| 1. |
- Albers, Eva, 1966, et al.
(författare)
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Comparison of industrial xylose fermentation with yeast performed at different process scale
- 2012
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Ingår i: 13th International Congress on Yeasts, ICY 2012, August 26-30, Madison, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Second generation of bioethanol production with yeast from lignocellulosic material may contribute to a sustainable production of energy. However, the commercialization of cellulose-to-ethanol remains challenging due to various limitations in process technology and microbial physiology. Despite that the technical progress lately has come far, lignocellulose bioethanol production is still not well established in full production scale. Production scale demands large financial investments and to minimize the risk knowledge about cellular performance of the yeast as response to conditions of large scale is needed. Large scale may impose specific conditions that normally are not present in smaller scale. Such conditions are then needed to be identified and mimicked in smaller scale to obtain crucial scaling-up data. In this project, we wanted to establish scalable cultivation processes and compare the performance at different scales. Experiments were performed at three process scales: lab (1.5 l), process development unit (15 l) and demonstration (10 m3) scales, with an industrial recombinant xylose fermenting Saccharomyces cerevisiae strain and corn cob, bagasse, and spruce lignocellulosic material. It was found that separate fermentation and SSF experiments could be reproducible at all scales. An ethanol level could be obtained above 4 % which is the threshold for feasible down-stream processing. Demonstration scale experiments on xylose-rich liquid of pre-treated corn cobs resulted in a 90% conversion of xylose to ethanol and on the slurry in SSF cultivation an ethanol yield of 0.44 g/g xylose was obtained.
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| 2. |
- Albers, Eva, 1966, et al.
(författare)
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Development of industrial yeast strains for efficient xylose fermentation in lignocellulosic material
- 2012
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Ingår i: 13th International Congress on Yeasts, ICY 2012, August 26-30, Madison, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fermentation at large industrial scale poses several challenges for the fermenting microorganism to handle. Thus, for an efficient production it is desirable to have robust and efficient strains, which can cope with the specific conditions in the process. For bioethanol production by yeast from lignocellulosic material, one of the largest challenges is the mixture of sugars and the content of inhibitory compounds in the material. Wild-type strains of Saccharomyces cerevisiae can only convert hexose sugars but not the pentoses, xylose and arabinose, which may be present in these materials. However, strains have been genetically modified to allow for xylose conversion, but their performance need to be improved in terms of rate and efficiency. During the pre-treatment of lignocellulosic material the inhibitory compounds are formed; furans, phenolics and organic acids. In an industrial setting, a robust strain back ground (industrial yeast strains) is a prerequisite, in which first pentose fermenting traits should be incorporated and further improvement of the tolerance to inhibitory compounds need to follow. In the present project, we have used directed evolution to simultaneously improve the inhibitor tolerance and xylose conversion capability of recombinant yeast strains with an industrial background. The strains showed increased xylose utilization and ethanol production which was for some strains coupled to decreased xylitol formation. The resulting properties of the strains are highly dependent on the mode of directed evolution applied, which may also give rise to quite a number of clones with different properties.
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| 3. |
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| 4. |
- Franzén, Carl Johan, 1966, et al.
(författare)
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Multifeed simultaneous saccharification and fermentation enables high gravity submerged fermentation of lignocellulose.
