Operation of a Dual Stage Continuous Upflow Media Filter under Dynamic Conditions to Achieve Ultra-Low Phosphorus Limits

Increasingly stringent effluent phosphorus limits are driving plants to achieve ultra-low phosphorus concentrations. The City of Coeur d'Alene (Idaho) commenced a low phosphorus pilot program to test the ability of three different technologies to achieve low effluent total phosphorus concentrations when operated under variable conditions. The Spokane River dissolved oxygen total maximum daily load was finalized after the pilot program was commenced. The final TMDL included a phosphorus wasteload allocation for the City of Coeur d'Alene equivalent to 0.036 mg/L, which became one goal of the pilot. One of the technologies is a dual-stage continuous upflow media filter. Based on one year of operation, the dual stage filter is capable of achieving effluent total phosphorus concentrations less than 0.036 mg/L, but is susceptible to operations and equipment issues that can increase the monthly average above the goal.