What We Do
The first treatment phase begins as debris and grit and are removed and trucked to a landfill. The sewage then flows into primary sedimentation tanks that separate more than half of the suspended solids from liquid.
The liquid flows to secondary treatment tanks where oxygen is bubbled into it so microbes can break down organic matter. In the next stage of treatment, microbes convert ammonia into harmless nitrogen gas. Residual solids are settled out and the water is percolated down through sand filters that remove the remaining suspended solids and associated phosphorus. The water is disinfected, dechlorinated, and discharged into the Potomac River.
The solids —or sludge— from the primary sedimentation tanks go to tanks where gravity causes the dense sludge to settle to the bottom and thicken. Biological solids from the secondary and nitrification reactors are thickened separately using flotation thickeners. The thickened sludge is dewatered, lime is added to remove pathogens, and the organic biosolids are applied to agricultural land in Maryland and Virginia as nutrient-rich fertilizer.