City Of Houston 69th Street Wastewater Treatment Plant

FACILITY BASIC INFORMATION

• Plant Name: 69th Street Wastewater Treatment Plant
• Location: 2525 S/Sgt. Macario Garcia Drive, Houston, Harris County, Texas
• Operating Authority: City of Houston Public Works (Houston Water)
• Design Capacity: 200 MGD (Permitted Daily Average Flow)
• Peak 2-Hour Flow: 400 MGD
• Population Served: Approx. 1.2 – 1.5 million residents
• Service Area: Central Houston, North Loop, and surrounding metropolitan areas
• Receiving Water Body: Buffalo Bayou (Segment 1014)
• NPDES/TPDES Permit Number: WQ0010495004
• Year Commissioned: 1979

1. INTRODUCTION

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The 69th Street Wastewater Treatment Plant stands as the crown jewel of the City of Houston’s wastewater infrastructure and represents one of the largest wastewater treatment facilities in the American Southwest. Commissioned in 1979, this 200-MGD permitted facility handles approximately 40% to 50% of the city’s total wastewater flow. It is distinct in the region for its utilization of a two-stage High-Purity Oxygen (HPO) activated sludge process, a design choice necessitated by the need to treat high-volume loads within a compact urban footprint.

Discharging into Buffalo Bayou, a critical waterway feeding the Houston Ship Channel and Galveston Bay, the facility operates under strict regulatory scrutiny regarding dissolved oxygen and nutrient loading. Following the EPA Consent Decree impacting the City of Houston, the 69th Street facility is currently the focal point of significant capital investment aimed at modernizing aging electrical infrastructure, enhancing solids handling capabilities, and ensuring resilience against extreme weather events.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The facility serves a massive, densely populated service area encompassing downtown Houston, the medical center, and residential neighborhoods within and immediately outside the I-610 Loop. The collection system feeding the plant is complex, involving deep tunnels and major lift stations, including the Northside Lift Station. The influent profile is a mixture of domestic wastewater and significant commercial flows, with some industrial contributions controlled via pretreatment programs.

B. Operational Capacity

Designed with a permitted daily average flow of 200 million gallons per day (MGD), the plant is hydraulically capable of handling a peak 2-hour flow of 400 MGD. Historically, the plant operates at an average daily flow ranging between 110 and 140 MGD, providing sufficient buffer capacity for dry weather growth. However, Houston’s notorious wet weather events frequently test the hydraulic limits of the headworks and primary treatment systems. The facility is a “regional” sludge processing hub, accepting solids from other satellite plants in the Houston system for dewatering and drying.

C. Discharge & Compliance

Effluent is discharged via Outfall 001 into Buffalo Bayou. This receiving water body is tidally influenced and heavily urbanized. The TPDES permit places stringent limits on Carbonaceous Biochemical Oxygen Demand (CBOD), Total Suspended Solids (TSS), Ammonia-Nitrogen, and E. coli. Due to the impaired status of the receiving waters for bacteria and dissolved oxygen, the plant must maintain high-efficiency nitrification and disinfection year-round.

3. TREATMENT PROCESS

The 69th Street WWTP utilizes a sophisticated treatment train characterized by its High-Purity Oxygen (HPO) system, originally based on the UNOX process. This technology allows for higher mixed liquor suspended solids (MLSS) concentrations and shorter retention times compared to conventional aeration.

A. PRELIMINARY TREATMENT

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Raw wastewater enters the facility through massive interceptors at the headworks. The system utilizes mechanically cleaned coarse bar screens to remove large debris, followed by fine screens to protect downstream pumps. Grit removal is achieved via aerated grit chambers, where velocity is controlled to allow inorganic sands to settle while keeping organics in suspension. The extracted grit is washed and dewatered before landfill disposal. Odor control at the headworks is critical due to the plant’s proximity to residential areas and parks, utilizing chemical scrubbers (typically caustic/hypochlorite) to treat foul air.

