Green Bay Metropolitan Sewerage District De Pere Wastewater Treatment Plant

1. INTRODUCTION

The NEW Water De Pere Facility acts as a critical southern anchor for the Green Bay Metropolitan Sewerage District’s wastewater infrastructure. While smaller than the district’s main Green Bay Facility at the mouth of the Fox River, the De Pere plant is a sophisticated hydraulic and biological treatment hub serving the rapidly growing southern municipalities of the metro area, including the City of De Pere and the Village of Ashwaubenon.

Operating under the brand name “NEW Water,” the facility plays a pivotal role in the remediation of the Fox River and the ecological restoration of the Green Bay watershed. The plant utilizes advanced biological phosphorus removal and seasonal UV disinfection to meet some of the strictest effluent limits in the Great Lakes region. Unlike standalone facilities, the De Pere plant operates as an integrated component of a regional system, where liquid treatment occurs on-site, but solids are thickened and pumped via dual force mains to the main Green Bay Facility for incineration and energy recovery.

2. FACILITY OVERVIEW

A. Service Area & Coverage

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NEW Water serves a total area of approximately 285 square miles. The De Pere Facility specifically handles flows from the southern zone of this service area. The collection system feeding the De Pere plant includes a complex network of interceptors that navigate under the Fox River, requiring high-reliability lift stations and siphon systems. The service area is characterized by a mix of residential suburban growth, light industrial parks, and commercial corridors associated with the Green Bay Packers stadium district (Ashwaubenon).

B. Operational Capacity

The De Pere Facility is designed to handle an average daily flow of approximately 24 MGD, though it currently operates closer to an 8-10 MGD average. The plant is engineered to manage significant wet-weather peaking factors common in Wisconsin’s freeze-thaw climate cycles. While the hydraulic capacity is sufficient for current loads, the facility operates under a “manage and convey” strategy for solids, utilizing inter-plant force mains to consolidate biosolids processing at the larger Green Bay Facility.

C. Discharge & Compliance

Effluent is discharged directly into the Fox River, a major tributary to Green Bay and Lake Michigan. The facility operates under strict Total Maximum Daily Load (TMDL) requirements for Total Suspended Solids (TSS) and Phosphorus. The Fox River is a designated Area of Concern (AOC), making the effluent quality from the De Pere outfall a matter of high regulatory scrutiny. The facility consistently achieves compliance through a combination of biological treatment and watershed adaptive management strategies.

3. TREATMENT PROCESS

The De Pere Facility employs a conventional activated sludge process modified for biological nutrient removal, followed by seasonal disinfection.

A. Preliminary Treatment

Raw wastewater enters the facility through the main interceptor. Preliminary treatment consists of:

• Coarse Screening: Mechanically cleaned bar screens remove large debris, rags, and plastics to protect downstream pumps.
• Grit Removal: Vortex grit chambers utilize centrifugal force to separate inorganic heavy solids (sand, gravel, coffee grounds) from the organic waste stream. Grit is washed, dewatered, and disposed of in landfills.
• Flow Measurement: Parshall flumes monitor influent flow rates for process control pacing.

B. Primary Treatment

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Following headworks, flow enters rectangular primary clarifiers. These tanks reduce the velocity of the wastewater, allowing settleable organic 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 suspended solids and 30% of BOD. The primary sludge is pumped to the thickening complex before transfer to the Green Bay Facility.

C. Secondary Treatment (Activated Sludge)

The biological heart of the plant utilizes an Activated Sludge system configured for biological phosphorus removal (Bio-P).

• Anaerobic Selectors: The influent is mixed with Return Activated Sludge (RAS) in anaerobic zones to promote the growth of Phosphate Accumulating Organisms (PAOs). This biological stressor conditions the bacteria to uptake luxury amounts of phosphorus in the subsequent aerobic zones.
• Aeration Basins: Fine bubble diffusion provides oxygen to the mixed liquor. Here, microorganisms consume dissolved organic matter (BOD) and convert ammonia to nitrate (nitrification).
• Secondary Clarifiers: The mixed liquor flows to circular secondary clarifiers where the biomass settles out. Clear supernatant flows over the weirs to disinfection.
• RAS/WAS Pumping: Settled biomass is returned to the front of the aeration tanks (RAS). Excess biomass (Waste Activated Sludge or WAS) is removed to control the Mean Cell Residence Time (MCRT) and pumped to the solids handling system.

D. Disinfection

The facility utilizes Ultraviolet (UV) Disinfection rather than chlorination. This eliminates the need for hazardous chemical storage (chlorine gas or hypochlorite) and the subsequent need for dechlorination. Disinfection is required seasonally, typically from May 1 to October 31, to protect recreational users of the Fox River. The UV channels are equipped with high-intensity lamps that disrupt the DNA of pathogenic organisms, rendering them unable to reproduce.

E. Solids Handling (Inter-plant Transfer)

A unique engineering feature of the De Pere Facility is that it does not treat solids to Class A or B standards on-site. Instead:

• Primary sludge and WAS are co-thickened using gravity belt thickeners or rotary drum thickeners.
• The thickened liquid sludge is pumped via dual force mains approximately 8 miles north to the Green Bay Facility.
• At the Green Bay Facility, these solids enter the R2E2 (Resource Recovery and Electrical Energy) system, where they undergo anaerobic digestion and thermal processing (incineration) with energy recovery.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site is situated on the west bank of the Fox River in an urbanized area of De Pere. The compact footprint requires efficient use of vertical space and shared tank walls. The architecture is utilitarian brick, typical of mid-20th-century municipal infrastructure, with modern additions housing the UV and screening facilities.

