City Of Flint Wastewater Treatment Plant

FACILITY BASIC INFORMATION

• Plant Name: City of Flint Water Pollution Control Facilities (WPCF)
• Location: G-4652 Beecher Road, Flint, Genesee County, Michigan
• Operating Authority: City of Flint Department of Public Works / Utilities Division
• Design Capacity: 50 MGD (Dry Weather)
• Current Average Flow: ~18-22 MGD
• Population Served: Approx. 80,000 (City) plus regional contract communities
• Service Area: City of Flint and portions of Genesee County
• Receiving Water Body: Flint River
• NPDES Permit Number: MI0022730
• Year Commissioned: Original plant 1927; Major expansions 1960s, 1970s, 2010s

TARGET AUDIENCE

• Municipal consulting engineers evaluating aging infrastructure rehabilitation

Read more10 Surprising Benefits of Upgrading Your Aeration Tank System
• Wastewater treatment plant operators and managers
• Regulatory compliance officers (EGLE/EPA)
• Equipment vendors specializing in cold-weather treatment and incineration
• Environmental engineering students and researchers

1. INTRODUCTION

The City of Flint Water Pollution Control Facilities (WPCF) serves as the primary environmental safeguard for the Flint River watershed, treating an average of 20 million gallons of wastewater daily. Located on the western edge of the city, this tertiary treatment facility represents a critical component of Southeast Michigan’s hydrology. While the city has faced well-documented challenges regarding its potable water infrastructure, the WPCF has simultaneously navigated a complex trajectory of aging assets, declining user bases, and recent, massive capital investment.

With a design hydraulic capacity of 50 MGD and peak wet weather handling capabilities exceeding 100 MGD, the plant utilizes conventional activated sludge processes coupled with tertiary filtration and fluidized bed incineration for solids handling. Following the infrastructure crises of the mid-2010s, the WPCF became the focus of significant revitalization efforts, leveraging millions in State Revolving Funds (SRF) and federal grants to modernize headworks, aeration systems, and biosolids management. Today, it stands as a case study in stabilizing and upgrading legacy infrastructure under strict regulatory scrutiny.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The WPCF serves the City of Flint and maintains service agreements with surrounding Genesee County municipalities. The collection system is a hybrid of separate sanitary sewers and a legacy Combined Sewer Overflow (CSO) system. The service area is characterized by an urban core surrounded by suburban density. The collection network includes extensive interceptors and significant retention infrastructure designed to mitigate CSO events into the Flint River.

B. Operational Capacity

The facility is designed for a dry weather flow of 50 MGD. However, due to population shifts and industrial decline, current average daily flows hover between 18 and 22 MGD. This surplus hydraulic capacity provides operational flexibility but presents challenges in maintaining optimal biological loading ratios. During wet weather events, the plant’s hydraulic throughput is augmented by the Northwest Transfer Station and on-site retention basins, managing peak instantaneous flows to prevent untreated discharges.

Read more4D-Printed Smart Materials For Water Treatment

C. Discharge & Compliance

Treated effluent is discharged directly into the Flint River, a tributary of the Saginaw River which flows into Saginaw Bay (Lake Huron). Consequently, the plant operates under a strict National Pollutant Discharge Elimination System (NPDES) permit administered by the Michigan Department of Environment, Great Lakes, and Energy (EGLE). Stringent limits are placed on Phosphorus (due to Great Lakes nutrient concerns), E. coli, and Suspended Solids. The facility has historically utilized mixing zones but is moving toward higher-quality effluent standards through tertiary treatment upgrades.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

Raw wastewater enters the facility via the main interceptor. The headworks facility, which has undergone recent rehabilitation, utilizes mechanically cleaned coarse bar screens to remove large debris. Following screening, flow passes through aerated grit chambers where inorganic solids (sand, gravel) settle out. These systems are critical for protecting downstream pumping equipment and the integrity of the biosolids incinerator. Odor control at the headworks utilizes chemical scrubbers to mitigate neighborhood impact.

B. PRIMARY TREATMENT

The plant utilizes rectangular primary settling tanks equipped with chain-and-flight sludge collectors. In this stage, approximately 60-70% of Total Suspended Solids (TSS) and 30-40% of Biological Oxygen Demand (BOD) are removed. Primary sludge is pumped to gravity thickeners, while the supernatant flows to the secondary treatment aeration basins. Ferric chloride is often added at this stage or prior to secondary treatment to precipitate phosphorus.

