Invitation to Guest Talk: Jochen Büchs

by Jochen Büchs

Professor Dr.-Ing. AVT - Chair of Biochemical Engineering RWTH Aachen University

Jochen Büchs received his Doctor degree (1988) from the Research Center Jülich under the supervision of Professor Dr. C. Wandrey. He became a research associate at the Institute of Physical and Chemical Research (RIKEN) and at Tokyo University, Japan (scholarship by Mombusho & DAAD). After returning to Germany and receiving his PhD, he was member and later head of the "biochemical engineering team" at BASF group in Ludwigshafen, Germany (1988). Five years later (1993) he became head of the biotechnological pilot plant at BASF Group. In 1996 he accepted the full professor position for Biochemical Engineering at RWTH Aachen University, Germany. In the same year he also obtained the "Arnold-Eucken Prize" of the German Society of Chemical Engineering. His research interests are in the area of shaken culture systems, high pressure fermentation, small scale feeding technology and on-line monitoring. He has published more than 300 original papers and patents. Six novel technologies invented and developed at the Chair have been commercialized and are globally marketed.

You are cordially invited to join this talk:

Date: Monday, 20th of February 2023, 14h

Place: Muthgasse 18, MUG 1, 5th floor, Gr. SR (05/08 or new SR51)

ABSTRACT: From the discovery of the out-of-phase phenomenon in shake flasks to the development of a new type of parallel rheometer

Jochen Büchs, Carl Dinter, Michaela Sieben, Amizon Azizan, Kyra Hoffmann, AVT-Biochemical Engineering, RWTH Aachen University, Aachen/Germany, Andreas Gumprecht, Sven Hansen, Evonik Operations GmbH, Hanau, Marl/Germany

The ‘out-of-phase’ phenomenon

One of the (most) important parameters in fermentations of aerobic microbes is the specific power consumption. New methods have been introduced to accurately determine the power consumption in shaken bioreactors. During these studies, the ‘out-of-phase’ phenomenon has been discovered. This phenomenon is observed in non-baffled shake flasks at elevated viscosities It is observed in cases, when the viscous forces become larger than the centrifugal forces. The phenomenon is characterised by an increasing amount of liquid not following the movement of the shaker table, thus, reducing the specific power consumption, mixing intensity and the gas/liquid-mass transfer. The transition from suitable ‘in- phase’ to unsuited ‘out-of-phase’ conditions is a steady process. However, for the ease of handling and avoiding of the ‘out-of-phase’ phenomenon during routine laboratory work, a critical Phase number (of Ph = 1.26) was defined. A 10 % reduction of the specific power consumption relative to the reference ‘in- phase’ condition was (arbitrarily) selected as boundary condition. Apart from measurement of specific power consumption also mixing time was quantified. It was found that the mixing time drastically increases, as soon as the Phase number reaches the critical value of Ph = 1.26. Recently, the angle resolved contact line of the rotating bulk liquid and the glass wall of a shake flask relative to the direction of the centrifugal acceleration was assessed for multiple operating conditions. This data was compared to CFD calculations. Fortunately, the measured and calculated angle resolved contact line of the rotating bulk liquid and the glass wall of a shake flask agreed very well. From the CFD calculations also the average specific power consumption was derived. The results agreed astonishingly well with the measured values. The CFD calculations also could correctly predict the steady transition of the liquid flow from ‘in- phase’ to ‘out-of-phase’ conditions.

A new type of parallel rheometer

For studying the ‘out-of-phase’ phenomenon, a camera was mounted on the shaker table, which rotates around the flask, oriented into the direction of the centrifugal acceleration. It was discovered that the leading edge of the rotating bulk liquid in the flask is shifted against the direction of the rotation, depending on the viscosity. This effect can be exploited to establish a new type of rheometer. The measurement principle is based on detecting the angular position of a liquid sample in an orbitally shaken vessel, relative to the direction of centrifugal acceleration by a photoelectric barrier. The electronic parts required for the measuring set-up are rather inexpensive. Several vessels can easily be operated in parallel. The device can be used as an offline rheometer for any kind of samples or as an online rheometer, e.g. in combination with a Respiration Activity Monitoring System (RAMOS). The figure shows an example for such a combination. The advantage of low phosphate concentration is demonstrated. It induces the promotor for poly-γ-glutamic acid production and reduces growth and, therefore, channels the carbon flux into product formation. The response of the cells to these conditions is clearly recognized from the signal of the new type of rheometer.

Bacillus subtilis Ppst Δspo cultivation in modified V3 glucose minimal medium with varying phosphate concentrations. (A) shows the OTR and (B) the viscosity signal from the new type of parallel rheometer. Poly-γ-glutamic acid formation is responsible for the viscosity increase and is controlled by a phosphate starvation promotor. Oxygen limitation is intended for boosting the product formation: 20 g/L glucose, phosphate: 100% ? 3.4 g/L K2HPO4, 0.2 M MOPS; T = 37 °C, 250 mL shake flask, VL = 30 mL, n = 250 rpm, d0 = 50 mm.