Upgrade of wastewater treatment plant shows just what can be achieved!

28 September 2012

Arlington County’s Water Pollution Control Plant (WPCP) in South Arlington, Va., is located on 35 acres of land squeezed into a commercial/residential neighborhood less than a mile west of Ronald Reagan Washington National Airport. The facility treats flows from nearly all of Arlington. In addition, nearly 20 percent of the plant’s flow comes from neighboring localities such as Alexandria, Fairfax County, and Falls Church. Effluent from the plant is discharged into Four Mile Run to the south, which feeds into the Potomac River and, ultimately, the Chesapeake Bay.

Originally constructed in 1937, the facility had been upgraded several times in the 1950s, 1960s, 1970s and 1990s. In 2001, Arlington County officials recognized the need to address a number of long-term challenges. A growing population in the county’s residential and business communities was putting a strain on the aging WPCP infrastructure. There was insufficient treatment capacity to handle wet weather flows that could increase nearly fourfold. Additionally, site space constraints would present a challenge to the required huge construction effort. In a forward-looking approach, the county board decided in January 2003 to proactively upgrade the plant’s treatment process to provide “limit of technology” nutrient removal in advance of any requirements to do so. This would require upgrading the plant’s biological nutrient removal (BNR) 8 mg/l total nitrogen (TN) capability to meet an anticipated TN limit of approximately 3 mg/l with a concurrent low total phosphorous limit of 0.18 mg/l.

The goals have been achieved!

The Arlington County plant is one of the first major effluent denitrification facilities achieving effluent TN < 3.0 mg/l and TP < 0.18 mg/l. Since June 2010, the plant has consistently achieved < 2.5 mg/l TN and <0.1 mg/l TP. This has been accomplished by not only replacing effluent filters but also modifying all upstream processes. For example, to protect the treatment process against wide fluctuations in flow during wet weather, the plant’s design included increased equalization basin tankage and other primary treatment modifications.

If they can achieve this considerable achievement, one that will result in a significant reduction in nutrient loading to surface water resources, there is no reason why wastewater engineers elsewhere cannot do the same!  It is high time that this division of engineering stepped up to the plate and addressed the need to minimize a major cause of eutrophication.

Leave a Reply

Your email address will not be published. Required fields are marked *