Wisconsin Wastewater Treatment Plants

Introduction

Wisconsin’s wastewater infrastructure is defined by a unique combination of high-density urban treatment needs and significant industrial loading from the state’s robust food and paper processing sectors. The state operates under the regulatory oversight of the Wisconsin Department of Natural Resources (WDNR), which enforces some of the strictest phosphorus discharge limits in the United States. This regulatory environment drives substantial capital investment in nutrient removal technologies and watershed adaptive management strategies.

Currently, Wisconsin manages over 600 municipal wastewater treatment facilities ranging from massive regional reclamation districts to small lagoon systems. The state serves a population of nearly 6 million, protecting vital water resources including Lake Michigan, Lake Superior, and the Mississippi River basin. The infrastructure landscape is currently shifting from simple compliance to resource recovery, with major utilities like Milwaukee and Green Bay leading the nation in energy neutrality and biosolids reuse.

With the influx of federal funding through the Infrastructure Investment and Jobs Act (IIJA) and a robust Clean Water Fund Program (CWFP), Wisconsin is seeing a surge in project activity. Consulting engineers and vendors will find opportunities concentrated in aging infrastructure replacement, advanced phosphorus removal, PFAS mitigation, and energy optimization projects.

Wisconsin is profiled here as part of the site’s wider directory of US wastewater treatment plants, and it rewards comparative study on two counts. It set the national precedent for water quality trading and adaptive management as an alternative to end-of-pipe treatment, and it has produced the country’s longest-running resource recovery programs, with Milorganite in continuous production since the 1920s.

Recent Developments & Projects

In the last 36 months, Wisconsin’s wastewater sector has focused heavily on nutrient management and resiliency. The implementation of stricter phosphorus limits (NR 217) has forced hundreds of facilities to upgrade filtration systems or enter into Water Quality Trading partnerships. Notably, the state is a pioneer in “Adaptive Management,” allowing utilities to fund non-point source pollution controls (like agricultural buffers) rather than building gray infrastructure, creating unique consulting opportunities.

Major upgrades have also been driven by climate resilience. Following historic flooding events, facilities in the Driftless Area and along the Lake Michigan shoreline are hardening infrastructure. The Milwaukee Metropolitan Sewerage District (MMSD) continues to expand its world-renowned Deep Tunnel system to mitigate combined sewer overflows (CSOs).

Technologically, there is a distinct trend toward energy neutrality. Green Bay’s NEW Water recently completed its R2E2 project, a landmark achievement in solids incineration and energy generation. Similarly, smaller municipalities are increasingly adopting biological phosphorus removal and tertiary filtration to meet discharge permits as low as 0.075 mg/L.

Top 20 Largest Treatment Plants in Wisconsin

The following list ranks the largest wastewater treatment facilities in Wisconsin based on design flow capacity (MGD). These facilities represent the primary procurement hubs for large-scale equipment and engineering services.

*Note: South Shore and Jones Island capacities vary based on wet weather configuration; combined peak capacity exceeds 600 MGD.

Detailed Profiles: Top 5 Largest Plants

1. South Shore Water Reclamation Facility

• Location: Oak Creek, Milwaukee County, WI
• Design Capacity: 300 MGD (Peak)
• Average Flow: ~100 MGD
• Operating Authority: Milwaukee Metropolitan Sewerage District (MMSD)
• Receiving Water: Lake Michigan
• Treatment Process: Primary clarification, activated sludge, anaerobic digestion, disinfection.
• Infrastructure: Functions as the primary wet-weather handling facility for the district. Significant biosolids processing capacity via anaerobic digestion producing biogas for on-site power.
• Recent Upgrades: Ongoing aeration system rehabilitation and major improvements to primary clarification to handle wet weather flows.

