Brief Project Description
The Basham Simms Wastewater Facility (BSWF) is an existing 1.0 MGD facility that serves the Town of Purcellville, Virginia. The existing treatment process consists of influent pumping, coarse screening, grit removal, primary clarification, flow equalization, activated sludge (configured as a Modified Ludzak-Ettinger process for the removal of nitrogen), effluent filtration, and Ultraviolet (UV) disinfection. The facility discharges into a tributary of the North Fork of Goose Creek, which eventually flows into the Potomac River. Primary and secondary solids are aerobically digested, and the digested solids are stored in a lined lagoon for removal in liquid form.
In response to new regulatory requirements for the removal of nutrients, the facility must be upgraded to achieve enhanced nutrient removal (ENR). As part of this upgrade, the treatment capacity of the facility will also be expanded to 1.5 mgd. Based on the expanded capacity of the BSWF, the future discharge permit will limit the annual average effluent discharges of total nitrogen (TN) and total phosphorus (TP) to 18,274 pounds per year for TN and 1,371 pounds per year of TP, which is equivalent to annual average effluent concentrations of 4 mg/L for TN and 0.3 mg/L for TP at the design flow.
To achieve the future effluent requirements, the biological treatment process will be converted to a membrane bioreactor (MBR), which will be configured in a 4-stage Bardenpho arrangement (anoxic, aerobic, anoxic, aerobic zones). Methanol will be added to the second anoxic zone as a supplemental carbon source for the denitrification process. Ferric chloride will also be added to assist with phosphorus removal. Modifications to the biological treatment system will included the reconfiguration of the existing aeration basins, increased aeration capacity, new anoxic basins, a methanol storage and feed system, new membrane basins, and a membrane building to house the membrane equipment.
Other modifications to the liquids treatment processes of the existing facility will include an expansion and upgrade of the influent pump station, hydraulic improvements to the coarse screening structure and primary clarifiers, the addition of primary sludge pumping, flow equalization improvements to allow for equalization of both daily diurnal and wet weather flows, and the conversion of the exiting secondary clarifiers to serve as either recycle equalization or digested sludge storage tanks. Fine screens will be added to the process to eliminate the flow of fibrous materials to the biological and membrane treatment systems. The fine screens will be located between the primary clarification and biological treatment processes. All flow to the equalization basins will pass through the preliminary treatment and fine screening processes.
Aerobic digester capacity will be increased to accommodate the plant expansion, and biosolids dewatering capability will also be provided. A new solids building will be provided to accommodate digester blower, mechanical thickening, and dewatering equipment. One section of the building will be devoted to covered storage of dewatered biosolids. Approximately 100 days of storage will be provided for the dewatered biosolids.
The control building will be expanded to better accommodate current staff and the projected increase in the total number of staff who will be needed at the facility. A control room will be added as part of the control building expansion; the facility currently does not have a dedicated control room to house plant monitoring and control equipment. A new plant maintenance building will also be provided. Plant maintenance activities are currently located within the existing control building.
The total cost is estimated to be $35,995,876 with about $5,995,768 attributable to nutrient reduction technology.