Abstract: In a process for the treatment of wastewater containing carbonaceous and nitrogenous contaminants, wastewater is mixed with aerobic microorganisms capable of converting carbonaceous biological oxygen demand (CBOD) into carbon dioxide, water, and biological cell mass. Oxygen is supplied to the reaction mixture for supporting reduction of the CBOD by the aerobic microorganisms in the reaction mixture. To substantially prevent nitrification of the nitrogenous contaminants in the reaction mixture and avoid the cost of downstream denitrification, the hydraulic residence time of the nitrogenous contaminants in the reaction mixture is controlled by removing partially treated water with dissolved ammonia from the reaction mixture, while retaining the biological cell mass in the reaction mixture. This separates the nitrogen load from the carbon load and enables independent treatment of these contaminants.