Standardized Qualification of Stirred Bioreactors for Microbial Biopharmaceutical Production Processes

Abstract

An in 2016 published DECHEMA guideline concerning process engineering characterization and a new Escherichia coli model process were utilized for the qualification of two geometrically similar stirred stainless steel bioreactors (30 L and 100 L working volume). The achieved results demonstrate that performing an additional biological model process is a valuable complement to the process engineering characterization. Optical densities of 27 (100 L) and 39 (30 L) were reached in the batch cultivation process.

Development, Engineering and Biological Characterization of Stirred Tank Bioreactors

“…This effect is often also referred to as "flooding" [35,54], whereby in the present bioreactor design, the impeller running on the bottom does not pull down the bubbles emerged by the higher lying sparger, and is therefore not able to disperse them sufficiently due to radially acting forces. Compared with experiments on the 30 and 100 L scale, the value determined with the 20 mm impeller is three times smaller [42].…”

“…When using the larger impeller in combination with a more powerful drive and a resulting higher k L a value, an optical density of 65.3 ± 3.4 (21.6 ± 1.9 g•L −1 DCW) is reached. In reusable pilot bioreactors for microbial applications with 30 and 100 L previously tested, only optical densities of 39 ± 5 at higher oxygen transport rates of 735 and 745 h −1 were obtained [42]. This fact can only be attributed to the considerably shorter mixing times of 2.77 and 3.47 s (20 mm/40 mm) in the 2 L scale shown here.…”

“…The achieved mixing numbers are partly c H > 100 due to the impeller position at the vessel bottom, which are above the usual values for bioreactors equipped with different impeller types [35]. Mixing times are also below the 10 s recommended for microbial requirements [53], as is also the case in other conventional bioreactors up to pilot scale [42,70,71]. However, compared to systems with larger volumes, a possible increase in mixing time of up to 2 min must also be taken into account [10].…”

“…So it comes as no surprise that the specific power inputs obtained in the case study with the new bioreactor provide comparable results to other microbial bioreactor systems described in the literature. For bioreactors with sizes of 1-100 L, these are between 2.5 and 20 kW•m −3 [42,[67][68][69], whereby a minimum requirement of >5 kW•m −3 is generally assumed [10]. The achieved mixing numbers are partly c H > 100 due to the impeller position at the vessel bottom, which are above the usual values for bioreactors equipped with different impeller types [35].…”

“…Biological characterization focuses on the evaluation and comparison of bioreactor systems with respect to their biological performance. With the help of a model organism, it should be possible to make an exact prediction of the suitability of a bioreactor system for a desired purpose with a standardized cultivation procedure [42]. For example, two biological test procedures with respiratory yeast and mycelium-forming fungi were developed by Adler and Fiechter [43] and Wagner [44], since the physical characterization often only provides information about optimal bioreactor design conditions and information for improved scale transfer.…”