The aim of this joint project is the use of flue gas, electricity and air as feedstocks for the biotechnological production of polyhydroxybutyrate (“bioplastics”). An electrolithotrophic bacterial strain recently isolated by our project partner IAB is capable of using electricity as electron source to reduce carbon dioxide. The task of our subproject is the optimization of operating parameters and finally the construction of a Gas-Liquid-Contactor for the technical realization of this process. In this reactor, the bacteria will grow as biofilm covering the rotating discs (cathodes). These are partly immersed in a mineral solution and partly in contact with the gas phase containing the gaseous substrates carbon dioxide and oxygen. Uptake and conversion efficiency of substrates and electrons will strongly dependent on the structure of the developing biofilm. Thus, to correlate biofilm structure and biopolymer production, we apply Optical Coherence Tomography (OCT) to achieve three-dimensional visualization and structural analysis of the film.