San Francisco Southeast Water Pollution Control Plant

FACILITY BASIC INFORMATION

• Plant Name: Southeast Water Pollution Control Plant (SEP)
• Location: 1800 Jerrold Avenue, San Francisco, CA 94124
• Operating Authority: San Francisco Public Utilities Commission (SFPUC)
• System Type: Combined Sewer System (CSS)
• Dry Weather Capacity: 85 MGD
• Peak Wet Weather Capacity: 575 MGD (Primary + Secondary combined)
• Current Average Dry Weather Flow: ~57 MGD
• Population Served: ~660,000 (80% of San Francisco)
• Service Area: Bayside of San Francisco (East side)
• Receiving Water Body: San Francisco Bay
• NPDES Permit Number: CA0037664 (Order No. R2-2013-0029)
• Year Commissioned: 1952 (Major expansion 1982)

TARGET AUDIENCE

• Municipal consulting engineers evaluating Combined Sewer System (CSS) operations
• Wastewater treatment plant operators and managers
• Equipment vendors researching thermal hydrolysis and high-purity oxygen systems
• Environmental regulators and compliance officers
• Engineering firms pursuing SSIP (Sewer System Improvement Program) contracts

1. INTRODUCTION

The Southeast Water Pollution Control Plant (SEP) is the largest and most critical wastewater facility within the San Francisco Public Utilities Commission (SFPUC) network. Located in the Bayview-Hunters Point neighborhood, the facility treats approximately 80% of San Francisco’s sanitary and stormwater flow. Unlike most U.S. municipalities, San Francisco operates a Combined Sewer System (CSS), meaning the SEP must handle extreme hydraulic variability—ranging from a daily average of 57 MGD to peak wet weather flows exceeding 500 MGD.

Originally commissioned in 1952 and significantly expanded in 1982 following the Clean Water Act, the plant is currently the epicenter of the multi-billion dollar Sewer System Improvement Program (SSIP). The facility is transitioning from aging conventional infrastructure to state-of-the-art technologies, including the implementation of thermal hydrolysis for biosolids management. As the backbone of the city’s Bayside collection system, the SEP serves as a premier case study in urban infrastructure retrofit, seismic hardening, and environmental justice integration.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The SEP services the “Bayside” watershed of San Francisco, a dense urban environment covering approximately 28,500 acres. The service area encompasses the downtown Financial District, Mission District, and residential neighborhoods south to the San Mateo County line. The collection system feeding the SEP is entirely combined, capturing both sanitary sewage and urban runoff. This results in a heavy inorganic load during first-flush events, necessitating robust grit removal capabilities.

B. Operational Capacity & Hydraulics

Read moreA Day in the Life of a Wastewater Treatment Plant Manager

The facility operates under two distinct hydraulic regimes:

• Dry Weather Mode: Design capacity of 85 MGD with current flows averaging 57 MGD. All flow receives full secondary treatment.
• Wet Weather Mode: The plant is designed to handle up to 575 MGD of combined flow.
  • Up to 250 MGD receives full secondary treatment.
  • Flows exceeding secondary capacity (up to an additional 325 MGD) receive primary treatment and disinfection before blending with secondary effluent for discharge, compliant with the CSS control policy.

C. Discharge & Compliance

Treated effluent is discharged into the San Francisco Bay via the Pier 80 Outfall. The deep-water outfall extends roughly 800 feet offshore into the bay. The facility operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the San Francisco Bay Regional Water Quality Control Board. Due to the enclosed nature of the SF Bay, nutrient loading (nitrogen/phosphorus) is an emerging regulatory focus, influencing current master planning.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT (New Headworks Facility)

Historically, the SEP operated aging bar screens. However, the recently commissioned New Headworks Facility (part of SSIP) has modernized this stage to handle 250 MGD of peak flow.

• Screening: Heavy-duty coarse screens followed by fine band screens to protect downstream membrane and biological systems.
• Grit Removal: Advanced vortex grit removal systems designed to handle the heavy sand/silt load characteristic of San Francisco’s steep topography and combined system.
• Influent Pumping: Vertical turbine solids handling pumps lift flow to the primary clarifiers.

B. PRIMARY TREATMENT

The plant utilizes rectangular primary sedimentation tanks. These tanks reduce flow velocity, allowing settleable solids to drop out as primary sludge and floatables (grease/oil) to be skimmed.

