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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.


Schematic description of the model-based fed-batch design. After each 1 h simulation, the extent of cellulose degradation was checked. The process was simulated using  values of 30, 50, 60 and 80 % cellulose degradation. The upper boundary for the instantaneous concentration of WIS (WISUB) in the bioreactor was determined to be 12–13 % (w/w)
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Fig4: Schematic description of the model-based fed-batch design. After each 1 h simulation, the extent of cellulose degradation was checked. The process was simulated using values of 30, 50, 60 and 80 % cellulose degradation. The upper boundary for the instantaneous concentration of WIS (WISUB) in the bioreactor was determined to be 12–13 % (w/w)

Mentions: The hydrolysis model was integrated into a model-based control loop which was developed for determining the times and amounts of solid feedings that would enable good mixing while promoting rapid turnover of cellulose (Fig. 4). Basically, a sequence of 1 h batch processes were carried out in silico. At the end of each batch simulation, the extent of WIS solubilisation (assumed equal to the cellulose degradation) was checked. If a certain fraction () of the cellulose had been solubilized, a feeding event was triggered (Eq. 5). The amount of solids to be added was calculated based on the residual WIS and the mixing capacity of the reactors, expressed as an upper boundary for the WIS content in the reactor , empirically determined to be 12–13 % (w/w). Thus, at time i,Fig. 4


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)

Schematic description of the model-based fed-batch design. After each 1 h simulation, the extent of cellulose degradation was checked. The process was simulated using  values of 30, 50, 60 and 80 % cellulose degradation. The upper boundary for the instantaneous concentration of WIS (WISUB) in the bioreactor was determined to be 12–13 % (w/w)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig4: Schematic description of the model-based fed-batch design. After each 1 h simulation, the extent of cellulose degradation was checked. The process was simulated using values of 30, 50, 60 and 80 % cellulose degradation. The upper boundary for the instantaneous concentration of WIS (WISUB) in the bioreactor was determined to be 12–13 % (w/w)
Mentions: The hydrolysis model was integrated into a model-based control loop which was developed for determining the times and amounts of solid feedings that would enable good mixing while promoting rapid turnover of cellulose (Fig. 4). Basically, a sequence of 1 h batch processes were carried out in silico. At the end of each batch simulation, the extent of WIS solubilisation (assumed equal to the cellulose degradation) was checked. If a certain fraction () of the cellulose had been solubilized, a feeding event was triggered (Eq. 5). The amount of solids to be added was calculated based on the residual WIS and the mixing capacity of the reactors, expressed as an upper boundary for the WIS content in the reactor , empirically determined to be 12–13 % (w/w). Thus, at time i,Fig. 4

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.