The ejector loop reactor: Application for microbial fermentation and comparison with a stirred-tank bioreactor.

Ejector loop reactors (ELR) are successfully used in industrial chemical processes for gas/liquid reactions. They achieve higher mass transfer rates compared to the stirred-tank reactor (STR) at comparable specific power input. Insufficient oxygen transport and shear stress induced growth inhibition are limiting parameters during microbial fermentation. Due to its better mass transfer characteristics, the ELR was expected to have beneficial effects on biomass and recombinant protein production. One concern, however, was whether the ELR's shear stress characteristics would have a negative effect. This study evaluated the suitability of using the Buss-Loop® Reactor (BLR), one of the most advanced ELR technologies, as a bioreactor. The well-studied STR was used as a reference. A lab scale BLR was adapted for microbial fermentation. Mass transfer rates and specific power inputs were within the same order of magnitude in the ELR and the reference STR. Maximum values of 207 and 205 h at power inputs of 6.9 and 9.7 W/L were measured in the ELR and STR, respectively. During batch fermentation of K12 MG1655, maximum cell densities were higher in the ELR (OD600 of 22) than in the STR (OD600 of 18). Green fluorescence protein (GFP) production with pGS1 was comparable; however, more GFP was released into the media in the ELR. This indicates higher cell disruption compared to the STR. Despite this drawback of the first prototype, our work clearly demonstrates the potential of the ELR as a system for microbial fermentations.