Tulsa Metropolitan Utility Authority North Wastewater Treatment Plant

1. INTRODUCTION

The Northside Wastewater Treatment Plant (Northside WWTP) serves as a cornerstone of the Tulsa Metropolitan Utility Authority’s environmental infrastructure. Strategically located to serve the northern drainage basin of the Tulsa metropolitan area, this facility is the second largest of Tulsa’s four wastewater treatment plants. With a design flow capacity of 42.6 MGD and a peak hydraulic capacity significantly higher to manage wet weather events, the plant plays a pivotal role in protecting the water quality of Bird Creek and the downstream Verdigris River watershed.

Operated by the City of Tulsa on behalf of the TMUA, the Northside WWTP has evolved from a conventional secondary treatment facility into a modernized operation utilizing Ultraviolet (UV) disinfection and advanced biosolids handling. Following significant capital investment over the last decade, including the construction of massive Flow Equalization Basins (FEBs), the facility represents a model of municipal resilience against inflow and infiltration (I/I) challenges while adhering to strict Oklahoma Department of Environmental Quality (ODEQ) standards.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Northside WWTP services a rapidly developing geographic area encompassing approximately 55,000 acres. The sewershed includes the northern districts of the City of Tulsa, as well as significant flows from suburban municipalities including Owasso, Catoosa, and unincorporated areas of Rogers and Osage Counties. The service area is characterized by a mix of mature residential neighborhoods, expanding suburban developments, and heavy industrial zones near the Tulsa Port of Catoosa, necessitating a robust treatment train capable of handling variable influent characteristics.

B. Operational Capacity

The facility operates with a design average daily flow of 42.6 MGD. Historically, the plant experiences average daily flows ranging from 25 to 30 MGD, providing a capacity utilization of approximately 65-70% during dry weather. However, the operational reality of the Northside facility is defined by its peak flow management. Due to the age of the collection system in North Tulsa, the plant must manage substantial Inflow and Infiltration (I/I) surges. The plant is engineered to handle peak instantaneous flows exceeding 80 MGD through primary treatment, with excess flows diverted to on-site equalization storage.

C. Discharge & Compliance

Treated effluent is discharged via a single outfall into Bird Creek. The discharge is regulated under the Oklahoma Pollutant Discharge Elimination System (OPDES), administered by the ODEQ. The facility maintains a strong compliance record, specifically targeting Carbonaceous Biochemical Oxygen Demand (CBOD5), Total Suspended Solids (TSS), Ammonia-Nitrogen (NH3-N), and E. coli. As Bird Creek is a sensitive water body with recreational designations, the plant adheres to stringent seasonal limits, particularly for ammonia toxicity and dissolved oxygen requirements.

3. TREATMENT PROCESS

Read moreA Comparison Between Aerobic And Anaerobic Wastewater Treatment Technology

The Northside WWTP utilizes a conventional activated sludge process train, augmented by flow equalization and modern disinfection technologies. The treatment train is designed to reduce pollutant loads to levels safe for aquatic life in Bird Creek.

A. Preliminary Treatment

Raw wastewater enters the headworks where it passes through mechanically cleaned bar screens (typically 0.25 to 0.5-inch spacing) to remove rags, plastics, and large debris. Following screening, the flow enters vortex grit removal chambers. These systems utilize centrifugal force to settle out inorganic solids like sand, gravel, and eggshells, which are then washed and dewatered for landfill disposal. This stage is critical for protecting downstream pumps and preventing volume reduction in the digesters.

B. Primary Treatment

Flow proceeds to primary clarifiers—large circular concrete tanks where gravity settling occurs. Here, approximately 60% of suspended solids and 30-40% of organic load (BOD) are removed. The hydraulic retention time allows heavier organic solids to settle as primary sludge, while grease and oils float to the surface for skimming. The primary sludge is pumped directly to the solids handling complex for thickening and digestion.

C. Secondary Treatment

The biological heart of the plant is the Activated Sludge system. Effluent from primary clarifiers enters large aeration basins.

• Aeration Basins: The plant utilizes a plug-flow configuration equipped with fine-bubble diffusers to maximize oxygen transfer efficiency. Microorganisms (biomass) consume the remaining dissolved organic matter and convert ammonia to nitrate (nitrification) depending on the dissolved oxygen setpoints and retention time.
• Secondary Clarifiers: The mixed liquor flows into circular secondary clarifiers where the biological floc settles. Clear supernatant overflows the weirs as secondary effluent.
• RAS/WAS: A portion of the settled biology is returned to the aeration basins as Return Activated Sludge (RAS) to maintain the microbial population. The excess growth is removed as Waste Activated Sludge (WAS) and sent to solids processing.

D. Disinfection

In a major shift from historical chlorination/dechlorination practices, the Northside WWTP now employs Ultraviolet (UV) Disinfection. The effluent passes through channels containing banks of submerged low-pressure, high-intensity UV lamps. The UV light penetrates the cell walls of pathogens (bacteria and viruses), scrambling their DNA and rendering them unable to reproduce. This elimination of chemical disinfection byproducts ensures the effluent is non-toxic to sensitive aquatic species in Bird Creek.

E. Solids Handling

The facility processes solids through Anaerobic Digestion.

