The Dorchester County Water & Sewer Department has two wastewater treatment plants (WWTP). The Lower WWTP is located in North Charleston and the Upper WWTP is located in Saint George.

Upper WWTP

The treatment process at the Upper WWTP is an activated sludge process as well. The essential treatment units involved in the conventional activated sludge process includes the mixing in the aeration basin of pre-treated influent wastewater with return activated sludge that has settled out in the final clarifiers. Settled effluent passes through chlorine contact chambers where sulfur dioxide is added to strip out the chlorine residual before it enters the Polk Swamp. The wasted sludge is directed to the aerobic digester and is dewatered by a vacuum bed process before removal to the landfill. The permitted flow for this plant is 0.8 MGD

Lower WWTP

The treatment process at the Lower WWTP is an activated sludge process. The essential treatment units involved in the conventional activated sludge process includes the mixing in the aeration basin of pre-treated influent wastewater with return activated sludge that has settled out in the final clarifiers. Settled effluent passes to a separate chamber for filtering in tertiary filters, and then passes through ultraviolet disinfection prior to discharge. The wasted sludge is directed to the sludge holding basin first, and then pumped to two aerobic sludge digesters, and is dewatered at the sludge dewatering centrifuge before removal to the landfill. The permitted flow for this plant is 8 MGD.