Wastewater Treatment Plant

Wastewater treatment is the process of removing contaminants and other harmful items from wastewater, or sewage generated by domestic, commercial, and industrial users. Thereby, allowing it to be returned to the environment with minimal impact to wildlife, the public and the overall environment.

Water used in our daily lives by homes, industries and businesses is called wastewater, or sewage.  Used water includes substances such as human waste, food scraps, oils, soaps, and chemicals. It gets collected in the sanitary sewers and travels through a piping network called a sanitary sewer system eventually making its way to the Wastewater Treatment Plant (WWTP). Once received at the treatment plant it is known as an influent.  The influent then goes through numerous processes at the plant to remove the contaminants. The goal of wastewater treatment is to remove organic materials, suspended solids, nutrients (nitrogen and phosphorus) and pathogenic organisms which can harm human health and the environment.  Water that leaves the wastewater plant is known as effluent.



The Town of Warrenton's Advanced Wastewater Treatment Plant was originally built in 1958. It had a treatment capacity of .5 Million Gallons/Day (MGD) and consisted of two primary clarifiers, a trickling filter, a secondary clarifier, a chlorine contact tank, four sludge drying beds, and an anaerobic digester. The permitted treatment requirements were 36 milligrams/liter Biochemical Oxygen Demand (BOD5) and 36 milligrams per liter Total Suspended Solids (TSS).


The Wastewater Treatment Plant was upgraded in 1978. The treatment capacity was increased to 1.0 MGD. The following units were added:

  • Another primary clarifier
  • Another secondary clarifier
  • Another chlorine contact tank
  • Eight more sludge drying beds
  • Purifax® unit (for sludge oxidation)
  • Four Rotating Biological Contactors (RBCs)
  • Chemical addition equipment (Aluminum Sulfate and polymer)

The permitted treatment requirements were lowered to 18 milligrams per liter BOD5 and 18 milligrams per liter TSS.


The next upgrade to the WWTP was in 1990. This major upgrade consisted of the following:

  • Another anaerobic digester
  • Another primary clarifier
  • Four RBCs were integrated into the new 21 RBC units
  • New chlorine contact tanks (which replaced both the 1958 and 1978 units)
  • New de-chlorination building
  • New flocculators
  • New headworks
  • New post aerators
  • New secondary clarifier (which replaced the 1958 unit)
  • New secondary sludge pumping station
  • Primary sludge pumping station
  • Sludge dewatering press
  • Sludge thickener
  • Trickling filter was lowered and fitted with a new distributor and media
  • Wet well pumping capacity was increased

The permitted treatment requirements were lowered to 10 milligrams per liter BOD5 and 10 milligrams per liter TSS. A new limit for Total Kjeldahl Nitrogen (TKN) was set a 5 milligrams per liter and chlorine had to be neutralized before returning the treated water back into the stream.


In 1998 a discharge limit for Ammonia was set at 1.38 milligrams per liter and added to the discharge permit. This required a minor upgrade consisting of a 30,000-gallon storage tank for the belt press filtrate to be captured and metered into the plant for treatment.


In 2008, four above-ground sand filters were installed to enable the Wastewater Plant to comply with the regulations of the newly issued General Permit for total nitrogen and total phosphorus discharges and nutrient trading in the Chesapeake Bay Watershed in Virginia. This is referred to as the WWTP Denitrification Filter. At the same time, the chlorine gas disinfectant treatment process was replaced with a series of ultraviolet lights which is a safer and more ecologically sensitive system for operators to handle the disinfection process.


Our latest update in 2020 introduced a Moving Bed Biological Reactor (MBBR) treatment process to the Advanced Treatment Plant operations. This is a fixed-film biological treatment process to address the biological oxygen demand (BOD) while converting the influent ammonia thru a process to nitrogen that can be given off as a gas as part of the denitrification process. This plant addition allows the Town to retire the earlier Trickling Filter and RBC processes, using the existing tanks for those items as part of a flow equalization process during higher flow events caused by rainfall.

Tour of the Wastewater Treatment PlantTours

For information concerning school and private tours of our wastewater facilities, contact the Town of Warrenton Wastewater Superintendent, Mr. Allen Chichester, at (540) 347-1104.