A process and system for denitrification of wastewater. The process includes the steps of measuring an influent flow rate, measuring influent concentrations of nitrates, nitrites, and dissolved oxygen in the wastewater, and using the influent concentrations to determine a nominal amount of methanol to be provided for denitrification. The invention also contemplates the measurement of effluent concentrations of nitrates and nitrites (i.e., NO.sub.x), and optionally using the effluent concentrations to adjust the nominal amount of methanol being provided.