulignin (PDC), and was used for enzyme production and ethanol fermentation. The enzyme production was performed in a bioreactor with two inoculum concentrations (5 and 10% v/v). The fermentation inoculated with higher inoculum size reduced the time for maximum enzyme production (from 72 to 48). The enzyme extract was concentrated using tangential ultrafiltration in hollow fiber membranes, and the produced cellulase blend was evaluated for its stability at 37 °C, operation temperature of the simultaneous SSF process, and at 50 °C, optimum temperature of cellulase blend activity. The cellulolytic preparation was stable for at least 300 h at both 37 °C and 50 °C. The ethanol production was carried out by PDC fed-batch SSF process, using the onsite cellulase blend. The feeding strategy circumvented the classic problems of diffusion limitations by diminishing the presence of a high solid:liquid ratio at any time, resulting in high ethanol concentration at the end of the process (100 g/L), which corresponded to a fermentation efficiency of 78% of the maximum obtainable theoretically. The experimental results led to the ratio of 380 L of ethanol per ton of sugar cane bagasse PDC.

Ethanol production from wheat straw by recombinant Escherichia coli strain FBR5 at high solid loading

Ethanol production by a recombinant bacterium from wheat straw (WS) at high solid loading by separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) was studied. The yield of total sugars from dilute acid pretreated WS (150 g/L) after enzymatic saccharification was 86.3±1.5 g/L. The pretreated WS was bio-abated by growing a fungal strain aerobically in the liquid portion for 16 h. The recombinant Escherichia coli strain FBR5 produced 41.1±1.1 gethanol/L from non-abated WS hydrolyzate (total sugars, 86.6±0.3 g/L) in 168 h at pH7.0 and 35 °C. The bacterium produced 41.8±0.0 g ethanol/L in 120 h from the bioabated WS by SHF. It produced 41.6±0.7 g ethanol/L in 120 h from bioabated WS by fed-batch SSF. This is the first report of the production of above 4% ethanol from a lignocellulosic hydrolyzate by the recombinant bacterium.

Bioconversion of Agricultural Waste to Ethanol by SSF Using Recombinant Cellulase from Clostridium thermocellum

The effect of different pretreatment methods, temperature, and enzyme concentration on ethanol production from 8 lignocellulosic agrowaste by simultaneous saccharification and fermentation (SSF) using recombinant cellulase and Saccharomyces cerevisiae were studied. Recombinant cellulase was isolated from E. coli BL21 cells transformed with CtLic26A-Cel5-CBM11 full-length gene from Clostridium thermocellum and produced in both batch and fed-batch processes. The maximum cell OD and specific activity in batch mode were 1.6 and 1.91 U/mg, respectively, whereas in the fed-batch mode, maximum cell OD and specific activity were 3.8 and 3.5 U/mg, respectively, displaying a 2-fold increase. Eight substrates, Syzygium cumini (jamun), Azadirachta indica (neem), Saracens indica (asoka), bambusa dendrocalmus (bamboo), Populas nigra (poplar), Achnatherum hymenoides (wild grass), Eucalyptus marginata (eucalyptus), and Mangifera indica (mango), were subjected to SSF. Of three pretreatments, acid, alkali, and steam explosion, acid pretreatment Syzygium cumini (Jamun) at 30°C gave maximum ethanol yield of 1.42 g/L.

Improved one-step steam pretreatment of SO2-impregnated softwood with time-dependent temperature profile for ethanol production

In the production of ethanol from lignocellulosic material, pretreatment of the raw material before enzymatic hydrolysis and fermentation is essential to obtain high overall yields of sugar and ethanol. Two-step steam pretreatment results in higher ethanol yields from softwood than the standard one-step pretreatment process. However, the difficulty with separation and washing of the material at high pressure between the two pretreatment steps is a major drawback. In this study, a new one-step pretreatment procedure was investigated, in which the time-temperature profile was varied during pretreatment. The efficiency of pretreatment was assessed by performing simultaneous saccharification and fermentation on the pretreated slurries. Pretreatment of SO(2)-impregnated softwood performed by varying the temperature (190-226 degrees C), the residence time (5-10 min), and the mode of temperature increase (linear or stepwise), resulted in recovery of about 90% of the mannose and glucose present in the raw material. The highest ethanol yield, 75% of theoretical based on the glucan and mannan content of the raw material, was obtained at pretreatment conditions of 190 degrees C for 12 min. Similar ethanol yields were achieved when running the pretreatment as one-step (190-200 degrees C), two levels of temperature, at shorter residence time (7 min), which results in lower capital costs for the process.

