Western Branch Wastewater Treatment Plant Prince Georges County

FACILITY BASIC INFORMATION

Plant Name: Western Branch Wastewater Treatment Plant

Location: Upper Marlboro, Prince George’s County, Maryland

Operating Authority: WSSC Water (Washington Suburban Sanitary Commission)

Design Capacity: 30.0 MGD

Current Average Flow: ~20-24 MGD

Population Served: ~275,000 residents

Service Area: Central Prince George’s County (Upper Marlboro, Bowie, Largo)

Receiving Water Body: Western Branch of the Patuxent River (Chesapeake Bay Watershed)

NPDES Permit Number: MD0021741

Read more4D-Printed Smart Materials For Water Treatment

Year Commissioned: 1970s (Major ENR Upgrades 2010s)

1. INTRODUCTION

The Western Branch Wastewater Treatment Plant (WWTP) serves as a critical environmental safeguard for the Patuxent River watershed and the broader Chesapeake Bay ecosystem. Operated by WSSC Water, one of the largest water and wastewater utilities in the United States, this 30-MGD facility provides advanced wastewater treatment for the rapidly growing central region of Prince George’s County, Maryland.

Distinguished by its role as a regional solids processing hub, Western Branch not only treats liquid waste but also handles biosolids incineration for multiple facilities within the WSSC network. Following a comprehensive transition to Enhanced Nutrient Removal (ENR) technology, the plant consistently achieves effluent nitrogen levels below 3.0 mg/L and phosphorus levels below 0.3 mg/L. As WSSC Water invests in resilient infrastructure, Western Branch stands as a primary example of balancing hydraulic capacity, regulatory compliance, and environmental stewardship in a sensitive tributary location.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The facility services a diverse sewershed in central Prince George’s County. The collection system funnels wastewater from residential hubs including the City of Bowie, Upper Marlboro, and the dense commercial corridors of Largo and Landover. The service area is characterized by a mix of suburban residential developments and light industrial zones. The collection system relies on a network of major interceptors along the Western Branch tributary, supported by regional pumping stations that lift flow to the plant’s headworks.

B. Operational Capacity

While the plant is permitted for a design flow of 30.0 MGD, it typically operates at an average daily flow of approximately 22 MGD, providing a capacity utilization of roughly 73%. This headroom allows the facility to manage wet-weather peaking events effectively. Historical flow data indicates significant fluctuations correlated with rainfall, necessitating robust wet-weather management protocols to prevent sanitary sewer overflows (SSOs) or process washouts. WSSC maintains a hydraulic planning horizon that accounts for continued growth in the Prince George’s County corridor.

C. Discharge & Compliance

Treated effluent is discharged into the Western Branch of the Patuxent River. Because the Patuxent is a major tributary to the Chesapeake Bay, the facility operates under some of the strictest nutrient limits in the nation. The NPDES permit dictates rigorous limits on Total Nitrogen (TN) and Total Phosphorus (TP) to combat eutrophication in the Bay. The plant consistently earns recognition from the National Association of Clean Water Agencies (NACWA) for permit compliance.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

Read moreA Comparison Between Aerobic And Anaerobic Wastewater Treatment Technology

Raw wastewater enters the headworks where it undergoes physical screening. The plant utilizes mechanically cleaned bar screens to remove large debris, rags, and plastics that could damage downstream pumps. Following screening, flow enters aerated grit chambers. These chambers introduce air to reduce the specific gravity of the wastewater, allowing heavier inorganic grit (sand, coffee grounds) to settle while keeping lighter organic material in suspension. The extracted grit and screenings are washed, compacted, and hauled off-site to a landfill.

B. PRIMARY TREATMENT

Flow proceeds to the primary sedimentation basins. Western Branch utilizes circular primary clarifiers equipped with surface skimmers and bottom scrapers. Here, flow velocity is reduced to allow settlable solids to drop to the bottom as primary sludge, while fats, oils, and grease (FOG) float to the surface for skimming. Primary treatment typically removes 50-60% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD).

