| 1. |
- Wang, Ruifei, 1985, et al.
(författare)
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Kinetic modeling-based optimization of multi-feed simultaneous saccharification and co-fermentation of wheat straw for ethanol production
- 2015
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Ingår i: 37th Symposium on Biotechnology for Fuels and Chemicals, Oral presentation.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fed-batch simultaneous saccharification and co-fermentation (SSCF) enables production of lignocellulosic ethanol with high content of water insoluble solids (WIS), and therefore high cellulose loadings (the major sugar source in lignocellulose). The viscosity of the SSCF broth and the mass/heat transfer efficiency, depend on the feeding frequency of solid substrates and the hydrolytic activities of the added cellulases. An ideal feeding scheme should avoid over-feeding which leads to mixing problems, while feeding as much substrates as possible to shorten the process time and increase the final ethanol titer. A previously developed kinetic model [1] was modified to predict the performance of cellulases on steam pre-treated wheat straw, and to decide when and how much WIS to feed in the next feeding event. With this approach, mixing problems could be completely avoided up to 22.2% WIS in lab scale stirred tank reactors, and ethanol concentrations reached 56 g/L within 72 hours of SSCF. The process was tested at demonstration scale in 10 m3 reactors, and a similar fermentation performance as that in lab scale was observed. Further feeding of solid substrate (>20% WIS) did not lead to increases in the ethanol concentration, while a substantial loss of yeast viability (colony forming unit) were observed in SSCF medium at high WIS contents. This was likely due to toxic compounds retained in the pre-treated lignocellulose. We are currently investigating different xylose fermenting Saccharomyces cerevisiae strains in the SSCF process to increase the ethanol titer further. [1] Wang et al. Bioresour. Technol., 2014
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| 2. |
- Wang, Ruifei, 1985, et al.
(författare)
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Model-based optimization and scale-up of multi-feed simultaneous saccharification and co-fermentation of steam pre-treated lignocellulose enables high gravity ethanol production.
- 2016
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 9:1, s. 88-
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Tidskriftsartikel (refereegranskat)abstract
- High content of water-insoluble solids (WIS) is required for simultaneous saccharification and co-fermentation (SSCF) operations to reach the high ethanol concentrations that meet the techno-economic requirements of industrial-scale production. The fundamental challenges of such processes are related to the high viscosity and inhibitor contents of the medium. Poor mass transfer and inhibition of the yeast lead to decreased ethanol yield, titre and productivity. In the present work, high-solid SSCF of pre-treated wheat straw was carried out by multi-feed SSCF which is a fed-batch process with additions of substrate, enzymes and cells, integrated with yeast propagation and adaptation on the pre-treatment liquor. The combined feeding strategies were systematically compared and optimized using experiments and simulations.
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| 3. |
- Wang, Ruifei, 1985, et al.
(författare)
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Process optimization of multi-feed SSCF
- 2014
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Ingår i: 10th European Symposium on Biochemical Engineering Sciences and 6th International Forum on Industrial Bioprocesses.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Economical production of bio-ethanol from lignocellulosic materials requires an efficient and robust process which enables high-solid fermentation of pretreated lignocellulose to achieve high ethanol fermentation performance. In this work, we design and optimize a high-solid fed-batch simultaneous saccharification and co-fermentation (SSCF) process with a feed of substrate, enzyme and yeast cell for efficient production of ethanol from pretreated wheat straw in both lab and pilot scale. The yeast is prepared by pre-cultivation and adaptation in a semi-continuous cultivation in liquid hydrolysate medium in order to achieve high fermentation capacity. The feeding profiles in both pre-cultivation and SSCF steps are optimized based on a previously developed multi-feed SSCF model [1] in order to maintain high activities of both hydrolytic enzyme and yeast cell resulting in highest biomass yield during pre-cultivation and highest ethanol production efficiency during SSCF process. We also demonstrate scale up of fed-batch SSCF process in a 10 m3 pilot-scale bioreactor. The fed-batch SSCF with an optimized feed of substrate, cell and enzymes reaches high ethanol fermentation performance suggesting it to be a promising process for efficient bioconversion of lignocellulosic materials to ethanol.[1] Wang et al. Bioresour. Technol., 2014
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| 4. |
- Westman, Johan, 1983, et al.
(författare)
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Scale-up of multi feed fed-batch simultaneous saccharification and co-fermentation of pretreated wheat straw to ethanol
- 2015
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Ingår i: 37th Symposium on Biotechnology for Fuels and Chemicals.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A major remaining issue with second-generation bioethanol production is the difficulty of reaching high enough titers to facilitate an overall economical process. Utilization of approximately 20% pretreated insoluble lignocellulosic material in the process is necessary to reach an often mentioned ethanol concentration of 4-5% (w/w). The viscosity at this solids concentration becomes higher than what is easily attainable in most reactor set-ups. We have designed a fed-batch simultaneous saccharification and co-fermentation (SSCF) process for ethanol production from pretreated wheat straw up to 21% water insoluble solids in a stirred tank reactor. In addition to feeding of solids at different time points, feeding of fresh cells at different time points was found to be beneficial for the process. The fed cells were adapted to the toxic environment by pre-cultivation in the liquid fraction from the pretreatment. Enzyme addition at different time points did however not improve the process, compared to addition of the same total amount in the beginning of the fed-batch. The effectiveness of the optimized process has been proven at demonstration scale in a 10 m3 SSCF reactor, reaching ethanol concentrations of 5% (w/w). A further increase was hindered by the toxicity of the medium, lowering the cells’ fermentation capacity. We have previously shown that strong flocculation can increase the ability of yeast to ferment toxic lignocellulose hydrolysates [1]. We therefore created strongly flocculating xylose fermenting Saccharomyces cerevisiae strains and are currently investigating these in the SSCF process.[1] Westman et al. Appl Environ Microbiol, 2014.
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