Application of Real-time Process Control and Post-anoxic Denitrification via Internally Stored Carbon to Achieve Low TN Discharge Limits

The North Durham Water Reclamation Facility (NDWRF) is a 20 mgd advanced biological nutrient removal (BNR) treatment facility, owned and operated by the City of Durham, NC that discharges to Falls Lake. In 2016 the facility began implementing state of the art control strategies in concert with excellent operational practices to reduce their effluent TN from approximately 6.0 mg/L in 2016 to 2.0 mg/L in 2019. From 2019 through 2022 the facility has averaged an effluent TN of 1.9 mg/L. Staff has been continuously optimizing the facility, pushing the limits of conventional treatment technologies. The NDWRF currently implements the following state of the art control strategies to reduce effluent TN and TP below typical conventional treatment limits: • Feed forward and feedback ammonia based aeration control (ABAC) • Nitrate based carbon addition • Diurnal ammonia based primary effluent equalization • Automatic SRT control utilizing solids analyzers • Sidestream Equalization This paper will i) detail the advanced control strategies the facility currently implements and the necessary operator maintenance/intervention necessary to ensure the programs run smoothly, and ii) demonstrate how process control has allowed operators to reduce supplemental carbon demand by leveraging internal carbon driven denitrification