Reconstruction of the oxygen uptake and carbon dioxide evolution rates of microbial cultures at near-neutral pH during highly dynamic conditions

• Highly dynamic OUR and CER are disturbed by dispersion and sensor dynamics.
• The CER is also disturbed by interconversion between dissolved CO2 and bicarbonate.
• We developed a model to describe these disturbances.
• We successfully applied the model to reconstruct highly dynamic OUR and CER.

The reconstruction of the dynamically changing rates of O2 uptake and CO2 production during short term bioreactor perturbation experiments, from dissolved oxygen and offgas O2 and CO2 measurements, requires a model describing the mass transfer and dispersion of O2 and CO2 in the system as well as the sensor dynamics. Additionally, if perturbation experiments are carried out at near-neutral pH levels, also the inter conversion of dissolved carbon dioxide and bicarbonate needs to be taken into account. While developing such a model we found that for an accurate description of the systems dynamic response on a time-scale of seconds, it is required to incorporate not only the mass transfer between gas bubbles and broth, but also between headspace and broth. The delay and dispersion in the measurements of the gas analyser, due to the length and complexity of the offgas system, was accounted for by determining the impulse response of the offgas system. This model could be fitted excellently to an identification data set. Finally the model was successfully applied to reconstruct the dynamic rates of O2 uptake and CO2 production of a culture of Penicillium chrysogenum, which was perturbed by a glucose pulse.