This paper presents a systematic procedure for multiobjective optimization of control strategies in environmental systems. The optimization of control strategies in environmental systems is a complex activity due to the large number of objectives that must be considered simultaneously e.g. economic, environmental, technical, legal. The accomplishment of those objectives generates significant synergies, but in many cases they are subject of clear trade-offs. This procedure is approached as a multicriteria decision analysis (MCDA) and involves the quantification and normalization of a set of evaluation criteria and a weighted sum. A sensitivity analysis is also included in order to show the variation of the selected option when the relative importance of the control objectives is changed. The usefulness of the proposed procedure is demonstrated by optimizing PI control loops for aeration and internal recirculation in the IWA/COST benchmark plant.