A method and system for treating wastewater is disclosed. In one embodiment the method includes introducing the wastewater into an aerated anoxic treatment unit, flowing an oxygen containing gas into the wastewater in the aerated anoxic treatment unit at a first flow rate, measuring a concentration of a nitrogen species in the wastewater in the aerated anoxic treatment unit, comparing the measured concentration of the nitrogen species to a target nitrogen species concentration, adjusting the flow of the oxygen containing gas into the wastewater in the aerated anoxic treatment unit to a second flow rate in response to a difference in the nitrogen species and the target nitrogen species concentrations, and maintaining the second flow rate for a time period sufficient for the wastewater to be treated in the aerated anoxic treatment unit and form an anoxically treated liquid having a reduced concentration of the nitrogen species.