City Of Waterbury Water Pollution Control Plant

1. INTRODUCTION

The Waterbury Water Pollution Control Plant (WPCP) stands as a critical environmental safeguard for the Naugatuck River Valley and a cornerstone of Connecticut’s regional wastewater infrastructure. Treating an average of 16 million gallons daily (MGD) with a design capacity of 27 MGD, the facility serves the dense urban population of Waterbury and surrounding communities including Watertown and Wolcott.

Operated through a strategic public-private partnership between the City of Waterbury and Jacobs (formerly CH2M Hill), the plant is unique in its dual function: it operates as a sophisticated wastewater treatment facility and a regional merchant sludge processing center. The facility houses one of the few remaining fluidized bed incinerators in the region, processing biosolids for nearly 30 Connecticut municipalities. Following a significant capital investment in 2018 to install advanced CoMag® tertiary treatment, the Waterbury WPCP has achieved compliance with some of the strictest phosphorus discharge limits in the Northeast, playing a pivotal role in the ecological restoration of the historic Naugatuck River.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Waterbury WPCP provides sanitary sewer service to a highly urbanized and industrial service area. The collection system encompasses the City of Waterbury and receives bulk flow from the Watertown Fire District and the Town of Wolcott. The collection system is complex, consisting of approximately 300 miles of sanitary and combined sewers. As one of Connecticut’s older industrial cities, Waterbury manages a Combined Sewer Overflow (CSO) system, which presents significant hydraulic challenges during precipitation events. The facility also serves as a regional hub for sludge disposal, accepting liquid and cake sludge from approximately 25-30 other wastewater treatment plants across the state.

B. Operational Capacity

The facility is designed for an average daily flow of 27.0 MGD. Historically, flows average between 15 and 18 MGD during dry weather, but the hydraulic peaking factor is significant due to the combined collection system. During heavy storm events, influent rates can surge dramatically, requiring robust wet weather management protocols. The plant manages these fluctuations through a series of wet weather bypass/treatment strategies and CSO regulators located throughout the collection system.

C. Discharge & Compliance

The treated effluent is discharged into the Naugatuck River, a water body that has transitioned from an “open sewer” in the mid-20th century to a recovering cold-water fishery today. The NPDES permit (CT0100625) enforces stringent limits, particularly regarding heavy metals (legacy of the brass industry) and nutrients. The facility has maintained an exemplary compliance record following recent upgrades, specifically targeting seasonal phosphorus limits required to mitigate eutrophication in the receiving waters.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

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Raw influent enters the headworks where it undergoes aggressive screening and grit removal to protect downstream equipment. The system utilizes mechanically cleaned bar screens to remove large debris, rags, and plastics. Following screening, flow velocity is reduced in aerated grit chambers, allowing inorganic sands and gravel to settle while keeping organic matter in suspension. The grit is washed and dewatered prior to disposal. This stage also includes septage receiving stations for trucked waste, which is integrated into the headworks flow.

B. PRIMARY TREATMENT

Flow proceeds to rectangular primary settling tanks. Here, the hydraulic velocity is minimized to facilitate the gravity settling of settleable solids (primary sludge) and the flotation of fats, oils, and grease (FOG). Scraper mechanisms collect the bottom sludge and surface scum. The primary sludge is pumped to the solids handling train for thickening and incineration. Primary treatment typically removes 50-60% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD).

C. SECONDARY TREATMENT

The biological treatment utilizes a conventional Activated Sludge process. Settled wastewater flows into aeration basins where it is mixed with Return Activated Sludge (RAS) to form mixed liquor. Mechanical surface aerators or diffused air systems provide the necessary oxygen for microorganisms to metabolize dissolved organic matter. Following aeration, the mixed liquor flows to secondary clarifiers where the biological solids settle out. A portion of these solids is returned to the aeration tanks (RAS), while the excess is removed as Waste Activated Sludge (WAS) for processing.

D. TERTIARY TREATMENT (Phosphorus Removal)

To meet the Connecticut Department of Energy and Environmental Protection (CT DEEP) low-level phosphorus limits (seasonal limits often averaging 0.2 mg/L or lower), the plant employs the CoMag® System. This high-rate clarification technology utilizes magnetite (Fe3O4) as a ballasting agent. Coagulants (alum or ferric chloride) and polymer are added to precipitate phosphorus and flocculate solids. The heavy magnetite is impregnated into the floc, vastly increasing the settling rate compared to conventional gravity settling. The magnetite is then recovered via magnetic drums and reused in the system, while the chemical sludge is sent for processing. This system allows the plant to handle high hydraulic variations while maintaining strict effluent quality.

E. DISINFECTION

Disinfection is achieved using liquid sodium hypochlorite (chlorination) to eliminate pathogenic organisms. The flow passes through chlorine contact tanks designed to provide sufficient detention time at peak flows. Prior to discharge into the Naugatuck River, the effluent undergoes dechlorination using sodium bisulfite to prevent aquatic toxicity, ensuring the residual chlorine is neutralized.

F. SOLIDS HANDLING & INCINERATION

Solids handling is a distinctive feature of the Waterbury WPCP. The facility operates as a Merchant Sludge Incinerator.

