WWTP Optimization to Achieve Effluent Total Phosphorus Levels Less Than 0.15 mglL Without Chemicals or Filtration

Conventional biological phosphorus removal strives for effluent total phosphorus levels of 1 to 2 mg/L. Phosphorus is becoming a critical pollutant in man y watersheds and very low permit limits are becoming more common. Satisfying stringent permit limits requires significantly improved biological performance and frequently the use of chemicals and filtration. In 2002, the City of Moscow, Idaho, wastewater treatment plant (WWTP), which was designed for enhanced biological phosphorus removal, had an average effluent total phosphorus level of 0.91 mg/L, but a stringent limit of 0.136 mg/L was looming in the NPDES permit. The City entered into a longterm process to optimize the facility for effluent total phosphorus without chemicals or filtration. This paper presents the control theories the City adopted, operating characteristics of the WWTP, and process changes undertaken with existing treatment basins leading to an average effluent total phosphorus level of 0.254 mg/L in 2008 and 0.133 mg/L during the permit period ofMay 15 through October 15 in 2008.