U.S. ENVIRONMENTAL PROTECTION AGENCY-- REGION 3
1650 Arch Street
Philadelphia, Pennsylvania 19103
Date of Categorical Exclusion: February 25, 2014
NOTICE: The U.S. Environmental Protection Agency (EPA), Region 3 has concluded that the following project is consistent with the categories of actions eligible for a categorical exclusion. This means that an environmental information document will not be required, and an environmental assessment or environmental impact statement will not be prepared for this project.
Official Project Name:
Filtrate Treatment Facility
Blue Plains Advanced Wastewater Treatment Plant
District of Columbia Water and Sewer Authority
5000 Overlook Avenue, S.W.
Washington, D.C. 20032
NEED AND DESCRIPTION:
The proposed project involves the upgrading of the Blue Plains Advanced Wastewater Treatment Plant (Blue Plains) in Washington, D.C. The plant is owned and operated by the District of Columbia Water and Sewer Authority (aka “DC Water” and “DC WASA”). The Blue Plains service area includes the District of Columbia; portions of Fairfax and Loudoun Counties in Virginia; and Montgomery and Prince Georges Counties in Maryland. See Figure 1 in “Attachments”. The estimated population in the service area is 2.4 million.
Blue Plains has a nominal treatment capacity of 370 million gallons per day (MGD) and is located along the east bank of the Potomac River. It is south of Bolling Air Force Base and the U.S. Naval Research Laboratory, and west of the Anacostia Freeway (I-295) in Washington, D.C. Blue Plains has been operated by the District of Columbia since 1938. The original facility consisted of a 130 MGD primary treatment plant, which was expanded to a 240 MGD secondary treatment facility in the 1950's. A major construction program was initiated between 1972 and 1983 to expand the plant’s capacity to 309 MGD and to provide advanced treatment. Another construction program, between 1986 and 1997, expanded the plant’s capacity to 370 MGD.
DC Water was created by the government of the District of Columbia in October 1996 to provide water distribution and wastewater service to the District of Columbia, as well as wastewater service to significant areas of suburban Maryland and Virginia. The plant is operated under National Pollutant Discharge Elimination System (NPDES) Permit No. DC002119. The permit was issued by the U.S. Environmental Protection Agency (EPA) and contains stringent effluent discharge limitations for carbonaceous biochemical oxygen demand, total suspended solids, total phosphorous, ammonia nitrogen, total nitrogen discharge, dissolved oxygen, total chlorine residual, and pH.
This grant project involves the construction of a new side stream Filtrate Treatment Facility (FTF) at Blue Plains. The purpose of this facility is to reduce the ammonia and carbon in the filtrate or recycle stream from the dewatering process before it goes back into the main wastewater treatment process. Direct discharge of the ammonia-laden dewatering recycle into the mainstream wastewater treatment process would increase the cost and decrease the effectiveness of nitrogen removal in the mainstream.
The goal of the project is to reduce ammonia concentration more reliably and cost-effectively without any impact on the current nitrogen removal process. See Figure 2 in “Attachments” for location of the work area in Blue Plains.
The scope of work for the proposed facility includes:
- A new Filtrate Treatment Facility to include a large filtrate feed tank and six reactors equipped with mechanical mixers, air diffusers, air blowers, decanters, pumps, and hydrocyclones.
- A new Electrical Building to include electrical equipment (i.e. motor control centers, unit substations and lighting and power panels and auxiliary transformers) necessary to supply power to the Filtrate Treatment Facility and Phosphorus Building.
- A new Phosphorus Building to include two phosphoric acid storage tanks and chemical feed pumps.
- All associated piping and electrical modifications within existing tunnels and galleries.
- Excavation and site work.
Currently, the dewatered filtrate is pumped to the Waste Liquor Return Channel, which conveys recycle streams from the Solids Processing Building to the West Secondary Activated Sludge Process which must treat both the dewatered filtrate and the nitrogen load in the plant’s mainstream. In West Secondary Activated Sludge Process, biodegradable organic carbon in the filtrate is oxidized to carbon dioxide and water, resulting in the production of biomass (“sludge”). The filtrate ammonia load is oxidized to nitrate using large amounts of aeration and energy in the Second Stage Nitrification Reactors. The nitrate is further reduced to gaseous nitrogen in the Tertiary Denitrification Process through the addition of methanol. At times, caustic soda is added to ensure complete nitrification and to adjust the plant’s effluent pH levels to comply with its permit limits. All secondary treatment effluent is treated in the Enhanced Nitrogen Removal (ENR) Facilities, which reduces the nitrogen concentration in the wastewater flow.
