Madison Metropolitan Sewerage District Nine Springs Wastewater Treatment Plant

FACILITY BASIC INFORMATION

Plant Name: Nine Springs Wastewater Treatment Plant

Location: 1610 Moorland Road, Madison, Dane County, Wisconsin

Operating Authority: Madison Metropolitan Sewerage District (MMSD)

Design Capacity: 50 MGD (Average Daily Flow) / 106 MGD (Peak)

Current Average Flow: ~41 MGD

Population Served: ~429,000 residents

Service Area: 187 square miles (Madison, Middleton, Fitchburg, Verona, and 20+ other municipalities)

Receiving Water Body: Badfish Creek and Badger Mill Creek (part of Yahara River Watershed)

WPDES Permit Number: WI-0020192

Read more4D-Printed Smart Materials For Water Treatment

Year Commissioned: 1928 (Original construction)

1. INTRODUCTION

The Nine Springs Wastewater Treatment Plant is the cornerstone of water resource recovery for the Madison, Wisconsin metropolitan area. Operated by the Madison Metropolitan Sewerage District (MMSD), this facility is widely recognized in the engineering community for its pioneering adoption of biological nutrient removal (BNR) and resource recovery technologies. Treating an average of 41 million gallons per day (MGD) for over 400,000 residents, Nine Springs serves a complex service area comprising cities, villages, and sanitary districts across 187 square miles.

Distinguished by its aggressive pursuit of energy neutrality and nutrient harvesting, Nine Springs was the first facility in Wisconsin to implement the Ostara Pearl® nutrient recovery process, transforming problematic phosphorus struvite buildup into marketable fertilizer. With a capital infrastructure valued in excess of $500 million and continuous modernization efforts, the plant consistently meets stringent effluent limits to protect the sensitive Rock River watershed while serving as a model for sustainable municipal utility management in the Great Lakes region.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The District serves a rapidly growing region in Dane County. The collection system spans approximately 187 square miles, accepting flow from five cities (including Madison, Middleton, Fitchburg, Monona, and Verona), seven villages, and various town sanitary districts. The infrastructure includes over 145 miles of interceptor sewers and 18 regional pumping stations that convey wastewater to the Nine Springs campus. The service area is characterized by a mix of residential (high density and suburban), commercial, and light industrial users, with significant institutional flow from the University of Wisconsin-Madison.

B. Operational Capacity

Nine Springs is designed to handle an average daily flow of 50 MGD, with a hydraulic peak capacity exceeding 100 MGD during wet weather events. Historical trends indicate steady flow rates despite population growth, attributed to successful water conservation efforts and inflow/infiltration (I/I) reduction programs. Currently, the plant operates at approximately 82% of its average design hydraulic capacity, processing roughly 15 billion gallons of wastewater annually.

C. Discharge & Compliance

Treated effluent is discharged into two distinct receiving waters: Badfish Creek (via a 5-mile outfall pipeline) and Badger Mill Creek. Both streams eventually feed into the Yahara River and the Rock River system. The facility operates under a Wisconsin Pollutant Discharge Elimination System (WPDES) permit issued by the Wisconsin Department of Natural Resources (WDNR). The plant is subject to rigorous limitations, particularly regarding phosphorus and chlorides, due to the impaired status of the Rock River Basin. MMSD is a leader in the “Yahara WINS” adaptive management program, a watershed-based approach to phosphorus compliance.

3. TREATMENT PROCESS

The Nine Springs facility utilizes an advanced secondary treatment process with biological nutrient removal, ultraviolet disinfection, and tertiary resource recovery.

Read moreA Comparison Between Aerobic And Anaerobic Wastewater Treatment Technology

A. PRELIMINARY TREATMENT

Influent enters the headworks where it passes through mechanical bar screens to remove large debris, rags, and plastics. Following screening, the flow enters vortex grit removal systems where sand, gravel, and other heavy inorganic materials are settled out by centrifugal force. The grit is washed and dewatered before being disposed of in a landfill. The headworks area utilizes chemical scrubbers and biofilters for active odor control to mitigate impacts on neighboring communities.

B. PRIMARY TREATMENT

Wastewater flows into rectangular primary clarifiers. Here, flow velocity is reduced to allow heavier organic solids to settle as primary sludge, while grease and oils float to the surface for skimming. Approximately 50-60% of suspended solids and 30-35% of BOD are removed in this stage. Primary sludge is pumped directly to the anaerobic digesters, while the clarified effluent proceeds to the biological treatment stage.

C. SECONDARY TREATMENT (BNR)

The heart of the Nine Springs process is its Biological Nutrient Removal (BNR) system. The facility utilizes a modified University of Cape Town (UCT) process within its aeration basins. This configuration creates specific anaerobic, anoxic, and aerobic zones to cultivate distinct bacterial populations:

• Phosphorus Removal: Phosphate-accumulating organisms (PAOs) absorb phosphorus from the wastewater, incorporating it into the cell biomass.
• Nitrification/Denitrification: Ammonia is converted to nitrate (nitrification) and subsequently to nitrogen gas (denitrification), which is released into the atmosphere.

Air is supplied to the aerobic zones via fine-bubble diffusers powered by high-efficiency turbo blowers. Following aeration, the mixed liquor settles in circular final clarifiers. The clean water flows over weirs, while the settled biomass is returned as Return Activated Sludge (RAS) or harvested as Waste Activated Sludge (WAS).

D. TERTIARY NUTRIENT RECOVERY (Ostara Process)

MMSD employs the Ostara Pearl® process to treat centrate (liquid from dewatered biosolids) and WAS filtrate. This stream is high in phosphorus and ammonia. By adding magnesium chloride and controlling pH in a fluidized bed reactor, the facility precipitates these nutrients into high-purity struvite pellets. This recovers phosphorus as a slow-release commercial fertilizer (Crystal Green®) and prevents struvite scale from clogging plant piping.

