Investigation of the bacitracin biosynthesis in an airlift bioreactor

Results of pilot plant studies using an external-loop airlift bioreactor (170 l fermentation volume, liquid height-to-riser diameter: 27, loop-to-tower cross-section-area: 0.1225) have proven the relative merits of such a system in the bacitracin biosynthesis produced by the Bacillus licheniformis submerged aerobic cultivation. The results were compared to those obtained in a pilot-scale stirred-tank bioreactor with the same values of k_La. Excepting the aeration rate of 0.2 vvm, the fermentation process performed at 0.5 vvm and 1/0 vvm, respectively, unfolded similarly in the two fermentation devices with respect to the cell mass production, substrate utilization and bacitracin production during the fermentation process. In the riser section of the airlift bioreactor, the dissolved oxygen levels were higher, while in the downcomer section they were lower than those realized in the stirred tank bioreactor. Power requirements of the airlift fermenter were by 17–64% lower than those for a mechanically agitated system, depending on the aeration rates, which led to an important energy saving. Moreover, the lack of mechanical devices in the airlift system provides safety and a more gentle environment for the cultivation of microorganisms.