Ethanol production from high dry matter corncob using fed-batch simultaneous saccharification and fermentation after combined pretreatment

To obtain high concentration of ethanol from cellulose, corncob was pretreated with acid and alkali to remove non-cellulose components, and then subjected to simultaneous saccharification and fermentation (SSF). An ethanol concentration as high as 69.2 g/L was achieved with 19% dry matter (DM) using batch SSF, resulting in an 81.2% overall ethanol yield. A fed-batch process using a high solid concentration was also investigated. Fresh substrate was pretreated with dilute sulfuric acid-sodium hydroxide, and then added at different amounts during the first 24 h, to yield a final dry matter content of 25% (w/v). SSF conditions with cellulose loading of 22.8 FPU/g glucan, dry yeast (Saccharomyces cerevisiae) loading of 5 g/L and substrate supplementation every 4h yielded the highest ethanol concentration of 84.7 g/L after 96 h. This corresponded to a 79% overall ethanol yield.

Process design and economics of on-site cellulase production on various carbon sources in a softwood-based ethanol plant

On-site cellulase enzyme fermentation in a softwood-to-ethanol process, based on SO(2)-catalysed steam pretreatment followed by simultaneous saccharification and fermentation, was investigated from a techno-economic aspect using Aspen Plus© and Aspen Icarus Process Evaluator© softwares. The effect of varying the carbon source of enzyme fermentation, at constant protein and mycelium yields, was monitored through the whole process. Enzyme production step decreased the overall ethanol yield (270 L/dry tonne of raw material in the case of purchased enzymes) by 5-16 L/tonne. Capital cost was found to be the main cost contributor to enzyme fermentation, constituting to 60-78% of the enzyme production cost, which was in the range of 0.42-0.53 SEK/L ethanol. The lowest minimum ethanol selling prices (4.71 and 4.82 SEK/L) were obtained in those scenarios, where pretreated liquid fraction supplemented with molasses was used as carbon source. In some scenarios, on-site enzyme fermentation was found to be a feasible alternative.

Effects of enzyme feeding strategy on ethanol yield in fed-batch simultaneous saccharification and fermentation of spruce at high dry matter

BACKGROUND

To make lignocellulosic fuel ethanol economically competitive with fossil fuels, it is necessary to reduce the production cost. One way to achieve this is by increasing the substrate concentration in the production process, and thus reduce the energy demand in the final distillation of the fermentation broth. However, increased substrate concentration in simultaneous saccharification and fermentation (SSF) processes has been shown to result in reduced ethanol yields and severe stirring problems. Because the SSF medium is being continuously hydrolyzed, running the process in fed-batch mode could potentially reduce the stirring problems and lead to increased ethanol yields in high-solids SSF. Different enzyme feeding strategies, with the enzymes either present in the reactor from start-up or fed into the reactor together with the substrate, have been studied, along with the influence of the enzyme feeding strategy on the final ethanol yield and productivity.

RESULTS

In the present study, SSF was run successfully with 10% and 14% water-insoluble solids (WIS) in batch and fed-batch mode. The mixing of the material in the reactor was significantly better in fed-batch than batch mode, and similarly high or higher ethanol yields were achieved in fed-batch mode compared with batch SSF in some cases. No general trend in the dependence of ethanol yield on enzyme feeding strategy was found.

CONCLUSIONS

The optimum enzyme feeding strategy appears to depend on the conditions during SSF, such as the WIS concentration and the concentration of inhibitory compounds in the SSF medium.

Dilute sulfuric acid hydrolysis of sugar maple wood extract at atmospheric pressure

Acid hydrolysis of hot-water wood extract was investigated. Sugar maple wood extract was obtained by hot-water extraction at 160 degrees C for 120min, followed by further concentration and solid removal by membrane filtration. Acid hydrolysis was performed at different temperatures (85 degrees C, 95 degrees C and 105 degrees C) and concentrations of sulfuric acid (wt.%: 1.5%, 3.1% and 6.2%). Hydrolyzate was analyzed by (1)H NMR spectroscopy. The concentrations of several major substances in the hydrolyzate were discussed in detail. Higher temperature, higher acid concentration and longer residence time all favor the depolymerization of hemicellulose wood extracts. Mainly xylose and acetic acid are recovered from the hydrolysis process.

Ethanol production from the organic fraction obtained after thermal pretreatment of municipal solid waste

In this work, the use of organic fraction from municipal solid waste (MSW) as substrate for ethanol production based on enzymatic hydrolysis was evaluated. MSW was subjected to a thermal pretreatment (active hygienization) at 160 degrees C from 5 to 50 min. The organic fiber obtained after 30 min was used as substrate in a simultaneous saccharification and fermentation (SSF) and fed-batch SSF process using cellulases and amylases. In a fed-batch mode with 25% (w/w) substrate loading, final ethanol concentration of 30 g/L was achieved (60% of theoretical). In these conditions, more than 160 L of ethanol per ton of dry matter could be produced from the organic fraction of MSW.