| 1. |
- Franzén, Carl Johan, 1966, et al.
(author)
-
Multifeed simultaneous saccharification and fermentation enables high gravity submerged fermentation of lignocellulose.
- 2015
-
In: Recent Advances in Fermentation Technology (RAFT 11), Clearwater Beach, Florida, USA, November 8-11, 2015. Oral presentation..
-
Conference paper (other academic/artistic)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.
|
|
| 2. |
- Wang, Ruifei, 1985, et al.
(author)
-
Kinetic modeling-based optimization of multi-feed simultaneous saccharification and co-fermentation of wheat straw for ethanol production
- 2015
-
In: 37th Symposium on Biotechnology for Fuels and Chemicals, Oral presentation.
-
Conference paper (other academic/artistic)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
|
|
| 3. |
- Westman, Johan, 1983, et al.
(author)
-
Factors affecting the viability of Saccharomyces cerevisiae in Simultaneous Saccharification and co-Fermentation of pretreated wheat straw to ethanol
- 2015
-
In: 32nd International Specialized Symposium on Yeasts.
-
Conference paper (other academic/artistic)abstract
- The recalcitrance of lignocellulosic materials makes economic production of second generation ethanol difficult and necessitates pretreatment prior to hydrolysis and fermentation. Dilution in these steps limits the final ethanol titre reached in the fermentation, even at high yields. A higher concentration of the raw material already in the hydrolysis step is thus required to obtain good process economy. However, this also increases the amount of toxic compounds in the fermentation.Through simultaneous saccharification and co-fermentation, SSCF, with feeding of pretreated solids, higher substrate concentrations can be reached (Wang et al 2014). Yeast cells can be adapted to the material if they are propagated in fed-batch cultivation on a medium containing the liquid fraction from the pretreatment. Yet, even with such preadaptation, the activity of the cells added to our SSCF process dropped over time. To overcome this issue, we added fresh cells to the SSCF at different time points. We observed that the viability and fermentation capacity of the cells still decreased during the process. Nutrient supplementation could not help in improving the dropping viability. However, by adding ethanol to shake flask SSCF experiments we could see that the ethanol produced in the process was likely a contributing factor to the low viability. Drop tests on agar plates containing ethanol and/or pretreatment liquor, incubated at both 30°C and 35°C, further indicated that the decreased viability was an effect of the combination of the temperature in the reactor, the inhibitors in the material, and the ethanol produced in the process.Decreasing the temperature in the reactor to 30°C when the ethanol concentration reached 40-50 g L-1 resulted in rapid initial hydrolysis and maintained fermentation capacity. The residual amount of unfermented glucose and xylose at the end of the process was reduced. With the optimized process, ethanol concentrations of more than 60 g L-1 were reached. REFERENCE: Wang R, Koppram R, Olsson L, Franzén CJ (2014) Kinetic modeling of multi-feed simultaneous saccharification and co-fermentation of pretreated birch to ethanol. Bioresour Technol 172:303–311
|
|
| 4. |
- Westman, Johan, 1983, et al.
(author)
-
Scale-up of multi feed fed-batch simultaneous saccharification and co-fermentation of pretreated wheat straw to ethanol
- 2015
-
In: 37th Symposium on Biotechnology for Fuels and Chemicals.
-
Conference paper (other academic/artistic)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.
|
|