- 2015
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Ingår i: Recent Advances in Fermentation Technology (RAFT 11), Clearwater Beach, Florida, USA, November 8-11, 2015. Oral presentation..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Today, second generation bioethanol production is becoming established in production plants across the world. In addition to its intrinsic value, the process can be viewed as a model process for biotechnological conversion of recalcitrant lignocellulosic raw materials to a range of chemicals and other products. So called High Gravity operation, i.e. fermentation at high solids loadings, represents continued development of the process towards higher product concentrations and productivities, and improved energy and water economy. We have employed a systematic, model-driven approach to the design of feeding schemes of solid substrate, active yeast adapted to the actual substrate, and enzymes to fed-batch simultaneous saccharification and co-fermentation (Multifeed SSCF) of steam-pretreated lignocellulosic materials in stirred tank reactors. With this approach, mixing problems were avoided even at water insoluble solids contents of 22%, leading to ethanol concentrations of 56 g/L within 72 hours of SSCF on wheat straw. Similar fermentation performance was verified in 10 m3 demonstration scale using wheat straw, and in lab scale on birch and spruce, using several yeast strains. The yeast was propagated in the liquid fraction obtained by press filtration of the pretreated slurry. Yet, even with such preadaptation and repeated addition of fresh cells, the viability in the SSCF dropped due to interactions between lignocellulose-derived inhibitors, the produced ethanol and the temperature. Decreasing the temperature from 35 to 30°C when the ethanol concentration reached 40-50 g/L resulted in rapid initial hydrolysis, maintained fermentation capacity, lower residual glucose and xylose and ethanol concentrations above 60 g/L.
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| 5. |
- Koppram, Rakesh, 1986, et al.
(författare)
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A novel process configuration of Simultaneous Saccharification and Fermentation for bioethanol production at high solid loadings
- 2012
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Ingår i: Advanced Biofuels in a Biorefinery Approach, February 28 - March 1, 2012, Copenhagen, Denmark.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Simultaneous saccharification and fermentation (SSF) is a process option for lignocellulosic bioethanol production that has proven to have several advantages compared to separate hydrolysis and fermentation. The economical viability and commercialization of cellulose-to-ethanol demands the process to work under high-solid loadings to result in high sugar yield and final ethanol titer in S. cerevisiae based SSF process. In a conventional batch SSF process practical limitations to high-solid loadings include, poor mixing and accessibility of enzymes to substrates and high inhibitors concentration that reduces the yeast viability and metabolism. In order to overcome these limitations, we propose a novel SSF process configuration involving feeding of substrate, enzyme and yeast. It is possible to overcome mixing issues associated with a batch SSF at high-solid loadings by a feed of substrate, enzyme and yeast. The feed of freshly cultivated yeast throughout the fermentation process ensures active metabolic state of yeast. In addition, the substrate feed ensures low inhibitors concentration at any given time point increasing the survival ability of yeast compared to a batch SSF. The enzyme feed ensures slow release of glucose providing an opportunity for xylose consuming yeast strain to co-consume xylose together with glucose. The aim of the current work is to understand how different combinations of feeding strategies influence the outcome of the SSF process. In the longer perspective, we aim at deducing an optimized SSF process that can handle very high-solid loadings with efficient hydrolysis and fermentation process at low enzyme and yeast loadings, respectively.
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| 6. |
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| 7. |
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| 8. |
- Koppram, Rakesh, 1986, et al.
(författare)
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CHALLENGES AND POSSIBILITIES OF SECOND GENERATION BIOETHANOL PRODUCTION PROCESS AT HIGH SUBSTRATE
- 2012
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Ingår i: Science and Technology Day 2012, March 27, 2012, Göteborg, Sweden.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the scientific battle of alleviating green house gas emissions, second generation bioethanol produced from cheap, renewable and abundantly available lignocellulosic materials, is believed to play a major role. However, the commercialization of cellulose-to-ethanol remains challenging due to various limitations in process technology and microbial physiology. An important process parameter is the ability to work under high-solids concentration for the energy balance and economical viability of bioethanol production. Maintaining high substrate concentration presumed to result in high sugar yield and high ethanol concentration in subsequent yeast based fermentation. Practical limitations to a high-solids process include, poor mixing and accessibility of enzymes to substrates and high inhibitors concentration that reduces the yeast viability and metabolism. The current work involves testing various feeding strategies with enzymes and substrates yeast in a simultaneous saccharification and fermentation (SSF) process in contrast to a conventional batch SSF process. The aim is to understand how different combination of feeding strategies that influence the outcome of the SSF process. In the longer perspective, we aim at deducing an optimized SSF process that can handle very high-solids concentration with efficient hydrolysis and fermentation process at low enzyme and yeast loadings, respectively.