C. SECONDARY TREATMENT

The core biological treatment is a conventional Activated Sludge process. The facility operates multiple aeration batteries (Battery A and Battery B) utilizing fine-bubble diffusion systems, which were upgraded from coarse bubble/mechanical systems to improve oxygen transfer efficiency (OTE) and reduce energy costs. The mixed liquor flows to secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is recycled to the head of the aeration tanks, while Waste Activated Sludge (WAS) is sent to solids processing.

D. TERTIARY TREATMENT

To meet strict effluent limits, particularly for suspended solids and particulate phosphorus, the Flint WPCF employs tertiary filtration. The effluent from secondary clarifiers passes through sand filters (rapid gravity filtration). This polishing step is essential for maintaining compliance during periods of process upset or high hydraulic loading, ensuring the effluent meets the stringent clarity requirements for river discharge.

E. DISINFECTION

Disinfection is achieved using liquid chlorine (sodium hypochlorite) in contact tanks to eliminate pathogenic organisms. Following the required contact time, the effluent undergoes dechlorination using sodium bisulfite before being discharged into the Flint River. This chlorination/dechlorination process is typically seasonal (April through October) in accordance with Michigan state regulations for protecting recreational water bodies.

F. SOLIDS HANDLING & INCINERATION

Flint WPCF is notable for its solids disposal method. Primary sludge and WAS are thickened and dewatered using centrifuges. The resulting sludge cake is disposed of via a Fluidized Bed Incinerator (FBI). The FBI technology is cleaner and more efficient than older multiple-hearth furnaces, utilizing a sand bed suspended by air to achieve complete combustion at high temperatures (~1400°F). The resulting inert ash is collected via scrubbers and electrostatic precipitators and hauled to a landfill. This thermal reduction reduces sludge volume by over 90%.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site spans a significant industrial footprint along Beecher Road. Major structures include the Headworks Building, Primary Tanks, Aeration Batteries A & B, the Incinerator Complex, and the Administration/Laboratory building. The site also features large retention basins for wet-weather flow equalization.

B. Energy Systems

The WPCF is the largest single energy consumer in the City of Flint government operations. Recent capital projects have focused heavily on energy reduction, specifically replacing blower systems for aeration and installing Variable Frequency Drives (VFDs) on major raw sewage pumps. The Fluidized Bed Incinerator includes heat recovery systems to preheat combustion air, improving thermal efficiency.

C. Odor Control

Given the plant’s proximity to residential zones and the nature of the collection system, odor control is a priority. The facility employs wet chemical scrubbers and activated carbon adsorption units, particularly at the headworks and sludge handling facilities. Recent upgrades have targeted the sealing of process tanks and improved ventilation capture to minimize fugitive emissions.

5. RECENT UPGRADES & MAJOR PROJECTS

Since 2016, the Flint WPCF has been the recipient of substantial investment through the EPA’s Water Infrastructure Improvements for the Nation (WIIN) Act and the Michigan State Revolving Fund (SRF). These projects aim to address deferred maintenance and modernize the treatment train.

Northwest Transfer Station & Third Ave Pump Station Rehab (2018-2022)

• Project Budget: Part of a ~$100M Water/Wastewater master funding package.
• Scope: Complete rehabilitation of major pump stations that feed the WPCF. Replacement of screw pumps, installation of new bar screens, and electrical gear modernization.
• Technical Highlights: Installation of heavy-duty, clog-resistant pumping systems to handle modern ragging issues.
• Impact: Restored reliability to the collection system and reduced the risk of basement backups and CSO events.

Aeration & Blower System Improvements (2019-2023)

• Funding Source: State Revolving Fund (SRF) / WIIN Grant.
• Scope: Replacement of aging centrifugal blowers with high-efficiency turbo blowers and air bearing technology. Replacement of coarse bubble diffusers with fine bubble membrane diffusers in Battery A.
• Technical Highlights: Implementation of DO (Dissolved Oxygen) control loops to automatically adjust airflow based on real-time biological demand.
• Results: Significant reduction in electrical consumption (estimated >20% reduction in aeration energy) and improved nitrification performance.

