How We Clean Wastewater


How We Clean Wastewater

Ever wonder what happens to the dirty water that goes down the drain in your house? The City of Alexandria’s underground pipes and AlexRenew’s interceptor sewer system, pump stations, and treatment facility play an integral role in making that dirty water clean before it is released back into our waterways

Our Process Begins with the Interceptor Sewer System

An elaborate system of underground pipes brings sanitary flow to AlexRenew. While the City of Alexandria owns and maintains the small pipes that collect water from businesses and neighborhoods within its boundaries, AlexRenew owns and maintains the large interceptor sewers that transport flows to our treatment facility.

Our interceptors are designed to allow wastewater to flow by gravity to our treatment facility, or route it to a pump station to be lifted high enough to flow to our facility. AlexRenew maintains four, off-site pump stations with a total pumping capacity of about 25 million gallons per day.

The interceptor system also includes nearly 20 miles of the bigger, round sewers that range in size from 2.5 feet all the way up to 6 feet in diameter. Our system covers the majority of the City of Alexandria and a portion of Fairfax County. The area of Fairfax County served by AlexRenew includes Dowden Terrace, Cameron Run, and Jones Point.

AlexRenew Service Area Map

Treatment Process

Our Water Resource Recovery Facility is designed to treat an average daily flow of 54 million gallons per day and is among the most advanced in the world. 

How We Clean Wastewater Infographic

Once flows reach our facility from our interceptor system, they go through coarse screens, fine screens, and grit removal to remove large solids (like food and trash) that can damage our equipment. Flows are then transported into rectangular settling tanks for primary treatment and removal of suspended solids and fats, oils and grease. Afterwards, the flow goes to our Biological Reactor Basins (BRBs) for nutrient removal. While in the BRBs, flows are added to microorganisms, called activated sludge, for nitrogen removal. The water settles again and then we remove the phosphorous and filter out any remaining solids. Finally, flows are disinfected using ultraviolet (UV) light.

Over the past ten years, AlexRenew has made significant enhancements to its treatment process through our State-of-the-Art Nitrogen Upgrade Program (SANUP). These upgrades were important, because they helped AlexRenew meet the requirements to remove nitrogen from the Chesapeake Bay and improve the overall water quality in the Chesapeake Bay.

To meet these new and very stringent removal standards, AlexRenew developed SANUP, an innovative program to achieve additional nitrogen removal through a combination of strategies. These strategies include the design and construction of a Centrate Pre-treatment Facility that utilizes ANAMMOX bacteria to reduce ammonia nitrogen and a Nutrient Management Facility that will help optimize our treatment process.

AlexRenew - In Urban Area