A denitrification system for denitrified wastewater or nitrified water treatment using a detergent or detergent-like compound comprising available carbon. The system comprises a plurality of interconnected tanks including a mixing tank which feeds detention tanks which in combination provide a detention time period for the effluent. A controller determines the amount of detergent dispensed into the mixing tank in accordance with the measured volume of effluent to be treated. The mixing tank comprises a heater for maintaining the nitrified effluent temperature above 50 degrees F. An optional line filter can be added to the output of the system for further reducing organic nitrogen concentration. An alternate embodiment comprises passing the final denitrified effluent through a pump chamber for pumping of the effluent to a sand filter capable of reducing bacterial populations.