| 1. |
- 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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| 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. |
- Ylitervo, Päivi, et al.
(författare)
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Continuous Ethanol Production with a Membrane Bioreactor at High Acetic Acid Concentrations
- 2014
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Ingår i: Membranes. - : MDPI. - 2077-0375. ; 4:3, s. 372-387
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Tidskriftsartikel (refereegranskat)abstract
- The release of inhibitory concentrations of acetic acid from lignocellulosic raw materials during hydrolysis is one of the main concerns for 2nd generation ethanol production. The undissociated form of acetic acid can enter the cell by diffusion through the plasma membrane and trigger several toxic effects, such as uncoupling and lowered intracellular pH. The effect of acetic acid on the ethanol production was investigated in continuous cultivations by adding medium containing 2.5 to 20.0 g•L−1 acetic acid at pH 5.0, at a dilution rate of 0.5 h−1. The cultivations were performed at both high (~25 g•L−1) and very high (100–200 g•L−1) yeast concentration by retaining the yeast cells inside the reactor by a cross-flow membrane in a membrane bioreactor. The yeast was able to steadily produce ethanol from 25 g•L−1 sucrose, at volumetric rates of 5–6 g•L−1•h−1 at acetic acid concentrations up to 15.0 g•L−1. However, the yeast continued to produce ethanol also at a concentration of 20 g•L−1 acetic acid but at a declining rate. The study thereby demonstrates the great potential of the membrane bioreactor for improving the robustness of the ethanol production based on lignocellulosic raw materials.
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| 4. |
- Westman, Johan, 1983, et al.
(författare)
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Current progress in high cell density yeast bioprocesses for bioethanol production
- 2015
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Ingår i: Biotechnology journal. - : Wiley. - 1860-6768 .- 1860-7314. ; 10:8, s. 1185-1195
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Forskningsöversikt (refereegranskat)abstract
- High capital costs and low reaction rates are major challenges for establishment of fermentation-based production systems in the bioeconomy. Using high cell density cultures is an efficient way to increase the volumetric productivity of fermentation processes, thereby enabling faster and more robust processes and use of smaller reactors. In this review, we summarize recent progress in the application of high cell density yeast bioprocesses for first and second generation bioethanol production. High biomass concentrations obtained by retention of yeast cells in the reactor enables easier cell reuse, simplified product recovery and higher dilution rates in continuous processes. High local cell density cultures, in the form of encapsulated or strongly flocculating yeast, furthermore obtain increased tolerance to convertible fermentation inhibitors and utilize glucose and other sugars simultaneously, thereby overcoming two additional hurdles for second generation bioethanol production. These effects are caused by local concentration gradients due to diffusion limitations and conversion of inhibitors and sugars by the cells, which lead to low local concentrations of inhibitors and glucose. Quorum sensing may also contribute to the increased stress tolerance. Recent developments indicate that high cell density methodology, with emphasis on high local cell density, offers significant advantages for sustainable second generation bioethanol production.
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| 5. |
- Aulitto, Martina, 1991, et al.
(författare)
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Seed culture pre-adaptation of Bacillus coagulans MA-13 improves lactic acid production in simultaneous saccharification and fermentation
- 2019
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Lignocellulosic biomass is an abundant and sustainable feedstock, which represents a promising raw material for the production of lactic acid via microbial fermentation. However, toxic compounds that affect microbial growth and metabolism are released from the biomass upon thermochemical pre-treatment. So far, susceptibility of bacterial strains to biomass-derived inhibitors still represents a major barrier to lactic acid production from lignocellulose. Detoxification of the pre-treated lignocellulosic material by water washing is commonly performed to alleviate growth inhibition of the production microorganism and achieve higher production rates. Results In this study, we assessed the feasibility of replacing the washing step with integrated cellular adaptation during pre-culture of Bacillus coagulans MA-13 prior to simultaneous saccharification and lactic acid fermentation of steam exploded wheat straw. Using a seed culture pre-exposed to 30% hydrolysate led to 50% shorter process time, 50% higher average volumetric and 115% higher average specific productivity than when using cells from a hydrolysate-free seed culture. Conclusions Pre-exposure of B. coagulans MA-13 to hydrolysate supports adaptation to the actual production medium. This strategy leads to lower process water requirements and combines cost-effective seed cultivation with physiological pre-adaptation of the production strain, resulting in reduced lactic acid production costs.
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| 6. |
- Nickel, David, 1990, et al.
