Brief Project Description
The existing Town of Colonial Beach WWTF has a permitted capacity of 2.0 MGD with two parallel treatment trains each rated to treat an average daily wastewater flow of 1.0 MGD. The activated sludge process was not designed for nutrient removal. The liquid process consists of a mechanical bar screen, two grit chambers, a raw wastewater pump station, two aerated Flow Equalization Basins (FEBs) with a nominal capacity of 1.0 MG each, a FEB effluent pump station, two 1.55 MG complete mix extended aeration activated sludge treatment basins, two 78-foot diameter clarifiers, chlorination followed by dechlorination and post aeration. A final effluent pump station transfers the treated water to an outfall diffuser pipe in Monroe Bay. The solids handling system consists of two 300,000 gallon aerobic digester tanks and one 1.2 meter belt filter press. The treated solids are currently land filled.
Under the proposal submitted for nutrient removal cost share, the existing process will be upgraded to provide State of the Art (SOA) nutrient removal. The upgrade will include a retrofit of the existing aerated FEBs such that they will continue to provide hydraulic flow equalization but will also serve as first stage anoxic reactors. The two existing aeration basins will be operated as second stage aerobic reactors to provide nitrification (convert ammonia nitrogen to nitrate). Nitrified liquor recycle pumps and piping will be installed between the modified FEBs and the aerobic reactors. New continuous backwash up-flow denitrifying sand filters will be installed to provide tertiary filtration of suspended solids and biological denitrification with supplemental carbon addition. New chemical feed equipment will be installed to provide bulk storage tanks and chemical solution pumps for alum, lime, and supplemental carbon used for nutrient removal. A new ultraviolet (UV) contact channel and UV light equipment will be installed for final effluent disinfection upstream of the new filters to replace the existing chlorination/dechlorination system; and to eliminate the need to pump to the new filters. The existing chlorine contact basin will be modified to function as a final effluent post aeration basin.
In summary, the upgrade project will consist of the following:
- Retrofit the existing FEBs to function for both hydraulic equalization basins and first stage anoxic reactors
- Retrofit the existing activated sludge basins to operate as aerobic reactors for nitrification
- Install nitrified recycle piping and pumps
- Install continuous backwash up-flow denitrifying sand filters
- Install new coagulant and supplemental carbon chemical feed and storage equipment
- Install UV disinfection (not grant eligible)
- Modify chlorine contact basin to serve as effluent post aeration