Chemical & Process Engineering


Philipp Waldherr

Research Associate

+49 30 314 72622

Room MAR 2.051 / ACK Z 66
Address Marchstr. 23
10587 Berlin
Office houron appointment, see ISIS course

Experimental und CFD-based investigation of mechanical stress on filamentous microorganisms in stirred tank reactors


Filamentously growing microorganisms are already used industrially in a variety of ways to manufacture products for the food, pharmaceutical or consumer goods industries (citric acid, antibiotics, enzymes for detergents), for example. Due to the high complexity of biotechnological processes, there is still great potential to increase product yield and process efficiency.

Cultivations are usually carried out in stirred tanks. An important influencing factor is the mechanical stress caused by the stirrer, as the microorganisms can be damaged by shear and elongation forces. The aims of this work include characterizing stirrers with regard to their shear stress and developing low-shear stirrers.

CFD - numerical work

Previous research suggests that the shear stress of a stirrer is a combination of the maximum load and the frequency of experiencing high loads. This stress history is assessed numerically using particle trajectories of massless parcels using the particle tracking method. The local shear rates traversed by a parcel can be recorded in this process (cf. Fig. 1a). The plot of the residence time at a given shear rate versus the corresponding shear rate value (Fig. 1b) shows a significantly higher shear stress due to the waveband agitator compared to the disk agitator.

Experimental work

As an example, the investigations are carried out on the filamentous growing fungus Aspergillus niger, whose growth form (morphology) can be specifically adjusted. Whether spherical pellets or mycelial growth (cf. Fig. 2) is present is adjusted by the osmolality of the cultivation medium. The influence of mechanical stress on the productivity of the microorganisms is investigated.



Waldherr, Philipp; Bliatsiou, Chrysoula; Böhm, Lutz; Kraume, Matthias
Comparative Study of Fluid Dynamic Stress on Aspergillus niger and Model Systems 
Chemie Ingenieur Technik, 96 (4) :471-485


Waldherr, P.; Bliatsiou, C.; Böhm, L.; Kraume, M.
Fragmentation of Aspergillus niger pellets in stirred tank bioreactors due to hydrodynamic stress
Chemical Engineering Research & Design, 195 :116-131


Waldherr, P.; Bliatsiou, C.; Panckow, R.; Böhm, L.; Kraume, M.
Characterizing particulate systems towards the analysis of hydrodynamic stress in stirred-tank (bio)reactors
Chemie Ingenieur Technik, 94 (9) :1336


Bliatsiou, C.; Schrinner, K.; Waldherr, P.; Tesche, S.; Böhm, L.; Kraume, M.; Krull, R.
Rheological characteristics of filamentous cultivation broths and suitable model fluids
Biochemical Engineering Journal, 163 :107746


Jurtz, N.; Waldherr, P.; Kraume, M.
Numerical Analysis of the Impact of Particle Friction on Bed Voidage in Fixed-Beds
Chemie Ingenieur Technik, 91 (9) :1260-1266