Milwaukee Metropolitan Sewerage District South Shore Water Reclamation Facility Oak Creek

1. INTRODUCTION

The South Shore Water Reclamation Facility (SSWRF) is one of two major wastewater treatment plants serving the Greater Milwaukee area, operating as a critical component of the Milwaukee Metropolitan Sewerage District’s (MMSD) infrastructure. Located on the shores of Lake Michigan in Oak Creek, Wisconsin, this facility works in tandem with the Jones Island Water Reclamation Facility to serve over 1.1 million residents and 28 municipalities.

Commissioned in 1968 and substantially expanded in subsequent decades, South Shore handles the majority of the wastewater generated in the southern portion of the 411-square-mile service area. While Jones Island is famous for its production of Milorganite® fertilizer, South Shore is the workhorse for hydraulic capacity and energy sustainability. The facility is distinguished by its integration of renewable energy sources, specifically the utilization of landfill gas for power generation, and its pivotal role in protecting the water quality of Lake Michigan.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The SSWRF serves the southern portion of the MMSD service area, which encompasses approximately 411 square miles. This includes the City of Oak Creek, Franklin, Hales Corners, Greenfield, and portions of Milwaukee and West Allis. The collection system feeding South Shore is distinct from the older combined sewer area served primarily by Jones Island; the South Shore service area consists largely of separated sanitary sewers, though inflow and infiltration (I/I) remain significant factors during wet weather events.

B. Operational Capacity

The facility is designed to treat an average daily flow of approximately 85 to 100 million gallons per day (MGD). However, its role in the region’s wet-weather management strategy is paramount. The plant has a peak hydraulic capacity of 300 MGD for full secondary treatment. During extreme wet weather events, the facility coordinates with the Inline Storage System (the “Deep Tunnel”) to manage surges and prevent sanitary sewer overflows (SSOs).

C. Discharge & Compliance

Treated effluent is discharged into Lake Michigan via a submerged outfall located approximately 10,000 feet offshore. Operating under the Wisconsin Pollutant Discharge Elimination System (WPDES), the plant faces stringent limits on phosphorus, BOD, and suspended solids given the sensitive nature of the Great Lakes watershed. The facility consistently achieves compliance rates exceeding 99%, utilizing chemical precipitation strategies to meet Wisconsin’s rigorous phosphorus standards.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

Raw wastewater enters the facility through the High Level and Low Level Interceptors. The headworks facility utilizes mechanically cleaned bar screens to remove large debris, followed by grit removal tanks. The grit removal system is designed to protect downstream pumps and biosolids infrastructure from abrasion. Extracted grit and screenings are washed, compacted, and transported to landfills for disposal.

B. PRIMARY TREATMENT

The primary treatment complex consists of 16 circular primary clarifiers. These tanks reduce the velocity of the wastewater, allowing settleable solids to drop to the bottom as primary sludge, while grease and oils float to the surface for skimming.
Performance: Typical removal efficiencies in this stage are 50-60% for Total Suspended Solids (TSS) and 30-35% for Biochemical Oxygen Demand (BOD).

C. SECONDARY TREATMENT

South Shore utilizes a conventional activated sludge process to remove dissolved organic matter.

• Aeration Basins: The plant operates 24 aeration basins equipped with fine-bubble and coarse-bubble diffusion systems. The biology is maintained to optimize carbon oxidation and nitrification. Ferric chloride is added at this stage (or prior) to precipitate phosphorus, a critical requirement for Lake Michigan discharge.
• Secondary Clarification: Mixed liquor flows to 24 secondary clarifiers where biological floc settles out. A portion of the settled solids is returned to the aeration basins as Return Activated Sludge (RAS), while the excess is removed as Waste Activated Sludge (WAS).

D. DISINFECTION

Before discharge, the effluent undergoes disinfection using sodium hypochlorite (chlorination) to eliminate pathogenic organisms. To protect aquatic life in Lake Michigan, the water is subsequently dechlorinated using sodium bisulfite before entering the outfall. This chemical balance is monitored continuously to ensure residual chlorine limits are never exceeded.

E. SOLIDS HANDLING & INTERPLANT SYNERGY

Solids handling at South Shore represents a unique regional engineering strategy:

• Thickening: Primary sludge and WAS are thickened separately. Dissolved Air Flotation (DAF) units have historically been used for WAS thickening.
• Anaerobic Digestion: Thickened sludge is processed in anaerobic digesters. These digesters stabilize the solids and produce methane-rich biogas.
• Interplant Solids Pipeline (ISP): Unlike many facilities that dewater and dispose of all solids on-site, South Shore pumps the majority of its liquid digested sludge and some raw sludge via the Interplant Solids Pipeline to the Jones Island Water Reclamation Facility. There, it is combined with Jones Island sludge to produce Milorganite®, a commercially sold slow-release fertilizer.
• Redundancy: South Shore retains dewatering capabilities (centrifuges and plate-and-frame presses) and cake storage facilities to handle solids if the ISP is offline or during peak production periods.

