Metropolitan District Commission Hartford Water Pollution Control Facility

FACILITY BASIC INFORMATION

Plant Name: Hartford Water Pollution Control Facility (HWPCF)

Location: 240 Brainard Road, Hartford, Hartford County, Connecticut

Operating Authority: The Metropolitan District Commission (MDC)

Design Capacity: 82 MGD (Average Daily Flow)

Peak Hydraulic Capacity: 200+ MGD (Wet Weather)

Population Served: ~400,000 residents

Service Area: Hartford, West Hartford, East Hartford, Newington, Wethersfield, Rocky Hill, Bloomfield, Windsor

Receiving Water Body: Connecticut River

NPDES Permit Number: CT0100251

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Year Commissioned: 1938 (Major expansions in 1970s, 2010s)

1. INTRODUCTION

The Hartford Water Pollution Control Facility (HWPCF) serves as the flagship wastewater treatment asset for The Metropolitan District (MDC) and stands as the largest wastewater treatment plant in the State of Connecticut. Treating an average of 60 to 80 million gallons daily (MGD) for a population of roughly 400,000 across the Greater Hartford region, this facility is the lynchpin of the Clean Water Project—a multi-billion dollar initiative designed to address combined sewer overflows (CSOs) and protect the Connecticut River ecosystem.

Originally commissioned in 1938 as a primary treatment plant and upgraded to secondary treatment in the 1970s, the HWPCF has evolved into a sophisticated 82-MGD secondary treatment facility with advanced solids handling and renewable energy capabilities. The plant is currently the focal point of massive infrastructure investment aimed at maximizing wet weather processing capacity and reducing nitrogen loading to the Long Island Sound watershed. With unique features such as a heat recovery facility that generates power from sludge incineration, the HWPCF represents a blend of historic infrastructure resilience and modern sustainability engineering.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The HWPCF accepts flows from the MDC’s core member towns, creating a regionalized treatment hub. The collection system serving the plant is a complex network comprising over 1,000 miles of sewers. Crucially, Hartford utilizes a Combined Sewer System (CSS) in older sections of the city, where stormwater and sanitary sewage share the same conveyance piping. This infrastructure characteristic dictates much of the plant’s operational strategy, necessitating massive peak flow management capabilities during precipitation events.

B. Operational Capacity

The facility is designed for an Average Daily Flow (ADF) of 82 MGD. However, due to the combined collection system, the plant must handle extreme hydraulic variability.

• Design Average Flow: 82 MGD
• Current Average Flow: ~60 MGD
• Peak Secondary Capacity: ~130 MGD
• Total Peak Wet Weather Capacity: ~200 MGD (utilizing auxiliary processing)

The facility operates at approximately 75% of its average design capacity during dry weather, allowing significant headroom for diurnal peaks and minor storm events.

C. Discharge & Compliance

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Treated effluent is discharged via a gravity outfall into the Connecticut River, the longest river in the New England region. The facility operates under a strict NPDES permit administered by the Connecticut Department of Energy and Environmental Protection (CT DEEP). Key compliance drivers include seasonal disinfection (May through September) to protect recreational users and stringent total nitrogen limits to mitigate hypoxia in Long Island Sound. The facility is a major participant in Connecticut’s Nitrogen Credit Exchange program.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

Raw influent enters the headworks where it undergoes rigorous physical separation to protect downstream equipment. The headworks facility utilizes multiple mechanically cleaned bar screens to remove rags, plastics, and large debris. Following screening, flow velocity is reduced in aerated grit chambers, allowing inorganic sands and gravel to settle while keeping organic matter in suspension. The collected screenings and grit are washed, dewatered, and disposed of off-site. Odor control at the headworks is managed via chemical scrubbers (typically sodium hypochlorite and sodium hydroxide) to neutralize hydrogen sulfide emissions.

B. PRIMARY TREATMENT

Flow proceeds to the primary sedimentation basins. The HWPCF utilizes rectangular primary clarifiers equipped with chain-and-flight sludge collectors. These tanks reduce flow velocity to allow settleable solids to drop to the hopper and floatable grease/scum to be skimmed from the surface.

