Online monitoring-based methodologies to assess microaerobic 2,3-Butanediol production
- Methoden zur Evaluierung der microaeroben 2,3-Butandiol Produktion basierend auf Online-Prozessüberwachungstechnologien
Heyman, Benedikt; Büchs, Jochen (Thesis advisor); Prüße, Ulf (Thesis advisor)
Aachen (2019, 2020)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2019
Biotechnological production of platform chemicals from renewable carbon sources is a promising measure to decrease the consumption of fossil resources in the chemical industry and the fuel sector. Reduced platform chemicals like 2,3-butanediol are often produced in microaerobic cultivation processes. Under these oxygen-limited conditions, the precise adjustment of the oxygen availability is crucial to obtain the desired metabolic activity. In this thesis, 2,3-butanediol production with Bacillus licheniformis was used as model bioprocess to develop online monitoring-based methodologies to assess microaerobic cultivations. A fast and reliable shake flask methodology is presented to determine the optimum oxygen availability. Comparable results and well-characterized experimental conditions were obtained by application of a defined two-stage cultivation profile and a novel technique to determine the maximum 2,3-butanediol concentration. As the obtained results are applicable to stirred tank reactor cultivations, the product and by-product spectrum can be optimized at reduced effort and costs. Still, a drawback for microaerobic process development is the limited availability of online monitoring techniques to determine the metabolic activity with respect to oxygen availability. Therefore, online monitoring of the respiratory quotient was combined with stoichiometric analyses to reveal the metabolic activity during distinct cultivation phases. Furthermore, monitoring of the redox potential was used to monitor the dissolved oxygen tension (DOT) at trace levels that cannot be resolved with conventional DOT probes. The influence of DOT, pH and media components on the redox potential was characterized and quantified in abiotic experiments. On this basis, a corrected redox potential is obtained that solely reflects changes of the DOT, even if the pH strongly fluctuates during the cultivation. Overall, the developed methodologies are transferable to other microorganisms or products and increase the information content from online monitoring during microaerobic cultivations. Respiratory quotient and redox potential provide detailed and complementary information on the metabolic activity during microaerobic cultivations. Together with the presented approach to investigate the effects of oxygen availability, this contributes to the development of improved microaerobic cultivation processes for the production of diverse bio-based compounds.