The Arlington County Wastewater Pollution Control Plant (ACWPCP) is located in the southern part of Arlington County, Virginia, USA and discharges to the Potomac River via the Four Mile Run. The ACWPCP was originally constructed in 1937. In 2001, Arlington County, Virginia (USA) committed to expanding their 113,500 m³/d, (300,000 pe) secondary treatment plant to a 151,400 m³/d (400,000 pe) to achieve 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 to simultaneously achieve both low effluent TN and TP concentrations. A challenge with implementing this technology is maintaining a health denitrifying biomass within the denitrification filters while reducing an essential nutrient, phosphorus, to very low concentrations. This paper will review the steps from concept to the first year of operation, including pilot and full-scale operating data and the capital cost for the denitrification filters.

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The Arlington County Wastewater Pollution Control Plant (ACWPCP) expanded from a 113,500 m 3 /d, (300,000 pe) secondary treatment plant to a 151,400 m 3 /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 m 3 (40 mgd) facility utilizing stepfeed activated sludge and deep bed denitrification 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).