Full-Scale Operating Experience of Deep Bed Denitrification Filter Achieving < 1.5 mg/l Total Nitrogen and < 0.05 mg/l Total Phosphorus

The Arlington County Wastewater Pollution Control Plant (ACWPCP) expanded from a 113,500 m3/d, (300,000 pe) secondary treatment plant to a 151,400 m3/d (400,000 pe) “limit of technology” (LOT) treatment facility to achieve anticipated effluent total nitrogen (TN) to < 3 mg/l and total phosphorus (TP) < 0.18 mg/l. Key to this conversion was the implementation of deep bed denitrification filters and the challenge of maintaining a healthy denitrifying biomass within the denitrification filters while reducing an essential nutrient, phosphorus, to very low concentrations. This paper will present full-scale operating experience and strategies from the first large-scale 151,400 m3 (40 mgd) facility utilizing step-feed activated sludge and deep bed de nitrification filter which have allowed the Arlington County WPCP to from June 2011 to June 2014, the effluent TN has averaged < 0.9 mg/L TN and < 0.05 mg/L total phosphorus (TP).