City of Richmond, Virginia Meets Challenge of Disposing Combined Water and Wastewater Treatment Plant Sludges

The City of Richmond, Virginia owns and operates a water purification plant (WPP) and a wastewater treatment plant (WWTP). The WPP takes its water from the James River and is located generally upstream of the City. The WWTP serves the City's combined and separate sanitary sewer system and discharges into the James River generally downstream of the City. The Richmond WPP treats water withdrawn from the river by the addition of aluminum sulfate (alum). For a time, the resulting alum sludge was discharged solely to on-site lagoons, located adjacent to the river. In the mid-1980's the City recognized that the lagoons were beginning to become full and that alternate means of sludge disposal would be needed. A study was conducted at that time to determine if the alum sludge could be disposed of with the wastewater sludge. The study involved both theoretical analysis and a full-scale demonstration project to determine the feasibility of the concept of combined sludge disposal. A wastewater pumping station located near the WPP is used to convey the alum sludge to the WWTP through the wastewater collection and transmission system. This paper describes the results of the 1986 study, which resulted in the implementation of the combined sludge disposal program. The paper also describes a current uptake to the 1986 study and summarizes the full-scale results of about 15 years of operation in this manner.