North Texas Municipal Water District Wilson Creek Wastewater Treatment Plant

1. Introduction

The Wilson Creek Regional Wastewater Treatment Plant (RWWTP) serves as a cornerstone of environmental infrastructure for the rapidly growing Collin County region of North Texas. Owned and operated by the North Texas Municipal Water District (NTMWD), this facility manages a permitted annual average daily flow of 64 million gallons per day (MGD), serving a significant portion of the distinct population centers north of Dallas.

Commissioned to handle the explosive suburban growth of the late 20th and early 21st centuries, Wilson Creek RWWTP is strategically critical not only for sanitation but for regional water supply protection. The plant discharges high-quality effluent into Wilson Creek, which flows directly into Lavon Lake—a primary source of raw drinking water for millions of North Texas residents. Consequently, the facility operates under stringent discharge parameters, utilizing advanced biological nutrient removal and tertiary filtration to ensure the protection of the watershed.

2. Facility Overview

A. Service Area & Coverage

The Wilson Creek RWWTP operates as a regional facility, accepting wastewater flows from a consortium of high-growth municipalities. The service area encompasses approximately 200,000 to 300,000 residents and associated commercial sectors. The primary contributing member cities include:

• City of Allen
• City of Plano (Northern portions)
• City of McKinney
• City of Frisco
• Town of Prosper

Read more4D-Printed Smart Materials For Water Treatment

The collection system feeding the plant is characterized by large-diameter interceptors designed to leverage gravity flow where possible, supplemented by regional lift stations to manage the topography of the Wilson Creek watershed.

B. Operational Capacity

Following a series of phased expansions, the facility currently operates with a design capacity of 64 MGD (Annual Average Daily Flow) and a significantly higher peak 2-hour flow capacity to manage wet weather events common in North Texas. Historical flow trends have shown a steady upward trajectory, mirroring the population boom in Collin County, necessitating a near-continuous state of capital expansion over the last two decades. The plant is designed to handle peak wet weather flows exceeding 190 MGD.

C. Discharge & Compliance

The facility discharges under a Texas Pollutant Discharge Elimination System (TPDES) permit issued by the Texas Commission on Environmental Quality (TCEQ). Because the receiving stream (Wilson Creek) feeds Lavon Lake, the permit includes strict limits on nutrients to prevent eutrophication in the drinking water reservoir. The facility consistently achieves effluent quality exceeding regulatory requirements for Carbonaceous Biochemical Oxygen Demand (CBOD), Total Suspended Solids (TSS), Ammonia-Nitrogen (NH3-N), and Total Phosphorus.

3. Treatment Process

The Wilson Creek RWWTP utilizes an advanced activated sludge process configured for biological nutrient removal, followed by tertiary filtration and ultraviolet disinfection. The treatment train is designed to produce reuse-quality water suitable for discharge into a raw water supply reservoir.

A. Preliminary Treatment

Raw wastewater enters the headworks facility where it undergoes mechanical screening and grit removal.

• Screening: Mechanical bar screens remove large debris, rags, and plastics to protect downstream pumps and process equipment. Screenings are washed, compacted, and disposed of off-site.
• Grit Removal: Vortex grit chambers utilize centrifugal force to separate inorganic solids (sand, gravel, eggshells) from the organic waste stream. This protects mechanical equipment from abrasion and prevents volume loss in the bioreactors.
• Odor Control: The headworks area is enclosed and ventilated to biological or chemical scrubbers to mitigate nuisance odors for nearby residential developments.

B. Primary Treatment

Read moreA Comparison Between Aerobic And Anaerobic Wastewater Treatment Technology

Flow is directed to primary clarifiers where gravity settling occurs. These circular basins allow settleable organic solids to collect at the bottom as primary sludge, while fats, oils, and grease (FOG) are skimmed from the surface. The primary treatment stage reduces the organic loading (BOD and TSS) on the secondary biological system by approximately 30-40%.

C. Secondary Treatment (Biological)

The core of the treatment process is the activated sludge system. The facility utilizes aeration basins configured for biological nutrient removal (BNR).

