Bio-electrochemical activity of Clostridium ljungdahlii at different cathodic potentials

Abstract

Humans are responsible for a large portion of the emissions of CO2 gas since the industrial revolution. These emissions must decrease so that the increase of temperature should not exceed an increase of 2 °C by the end of this century. Gas fermentation is a promising technology that could reduce the emissions of CO2 into the atmosphere. Clostridium ljungdahlii is an interesting anaerobic microorganism capable of CO2 fixation and produce valuable chemicals such as ethanol. C. ljungdahlii is also known for the capability of accepting electrons from an electrode in a bio-electrochemical system. The bio electrochemical activity of C. ljungdahlii was thus investigated at the cathodic potentials - 400, -600, -800 and -1000 mV. This was done by running biotic and abiotic bio electrochemical system experiments at the mentioned potentials, as well as serum flask control experiments. The results were analysed by investigating product formation, growth, pH, current consumption, and the mechanism of electron transfer in the bio-electrochemical system reactors. No planktonic cell growth was observed in the optical density measurements, but CO2 fixation by C. ljungdahlii in a bio-electrochemical system was observed. C. ljungdahlii could in a bio-electrochemical system produce 2,3-butanediol at - 800 mV, and though not reproducible, also ethanol at -600 mV. C. ljungdahlii seem on the other hand to consume formate at all potentials applied. The current consumption of C. ljungdahlii was very low indicating that H2 could have been produced but was not consumed by C. ljungdahlii.