A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol
Abstract
:1. Introduction
2. Results and Discussion
2.1. Cell Growth
Hour | Change in reactor condition (Figure 2B,G) | Effect on reactor performance (Figure 2A, C–E) | ||
---|---|---|---|---|
Stage one | Stage two | Stage one | Stage two | |
0–650 | D = 0.039 h−1 pH = 5.5 | D = 0.010 h−1 pH = 4.4–4.8 | Growth at equilibrium, OD600 at ~2.0 | Inoculation; OD600 increased at an initial rate of 0.37/day to ~9.9 |
650–888 | Activated media bypass channel (Figure 1), increased overall media flow rate by 50% to 62 mL/h; increased dilution rate in stage 2 relatively to stage 1 | OD600 increased to ~2.4 | OD600 increased to 17.8; higher reactor performance (Figure 2C–E) | |
888 | ACCIDENT: ambient air drawn into stage 1 | OD600 declined to 0.37, recovery completed at 1013 h | OD600 was not affected, but metabolic rates declined (Figure 2C–E) | |
1056 | D = 0.039 h−1 | D = 0.020 h−1 | OD600 decreased to ~2.0 | OD600 increased to ~30.0 |
1347 | ACCIDENT: Media pump stopped for several hours | Rapid increase of ethanol concentration from 393 to 576 mM; stabilized at 400–450 mM ethanol within 100 h after repairing the pump | ||
1366 | Raised gas recycle rate from 180 to 430 mL/min to increase syngas retention time and mass transfer | Stage 2: sudden rise of OD600 to 41.7 (Figure 2A) due to stir up of settled cells. OD600 stayed at higher level until end of experiment.Syngas consumption did not improve significantly (Figure 2E) | ||
1535–1632 | 2× medium was exchanged with 4× medium in the reservoir for 97 h to improve supply with nutrients | OD600 declined from 2.0 to 0.1. Recovery completed at 1749 h. | Salt shock did not affect OD600, but metabolic rates declined. Recovery started at 1800 h | |
1679 | D = 0.046 h−1 | D = 0.023 h−1 | New OD600 level settled at ~1.8 | New OD600 level settled at ~43.4 |
1800 | D = 0.039 h−1 | D = 0.020 h−1 | OD600 back at ~2.0 | Recovery from salt shock started |
2014 | End of experiment | Final OD600 of 46.2; ethanol concentration of 394 mM |
Compound | Concentrations | ||
---|---|---|---|
Outlet stage 1 | Outlet stage 2 | Inlet stages 1 & 2 | |
CO (G), (vol%) | 53 | 19 | 60 |
H2 (G), (vol%) | 34 | 14 | 35 |
CO2 (G), (vol%) | 13 | 63 | 5 |
Ethanol (L), (mM) | 11.5 | 428.4 | NA |
Acetic acid (L), (mM) | 146.5 | 142.5 | NA |
Bacteria (g DW/L) | 0.476 | 9.34 | NA |
Compounds | Rates [mmol/(L·min)] | ||
Stage 1 | Stage 2 | Total | |
CO in | 0.607 | 0.808 | 0.768 |
CO out | 0.330 | 0.110 | 0.154 |
CO consumption | 0.277 | 0.698 | 0.614 |
H2 in | 0.354 | 0.471 | 0.448 |
H2 out | 0.182 | 0.085 | 0.105 |
H2 consumption | 0.172 | 0.386 | 0.343 |
CO2 in | 0.051 | 0.067 | 0.064 |
CO2 out | 0.085 | 0.371 | 0.314 |
CO2 production | 0.034 | 0.303 | 0.250 |
Ethanol production | 0.007 | 0.136 | 0.110 |
Acetic acid production | 0.094 | 0.025 | 0.039 |
Compounds | Efficiencies (%) | ||
Stage 1 | Stage 2 | Total | |
CO consumption | 46 | 86 | 80 |
H2 consumption | 49 | 82 | 77 |
2.2. Substrate Consumption and Product Formation
3. Experimental Section
3.1. Biocatalyst and Growth Conditions
3.2. Reactor Setup
3.3. Analytical Procedures
4. Conclusions and Outlook
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- The relatively low ethanol concentration of 2% in the effluent requires advanced strategies for distillation to keep the energy balance of the entire process positive. A promising method has been described recently [24];
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Acknowledgements
Conflict of Interest
References
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Richter, H.; Martin, M.E.; Angenent, L.T. A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol. Energies 2013, 6, 3987-4000. https://doi.org/10.3390/en6083987
Richter H, Martin ME, Angenent LT. A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol. Energies. 2013; 6(8):3987-4000. https://doi.org/10.3390/en6083987
Chicago/Turabian StyleRichter, Hanno, Michael E. Martin, and Largus T. Angenent. 2013. "A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol" Energies 6, no. 8: 3987-4000. https://doi.org/10.3390/en6083987