B. PRIMARY TREATMENT

Following preliminary treatment, flow enters a battery of rectangular primary clarifiers. These tanks reduce the organic load on the secondary system by settling out settleable solids (removing approx. 60% TSS and 30-35% BOD). Primary sludge is pumped directly to the solids handling complex, while surface skimmers remove fats, oils, and grease (FOG).

C. SECONDARY TREATMENT (High-Purity Oxygen)

The core of the treatment process is the HPO activated sludge system. Unlike conventional plants that blow ambient air into the basins, 69th Street generates pure oxygen on-site using a Cryogenic Air Separation plant.

• Reactors: The aeration basins are covered (gastight) to maintain oxygen partial pressure and prevent gas escape.
• Oxygen Dissolution: Surface aerators inside the covered tanks mix the pure oxygen into the wastewater.
• Efficiency: This process supports higher biomass concentrations, allowing the plant to treat 200 MGD in a physical footprint roughly half the size required for a conventional air system.
• Clarification: Mixed liquor flows to secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is recycled to the reactors, and Waste Activated Sludge (WAS) is sent to thickening.

D. TERTIARY FILTRATION

To meet strict TSS and BOD limits, the facility employs a deep-bed gravity filtration system. These filters use a granular media (typically sand/anthracite) to polish the secondary effluent, removing remaining pin floc and particulate matter. This step is crucial for maintaining compliance during peak flow events when secondary clarifier blankets may rise.

E. DISINFECTION

The filtered effluent undergoes chlorination for pathogen destruction. Liquid chlorine (gas) is typically used for disinfection in chlorine contact basins, ensuring sufficient contact time (CT) to meet E. coli limits. Prior to discharge into Buffalo Bayou, the water is dechlorinated using Sulfur Dioxide (SO2) or Sodium Bisulfite to prevent toxicity to aquatic life in the bayou.

F. SOLIDS HANDLING (Hou-Actinite Production)

The 69th Street plant operates a large-scale biosolids manufacturing facility.

• Thickening: Primary and secondary sludges are thickened (gravity thickening for primary, dissolved air flotation or centrifugation for WAS).
• Dewatering: Thickened sludge is dewatered using high-solids centrifuges or belt filter presses.
• Thermal Drying: The dewatered cake is processed in natural gas-fired rotary drum dryers. The high temperature kills pathogens and reduces moisture content to <5%.
• Product: The result is Class A Exceptional Quality (EQ) biosolids pellets, marketed and sold under the trade name “Hou-Actinite.” This fertilizer is sold commercially for agriculture and turf application, representing a successful resource recovery operation.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site occupies over 130 acres along the bayou. The layout is dominated by the enclosed reactor trains and the towering cryogenic oxygen generation stacks. The facility includes extensive maintenance shops, a comprehensive SCADA control center, and an on-site laboratory certified for TPDES parameter testing.

B. Energy Systems

The 69th Street plant is one of the largest municipal energy consumers in Houston. The cryogenic oxygen plant acts as a massive parasitic load, requiring megawatts of power to compress and cool air for oxygen separation. Recent initiatives have focused on Variable Frequency Drives (VFDs) for major pumps and lighting retrofits to improve efficiency.

5. RECENT UPGRADES & MAJOR PROJECTS

Electrical Distribution System Improvements (2020-2024)

Budget: ~$60 Million
Project Scope: A critical replacement of the plant’s aging main electrical substation and distribution gear. The original 1970s switchgear posed a reliability risk. This project involved constructing a new substation, replacing medium-voltage feeds to major process equipment (blowers, pumps, cryo plant), and hardening the electrical system against flooding.

Sanitary Sewer Overflow (SSO) Consent Decree Projects

Context: Under the EPA Consent Decree, Houston is investing billions in wastewater infrastructure. At 69th Street, this includes:

• Headworks Modernization: Replacement of aging bar screens with higher capture efficiency screens to protect downstream pumps and reduce ragging.
• Lift Station Rehabilitation: Upgrades to the on-site and feeder lift stations to ensure peak wet weather pumping capacity (400 MGD) can be consistently met.
• Structural Rehab: Concrete rehabilitation of the aeration basins and clarifiers to extend asset life.

