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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.

Wang R, Unrean P, Franzén CJ - Biotechnol Biofuels (2016)

Bottom Line: The combined feeding strategies were systematically compared and optimized using experiments and simulations.The process was reproducible and resulted in 52 g L(-1) ethanol in 10 m(3) scale at the SP Biorefinery Demo Plant.The optimization routine presented in this work can easily be adapted for optimization of other lignocellulose-based fermentation systems.

View Article: PubMed Central - PubMed

Affiliation: Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden.

ABSTRACT

Background: 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.

Results: For high-solid SSCF process of SO2-catalyzed steam pre-treated wheat straw, the boosted solubilisation of WIS achieved by having all enzyme loaded at the beginning of the process is crucial for increased rates of both enzymatic hydrolysis and SSCF. A kinetic model was adapted to simulate the release of sugars during separate hydrolysis as well as during SSCF. Feeding of solid substrate to reach the instantaneous WIS content of 13 % (w/w) was carried out when 60 % of the cellulose was hydrolysed, according to simulation results. With this approach, accumulated WIS additions reached more than 20 % (w/w) without encountering mixing problems in a standard bioreactor. Feeding fresh cells to the SSCF reactor maintained the fermentation activity, which otherwise ceased when the ethanol concentration reached 40-45 g L(-1). In lab scale, the optimized multi-feed SSCF produced 57 g L(-1) ethanol in 72 h. The process was reproducible and resulted in 52 g L(-1) ethanol in 10 m(3) scale at the SP Biorefinery Demo Plant.

Conclusions: SSCF of WIS content up to 22 % (w/w) is reproducible and scalable with the multi-feed SSCF configuration and model-aided process design. For simultaneous saccharification and fermentation, the overall efficiency relies on balanced rates of substrate feeding and conversion. Multi-feed SSCF provides the possibilities to balance interdependent rates by systematic optimization of the feeding strategies. The optimization routine presented in this work can easily be adapted for optimization of other lignocellulose-based fermentation systems.

No MeSH data available.


Related in: MedlinePlus

Optimization of seed cultivation in wheat straw pre-treatment liquor medium. a Effect of pre-treatment liquor concentration (% v/v) on cell yield after 24 h shake flask batch cultivation. The asterisks indicate that yeast growth was not sufficient to calculate the yield. Error bars indicate standard deviation of duplicate experiments. b Effects of the feed rate and the pre-treatment liquor concentration (% v/v) in feed medium on cell growth during fed-batch cultivation. Fed batch was started after a 24-h batch phase in 20 % (v/v) pre-treatment liquor medium. B_Yield, cell yields over the batch phase. FB_Yield, overall cell yield over the fed-batch phase, FB_Productivity, average cell productivity over the fed-batch phase. c Fermentation capacity of cells after batch and fed-batch cultivation. The conditions for seed cultivation in the subsequent multi-feed experiments were 20 % (v/v) pre-treatment liquor batch cultivation, followed by 50 % (v/v) pre-treatment liquor fed-batch cultivation at feed rate of 0.05 h−1
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Fig2: Optimization of seed cultivation in wheat straw pre-treatment liquor medium. a Effect of pre-treatment liquor concentration (% v/v) on cell yield after 24 h shake flask batch cultivation. The asterisks indicate that yeast growth was not sufficient to calculate the yield. Error bars indicate standard deviation of duplicate experiments. b Effects of the feed rate and the pre-treatment liquor concentration (% v/v) in feed medium on cell growth during fed-batch cultivation. Fed batch was started after a 24-h batch phase in 20 % (v/v) pre-treatment liquor medium. B_Yield, cell yields over the batch phase. FB_Yield, overall cell yield over the fed-batch phase, FB_Productivity, average cell productivity over the fed-batch phase. c Fermentation capacity of cells after batch and fed-batch cultivation. The conditions for seed cultivation in the subsequent multi-feed experiments were 20 % (v/v) pre-treatment liquor batch cultivation, followed by 50 % (v/v) pre-treatment liquor fed-batch cultivation at feed rate of 0.05 h−1

Mentions: The cell propagation consisted of batch and fed-batch phases, and we optimized the medium composition for each phase (Fig. 2). In the batch phase, cell growth in 10 % (v/v) pre-treatment liquor medium was very similar to growth in the pre-treatment liquor-free medium, suggesting that at 10 % (v/v), this particular pre-treatment liquor was not toxic enough to affect cell growth. In 20 % (v/v) pre-treatment liquor medium, however, yeast cells grew only after a 12-h lag phase and the cell yield after 24 h was approximately 40 % lower than the yield obtained in 10 % (v/v) medium. In medium containing 30 % (v/v) pre-treatment liquor or more, no growth was observed within 24 h. Therefore, among the tested pre-treatment liquor contents in batch media, 20 % (v/v) was chosen as it imposed a significant pressure on cells for adaptation, while allowing sufficient cell growth in 1 day (Fig. 2a).Fig. 2


Model-based optimization and scale-up of multi-feed simultaneous saccharification and co-fermentation of steam pre-treated lignocellulose enables high gravity ethanol production.

