Lessons Learned from Startup of the Largest Tertiary Ballasted Settling System in the U. S.

In February 2005, Onondaga County (County) began operating a 492,000 m³ /day (130 mgd) peak flow ballasted settling system at the Metropolitan Syracuse Wastewater Treatment Plant (Metro WWTP) for tertiary phosphorus removal.

The system was designed to reduce the total phosphorus concentration in the BAF effluent from 0.75 to 0.12 milligrams per liter (mg/L). This performance was to be achieved at a ferric chloride dosage not to exceed 25 mg/L (as FeC1₃ ) and a polymer dosage not to exceed 0.6 mg/L (active polymer).

Shortly following startup, it became apparent that the system was falling slightly short of expectations. Daily effluent total phosphorus concentrations were generally ranging from approximately 0.15 to 0.20 mg/L. To improve the performance of the system, the County began evaluating a series of changes in operation and maintenance of the system with assistance from the system vendor, Kruger Inc., and the system design engineer, Environmental Engineering Associates, LLP (EEA). These changes included modification of recommended procedures for cleaning of the lamella tube settling modules in each train, varying ferric chloride and polymer dosages, and experimentation with alternative coagulants.