Transient response, model structure and systematic errors in hybrid respirometers: structural identifiability analysis based on OUR and DO measurements

Experimental respirometry shows oxygen uptake rate (OUR) transients which are not predicted by standard ASM models. These transients were analysed from a detailed modelling of hybrid respirometers. Structural identifiability analysis of several models based on local isomorphism transformation approach is carried out. It can be concluded that the knowledge of the OUR does not help positively on an accurate determination of biokinetic parameters. The measure of dissolved oxygen (DO) is just enough to calculate the group of identifiable parameters from the models in a calibration process. The analysis suggests to use only the DO data to avoid the systematic errors associated to OUR calculations. Furthermore, the existence of OUR transients after a precise modelling of the hybrid respirometer is deduced. The duration of these transients are the result of the coupling between the kinetics of the biological process and the residence time in the respiration chamber of the instrument. An expression for the duration of these transients is proposed.