Under an administrative order to eliminate untreated combined sewer overflows (CSO) into Puget Sound and to treat CSOs to meet current water quality standards, Bremerton called on CDM to design the nation's first CSO treatment facility using high-rate clarification (HRC). The facility is used during wet weather events to treat flows up to 20 mgd. The design is saving the city at least $5 million over the next least-cost alternative--construction of relief sewers to carry overflows to the existing wastewater treatment plant 7 miles away. The HRC process requires a start-up period of only 15 minutes to achieve very high suspended solids removal at 50 times the normal clarifier loading rate. The clarifier separates solids from water by ballasted flocculation-a physical-chemical process involving the fixing of sludge flocs to sand with the aid of a coagulant-and removes more than 90 percent of solids. Effluent is treated with ultraviolet disinfection, while sludge is treated at the existing wastewater treatment plant.
This project won the 2002 Grand Award in Small Projects from the American Academy of Environmental Engineers.
CLIENT: Public Works and Utililties
LOCATION: Bremerton, Washington