Wastewater Treatment
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Wastewater Treatment Service Area

WASA operates the Blue Plains Advanced Wastewater Treatment Plant, the world's largest advanced wastewater treatment facility. At Blue Plains, WASA provides wastewater treatment services to over two million people in our service area, including residents of the District of Columbia and significant portions of Montgomery and Prince George's Counties in Maryland and Fairfax and Loudoun Counties in Virginia. 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. Blue Plains is rated for an average flow of 370 million gallons per day (MGD), and is required by its National Pollutant Discharge Elimination System (NPDES) permit to treat a peak flow rate of 740 MGD through the complete treatment process for up to four hours, and continuous peak complete treatment flows of 511 MGD thereafter. The plant treats these flows to a level that meets one of the most stringent NPDES discharge permits in the United States. Additionally, up to 336 MGD storm water flow must receive partial treatment, resulting in a total plant capacity of 1,076 MGD.

Overview of the Wastewater Treatment Process

Wastewater Treatment Process

The first wastewater treatment phase begins as debris and grit are removed by screens and grit chambers and trucked to a landfill. The sewage then flows into primary sedimentation tanks that separate about half of the suspended solids from the liquid. The liquid flows to the secondary treatment process where oxygen is provided to allow bacteria to break down the organic matter. In the next stages of treatment, bacteria convert ammonia into other forms of nitrogen and then into harmless nitrogen gas. Residual solids are settled out in each biological process. The water is percolated down through dual- media effluent filters, removing most of the remaining suspended solids. The water is disinfected and then treated to remove residual chlorine and discharged into the Potomac. The solids from primary sedimentation tanks go to gravity thickening process units where the dense sludge settles to the bottom and thickens. Biological solids from the secondary and nitrification reactors are thickened separately using flotation thickeners. All thickened sludge is dewatered, lime is added to reduce pathogens, and the organic biosolids are applied to agricultural land in Maryland and Virginia.

Project lifetime budgets in the Wastewater Treatment Service Area total $1.2 billion, or 57 percent of the total capital improvement program. As described in more detail below, capital projects in the Wastewater Treatment Service Area are required to rehabilitate, upgrade or provide new facilities at Blue Plains to ensure that it can reliably meet its NPDES permit requirements and produce a consistent, high- quality dewatered solids product for land application. In addition to meeting permit requirements, WASA strives to reduce biosolids odors, and both onsite and in the final product leaving Blue Plains.

In general, interim improvements to the plant necessary to ensure plant process performance have been completed over the last five years. Twenty- seven interim construction projects with a combined value of $48 million were complete or nearing completion late in FY 2003. A major project that included rebuilding the two primary sedimentation tanks, upgrading the sludge blending tanks to improve dewatering performance, and providing a means of loading contractor- produced sludge cake into the storage facilities, was completed in FY 2002. Long-term upgrade projects now under construction include:

  • Area Substation 5 — a new electrical substation will replace an out- of- date facility, and will service gravity thickening and digestion facilities, and the Solids Processing, Chemical, and Central Maintenance buildings
  • Additional Chemical Systems. Phases I and 2 — new centralized chemical receiving and storage facilities will be constructed, as well as pipe chases and galleries to contain chemical piping
  • Alternate Disinfection — construction of facilities to replace use of chlorine and sulfur dioxide with sodium hypochlorite and sodium bisulfite in the disinfection process, providing safety for plant workers and neighborhoods surrounding the plant
  • Additional Dewatering Facilities — construction of seven new centrifuge dewatering units
  • Primary Treatment Facilities — rehabilitation of east and west primary sedimentation tanks, control house upgrades and new pumps
  • Process Control Computer System — system will provide automated monitoring and control for processes throughout the plant, and will improve treatment, control and optimize chemical and power costs, and increase reliability of the facilities
  • Secondary Treatment Facilities, Phases I and 2 — concrete basin structures will replace deteriorated structures, new sludge and scum collection equipment will be provided, and aeration blowers and motors will be rehabilitated
  • Gravity Thickener Facilities — replacement of thickener mechanisms, pumps, and piping to improve process efficiency and reliability of the facilities
  • Grit and Screen Facilities — upgrade grit chamber buildings, influent screens, grit chambers, and conveyance and loading systems to facilitate off- site grit disposal

These projects, which have a combined cost of $350 million, will rebuild significant portions of the plant and add new sludge dewatering capability.

Take a virtual tour of Blue Plains Advanced Wastewater Treatment Plant.

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Liquid Processing Program — $437.3 million

Projects in this program area encompass upgrading and rehabilitating facilities involved in handling flows from the sanitary and combined sewer systems. These flows progress sequentially through the 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/ denitrification facilities that remove nitrogen using a biological process, and effluent filtration, disinfection, and dechlorination facilities.

