The disclosed process and system are used for the denitrification of wastewater. The system comprises: an influent flow meter for measuring an influent flow Q; an influent concentration analyzer for measuring an influent dissolved oxygen concentration DOin, an influent nitrate concentration NO3—Nin, and an influent nitrite concentration NO2—Nin; an effluent concentration analyzer for measuring an effluent nitrate concentration NO3—Neff, and an effluent nitrite concentration NO2—Neff′, and a feed chemical controller for providing a feed chemical at a controlled rate. The feed chemical controller is responsive to one or more output signals provided by an automated control loop that accepts input signals from the influent concentration analyzer and the effluent concentration analyzer, which input signals relate to at least NO3—Nin, NO2—Nin, NO3—Neff, and NO2—Neff.