Biosolids Dryer Rehabilitation

Recent capital projects have focused on refurbishing the rotary drum dryers in the sludge processing facility to maintain the reliability of the Hou-Actinite production and ensure Class A compliance.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under TPDES Permit No. WQ0010495004.

• CBOD5: 10 mg/L (30-day avg)
• TSS: 15 mg/L (30-day avg)
• Ammonia-Nitrogen: 3 mg/L (30-day avg)
• Min Dissolved Oxygen: 4.0 mg/L

B. Compliance History

Historically, the 69th Street plant has maintained a strong record for effluent quality, often discharging water cleaner than the receiving bayou. Challenges occasionally arise during extreme wet weather events (hurricanes, tropical storms) where inflow and infiltration (I&I) can overwhelm hydraulic capacity, leading to bypasses or solids washout. The city is actively addressing these challenges through collection system improvements mandated by federal oversight.

7. OPERATIONAL EXCELLENCE

The facility is staffed 24/7 by a team of licensed wastewater operators (Class A and B Texas Commission on Environmental Quality certifications), industrial electricians, millwrights, and chemists. The plant utilizes a distributed control system (DCS) for automated process control, particularly for balancing the oxygen generation rate with biological demand in the reactors.

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

Commissioned in 1979, the plant is approaching 50 years of service. Concrete corrosion, mechanical fatigue in the clarifier drives, and obsolescence of the original cryogenic plant components are ongoing challenges requiring a robust asset management strategy.

B. Climate Resilience

Located near sea level along the bayou, the plant is vulnerable to flooding (as seen during Hurricane Harvey). Future planning involves elevating critical electrical gear, hardening perimeter flood walls, and installing redundant backup power generation to ensure continuity during grid failures.

C. Biosolids Disposal

Managing the massive volume of solids produced by the plant (and imported solids) requires constant dryer availability. If dryers go offline, the city faces significant costs to haul wet cake to landfills. Maintaining the thermal drying facility is a top priority for operational cost control.

9. TECHNICAL SPECIFICATIONS SUMMARY

10. RELATED FACILITIES

• Northside Lift Station: One of the primary pumping stations delivering raw wastewater to the 69th Street facility.
• Sims Bayou & Almeda Sims WWTPs: Other major facilities in the Houston system; sludge from these plants is often trucked to 69th Street for processing.
• Southeast Water Purification Plant: While a water plant, it represents the other side of Houston Water’s massive infrastructure portfolio.

11. FAQ SECTION

Technical Questions

Q: Why does 69th Street use High-Purity Oxygen instead of air?

A: HPO systems were selected in the late 1970s to treat high organic loads in a smaller tank volume. The pure oxygen increases the driving force for oxygen transfer, allowing for higher mixed liquor concentrations and a smaller physical footprint compared to conventional aeration basins.

Q: What is the permitted capacity of the plant?

A: The facility is permitted for an annual average daily flow of 200 MGD.

Q: How are biosolids handled at the facility?

A: Sludge is thickened, dewatered, and then heat-dried in rotary drum dryers to produce Class A fertilizer pellets known as “Hou-Actinite.”

Q: Does the plant perform nutrient removal?

A: The plant is designed for nitrification (ammonia removal) to meet the 3 mg/L limit. It does not currently have strict total nitrogen or phosphorus limits that would require biological nutrient removal (BNR) configurations, though this may change with future regulations.

General Public Questions

Q: Where does the water go after treatment?

A: The treated water (effluent) is discharged into Buffalo Bayou, which flows into the Houston Ship Channel and eventually Galveston Bay.

Q: Can I buy the fertilizer produced at the plant?

A: Yes, Hou-Actinite is sold commercially and is often used on golf courses, farms, and general landscaping across the region.

Q: Does the plant smell?

A: Like all wastewater facilities, odors are possible. However, the 69th Street plant employs chemical scrubbers at the headworks and utilizes covered aeration basins (part of the HPO process), which significantly contains process odors compared to open-air plants.