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