Optimization of a full‐scale site to achieve total nitrogen removal through implementation of a denitrification‐submerged anoxic filter

A full‐scale wastewater treatment plant with a 5500 population equivalent was retrofitted with a pre‐denitrification‐submerged anoxic filter (SAnoF) in order to achieve new total nitrogen (TN) consent of 35 mg/L. A 36 m3 SAnoF was installed downstream the primary settling tanks. The optimal operation of the anoxic SAnoF was investigated by varying the recirculation ratio, the carbon‐to‐nitrate ratio, and the hydraulic retention time. After stable operation was achieved, nitrate was removed by 80% at a loading of 0.5 kg NO3/m3 day and a retention time of 60 min. The SAnoF presented a number of advantages, including the use of internal carbon for denitrification, decrease of carbon load to the trickling filter by 30%, and production of alkalinity required for nitrification in the trickling filter (11 mg CaCO3/mg NH4 removed). Overall, the SAnoF was satisfactory and the effluent TN concentration reached 20–25 mg TN/L.