Parkway Wastewater Treatment Plant Anne Arundel County

1. Introduction

The Parkway Wastewater Treatment Plant (WWTP) is a critical infrastructure asset within the Anne Arundel County Department of Public Works (DPW) system, serving the rapidly growing western portion of the county. Commissioned originally in the 1980s and substantially upgraded to Enhanced Nutrient Removal (ENR) standards in 2012, the facility operates with a design capacity of 7.5 million gallons per day (MGD).

Unique among the county’s facilities, Parkway serves a dual purpose: it acts as a liquid treatment facility for its specific service shed and functions as the regional solids processing hub for Anne Arundel County. The co-located Parkway Biosolids Management Facility processes sludge imported from the county’s other major plants (Cox Creek and Annapolis WRF), making it a cornerstone of the region’s environmental compliance strategy. Discharging into the Little Patuxent River, the plant plays a vital role in meeting the rigorous Total Maximum Daily Load (TMDL) requirements set forth for the restoration of the Chesapeake Bay.

2. Facility Overview

A. Service Area & Coverage

The Parkway WWTP services the western tier of Anne Arundel County, an area characterized by a mix of dense residential developments, commercial corridors, and significant federal installations. The service area includes:

• Municipalities/Communities: Maryland City, Russett, parts of Laurel, and the Jessup area.
• Key Federal/Commercial Clients: Portions of Fort George G. Meade and the associated defense contractor corridor, as well as the Maryland Live! Casino and Arundel Mills commercial district.
• Collection System: The plant receives flow via a network of gravity sewers and major force mains, including flows from the Maryland City and Russett pump stations.

B. Operational Capacity

The liquid treatment train is designed for an average daily flow of 7.5 MGD, with peak hydraulic capacities exceeding 15 MGD during wet weather events. Historical flow data indicates an average utilization between 5.5 and 6.5 MGD, reflecting the dense urbanization of the sewershed. However, the solids handling capacity is distinct, designed to process sludge from a total county wastewater flow of over 30 MGD.

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C. Discharge & Compliance

The facility discharges treated effluent into the Little Patuxent River, a tributary of the Patuxent River, which eventually flows into the Chesapeake Bay. Adhering to the Maryland Department of the Environment (MDE) NPDES Permit MD0021601, the plant operates under strict “Bay Restoration” limits. As an ENR facility, it is mandated to achieve annual average effluent concentrations of Total Nitrogen (TN) at 3.0 mg/L and Total Phosphorus (TP) at 0.3 mg/L, standards it consistently meets or exceeds.

3. Treatment Process

The Parkway WWTP utilizes an advanced oxidation ditch process coupled with deep bed denitrification filters to achieve high-level nutrient reduction. The treatment train is divided into liquid processing and the regional solids processing facility.

A. Preliminary Treatment

Raw influent enters the headworks building where it undergoes physical screening and grit removal to protect downstream mechanical equipment.

• Screening: Mechanical fine bar screens remove rag, plastics, and large debris. Screenings are washed, compacted, and disposed of in landfills.
• Grit Removal: Vortex grit chambers utilize centrifugal force to separate heavy inorganic solids (sand, gravel) from the organic waste stream.

B. Secondary Treatment (Biological)

The core of the liquid treatment is the Oxidation Ditch system. This extended aeration activated sludge process is highly effective for both BOD removal and nitrification (conversion of ammonia to nitrate).

• Configuration: The plant operates multiple oxidation ditch trains (typically “racetrack” configuration).
• Aeration: Mechanical surface aerators or brush rotors provide oxygen transfer and maintain mixing velocities to keep solids in suspension.
• Process Control: The system is operated to create anoxic zones within the ditches to promote simultaneous nitrification and denitrification.
• Secondary Clarification: Mixed liquor flows to circular secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is pumped back to the ditches, while Waste Activated Sludge (WAS) is sent to the solids holding tanks.

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C. Tertiary/Advanced Treatment (ENR)

To meet the strict Chesapeake Bay limits, the plant employs tertiary treatment specifically for nutrient removal.

• Denitrification Filters: Effluent from secondary clarifiers is pumped to deep-bed sand filters (Tetra Denite or similar technology). A carbon source (typically methanol) is added to fuel heterotrophic bacteria that convert remaining nitrates into nitrogen gas.
• Phosphorus Removal: Chemical precipitation (using alum or ferric chloride) is utilized, typically added prior to secondary clarification or filtration, to precipitate soluble phosphorus out of the liquid stream.

D. Disinfection

The filtered effluent passes through a Ultraviolet (UV) Disinfection system. High-intensity UV lamps disrupt the DNA of pathogenic organisms (bacteria, viruses), rendering them unable to reproduce. This method eliminates the need for chlorination and subsequent dechlorination, reducing chemical hazards and aquatic toxicity.

E. Solids Handling (Regional Facility)

The Parkway Biosolids Management Facility is the most complex operational unit on-site.

• Imported Sludge: Liquid sludge is trucked or piped in from Cox Creek and Annapolis WRFs.
• Thickening & Dewatering: The combined sludge (primary and WAS) is thickened using Gravity Belt Thickeners (GBT) and then dewatered using high-speed centrifuges to achieve a cake solid concentration suitable for thermal processing.
• Incineration: The facility utilizes a Fluidized Bed Incinerator (FBI). In this process, air is blown through a bed of hot sand, suspending it in a fluid-like state. Dewatered biosolids are injected into the bed, where they combust instantly. This reduces the volume of waste by over 90%, leaving only sterile ash.
• Emission Control: The incinerator is equipped with an advanced scrubbing system (venturi scrubbers, wet electrostatic precipitators) to meet strict air quality standards.