• Aeration Basins: The basins employ fine-bubble diffused aeration to maximize oxygen transfer efficiency. The biological process is operated to achieve both carbon oxidation (BOD removal) and nitrification (conversion of ammonia to nitrate).
• Nutrient Removal: Specific zones within the basins (anoxic/anaerobic selectors) may be utilized to facilitate denitrification and biological phosphorus removal, supplemented by chemical precipitation (typically alum or ferric salts) to ensure strict Total Phosphorus limits are met.
• Secondary Clarifiers: Mixed liquor flows to large circular secondary clarifiers where the biological floc settles. Return Activated Sludge (RAS) is pumped back to the aeration basins to maintain the biomass population, while Waste Activated Sludge (WAS) is removed for solids processing.

D. Tertiary / Advanced Treatment

To meet the stringent standards for discharge into a drinking water reservoir, the plant employs tertiary treatment.

• Filtration: Effluent from secondary clarifiers passes through deep-bed granular media filters or cloth media disc filters. This step polishes the water, removing remaining suspended solids and particulate-bound phosphorus, resulting in highly clear effluent with low turbidity.

E. Disinfection

The Wilson Creek facility utilizes Ultraviolet (UV) Disinfection rather than chlorination.

• Method: Flow passes through banks of UV lamps submerged in channels. The UV light penetrates the cell walls of pathogens (bacteria, viruses, protozoa), disrupting their DNA and preventing replication.
• Benefit: UV disinfection eliminates the formation of chlorinated disinfection byproducts (DBPs) and creates a safer effluent for aquatic life in Wilson Creek and Lavon Lake.

F. Solids Handling

Solids removed during primary and secondary treatment are processed to reduce volume and stabilize the organic matter.

• Thickening: Primary sludge and WAS are thickened (using gravity thickeners or mechanical belts/drums) to increase solids concentration.
• Digestion: The facility operates anaerobic digesters to stabilize the sludge, reduce pathogens, and reduce volatile solids. This process generates biogas (methane).
• Dewatering: Digested sludge is dewatered using high-solids centrifuges or belt filter presses to produce a “cake.”
• Disposal: The dewatered biosolids are transported off-site for disposal at the NTMWD regional landfill or for beneficial reuse via composting, depending on current district management strategies.

4. Infrastructure & Facilities

A. Physical Plant

The Wilson Creek RWWTP occupies a substantial footprint surrounded by parks and residential zones in Allen, Texas. The site layout is modular, reflecting its history of phased expansions. Key structures include the Administration Building (housing SCADA control and laboratory facilities), the Maintenance Building, and the massive concrete tankage required for the liquid and solids treatment trains.

B. Power & Reliability

Given the critical nature of the facility, it is equipped with extensive backup power generation capabilities to maintain hydraulic control and treatment during grid outages. Dual-feed electrical service from the local utility provider offers redundancy, while on-site diesel generators provide emergency power for essential pumps and biological life-support systems.

C. Odor Control Systems

Due to the encroachment of residential neighborhoods (including the immediate proximity to Fairview and Allen developments), NTMWD has invested heavily in odor control. This includes covering primary clarifiers and headworks channels, and treating foul air through multi-stage chemical scrubbers and biotrickling filters to remove hydrogen sulfide and mercaptans.

5. Recent Upgrades & Major Projects

The history of Wilson Creek is one of continuous expansion. Key recent projects include:

Expansion to 64 MGD (Completed approx. 2020)

• Project Scope: This major capital improvement project increased the plant’s rated capacity from 56 MGD to 64 MGD.
• Technical Highlights:
  • Construction of new aeration basins and secondary clarifiers.
  • Upgrades to the tertiary filtration complex.
  • Enhancements to the electrical distribution system.
  • Installation of additional UV disinfection banks.

• Drivers: Accommodating the rapid population influx in Frisco, Prosper, and McKinney.

Advanced Treatment & Aeration Improvements (Ongoing/Recent)

• Scope: Rehabilitation of older aeration basins and replacement of coarse bubble diffusers with high-efficiency fine bubble membrane diffusers.
• Benefits: Significant reduction in energy consumption for the blowers (the largest energy consumer in the plant) and improved oxygen transfer efficiency.