Specific major projects under this program include:

  • Raw Wastewater Pumping Station 1 Upgrade $7.4 million — This project will rehabilitate pumping equipment and appurtenances in one of the two stations that pump incoming wastewater into the plant. Design was started in FY 2002.
  • Influent Screening Facilities Upgrade $35.3 million — This project will install fine screens to replace existing coarse screens at the head of the plant, as well as screenings conveyance, storage and outloading facilities. The project was bid in conjunction with the Grit Chamber Facilities Upgrade. Construction bids were received in September 2001. However only one bid, substantially higher than the project budget, was received. Upon rebidding the project in conjunction with the West Grit Chamber Facilities Upgrade, satisfactory bids were received and construction began in early FY 2003.
  • Grit Chamber Facilities Upgrade $64.7 million — This project provides for the construction of an automated, continuous grit removal system in all sixteen chambers. Impacts on operations include the elimination of current manual cleaning of each grit tank and lowered maintenance costs of tanks and pumps. The project was bid in conjunction with the Influent Screening Facilities Upgrade. Construction bids were received in September 2001. However only one bid, substantially higher than the project budget, was received. Upon re- bidding the project in conjunction with the West Grit Chamber Facilities Upgrade, satisfactory bids were received and construction began in early FY 2003. The East Grit Chamber Facilities Upgrade was re- bid in FY 2003 and construction is now underway.
  • Primary Treatment Facilities Upgrade $38.2 million -- This project involves the replacement of clarifier mechanisms in the East Process and modifications of the clarifiers in the West Process, which will result in improved overall plant efficiency and lowered maintenance costs. Construction began in early FY 2002 and is scheduled to be complete in early FY 2006.
  • Secondary Treatment Facilities Upgrade Phase I $66.2 million (for phases I and II) — Rehabilitation of the East Secondary Treatment facilities, and rehabilitation of support equipment and facilities are included in this project. This project will result in lowered maintenance costs. Construction started in FY 2002 and is scheduled to be complete in late FY 2004.
  • Secondary Treatment Facilities Upgrade Phase II — This project includes the rehabilitation of the West Secondary Sedimentation Basins (basins number 1- 12) and the West Secondary Reactors. This will result in improved process efficiency, lowered chemical usage and lower maintenance costs. Construction started in FY 2003 and is scheduled to be complete in late FY 2007.
  • Nitrification/ Denitrification Facilities Upgrade $76 million — This project is comprised of two liquid processing projects, one for rehabilitation and upgrade of nitrification facilities and one for improvement of denitrification- related process components. This project will result in lowered maintenance and energy costs due to improved efficiency. Final design will be completed and the project will be advertised for construction bids in FY 2004.
  • Filtration and Disinfection Facilities Upgrade $56.0 million — Replacement of existing filter media and the addition of an air/ water backwash system and improvements to pump operation will result in reduced power usage and treatment costs due to reduced backwash water usage. This project was split into two contracts in order to expedite the full rehabilitation of the facility, which has experienced filter failures. The first contract will result in all of the filters being restored to operability with new filter blocks and media. The second contract will improve backwashing controls and instrumentation. Design started in FY 2002 and the first construction contract was advertised for bidding in FY 2003. Design for the second contract is scheduled to be done in FY2004.

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Solids Processing Program — $459.8 million

Wastewater Treatment Process

Biosolids processing involves reductions in volume along with treatment to meet federal or state and local requirements, as applicable, for the ultimate disposal method. Treatment is provided by a system of processing facilities that include gravity thickening of primary sludge, floatation thickening of the biological waste sludges produced by the secondary and nitrification/ denitrification processes, digestion of all biosolids streams, dewatering by centrifuge or belt press and lime stabilization. Dewatered biosolids are conveyed to the Dewatered Sludge Loading Facility for outloading to tractor- trailers for hauling to offsite land application sites, silviculture, and land reclamation sites. Solids processing facilities are required to produce a biosolids product that can be reused or disposed of in an economical and environmentally acceptable manner.

WASA has conducted a comprehensive Decision Science planning process to develop a long- term plan for biosolids processing and disposal. Currently, 1,350 tons of biosolids are generated daily at Blue Plains. The predominant means of disposal is land application in Virginia, although changes in the regulatory environment and local restrictions on land application may limit the availability of this disposal means in the long run. The Decision Science planning process identified a number of alternatives, all of which included full digestion as a key component. As a result of this process, the Board adopted a Biosolids Management Plan that approved full biosolids digestion as our primary long- term alternative and continuing land application as long as it is financially advantageous.

