Removal of N and P in a Rotating Biological Contactor Plant: Case Study Agnita, Romania

Abstract

The wastewater treatment plant of Agnita, Romania was designed with a rotational biological contactor system for a population of approximately 9500, but for environmental protection reasons it must comply with regulations concerning nitrogen and phosphorus designed for larger communities. In order to achieve the prescribed limits for these pollutants, we have used a 40% FeCl3 solution, continuously added to the distributor, without changes in flow or equipment. Its use boosts the removal of ammonia nitrogen, and phosphorus, bringing them within the limits and with reasonable cost. To determine the ferric chloride to be used we considered, aside from the pollutant load, the water temperature, and introduced a new parameter: specific removal power that enabled us to optimize the volume of FeCl3. A major contribution to nitrogen removal was achieved by the denitrification bacteria favored by the presence of ferric ions, which also precipitate phosphorus. The results of this study, performed since September 2021, enable us to continue to use this method and enlarge its application to other plants owned by the local operator.