| 1. |
- Albers, Eva, 1966, et al.
(författare)
-
Comparison of industrial xylose fermentation with yeast performed at different process scale
- 2012
-
Ingår i: 13th International Congress on Yeasts, ICY 2012, August 26-30, Madison, USA.
-
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.
|
|
| 2. |
- Albers, Eva, 1966, et al.
(författare)
-
Development of industrial yeast strains for efficient xylose fermentation in lignocellulosic material
- 2012
-
Ingår i: 13th International Congress on Yeasts, ICY 2012, August 26-30, Madison, USA.
-
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.
|
|
| 3. |
- Koppram, Rakesh, 1986, et al.
(författare)
-
A novel process configuration of Simultaneous Saccharification and Fermentation for bioethanol production at high solid loadings
- 2012
-
Ingår i: Advanced Biofuels in a Biorefinery Approach, February 28 - March 1, 2012, Copenhagen, Denmark.
-
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.
|
|
| 4. |
- Koppram, Rakesh, 1986, et al.
(författare)
-
CHALLENGES AND POSSIBILITIES OF SECOND GENERATION BIOETHANOL PRODUCTION PROCESS AT HIGH SUBSTRATE
- 2012
-
Ingår i: Science and Technology Day 2012, March 27, 2012, Göteborg, Sweden.
-
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.
|
|
| 5. |
- Koppram, Rakesh, 1986, et al.
(författare)
-
Evolutionary engineering strategies to enhance tolerance of xylose utilizing recombinant yeast to inhibitors derived from spruce biomass
- 2012
-
Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 5, s. Art. no. 32-
-
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.
|
|
| 6. |
- Koppram, Rakesh, 1986, et al.
(författare)
-
Simultaneous Saccharification and Fermentation with substrate, enzyme and yeast feed facilitate bioethanol production at high solids loadings
- 2012
-
Ingår i: From Human Health to Biosustainability - Future Challenges for Life Science at Chalmers, November 19, 2012, Göteborg, Sweden.
-
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.
|
|
