Reactor heterogeneity with Saccharopolyspora erythraea airlift fermentations

Abstract

Bioreactor heterogeneity has been studied in a multiconfigurable pilot-scale airlift reactor (0.25 m 3 ) which created different degrees of heterogeneity. The impact of the two sparger configurations, i.e. in the draft tube or the annulus, in conjunction with a marine propeller fitted at the base of the downcomer, on the physiology of Saccharopolyspora erythraea was studied. Cellular growth, morphology, and productivity were compared between airlift and stirred tank reactors. Dissolved oxygen tension heterogeneity caused by differences in dissolved oxygen tension around the vessel did not affect growth, but the reduction of heterogeneity improved the specific erythromycin production rate and final specific production. Erythromycin production was shown to be proportional to the energy dissipation rate. The enhancement of bubble coalescence with increasing apparent viscosity led to the reduction of the sectional gas holdups and the improvement of liquid mixing. The extent of the changes with increasing apparent viscosity was dependent on the broth morphology, reactor configurations, and operating conditions.

Oxygen transfer and mixing in mechanically agitated airlift bioreactors

“…Highly directional and enhanced circulation of fluid means an improved capability for suspending solids and reduced axial gradients of concentration of nutrients and oxygen. Such gradients are known to occur in tall airlift reactors and affect performance adversely [1,[6][7][8][9]. Furthermore, in the hybrid configuration, the gas is sparged in the annular riser zone and not beneath the impeller; therefore, flooding becomes less of a concern.…”

“…It has also been found useful with less viscous yeast broths [7,11]. In highly viscous, non-Newtonian, broths of Saccharopolyspora erythraea, the use of a marine propeller located near the bottom of the draft-tube has been reported [6] to enhance the yield of the antibiotic erythromycin by ca 45% compared to the basic annulus-sparged airlift configuration. For similar highly viscous broths of the microfungus N. sitophila in annulus-sparged draft-tube reactors, Moo-Young et al [10] had earlier established that the airlift configuration supplemented with a low-shear axial flow impeller in the draft-tube was better than the pure airlift device.…”

“…Prochem hydrofoils have been evaluated for use in bioreactors in the past, but mostly only in the conventional baffled stirred tank configuration [16][17][18][19][20]. A few studies have been reported in reactors with axial flow marine propellers inside draft-tubes, but only in relatively small (≤250 l) vessels [6,11,21,22].…”

Hydrodynamic and Mass Transfer Study in a Mechanically Stirred Hybrid Airlift Bioreactor Based on Impeller Type

“…Mechanically stirred airlift bioreactors are a viable alternative, for presenting some characteristics from both the traditional airlift reactors, and the aerated mechanically stirred tanks. Mechanically stirred hybrid airlift bioreactors have been described in the literature [3], [6], [7], with the objective of improving the process, by increasing the mass transfer from the gas to the liquid phases. Bang et al, [6] proposed a new type of mechanically stirred airlift reactor, in which the agitator is located at the bottom of the reaction vessel, centered on the riser.…”

“…According to these authors, the volumetric coefficient mass transfer increased up to four times, compared to a standard airlift reactor; this increase is due primarily to the bubbles collapse caused by the impeller, which also is directly related to the increase of the gas holdup. Pollard et al, [7] by using an impeller close to the bottom of the draft tube of an airlift bioreactor, were able to increase by 45% the productivity of the erythromycin antibiotic, when compared with a standard airlift bioreactor. Chisti and Jauregui-Haza [3] compared the mixture and oxygen transfer in a standard airlift bioreactor with two mechanical agitators; the first located near the center and another at the end of the draft tube.…”