2. Jones Island Water Reclamation Facility

• Location: Milwaukee, Milwaukee County, WI
• Design Capacity: 300 MGD (Peak)
• Operating Authority: Milwaukee Metropolitan Sewerage District (MMSD)
• Notable Feature: Home to the production of Milorganite®, a commercially sold organic nitrogen fertilizer made from heat-dried microbes.
• Treatment Process: Advanced secondary treatment using activated sludge, unique heavy solids loading for fertilizer production.
• Compliance: Famous for high-level pathogen kill requirements to produce Class A biosolids.
• Link: View MMSD Plant Profile

3. Nine Springs Wastewater Treatment Plant

• Location: Madison, Dane County, WI
• Design Capacity: 56 MGD
• Average Flow: 42 MGD
• Operating Authority: Madison Metropolitan Sewerage District
• Receiving Water: Badfish Creek / Rock River
• Treatment Process: Advanced biological nutrient removal (BNR), UV disinfection.
• Innovation: Features the Ostara Nutrient Recovery process, which harvests phosphorus and nitrogen to create crystal fertilizer (struvite), preventing struvite scaling in pipes and reducing phosphorus discharge.
• Energy: extensive biogas utilization program.

4. Green Bay Facility (NEW Water)

• Location: Green Bay, Brown County, WI
• Design Capacity: 48 MGD
• Operating Authority: NEW Water (Green Bay Metropolitan Sewerage District)
• Receiving Water: Fox River / Green Bay (Lake Michigan)
• Recent Upgrades: The R2E2 (Resource Recovery and Electrical Energy) project. This state-of-the-art facility uses fluid bed incineration and steam turbines to generate electricity, moving the plant toward energy independence.
• Service Area: Handles significant industrial load from local paper mills and dairy processing.

5. Racine Wastewater Utility

• Location: Racine, Racine County, WI
• Design Capacity: 36 MGD
• Average Flow: 18 MGD
• Operating Authority: City of Racine
• Receiving Water: Lake Michigan
• Treatment Process: Activated sludge with anaerobic digestion.
• Infrastructure: Critical facility for protecting Lake Michigan beaches. Recent focus has been on UV disinfection upgrades and wet weather flow management to prevent sewer backups.

Facility Profiles & Plant Records

Wisconsin’s treated flow concentrates in four metropolitan sewerage districts plus a handful of independent city utilities along the Lake Michigan shoreline. The records below cover the individual facilities documented in detail on this site, organized by operating district.

MMSD Jones Island Water Reclamation Facility

The Milwaukee Metropolitan Sewerage District Jones Island Water Reclamation Facility occupies a constrained harbor site at the mouth of the Milwaukee River and carries a peak design capacity near 300 MGD. Its defining feature is the Milorganite operation, the oldest continuously produced heat-dried biosolids fertilizer in the United States and a commercial product rather than a disposal pathway. That distinction changes the engineering problem substantially: solids are managed to a fertilizer specification, with pathogen kill, nutrient content, and product consistency all becoming process control variables rather than merely permit conditions. Drying, granulation, and product handling equipment at Jones Island therefore sit under quality requirements more typical of a manufacturing plant than a POTW. Engineers evaluating heat drying and Class A biosolids marketing anywhere in the country generally start with the Jones Island precedent, since it has close to a century of operating history behind it.

MMSD South Shore Water Reclamation Facility, Oak Creek

The Milwaukee Metropolitan Sewerage District South Shore Water Reclamation Facility Oak Creek matches Jones Island at roughly 300 MGD peak capacity but averages closer to 100 MGD, and that gap is the point: South Shore is the district’s primary wet weather facility, sized to absorb what the Deep Tunnel dewaters after a storm rather than to run at design flow routinely. It uses conventional primary clarification and activated sludge with anaerobic digestion producing biogas for on-site power, a different solids philosophy than Jones Island’s drying operation. Current work centers on aeration system rehabilitation and primary clarification improvements aimed specifically at wet weather performance. Reading the two MMSD plants together shows a district running two deliberately different solids strategies, which hedges against changes in fertilizer markets and energy prices alike. Engineers should not evaluate either plant without understanding the tunnel that feeds them.

