Great Lakes Water Authority Water Resource Recovery Facility Detroit

1. INTRODUCTION

The Great Lakes Water Authority (GLWA) Water Resource Recovery Facility (WRRF) is widely recognized as the largest single-site wastewater treatment facility in North America and one of the largest in the world. Located at the confluence of the Rouge and Detroit Rivers, this massive infrastructure asset serves nearly 30% of Michigan’s population. Originally commissioned in 1940 and previously operated by the Detroit Water and Sewerage Department (DWSD), the facility is now managed by GLWA, a regional authority established in 2016.

Treating an average daily flow of approximately 615 million gallons (MGD) with a wet-weather peak hydraulic capacity exceeding 1,700 MGD, the WRRF is a critical safeguard for the Great Lakes basin. The plant manages a vast combined sewer system, necessitating complex wet-weather treatment strategies. Following billions in capital investment, including the recent Biosolids Dryer Facility and Rouge River Outfall projects, the plant continues to evolve from a traditional treatment plant into a modern resource recovery center, prioritizing water quality in the Detroit River and Lake Erie.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The GLWA WRRF serves a massive 946-square-mile area encompassing the City of Detroit and 76 surrounding suburban communities. The service area is a dense mix of residential, heavy industrial (automotive and manufacturing), and commercial zones. The collection system is primarily a Combined Sewer System (CSS) in the older urban core (Detroit), meaning stormwater and sanitary sewage flow through the same pipes. This necessitates a collection network that includes extensive interceptors and regional Combined Sewer Overflow (CSO) retention treatment basins (RTBs) that feed into the main plant.

B. Operational Capacity

The facility’s capacity is bifurcated into dry and wet weather operations:

• Secondary Treatment Capacity: Rated for approximately 930 MGD.
• Primary Treatment Capacity: Rated for 1,700 MGD to handle massive storm surges.
• Average Daily Flow: Ranges between 600–650 MGD.

Flow trends have stabilized in recent years due to water conservation efforts and population shifts, though wet weather volatility remains a primary operational driver. The facility consistently operates at high capacity utilization relative to peer facilities due to the regional consolidation of wastewater flows.

C. Discharge & Compliance

The plant discharges treated effluent primarily into the Detroit River (Great Lakes connecting channel) via a deep-water outfall. During high-flow wet weather events, treated primary effluent may also be discharged to the Rouge River via the Rouge River Outfall (RROD). The facility operates under a stringent National Pollutant Discharge Elimination System (NPDES) permit issued by the Michigan Department of Environment, Great Lakes, and Energy (EGLE). Recent compliance efforts focus heavily on phosphorus reduction to combat harmful algal blooms in Lake Erie and total residual chlorine limits.

3. TREATMENT PROCESS

The GLWA WRRF utilizes a complex treatment train capable of handling rapid hydraulic loading fluctuations associated with combined sewer systems. The plant employs High Purity Oxygen (HPO) Activated Sludge for secondary treatment.

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A. PRELIMINARY TREATMENT

The headworks are designed to protect downstream equipment from debris carried by the combined sewers.

• Pumping: Two massive pump stations (PS-1 and PS-2) lift raw sewage from the deep interceptors to the surface level for gravity flow through the plant. These stations house some of the largest centrifugal pumps in the world.
• Screening: 22 mechanical bar screens remove large debris, rags, and timber.
• Grit Removal: 18 grit chambers utilize velocity control to settle out sand, gravel, and heavy inorganics to prevent abrasion on downstream pumps.

B. PRIMARY TREATMENT

Due to the scale of the facility, primary treatment is divided into multiple banks of clarifiers.

• Clarifiers: The facility operates 18 primary clarifiers, including massive circular tanks and rectangular configurations.
• Performance: Primary treatment removes approximately 50-60% of Total Suspended Solids (TSS) and 30-35% of Biochemical Oxygen Demand (BOD).
• Wet Weather Mode: During peak storm events exceeding secondary capacity, excess flow receives primary treatment and disinfection before discharge via the Rouge River Outfall (RROD).

