Mar 03, 2017

More With Less

Alexandria, Va., facility provides intelligent water treatment in a compact space

The NMF lies beneath Limerick Street Field, a multi-purpose athletic field that was donated to the City of Alexandria by AlexRenew. 
  • Name: Nutrient Management Facility
  • Location: Alexandria, Va.
  • Size: 18 million gal
  • Infrastructure: Tanks, pumps, valves, ammonia monitor, carbon odor control towers

In densely populated urban areas, it can be difficult to find sufficient space to create new public works facilities or expand existing ones. These projects require engineers and operators to develop innovative solutions in order to maximize operational efficiency. The Nutrient Management Facility (NMF) in Alexandria, Va., is one such creation. It has helped the utility overcome its space constraints with an inventive design that has made it an integral part of its community.

A Field Apart

The NMF is part of the 54-million-gal-per-day Alexandria Renew Enterprises (AlexRenew) water resource recovery facility, which occupies 33 acres in the Carlyle/Eisenhower neighborhood of Alexandria. Located just south of Washington, D.C., Alexandria is one of Virginia’s largest cities, and until the AlexRenew facility opened in 1956, when the utility was known as the Alexandria Sanitation Authority, its untreated wastewater drained directly into the Potomac River. This contributed to high pollutant levels in the Potomac River and Chesapeake Bay, into which the Potomac drains.

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In the years since it opened, the AlexRenew facility has frequently been improved to conform to new rules and regulations designed to protect the Potomac watershed and Chesapeake Bay. In 2009, the utility introduced the State-of-the-Art Nitrogen Upgrade Program, which included the design and construction of the NMF, among other projects.

AlexRenew purchased a parcel of land to the west of the existing plant for construction of the NMF, but the first proposed design was met with resistance from stakeholders.

“The initial design concept for the western site consisted of five 65-ft-tall cylindrical tanks,” said AlexRenew CEO Karen Pallansch. “AlexRenew shared this initial design with the city of Alexandria planning staff and adjacent landowners. While both understood the need for such facilities, the city was concerned that the proposed tanks would be incompatible with immediately adjacent residential uses, and the owners of the undeveloped blocks were concerned that they would be unable to finance, market and build their planned projects.”

Ultimately, the city, the utility and the adjacent landowner settled on a unique design concept that features a multipurpose community athletic field built atop the facility instead of the tall tanks that were originally proposed.

“With input from the community and the city, our design consultant’s initial idea of managing nutrient load in tall cylindrical tanks was replaced with the concept of an integrated wastewater function within a community-facing form,” Pallansch said. “This concept was based on community input during the design process that repeatedly lamented the lack of athletic fields in the Eisenhower East area of Alexandria.”

The athletic field—Limerick Street Field—was presented to the city of Alexandria in October 2015. The NMF began operation in May 2016.

The NMF can store up to 18 million gal of wastewater and feeds into the larger AlexRenew facility.

Nullifying Nitrogen

The NMF is designed to help regulate the amount of nitrogen that enters the AlexRenew facility’s biological treatment process by accepting some of the primary effluent flow from the utility’s primary effluent pump station during periods of high flow. The effluent is stored in the NMF’s four tanks, which offer a total storage capacity of 18 million gal. The effluent is stored in the NMF until periods of low flow, when the stored water is fed into the facility’s biological reactor basins (BRBs) for treatment. This makes the treatment process more energy efficient by normalizing the amount of aeration administered in the BRBs, which in turn helps reduce the amount of nitrogen that enters the Potomac watershed when the AlexRenew facility discharges treated water into Hunting Creek and the Potomac River.

“The NMF is the only one of its kind in the United States,” said AlexRenew Chief Production Officer Charlie Logue. “The facility has allowed for a significant reduction in need for a second aeration blower to be placed in service due to steadier loading to the BRBs. As the operations staff becomes more comfortable with the full array of flexibility of the facility, greater reductions in aeration needs will be realized.”

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Awarding Efficiency

In November 2016, the Institute for Sustainable Infrastructure awarded the NMF with its Envision rating system’s Platinum Award in recognition of the new facility’s positive environmental impact and social contributions to city resident. It is the first Envision award given to a facility in the Washington metropolitan area since the rating system was created in 2012.

“This new concept transformed how wastewater treatment could be built in a densely urban environment,” Pallansch said. 

About the author

Michael Meyer is associate editor for W&WD. Meyer can be reached at [email protected] or 847.954.7940.

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