Wastewater Management operates its treatment facility 24 hours a day, 365 days a year to meet the wastewater treatment needs of the community residents and businesses while improving the environment. 

Preliminary and Primary Treatment

Raw sewage enters the plant and passes through mechanically cleaned screens to remove large objects such as paper, plastics, sticks, and rags. The screened wastewater is pumped to large clarification tanks where solid matter either settles (sludge) or floats (scum). The solid matter is separated and removed for further processing and disposal.

Secondary Treatment

This is a two-step process which uses biological and physical methods to remove the wastewater pollutants, with an emphasis on nitrogen removal. First, the effluent flows to aeration tanks where air is bubbled through the wastewater to supply oxygen to microorganisms living in the tanks; these microorganisms, under proper operating conditions, use the organic matter and nutrients in the wastewater as food. As a result, they grow and reproduce rapidly.

Second, the wastewater flows to clarifiers where the microorganisms, which have formed clusters, settle as sludge. Most of the wastewater is returned to the aeration tanks to continue the biological process, while the sludge is sent to processing facilities for treatment prior to disposal.

Tertiary Treatment

Secondary-treated wastewater is pumped to tertiary clarifiers to remove phosphorus. This is a critical step in reducing nutrients and maintaining water quality in the Chesapeake Bay.

Disinfection and Filtration

As the last step, effluent from the tertiary clarifiers is disinfected (by chlorination with sodium hypochlorite) and filtered. The wastewater flows through filter beds which remove most of the remaining solids.

Solids Dewatering

Solids, in the form of sludge, are collected at the primary and secondary clarifiers. In the solids dewatering facility, a mixture of primary and secondary sludge is chemically conditioned then mechanically dewatered by centrifuge machines to reduce the water content in the sludge.

Incineration

Dewatered sludge and primary scum are incinerated in multiple hearth incinerators. The final product, inert ash, is reduced in volume to about 10 percent of the original sludge volume, and is hauled by truck to ash-fill at the I-95 sanitary landfill.

Air quality/Odor control

Incinerator stack emissions pass through a multi-stage air pollution control system to eliminate odors, volatile organic compounds, and fine particles. Incineration emissions must comply with standards set forth in the air operating permit issued by the Virginia Department of Environmental Quality.

The plant controls odor through a variety of methods. A two-stage odor reduction system uses chemicals to remove odor compounds in air withdrawn from buildings or covered tanks. Activated carbon filters also remove odorous compounds in a manner similar to water purifiers.

To prevent adverse effects on aquatic life in the receiving stream, filtered water is dechlorinated with the addition of sodium bisulfite. Finally, treated water is discharged through an outfall to Pohick Creek, a tributary to the Potomac.

To report an odor complaint, call the Odor Hotline at 703-550-9740, extention 278, TTY 711.