C. SECONDARY TREATMENT (Activated Sludge)

The biological heart of the plant is the activated sludge process. The aeration basins are configured for Biological Nutrient Removal (BNR). In these basins, a culture of microorganisms consumes organic matter. The system utilizes fine-bubble diffusion to maximize oxygen transfer efficiency. The process includes anoxic zones to facilitate denitrification (conversion of nitrates to nitrogen gas). Mixed liquor flows from the aeration basins to secondary clarifiers, where the biomass settles out. A portion is returned to the head of the aeration tanks (RAS), while excess biomass is wasted (WAS) to solids handling.

D. TERTIARY/ADVANCED TREATMENT (ENR)

To meet the rigorous Chesapeake Bay ENR standards, Western Branch employs advanced tertiary treatment.

• Denitrification Filters: Following secondary clarification, effluent passes through deep-bed denitrification filters. Methanol is added as a carbon source to feed bacteria that convert remaining nitrates into nitrogen gas.
• Chemical Precipitation: Alum or ferric chloride is added to precipitate phosphorus, which is then captured in the tertiary filtration stage.
• Target Performance: This stage is critical for achieving effluent concentrations of TN < 3.0 mg/L and TP < 0.3 mg/L.

E. DISINFECTION

Historically, the plant used chlorination, but WSSC Water completed a conversion to Ultraviolet (UV) Disinfection. The UV system alters the DNA of pathogenic bacteria and viruses, rendering them unable to reproduce. This method eliminates the risk of chlorinated byproducts entering the Patuxent River and removes the safety hazards associated with storing bulk chlorine gas on-site. Following UV treatment, the water is re-aerated (cascade aeration) to ensure sufficient dissolved oxygen levels before discharge.

F. SOLIDS HANDLING & INCINERATION

Western Branch is a regional solids processing facility. It treats sludge generated on-site as well as sludge imported from the Parkway WWTP.

• Thickening: Primary sludge is gravity thickened, while waste activated sludge (WAS) is thickened using Dissolved Air Flotation (DAF) units.
• Dewatering: Thickened sludge is processed through high-speed centrifuges to remove water, producing a “cake” with higher solids content.
• Incineration: The dewatered cake is incinerated in Multiple Hearth Incinerators (MHIs). The ash generated is collected and hauled to a landfill. The incineration process significantly reduces the volume of waste requiring disposal.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The facility occupies a substantial footprint along the riverbank. The site includes the main process train, a dedicated solids handling building, maintenance shops, and an administration building housing the control center and laboratory. The site layout is designed to allow for truck traffic related to the hauling of ash and the delivery of methanol and other process chemicals.

B. Energy Systems

Western Branch is an energy-intensive facility due to the aeration blowers, influent pumping, and incineration systems. WSSC has implemented various energy efficiency measures, including the installation of Variable Frequency Drives (VFDs) on major pumps and blowers. The incineration process requires natural gas support to maintain combustion temperatures, particularly when sludge solids content fluctuates.

C. Odor Control

Given the suburban encroachment near the facility, odor control is a priority. The plant utilizes chemical scrubbers and biofilters, particularly around the headworks, primary clarifiers, and the sludge dewatering complex. These systems treat foul air to remove hydrogen sulfide and other odor-causing compounds before release.

5. RECENT UPGRADES & MAJOR PROJECTS

Incinerator Emissions Upgrade (2016-2020)

• Project Scope: Upgrades to the Multiple Hearth Incinerators to meet EPA’s new Sewage Sludge Incineration (SSI) Maximum Achievable Control Technology (MACT) standards.
• Budget: ~$15 – $20 Million (part of a larger solids program).
• Technical Highlights: Installation of mercury control modules and advanced scrubber systems to reduce particulate matter and heavy metal emissions.
• Driver: Clean Air Act compliance.