• Thickening: Primary sludge and WAS are thickened (often via gravity belt thickeners or rotary drums) before digestion.
• Digestion: The thickened sludge enters mesophilic anaerobic digesters (heated to ~98°F). In the absence of oxygen, bacteria break down the volatile solids, reducing sludge volume and pathogen counts while producing methane gas.
• Dewatering: Digested biosolids are dewatered using Belt Filter Presses to achieve a cake solid concentration suitable for transport.
• Disposal: The Class B biosolids are trucked off-site for beneficial reuse via land application on permitted agricultural fields, recycling nutrients back into the soil.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The Northside WWTP occupies a sprawling site north of Tulsa International Airport. The campus includes the headworks building, blower buildings, multiple clarifier batteries, digestion complex, and a dedicated administration and laboratory building. The site layout is designed for redundancy, with dual process trains allowing for maintenance without full plant shutdowns.

B. Energy Systems

The plant is a significant energy consumer, primarily due to the aeration blowers and influent pumping. However, the facility employs energy recovery strategies. The methane gas (biogas) produced during anaerobic digestion is captured and utilized in boilers to heat the digesters, maintaining the mesophilic process temperature and reducing the reliance on natural gas. Recent upgrades have focused on replacing older centrifugal blowers with high-efficiency turbo blowers to reduce electrical load.

C. Flow Equalization

A distinctive feature of the Northside infrastructure is the massive Flow Equalization Basins (FEB). These large concrete reservoirs provide temporary storage for excess wet-weather flow. During storm events, peak flows that exceed the secondary treatment capacity are diverted to the FEB. Once the storm subsides, this water is pumped back to the head of the plant for full treatment, effectively eliminating sanitary sewer overflows at the plant headworks.

5. RECENT UPGRADES & MAJOR PROJECTS

Upcoming Planning (2024-2028): The TMUA capital plan includes provisions for aeration basin rehabilitation, further electrical grid upgrades for resiliency, and potential evaluation of nutrient removal technologies should ODEQ permit limits for nitrogen and phosphorus tighten in the future.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

The Northside WWTP operates under OPDES Permit OK0026221. The facility is subject to strict monitoring frequencies, typically requiring daily analysis of effluent quality.

• BOD/TSS: The plant consistently achieves high removal rates, typically exceeding 90-95% removal of BOD and TSS, well within the 30-day average limits (usually 30 mg/L for secondary treatment).
• Ammonia: Due to the limited dilution capacity of Bird Creek during summer months, the plant must nitrify effectively. Recent operational data indicates consistent compliance with ammonia limits.
• Bacteria: Since the conversion to UV disinfection, the facility consistently meets E. coli geometric mean limits during the recreation season (May-September).

7. OPERATIONAL EXCELLENCE

The facility is staffed 24/7/365. The workforce consists of state-licensed operators (Class A, B, C, and D), industrial maintenance mechanics, electricians, and instrumentation technicians.

SCADA Integration: The entire plant is monitored via a Supervisory Control and Data Acquisition (SCADA) system. This allows operators to monitor dissolved oxygen levels, tank levels, and pump statuses in real-time from a central control room. The system automates critical functions such as RAS/WAS flow rates based on influent flow pacing.

Laboratory: The Northside WWTP houses a process control laboratory capable of performing immediate analysis for settleability, pH, and dissolved oxygen, while compliance samples are generally processed by the central TMUA laboratory or certified third-party labs.

8. CHALLENGES & FUTURE PLANNING

Aging Infrastructure & Corrosion

Like many facilities of its era, Northside faces challenges related to concrete corrosion caused by hydrogen sulfide (H2S). The TMUA has an aggressive asset management program to line pipes and coat concrete structures to extend their service life.

Wet Weather Management

Despite the FEB additions, Inflow and Infiltration (I/I) remains a primary challenge. During extreme weather events, the hydraulic load can increase four-fold. Future planning focuses heavily on collection system rehabilitation to stop the water before it reaches the plant, rather than just expanding plant capacity.

Nutrient Regulations

While currently compliant, the trend in wastewater regulation is toward stricter Total Nitrogen and Total Phosphorus limits. Future master planning for Northside likely includes reserved footprint or hydraulic profile adjustments to accommodate Biological Nutrient Removal (BNR) processes if required.

9. TECHNICAL SPECIFICATIONS SUMMARY

10. FAQ SECTION

Technical Questions

Q: What is the design capacity of the Northside WWTP?
A: The plant is designed to treat an average daily flow of 42.6 Million Gallons per Day (MGD).

Q: Does the plant use chemical disinfection?
A: No. The facility has converted to Ultraviolet (UV) disinfection, eliminating the use of chlorine gas for effluent disinfection.

Q: How does the plant handle peak wet weather flows?
A: Excess flows are diverted to large on-site Flow Equalization Basins (FEBs), stored, and then pumped back through the treatment process once flows subside.

Q: Is there energy recovery at the site?
A: Yes, the plant recovers methane biogas generated during anaerobic digestion and uses it to fire boilers that heat the digestion process.

Public Interest Questions

Q: Where does the treated water go?
A: The treated water, often cleaner than the river itself, is discharged into Bird Creek.

Q: How does the plant control odors?
A: The plant uses various methods including chemical scrubbers at headworks and keeping solids handling processes enclosed to minimize odor impact on neighbors.

Q: Who operates the Northside Plant?
A: It is operated by the City of Tulsa Water and Sewer Department under the authority of the Tulsa Metropolitan Utility Authority (TMUA).