Knoxville Kuwahee Wastewater Treatment Plant

1. INTRODUCTION

The Kuwahee Wastewater Treatment Plant (WWTP) serves as the flagship facility for the Knoxville Utilities Board (KUB) and a critical component of East Tennessee’s water infrastructure. Situated along the banks of the Tennessee River, mere minutes from downtown Knoxville and the University of Tennessee campus, Kuwahee is the largest of KUB’s four wastewater treatment facilities. With a design capacity of 44 million gallons per day (MGD) and a peak hydraulic capacity of 120 MGD, it manages wastewater for the city’s densest urban corridors.

Originally commissioned in the mid-1950s, the facility has evolved from a primary treatment plant into a sophisticated advanced secondary treatment complex. Under the KUB “Century II” infrastructure management program, Kuwahee has recently integrated state-of-the-art Biologically Enhanced High-Rate Clarification (BEHRC) technology to manage wet-weather flows and a Combined Heat and Power (CHP) cogeneration facility that offsets nearly 40% of the plant’s energy needs. These advancements position Kuwahee as a regional model for hydraulic resilience and energy sustainability.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Kuwahee WWTP services the “Kuwahee Basin,” which encompasses approximately 46 square miles of the metropolitan area. This basin includes the central business district, the University of Tennessee, heavy commercial zones along the I-40 corridor, and the residential areas of South and West Knoxville. The collection system feeding Kuwahee is characterized by older infrastructure, necessitating robust inflow and infiltration (I&I) management strategies at the plant headworks.

B. Operational Capacity

The plant operates with a design average daily flow of 44 MGD. However, due to the age of the collection system in the historic parts of Knoxville, the facility experiences significant peaking factors during precipitation events. To mitigate Sanitary Sewer Overflows (SSOs), the plant was engineered to handle peak hydraulic flows of up to 120 MGD. Current average daily flows typically range between 34 and 36 MGD, providing adequate dry-weather reserve capacity for projected urban density growth.

C. Discharge & Compliance

Treated effluent is discharged into the Tennessee River (Fort Loudoun Lake reservoir) via a submerged multi-port diffuser. The facility operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Tennessee Department of Environment and Conservation (TDEC). The plant consistently achieves high compliance rates, frequently receiving the National Association of Clean Water Agencies (NACWA) Peak Performance Awards for permit compliance.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

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Raw wastewater enters the facility through the Main Pump Station. Preliminary treatment consists of mechanical bar screens to remove large debris, rags, and plastics. Following screening, flow passes through aerated grit chambers where inorganic solids (sand, gravel, coffee grounds) settle out to protect downstream mechanical equipment. The grit is washed and dewatered before landfill disposal. Odor control at the headworks is a critical operational priority due to the plant’s proximity to public parks and the university.

B. PRIMARY TREATMENT

Flow proceeds to primary clarification, where gravity settling removes approximately 60-70% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD). Kuwahee utilizes rectangular primary clarifiers equipped with chain-and-flight sludge collectors. Primary sludge is pumped directly to the solids handling train (gravity thickeners), while the primary effluent flows to the biological treatment stage.

C. SECONDARY TREATMENT

The core of Kuwahee’s process is a conventional Activated Sludge system. Primary effluent enters aeration basins where it is mixed with Return Activated Sludge (RAS) to form mixed liquor.
Aeration System: The basins utilize a combination of mechanical surface aerators and diffused air systems to provide the necessary oxygen for microorganisms to metabolize organic matter. The hydraulic retention time is managed to optimize BOD removal and nitrification efficiency.

D. SECONDARY CLARIFICATION

Mixed liquor from the aeration basins flows to secondary clarifiers. These large circular tanks allow the biological floc to settle, separating the treated water from the biomass. A portion of the settled solids is returned to the aeration basins (RAS), while the excess biomass is removed as Waste Activated Sludge (WAS) for processing.

E. DISINFECTION

Kuwahee utilizes chlorination for disinfection. Chlorine gas is injected into the contact chambers to neutralize pathogenic organisms (fecal coliform/E. coli). Prior to discharge into the Tennessee River, the effluent undergoes dechlorination using sulfur dioxide (SO2) to remove residual chlorine, ensuring no toxicity to aquatic life in the receiving water body.

F. SOLIDS HANDLING

Solids management at Kuwahee is comprehensive:

• Thickening: Primary sludge is thickened in gravity thickeners; WAS is thickened using gravity belt thickeners.
• Digestion: Thickened sludge is stabilized in anaerobic digesters. These digesters are heated to mesophilic temperatures (approx. 98°F) to reduce volatile solids and pathogen counts.

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• Dewatering: Digested biosolids are dewatered using high-solids centrifuges to produce a “cake” suitable for transport.
• Disposal/Reuse: KUB operates a Biosolids Beneficial Reuse Program. The Class B biosolids are certified for land application as fertilizer on permitted agricultural sites in surrounding counties.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The Kuwahee site occupies a significant footprint along Neyland Drive. The architecture is functional and industrial, featuring extensive gallery systems for pipe routing. The site houses a fully equipped laboratory accredited for NPDES compliance testing, maintenance shops, and administrative offices for KUB’s wastewater division leadership.

B. Energy Systems & Cogeneration

Kuwahee is a leader in energy recovery in the Southeast. The facility utilizes a Combined Heat and Power (CHP) system.

