Mixing in the Fermentation and Cell Culture Industries

Studies supporting the use of mechanical mixing in large scale beer fermentations

“…Given these findings with animal cells, it might be expected that yeast cells  is at the upper limit of that used at an industrial scale for aerobic fermentations (Amanullah et al, 2003) and very much higher than that of about 0.035 W/kg generated by the maximum rate of CO 2 release during a beer fermentation of 300 m 3 (Luyben, 1997) (Figure 2). …”

“…These conditions were simulated at the bench scale using a stirred fermenter with plug flow loop (STR-PFR). This combination has been successfully used for other scale down studies (Amanullah et al 2003) and has been particularly successful at mimicking large scale E. coli fermentations (Onyeaka et al 2003;). The work reported here is the first in which temperature gradients in a bioreactor have been simulated.…”

Effect of Mixing on Microorganism Growth in Loop Bioreactors

“…Large-scale bioreactors have been shown to exhibit heterogeneous hydrodynamic and concentration fields with the cells circulating through such reactors being submitted to an extracellular fluctuating environment [12]. Insufficient macromixing can consequently induce modifications of the cell metabolism, leading to the formation of byproducts and decreasing the overall reactor performance with large-scale cultivations exhibiting lower carbon conversion yields than expected from lab-scale experiments [13].…”

The scale-up of microbial batch and fed-batch fermentation processes

“…The size of this region may be estimated by intuition, by flow visualisation (again on the small-scale) or by computational fluid dynamics (Enfors et al, 2001). Typically, in the small-scale simulation, the addition zone is represented by a relatively small plug-flow reactor (PFR), and the bulk region by a stirred tank reactor (STR) (Amanullah et al, 2003).…”

“…In this case, the volume of the well oxygenated region is typically made of the order of 25% of the poorly oxygenated region. The STR-STR and STR-PFR have been compared for batch fermentations of Bacillus subtilis with respect to pH and dO 2 fluctuations (Amanullah et al, 2003). In both cases, significant differences were found compared to the well mixed case, which depended on the relative size of the 2 zones and the recirculation rate between them.…”