Bioconversion of Carbon Dioxide and Polluting Gases into Products with High Added Value

Abstract

Using polluting or greenhouse gases such as carbon dioxide and carbon monoxide as substrates to produce bulk chemicals is one possibility to close carbon cycles and to establish a circular economy. Syngas fermentation is the process in which these gases are converted into chemicals like ethanol, acetic acid and butanol by acetogenic bacteria. The first aim of this thesis was to show the ethanol production capability of an acetogen, Clostridium aceticum. In the first step optimum pH values for acid and solvent productions were determined individually and in the second step ethanol production was enhanced by applying different pH-regulating strategies. Following this finding, the influence of carbon sources was investigated with the purpose of enhancing ethanol production. The product formation pattern of this strain, while growing on different carbon sources, fructose and CO, was also showed. Ultimately, acetone production, which is not a native product of Acetobacterium woodii, was screened in four different metabolically engineered strains. Feasibility of a continuous fermentation process with full cell retention was demonstrated.