Enhanced Nutrient Removal (ENR) Upgrade (Completed ~2014)

• Project Scope: Major retrofit of the biological and tertiary systems to reduce nutrient loads to the Chesapeake Bay.
• Funding: Supported by the Maryland Bay Restoration Fund (“Flush Tax”).
• Results: Successfully lowered effluent Nitrogen to < 3 mg/L and Phosphorus to < 0.3 mg/L, making the plant one of the top performers in the watershed.

Current/Upcoming: Holistic Energy Project

WSSC Water is currently evaluating a utility-wide bio-energy strategy. While Piscataway WRRF was selected for the major bio-energy facility (THP and Anaerobic Digestion), Western Branch continues to undergo electrical infrastructure renewals, including switchgear replacement and SCADA modernization to improve resiliency against power failures.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

Permit Requirements

The facility operates under NPDES Permit MD0021741. Key parameters include:

• Total Nitrogen (Annual Avg): ~3.0 mg/L
• Total Phosphorus (Annual Avg): ~0.3 mg/L
• BOD5/TSS: Monthly average limits typically < 10 mg/L
• Bacteria: Strict limits on E. Coli/Enterococci, achieved via UV disinfection.

Compliance History

Western Branch maintains a strong compliance record. Occasional challenges have arisen related to wet weather flows and incinerator emissions testing, but the facility consistently meets its core liquid stream parameters. WSSC regularly receives Peak Performance Awards from NACWA for this facility.

7. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

Like many plants built in the 1970s, Western Branch faces the challenge of aging concrete and mechanical systems. WSSC’s Asset Management Program prioritizes the rehabilitation of clarifier mechanisms, concrete repairs in aeration basins, and the replacement of underground piping networks.

B. Solids Handling Strategy

The reliance on Multiple Hearth Incinerators presents a long-term challenge. MHIs are energy-intensive and operationally complex. WSSC’s long-term master plan involves evaluating the lifecycle costs of maintaining these incinerators versus diverting solids to the new Bio-Energy facility at Piscataway or converting Western Branch to a different solids processing technology in the future.

C. Climate Resilience

Located near a river, the plant must plan for potential flooding and changing precipitation patterns. Future capital improvements will focus on hardening critical electrical infrastructure and raising sensitive equipment above projected flood elevations.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

Western Branch is part of the integrated WSSC Water system. It works in conjunction with:

• Parkway WWTP: A nearby WSSC facility that sends its solids to Western Branch for incineration.
• Piscataway Bio-Energy Facility: WSSC’s new centralized solids handling hub (though Western Branch currently maintains its own incineration capabilities).
• Regional Pump Stations: Large lift stations in Bowie and Upper Marlboro that feed the Western Branch collection system.

12. FAQ SECTION

Technical Questions

1. What is the ENR capability of Western Branch?
The plant is designed for Enhanced Nutrient Removal, targeting Total Nitrogen < 3.0 mg/L and Total Phosphorus < 0.3 mg/L.

2. How does the plant handle biosolids?
Biosolids are thickened via gravity and DAF, dewatered using centrifuges, and incinerated on-site using Multiple Hearth Incinerators.

3. Does Western Branch accept hauled waste?
Yes, Western Branch has historically served as a receiving point for hauled waste and septage, though specific policies should be confirmed with WSSC Trucked Waste Division.

4. What disinfection method is used?
The plant utilizes high-intensity Ultraviolet (UV) light, having moved away from chlorine gas for safety and environmental reasons.

General Questions

5. Does the plant smell?
While wastewater treatment naturally generates odors, Western Branch employs advanced scrubbers and biofilters to neutralize odors before they leave the property line. WSSC maintains a 24-hour hotline for odor complaints.

6. Can I tour the facility?
WSSC Water occasionally offers tours for educational groups and engineering students. Requests must be made through the WSSC Office of Communications and Community Relations.