Process integration of gas fermentation and microbial oil production

(M.Sc. Fabian Herrmann)

Acetogenic microorganisms can efficiently reduce CO2 with H2 and convert it into acetate under anaerobic conditions. However, the synthesis of longer-chain carbon compounds is challenging under these conditions. In contrast, the production of microbial oils is particularly successful with oil-producing yeasts under aerobic conditions.

The objective of this doctoral project is the process integration of anaerobic acetic acid production using Acetobacterium woodii and aerobic yeast oil production using Cutaneotrichosporon oleaginosus. In the anaerobic bioreactor, acetic acid is formed from CO2 and H2, while in the aerobic bioreactor, this acetic acid should be converted into microbial oils. Sugar hydrolysates derived from lignocellulosic residues produced industrially will be used as the energy source for the oil yeasts. The CO2 produced during aerobic conversion will be purified and recycled for gas fermentation.

The coordination of the two microbial processes running in parallel or intermittently in different bioreactors plays a crucial role in order to avoid concentrating the anaerobic acetic acid solution and still be able to obtain oil yeasts with high lipid content while achieving a complete conversion of carbon into microbial oils.