City Of St Petersburg Southwest Wastewater Treatment Plant

1. Introduction

The Southwest Water Reclamation Facility (SWWRF) serves as the cornerstone of the City of St. Petersburg’s wastewater infrastructure and is a pivotal component of one of the nation’s largest water reclamation systems. Located adjacent to Eckerd College and the biological richness of Boca Ciega Bay, the facility treats an average of 18 million gallons daily (MGD) serving a significant portion of southern Pinellas County. Originally commissioned in the late 1970s and operated by the City of St. Petersburg Water Resources Department, the SWWRF has evolved from a conventional treatment plant into a sophisticated resource recovery hub.

The facility is distinct not only for its liquid treatment train but for serving as the centralized biosolids handling facility for the city’s three treatment plants. Following a comprehensive infrastructure modernization initiative post-2016, the SWWRF recently integrated a cutting-edge Biosolids-to-Energy (B2E) system, transitioning the facility toward energy neutrality. As a zero-discharge facility under normal operations, the plant provides high-quality reclaimed water for irrigation throughout the city, embodying the region’s commitment to sustainable water resource management.

2. Facility Overview

A. Service Area & Coverage

The SWWRF services the southern quadrant of St. Petersburg, a densely populated peninsula including residential districts, the commercial corridors of US-19, and coastal communities. The service area encompasses:

• Geographic Range: Southern St. Petersburg, extending to the Sunshine Skyway approach and bordering the Gulfport service area.
• Population Served: Approximately 120,000 to 140,000 residents within the specific sewershed, plus handling solids for the city’s total population of approx. 260,000.
• Collection System: The facility is fed by a network of gravity mains and master pump stations designed to navigate the flat topography and high water table characteristic of the Floridan coastal plain.

B. Operational Capacity

The facility operates under a Florida Department of Environmental Protection (FDEP) permit with the following capacity parameters:

• Permitted Capacity (AADF): 20.0 MGD
• Current Average Daily Flow: ~16-18 MGD

Read more10 Surprising Benefits of Upgrading Your Aeration Tank System
• Peak Hydraulic Capacity: Capable of sustaining significantly higher flows during wet weather events via flow equalization and deep well injection management.
• Utilization: The plant operates near 85-90% of its rated capacity, driving recent initiatives for capacity expansion and hydraulic optimization.

C. Discharge & Compliance

St. Petersburg operates one of the oldest and largest reclaimed water systems in the United States. The SWWRF operates as a Zero Discharge facility to surface waters under normal conditions.

• Primary Discharge (Reuse): Treated effluent meets “Public Access Reuse” standards and is pumped into the city’s master reuse loop for lawn irrigation, golf courses, and cooling towers.
• Secondary Discharge (Disposal): Excess treated effluent that cannot be utilized (primarily during wet seasons) is injected into the Floridan Aquifer via Class I Deep Injection Wells (DIW).
• Receiving Water Body: Technically none for surface discharge; however, emergency outfalls exist for Clam Bayou/Boca Ciega Bay (Outstanding Florida Waters) strictly for catastrophic wet weather management, regulated heavily by Consent Orders.

3. Treatment Process

The SWWRF utilizes a multi-stage process designed to achieve high-level disinfection and nutrient reduction suitable for un-restricted public access reuse. The treatment train emphasizes reliability and pathogen removal.

A. Preliminary Treatment

Raw wastewater enters the headworks where it undergoes physical separation to protect downstream mechanical equipment.

• Screening: Mechanical step screens remove large debris, rags, and non-flushables.
• Grit Removal: Vortex grit chambers utilize centrifugal force to settle out sand, gravel, and coffee grounds, preventing abrasion in pumps and accumulation in the digesters.
• Odor Control: The headworks are enclosed and vented to biological and chemical scrubbers, critical due to the facility’s proximity to Eckerd College and residential zones.

Read more4D-Printed Smart Materials For Water Treatment

B. Secondary Treatment

The biological core of the plant utilizes Contact Stabilization and conventional Activated Sludge processes, optimized for Florida’s warm climate.

• Aeration Basins: The facility employs fine-bubble diffused aeration. The biological process is configured to achieve BOD and TSS removal while initiating nitrification.
• Clarification: Mixed liquor flows to secondary clarifiers (circular configuration) where solids settle via gravity. The hydraulic retention time allows for effective separation of the biomass from the treated liquid.
• RAS/WAS: Return Activated Sludge is recycled to the aeration basins to maintain mixed liquor suspended solids (MLSS) concentrations, while Waste Activated Sludge is pumped to the thickening complex.

C. Tertiary Treatment & Filtration

To meet Florida’s rigorous Part III Public Access Reuse standards, tertiary filtration is mandatory.

• Filtration: The plant utilizes Deep Bed Sand Filters (or denitrification filters in upgraded trains). These filters reduce turbidity to below 2.0 NTU, ensuring that suspended solids do not shield pathogens during the disinfection phase.
• Performance: This stage is critical for removing helminth eggs and protozoan cysts (Giardia/Cryptosporidium).