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| 9. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Combined substrate, enzyme and yeast feed in simultaneous saccharification and fermentation allow bioethanol production from pretreated spruce biomass at high solids loadings
- 2014
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Evolutionary engineering strategies to enhance tolerance of xylose utilizing recombinant yeast to inhibitors derived from spruce biomass
- 2012
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 5, s. Art. no. 32-
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundOne of the crucial factors for a sustainable and economical production of lignocellulosic based bioethanol is the availability of a robust fermenting microorganism with high tolerance to inhibitors generated during the pretreatment of lignocellulosic raw materials, since these inhibitors are known to severely hinder growth and fermentation.ResultsA long-term adaptation in repetitive batch cultures in shake flasks using a cocktail of 12 different inhibitors and a long-term chemostat adaptation using spruce hydrolysate were used as evolutionary engineering strategies to improve the inhibitor tolerance in the metabolically engineered xylose utilizing Saccharomyces cerevisiae strain, TMB3400. The yeast was evolved for a period of 429 and 97 generations in repetitive batch cultures and chemostat cultivation, respectively. During the evolutionary engineering in repetitive batch cultures the maximum specific growth rate increased from 0.18 h-1 to 0.33 h-1 and the time of lag phase was decreased from 48 h to 24 h. In the chemostat adaptation, after 97 generations, the specific conversion rates of HMF and furfural were found to be 3.5 and 4 folds higher respectively, compared to rates after three generations. Two evolved strains (RK60-5, RKU90-3) and one evolved strain (KE1-17) were isolated from evolutionary engineering in repetitive batches and chemostat cultivation, respectively. The strains displayed significantly improved growth performance over TMB3400 when cultivated in spruce hydrolysate under anaerobic conditions, the evolved strains exhibited 25 to 38% increase in specific consumption rate of sugars and 32 to 50% increased specific ethanol productivity compared to TMB3400. The evolved strains RK60-5 and RKU90-3 were unable to consume xylose under anaerobic conditions, whereas, KE1-17 was found to consume xylose at similar rates as TMB3400.ConclusionUsing evolutionary engineering strategies in batch and chemostat cultivations we have generated three evolved strains that show significantly better tolerance to inhibitors in spruce hydrolysate and displayed a shorter time for overall fermentation of sugars compared to the parental strain.
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| 11. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Lignocellulosic ethanol production at high-gravity: Challenges and perspectives
- 2014
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Ingår i: Trends in Biotechnology. - : Elsevier BV. - 0167-7799 .- 1879-3096. ; 32:1, s. 46-53
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Forskningsöversikt (refereegranskat)abstract
- In brewing and ethanol-based biofuel industries, high-gravity fermentation produces 10-15% (v/v) ethanol, resulting in improved overall productivity, reduced capital cost, and reduced energy input compared to processing at normal gravity. High-gravity technology ensures a successful implementation of cellulose to ethanol conversion as a cost-competitive process. Implementation of such technologies is possible if all process steps can be performed at high biomass concentrations. This review focuses on challenges and technological efforts in processing at high-gravity conditions and how these conditions influence the physiology and metabolism of fermenting microorganisms, the action of enzymes, and other process-related factors. Lignocellulosic materials add challenges compared to implemented processes due to high inhibitors content and the physical properties of these materials at high gravity. © 2013 Elsevier Ltd.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Simultaneous saccharification and co-fermentation for bioethanol production using corncobs at lab, PDU and demo scales
- 2013
