Amid $1.7 billion in capital improvements, the D.C. Water & Sewer Authority’s Blue Plains Advanced Wastewater Treatment Facility is one of the largest facilities of its type in the world. The facility collects wastewater from the District of Columbia as well as the surrounding suburbs in both Maryland and Virginia—serving approximately 2 million people.
The Blue Plains facility has a rated annual average daily capacity of 370 mgd—enough to fill Lake Erie—in addition to a peak wet weather capacity of 1.076 bgd.
To collect wastewater, the D.C. Water & Sewer Authority operates approximately 1,800 miles of sanitary and combined sewers, 22 flow-metering stations, nine off-site wastewater pumping stations and 16 storm water pumping stations within the District of Columbia. Separate sanitary and storm water sewers serve two-thirds of the city, while combined sewers are incorporated in the remaining areas.
Wastewater treatment includes liquid process facilities that provide treatment for both sanitary wastewater flows and peak storm flows, along with solids processing facilities that treat the residual solids removed by the liquid process facilities.
The wastewater treatment processes at the facility consist of preliminary treatment, secondary treatment, nitrification/denitrification, effluent filtration, chlorination/dechlorination and postaeration.
Solids treatment consists of thickening and dewatering processes for primary sludge, secondary waste activated sludge and nitrification/denitrification waste activated sludge. The facility also involves screen and degritting, gravity thickeners, dissolved air flotation thickeners, sludge blending, centrifuge dewatering and lime stabilization in their sludge treatment processes.
Recently, the Blue Plains facility incorporated plans to install an egg-shaped anaerobic digester system. According to Blue Plains facility management, in the digester system, solids are degraded by microorganisms in a heated, mixed, oxygen-free environment wherein half of the solids are converted to methane gas, which can produce enough power for 10,000 homes, this system reduces the volume of material by 50%, saving at least $16 million in operation and maintenance costs, and reducing application odor problems.
The egg-shaped digester system includes eight 4.5 million gallon digesters; two 2.5 million gallon silos; two additional temperature-phased anaerobic digestion silos; an operations building; and ancillary facilities and equipment.
The first four digesters will be in service by 2010 with all eight digesters operating by the middle of 2011.
Other ongoing projects at the Blue Plains facility include their Liquid Processing Program, which encompasses upgrading and rehabilitating facilities involved in handling flows from the sanitary and combined sewer systems.
The flow progresses sequentially through the Blue Plains plant processes to ultimate discharge of the treated effluent into the Potomac River. Liquid treatment systems include headworks facilities that screen and pump the wastewater flows; grit facilities that remove sand and grit particles; primary treatment facilities that remove solids by sedimentation; secondary treatment facilities that remove organic pollutants using a biological process; nitrification/dentrification facilities that remove nitrogen using a biological process; and effluent filtration, disinfection and dechlorination facilities.
Additionally, the Plant Facilities Program provides for upgrading, rehabilitating or installing support systems and facilities that are required for both the liquid processing and solids processing program. Systems include a process control and computer system for monitoring and control of all processes and facilities; upgrades to city and plant water systems; chemical systems, electrical power and distribution system upgrades; and telephone service and data highway infrastructure for process, safety, security and information needs.
Facilities comprise chemical receiving, storage, transmission and feed systems for chemicals used throughout the liquid and solids processes, including metal salts, polymers, sodium hypochlorite, and sodium bisulfate. Support facility projects include the rehabilitation of the central operations facility and the central maintenance facility.
To find out even more information about the D.C. Water & Sewer Authority, Blue Plains Advanced Wastewater Treatment Facility, visit www.dcwasa.com.