MMSD Combined Sewer Overflow Control and the Deep Tunnel

The record covering the Milwaukee Metropolitan Sewerage District Combined Sewer Overflow Treatment Facility addresses the district’s overflow control infrastructure, the Deep Tunnel system that has become one of the most studied CSO programs in North America. The tunnel stores combined flow during storms in deep rock beneath the metropolitan area and dewaters it to Jones Island and South Shore once capacity returns, which is why the two plants carry peak-to-average ratios of roughly three to one. MMSD reports capture rates above 98 percent of combined flow in a typical year, a figure other tunnel programs benchmark against. The system’s more recent evolution has been to pair the gray infrastructure with a large green infrastructure and floodplain renaturalization program rather than to build additional storage volume. That combination is the district’s most transferable lesson: tunnel capacity has diminishing returns, and watershed-scale peak reduction is often the cheaper next increment.

Madison MSD Nine Springs Wastewater Treatment Plant

The Madison Metropolitan Sewerage District Nine Springs Wastewater Treatment Plant treats 56 MGD design against roughly 42 MGD average for about 380,000 people, discharging not to the nearby Yahara lakes but through constructed effluent conveyance to Badfish Creek and the Rock River. That routing decision, made decades ago to protect the Madison lake chain, is one of the more consequential effluent management choices in the Midwest and still shapes the district’s permit position today. The plant runs advanced biological nutrient removal with UV disinfection and operates an Ostara struvite recovery process that harvests phosphorus and nitrogen into a marketable crystalline fertilizer while eliminating struvite scaling in downstream piping. Current capital work targets the aging secondary treatment trains, with roughly $85 million committed to aeration tank rehabilitation, blower replacement, and flow distribution. For engineers, Nine Springs is the state’s reference site for nutrient recovery integrated into a conventional BNR plant.

NEW Water De Pere Facility, Green Bay

The Green Bay Metropolitan Sewerage District De Pere Wastewater Treatment Plant is the district’s second facility alongside the main Green Bay plant, and together they handle an unusual industrial load from the Fox Valley paper mills and dairy processors. High-strength industrial influent changes the design basis considerably: BOD and nutrient loading per gallon run well above municipal norms, which affects aeration sizing, solids production, and digester or incinerator capacity throughout the system. The district’s R2E2 program, a roughly $170 million investment in fluid bed incineration and energy recovery, was driven substantially by that solids volume and now supplies close to half the plant’s electrical demand. NEW Water is also a leading participant in Wisconsin’s adaptive management framework, addressing Fox River phosphorus through watershed work rather than end-of-pipe treatment alone. Engineers working industrial-influenced systems should treat Green Bay as the state’s clearest case study.

Racine Wastewater Treatment Plant

The Racine Wastewater Treatment Plant handles 36 MGD design against roughly 18 MGD average flow, discharging to Lake Michigan just south of the Milwaukee metro. Its operating priority is beach water quality: Racine’s shoreline beaches have been the subject of sustained monitoring and public attention, which puts disinfection reliability and wet weather overflow prevention under scrutiny that a comparable inland plant would not face. Recent work has concentrated on UV disinfection upgrades and wet weather flow management to prevent basement backups and shoreline releases. The two-to-one design-to-average ratio gives the plant more wet weather headroom than most mid-size facilities, which is a deliberate response to the same combined and infiltrated flow issues that drove Milwaukee’s tunnel. For mid-size Lake Michigan dischargers, Racine is the closest peer comparison in the state.

Phosphorus Compliance and Adaptive Management in Practice

Wisconsin’s NR 217 phosphorus rule produced the country’s most developed alternative compliance framework, and understanding how utilities have actually used it matters more than knowing the numeric limits.

Madison and the Effluent Management Precedent

The broader record for the Madison Metropolitan Sewerage District Sewage Treatment Plant covers the district’s long history of managing where its effluent goes as a compliance strategy in its own right, from the original decision to convey treated water away from the Yahara lakes through to its current adaptive management work in the Yahara watershed. Madison has been among the most active participants in watershed-scale phosphorus reduction, funding agricultural practice changes and manure management upstream rather than pursuing incremental treatment below limits already near the technical floor. The arithmetic favors it: removing the next increment of phosphorus at the plant costs far more per pound than removing it from agricultural runoff in the same basin. The tradeoff is that watershed results are harder to verify and slower to appear than an effluent number, which is why WDNR requires monitoring commitments and interim milestones. Utilities considering adaptive management elsewhere should study Madison’s verification framework as closely as its economics.