• Configuration: Multiple rectangular basins with chain-and-flight collectors.
• Performance: Typically achieves 50-60% TSS removal and 25-35% BOD removal.
• Wet Weather Strategy: During storm events, designated primary tanks act as decant facilities for excess flow that bypasses the secondary system.

C. SECONDARY TREATMENT (High Purity Oxygen)

The core biological treatment utilizes a High Purity Oxygen (HPO) Activated Sludge process. This technology was selected in the 1980s for its ability to treat high-strength waste in a smaller footprint than conventional air activated sludge—critical for the land-constrained site.

• Oxygen Generation: On-site cryogenic oxygen generation plant (Pressure Swing Adsorption or VSA units) produces >90% pure oxygen.
• Reactors: Covered aeration basins maintain a high partial pressure of oxygen, driving high dissolution rates.
• Secondary Clarifiers: 14 circular secondary clarifiers separate the mixed liquor.
• Performance: Consistent removal of BOD and TSS to < 30 mg/L (monthly average).

D. DISINFECTION

• Method: Sodium Hypochlorite (12.5% solution) is injected for pathogen inactivation.
• Dechlorination: Sodium Bisulfite is added prior to discharge to neutralize residual chlorine, protecting aquatic life in the Bay.
• Structure: A dedicated chlorine contact channel ensures sufficient residence time at peak flows.

E. SOLIDS HANDLING (Major Transition)

The solids handling train is currently undergoing a complete replacement via the Biosolids Digester Facilities Project (BDFP).

• Current/Legacy Process: Gravity belt thickening, mesophilic anaerobic digestion in floating cover digesters (Class B biosolids), and dewatering via centrifuges.
• Future Process (Under Construction): The new facility will feature Thermal Hydrolysis Process (THP)—likely the CAMBI system.
  • THP Benefits: Pre-treats sludge at high heat/pressure to sterilize it and break down cell walls.
  • Digestion: High-rate anaerobic digestion producing Class A (exceptional quality) biosolids.
  • Dewatering: High-solids centrifuges or screw presses to maximize cake dryness for reduced hauling costs.

F. PROCESS CONTROL

The facility utilizes a distributed control system (DCS), currently being migrated to the Emerson Ovation platform as part of the upgrade cycle. The system manages complex wet-weather control logic, automatically diverting flows and starting storm pumps based on hydraulic setpoints.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The SEP occupies approximately 40 acres in the Bayview neighborhood. The site is physically constrained by active commercial corridors and residential zones, requiring vertical construction and high-rate treatment technologies. Architectural treatments on new facilities focus on blending with the urban fabric, featuring artistic facades designed in collaboration with the local community.

B. Energy Systems

The plant is a significant energy consumer but also a producer.

• Cogeneration: Methane gas (biogas) produced in the digesters fuels cogeneration engines to produce electricity and heat for the plant.
• Energy Recovery: The new BDFP aims to maximize energy recovery, potentially making the solids handling process energy positive.
• Solar: Photovoltaic arrays are integrated into the roofs of new administration and process buildings.

C. Odor Control

Given the proximity to residential housing, odor control is a primary design driver.

• Technologies: Multi-stage systems employing biotrickling filters followed by activated carbon polishing.
• Coverage: All new process areas, including headworks and solids handling, are fully enclosed and ventilated to odor control scrubbers.

5. RECENT UPGRADES & MAJOR PROJECTS (SSIP)

The SFPUC is executing the Sewer System Improvement Program (SSIP), a citywide investment to upgrade aging infrastructure. The SEP is the primary beneficiary of Phase 1.

Biosolids Digester Facilities Project (BDFP) – ~$3.0+ Billion

• Status: Under Construction (Completion expected ~2026/2027).
• Contractor: MWH/Webcor Joint Venture.
• Scope: Demolition of existing 1950s digesters and construction of new solids treatment train.
• Technical Highlights: Implementation of Thermal Hydrolysis Process (THP) to produce Class A biosolids. This reduces volume by 50% and allows for diverse beneficial reuse options (landscaping, agriculture) rather than landfill or limited agricultural application.
• Resilience: Designed to withstand maximum credible earthquake events and account for sea-level rise.

New Headworks Facility – ~$618 Million

• Status: Construction Substantially Complete / Commissioning.
• Contractor: Sundt/Walsh Joint Venture.
• Scope: Replacement of the preliminary treatment building.
• Technical Highlights: Increased peak capacity to 250 MGD. Installation of heavy-duty varying-aperture screens to handle CSS debris. Advanced odor control systems to mitigate community impacts.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The SEP operates under a complex NPDES permit due to the CSS nature.