Wang R, Unrean P, Franzén CJ - Biotechnol Biofuels (2016)

Optimization of seed cultivation in wheat straw pre-treatment liquor medium. a Effect of pre-treatment liquor concentration (% v/v) on cell yield after 24 h shake flask batch cultivation. The asterisks indicate that yeast growth was not sufficient to calculate the yield. Error bars indicate standard deviation of duplicate experiments. b Effects of the feed rate and the pre-treatment liquor concentration (% v/v) in feed medium on cell growth during fed-batch cultivation. Fed batch was started after a 24-h batch phase in 20 % (v/v) pre-treatment liquor medium. B_Yield, cell yields over the batch phase. FB_Yield, overall cell yield over the fed-batch phase, FB_Productivity, average cell productivity over the fed-batch phase. c Fermentation capacity of cells after batch and fed-batch cultivation. The conditions for seed cultivation in the subsequent multi-feed experiments were 20 % (v/v) pre-treatment liquor batch cultivation, followed by 50 % (v/v) pre-treatment liquor fed-batch cultivation at feed rate of 0.05 h−1
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4835939&req=5

Fig2: Optimization of seed cultivation in wheat straw pre-treatment liquor medium. a Effect of pre-treatment liquor concentration (% v/v) on cell yield after 24 h shake flask batch cultivation. The asterisks indicate that yeast growth was not sufficient to calculate the yield. Error bars indicate standard deviation of duplicate experiments. b Effects of the feed rate and the pre-treatment liquor concentration (% v/v) in feed medium on cell growth during fed-batch cultivation. Fed batch was started after a 24-h batch phase in 20 % (v/v) pre-treatment liquor medium. B_Yield, cell yields over the batch phase. FB_Yield, overall cell yield over the fed-batch phase, FB_Productivity, average cell productivity over the fed-batch phase. c Fermentation capacity of cells after batch and fed-batch cultivation. The conditions for seed cultivation in the subsequent multi-feed experiments were 20 % (v/v) pre-treatment liquor batch cultivation, followed by 50 % (v/v) pre-treatment liquor fed-batch cultivation at feed rate of 0.05 h−1
Mentions: The cell propagation consisted of batch and fed-batch phases, and we optimized the medium composition for each phase (Fig. 2). In the batch phase, cell growth in 10 % (v/v) pre-treatment liquor medium was very similar to growth in the pre-treatment liquor-free medium, suggesting that at 10 % (v/v), this particular pre-treatment liquor was not toxic enough to affect cell growth. In 20 % (v/v) pre-treatment liquor medium, however, yeast cells grew only after a 12-h lag phase and the cell yield after 24 h was approximately 40 % lower than the yield obtained in 10 % (v/v) medium. In medium containing 30 % (v/v) pre-treatment liquor or more, no growth was observed within 24 h. Therefore, among the tested pre-treatment liquor contents in batch media, 20 % (v/v) was chosen as it imposed a significant pressure on cells for adaptation, while allowing sufficient cell growth in 1 day (Fig. 2a).Fig. 2

Bottom Line: The combined feeding strategies were systematically compared and optimized using experiments and simulations.The process was reproducible and resulted in 52 g L(-1) ethanol in 10 m(3) scale at the SP Biorefinery Demo Plant.The optimization routine presented in this work can easily be adapted for optimization of other lignocellulose-based fermentation systems.

View Article: PubMed Central - PubMed

Affiliation: Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden.

ABSTRACT

Background: 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.

Results: For high-solid SSCF process of SO2-catalyzed steam pre-treated wheat straw, the boosted solubilisation of WIS achieved by having all enzyme loaded at the beginning of the process is crucial for increased rates of both enzymatic hydrolysis and SSCF. A kinetic model was adapted to simulate the release of sugars during separate hydrolysis as well as during SSCF. Feeding of solid substrate to reach the instantaneous WIS content of 13 % (w/w) was carried out when 60 % of the cellulose was hydrolysed, according to simulation results. With this approach, accumulated WIS additions reached more than 20 % (w/w) without encountering mixing problems in a standard bioreactor. Feeding fresh cells to the SSCF reactor maintained the fermentation activity, which otherwise ceased when the ethanol concentration reached 40-45 g L(-1). In lab scale, the optimized multi-feed SSCF produced 57 g L(-1) ethanol in 72 h. The process was reproducible and resulted in 52 g L(-1) ethanol in 10 m(3) scale at the SP Biorefinery Demo Plant.

Conclusions: SSCF of WIS content up to 22 % (w/w) is reproducible and scalable with the multi-feed SSCF configuration and model-aided process design. For simultaneous saccharification and fermentation, the overall efficiency relies on balanced rates of substrate feeding and conversion. Multi-feed SSCF provides the possibilities to balance interdependent rates by systematic optimization of the feeding strategies. The optimization routine presented in this work can easily be adapted for optimization of other lignocellulose-based fermentation systems.

No MeSH data available.


Related in: MedlinePlus