• Thickening/Dewatering: Primary and secondary sludges are thickened (gravity belt thickeners or rotary drums) and dewatered using centrifuges to increase solids content/dryness to reduce fuel consumption during incineration.
• Incineration: The core of the solids process is a Fluidized Bed Incinerator. This technology uses a heated bed of sand suspended by an upward flow of air to burn sludge rapidly and efficiently at temperatures exceeding 1,400°F.
• Emissions Control: The incinerator is equipped with advanced air pollution control systems, including venturi scrubbers and wet electrostatic precipitators (WESP), to meet strict EPA Maximum Achievable Control Technology (MACT) standards for sewage sludge incineration (SSI).
• Ash Disposal: The resulting inert ash is collected and hauled to a sanitary landfill.

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G. PROCESS CONTROL

The facility utilizes a centralized SCADA (Supervisory Control and Data Acquisition) system allowing operators to monitor tank levels, dissolved oxygen, chemical feed rates, and equipment status in real-time. The partnership with Jacobs brings advanced asset management software and predictive maintenance protocols to the operation.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site is situated along the western bank of the Naugatuck River, encompassing several acres of industrial-zoned land. Key structures include the Administration Building (housing SCADA control and certified laboratories), the Solids Handling Building (containing the incinerator and centrifuges), and the massive tankage required for primary and secondary treatment.

B. Energy Systems

Wastewater treatment is energy-intensive. The Waterbury facility has implemented Variable Frequency Drives (VFDs) on major pumps and blowers to match energy usage with biological demand. The fluidized bed incinerator also incorporates heat recovery systems to preheat combustion air, improving thermal efficiency and reducing the consumption of auxiliary fuel (natural gas/oil).

C. Odor Control

Given the high volume of merchant sludge import, odor control is critical. The facility utilizes negative pressure containment in sludge off-loading areas and the sludge processing building. Foul air is routed through chemical scrubbers (typically multi-stage packed towers using acid/bleach/caustic solutions) or activated carbon filters to neutralize hydrogen sulfide and organic odors before release.

5. RECENT UPGRADES & MAJOR PROJECTS

Phosphorus Reduction Project (2016-2018)

• Project Budget: ~$35-40 Million
• Project Drivers: Compliance with CT DEEP’s Interim Phosphorus Strategy requiring reduction of nutrient loading to the Naugatuck River.
• Technical Highlights: Installation of the CoMag® ballasted settling system. This technology was chosen for its small footprint and ability to handle wet-weather flows without washing out solids.
• Results: The plant now consistently achieves effluent phosphorus concentrations below 0.2 mg/L during the season (April-October), significantly reducing algae blooms in the receiving watershed.

Incinerator Emissions Upgrade (Recent)

• Scope: Upgrades to the air pollution control train to comply with new federal Sewage Sludge Incineration (SSI) MACT standards.
• Technology: Installation of mercury control modules and high-efficiency wet electrostatic precipitators.
• Outcome: Ensures the continued viability of the plant as a regional solids handling revenue source for the City of Waterbury while protecting regional air quality.

6. REGULATORY COMPLIANCE

The facility operates under NPDES Permit No. CT0100625. Key parameters monitored include:

• BOD5 & TSS: 30 mg/L (Monthly Average), with 85% removal efficiency required.
• Total Phosphorus: Seasonal limits dependent on river flow, utilizing mass-loading caps (lbs/day).
• Nitrogen: Monitoring required under the General Permit for Nitrogen Discharges (Long Island Sound TMDL).
• Metals: Copper and Zinc monitoring due to local industrial history.
• Toxicity: Whole Effluent Toxicity (WET) testing using Daphnia pulex and Pimephales promelas.

7. CHALLENGES & FUTURE PLANNING

A. CSO Management

Like many New England cities, Waterbury faces the challenge of Combined Sewer Overflows. The Long Term Control Plan (LTCP) requires ongoing investments to separate sewers where feasible and increase capture rates, reducing untreated discharges during storm events.

B. Aging Infrastructure

While the process technology (CoMag) is new, the civil structures (concrete tanks) and underground conveyance systems are aging. A robust Capital Improvement Plan (CIP) focuses on rehabilitating concrete, replacing end-of-life pumps, and upgrading electrical distribution systems.

C. Emerging Contaminants

PFAS (Per- and polyfluoroalkyl substances) regulation represents a looming challenge for all facilities with incinerators and effluent discharge. The plant is monitoring regulatory developments closely to determine future treatment requirements for both water and air emissions.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical Questions

Q: What is the specific phosphorus limit for the Waterbury WPCP?
A: Limits are seasonal (April 1 – Oct 31) and are generally mass-based (lbs/day), roughly translating to concentrations below 0.2 mg/L depending on river flow tiers established by CT DEEP.

Q: Does the facility generate energy from the incinerator?
A: The facility utilizes waste heat recovery to preheat combustion air, reducing fuel costs, but it does not currently generate electricity (steam turbine) from the incineration process.

Q: How does CoMag work compared to traditional sand filtration?
A: CoMag uses magnetite (heavy iron ore) to weigh down chemical floc, allowing it to settle much faster than conventional floc. This allows for tertiary treatment in a much smaller footprint than sand filters and provides resilience against hydraulic surges.

Public Interest Questions

Q: Who operates the plant?
A: While the City of Waterbury owns the assets, the daily operations and maintenance are contracted to Jacobs (formerly CH2M), a global engineering and operations firm.

Q: What is the “steam” seen rising from the plant?
A: The plume visible from the facility is primarily water vapor from the scrubber system that cleans the incinerator exhaust. It is thoroughly treated to meet air quality standards before release.

Q: Does the plant smell?
A: As a wastewater plant handling regional sludge, odors can occur. However, the plant employs advanced chemical scrubbers and carbon filters to capture and treat odorous air from the sludge handling buildings to minimize impact on the neighborhood.