• Configuration: Rectangular longitudinal tanks
• Removal Efficiency: Targets ~60% Total Suspended Solids (TSS) and ~30-35% Biochemical Oxygen Demand (BOD) reduction.
• Wet Weather Mode: During high flow events exceeding secondary capacity, a portion of primary effluent may be diverted to disinfection (depending on permit allowances for wet weather blending) or auxiliary storage to prevent biological washout.

C. SECONDARY TREATMENT

The core biological treatment utilizes a conventional activated sludge process.

• Aeration Basins: The plant employs a plug-flow aeration configuration. Air is supplied via fine-bubble diffusers to maximize oxygen transfer efficiency, powered by large centrifugal blowers. The biological environment is managed to oxidize carbonaceous BOD and convert ammonia-nitrogen to nitrate (nitrification) during warmer months.
• Secondary Clarifiers: Mixed liquor flows to secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is pumped back to the aeration basins to maintain the microbial population, while Waste Activated Sludge (WAS) is thickened and sent to solids handling.
• Process Control: Dissolved Oxygen (DO) probes and Mean Cell Residence Time (MCRT) are the primary control parameters used by operators to maintain effluent quality.

D. DISINFECTION

The HWPCF utilizes liquid chemical disinfection rather than UV, largely due to the scale of the facility and the turbidity variations during wet weather.

• Chlorination: Sodium Hypochlorite (15%) is injected into the chlorine contact tanks to inactivate pathogens (fecal coliform/E. coli).
• Dechlorination: To protect aquatic life in the Connecticut River from chlorine toxicity, Sodium Bisulfite is added at the end of the contact period to neutralize residual chlorine prior to discharge.
• Seasonality: Disinfection is generally required from May 1st to September 30th annually.

E. SOLIDS HANDLING & ENERGY RECOVERY

The Hartford facility is unique in its approach to solids processing, functioning as a regional solids processing center.

• Thickening: Primary sludge is gravity thickened; WAS is thickened using gravity belt thickeners or dissolved air flotation (DAF).
• Dewatering: Thickened sludge is conditioned with polymer and dewatered using high-solids centrifuges to create a sludge cake (approx. 20-25% solids).
• Incineration: The facility operates three multiple-hearth sewage sludge incinerators. These units thermally reduce the sludge volume by over 90%, leaving only sterile ash which is disposed of at landfills.
• Heat Recovery: A critical innovation at HWPCF is the Heat Recovery Facility. Waste heat from the incinerator exhaust stacks is captured to generate steam. This steam drives a turbine generator, producing electricity to offset a significant portion of the plant’s parasitic load, reducing operating costs and carbon footprint.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

Situated on Brainard Road, the facility occupies a substantial footprint adjacent to the Hartford-Brainard Airport and the Connecticut River. The site is protected by a dike system to prevent inundation during river flood stages, a critical resilience feature given the plant’s low elevation. The campus includes the main process buildings, the massive incinerator complex, administration/SCADA centers, and fleet maintenance garages.

B. Energy Systems

The HWPCF is a high-demand energy consumer, typical of plants its size. However, the MDC has implemented an aggressive energy management strategy.

• Heat Recovery Facility (HRF): Commissioned as part of recent upgrades, this system captures thermal energy from incineration to generate up to 1.8 MW of power.
• Efficiency: Variable Frequency Drives (VFDs) are standard on major pumps and blowers to match energy consumption with hydraulic load.

5. RECENT UPGRADES & MAJOR PROJECTS

The HWPCF has been the beneficiary of the “Clean Water Project,” a $2.4 billion district-wide program to address consent decrees and aging infrastructure.

Clean Water Project Phase I & II (2008-2022)

• Project Scope: Comprehensive upgrades to reduce Combined Sewer Overflows (CSOs) and improve nitrogen removal.
• South Hartford Conveyance Tunnel (SHCT): A massive 4-mile long, 18-foot diameter storage tunnel was constructed to intercept wastewater and store it during storms, preventing overflows. The tunnel terminates at the HWPCF, where a new pump station lifts flow for treatment.
• Wet Weather Capacity Expansion: Upgrades allowed the plant to increase peak treatment from roughly 130 MGD to nearly 200 MGD for limited durations to treat stored tunnel flow.
• Funding: Combination of Clean Water Fund (State of CT) grants/loans and municipal revenue bonds.