A detailed facilities plan for this program has been prepared with a total cost of approximately $440 million. These costs are primarily included in the Solids Processing Program, although some costs, such as the second phase of the process control computer system, are included in the Plantwide Facilities Program. The centerpiece of the program is design and construction of 36 million gallon total capacity egg- shaped digesters, sized for the total biosolids production of the plant. The permitting and public acceptance process has begun.

Specific major projects under this program include:

  • Egg- Shaped, Anaerobic Digestion Facilities $257 million — This project entails the replacement of the existing digesters, with substantially increased digester capacity. When the new digesters are operational in FY 2008, operating costs, particularly hauling and chemical purchases, will be substantially reduced. This facility will result in an end product which is far less odorous, more consistent, lower in volume and more acceptable for agricultural use. Design work started in August 2002 and construction is scheduled to begin in late 2004 or early 2005.
  • Additional Dewatering Facilities $79.4 million — This project provides additional centrifuge dewatering equipment and modification of existing centrifuges to reduce dewatered solids generation. Impacts on operational costs include reductions in hauling and contract dewatering costs. It also includes first- in/ first- out silos for biosolids cake storage to minimize odors that occur from biosolids being stored for extended periods. Construction commenced in December 2001 and is scheduled for completion in FY 2005.
  • Biological Sludge Thickening Facilities $52.1 million — This project will evaluate the potential for upgrading the existing dissolved air flotation thickening units along with the provision of mechanical thickening equipment. Improvements are expected to reduce sludge processing and chemical costs through improved efficiency. A design study commenced in late FY 2003.
  • Gravity Thickening Facility Upgrade $19.8 million — This project includes the rehabilitation of gravity thickeners 1- 6 and all sludge and scum pumping systems. Also planned are the rehabilitation of equipment in the degritting and grinding facility and the addition of the ability to add chemicals to the influent flow for odor control. Design is complete, the project has been bid and construction is expected to start early in FY 2004.

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Plantwide Facilities Program — $289.4 million

Wastewater Treatment Process

This program provides for upgrading, rehabilitating, or installing support systems and facilities that are required for both the liquid processing and solids processing programs. 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 systems upgrade, 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 bisulfite. Support facilities projects include the rehabilitation of the Central Operations Facility and the Central Maintenance Facility. Specific projects under this program include:

  • Nitrification Sodium Hydroxide Facility $3 million — In FY 2002, WASA completed the construction of an interim replacement of the current outdated nitrification lime feed system with a nitrification sodium hydroxide facility. Sodium hydroxide, while more expensive, is much easier to handle and the feed equipment is simpler and more reliable. Impacts on operations include higher chemical costs and lowered facilities maintenance costs.
  • Additional Chemical Systems — Phase I $73.5 million (for both phases I and II) — This project replaces all of the chemical storage, transmission, and feed facilities at Blue Plains that are used for metal salts. Construction of this project was initiated in April 2001 and is scheduled to be completed in FY 2004.
  • Additional Chemical Systems — Phase II — This project involves installation of new centralized bulk dry polymer receipt, batching, storage and feed facilities for the entire plant's polymer needs. This new installation will result in improved process efficiencies and reduced maintenance requirements. The construction contract was initiated in August 2002 and is scheduled to be completed in FY 2004.
  • Alternate Disinfection Facilities $16. 3 million — This project replaces the current interim facilities that use liquid sodium hypochlorite (concentrated bleach) and liquid sodium bisulfite. In the past, chlorine and sulfur dioxide were shipped to Blue Plains in 90- ton railcars, and have historically posed handling and safety concerns. In response to the events of September 11, 2001, an interim system was put into place in December 2001, which allowed the removal of the highly hazardous chlorine and sulfur dioxide chemicals from Blue Plains. As part of our safety initiatives, WASA accelerated this project for permanent replacement of the chlorine facility, and it will be completed before the end of calendar year 2003.
  • Process Control and Computer System (Phases 1, 2 and 3) $51.7 million — This new system allows for automation of a significant number of plant processes at Blue Plains, and better management of processes that are currently manually monitored. Operating savings are anticipated from lowered chemical usage and electricity consumption, due to minimizing peak demand, as well as lower staffing levels. This project is critical to achieving the goals presented in the Blue Plains Internal Improvement Plan. The new system is being implemented in three phases, beginning with the grit chambers, primary and secondary treatment facilities, and dewatering processes. Phase II will include nitrification, filtration, disinfection facilities, and Phase III will add the solids processing facilities. WASA has selected an equipment vendor and construction began in August 2002 and will continue through 2009.

Changes in Service Area Budget in FY 2004

The proposed FY 2003 — FY 2012 plan for the Wastewater Treatment Service Area has increased by $22.2 million compared to last year's plan. This is attributable to project budget increases for the filtration/ disinfection facility ($ 12.9 million), plant access upgrades and other facility and security improvements ($ 7.7 million), and a new project for automated sampling ($ 1 million).

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