When Adaptive Management Works and When It Does Not

Adaptive management is not universally available or advisable. It works where a facility’s watershed carries a substantial non-point phosphorus load, where the utility can secure durable agreements with landowners, and where the compliance schedule allows years for watershed results to materialize. It works poorly where the discharger is the dominant load in its receiving water, where the watershed is heavily urban with little agricultural runoff to address, or where the utility lacks staff to manage what amounts to a long-term land management program. Water quality trading is the middle option, purchasing verified reductions rather than running the program directly. Engineers advising a client through this decision should model both the treatment capital path and the watershed path over twenty years, including the cost of the monitoring obligation, because the comparison frequently reverses once verification costs are counted.

Plants with Approved Budgets & Expansion Projects

Wisconsin’s current capital improvement landscape is dominated by phosphorus compliance, aging infrastructure rehabilitation, and energy optimization. The following projects represent confirmed activity derived from CIPs, bond issuances, and SRF Intended Use Plans.

A. Major Projects Under Construction (2024-2026)

Madison MSD – Liquid Processing Improvements (Phase 3 & 4)

• Location: Madison, WI
• Total Budget: ~$85 Million
• Project Scope: Comprehensive rehabilitation of the secondary treatment trains, including aeration tank concrete repairs, blower replacement, and flow distribution improvements.
• Funding: Clean Water Fund Program (SRF) Loans, District Capital Funds.
• Timeline: Construction active through 2026.
• Drivers: Aging infrastructure (50+ years old) and energy efficiency.
• Key Tech: High-efficiency turbo blowers, fine bubble diffusion.

Waukesha Clean Water Plant – Return Flow Capital Project

• Location: Waukesha, WI
• Total Budget: ~$25 Million (Component of larger Water Supply Program)
• Project Scope: As part of Waukesha’s switch to Lake Michigan water, the WWTP must construct return flow pumping infrastructure to return treated effluent to the Root River (flowing back to the Great Lakes) to meet the Great Lakes Compact requirements.
• Timeline: Completion expected late 2024/early 2025.
• Drivers: Regulatory compliance (Great Lakes Compact).
• Expected Benefits: Ensures 100% flow return to the Lake Michigan basin.

Heart of the Valley MSD – Interceptor Rehabilitation

• Location: Kaukauna, WI
• Total Budget: ~$18 Million
• Project Scope: Rehabilitation of major interceptor sewers using CIPP (Cured-in-Place Pipe) technology to reduce inflow and infiltration (I/I) and corrosion.
• Status: Construction active.
• Key Contractors: Visu-Sewer (Primary contractor for segments).

B. Projects in Design/Planning Phase (2025-2027)

Sheboygan Regional WWTP – Solids Handling Improvements

• Estimated Budget: $15 – $20 Million
• Funding: Pending SRF Loan application.
• Scope: Upgrade of anaerobic digesters and dewatering equipment to improve biogas production and reduce disposal volume.
• Anticipated Start: 2025.

Milwaukee MSD – Watercourse & Flood Management

• Estimated Budget: $40+ Million (Annual recurring capital)
• Scope: Removal of concrete channels and renaturalization of waterways (Kinnickinnic River) to improve flood retention and reduce peak flows into the treatment plants.
• Status: Ongoing multi-year phases.

C. Recently Completed Major Projects (2022-2024)

NEW Water (Green Bay) – Solid Waste Management (R2E2)

• Investment: $170 Million (Final phases optimized recently)
• Key Improvements: Installation of fluid bed incineration and energy recovery loops.
• Results: The plant now generates nearly 50% of its own electricity demand and has significantly reduced greenhouse gas emissions.

Stevens Point WWTP – Nutrient Removal Upgrade

• Investment: $18 Million
• Key Improvements: Installation of new final clarifiers and chemical feed systems for low-level phosphorus compliance.
• Completion: 2023.

