Simultaneous nitrification-denitrification process is a viable approach for the improvement of nitrogen-removal efficiency. This process is achieved by particular conditions in the biological reactor, which allow simultaneous nitrification and denitrification, without alternating anoxic and aerobic phases (in time or in space). The process was applied to a full-scale plant (influent hydraulic flow rate = 80.000 m3/d) comprising four parallel lines, one of which was equipped with the simultaneous nitrification-denitrification process, while the other sections worked according to the conventional pre-denitrification scheme. A slightly greater COD removal efficiency (up to 98 %) and about the same nitrogen removal efficiency (80 - 85%) were achieved with respect to the conventional pre-denitrification process. In addition, a saving of about of about 50% of the energy required for tank aeration was obtained. The control of the aeration system may be based on dissolved oxygen and redox potential measurements using a programmable logic controller or a fuzzy logic system.