Brief Project Description
HRSD owns and operates the Army Base Treatment Plant (ABTP), which provides secondary treatment for a permitted design flow of 18 MGD. The existing ABTP consists of primary treatment, secondary treatment, effluent disinfection and dechlorination, with discharge to the Elizabeth River. Solids handling processes include combined primary and waste activated solids thickening, dewatering and incineration.
Under new nutrient discharge control regulations for the Chesapeake Bay and its tributaries, HRSD has received a combined, bubble waste load allocation for nitrogen and phosphorus for its seven treatment plants discharging within the James watershed. Providing nutrient removal at the ABTP is a key element in HRSD’s long-term strategy for meeting the bubble waste load allocation and improving local water quality.
Under a plan referenced as the ABTP Phase III Project, HRSD will upgrade the existing secondary treatment process to an enhanced nutrient removal system designed for annual average effluent concentrations of 5.0 mg/l total nitrogen and 1.0 mg/l total phosphorus. The Phase III Project also includes improvements to other plant treatment processes and support systems to provide reliability for a 20 year design life and will be implemented as two separate construction contracts. Incinerator improvements (not grant funded and omitted from this scope of work) will be implemented under an initial contract due to the condition of existing incinerator equipment.
Facilities included in the Phase III Project are described as follows:
Preliminary Treatment: A new Preliminary Treatment Facility (not grant eligible) will be constructed to provide raw wastewater influent screening, pumping, grit removal and residuals handling
Secondary Treatment: Secondary treatment facilities and upgrades for a 5-stage activated sludge, biological nutrient removal process includes the following.
- Four new Aeration Tanks configured to provide anaerobic, primary anoxic and primary aerobic zones. Mixers will be installed in the anaerobic and anoxic zones and fine-bubble membrane diffusers are proposed for the aerobic zones. A new process blower building will be constructed to house new process aeration blowers.
- Existing aeration tanks will be modified to provide the secondary anoxic zone and final aerobic polishing zone for nutrient removal. Modifications include: a new influent channel, mixers for the anoxic zones, and reconfiguration of the existing surface aerators to meet process air requirements.
- Existing Secondary Clarifier modifications will include new influent wells, suction header solids collection, full-diameter foam collection with positive foam wasting and effluent launders.
- A Nitrification Enhancement Facility (NEF) will provide a side stream activated sludge process to treat incinerator scrubber water to remove compounds that can inhibit nitrification. The NEF will consist of converting the existing Digester No. 2 tank into an aeration tank and clarifier equipped with RAS and solids wasting pumps, process aeration blowers and diffusers. Waste activated solids (WAS) from the main activated sludge nutrient removal process will provide the mixed liquor for the NEF process.
Primary Solids Thickening and Storage: The current practice of co-thickening primary and waste activated solids in the primary clarifiers will be discontinued to reduce solids and BOD loads to the activated sludge nutrient removal process. The existing Gravity Thickener will be rehabilitated with new mechanical equipment and used for thickening and storage of primary solids. The existing Biosolids Holding Tank will be used in conjunction with the gravity thickener to provide primary solids storage.
Waste Activated Solids Thickening Improvements: Two new Gravity Belt Thickeners (GBTs) will be provided to thicken waste activated solids from the secondary treatment process. Provision of new GBTs for thickening of waste activated solids, which will no longer be co-thickened with primary solids in the primary clarifiers, will allow the continued use of the existing centrifuges for dewatering. New GBTs and related polymer feed equipment will be installed.
Foreign Biosolids Receiving Station (FBRS): Improvements to the existing FBRS facility (not grant eligible) include increasing its capacity and upgrading the existing progressing cavity pumps that feed biosolids to the incinerators.
Odor Control Systems (OCS): The existing OCS Unit ‘A’ will be modified to treat odorous air from the solids handling areas, the primary clarifiers and a portion of the new aeration tanks. A new OCS Unit ‘B’ will be constructed to treat odorous air from the new Preliminary Treatment Facility.
Chemical Feed Systems: ABTP has existing chemical storage and feed systems for chemical phosphorus removal, disinfection and foam control, dechlorination, and odor control. Additional feed pumps will be installed to serve increased demands at the Odor Control Stations and foam control spray water systems for the secondary treatment, nutrient removal process. A new chemical storage and feed system will be provided for alkalinity addition for the nitrification process and for the new Odor Control Station B. A new methanol storage and feed system to provide supplemental carbon to the second-stage denitrification process will also be constructed and funded for nitrogen reduction; chemical storage and feed for phosphorus reduction is not being funded under this project.
Process Piping Improvements: The existing piping for the primary clarifier influent and aeration tank influent will be replaced or rehabilitated. Major new process piping connections between new and existing facilities will include the following.
- Extension of the raw wastewater influent line to the new PTF.
- A connection from the new PTF to the primary clarifier influent.
- A connection from the Intermediate Pumping Station discharge main to the new aeration tanks.
- Extension of the RAS force main to the new aeration tanks.
- A MLSS transfer pipe to convey mixed liquor from the new aeration tanks to the existing, modified aeration tanks.
Electrical System Improvements: Much of the existing electrical distribution system will be replaced, based on a condition assessment. Additional loads for the new process facilities will be served by new switchgear to be located in the existing Generator and Switchgear Building, along with a new standby generator.
Distributed Control System: A new plant-wide distributed control system will be provided to improve treatment plant automation and control.