Liquid Fuel Production from Synthesis Gas via Fermentation Process in a Continuous Tank Bioreactor (CSTBR) Using Clostridium ljungdahlii

The potential bioconversion of synthesis gas (syngas) to fuels and chemicals by microbial cell has attracted considerable attention in past decade. The feasibility of enhancing syngas bioconversion to ethanol and acetate using Clostridium ljungdahlii in a continuous tank bioreactor (CSTBR), kinetics and mass transfer coefficient of carbon monoxide (CO) utilization were evaluated. Two different types of syngas and pure CO were used for CO limitation, in order to achieve high bioconversion of syngas in a single bioreactor. The CO conversion increased with an increase in gas flow rate and agitation speed. For a gas flow rate of 14 ml/min and an agitation rate of 550 rpm, the cell concentration and conversion of pure CO were 1.92 g/l and 80%,respectively. The cell concentration also increased with an increase in CO percentage in the gas phase. Maximum cell dry weight of 2 g/l and CO conversion of 93% were achieved with 70% CO blended syngas at a gas flow rate of 14 ml/min and agitation rate of 500 rpm. The total amounts of ethanol and acetate concentrations were approximately 11 g/l. The mass transfer coefficient was calculated for the culture of C.ljungdahlii with pure CO in the CSTBR. The maximum mass transfer coefficient (KLa) was 135 h-1 at an agitation speed of 550 rpm. The KLa correlation based on various gas flow rates and agitation speeds was fitted with experimental data and the predicted model was in good conformity with the obtained data.