CSTRs are the most commonly employed bioreactors in syngas fermentation. The CSTR has a continuous gas supply into the liquid phase, while agitator controls the gas-liquid mass transfer (Vega et al., 1990). Higher agitation speeds lead to a higher mass transfer rate between the substrate gases and the microbes. However, in industrial-scale fermentors, higher agitation speeds increase the agitator’s power consumption, thus increasing the operational cost of the plant. Table 2 summarizes some of the performance parameters for various bioreactors.
|
TABLE 2 Volumetric Mass Transfer Coefficients (k]_a) for Various Reactor Configurations and Hydrodynamic Conditions (Adopted from Munasinghe and Khanal, 2010 (b))
Volumetric Mass
|
Reactor
Configurations
|
Na
(rpm)
|
Microorganisms
|
Gaseous
Substrates
|
Transfer Coefficient (kLa) (h-1)
|
Reference
|
|
Trickle bed
|
n/a
|
n/a
|
Syngas
|
22
|
Cowger et al.
|
|
Continuous stirred tank
|
n/a
|
n/a
|
Syngas
|
38
|
(1992)
|
|
Continuous stirred tank
|
200
|
B.
methylotrophicum
|
CO
|
14.2
|
Bredwell et al. (1999)
|
|
Continuous stirred tank
|
300
|
SRBb mixed culture
|
Syngas
|
31 for CO, 75 for H2
|
|
|
Continuous stirred tank
|
300
|
C. ljungdahlii
|
Syngas
|
35 for CO
|
|
|
Continuous stirred tank
|
300
|
R. rubrum
|
Syngas
|
28.1 for CO
|
|
|
Continuous stirred tank
|
450
|
R. rubrum
|
Syngas
|
101 for CO
|
|
|
Stirred tank— microbubble sparger
|
200
|
B.
methylotrophicum
|
CO
|
90.6
|
|
|
Stirred tank— microbubble sparger
|
300
|
SRBb mixed culture
|
Syngas
|
104 for CO, 190 for H2
|
|
|
Packed bubble column
|
n/a
|
R. rubrum
|
Syngas
|
2.1
|
|
|
Trickle bed
|
n/a
|
R. rubrum
|
Syngas
|
55.5
|
|
|
Trickle bed
|
n/a
|
SRBb mixed culture
|
Syngas
|
121 for CO, 335
for H2
|
|
|
Trickle bed
|
n/a
|
C. ljungdahlii
|
Syngas
|
137 for CO
|
|
|
Batch-stirred tank
|
n/a
|
P. productus
|
CO
|
7.15
|
Vega et al. (1990)
|
|
Stirred tank
|
300
|
C. ljungdahlii
|
CO
|
14.9
|
Klasson et al.
|
|
Stirred tank
|
400
|
C. ljungdahlii
|
CO
|
21.5
|
(1993)
|
|
Stirred tank
|
500
|
C. ljungdahlii
|
CO
|
22.8
|
|
|
Stirred tank
|
600
|
C. ljungdahlii
|
CO
|
23.8
|
|
|
Stirred tank
|
700
|
C. ljungdahlii
|
CO
|
35.5
|
|
|
Bubble column
|
n/a
|
n/a
|
CO
|
72
|
Chang et al. (2001)
|
|
Stirred tank
|
400
|
n/a
|
CO
|
10.8-155
|
Riggs and
|
Heindel (2006)
|
|
TABLE 2 Volumetric Mass Transfer Coefficients (k]_a) for Various Reactor Configurations and Hydrodynamic Conditions (Adopted from Munasinghe and Khanal, 2010 (b))—Cont’d
Volumetric Mass
|
Reactor
|
Na
|
|
Gaseous
|
Transfer Coefficient
|
|
|
Configurations
|
(rpm)
|
Microorganisms
|
Substrates
|
(kLa) (h-1)
|
Reference
|
|
Stirred tank
|
500
|
R. rubrum
|
Syngas
|
71.8
|
Younesi et al. (2008)
|
|
Column diffuser
|
n/a
|
n/a
|
CO
|
2.5-40.0
|
Munasinghe and Khanal (2010 (b))
|
|
20-gm bulb diffuser
|
n/a
|
n/a
|
CO
|
31.7-78.8
|
|
Sparger only
|
n/a
|
n/a
|
CO
|
29.5-50.4
|
|
|
Sparger with mechanical mixing
|
150
|
n/a
|
CO
|
33.5-53.3
|
|
|
Sparger with mechanical mixing
|
300
|
n/a
|
CO
|
34.9-55.8
|
|
|
Submerged composite hollow fiber membrane (CHFM) module
|
n/a
|
n/a
|
CO
|
0.4-1.1
|
|
|
Air-lift combined with a 20-gm bulb
diffuser
|
n/a
|
n/a
|
CO
|
49.0-91.1
|
|
|
Air-lift reactor
|
n/a
|
n/a
|
CO
|
16.6-45.0
|
|
|
combined with a single-point gas entry
n/a, not applicable.
aAgitation speed. bSulfate-reducing bacteria.
