H. L. Mooney Advanced Water Reclamation Facility

History
Construction of the H. L. Mooney Advanced Water Reclamation Facility (AWRF) was completed in 1979 under the United States Environmental Protection Agency’s (EPA) Clean Water Act Grant Program, with a sewage treatment capacity of 12 million gallons per day (MGD). The Facility was named for Mr. H. L. Mooney, the former Administrator of the Occoquan-Woodbridge-Dumfries-Triangle Sanitary District (OWDTSD). The first major upgrade to the Facility was completed in 1997, which also increased treatment capacity to 18 MGD.

Influent Treatment Overview
The H. L. Mooney AWRF treats influent wastewater from nearly 48,000 residences and businesses located in the eastern half of Prince William County 24-hours a day, 365 days a year. The Facility utilizes a biological nutrient removal (BNR) activated sludge process in conjunction with advanced (tertiary) treatment, including chemical addition and denitrification filters. Prior to discharging effluent into the Neabsco Creek, the water is irradiated with ultraviolet light for disinfection and is then oxygenated. The waste byproducts of the process – settled and undigested biosolids – are dewatered using high-speed centrifuges and then incinerated within a fluidized bed incinerator. The inert ash from this process is disposed of at the Prince William County Landfill. The Facility produces a high quality effluent consistently averaging biochemical oxygen demand, suspended solids and nutrient (nitrogen and phosphorus) discharges of under 3 parts per million. This represents a 99 percent reduction of pollutants in wastewater received by the Facility. Annually, the Mooney AWRF removes approximately 140 tons per year of phosphorous and 730 tons per year of nitrogen from the water before it is discharged into Neabsco Creek, a Potomac River tributary.

Activated Sludge
Conventional activated sludge is a highly stable and reliable microbiological process. In the activated sludge process, concentrated micro-organisms suspended within the oxygenated wastewater break down the proteins, carbohydrates, oils and fats contained in the sewage. Ferric chloride and polymers are added to the system to remove phosphorus and enhance the settling process. Excess biosolids are removed from the process and dewatered in high-speed centrifuges and then incinerated, resulting in a fine powdered ash.

Nitrification/Denitrification (BNR)
Presently, the H. L. Mooney AWRF staff operates the activated sludge process in BNR mode, a fairly recent advancement to the activated sludge process wherein the ammonia that is naturally inherent in wastewater is biologically broken down into nitrates and nitrites. During denitrification, the nitrates and nitrites are stripped of their oxygen content by bacteria operating in a very low-oxygen (anoxic) environment. Nitrogen gas is released into the atmosphere. This reduction of ammonia and nitrogen helps to minimize algae growth by eliminating a key nutrient: nitrogen. Lime is added for pH control.

The Case for Nutrient Removal
The H. L. Mooney AWRF reduces the level of total nitrogen in the effluent to 3 mg per liter or lower and the additional removal of phosphorous further reduces the likelihood of excessive algal growth in Neabsco Creek, the Potomac River, and ultimately the Chesapeake Bay. Nitrogen and phosphorous are nutrients that encourage the growth of aquatic algae. Although some algae are desirable, a problem is encountered when algae grow out of proportion to the normal balance of the aquatic ecosystem. Algae are a natural and critical part of the Potomac River and Chesapeake Bay ecosystems. Algae, like land plants, capture the sun’s energy and support the food web that benefits fish and shellfish. They occur in sizes ranging from tiny microscopic cells floating in the water column (phytoplankton) to large mats of visible macro algae that grow on bottom sediments. Algae may become harmful if they occur in unnaturally-high abundance or if they produce a toxin. A high abundance of algae can block sunlight to underwater grasses. They may also consume too much oxygen in the water, leading to fish kills, surface scum and odors that interfere with the feeding of shellfish and other organisms which filter water to obtain their food. Some algal species can also produce chemicals that are toxic to humans and aquatic life. Fortunately, of the more than 700 species of algae in the Chesapeake Bay, less than two percent of them are believed to have the ability to produce toxic substances.

Serving an Expanding Population
The Service Authority completed a $131.7 million upgrade of the H. L. Mooney AWRF in 2010 to help further safeguard the Chesapeake Bay through more intensive nitrogen and phosphorus removal. The project also expanded the Facility’s treatment capacity to 24 MGD to accommodate continuing growth in the County.

Continuing Improvements
Construction of the Durward E. Grubbs, Jr. Environmental Center began in early 2013 on the campus of the H. L. Mooney AWRF. The new $12.4 million facility will primarily accommodate a new state-of-the-art water quality laboratory designed to meet stringent modern water and wastewater testing standards. The structure will also provide necessary space for administrative and laboratory staff, as well as lab equipment. Though the H. L. Mooney AWRF has undergone two major process upgrades, the laboratory and administration offices have not expanded with the rest of the Facility over the past three decades. When completed in late summer 2014, the building will provide adequate workspace for those two essential departments. Additionally, it will allow for a small portion of the new structure to be used as a welcome station for visitors to the Facility that also provides an opportunity to learn about the value of water and the services PWCSA provides to a quarter of a million people throughout Prince William County.

Visit the Facility
Tours of the Facility are made available to professionals, other adults and youth groups. The H. L. Mooney AWRF is located at 1851 Rippon Boulevard, Woodbridge, Virginia 22191. To arrange an age-appropriate tour, please call (703) 335-7900.