Summary Statistics

• Total Active Capital Investment: >$450 Million currently programmed in major WI utilities.
• Primary Project Drivers:
  • Phosphorus Compliance (NR 217): 40% of projects.
  • Aging Infrastructure/Replacement: 35% of projects.
  • Energy/Biogas: 15% of projects.

• Funding Source Breakdown: Wisconsin Clean Water Fund Program (CWFP) provides subsidized interest loans for approximately 70% of municipal projects.

Regulatory & Compliance Landscape

Wisconsin is widely considered to have one of the most rigorous regulatory environments for wastewater in the Midwest, particularly regarding nutrients. Consulting engineers must be intimately familiar with the following:

• Phosphorus Rule (NR 217): Wisconsin establishes site-specific phosphorus criteria. Many plants face limits as low as 0.075 mg/L or even 0.04 mg/L. This drives the market for tertiary filtration (disk filters, cloth media) and chemical polishing.
• Adaptive Management & Water Quality Trading: The WDNR allows facilities to offset discharge by funding non-point source reductions (e.g., paying farmers for cover crops) within the same watershed. This is a vital “soft infrastructure” market in Wisconsin.
• PFAS (Forever Chemicals): The WDNR is aggressively sampling for PFAS. While final effluent limits are evolving, many utilities are actively conducting source tracking and pilot testing GAC (Granular Activated Carbon) and Ion Exchange solutions.
• Chlorides: Communities utilizing water softeners are facing strict chloride limits at the WWTP, leading to “Lime Softening” initiatives at water plants or source reduction campaigns.

Why Chlorides Are a Wisconsin-Specific Problem

Chloride limits deserve more attention than they typically receive outside the state, because Wisconsin’s hard groundwater makes residential water softening near-universal in many communities and there is no practical treatment for chloride at a conventional POTW. Ion exchange softener regeneration discharges brine to the sewer, and once it arrives at the plant it passes straight through to the receiving water. That makes chloride the rare parameter where the only viable compliance path runs through source reduction rather than treatment: softener optimization programs, high-efficiency unit rebates, or centralized softening at the drinking water plant. Utilities facing a chloride limit should budget for a public engagement and rebate program rather than a capital project, which is an unfamiliar posture for most engineering departments. Winter road salt compounds the problem in urban watersheds and is outside utility control entirely.

Preparing for PFAS Without a Final Number

WDNR sampling has advanced further than final effluent limits have, which leaves utilities planning against a moving target. The prudent posture most Wisconsin utilities have adopted is source tracking first: identifying industrial contributors through pretreatment monitoring is far cheaper than treating the whole plant flow and is the only intervention that reduces mass loading rather than shifting it. Biosolids are the larger exposure, since land application is the dominant disposal route for most of the state and any restriction there would reshape solids economics quickly. Facilities running incineration, including Green Bay and Jones Island’s drying operation, sit in a different position than land-applying plants. Engineers scoping biosolids projects in Wisconsin should build an explicit contingency for a change in the end-use pathway.

Technology Trends in Wisconsin

Due to the specific industrial and regulatory pressures in the state, several technologies are seeing higher-than-average adoption rates:

• Resource Recovery: Following the lead of MMSD (Milorganite) and Madison (Struvite), mid-sized plants are exploring biosolids drying and fertilizer production.
• Advanced Filtration: Cloth media disk filters are the standard choice for meeting strict TSS and Phosphorus limits in tertiary treatment steps.
• Biogas Utilization: Combined Heat and Power (CHP) systems are increasingly common in plants >5 MGD to offset rising electrical costs.
• Real-Time Control (RTC): Use of ammonia and nitrate sensors to automate aeration blowers, reducing energy consumption in the harsh Wisconsin winters.

Resources for Engineers & Operators

• Wisconsin DNR – Wastewater Program: The primary regulatory authority. Visit WDNR.
• WWOA (Wisconsin Wastewater Operators’ Association): The main networking body for plant staff, hosting regional meetings and an annual conference.
• CSWEA (Central States Water Environment Association): The regional WEF member association covering Wisconsin, Illinois, and Minnesota—vital for consulting engineers.
• Clean Water Fund Program (CWFP): The state’s SRF program administering low-interest loans for infrastructure.

