Experimental determination of wastewater characteristics and model parameters is required for robust modeling of in-sewer processes. Respirometric assays can be used to determine some of the model parameters, thus reducing the number of model parameters to be determined by model calibration and verification. However, the model structure has to be considered for this purpose. The model used consists of three main modules, namely hydrodynamics, advection and dispersion, and biochemical processes, and is applicable in sewers under aerobic dry-weather flow conditions. A procedure is proposed to determine important chemical oxygen demand (COD) fractions and model parameters for biochemical processes. Cumulative oxygen utilization proves to be useful for process identification, providing extra information on substrate availability during the assay. While the values obtained for both COD fractions and parameters depend on the model structure adopted, the procedure used can easily be adapted to other model formulations.