Limits...
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.


Comparison of lab and demo-scale SSCF. Time courses of cell viability, cumulative WIS addition, concentrations of sugars, ethanol and major by-products of multi-feed SSCF in lab scale (a, c) and in demo plant (b, d). The changes in WIS content indicate addition of solids, and the arrows between the panels indicate addition of yeast cells. Concentrations in C and D are averages from two biological replicates. Most data points showed deviation below 5 % between duplicate experiments. Error bars in a and b are standard deviations in duplicate experiments. Furfural and 5-hydroxymethyl furfural concentrations were below 0.5 and 0.2 g L−1 in the lab case, and below 0.1 and 0.05 g L−1 in the demo case
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig6: Comparison of lab and demo-scale SSCF. Time courses of cell viability, cumulative WIS addition, concentrations of sugars, ethanol and major by-products of multi-feed SSCF in lab scale (a, c) and in demo plant (b, d). The changes in WIS content indicate addition of solids, and the arrows between the panels indicate addition of yeast cells. Concentrations in C and D are averages from two biological replicates. Most data points showed deviation below 5 % between duplicate experiments. Error bars in a and b are standard deviations in duplicate experiments. Furfural and 5-hydroxymethyl furfural concentrations were below 0.5 and 0.2 g L−1 in the lab case, and below 0.1 and 0.05 g L−1 in the demo case

Mentions: The resulting model was integrated into the process design loop to determine the amounts and times for solid feeds (Fig. 4). Since inhibition of enzyme by glucose was weaker, the hydrolysis was faster and solid feeds were scheduled earlier in the SSCF compared to those in the separate hydrolysis process. SSCF experiments with substrate feeding based on the model prediction were carried out in both laboratory and demonstration scales. 22 % (w/w) overall WIS addition was achieved without mixing problem throughout the process (Figs. 5, 6).Fig. 5


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)

Comparison of lab and demo-scale SSCF. Time courses of cell viability, cumulative WIS addition, concentrations of sugars, ethanol and major by-products of multi-feed SSCF in lab scale (a, c) and in demo plant (b, d). The changes in WIS content indicate addition of solids, and the arrows between the panels indicate addition of yeast cells. Concentrations in C and D are averages from two biological replicates. Most data points showed deviation below 5 % between duplicate experiments. Error bars in a and b are standard deviations in duplicate experiments. Furfural and 5-hydroxymethyl furfural concentrations were below 0.5 and 0.2 g L−1 in the lab case, and below 0.1 and 0.05 g L−1 in the demo case
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig6: Comparison of lab and demo-scale SSCF. Time courses of cell viability, cumulative WIS addition, concentrations of sugars, ethanol and major by-products of multi-feed SSCF in lab scale (a, c) and in demo plant (b, d). The changes in WIS content indicate addition of solids, and the arrows between the panels indicate addition of yeast cells. Concentrations in C and D are averages from two biological replicates. Most data points showed deviation below 5 % between duplicate experiments. Error bars in a and b are standard deviations in duplicate experiments. Furfural and 5-hydroxymethyl furfural concentrations were below 0.5 and 0.2 g L−1 in the lab case, and below 0.1 and 0.05 g L−1 in the demo case
Mentions: The resulting model was integrated into the process design loop to determine the amounts and times for solid feeds (Fig. 4). Since inhibition of enzyme by glucose was weaker, the hydrolysis was faster and solid feeds were scheduled earlier in the SSCF compared to those in the separate hydrolysis process. SSCF experiments with substrate feeding based on the model prediction were carried out in both laboratory and demonstration scales. 22 % (w/w) overall WIS addition was achieved without mixing problem throughout the process (Figs. 5, 6).Fig. 5

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.