4. Infrastructure & Facilities

A. Physical Plant

The site is situated on approximately 40 acres adjacent to the Baltimore-Washington Parkway. The layout is bifurcated into the liquid treatment train (headworks, ditches, clarifiers, filters) and the large industrial complex housing the solids handling and incineration equipment.

B. Energy & Sustainability

Wastewater treatment is energy-intensive. Parkway incorporates Variable Frequency Drives (VFDs) on major pumps and aeration blowers to match energy use with hydraulic demand. The fluid bed incinerator utilizes autogenous combustion when possible, minimizing the use of auxiliary fuel (natural gas/oil) once the system reaches operating temperature.

C. Odor Control

Given the facility’s role in processing regional sludge and its proximity to residential areas and the Maryland City commercial district, odor control is paramount. The facility utilizes:

• Chemical Scrubbers: Multi-stage wet scrubbers treat foul air extracted from the headworks and sludge processing buildings.
• Biofilters: Organic media beds are used for polishing air streams with lower concentrations of hydrogen sulfide.

5. Recent Upgrades & Major Projects

Anne Arundel County has invested heavily in Parkway to maintain regulatory compliance and infrastructure reliability.

Biosolids Facility Rehabilitation (Ongoing/Recent)

Project Scope: The existing fluidized bed incinerator and associated solids handling equipment, originally commissioned in the early 1990s, have reached the end of their useful life. The county has undertaken various interim repairs to the centrifuges and scrubber systems to maintain operations.

Future Direction: The county is currently evaluating long-term strategies for regional biosolids management. This includes the potential construction of a new centralized solids processing facility (potentially moving towards thermal hydrolysis and anaerobic digestion for energy recovery) or a complete rehabilitation of the existing incineration train at Parkway.

Electrical Distribution Upgrades

Recent CIP (Capital Improvement Program) projects have focused on replacing aging switchgear and motor control centers (MCCs) to improve the electrical reliability of the plant, ensuring resilience against power fluctuations.

6. Regulatory Compliance & Environmental Performance

A. NPDES Permit Limits

Operating under NPDES Permit No. MD0021601, Parkway is classified as a Major Municipal discharger. Key parameters include:

• Total Nitrogen (TN): 3.0 mg/L (Annual Average) / 4.0 mg/L (Summer Monthly Avg)
• Total Phosphorus (TP): 0.3 mg/L (Annual Average)
• BOD5: 10 mg/L (Monthly Average)
• TSS: 10 mg/L (Monthly Average)
• Bacteria (E. Coli): 126 MPN/100 mL

B. Compliance History

Parkway WWTP generally maintains a strong compliance record regarding liquid effluent. However, the facility faces challenges related to the reliability of the aging incineration system. While liquid effluent consistently meets Bay Restoration goals, mechanical downtime in the solids facility occasionally necessitates the hauling of dewatered cake to landfills, increasing operational costs and trucking traffic.

7. Challenges & Future Planning

A. Aging Solids Infrastructure

The primary challenge facing the facility is the reliability of the regional biosolids equipment. The incinerator requires frequent maintenance, and obtaining parts for legacy systems is difficult. The Department of Public Works is actively planning a comprehensive Capital Improvement Project to address the county-wide biosolids strategy.

B. PFAS Regulation

Like all wastewater facilities, Parkway is monitoring emerging regulations regarding Per- and Polyfluoroalkyl Substances (PFAS). As a regional solids hub, the fate of PFAS through the incineration process and in the ash is a subject of technical evaluation.

C. Capacity Management

The western county area is a growth corridor. While the 7.5 MGD liquid capacity is currently sufficient, ongoing development around Fort Meade requires constant monitoring of flow projections to time future expansion needs appropriately.

8. Technical Specifications Summary

9. Frequently Asked Questions

Technical Questions

1. What is the liquid treatment capacity of the Parkway WWTP?
The plant has a design rated capacity of 7.5 MGD (Million Gallons per Day).

2. Does Parkway WWTP use anaerobic digestion?
No. Currently, the facility utilizes thermal processing (Fluidized Bed Incineration) for solids reduction, rather than anaerobic digestion.

3. What technology is used for denitrification?
The plant utilizes deep bed denitrification filters (sand filters with methanol addition) to polish nitrates from the secondary effluent.

4. Where does the incinerator ash go?
The sterile ash produced by the fluid bed incinerator is collected and hauled to a sanitary landfill for disposal or used as daily cover.

Public Interest Questions

5. Does the plant smell?
Wastewater treatment generates odors, particularly at the headworks and solids handling areas. Parkway employs chemical scrubbers and biofilters to capture and treat odorous air before it is released, though occasional odors may occur during maintenance events.

6. Where does the treated water go?
After being treated to high environmental standards and disinfected, the water is discharged into the Little Patuxent River.

7. Who operates the plant?
The plant is owned and operated by the Anne Arundel County Department of Public Works, Bureau of Utility Operations.