Although the activated sludge models for waste water treatment plants (WWTPs) offer comprehensive description of their involved biochemical and physical processes, it is a challenging task to calibrate the model for the operational plant. The article first presents a systematic calibrating procedure applied to the Activated Sludge Model No.1 (ASM 1), showing its potential to be extended to other WWTPs. It particularly addresses cases when comprehensive knowledge on the WWTP influent composition does not exist. An optimisation‐based approach is used for the WWTP model calibration and for finding the partially unknown influent composition. Dynamic model validation shows good match between model predicted values and WWTP measured data. Second, a new feed‐forward control strategy is designed for the WWTP and compared with the conventional nitrate‐nitrite nitrogen and dissolved oxygen control. The evaluation based on the effluent quality index, pumping and aeration energy and the number of effluent violations assessment tools, demonstrates incentives for the proposed control approach.