Biosolids/Incinerator Upgrades (Ongoing)

• Scope: Maintenance and upgrades to the Fluidized Bed Incinerator, including refractory repair, heat exchanger maintenance, and scrubber system improvements to meet new Sewage Sludge Incineration (SSI) MACT standards.
• Drivers: Compliance with Clean Air Act emissions standards and reliability of solids disposal.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit No. MI0022730. Key discharge limitations include:

• CBOD5: Monthly average limits typically around 15-25 mg/L.
• TSS: Monthly average limits typically around 30 mg/L.
• Total Phosphorus: 1.0 mg/L (monthly average) to protect the Saginaw Bay watershed.
• E. Coli: 126/100ml (30-day geometric mean) during recreation season.

B. Compliance History

The Flint WPCF has faced challenges associated with aging infrastructure leading to periodic CSO discharges during extreme weather events. However, post-upgrade performance has shown stabilization. The facility is strictly monitored by EGLE, and recent capital improvements were mandated partly to ensure consistent compliance with effluent limits and to reduce the frequency and volume of untreated overflows.

C. Environmental Stewardship

The plant plays a pivotal role in the health of the Flint River. By strictly controlling phosphorus, the plant helps mitigate algal blooms in the downstream watershed. The switch to Fluidized Bed Incineration also represents a move toward lower-emission solids handling compared to previous technologies.

7. OPERATIONAL EXCELLENCE

A. Staffing

The plant requires Class A certified wastewater operators due to its size and complexity. The workforce includes operations specialists, industrial electricians, millwrights, and laboratory technicians. Following years of staffing austerity, the department has engaged in aggressive recruiting and training programs to bridge the “knowledge gap” as senior operators retire.

B. Technology & Monitoring

The facility utilizes a SCADA (Supervisory Control and Data Acquisition) system that is being progressively modernized. Real-time monitoring of Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), and flows allows for automated process adjustments. The on-site laboratory is state-certified for producing compliance data for NPDES reporting.

8. CHALLENGES & FUTURE PLANNING

A. Current Challenges

• Revenue Stability: The decline in the industrial and residential customer base in Flint places pressure on utility rates required to fund operations and maintenance.
• Wet Weather Management: Despite retention basins, managing high-volume inflows during rapid snowmelt or intense storms remains a hydraulic challenge for the headworks and primary treatment.
• Emerging Contaminants: Like all modern WWTPs, Flint is evaluating future impacts of PFAS regulations on biosolids disposal and effluent limits.

B. Future Planning

The City’s Capital Improvement Plan (CIP) prioritizes the continued separation of sewers to reduce CSO volume. Future phases of the Master Plan include further automation of the solids handling facility, structural rehabilitation of secondary clarifiers, and potential evaluation of UV disinfection to replace chlorination, thereby eliminating chemical safety risks associated with chlorine gas/liquid storage.

10. TECHNICAL SPECIFICATIONS SUMMARY

12. FAQ SECTION

Technical/Professional Questions

1. What is the solids retention time (SRT) target at Flint WPCF?

While variable based on season, the plant typically targets a conventional activated sludge SRT to ensure complete nitrification, generally in the range of 10-15 days during colder months.

2. How does the plant handle phosphorus removal?

Phosphorus is removed chemically using Ferric Chloride (FeCl3) addition, usually upstream of the primary clarifiers or aeration basins, followed by physical removal in the tertiary sand filters to meet the 1.0 mg/L limit.

3. Is the Fluidized Bed Incinerator currently operational?

Yes, the FBI is the primary method of solids disposal. It operates under strict Maximum Achievable Control Technology (MACT) standards for sewage sludge incineration.

4. Does the plant accept hauled waste?

The facility has provisions for septage receiving, though specific acceptance policies are determined by the Utilities Division based on capacity and waste characterization.

Public Interest Questions

5. Is this the same plant involved in the Flint Water Crisis?

No. The Flint Water Crisis involved the Water Treatment Plant (which treats river water for drinking). This facility is the Water Pollution Control Facility (Wastewater), which treats sewage before returning it to the river.

6. Does the plant smell?

Wastewater treatment inherently generates odors, but the Flint WPCF employs chemical scrubbers and other odor control technologies to minimize impact on the surrounding community.

7. Where does the water go after treatment?

The clean, treated water is discharged into the Flint River, eventually flowing into the Saginaw River and out to Lake Huron.