C. SECONDARY TREATMENT

The core biological treatment utilizes a High Purity Oxygen (HPO) Activated Sludge process, selected for its ability to treat high-strength waste within a smaller physical footprint than conventional aeration.

• Oxygen Generation: On-site cryogenic oxygen plants generate pure oxygen, which is fed into covered aeration decks.
• Aeration Decks: The plant utilizes four massive aeration decks containing multiple trains. The enclosed reactors maximize oxygen transfer efficiency.
• Secondary Clarifiers: 25 secondary clarifiers (circular) separate the biological biomass from the treated water.
• RAS/WAS: Return Activated Sludge (RAS) is pumped back to the aeration decks, while Waste Activated Sludge (WAS) is sent to solids handling.

D. DISINFECTION

The plant utilizes chemical disinfection to manage pathogen levels before discharge.

• Chlorination: Sodium hypochlorite is added to the effluent. The facility has moved away from gaseous chlorine gas for safety reasons.
• Dechlorination: Sodium bisulfite is added prior to discharge to neutralize residual chlorine, protecting aquatic life in the Detroit River.
• RROD Disinfection: A dedicated facility handles disinfection for wet-weather primary effluent discharged to the Rouge River.

F. SOLIDS HANDLING

The WRRF is a regional hub for biosolids processing.

• Thickening: Gravity thickeners reduce the volume of primary sludge, while centrifuges or gravity belt thickeners manage waste activated sludge.
• Dewatering: A battery of belt filter presses and centrifuges dewater the sludge to produce “cake.”
• Biosolids Dryer Facility (BDFA): A major recent addition, this facility converts wastewater solids into dried, pelletized biosolids (Class A EQ status) suitable for use as fertilizer or fuel. This reduces reliance on incineration.
• Incineration: The plant retains multiple hearth incinerators (Complex I and II) to thermally reduce solids volume when necessary, though the strategic shift is toward drying and beneficial reuse.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site spans approximately 190 acres along the riverfront. It is a city-within-a-city, featuring its own internal road network, electrical substations, maintenance complexes, and a fully accredited laboratory. The architecture reflects its 1940s industrial heritage mixed with modern industrial processing structures.

B. Energy Systems

The WRRF is one of the largest electricity consumers in Detroit. Energy efficiency is a primary driver for upgrades. The plant utilizes heat recovery from incineration processes where applicable and has investigated co-generation opportunities. The shift from cryogenic oxygen generation (extremely energy-intensive) to newer aeration technologies is a long-term consideration for energy reduction.

C. Odor Control

Given the plant’s proximity to the Delray neighborhood, odor control is a critical operational parameter. The facility employs:

• Biofilters: Used extensively for treating air from headworks and primary clarifiers.
• Chemical Scrubbers: Deployed in sludge processing areas.
• Activated Carbon: Used for polishing air in critical zones.

5. RECENT UPGRADES & MAJOR PROJECTS

GLWA has executed a robust Capital Improvement Plan (CIP) focused on regulatory compliance, asset renewal, and modernization.

Upcoming Projects (2024-2027)

The 5-year CIP includes significant investment in:

• Central Offload Facility: To streamline the receiving of septage and high-strength waste.
• Aeration Deck Rehabilitation: Structural repairs and diffuser upgrades to improve oxygen transfer efficiency.
• Electrical Distribution Upgrades: Modernizing the 24kV and 13.2kV distribution systems to improve reliability.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit No. MI0022802. Key parameters include:

• Total Phosphorus (TP): Strict limits (typically 0.6 – 0.7 mg/L monthly average) to protect the Western Lake Erie Basin.
• E. coli: Seasonal limits requiring effective disinfection April through October.
• Total Residual Chlorine (TRC): Must be virtually non-detectable at discharge (typically <0.038 mg/L).
• Mercury: Stringent monitoring and minimization plans required.

