Estimation of kinetic parameters of the acetogen Clostridium autoethanogenum on carbon monoxide

Master thesis (2022)

Authors

C. Korkontzelos Applied Sciences

Contributors

R. Kleerebezem BT/Environmental Biotechnology - AS (supervisor 2)
M.T. Allaart BT/Environmental Biotechnology - AS (supervisor 1)
Faculty
Applied Sciences
Copyright: © 2022 Harry Korkontzelos
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Published Date

14-06-2022

Language

English

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Faculty

Applied Sciences

Abstract

The increasing demands for chemicals and fuels combined with the fuel versus food competition over first generation feedstocks requires the development of more sustainable alternatives. Syngas fermentation offers a sustainable production of fuels and recycling of gaseous and solid waste utilizing gas
fermenting bacteria. Acetogens, such as Clostridium autoethanogenum (CA) can grow on syngas (CO, CO2 and H2) and produce acetate and ethanol via the Wood-Ljungdahl pathway (WLP). Numerous studies have been conducted to optimize the ethanol production by changing different parameters such
as the pH, the mineral medium and the ingas composition. These changes can be effectively predicted through kinetic modelling, which requires the knowledge of key kinetic parameters such as the maximum biomass specific substrate uptake rate and the maximum growth rate. Batch fermentation is not a realistic option considering the low solubility of gases such as CO in the liquid, while obtaining the kinetic parameters in chemostats by increasing the dilution rate can be time intensive. To acquire these parameters, CA was cultivated in chemostats and was grown on carbon monoxide as the sole energy and carbon source. Feeding disturbances were carried out by increasing the CO molar fraction in the
inlet gas for a short period of time to ensure constant biomass concentration levels. Continuous off-gas analysis revealed that the fermentation is mass transfer limited until the end of the pulse experiments at 85% of CO in the inlet gas. A biomass specific substrate uptake rate of 89.1 ± 0.23 mmol/gDCW /h
was calculated, which is the highest value achieved so far in literature.The calculated growth rate was 0.083 h−1. pH profile provided evidence about the metabolism of the microorganism, while the increase of CO2 to CO yield at higher CO molar fractions was closely related to acetate reduction to ethanol
so that the cells can regulate their metabolism.