How Wastewater is Treated

Wastewater treatment begins with the removal of debris through bar screens and a grit chamber, where the debris settles to the bottom of the chamber and is removed. From there, the wastewater is passed to primary clarifiers where other solid material settles to the bottom as sludge and is removed along with scum which forms on the primary clarifiers’ surface. Once these materials are removed, the wastewater enters the activated sludge basin, or a set of chambers where microbes remove contaminants. This process is facilitated by the pumping of air into the chambers. Once the contaminants have been removed, the wastewater moves to the final clarifier, where the water is separated from the remaining heavier-than-water material.

Once all solid matter has been removed, the water moves to a chlorine chamber, where chlorine is used to kill bacteria. The water then filters through a contact basin that holds the water for about 90 minutes while the chlorine disinfects the water. Once treatment is completed, which typically requires 24 hours, the water is returned to the Yadkin River at Muddy Creek’s confluence with the river.

Take a virtual tour of Archie Elledge Wastewater Treatment Plant!
WWTP Process
Wastewater Treatment Process (PDF)
Planta de Tratamiento de Agua Potable (PDF)

What Happens to Sludge?

Sludge is a byproduct removed during the treatment process. Once removed, sludge goes through a two-step digester process that ferments the organic part of the sludge into products like methane gas, carbon dioxide and water. Sludge is treated with a polymer that flocs the solids and releases the water. The water is removed using belt filter presses or centrifuges. The resulting "cake" is pumped to our Biosolids Drying Facility which is fueled by methane produced on-site and pelletizes the biosolids. These pellets are sold for use as a soil amendment, providing additional revenue for the department.