Construction of a corrosion-resistant 15 L-pilot-bioreactor for the cultivation of extremely halophilic microorganisms

Abstract

Halophiles are microorganisms that can thrive in hostile, hypersaline environments, for example in salt lakes. Due to adaptation to their extreme living conditions they have developed unique features that offer a huge biotechnological potential: halophiles can grow on an exceptionally large variety of substrates and allow cost-effective, non-sterile continuous production of bioproducts. Potential biotechnological applications of halophilic organisms are for example industrial wastewater treatment and the production of carotenoids, biopolymers or the unique photoactive biomolecule bacteriorhodopsin. However, only a few halophilic organisms are currently commercially used because efficient and economical biotechnological processes for their cultivation on industrial scale have not been developed yet. A process for biotechnological treatment of industrial waste water by halophiles has been developed by the department of bioprocess engineering at Vienna University of Technology in recent years in a 1 L lab-scale bioreactor. To make this process available for the industry, it has to be scaled up and its simplicity, robustness as well as efficiency have to be demonstrated. For this reason, a worldwide unique pilot plant on 15 L-scale for the cultivation of halophiles with high productivity is constructed that is customized for the special requirements of these microorganisms. To reduce shear stress to the cells, an airlift bioreactor is used. Due to the high corrosiveness of the medium, the corrosion-resistant nickel-based alloy Hastelloy C-22 and plastic components are utilized. The bioreactor can be operated at increased pressures to enhance the solubility of oxygen in the medium. Moreover, a cell retention loop is attached to the vessel to increase the productivity of the slow growing halophiles. The process can be operated in batch as well as in continuous mode and allows online monitoring of the main process parameters. The targets of this master thesis are the construction of the novel bioreactor setup and to make it operational for subsequent research on the biotechnological application of halophiles. The thesis includes the design, specification, installation and testing of the pilot plant as well as documentation. The main challenge is the selection and especially the combination of equipment that is feasible for the highly corrosive medium as well as pressure-resistant. After implementation of the pilot plant, test fermentations with a halophilic strain are performed to demonstrate the operability of the System.