Evaluation of Several Water Reclamation Facilities Employing Biological Nutrient Removal In North Carolina

As an increasing number of lakes and streams are being classified as impaired or nutrient sensitive, a greater burden is placed on municipalities to comply with water quality restrictions. During the past decade in North Carolina, specifically in the Neuse River and Tar-Pamlico River Basins, many municipalities were required to upgrade their wastewater treatment plants for nutrient removal capability, either nitrogen or phosphorus or both. Municipalities discharging to the Neuse River Basin are required to meet some of the most stringent effluent limits in North Carolina. All streams and rivers in the Neuse River Basin were classified as nutrient sensitive waters and a 2.0 mg/L phosphorus limit was imposed on direct discharge facilities. A Total Maximum Daily Load (TMDL) for a 30% nitrogen reduction goal was also imposed in the Neuse Basin. The Tar-Pamlico River Basin was declared nutrient sensitive in the late 1980's for nitrogen and phosphorus, and a goal was established to reduce nitrogen and phosphorus in combination by 30% compared to 1991 levels. The purpose of this paper is to provide an evaluation and overview of several biological nutrient removal facilities currently in operation in the Neuse River and Tar-Pamlico River Basins of North Carolina.A flexible design of a wastewater treatment plant is critical to meeting nutrient limits under changing regulation and possibly changing influent wastewater characteristics. The selected facilities are almost fully optimized for biological nutrient removal, even under carbon limited influent conditions. All of the facilities discharge nitrogen and/or phosphorus at current effluent limits below what is required by the permit. It is likely that these facilities will be able to meet an additional 10% reduction in nitrogen in the near term and will most likely meet an additional nitrogen reduction requirement in the future. Although, as the target effluent nitrogen concentration decreases the probability of compliance may decrease. Achieving a lower target concentration of effluent nitrogen will be less probable based on day-to-day plant operations under dynamic conditions.