Cell inactivation in the presence of sparging and mechanical agitation

Abstract

Microbial cells are more readily rendered nonviable by the combined action of air sparging and mechanical agitation than by either action along. A. bubble breakup/coalescence model that incorporates the cell-bubble encounter rate, bubble breakup rate, and death probability is proposed to describe cell inactivation in the presence of bubbles maintained through the joint action of agitation and air, which is continually fed into the impeller stream region via passive vortex entrainment from the surface above or via active sparging from below. Experimental results obtained from a fragile algal (Ochromonas malhamensis) culture are consistent with the model prediction. In particular, the specific cell death rate is linearly related to the specific bubble interfacial surface area. It is shown that cells exhibit sparging-sensitive characteristics when agitation is mild, but become sensitive to surface vortexing when agitation turns vigorous enough to introduce air entrainment. Experimental data obtained from different stirrer sizes are in good agreement with the model.

Effects of agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum

“…Rising bubbles, specially small ones, have been shown to carry cells with them in their wakes and adsorbed to the surface [53][54][55]. Furthermore, the rupture of small bubbles is known to be more damaging to cells than is the rupture of large bubbles [13,16,27,[55][56][57][58]. Presence of Pluronic, a surfactant, is known to reduce the attachment of cells to bubbles; hence in the presence of Pluronic fewer cells are carried to the surface where the rupture events cause damage.…”

“…For example, damage to 8-20 lm average diameter cells of the microalgae Ochromonas malhamensis was investigated by Yang and Wang [27] for various agitation-aeration combinations. A 14 L fermenter with a six-bladed Rushton turbine was used.…”

“…In the absence of sparging, agitation speeds below 350 rpm (tip speed of 1.4 m s -1 ) produced no damage, but damage occurred above 350 rpm apparently because high-intensity agitation was accompanied by gas entertainment due to vortexing. Under damaging conditions of agitation, aeration at rates that alone had caused no cell damage, enhanced the damaging effect [27].…”

Equipment characterization to mitigate risks during transfers of cell culture manufacturing processes

“…More details about CO 2 -depletion phenomenon and the limitation of carbon dioxide stripping for larger cell culture reactors ([200 L) can be found in Sieblist et al (2011a). Shear force and the impact to cell culture have been discussed in literature by several authors (Cherry 1993;Elias et al 1995;Godoy-Silva et al 2010;Joshi et al 1996;Kretzmer and Schügerl 1991;Nienow 1998;van der Pol and Tramper 1998;Sieck et al 2013;Sorg et al 2011;Yang and Wang 1992). The influence of shear stress and appropriate scaling strategies are as well discussed by Nienow and colleagues (Nienow 2014;.…”

Local gas holdup measurement in aerated agitated bioreactors

“…In general, the gas holdup increased as the agitation intensity was raised. A typical set of measurements performed at low gas holdups with the second apparatus are shown in Figure 4, in which tlie measured gas holdup is plotted against the average energy dissipation rate calculated via a procedure described by Yang and Wang (1991). The slope obtairlcd from linear regression indicates that the local gas holdup at the specific point indicated in Figure 3 is related to the 0.76 power of the average energy dissipation rate.…”