The Roanoke Regional Water Pollution Control Plant provides tertiary treatment for an average of 37-million gallons of sanitary sewer a day from all jurisdictions in the Roanoke Valley. A drop of water entering the Regional Water Pollution Control Plant takes approximately 24 hours to move through all levels of the liquid treatment process.

Along the way, more than 3,000 lab tests are conducted every month to verify that the liquid treatment process is meeting or exceeding water quality standards. The Regional Water Pollution Control Plant has some of the most stringent requirements for treatment of any plant in Virginia.

Facility Improvements

Download our Treatment Process Brochure

Download our Wastewater Epidemiology Brochure

Our Treatment Process

Headworks

Before the wastewater begins the series of treatment processes, the flow travels up the new Archimedes screw pumps to begin preliminary treatment. Bar screens remove large objects that are disposed of in the landfill. This new equipment will convey and treat significantly higher wet weather flows.

Primaries

Metal bars, known as flights, skim across the surface of the water in the settling tanks to remove the floating scum before turning downward to scrape away the material that has settled at the bottom of the tank.

Aeration

After leaving the primary clarifiers, wastewater travels to one of 16 aeration tanks where air is blown into the flow to raise the dissolved oxygen levels, sustaining the microorganisms that consume the organic material (carbonaceous Biochemical Oxygen Demand - BOD) in the wastewater. This process takes 4-6 hours; all the while microorganisms are feeding on and removing the organic matter carried in the flow.

The WPC Plant has a modern design which utilizes a common aeration basin to complete carbonaceous BOD removal and nitrification in one unit. Modification to this “single stage process” allowed a substantial capacity increase through better use of existing infrastructure.

Coagulation

By this step of the treatment process, only very small particles remain. Chemicals, such as iron salts (ferric chloride) and polymers, are added to make the tiny particles bind together in masses called floc. The floc is large enough to settle to the bottom of the coagulation tanks or be caught in the filtration process.

Filtration

The flow is passed through one of ten deep bed monomedia filters as the final purification process before the flow goes to the chlorine chamber for disinfection.

Disinfection

Pathogens are removed throughout the treatment process, but the final step of chlorination guarantees the quality and safety of the water discharged into the Roanoke River. The water must remain in contact with the chlorine for 20 minutes to ensure that all the pathogens are killed. The water is then treated with sulfur dioxide to remove all chlorine before the flow enters the river. 

Receiving River

After more than 24-hours of treatment, the water is fully treated and ready to go to the receiving river where it will be used many times again for drinking water, recreation and aquatic habitat.  The Roanoke Regional Water Pollution Control Plant consistently meets some of the strictest permitting standards in the state to ensure that only healthy, clean water is discharged into the river.

Solids Treatment

---

Digestion

Sludge from primary and secondary clarifiers is heated and mixed to promote the anaerobic consumption of organic material by bacteria contained within the tanks. First, acid forming bacteria use the organic material energy supply to produce organic acids and carbon dioxide. A second group of bacteria, the gas formers, breaks down the organic acids to make methane and carbon dioxide gas. The waste methane is then cleaned and converted into electricity and thermal heat to offset energy costs at the plant.

Biosolid Lagoons

After the digestion is finished, the sludge is pumped to the lagoons to complete treatment. Both anaerobic and aerobic bacteria consume any remaining organic matter and solids settle to the bottom of the ponds.

Land Application

After about nine months, the fully processed material is applied to non-food crop farms as fertilizer at no cost to the farmers. The application process and quality of the biosolids is held to strict standards set forth and enforced by the EPA.

Learn more about our Biosolid Land Application process.

Learn more about the Biogas to Renewable Natural Gas Project