Frequently Asked Questions

What is the largest wastewater treatment plant in Wisconsin?

The Jones Island and South Shore Water Reclamation Facilities in Milwaukee are the largest, both operated by MMSD. They have a combined peak design capacity exceeding 600 MGD.

What are the phosphorus limits for Wisconsin treatment plants?

Limits vary by watershed, but many new permits require effluent phosphorus concentrations between 0.075 mg/L and 0.1 mg/L, which is significantly lower than the national average.

How many wastewater treatment plants are in Wisconsin?

There are approximately 620 regulated wastewater facilities in Wisconsin, ranging from large mechanical plants to smaller stabilization lagoon systems.

What is “Adaptive Management” in Wisconsin wastewater compliance?

Adaptive Management is a regulatory compliance option where a treatment plant funds phosphorus reduction in the watershed (agriculture/urban runoff) to improve overall water quality, rather than building expensive filtration at the plant.

Is there funding available for WWTP upgrades in Wisconsin?

Yes. The Clean Water Fund Program (CWFP) provides subsidized loans. Additionally, IIJA (Bipartisan Infrastructure Law) funds are flowing through the state for emerging contaminants (PFAS) and energy efficiency projects.

Which engineering firms are active in Wisconsin wastewater?

Major firms with significant market share in Wisconsin include Donohue & Associates, Strand Associates, AECOM, Jacobs, Ruekert & Mielke, and MSA Professional Services.

What is Milorganite and why does it matter?

Milorganite is the heat-dried biosolids fertilizer produced at MMSD’s Jones Island facility, in continuous commercial production since the 1920s and the longest-running program of its kind in the United States. It matters because it treats biosolids as a manufactured product rather than a disposal problem: pathogen kill, nutrient content, and granule consistency become process control targets, and the revenue offsets solids handling costs. Utilities evaluating heat drying anywhere in the country benchmark against it.

Why does Madison discharge to Badfish Creek instead of the local lakes?

The district routes treated effluent away from the Yahara lake chain through constructed conveyance to Badfish Creek and the Rock River, a decision made decades ago to protect the lakes from nutrient loading. It remains one of the more consequential effluent management choices in the Midwest and still shapes the district’s permit position, since the receiving water conditions that govern its limits are those of the Rock River basin rather than the lakes it sits beside.

How does the Milwaukee Deep Tunnel affect the treatment plants?

Directly, and it explains their sizing. The tunnel stores combined flow during storms and dewaters it to Jones Island and South Shore once capacity returns, which is why both plants carry peak-to-average ratios near three to one. South Shore in particular functions as the district’s wet weather facility, averaging around 100 MGD against a 300 MGD peak design. MMSD reports capture above 98 percent of combined flow in a typical year.

Related Topics

Wisconsin’s nutrient policy and Great Lakes obligations are best benchmarked against its regional peers. Across Lake Michigan, Michigan wastewater treatment plants share the same receiving water and comparable large-district overflow control programs, making Michigan the closest basin peer. To the west, Minnesota wastewater treatment plants face similar cold-climate nutrient removal challenges and operate under Mississippi headwaters phosphorus policy that parallels Wisconsin’s own. To the south, Illinois wastewater treatment plants include the Chicago tunnel and reservoir system that Milwaukee’s Deep Tunnel is most often compared against.

Conclusion

Wisconsin is a technically demanding but well-supported market. The state pairs some of the country’s strictest nutrient limits with an unusually flexible compliance framework and a Clean Water Fund Program that subsidizes roughly 70 percent of municipal projects, which is why more than $450 million is currently programmed across the major utilities despite a relatively modest population base. The state has also been willing to let utilities solve problems outside the fence line, which is rarer than it should be.

For engineers, operators, and suppliers, the productive first question is whether a client’s problem is a treatment problem at all. Phosphorus below the technical floor, chloride from residential softeners, and PFAS from industrial contributors each have a cheaper answer upstream of the plant than inside it, and Wisconsin’s regulatory framework permits pursuing those answers. The facility and compliance records linked throughout this guide are the starting point for that analysis.