Anaerobic bioconversion of C1-gases into medium-chain fatty acids in bioreactors

Abstract

The expected scarcity of fossil fuels and their association with environmental problems highlight the urgency to look for more sustainable energy options. This doctoral thesis focuses on the bioconversion of C1 gases and other soluble substrates into high value-added products. Syngas can be metabolized by acetogenic bacteria to produce acetate and ethanol. These compounds can be revalorized by elongating their hydrocarbon chain through a cyclic process based on the reverse β-oxidation pathway, generating medium-chain fatty acids (MCFAs), such as n-caproate and n-caprylate.Furthermore, the effects of various experimental conditions on the anaerobic production of MCFAs using pure bacterial cultures in bioreactors were investigated. First, syngas fermentation and chain elongation technologies were combined in a single bioreactor with a co-culture of Clostridium aceticum and Clostridium kluyveri. Next, the study focused on the chain elongation process, evaluating parameters such as fermentation pH, operational mode, substrate ratio and biocatalyst (Clostridium kluyveri and/or Megasphaera hexanoica). Finally, the abiotic liquid-liquid extraction of n-caproic acid with different organic solvents was examined.Therefore, this thesis contributes to the knowledge of the behavior of chain elongating microorganisms.