BACKGROUNDA validated model describing the nitritation-anammox process in a granular sequencing batch reactor (SBR) system is an important tool for: (a) design of future experiments; and (b) prediction of process performance during optimization, while applying process control, or during system scale-up. RESULTSA model was calibrated using a step-wise procedure customized for the specific needs of the system. The important steps in the procedure were initialization, steady-state and dynamic calibration, and validation. A fast and effective initialization approach was developed to approximate pseudo steady-state in the biofilm system. For oxygen mass transfer coefficient (k(L)a) estimation, long-term data, removal efficiencies, and the stoichiometry of the reactions were used. For the dynamic calibration a pragmatic model fitting approach was used - in this case an iterative Monte Carlo based screening of the parameter space - to find the best fit of the model to dynamic data. Finally, the calibrated model was validated with an independent data set. CONCLUSIONThe calibration procedure presented is the first customized procedure for this type of system and is expected to contribute to achieving a fast and effective model calibration, an important enabling tool for various biochemical engineering design, control and operation problems. (c) 2013 Society of Chemical Industry