One Utility’s Success Story Exceeding Regulatory Goals: Design, Operation and Performance Optimization of IFAS Upgrades at Two WWTPs for Enhanced Nitrogen Removal

Many utilities are facing the need to upgrade their treatment facilities to address nutrient removal requirements, with new operating challenges. One such utility is the Chesterfield County Department of Utilities, which operates the 45,400 m3/d (12.0 mgd) Falling Creek and 102,200 m3/d (27.0 mgd) Proctors Creek wastewater treatment plants. Both facilities were required to meet stringent Chesapeake Bay Watershed average annual nutrient limits, equivalent to 5.8 g/m3 total nitrogen and 0.6 g/m3 total phosphorus at the design flows. To meet the new limits a four-stage integrated fixed-film activated sludge biological nutrient removal process was installed at each facility, coupled with chemical phosphorus removal. Lessons learned during start-up led to design enhancements incorporated during construction. Following construction, staff focus shifted to optimizing operations and treatment efficiency. This paper will discuss the lessons learned during start-up and operation and the optimization efforts to reduce operational costs and efficiently achieve effluent quality targets.