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundWhile simultaneous saccharification and co-fermentation (SSCF) is considered to be a promising process for bioconversion of lignocellulosic materials to ethanol, there are still relatively little demo-plant data and operating experiences reported in the literature. In the current work, we designed a SSCF process and scaled up from lab to demo scale reaching 4% (w/v) ethanol using xylose rich corncobs.ResultsSeven different recombinant xylose utilizing Saccharomyces cerevisiae strains were evaluated for their fermentation performance in hydrolysates of steam pretreated corncobs. Two strains, RHD-15 and KE6-12 with highest ethanol yield and lowest xylitol yield, respectively were further screened in SSCF using the whole slurry from pretreatment. Similar ethanol yields were reached with both strains, however, KE6-12 was chosen as the preferred strain since it produced 26% lower xylitol from consumed xylose compared to RHD-15. Model SSCF experiments with glucose or hydrolysate feed in combination with prefermentation resulted in 79% of xylose consumption and more than 75% of the theoretical ethanol yield on available glucose and xylose in lab and PDU scales. The results suggest that for an efficient xylose conversion to ethanol controlled release of glucose from enzymatic hydrolysis and low levels of glucose concentration must be maintained throughout the SSCF. Fed-batch SSCF in PDU with addition of enzymes at three different time points facilitated controlled release of glucose and hence co-consumption of glucose and xylose was observed yielding 76% of the theoretical ethanol yield on available glucose and xylose at 7.9% water insoluble solids (WIS). With a fed-batch SSCF in combination with prefermentation and a feed of substrate and enzymes 47 and 40 g l-1 of ethanol corresponding to 68% and 58% of the theoretical ethanol yield on available glucose and xylose were produced at 10.5% WIS in PDU and demo scale, respectively. The strain KE6-12 was able to completely consume xylose within 76 h during the fermentation of hydrolysate in a 10 m3 demo scale bioreactor.ConclusionsThe potential of SSCF is improved in combination with prefermentation and a feed of substrate and enzymes. It was possible to successfully reproduce the fed-batch SSCF at demo scale producing 4% (w/v) ethanol which is the minimum economical requirement for efficient lignocellulosic bioethanol production process.
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| 16. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Simultaneous saccharification and co-fermentation for bioethanol production using corncobs at lab, PDU and demo scales
- 2015
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Ingår i: Fuel production from non-food biomass: Corn stover. - : Apple Academic Press. - 9781498728430 - 9781771881234 ; , s. 155-179
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The global CO2 emissions in 2010 from fossil energy use grew at the fastest rate since 1969. The year 2010 also witnessed that the global oil production did not match the rapid growth in consumption [1]. These recent data further intensify worldwide concerns about greenhouse gas emissions and energy security for a sustained economic development. For a reduced dependence on oil from fossil reserves, use of biofuels such as bioethanol from abundantly available lignocellulosic biomass is of great interest nowadays because they will count towards meeting the mandate of 10% binding target for biofuels from renewable sources in the transport for all European member states by 2020 [2]. Along with this interest comes increased interest in commercializing ethanol production technology from inexpensive lignocellulosic feedstocks which includes wood biomass, agricultural and forestry residues, biodegradable fraction of industrial and municipal wastes. Irrespective of type, the basic structural composition of lignocellulosic biomass consists of cellulose, hemicellulose and lignin. The cellulose and hemicellulose that form the polysaccharide fraction are embedded in a recalcitrant and inaccessible arrangement [3] and therefore requires a pretreatment step to disrupt the structure and make it accessible for subsequent steps. Since lignocellulosic materials are very complex, not one pretreatment method can apply for all the materials. Several methods that are classified in to physical, physico-chemical, chemical and biological pretreatment have been investigated and an elaborate review on each of these methods has been presented by Taherzadeh and Karimi [4]. One of the most commonly used pretreatment methods is steam explosion, with the addition of H2SO4 or SO2, which removes most of the hemicellulose, followed by enzymatic hydrolysis to convert cellulose to glucose [5,6].