• Secondary Effluent Limits: Conventional TSS and BOD removal requirements (30 mg/L monthly avg).
• Combined Sewer Discharge (CSD) Policy: The EPA’s CSD Control Policy requires the maximization of flow to the treatment plant during wet weather and the minimization of combined sewer overflows (CSOs) to the Bay shoreline. The plant’s ability to ramp up to 575 MGD is a specific permit compliance strategy.

B. Environmental Stewardship

SFPUC is a leader in “One Water” management. The upgraded SEP will produce high-quality biosolids for soil amendment, sequestering carbon. Furthermore, the facility participates in the Bay Area Clean Water Agencies (BACWA) nutrient watershed permit, monitoring nitrogen loads to the Bay to prevent algal blooms.

7. OPERATIONAL EXCELLENCE

A. Staffing & Workforce

The SEP is staffed 24/7 by a team of Grade I-V certified wastewater treatment operators, stationary engineers, and laboratory technicians. SFPUC maintains an internal apprenticeship program to combat industry-wide “silver tsunami” retirement trends.

B. Technology & Innovation

The facility serves as a testing ground for urban wastewater innovation. The shift to THP places SEP among a select group of North American facilities (like DC Water’s Blue Plains) adopting this advanced European technology. The move requires specialized operator training for high-pressure/high-temperature steam systems.

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure vs. Construction Logistics

The greatest challenge is maintaining 100% permit compliance while rebuilding the entire plant footprint simultaneously. The “surgery while the patient is awake” complexity requires intricate bypass pumping and temporary process phasing.

B. Climate Change & Seismic Resilience

Located on the Bay margin, the SEP is vulnerable to sea-level rise. New structures are elevated or hardened against projected water levels for the year 2100. Furthermore, the proximity to the San Andreas and Hayward faults necessitates robust seismic design (Importance Factor 1.5) to ensure post-earthquake functionality.

C. Nutrient Management

While not currently under strict nutrient limits, the SF Bay is trending toward nutrient regulation. Future master plans account for the potential conversion of aeration basins to Biological Nutrient Removal (BNR) configurations or the addition of tertiary filtration.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

The SEP operates in conjunction with several key off-site assets:

• Oceanside Water Pollution Control Plant: The sister facility handling the Westside watershed (Pacific Ocean discharge).
• North Point Wet Weather Facility: A specialized facility near Fisherman’s Wharf that activates only during storm events to provide primary treatment and disinfection for excess flows before discharge.
• Channel Pump Station: One of the city’s largest lift stations, critical for conveying flow from the lower-lying areas to the SEP.

12. FAQ SECTION

Technical Questions

1. What is the peak capacity of the SEP?

The plant has a total hydraulic peak capacity of 575 MGD. Of this, up to 250 MGD receives secondary treatment, while the remainder receives primary treatment and disinfection during extreme storm events.

2. Does the SEP use pure oxygen for aeration?

Yes. The plant utilizes a High Purity Oxygen (HPO) activated sludge system, which requires on-site cryogenic oxygen generation. This allows for higher biomass concentrations and a smaller footprint compared to air-activated systems.

3. What is the status of the Biosolids Digester Facilities Project?

As of 2024, the BDFP is under active construction with completion targeted for the 2026-2027 timeframe. It involves replacing existing digesters with Thermal Hydrolysis Process (THP) units.

4. How are biosolids currently disposed of?

Current Class B biosolids are dewatered and primarily hauled for land application or agricultural use in Solano and Sonoma counties. Future Class A biosolids will have expanded use cases including local landscaping.

General Interest Questions

5. Why is the plant located in a residential neighborhood?

The plant was built in 1952 when the area was largely industrial. Residential density grew around it over decades. Current upgrades heavily prioritize odor control and aesthetic improvements to address environmental justice concerns in the Bayview community.

6. Does the plant treat rainwater?

Yes. Because San Francisco has a Combined Sewer System, the plant treats a mixture of sanitary sewage and stormwater runoff from streets and roofs.

7. How much is being spent to upgrade the facility?

The Sewer System Improvement Program (SSIP) is investing over $3 billion specifically into the Southeast Plant upgrades, including the new Headworks and Biosolids facilities.