NITROGEN REMOVAL IN A PARTIAL NITRIFICATION COMPLETE DENITRIFICATION PROCESS

Using computer modeling and experimentation with a bench-scale prototy pe, a novel process for partial nitrification/complete denitrification (PN/CD) to achieve nitrogen removal equivalent to that obtained with the Ludzack-Ettinger (LE) process is demonstrated. Based on simulation results, the PN/CD process reduces aeration energy costs by up to 16% and energy requirements for recirculation and recycle pumping by up t o 28% compared to the LE process. Furthermore, the total reactor volum e of the PN/CD process is 26 to 44% less than that required by the LE process for equivalent nitrogen removal. The bench-scale PN/CD process was operated to confirm the feasibility of the proposed approach. The wastewater feed to this system was settled domestic wastewater supple mented with ammonia and acetate. The experimental PN/CD process met a 12-mg/L discharge limit on total nitrogen. Relative concentrations of ammonia and nitrate in the effluent were successfully controlled by va rying the rate of mixed liquor recirculation. Process performance was not sensitive to dissolved oxygen concentrations of 1 to 3 mg/L in the aerated reactors.