The purpose of the Filtrate Treatment Facility is to reduce the highly concentrated ammonia load from the final dewatering facility recycle before it is delivered into the mainstream process. Discharging the ammonia-laden recycle stream directly into the mainstream Enhanced Nitrogen Removal Process would require additional methanol for denitrification and increased aeration for oxygen demand in the recycle stream. The facility will enable consistency and reliability of the downstream processes for meeting discharge limits specified in its NPDES permit. The Filtrate Treatment Facility will contribute to continuing high quality effluent discharge from Blue Plains into the Potomac River.
Three filtrate treatment alternatives were evaluated:
- Treatment of Filtrate in the Mainstream Treatment Plant. (Current situation).
- Pretreatment of Filtrate in a Physical/Chemical Process followed by Final Treatment in the Mainstream Treatment Plant.
- Pretreatment of Filtrate in a Deammonification Process followed by Final Treatment in the Mainstream Treatment Plant. (The selected alternative).
Based on a number of factors, a separate filtrate pretreatment facility was selected to minimize the impact of the filtrate ammonia load on the performance of the mainstream plant. Furthermore, the alternatives analysis revealed that a biological deammonification process was the most cost-effective means for filtrate pretreatment. A new biological process called DEMON® (from the word DEamMONification) will be constructed to treat and remove ammonia nitrogen from the filtrate prior to its recycle to the mainstream treatment process. DEMON® utilizes a series of sequencing batch reactors and varying aeration levels to create the necessary aerobic and non-aerobic conditions for specific microbes to metabolize ammonia nitrogen and convert it into harmless gaseous nitrogen.
The uniqueness of this new process depends on a highly specialized microbe belonging to the bacterial phylum Planctomycetses. This microbe has the ability to remove nitrogen without the addition of chemicals (i.e. methanol) and the significant power requirements that are normally associated with the removal of nitrogen. The metabolic and chemical pathways for the more conventional Nitrification-Denitrification Process being used in the plant’s mainstream and Deammonification Process for this waste stream are contrasted in See Figure 3 in “Attachments”.
A conventional Nitrification-Denitrification Process requires significant amounts of aeration to fully convert the ammonia to nitrate and the addition of methanol to change the nitrate into nitrite and finally gaseous nitrogen. DEMON® utilizes another method. In the first step of the deammonification process, approximately half of the filtrate ammonia is oxidized under aerobic conditions to nitrite. The operating conditions in the process prevent further aerobic oxidation of nitrite to nitrate. In the second reaction, nitrite and much of the remaining ammonia are converted under oxygen-free conditions to gaseous nitrogen and nitrate in a process called Anaerobic Ammonium Oxidation (Anammox). The DEMON® process is anticipated to remove approximately 90% of the ammonia and 90% of the total inorganic nitrogen from the pretreated filtrate. The pretreated filtrate then goes to the plant’s mainstream where the residual ammonia load is nitrified and denitrified with methanol.
The operational cost savings in implementing DEMON® for filtrate treatment at Blue Plains are substantial. This savings is attributable to reductions in the usage of supplemental organic carbon source (e.g. methanol), sodium hydroxide, electrical power mainly for aeration, and sludge hauling.
The proposed project was included in DC Water’s Capital Improvement Program and was also listed on the DC Department of the Environment’s (DDOE) FY 2013 – 2014 Clean Water Project Priority List. Advertized public hearings were held by DDOE on the project priority list on August 13, 2013. All projects were described including this one. The proposed priority list was posted on the internet by DDOE and DC Water. No adverse public comments were expressed at these hearings or during the comment periods provided on this project.
The project’s construction is estimated to be $49,049,774. Blue Plains receives wastewater flows from Washington and surrounding areas. The jurisdictions contributing flows to Blue Plains would provide the local share of the required funding based upon their proportional flows. The District of Columbia’s share is approximately 41.21% or $20,213,411 of the total cost based upon its flow and the Inter-Municipal Agreement of 1985. EPA has determined that DC Water is eligible to receive a 55% grant or $11,117,377 under Title II of the Clean Water Act based upon the District of Columbia’s financial share.
The proposed project is not anticipated to have a significant impact on existing environmental resources. Environmental impacts will be confined to the treatment plant site and may include temporary construction-related issues such as dust, sediment and erosion, noise. These will be temporary and of short duration. Measures will be specified in the contract documents to mitigate these issues. Air contaminant emissions from construction vehicles and basins will be minimal and confined to the treatment plant site.
There are no long-term negative impacts to existing environmental resources anticipated. The completed project will have an environmental benefit since it will enable the plant to consistently and reliably meet its NPDES permit limits in its discharge to the Potomac River under all reasonably foreseeable conditions.
FOR ADDITIONAL INFORMATION: A copy of the EPA decision is available upon request. Please notify the contact below if you are aware of any reason why the decision should be revoked.
Comments should be sent to:
Office of Infrastructure and Assistance (3WP50)
EPA Region 3
1650 Arch Street
Philadelphia, PA 19103
Kenneth C. Pantuck (215) 814-5769
Interested parties may contact the above EPA representative to learn more about this action.