B. Compliance History

Historically, the facility faced challenges leading to federal oversight. However, since the formation of GLWA and the lease of the facility, compliance has improved dramatically. The facility has largely met its Consent Judgment requirements regarding CSO control and secondary treatment performance. The transition to the BDFA has also improved air quality compliance regarding incinerator emissions.

7. OPERATIONAL EXCELLENCE

Staffing: The WRRF is staffed 24/7 by a team of over 400 professionals, including state-licensed operators (Michigan Class A certifications), skilled tradespeople (electricians, millwrights, instrument technicians), and laboratory scientists.

Technology: The facility utilizes a centralized SCADA system for process monitoring. GLWA has implemented the “WAM” (Work and Asset Management) system utilizing Oracle/Maximo platforms to transition from reactive to predictive maintenance.

Innovation: GLWA partners with universities (Wayne State, University of Michigan) for research on emerging contaminants (PFAS) and viral markers (COVID-19 wastewater surveillance).

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

Operating a plant with core structures built in 1940 presents constant rehabilitation needs. Concrete degradation in primary tanks and corrosion in the conveyance tunnels require continuous capital infusion.

B. Climate Resilience

The intense rain events of recent years (notably Summer 2021) highlighted the limits of the regional collection system. While the plant itself has immense capacity, the conveyance of water to the plant during “rain bombs” is a hydraulic challenge. Future planning focuses on system optimization and regional retention to flatten peak flows.

C. Nutrient Limits

With Lake Erie’s recurring algal blooms, regulatory pressure to lower phosphorus limits further is expected. The plant may need to investigate advanced tertiary filtration or enhanced biological phosphorus removal in future master plans.

9. COMMUNITY & REGIONAL IMPACT

The GLWA WRRF enables the economic viability of Southeast Michigan. By treating wastewater for the automotive industry and 2.8 million people, it is the silent engine of the regional economy. GLWA has established a Community Advisory Group (CAG) to improve transparency with local Detroit neighborhoods, particularly regarding construction impacts and odor management.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

• CSO Retention Treatment Basins (RTBs): GLWA operates several major RTBs (e.g., Conner Creek, Baby Creek, Oakwood) that store and partially treat combined sewage during storms before it reaches the WRRF.
• Interceptor System: The North Interceptor and Detroit River Interceptor are the massive arteries feeding the plant, ranging up to 16 feet in diameter.

12. FAQ SECTION

Technical Questions

1. What is the difference between primary and secondary capacity at GLWA WRRF?
The plant can provide full secondary biological treatment for up to 930 MGD. Flows exceeding this (up to 1,700 MGD) receive primary treatment and disinfection before discharge, which is compliant with the permit for wet weather events.

2. How does the plant handle PFAS?
GLWA focuses on industrial pretreatment programs (IPP) to stop PFAS at the source before it enters the sewers. The plant monitors for PFAS but standard wastewater treatment does not remove these chemicals.

3. Why does the plant use High Purity Oxygen (HPO)?
HPO was chosen in the 1970s renovations because it allows for a higher biomass concentration and faster treatment rates, enabling the plant to treat massive volumes in a smaller physical footprint than conventional aeration.

Public Interest Questions

4. Does the plant smell?
Wastewater treatment inherently generates odors, but GLWA has invested millions in biofilters and scrubbers. Odors are generally contained, though maintenance events or atmospheric inversions can occasionally cause local issues.

5. Can I tour the facility?
Tours are generally restricted to educational groups, industry professionals, and university classes due to safety and security protocols. Requests must be made through GLWA public affairs.

6. Is the water safe to drink after treatment?
The treated water (effluent) is safe for the river environment but is not potable (drinking) water. It flows into the Detroit River, where it dilutes and eventually moves toward Lake Erie.