There is significant interest in using process models for WWTP design to complement the traditional design guidelines. However, transparent quantification of the differences in the design results obtained with the two approaches has not been done yet. The objective of this paper is to define a methodology to evaluate the expected performance of a designed WWTP. The use of this methodology will enable to identify inherent safety incorporated in design guidelines by verification with dynamic process models. The methodology includes two parts: first, multiple designs are made using a design guideline for different combinations of influent characteristics, effluent requirements, safety factors and operating preferences. Second, the results of the designs (eg reactor volumes) are applied in a process model that emulates WWTP behaviour. The effluent concentrations predicted by the process model are then compared to the effluent requirements which were imposed for the designs. The methodology is illustrated using the Metcalf & Eddy design guidelines for a nitrogen-removing process and the ASM1 process model.