D. Disinfection

Disinfection is achieved through Chlorination to ensure a residual is maintained throughout the extensive reclaimed water distribution network.

• Method: Chlorine gas or bulk sodium hypochlorite application.
• Contact Time: A dedicated chlorine contact chamber ensures adequate CT values (Concentration x Time) to achieve high-level disinfection (fecal coliform < 1 CFU/100mL).
• Residual Maintenance: Unlike facilities discharging to environment, SWWRF maintains a chlorine residual (approx. 4.0 mg/L) in the effluent to prevent biological regrowth in the reuse pipes.

E. Solids Handling (Biosolids Center of Excellence)

The SWWRF serves as the regional solids processing hub for St. Petersburg, receiving sludge from the Northeast and Northwest facilities.

• Thickening: Rotary drum thickeners (RDT) and gravity belt thickeners concentrate WAS prior to digestion.
• Anaerobic Digestion: The facility recently upgraded to temperature-phased anaerobic digestion (TPAD) or standard mesophilic anaerobic digestion. This process reduces volatile solids and produces methane-rich biogas.
• Dewatering: High-solids centrifuges dewater the digested sludge to produce a “cake” product.
• Class AA Biosolids: The upgraded process is designed to produce Class AA biosolids, suitable for unrestricted fertilizer use, significantly reducing disposal costs.

4. Infrastructure & Facilities

A. Physical Plant

The site occupies over 40 acres in the southwestern tip of the Pinellas peninsula. The architecture is utilitarian industrial, dominated by the massive egg-shaped or cylindrical anaerobic digesters which serve as visual landmarks. The site includes a modern SCADA control room, an accredited environmental laboratory, and extensive maintenance bays.

B. Energy Systems & Biogas

The crown jewel of the facility’s infrastructure is the Renewable Natural Gas (RNG) / Biogas utilization system.

• Biogas Production: The anaerobic digesters produce substantial biogas.
• Cogeneration: Biogas is scrubbed and utilized in Combined Heat and Power (CHP) engines to generate electricity for plant operations and heat for the digesters.
• Energy Neutrality Goals: This system offsets a significant percentage of the plant’s grid energy consumption, insulating the utility from fluctuating energy prices.

C. Injection Well System

The facility manages hydraulic balance via Class I Deep Injection Wells. These wells are drilled roughly 1,000+ feet deep into the boulder zone of the Floridan Aquifer, below the drinking water confinement layers. Recent upgrades added well capacity to ensure the plant can manage peak wet-weather flows without surface discharge.

5. Recent Upgrades & Major Projects

Following the 2015-2016 wet weather crisis, St. Petersburg initiated a massive Capital Improvement Plan (CIP) specifically targeting the SWWRF.

6. Regulatory Compliance & Environmental Performance

A. Permit Requirements

The facility operates under NPDES Permit FL0026131 (and associated Underground Injection Control permits).

• CBOD5 & TSS: Must meet 5.0 mg/L standards on annual average for high-level reuse.
• Nutrients: Strict monitoring of Total Nitrogen and Phosphorus, particularly regarding the reclaimed water applied to turf, to prevent nutrient runoff into the bay.
• Pathogens: Stringent fecal coliform limits (essentially non-detect) required for public access irrigation.

B. Compliance History

Historically, the facility faced challenges during the 2015-2016 climatic events, leading to a Consent Order with the FDEP. Since the implementation of the Wet Weather Master Plan and the commissioning of new injection wells, the facility has returned to a strong compliance posture, consistently meeting its “Zero Surface Discharge” goals and maintaining high-quality reclaimed water production.

7. Technical Specifications Summary

8. FAQ Section

Technical Questions

Q: What is the “Zero Discharge” status of the SWWRF?
A: Zero Discharge refers to the restriction against discharging treated effluent into surface waters (like Tampa Bay). Instead, SWWRF recycles water for irrigation or injects excess into deep wells. Surface discharge is only legally permitted during emergency wet weather events to prevent infrastructure failure.

Q: How does the Biosolids-to-Energy project benefit the facility?
A: By digesting sludge from all three city plants at SWWRF, the utility maximizes biogas production. This gas fuels generators to power the plant, reducing electricity costs, while the digestion process reduces the physical volume of sludge needing disposal by up to 50%.

Q: Is the facility capable of Nutrient Removal?
A: Yes. While not strictly an AWT (Advanced Wastewater Treatment) facility like those discharging directly to the bay, the reuse process requires significant biological nutrient control to produce high-quality irrigation water that doesn’t “burn” vegetation or cause excessive algae in storage ponds.

Public Interest Questions

Q: Does the plant smell?
A: Wastewater treatment inherently generates odors, but SWWRF employs advanced chemical scrubbers and biofilters, particularly at the headworks and biosolids loading areas, to mitigate impact on neighbors like Eckerd College.

Q: Is the water leaving the plant safe to drink?
A: No. The output is “Reclaimed Water” (identified by purple pipes). While highly treated, filtered, and disinfected, it is not potable (drinking) standard. It is safe for incidental contact and irrigation.