Brief Project Description
The Town of Warrenton owns and operates an advanced wastewater treatment plant, VPDES Permit #VA0021172, currently rated for 2.5 million gallons per day (MGD). The existing major unit processes include head works, primary clarifiers, a trickling filter, rotating biological contactors, coagulant and polymer addition and flocculation, secondary clarifiers, chlorination, dechlorination, and post aeration. The solids handling facilities include gravity thickening, anaerobic digestion, and belt filter press dewatering. The facility was upgraded in 1990 to achieve compliance with a Total Kjeldahl Nitrogen (TKN) effluent limit and upgraded again in 1998 to achieve compliance with an ammonia effluent limit.
As a result of the Water Quality Management Planning Regulation requirements for nutrient discharge control, technology-based concentration limits for total nitrogen and total phosphorus were developed. The Preliminary Engineering Report (PER) concluded that the addition of deep bed denitrification filters with supplemental methanol addition and chemical phosphorus removal via optimized poly-aluminum chloride addition (already in place and not funded through this grant) were the recommended process alternatives. The existing wastewater treatment plant upstream of the new denitrification filters was recommended to remain in service and will continue to provide an acceptable level of reliable nitrification (ammonia control). No design flow expansion will result from this upgrade project; the plant’s capacity will remain at a rating of 2.5 MGD.
The new facilities for the plant upgrade will include a filter influent pump station to lift the secondary effluent to the denitrification filters. The filter influent pumps will be located in a new Pump/Blower Building that will be constructed adjacent to the denitrification filter facility. The Pump/Blower Building will also house two positive displacement blowers that will be used for filter backwashing and will include a room for electrical equipment.
The proposed denitrification filter system will include four filter cells, a clear well to provide a reservoir for backwash water, a mud well for dirty backwash water, backwash and mud well pumps, and associated valves and control system. The deep bed denitrification filters will be located within the footprint of the existing chlorine contact tanks. The Town is proceeding with the design of a new UV disinfection facility to replace chlorination and this project is anticipated to be completed prior to the beginning of the nutrient removal upgrade construction. Demolition of the existing chlorine contact tanks will be included in the nutrient removal upgrade project as a cost eligible component; installation of the UV disinfection is proceeding separately and is not grant eligible. The denitrification filter facility will also include an enclosed pipe gallery and a control room for the main filter control panel and nitrate analyzer.
A methanol storage and feed system will be included to provide supplemental carbon addition to the filter influent to stimulate the biological growth of the denitrifying organisms on the filter media.