DO Gradient And Its Effect On Glutamic Acid Fermentation In Scale-down Reactor

In this paper, the dissolved oxygen gradient occurred in industrial production was simulated in the scale-down reactors, and its results verified the feasibility of scale-down method. At the same time the effect of dissolved oxygen heterogeneity on physiology of Corynebacterium glutamincum for glutamic acid fermentation was studied. The results showed that the scale-down method provided a new research tool for the study of bioprocess scale-up.Firstly, a laboratory scale one-compartment scale-down system was used to simulate dissolved oxygen (DO) gradients occurred in large-scale. The study was mainly focused on the influences of fluctuated DO (switch between 0% and 30% with cycle time ranging from 2h to 6h) on cell growth and metabolism of Corynebacterium glutamicum. It was shown that C. glutamicum preferred to use glucose for growth but not for product accumulation under oscillating DO condition, with much more byproduct, lactate, being produced at the same time.In order to better simulate DO heterogeneous environment of large-scale bioreactor, two-compartment scale-down reactors was designed. The flow characteristics of two-compartment scale-down reactors were studied by experiment combined with CFD simulation. It was shown that DO is significantly different between the main bulk of the reactor and the PFR part. DO heterogeneity occurred in large-scale reactor was achieved in this system.Finally, the glutamic acid fermentation was done in two-compartment scale-down reactors. It was found that DO heterogeneous conditions resulted in slower cell growth rate, longer growth period, and finally higher cell concentration. Meanwhile the glutamic acid production increased but lactate accumulation decreased. They were consistent with conclusions drawn in one-compartment scale-down reactors. Meanwhile it verified that the DO gradient occurred within the reactors, and provided the foundation for the establishment of scale-down method.