Online monitoring devices for lab scale synthesis gas fermentation using the model acetogen Clostridium Ijungdahlii
- Online Überwachungstechniken für laborskalierte Synthesegas Fermentationen unter Verwendung des Modellorganismus Clostridium Ijungdahlii
Mann, Marcel; Büchs, Jochen (Thesis advisor); Agler-Rosenbaum, Miriam (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021
In recent years, economic growth, and ongoing climate change have encouraged scientists globally to search for alternative and renewable resources. Microbial fermentation, a highly diverse conversion process, is one potential method that can be used to produce food, feed, pharmaceuticals, and platform chemicals from various renewable sources. One recently emerging field within fermentation processes is syngas fermentation that is used to convert gaseous waste streams (orgasified solid waste streams containing CO, CO2, and H2) into valuable products. By using these waste streams, containing some or all of the named gases, the exhaustion of gases or landfill and resulting environmental pollution can be prevented, while producing valuable products. In this thesis, methods to further develop syngas fermentation at lab scale were established and evaluated. Currently, hardly any small-scale cultivation devices that allow online monitoring are available for syngas fermentation. Thus, process development is limited to unsophisticated smallscale methods such as serum bottles and time-intensive fermentations in lab-scale bioreactors. Firstly, the anaRAMOS device was adapted and used for the cultivation of the model acetogen Clostridium ljungdahlii on fructose. After detecting an iron(II) limitation in a commonly used complex medium (YTF medium), a model was developed to calculate the necessary amount ofiron(II) for unlimited growth. Subsequently, the influence of iron(II), cobalt(II), and nickel(II) was investigated in the anaRAMOS, showing an effect on the product spectrum and CO2 production. Additionally, the cultivation conditions in the anaRAMOS were adapted to cultivation on defined ATCC 1754 medium. To enable cultivation on gaseous carbon sources, a new synRAMOS device was constructed that could be flexibly ventilated with CO, CO2, H2, and N2 as well as combinations thereof. Online monitoring of the carbon dioxide transfer rate (CO2TR) and gross gas transfer rate (GGTR) allowed calculation of the carbon monoxide transfer rate (COTR). The COTR was validated against a previously published calculation of the maximum oxygen transfer capacity (OTRmax) and by mass balancing using offline samples. The first steps towards a sophisticated fermentation control were taken by developing a dissolved carbon monoxide tension (DCOT) measurement method. The method was successfully established in a lab-scale fermenter and used to detect an increased alcohol production by increasing the DCOT in CO fermentation. Additionally, a critical DCOT of 16% was detected, which led to a halt of the metabolic activity in a CO and N2 fermentation.