The dairy industry produces large volumes of wastewater with high nitrogen concentrations. The most economical option to treat this wastewater is the biological nitrogen removal process, composed of two stages: nitrification and denitrification. However, it is possible to reduce the costs of this process even more by accumulating nitrite in the first stage, avoiding reconverting the nitrate generated into nitrite in the second stage. It has been observed that the nitrite accumulation in the first stage is an unstable dynamic process, which results in problems maintaining high levels of nitrite accumulation in the long term. This paper presents a formal study to determine optimal operating points where the process can accumulate high nitrite over a long time. In this study, through a search by an optimization method, we found four operating points feasible to be controlled and suitable to reduce the aeration cost and improve the residence time.