Sustainable ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous stirred tank bioreactor

BACKGROUND: Ethanol production from synthesis gas (syngas) by Clostridium ljungdahlii was autotrophically carried out in a continuous flow stirred tank bioreactor (CSTR). A 2 L bioreactor was operated at 37 degrees C and constant agitation rate of 500 rpm. The experiments were conducted at various media flow rates and uncontrolled culture pH condition while the gas flow rate was kept constant at 14 mL min-1. RESULTS: Continuous fermentation of the syngas containing 55% CO, 20% H2, 10% CO2 and 15% argon as internal standard resulted in cell dry weight of 2.34 g L-1 and CO conversion of 93%. Maximum concentration of ethanol and acetate was 6.50 g EthOH L-1 and 5.43 g Ac L-1. CONCLUSION: High ethanol concentration was achieved in continuous fermentation using C. ljungdahlii. The ethanol producing ability of this acetogene and succesful switch of the metabolic pathway from acetogenesis to solventogenesis during the fermentation process was confirmed. Copyright (c) 2012 Society of Chemical Industry