초록
The conversion of carbon monoxide (CO) into hydrogen (H<SUB>2</SUB>) by a Carboxydothermus hydrogenoformans pure culture was investigated and optimized in a 35 L gas-lift reactor. The reactor was operated with a continuous supply of gas for 3 months. Reactor performance was evaluated under various operational conditions, such as gas recirculation rates (0.3 and 1.5 L min<SUP>-1</SUP>), CO feeding rates (from 0.05 to 0.46 mol L<SUP>-1</SUP><SUB>reactor</SUB> day<SUP>-1</SUP>) and bacto-peptone addition to the medium. Overall, the H<SUB>2</SUB> yields were constant at 95 +/- 1% and 82 +/- 1% (mol<SUB>H'2</SUB>@?mol<SUB>CO</SUB><SUP>-1</SUP>) with growth supported by peptone and unsupported respectively, regardless of the operational conditions tested. At the highest biomass density, a maximum CO conversion activity of 0.17 mol<SUB>CO</SUB> L<SUP>-1</SUP><SUB>reactor</SUB> day<SUP>-1</SUP> or 3.79 L<SUB>CO</SUB> L<SUP>-1</SUP><SUB>reactor</SUB> day<SUP>-1</SUP> was achieved. The ratio of gas recirculation over CO feed flow rates (Q<SUB>R</SUB>:Q<SUB>in</SUB>) was the major parameter that impacted both biological activity and volumetric gas-liquid mass transfer. The CO conversion performance of the gas-lift reactor was kinetically limited over a Q<SUB>R</SUB>:Q<SUB>in</SUB> ratio of 40, and mass transfer limited below that ratio, resulting in a maximum conversion efficiency of 90.4 +/- 0.3% and a biological activity of 2.7 +/- 0.4 mol<SUB>CO</SUB> g<SUP>-1</SUP><SUB>VSS</SUB> day<SUP>-1</SUP>. Overall, the CO conversion performance in the gas-lift reactor was limited by a low cell density, typical of C. hydrogenoformans planktonic growth. This limitation was found to be the most restrictive factor for higher CO loading rates.