A comparison between the performance of continuously stirred‐tank bioreactors and a TORUS bioreactor with respect to highly viscous culture broths

Abstract Two different designs of stirred‐tank bioreactor, the ‘conventional’ continuously stirred‐tank bioreactor (CSTR, 42 dm3 and 300 dm3) and a horizontal‐loop bioreactor (TORUS, 114 dm3) were used for the cultivation of Xanthomonas campestris, and their performances with respect to oxygen‐transfer rates and xanthan production were compared. The strictly aerobic yeast Trichosporon cutaneum was also cultivated in the TORUS bioreactor in a synthetic medium with up to 3% (w/v) xanthan added. Xanthan solutions are pseudoplastic and therefore an apparent viscosity at a shear rate (y) of 28.8 s−1 was used to compare the rheological behavior of the different test media. Maximal apparent viscosities of 1100mPa s were measured with xanthan concentrations between 20 and 25 g dm−3. With apparent viscosities of up to 800 mPa s, the performance of the TORUS bioreactor was found to be equivalent to the performance of the CSTR bioreactor in terms of oxygen transfer and xanthan production rates. However, the amount of glucose converted to xanthan was greater in the TORUS bioreactor. Since the power consumption for the TORUS is lower compared to that for the CSTR, this new design is an interesting alternative to the CSTR for the production of xanthan.