Regional Wastewater System Improvements

• Context: While not within the plant fence line, NTMWD has constructed parallel large-diameter interceptors and expanded the regional lift stations that feed Wilson Creek, ensuring the collection system keeps pace with the plant’s expanded treatment capacity.

6. Regulatory Compliance & Environmental Performance

A. Permit Requirements

The facility operates under TPDES Permit No. WQ0010271003. As a major discharger into a water supply reservoir watershed, the effluent limits are among the strictest in the state.

• CBOD5: Typically ≤ 5 mg/L
• TSS: Typically ≤ 5 mg/L
• Ammonia-Nitrogen: Typically ≤ 2 mg/L (Summer) / 5 mg/L (Winter)
• Total Phosphorus: Strict limits (often ≤ 0.5 or 1.0 mg/L) to prevent algae blooms in Lavon Lake.
• E. coli: Standard recreational water quality limits via UV disinfection.

B. Environmental Stewardship

NTMWD employs a “One Water” approach. The highly treated effluent from Wilson Creek effectively recycles water back into the region’s supply. By discharging into Lavon Lake, the water is naturally attenuated, blended, and eventually withdrawn for treatment at NTMWD’s Wylie Water Treatment Plant, closing the loop on the urban water cycle.

8. Challenges & Future Planning

A. Rapid Urbanization

The primary challenge for Wilson Creek RWWTP is the velocity of growth in its service area. The “Golden Corridor” north of Dallas continues to see double-digit percentage growth in population, requiring the plant to operate near high capacity utilization rates and necessitating perpetual planning for the next expansion phase.

B. Peak Wet Weather Flows

Inflow and Infiltration (I&I) in the older sections of the satellite collection systems can cause hydraulic peaking during heavy North Texas storms. Managing these peaks without washing out the biological solids inventory requires sophisticated hydraulic modeling and flow equalization strategies.

C. Future Expansion (Sister Facilities)

Recognizing the physical site limits of the Wilson Creek footprint, NTMWD has strategically planned “Sister Plants” (such as the Sister Grove RWWTP) to divert future flows. This strategy prevents the Wilson Creek facility from becoming unmanageably large and diversifies the treatment locations within the regional system.

10. Technical Specifications Summary

11. Related Facilities

The Wilson Creek RWWTP is part of a larger interconnected system managed by NTMWD, which includes:

• Sister Grove RWWTP: A new regional facility currently under construction/commissioning designed to relieve pressure on Wilson Creek by taking flows from McKinney and New Hope.
• Rowlett Creek RWWTP: Serving the Garland/Plano area.
• Floyd Branch RWWTP: Serving Richardson/Plano.
• Regional Transfer Stations: Massive lift stations in Plano and McKinney that route flow between these treatment basins.

12. FAQ

Technical Questions

Q: What is the permitted capacity of Wilson Creek RWWTP?
A: The facility is currently permitted for an annual average daily flow of 64 MGD.

Q: Does the plant utilize chemical phosphorus removal?
A: Yes, while biological phosphorus removal is encouraged in the anaerobic zones, the plant utilizes chemical coagulants (typically alum or ferric) to ensure strict compliance with TPDES phosphorus limits for reservoir protection.

Q: What is the solids retention time (SRT) for the biological process?
A: While variable based on temperature and season, the SRT is typically maintained between 10 to 15 days to ensure full nitrification.

Public Interest Questions

Q: Is the water discharged safe for the environment?
A: Yes. The effluent is treated to near-drinking water standards, disinfected with UV light, and actually improves the base flow of Wilson Creek during dry months.

Q: Where does the treated water go?
A: The treated water flows into Wilson Creek, which travels a short distance into Lavon Lake. Lavon Lake is a primary reservoir for NTMWD, meaning the water is eventually reused after going through a separate water treatment plant.

Q: How does the plant handle odors?
A: The plant uses covered process units and advanced chemical scrubbers and biofilters to strip odorous compounds from the air before it is released.