A process and system for the reduction of nitrate to nitrogen in a fluid medium. Anaerobic bacteria fed by a carbon source are used for nitrate reduction. The addition rate of the carbon source and process residence time are controlled using the oxidation-reduction potential of the fluid medium to achieve a desired level of nitrate reduction. An industrial process control system may be used to monitor inputs and control outputs. A column of suspended beads may be used as the anaerobic bacterial bed for denitrification.