• Biogas Utilization: Methane gas produced during anaerobic digestion is captured, scrubbed, and conditioned.
• Power Generation: Two 1.6-megawatt engine generators run on the captured biogas.
• Efficiency: This system generates approximately 40% of the plant’s electrical demand. Additionally, waste heat from the engines is captured via heat exchangers to maintain the temperature of the anaerobic digesters, creating a closed-loop energy cycle.

5. RECENT UPGRADES & MAJOR PROJECTS

Kuwahee Wet Weather Storage & Treatment (2018-2022)

• Project Scope: Construction of the BioActiflo BEHRC system and associated pump stations.
• Budget: ~$45 – $50 Million (Part of the larger Century II initiative).
• Drivers: Regulatory compliance regarding SSOs and the need to treat peak wet weather flows without bypassing secondary treatment.
• Technical Highlight: The project included a new diversion structure and intermediate pump station capable of routing excess flows to the high-rate treatment train, ensuring all discharged water meets secondary treatment standards even during storm events.

Biogas Cogeneration Facility (Completed ~2011/2012)

• Project Scope: Installation of two 1,600 kW cogeneration engines and gas conditioning skid.
• Budget: ~$6.5 Million.
• Results: Reduced grid energy purchase by roughly 13 million kWh annually and reduced carbon footprint significantly.

Current/Upcoming Projects (2024-2027)

KUB continues to invest through the Century II program. Upcoming focuses include electrical gear replacement, further headworks screening improvements, and ongoing rehabilitation of the massive interceptors feeding the plant (specifically the Second Creek and Third Creek interceptors).

6. REGULATORY COMPLIANCE

A. Permit Requirements

Operating under NPDES Permit TN0023582, Kuwahee is subject to strict limits on:

• CBOD5: Monthly average limits typically around 25 mg/L (summer).
• TSS: Monthly average limits typically around 30 mg/L.
• E. Coli: Seasonal limits (geometric mean) to ensure water quality for recreation.
• Nutrients: Monitoring requirements for Nitrogen and Phosphorus to protect the Tennessee River watershed.

B. Consent Decree History

Like many older municipalities, Knoxville operated under a federal Consent Decree (CD) focused on eliminating SSOs. KUB successfully completed the requirements of this decree through the Century II program, which mandated over $650 million in system-wide wastewater improvements, with Kuwahee’s capacity upgrades playing a central role in achieving compliance.

7. OPERATIONAL EXCELLENCE

The facility is staffed 24/7 by a team of state-certified operators, industrial maintenance mechanics, and instrumentation technicians. KUB maintains a strong emphasis on professional development, with many operators holding Grade III and IV certifications (the highest in Tennessee). The plant utilizes a robust SCADA system for real-time process monitoring, integrating data from the collection system pump stations to predict flow surges before they arrive at the headworks.

8. CHALLENGES & FUTURE PLANNING

Inflow and Infiltration (I&I): Despite massive investments, the older housing stock and clay pipes in the Kuwahee basin continue to contribute significant I&I. Future planning involves continued lining and replacement of collection mains.

Nutrient Regulations: While currently compliant, KUB engineers are planning for potential future tightening of nutrient limits (Total Nitrogen and Total Phosphorus) by TDEC, which may require retrofitting the aeration basins for biological nutrient removal (BNR) configurations.

Urban Growth: As downtown Knoxville densifies with new high-rise residential developments, the baseload flow to Kuwahee is expected to rise, requiring careful asset management to maintain reserve capacity.

9. COMMUNITY & REGIONAL IMPACT

Kuwahee is not just a utility asset; it is a neighbor to the city’s most popular recreation areas. The plant is visible from the Neyland Greenway and adjacent to the university. Consequently, KUB invests heavily in aesthetics and odor control. The Biosolids Beneficial Reuse program supports local agriculture, returning nutrients to the soil rather than filling landfills, demonstrating a commitment to the circular economy.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

Kuwahee is the largest of KUB’s four wastewater plants. The system also includes:

• Fourth Creek WWTP: Serves West Knoxville.
• Loves Creek WWTP: Serves the northeast sector.
• Eastbridge WWTP: Serves the industrial park areas in East Knox County.

Kuwahee also processes sludge transferred from some of these satellite facilities for centralized digestion and dewatering.

12. FAQ SECTION

Technical Questions

1. What is the BEHRC system at Kuwahee?
BEHRC stands for Biologically Enhanced High-Rate Clarification. It is a parallel treatment process used during wet weather to treat excess flows that exceed the capacity of the standard aeration basins, using microsand and polymer to settle solids rapidly while maintaining biological treatment standards.

2. Does Kuwahee remove nutrients?
The plant achieves incidental nutrient removal through its biological process but is not currently permitted as a strict Biological Nutrient Removal (BNR) facility with low limits for Total Nitrogen or Phosphorus. Future upgrades may address this.

3. How much energy does the plant generate?
The Cogeneration facility produces approximately 40% of the plant’s electrical needs using biogas captured from the anaerobic digesters.

4. Is the plant under a Consent Decree?
KUB operated under a federal Consent Decree regarding SSOs for several years. The utility successfully completed the major capital requirements of this decree (via the Century II program) to the satisfaction of regulators.

Public Interest Questions

5. Why does the plant sometimes have an odor?
Wastewater treatment inherently involves organic breakdown which produces odors. However, Kuwahee employs scrubbers and biofilters to capture these odors. Occasional smells may occur during process upsets, extreme weather, or maintenance on odor control units.

6. Can I tour the Kuwahee WWTP?
KUB occasionally offers tours for educational groups, universities, and professional organizations. Public tours are generally arranged by request through the KUB community relations department.