E. DISINFECTION

The clarified effluent undergoes disinfection using high-intensity Ultraviolet (UV) light. The UV system disrupts the DNA of pathogenic bacteria and viruses, rendering them unable to reproduce. This chemical-free process eliminates the need for chlorination and subsequent dechlorination, reducing chemical hazards and protecting aquatic life in the receiving creeks from potential toxicity.

F. SOLIDS HANDLING & BIOSOLIDS

Solids handling at Nine Springs is a major operational focus:

• Thickening: Primary sludge and WAS are thickened using gravity belt thickeners.
• Anaerobic Digestion: Thickened sludge is processed in mesophilic anaerobic digesters. This process stabilizes the solids, reduces volume, and produces methane-rich biogas.
• Metrogro Program: The digested biosolids are stored and later applied to local agricultural land as a liquid fertilizer under the “Metrogro” program. This provides a sustainable nutrient loop for regional farmers.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The Nine Springs campus spans a substantial footprint south of the Madison Beltline. The site includes extensive maintenance shops, a state-of-the-art laboratory certified for permit compliance testing, and administration buildings. The architecture is functional industrial, with significant green space buffers to separate the plant from nearby recreational trails.

B. Energy Systems

MMSD is a leader in energy recovery. The anaerobic digesters produce biogas which fuels Combined Heat and Power (CHP) engines. These cogeneration units generate electricity to power plant operations and produce heat utilized to maintain digester temperatures and heat buildings.
The District also utilizes a geothermal heat exchange system using the treated plant effluent to heat and cool the operations building, further reducing the carbon footprint. These initiatives save the District hundreds of thousands of dollars annually in energy costs.

5. RECENT UPGRADES & MAJOR PROJECTS

MMSD consistently invests in Capital Improvement Projects (CIP) to maintain reliability and meet evolving regulations.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The WPDES permit sets strict limits on BOD, TSS, Ammonia Nitrogen, and Phosphorus. The most critical parameter for Nine Springs is Total Phosphorus (TP). Due to the TMDL (Total Maximum Daily Load) for the Rock River Basin, the plant faces extremely low phosphorus limits. Through the Yahara WINS adaptive management project, MMSD works with upstream agricultural partners to reduce phosphorus runoff, a strategy that is more cost-effective and environmentally beneficial than building massive filtration infrastructure at the plant.

B. Chloride Reduction

A major compliance challenge is Chloride (salt) levels in the effluent. Traditional wastewater treatment cannot remove dissolved salt. MMSD runs an aggressive “Wisconsin Salt Wise” source reduction program, encouraging water softener optimization and reduced road salt usage by municipalities to meet chronic toxicity limits.

7. OPERATIONAL EXCELLENCE

The facility is staffed by over 100 professionals, including certified wastewater operators, maintenance technicians, chemists, and engineers. The laboratory at Nine Springs is one of the most capable municipal labs in the state, conducting thousands of analyses annually for process control and regulatory reporting. The plant utilizes a robust SCADA system for real-time monitoring of dissolved oxygen, flow rates, and tank levels, allowing for precise automated control of the aeration blowers to minimize energy consumption.

8. CHALLENGES & FUTURE PLANNING

A. Salt and Chlorides

The persistence of chlorides in wastewater remains the most significant long-term regulatory challenge. If source reduction targets are not met, the District may eventually face capital costs exceeding $400 million to install reverse osmosis or similar desalination technologies.

B. PFAS Monitoring

Like many utilities, MMSD is actively monitoring for Per- and Polyfluoroalkyl Substances (PFAS). While the District does not produce PFAS, it receives them from ratepayers. The District is conducting source identification to prevent these “forever chemicals” from entering the sewer system and impacting biosolids management.

C. Infrastructure Resilience

Future planning includes the Northeast Interceptor Joint Grouting project and continued energy resiliency upgrades. The District’s 50-year master plan emphasizes resource recovery, envisioning the plant not just as waste treatment, but as a factory for clean water, energy, and nutrients.

9. TECHNICAL SPECIFICATIONS SUMMARY

10. FAQ SECTION

Technical Questions

1. Does Nine Springs perform Biological Nutrient Removal (BNR)?
Yes. The plant uses a modified University of Cape Town (UCT) process to biologically remove phosphorus and nitrogen, supplemented by the Ostara struvite recovery system for side-stream treatment.

2. What is the Metrogro program?
Metrogro is MMSD’s biosolids management program. Treated, stabilized biosolids are applied to local farmland as a liquid fertilizer, recycling nutrients back into the soil and reducing the need for synthetic fertilizers.

3. How does the facility handle peak wet weather flows?
The plant has a peak hydraulic capacity exceeding 100 MGD. Flow equalization and robust pumping strategies are used to manage surges from heavy rainfall and snowmelt.

4. What is the status of the Yahara WINS project?
Yahara WINS (Watershed Improvement Network) is fully operational. It is an adaptive management partnership where MMSD funds upstream agricultural conservation practices to reduce phosphorus runoff, complying with permit limits more sustainably than mechanical plant upgrades.

General Public Questions

5. Does the plant smell?
MMSD employs extensive odor control technologies, including biological towers and chemical scrubbers, particularly at the headworks and solids processing areas, to minimize odors for neighbors.

6. Can I tour the facility?
Yes, MMSD offers tours for schools, universities, and professional groups. Public tours are often arranged through their website or during specific open house events.

7. How is the plant powered?
While connected to the grid, the plant generates a significant portion of its own electricity using biogas produced in the anaerobic digesters to fuel onsite generators.