(författare)
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Multi-scale uncertainty analysis – A tool to systematically consider variability in lignocellulosic bioethanol processes
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Bioethanol production processes from lignocellulosic raw materials are highly prone to batch-to-batch variations. For example, raw material compositions and enzymatic activities required to release fermentable sugars from lignocellulose vary significantly between batches. To develop lignocellulosic biofuel processes and evaluate their performance regarding economics and sustainability consistently, tools are required to cope with this variability. In this presentation we will propose a multi-scale uncertainty analysis strategy to propagate input variability throughout system scales. In a first step, we use meta-data obtained from literature to define uncertainties in the process inputs. Utilizing these meta-data, uncertainty analysis is performed on a macro-kinetic model by sampling from the defined uncertain input space. The results of this uncertainty analysis are transferred to process simulations to analyze the impact of input uncertainties on the process mass- and energy balances, and on the economics of building this type of bioprocess. The generated data from process simulations (mass flows, energy integration, and economic data) are in the next step extracted and used as input to an environmental impact assessment of the process. This is done whilst keeping the simulation and systems modeling parameters constant, thus the input variability is propagated throughout the different system scales. The data generated in this integrated approach will then be compared with the variations and uncertainties observed with relevance to the estimated parameters in the process simulation and environmental impact assessment. Based on this consistent strategy, we can analyze the impact of input variability from different system perspectives, identify important bottlenecks for development, and suggest robust and sustainable process designs for different conditions and under given uncertainties. In a case study we demonstrate how integrated kinetic modeling (in Matlab), process simulation (in SuperPro Designer), and environmental impact assessment together with statistical analysis can be used for assessing how variability in enzymatic activities in bioethanol production can be propagated throughout system scales. A macro-kinetic model is used to describe the enzymatic breakdown of lignocellulose-derived polysaccharides into fermentable sugars (saccharification) and the simultaneous fermentation to bioethanol. We discuss the integration of the simulation results of the macro-kinetic model into the flowsheeting software for mass and energy balance generation, and then further on to assess environmental impacts of the process. We will evaluate different process designs regarding their robustness towards input variability. Finally, we also show how propagated uncertainties at different system scales can be integrated to design experiments at laboratory scale so that these focus on the most important parameters for developing robust kinetic models, and include the parameters that are most important for sustainable design of processes and value chains.
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| 7. |
- Nickel, David, 1990, et al.
(författare)
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Uncertainty analysis as a tool to consistently evaluate lignocellulosic bioethanol processes at different system scales
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic processes are highly prone to batch-to batch variability, e.g. of raw materials and enzyme activities. This variability can be propagated throughout system scales during process development and optimization, influencing the outputs of bioreaction models, techno-economic analyses and life cycle assessments. As these outputs are the main decision variables for designing and developing lignocellulose-based processes, tools are required to evaluate the influences of process variation at different system scales. Uncertainty analysis quantifies the effects of model input variations on model outputs. It is an effective tool to consistently propagate process variation throughout scales and analyse its influence on model outputs. As an example, we use a model describing multi-feed simultaneous saccharification and co-fermentation (SSCF) of wheat straw. During the process enzymes hydrolyse the lignocellulosic material to release glucose which can be converted by microorganisms into ethanol. To investigate the impact of batch-to-batch variability in enzyme cocktails, we collected literature data on the enzymatic activity of Cellic CTec2. Retrieved data were propagated in models at bioreactor, techno-economic analysis and life cycle assessment scale. We show how uncertainty analysis can be used to guide process development by comparing different modes of operation. The method can identify economically feasible process ranges with low environmental impact while increasing the robustness of bioprocesses with high variation in raw material inputs. Furthermore, uncertainty analysis could help to identify relevant parameters to choose as response variables in experimental designs.
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| 8. |
- 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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| 9. |
- Sárvári Horváth, Ilona, 1960, et al.
(författare)
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Effects of furfural on the respiratory metabolism of Saccharomyces cerevisiae in glucose-limited chemostats
- 2003
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 69:7, s. 4076-4086
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Tidskriftsartikel (refereegranskat)abstract
- Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD+. At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.
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| 10. |
- Westman, Johan, 1983, et al.
(författare)
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Encapsulation-Induced Stress Helps Saccharomyces cerevisiae Resist Convertible Lignocellulose Derived Inhibitors
- 2012
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 13:9, s. 11881-11894
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Tidskriftsartikel (refereegranskat)abstract
- The ability of macroencapsulated Saccharomyces cerevisiae CBS8066 to withstand readily and not readily in situ convertible lignocellulose-derived inhibitors was investigated in anaerobic batch cultivations. It was shown that encapsulation increased the tolerance against readily convertible furan aldehyde inhibitors and to dilute acid spruce hydrolysate, but not to organic acid inhibitors that cannot be metabolized anaerobically. Gene expression analysis showed that the protective effect arising from the encapsulation is evident also on the transcriptome level, as the expression of the stress-related genes YAP1, ATR1 and FLR1 was induced upon encapsulation. The transcript levels were increased due to encapsulation already in the medium without added inhibitors, indicating that the cells sensed low stress level arising from the encapsulation itself. We present a model, where the stress response is induced by nutrient limitation, that this helps the cells to cope with the increased stress added by a toxic medium, and that superficial cells in the capsules degrade convertible inhibitors, alleviating the inhibition for the cells deeper in the capsule.
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