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| 17. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Simultaneous Saccharification and Fermentation Performance of S. cerevisiae strains on spruce and bagasse slurries
- 2010
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Ingår i: 4th Conference on Physiology of Yeast and Filamentous Fungi (PYFF4), 2010, Rotterdam, Netherlands.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Simultaneous Saccharification and Fermentation (SSF) is considered to be the most preferred option for bioethanol production from lignocellulosic raw materials. It is a process where enzymatic hydrolysis of water insoluble solids (WIS) in a slurry and fermentation of hydrolyzed sugars takes place simultaneously. It is possible to achieve high final ethanol concentrations and a high overall ethanol yield by having high WIS content in a SSF process. A wide variety of lignocellulosic materials such as softwood, hardwood and grasses are available as options for raw materials and their compositions show huge diversity. Subsequently, the fermentation performance of yeast show large variations in these varied raw materials. The present work demonstrates the performance of two strains of S. cerevisiae (parental strain and RKU903) in a SSF process using spruce and bagasse slurries at 7.5% and 11% WIS content. Enzyme mixture from Novozymes (NS-22074) at 5 FPU/g WIS is used for saccharification with an initial cell concentration of 3 g dry weight/l. The process is maintained at pH 5.0 and 35 °C for a period of 96h. The analysis of SSF show that both strains perform well at 7.5% WIS spruce and no major differences observed between the strains in terms of consumption of sugars and ethanol production. However, at 11% WIS spruce both strains were not able to completely convert HMF and resulted in lower ethanol yields compared to SSF at 7.5% WIS spruce. On the other hand, at 7.5% WIS bagasse the parental strain displayed poor consumption of sugars despite low levels of HMF and furfural. This indicates the presence of other inhibitors which might limit the utilization of sugars by yeast cells. Analyses also show that considerable amounts of residual xylose were present at the end of SSF. The results from SSF experiments also suggests that for a complete characterization of yeast strains SSF at higher WIS contents in varied raw materials are needed to be performed.
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| 18. |
- Koppram, Rakesh, 1986, et al.
(författare)
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Simultaneous Saccharification and Fermentation with substrate, enzyme and yeast feed facilitate bioethanol production at high solids loadings
- 2012
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Ingår i: From Human Health to Biosustainability - Future Challenges for Life Science at Chalmers, November 19, 2012, Göteborg, Sweden.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Simultaneous saccharification and fermentation (SSF) is an interesting process option for lignocellulosic bioethanol production. The economical viability and commercialization of cellulose-to-ethanol demands the process to work under high-solid loadings to result in high sugar yield and final ethanol titer in S. cerevisiae based SSF process. In a conventional batch SSF process practical limitations to high-solid loadings include, poor mixing and accessibility of enzymes to substrates and high inhibitors concentration that reduces the yeast viability and metabolism. In order to overcome these limitations, we propose an improved SSF process configuration involving feeding of substrate, enzyme and yeast. It is possible to achieve maximum dilution effect with substrate, enzyme and yeast feed thereby overcoming the mixing issues associated with a batch SSF at high-solid loadings. The feed of freshly cultivated yeast throughout the fermentation process ensures active metabolic state of yeast. In addition, the substrate feed ensures low inhibitors concentration at any given time point increasing the survival ability of yeast in contrast to a batch SSF. The enzyme feed ensures slow release of glucose providing an opportunity to xylose consuming yeast strain to co-consume xylose together with glucose. With a feed of enzyme, cells and substrate, a SSF process with 20% WIS of spruce biomass yielded 40 g/l of ethanol compared to the conventional batch SSF that yielded only 13 g/l of ethanol with severe yeast and enzyme inhibition. This novel process was able to work even at 25% WIS of spruce biomass without any difficulties in mixing and therefore reducing the total power consumption due to stirring. These features make this novel configuration of SSF an extremely viable commercial approach to lignocellulosic bioethanol production at high solids loadings.
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| 19. |
- Koppram, Rakesh, 1986, et al.
