Simultaneous storage and growth model has recently gained increased acceptance among researchers that can better interpret the processes occurring in activated sludge processes during aerobic biodegradation of organic carbon. The model underwent further improvement and was successfully calibrated using respirometric measurements, acetate being a test substrate. However, model based interpretation of titrimetry needs to be verified for proper validation of this model since pH and dissolved oxygen dynamics occur simultaneously in a batch reactor. Hence, in this paper, it is aimed to modify the existing model by introducing stoichiometric parameters involved in titrimetry in each step of the growth and storage phases along with the consideration of non-linear carbon dioxide transfer rate in liquid phase. The model calibration was done for three different acetate concentrations using titrimetric, respirometric and combined respirometric-titrimetric measurements. The parameter estimation results from all three combinations were found to be very close that supports the validity of the model. (C) 2009 Elsevier Ltd. All rights reserved.