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Table 2 Summary of relevant parameters of bioreactor operation and process performance for H2/CO2 and CO fermentations

From: Modeling ethanol production through gas fermentation: a biothermodynamics and mass transfer-based hybrid model for microbial growth in a large-scale bubble column bioreactor

VariableSymbolUnitCO fermentationH2/CO2 fermentation
Performance indicators
 Ethanol volumetric productivity\(R_{\text{et}}\)g L−1 h−14.255.1
 Gas utilization\(U_{S}\)%17.122.9
Gas outflow composition
 Hydrogen\(y_{{{\text{H}}_{2} }}\)mol mol−10.000.71
 Carbon dioxide\(y_{{{\text{CO}}_{2} }}\)mol mol−10.110.24
 Carbon monoxide\(y_{\text{CO}}\)mol mol−10.840.00
 Ethanol\(y_{\text{et}}\)mol mol−10.010.01
 Water\(y_{w}\)mol mol−10.040.04
Concentrations in the fermentation brotha,b
 Hydrogen\(C_{{{\text{H}}_{ 2} }}\)
(\(C_{{{\text{H}}_{ 2} }}^{*}\))
mol m−30.00 (0.00)0.025 {0.033; 0.018}
(1.15 {1.63; 0.78})
 Carbon dioxide\(C_{{{\text{CO}}_{ 2} }}\)
(\(C_{{{\text{CO}}_{2} }}^{*}\))
mol m−30.32 {0.00; 4.22}12.46 {17.11; 8.94}
(13.09 {18.51; 8.86})
 Carbon monoxide\(C_{\text{CO}}\)
(\(C_{\text{CO}}^{ *}\))
mol m−32.7 × 10−3 {3.6 × 10−3; 2.0 × 10−3}
(1.62 {2.45; 1.01})
0.000 (0.000)
 Ethanol\(C_{et}\)mol L−1 (g L−1)0.96 (44.3)0.98 (45.0)
 Biomass\(C_{x}\)Cmol m−3 (g L−1)395 (10.0)399 (10.1)
Parameters estimated with thermodynamicsa
 Catabolic energy production\(\Delta G_{\text{cat}}^{{0^{\prime}}}\)kJ mol−1CS− 29.2 {− 48.2; − 24.0}− 19.9 {− 23.0 − 16.45}
 Biomass yield\(Y_{x/CS}\)Cmolx mol−1CS0.0410.020
Biomass specific consumption/production rates (logarithmic mean)
 Hydrogen\(q_{{{\text{H}}_{ 2} }}\)mol Cmol−1x h−10.00− 1.67
 Carbon dioxide\(q_{{{\text{CO}}_{2} }}\)mol Cmol−1x h−11.00− 0.56
 Carbon monoxide\(q_{\text{CO}}\)mol Cmol−1x h−1− 1.520.00
 Ethanol\(q_{\text{et}}\)mol Cmol−1x h−10.230.28
 Water\(q_{w}\)mol Cmol−1x h−1− 0.730.84
 Non-dimensional electron donor uptake rate\(q^{\prime}_{D}\)0.350.38
Streams entering and leaving the bioreactor
 Gas flow rate at the top\(F_{G,t}\)
mol s−1 (m3 s−1)462 (7.8)418 (7.1)
 Gas flow rate at the bottom\(F_{G,b}\) (\(\dot{V}_{G,b}\))mol s−1 (m3 s−1)479 (4.0)528 (4.4)
 Liquid outflow rate\(\dot{V}_{L,o}\)m3 h−130.039.3
 Fresh syngas\(F_{S}\)mol s−180.0118
Parameters regarding gas and liquid flows and mixing (logarithmic mean)
 Gas flow rate\(F_{G }\)(\(\dot{V}_{G}\))mol s−1 (m3 s−1)471 (5.6)471 (5.6)
 Superficial gas velocity (pressure-corrected)\(v_{sG}^{c}\)m s−10.140.14
 Liquid flow rate\(\dot{V}_{L}\)m3 s−126.926.9
 Mixing time\(t_{m}\)s60.4c
Mass transfer coefficients (logarithmic mean)
 Hydrogen\(k_{L} a_{{{\text{H}}_{2} }}\)s−10.0000.164
 Carbon dioxide\(k_{L} a_{{{\text{CO}}_{ 2} }}\)s−10.0000.098
 Carbon monoxide\(k_{L} a_{\text{CO}}\)s−10.1040.000
  1. aThe average value is shown first, followed by the values at the top and the bottom of the liquid column between curly brackets
  2. bThe values between round brackets represent the saturation concentrations of CO, H2 and CO2
  3. cSimulated using the 9 vertically stacked compartments model
  4. dCalculated with Eq. (21)