(författare)
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The Presence of Pretreated Lignocellulosic Solids from Birch during Saccharomyces cerevisiae Fermentations Leads to Increased Tolerance to Inhibitors - A Proteomic Study of the Effects
- 2016
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203 .- 1932-6203. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- The fermentation performance of Saccharomyces cerevisiae in the cellulose to ethanol conversion process is largely influenced by the components of pretreated biomass. The insoluble solids in pretreated biomass predominantly constitute cellulose, lignin, and -to a lesser extent-hemicellulose. It is important to understand the effects of water-insoluble solids (WIS) on yeast cell physiology and metabolism for the overall process optimization. In the presence of synthetic lignocellulosic inhibitors, we observed a reduced lag phase and enhanced volumetric ethanol productivity by S. cerevisiae CEN. PK 113-7D when the minimal medium was supplemented with WIS of pretreated birch or spruce and glucose as the carbon source. To investigate the underlying molecular reasons for the effects of WIS, we studied the response of WIS at the proteome level in yeast cells in the presence of acetic acid as an inhibitor. Comparisons were made with cells grown in the presence of acetic acid but without WIS in the medium. Altogether, 729 proteins were detected and quantified, of which 246 proteins were significantly up-regulated and 274 proteins were significantly down-regulated with a fold change >= 1.2 in the presence of WIS compared to absence of WIS. The cells in the presence of WIS up-regulated several proteins related to cell wall, glycolysis, electron transport chain, oxidative stress response, oxygen and radical detoxification and unfolded protein response; and down-regulated most proteins related to biosynthetic pathways including amino acid, purine, isoprenoid biosynthesis, aminoacyl-tRNA synthetases and pentose phosphate pathway. Overall, the identified differentially regulated proteins may indicate that the likelihood of increased ATP generation in the presence of WIS was used to defend against acetic acid stress at the expense of reduced biomass formation. Although, comparative proteomics of cells with and without WIS in the acetic acid containing medium revealed numerous changes, a direct effect of WIS on cellular physiology remains to be investigated.
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| 20. |
- Wang, Ruifei, 1985, et al.
(författare)
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Kinetic modeling of multi-feed simultaneous saccharification and co-fermentation of pretreated birch to ethanol
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 172, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- Fed-batch simultaneous saccharification and fermentation (SSF) is a feasible option for bioethanol production from lignocellulosic raw materials at high substrate concentrations. In this work, a segregated kinetic model was developed for simulation of fed-batch simultaneous saccharification and co-fermentation (SSCF) of steam-pretreated birch, using substrate, enzymes and cell feeds. The model takes into account the dynamics of the cellulase–cellulose system and the cell population during SSCF, and the effects of pre-cultivation of yeast cells on fermentation performance. The model was cross-validated against experiments using different feed schemes. It could predict fermentation performance and explain observed differences between measured total yeast cells and dividing cells very well. The reproducibility of the experiments and the cell viability were significantly better in fed-batch than in batch SSCF at 15% and 20% total WIS contents. The model can be used for simulation of fed-batch SSCF and optimization of feed profiles.
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| 21. |
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| 22. |
- Xiros, Charilaos, 1973, et al.
(författare)
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Toward a sustainable biorefinery using high-gravity technology
- 2017
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Ingår i: Biofuels, Bioproducts and Biorefining. - : Wiley. - 1932-1031 .- 1932-104X. ; 11:1, s. 15-27
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Tidskriftsartikel (refereegranskat)abstract
- The realization of process solutions for a sustainable bioeconomy depends on the efficient processing of biomass. High-gravity technology is one important alternative to realizing such solutions. The aims of this work were to expand the knowledge-base on lignocellulosic bioconversion processes at high solids content, to advance the current technologies for production of second-generation liquid biofuels, to evaluate the environmental impact of the proposed process by using life cycle assessment (LCA), and to develop and present a technically, economically, and environmentally sound process at high gravity, i.e., a process operating at the highest possible concentrations of raw material. The results and opinions presented here are the result of a Nordic collaborative study within the framework of the HG Biofuels project. Processes with bioethanol or biobutanol as target products were studied using wheat straw and spruce as interesting Nordic raw materials. During the project, the main scientific, economic, and technical challenges of such a process were identified. Integrated solutions to these challenges were proposed and tested experimentally, using wheat straw and spruce wood at a dry matter content of 30% (w/w) as model substrates. The LCA performed revealed the environmental impact of each of the process steps, highlighting the importance of the enzyme dose used for the hydrolysis of the plant biomass, as well as the importance of the fermentation yield.
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