Design and Startup of an Oxidation Ditch System for Lot TN Removal Without External Carbon – Lessons Learned

The City of Plant City (City) owns and operates a Water Reclamation Facility (WRF) located in Plant City, Florida. The WRF was placed under consent order by the Florida Department of Environmental Protection for nitrogen and toxicity levels. The WRF's capacity also had to be increased to accommodate anticipated growth in the service area. As a result, the City initiated a project to increase the capacity of the WRF from 8 to 10 mgd, and to meet annual average requirements 3 milligrams per liter (mg/L) total nitrogen (TN) and 1 mg/L total phosphorus (TP). The facility was modified under this project to achieve these strict effluent quality requirements via simultaneous nitrification/denitrification (SND) in oxidation ditches, thus avoiding the need for an external carbon source. This paper will describe the design implementation, construction, start-up and initial operations including a description of the process control system, the start-up challenges, and key lessons learned.