Bioprocess monitoring of dissolved oxygen using a computerized pulsing membrane electrode

A membrane oxygen electrode usually suffers from long-term signal deterioration due to environmental factors such as changes in hydrodynamic conditions and alteration of membrane oxygen diffusivity due to fouling. These problems can theoretically be overcome by the use of the same oxygen electrode in a pulsing mode. The effects of stirring rate, viscosity of the culture media, and addition of antifoam agents on the direct reading of this pulsing oxygen electrode were investigated, and the results were compared to the traditional pseudo-steady-state operation of the electrode. With a pulsing period controlled at 1 s and a rest period of longer than 5 min, the transient signal obtained can be quite stable, and it showed minimal interference from various environmental changes. Dissolved oxygen tension of a cephalosporin C fermentation was monitored using both this pulsing and the conventional pseudo-steady-state methods, and their readings were compared to those measured from an off-line newly calibrated oxygen electrode. The reading from the pulsed electrode showed more favorable agreement with that of the off-line measurement. The error encountered in using the conventional method of dissolved oxygen measurement could vary as much as 40% in comparison with the actual dissolved oxygen tension during a fermentation process.