B. Odor Control

Given the facility’s proximity to residential neighborhoods and the St. Norbert College campus, odor control is paramount. The facility utilizes biological odor control towers (biofilters) and chemical scrubbers at the headworks and primary sludge handling areas to treat hydrogen sulfide and mercaptans before air is released.

C. Energy Systems

While the De Pere facility consumes grid power for aeration and pumping, it contributes to the district’s energy neutrality goals by sending high-energy organic sludge to the Green Bay Facility’s R2E2 system, which generates electricity via methane combustion and heat recovery.

5. RECENT UPGRADES & MAJOR PROJECTS

Interceptor Rehabilitation and Cleaning (Ongoing)

The district maintains an extensive network of interceptors. Recent capital projects have focused on cleaning and lining the large-diameter interceptors feeding the De Pere plant to reduce inflow and infiltration (I/I). Reducing I/I is critical for maintaining concentration levels necessary for efficient biological treatment and preventing hydraulic washouts during storm events.

R2E2 System (District-Wide Impact) – 2018

Cost: ~$170 Million
While physically located at the Green Bay Facility, this project fundamentally changed De Pere’s operations. The project replaced aging incineration technology with a new solids processing train including fluid bed incineration and energy generation. For De Pere, this ensured a long-term, sustainable outlet for all biosolids produced at the southern plant.

Silver Creek Adaptive Management Pilot

NEW Water implemented a pilot project in the Silver Creek watershed (west of Green Bay) to test Adaptive Management strategies. This project successfully demonstrated that working with agriculture to reduce runoff is a more cost-effective method of meeting phosphorus limits than building massive tertiary filtration improvements at the De Pere or Green Bay plants. This success has informed the district’s long-term compliance strategy.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Phosphorus and the Fox River TMDL

The defining regulatory challenge for the De Pere Facility is Phosphorus. The Lower Fox River TMDL sets extremely low limits for phosphorus discharge to combat algae blooms and hypoxic zones in Green Bay (Lake Michigan). The facility uses Bio-P to achieve low effluent concentrations, but the ultimate compliance strategy relies on Adaptive Management.

Under Adaptive Management, NEW Water partners with upstream agricultural landowners to implement Best Management Practices (BMPs) like cover crops and buffer strips. These measures prevent phosphorus from entering the watershed, earning the district compliance credits that are often cheaper and environmentally superior to adding chemical filtration at the end of the pipe.

B. Compliance Record

NEW Water consistently receives recognition from the National Association of Clean Water Agencies (NACWA) for Peak Performance. The De Pere facility maintains a robust record of compliance with WPDES permit limits for BOD, TSS, and Ammonia.

7. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

Like many Midwestern utilities, NEW Water faces the challenge of replacing assets from the 1970s expansion era. The De Pere facility requires ongoing investment in concrete rehabilitation, pump replacement, and electrical switchgear modernization to maintain reliability.

B. PFAS and Emerging Contaminants

Wisconsin is at the forefront of regulating PFAS (Per- and polyfluoroalkyl substances). While wastewater plants are not creators of PFAS, they are receivers. NEW Water is actively monitoring influent and effluent for PFAS compounds and working with industrial users on source reduction, as traditional treatment technologies at De Pere do not remove these “forever chemicals.”

8. COMMUNITY & REGIONAL IMPACT

The De Pere Facility allows for the continued economic expansion of the southern Green Bay metro area. By effectively treating wastewater, the facility protects the recreational value of the Fox River, a world-class walleye fishery and popular boating destination. NEW Water also engages heavily in public education, hosting open houses and STEM events to educate the public on the “One Water” concept.

9. TECHNICAL SPECIFICATIONS SUMMARY

10. FAQ SECTION

Technical Questions

1. Why does the De Pere Facility pump solids to the Green Bay Facility?
Consolidating solids processing at one location allows for economies of scale. The Green Bay Facility houses the R2E2 incineration complex, which recovers energy from the solids. It is more efficient to pump thickened sludge than to operate two separate digestion and incineration facilities.

2. Does the De Pere plant use chemical phosphorus removal?
The primary method is Biological Phosphorus Removal (Bio-P). However, the facility has the capability to add metal salts (like Ferric Chloride or Alum) as a backup or polishing step if biological upset occurs or if limits tighten beyond biological capabilities.

3. How does the facility handle peak wet weather flows?
The collection system includes storage and relief points, but the plant itself is designed with robust hydraulic capacity. The activated sludge basins can operate in different modes (such as contact stabilization or step feed) during high flows to prevent solids washout.

Public Interest Questions

4. Does the De Pere plant smell?
Wastewater treatment inherently generates odors, but the De Pere facility employs advanced biofilters and chemical scrubbers to capture and treat foul air. Most residents rarely notice odors unless there is a specific maintenance issue or atmospheric inversion.

5. Is the water released into the Fox River clean?
Yes. The treated water (effluent) meets stringent state and federal standards. While it is not potable (drinking quality), it is generally cleaner than the river water itself regarding suspended solids and organic matter.

6. What happens if the power goes out?
The facility is equipped with backup diesel generators capable of running critical pumping and treatment systems to prevent sewage backups or untreated discharge during power outages.