Resource provided the design of completely new 60,000-gallon per day sewage treatment plant and the sewage collection system for the Community of Callao. The community previously relied on individual septic tanks, which were failing due to poor soil conditions. A grinder pump and force main system was designed for the collection and a Membrane Bioreactor (MBR) wastewater treatment plant for the treatment. Resource assisted the County in the permitting process. The plant was the first MBR plant designed and placed in operation in Virginia. Resource assisted the County in funding assistance and setting the user rates.
Strategy and Services
The Callao Community had been trying to solve their wastewater problems since the 1970’s. Resource reviewed three potential collection system alternatives: Gravity, vacuum, and grinder pumps/force main. Based on the topography and Town configuration, the grinder system was recommended as the community was too flat for efficient use of gravity lines, and too rolling for efficient use of a vacuum system.
During design review, the state enacted stricter limits on discharges to the Chesapeake Bay. The originally planned conventional Extended Air Package Plant was determined to be unable to readily meet the Virginia DEQ requirements. The design analysis for treatment then was expanded to include an alternatives analysis comparing the older technology with more modern systems such as the Membrane Bioreactor (MBR) system. The MBR system was chosen because it used a smaller layout, and required less operator attention and met the DEQ requirements for nutrient removal. The plant utilizes alternating aerobic and anoxic zones to accomplish nutrient reduction, followed by membrane filtration and UV disinfection.
The treatment facility site was on a small available plot located on a former school property. Since the unit was located relatively close to residences, it was necessary to locate the unit behind a portion of forested land. The entrance road was designed to provide a route to the plant that would not allow a direct view of the plant from the public roadway. Special attention was paid to odors by utilizing an inlet of raw sewage directly into a recycled flow of partially treated and aerated liquid. Therefore, any odorous materials entering the plant would be immediately diluted in a non-septic environment.
The treatment system was designed to be well under the assigned discharge limits. The membranes will have approximately 9,000 square feet of surface area and a nominal pore size of 0.4 micron. Most waste, bacteria, viruses, cysts, and sludge will not pass through the pores. The discharge will be nearly clear, with any remaining harmful organisms killed by an ultraviolet light treatment unit. Occasionally, a small quantity of sludge will be drawn off the system for further treatment at the County's other plant. No effluent chlorination is done, so that chemicals used in the system are minimal. Space was allowed in the building in case future regulations require additional treatment equipment. The system is designed to allow remote computer monitoring to allow minimal operator attention on-site, and to allow on-line operational review by the system manufacturer.
The project included the closure and demolition of an adjacent small treatment plant originally designed for the former school, and subsequently used for the building's conversion to apartments. The former plant consisted of a septic tank, trickling sand filter, polishing lagoon, and tablet chlorination system. The closure design provided for the demolition of all above-ground structures and the filling of the lagoon.
Resource provided the following services on this project:
- Preliminary Engineering Report that included alternatives analysis for collection system and treatment technology
- Funding Assistance
- Assistance in Setting Rates
- Collection system and Treatment System design
- Construction administration
- Operating Manual Preparation