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Wastewater Treatment Process

Aerial photo of the H.L. Mooney Advanced Water Reclamation Facility
H.L. Mooney Advanced Water Reclamation Facility

There is a five-step process that influent wastewater to the AWRF undergoes.

  • First, fine screens remove rocks, food, hair, plastics and grit. At the same time, the plant adds a safe chemical to remove phosphorus.
  • In the second step, microscopic bugs remove nitrogen and other dissolved substances.
  • In the third step, the water travels through a deep, six-foot layer of sand to filter out any particles that still remain. Sometimes a safe chemical is added to the filters to remove additional nitrogen from the water.
  • In the next step, the plant uses ultraviolet light to disinfect it. This process kills harmful bacteria and disease-causing organisms.
  • Finally, the treated water travels over a series of cascades to aerate it before it is released into the Neabsco Creek, a tributary of the Potomac River.

The Upper Occoquan Service Authority (UOSA) Regional Water Reclamation Plant undergoes a five-step treatment process of wastewater.

  • In the first step, fine screens remove rocks, food, hair, plastics and grit, while heavy solids fall to the bottom of the tank.
  • Secondly, UOSA uses microscopic bugs that eat tiny waste particles before separating the bugs from the water.
  • In the third step, UOSA uses lime to remove phosphorus and viruses. In this step, the pH of the water is raised to 11 and, after the removal of the phosphorus, is brought to neutral using carbon dioxide gas.
  • The fourth step involves filtration using sand and other media followed by activated carbon to eliminate carbon-containing substances.
  • The final step involves disinfection using bleach. Once the bleach is removed, the treated water goes to an on-site reservoir owned by UOSA in order to acclimate and blend the discharge with the water found in the reservoir. Eventually, the water is released into Bull Run. Bull Run flows into the Occoquan Reservoir, which is the primary drinking source for eastern Prince William County and southern Fairfax County residents.
Corbalis and Griffith Plants

Corbalis and Griffith Plants use a six-step treatment process that ensures that its treated water is clean and safe to drink. In addition, the Service Authority continually monitors the water that is delivered to customers to ensure that it remains clean, safe and of the highest possible quality.

  • The first step is coagulation, which involves adding chemicals to the water. That causes small particles to adhere to one another, or coagulate.
  • The second step is called flocculation, in which larger particles called flocc form after coagulation.
  • Sedimentation occurs next when the heavy flocc settles to the bottom and is cleared away.
  • In the fourth step called ozonation, plant workers add a gas called ozone to destroy bacteria and other microorganisms as well as to improve taste.
  • From there, the water is filtered using granular activated carbon to remove any fine particles.
  • Finally, the sixth step is secondary disinfection, which involves adding chlorine to ensure a safe product is delivered to your home.
City of Manassas Treatment Plant

At the City of Manassas treatment plant, raw water from Lake Manassas enters the water treatment plant where pre-filtration chemicals are added. These pre-filtration chemicals cause the particles contained in raw water to adhere to one another, making them heavy enough to settle out in the settling basins. After settling, water is filtered through layers of anthracite, gravel and silicate sand. As smaller suspended particles are filtered out, clear water emerges. After filtration, the water is disinfected with sodium hypochlorite, which is the primary disinfectant and is important to the treatment process because it helps to kill harmful bacteria, viruses and other microbial contaminants. Following disinfection, ortho-phosphate is added to prevent pipe corrosion.