4. INFRASTRUCTURE & FACILITIES

A. Energy Systems & Biogas

MMSD has set aggressive goals for energy independence, and South Shore is a centerpiece of this strategy. The facility utilizes a sophisticated biogas system:

• Digester Gas: Methane produced during anaerobic digestion is captured and used to power dual-fuel engine generators.
• Landfill Gas Interconnection: A 1.6-mile pipeline connects the SSWRF to the nearby Emerald Park Landfill. Landfill gas is piped to South Shore to fuel engine generators, providing electricity and heat for the treatment process and buildings. This setup significantly reduces the plant’s reliance on the commercial power grid.

B. Odor Control

Given its proximity to residential areas and parks in Oak Creek, odor control is a priority. The facility utilizes chemical scrubbers and biofilters, particularly at the headworks and sludge handling areas, to mitigate hydrogen sulfide and other odorous compounds.

5. RECENT UPGRADES & MAJOR PROJECTS

Aeration System Improvements

Status: Ongoing / Recent Completion
Driver: Energy Efficiency

MMSD has invested heavily in optimizing the aeration system, which is typically the largest energy consumer in a wastewater plant. Projects have included the replacement of aging centrifugal blowers with high-efficiency turbo blowers and the retrofitting of aeration basins with advanced fine-bubble membrane diffusers. These upgrades allow for more precise dissolved oxygen (DO) control, reducing electrical consumption per pound of BOD removed.

South Shore Capacity Improvements

Status: Planning/Design
MMSD continuously evaluates hydraulic constraints. Recent planning focuses on eliminating bottlenecks in the gallery piping and return activated sludge (RAS) pumping systems to ensure the plant can sustain its 300 MGD peak capacity during increasingly intense climate-change-driven storm events.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under a WPDES permit issued by the Wisconsin Department of Natural Resources (WDNR). Key parameters include:

• Phosphorus: Wisconsin has some of the strictest phosphorus limits in the nation to prevent algae blooms in Lake Michigan. The plant targets effluent phosphorus concentrations often below 0.6 mg/L, utilizing ferric chloride dosing.
• BOD & TSS: Standard secondary treatment limits (30 mg/L monthly average), though the plant typically performs well below 10 mg/L.
• Fecal Coliform: Seasonal disinfection requirements to protect recreational water use.

B. Compliance History

South Shore has maintained an exemplary compliance record. The facility has received Platinum and Gold Peak Performance Awards from the National Association of Clean Water Agencies (NACWA), recognizing years of 100% compliance with NPDES permit limits.

7. OPERATIONAL EXCELLENCE

A. Public-Private Partnership

Since 2008, the daily operations of the SSWRF have been managed by Veolia Water Milwaukee under a contract with MMSD. This partnership is one of the largest of its kind in the United States. While MMSD retains ownership and financing of capital improvements, Veolia provides staffing, operations expertise, and routine maintenance. This model has been credited with generating significant operational savings and performance incentives.

B. Energy Independence

MMSD’s vision is to achieve 100% energy independence across its facilities. South Shore contributes to this via its engine generators fueled by both digester gas and landfill gas. Heat recovery loops capture thermal energy from the engines to heat the digesters and buildings, closing the energy loop.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical/Professional Questions:

1. How does South Shore handle biosolids compared to Jones Island?
While Jones Island produces Milorganite® fertilizer, South Shore primarily digests sludge for energy recovery and then pumps the remaining liquid solids to Jones Island via the Interplant Solids Pipeline for processing into Milorganite. South Shore retains dewatering capabilities for redundancy.

2. What is the peak hydraulic capacity of the facility?
The facility is rated for a peak hydraulic capacity of 300 MGD. Flows exceeding this during extreme events may be diverted to the Deep Tunnel (Inline Storage System) to prevent overflows.

3. Does the facility utilize renewable energy?
Yes. SSWRF is a leader in renewable energy, utilizing methane from on-site anaerobic digestion and a dedicated pipeline supplying gas from the nearby Emerald Park Landfill to power engine generators.

Public Interest Questions:

4. Who operates the plant?
The plant is owned by the Milwaukee Metropolitan Sewerage District (MMSD), a regional government agency, but daily operations are contracted to Veolia Water Milwaukee.

5. Is the treated water safe for Lake Michigan?
Yes. The effluent meets or exceeds all state and federal requirements for discharge into Lake Michigan, including strict limits on bacteria, phosphorus, and suspended solids.