Heat Recovery Facility Project (Completed ~2014)

• Investment: Approx. $40 Million
• Technical Highlights: Installation of waste heat boilers on incinerator stacks and a steam turbine generator.
• Result: Generates renewable electricity, reducing the plant’s reliance on the grid and saving ratepayers millions in long-term energy costs.

Current/Upcoming Projects (2024-2027)

• Incinerator Emissions Upgrades: Ongoing work to meet new EPA sewage sludge incineration (SSI) Maximum Achievable Control Technology (MACT) standards.
• Electrical Infrastructure Modernization: Replacement of aging switchgear and substations to ensure reliability during grid failures.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

Operating under NPDES Permit No. CT0100251, the HWPCF faces strict limits:

• BOD/TSS: Must maintain 85% removal efficiency and meet concentration limits (typically 30 mg/L monthly average).
• Nitrogen: As a major contributor to the Long Island Sound watershed, the plant operates under the General Permit for Nitrogen Discharges. The MDC buys/sells credits based on annual performance against a dropping nitrogen target (Lbs/day).

B. Compliance History

The facility has a strong record of compliance regarding dry-weather effluent standards. The primary regulatory challenges have historically been related to wet-weather bypasses and CSOs, which are being systematically eliminated via the Consent Decree driven Clean Water Project.

7. OPERATIONAL EXCELLENCE

The HWPCF operates 24 hours a day, 365 days a year, staffed by a team of licensed wastewater operators (Class IV certification typically required for management), mechanics, electricians, and laboratory technicians. The on-site laboratory is state-certified, conducting daily analysis of BOD, TSS, pH, Chlorine Residual, and Fecal Coliform to ensure real-time process control. The facility utilizes a centralized SCADA system to monitor thousands of I/O points, allowing for automated pacing of chemical feeds and blower outputs based on flow and load.

8. CHALLENGES & FUTURE PLANNING

A. Current Challenges

• Combined Sewer Overflows (CSOs): Despite the tunnel, managing extreme weather events remains the primary hydraulic challenge.
• Nitrogen Removal Limits: As the state lowers the nitrogen cap to restore Long Island Sound, the plant must balance aeration for nitrification with anoxic zones for denitrification within existing tankage volumes.
• Sludge Disposal Costs: While incineration reduces volume, maintaining aging incinerators and meeting air quality standards is increasingly capital intensive.

B. Future Planning

The MDC’s Integrated Plan focuses on the continued separation of sewers where feasible and the optimization of the tunnel system. Future capital projects will likely focus on “side-stream” treatment of nitrogen (treating the nitrogen-rich liquid from dewatering separately) to reduce the main plant load.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

The HWPCF does not operate in isolation. It is the terminus for the South Hartford Conveyance Tunnel, a major 4-mile storage asset. Additionally, the HWPCF accepts sludge from three smaller MDC satellite facilities: the East Hartford, Rocky Hill, and Windsor Water Pollution Control Facilities, serving as the regional solids processing hub for the entire district.

12. FAQ SECTION

Technical Questions

1. What is the hydraulic retention time (HRT) of the facility?
While variable based on flow, the typical HRT for the secondary process is approximately 4-6 hours during average flow conditions.

2. How does the plant handle nitrogen removal?
The plant utilizes biological nutrient removal (BNR) strategies by creating anoxic zones within the aeration basins to promote denitrification, converting nitrate to nitrogen gas.

3. Is the MDC Hartford facility under a Consent Decree?
Yes. The MDC is operating under a federal Consent Decree and a State Consent Order to address Combined Sewer Overflows (CSOs) and Sanitary Sewer Overflows (SSOs), driving the $2.4B Clean Water Project.

4. Does the facility generate its own power?
Yes. The Heat Recovery Facility captures heat from the sludge incinerators to generate approximately 40% of the plant’s electricity needs.

Public Interest Questions

5. How many towns does the Hartford WPCF serve?
The facility serves the MDC’s 8 member towns: Hartford, East Hartford, West Hartford, Wethersfield, Rocky Hill, Newington, Bloomfield, and Windsor.

6. What happens to the “sludge” removed from the water?
It is thickened, dewatered to remove moisture, and then incinerated on-site at high temperatures. The remaining ash is safely disposed of at a landfill.

7. Is the water discharged into the river safe?
Yes. The effluent is highly treated and disinfected (during summer months) to meet strict state and federal standards ensuring it is safe for the Connecticut River’s aquatic life and recreational use.