Tennessee Wastewater Treatment Plants

1. Introduction

Tennessee’s wastewater infrastructure landscape is currently undergoing its most significant transformation in decades, driven by rapid population growth in the Nashville-Murfreesboro corridor and massive consent decree-driven overhauls in Memphis, Chattanooga, and Nashville. The state operates under the regulatory oversight of the Tennessee Department of Environment and Conservation (TDEC), managing a network of over 260 public municipal wastewater treatment plants (WWTPs).

Currently, Tennessee facilities treat approximately 1.2 billion gallons of wastewater daily. The state faces a unique hydrological divide: West Tennessee facilities primarily discharge into the high-volume Mississippi River, allowing for different effluent limits compared to Middle and East Tennessee plants, which discharge into sensitive tributaries of the Cumberland and Tennessee Rivers. This dichotomy creates distinct engineering challenges, ranging from nutrient removal requirements in the east to massive hydraulic capacity needs in the west.

With the recent influx of American Rescue Plan (ARP) funds managed through the Tennessee Water Infrastructure Investment Plan (TWIIP), the state has allocated over $1.35 billion in grants, spurring a construction boom for consulting engineers and equipment vendors alike.

Tennessee is also a useful reference case for anyone studying how consent decrees reshape a state’s capital program. Four of its largest cities have operated under federal decrees simultaneously, producing a decade of comparable overflow-reduction work across very different geologies and receiving waters. Readers benchmarking the state against comparable systems can work from the national inventory of US wastewater treatment plants to see how Tennessee’s capacity, permit conditions, and funding levels sit against regional and national norms.

2. Recent Developments & Projects

The wastewater sector in Tennessee is currently defined by the convergence of federal funding and regulatory enforcement. In the last 24 months, the state has moved aggressively to address aging infrastructure that contributes to sanitary sewer overflows (SSOs).

Key developments include:

• TDEC ARP Grants: In late 2022 and throughout 2023, TDEC awarded over $1 billion in non-competitive grants to cities and counties for water infrastructure, requiring local matches that have mobilized nearly $2 billion in total capital activity.
• Memphis Consent Decree Work: The City of Memphis is midway through a $250 million update to its major plants to address EPA compliance, focusing on disinfection and biosolids.
• Regionalization Studies: TDEC is actively funding engineering studies to assess the viability of connecting struggling small utility districts to larger, more capable municipal systems, creating opportunities for pipeline and pump station engineering projects.
• Biosolids Innovation: Chattanooga continues to lead with its thermal hydrolysis process (THP) installation, setting a precedent for energy neutrality in the region.

3. Top 20 Largest Treatment Plants in Tennessee

The following table ranks Tennessee’s largest wastewater treatment facilities by Design Capacity (MGD). Data is aggregated from TDEC NPDES permits, EPA ECHO database, and municipal Capital Improvement Plans (CIP).

*Note: Moccasin Bend’s capacity fluctuates based on wet weather protocols; peak hydraulic capacity is significantly higher.

A note on the top two. Moccasin Bend and M.C. Stiles are within a few MGD of each other, and published figures for both vary depending on whether the source cites average daily design flow, wet-weather rated capacity, or permitted maximum. Moccasin Bend leads on the design figures used in this table; Stiles serves a substantially larger population. Engineers citing a “largest plant in Tennessee” figure should state which basis they are using and trace it to the facility’s NPDES permit.

Detailed Profiles of the Top 5 Largest Plants

4. Plants with Approved Budgets & Expansion Projects

Tennessee is currently seeing a surge in capital expenditure, primarily funded by State Revolving Funds (SRF), Revenue Bonds, and the TDEC-administered ARP grants. The following projects represent the most significant engineering opportunities in the state.

A. Major Projects Under Construction (2024-2026)

B. Projects in Design/Planning Phase (2025-2027)

• Smyrna WWTP Expansion Phase 3: Design phase for increasing capacity from 15.85 MGD to 22.5 MGD. Estimated Budget: $45 Million. Driver: Regional automotive and residential growth.
• Harpeth Valley Utility District Expansion: Planning stages to expand treatment capacity to accommodate western Davidson/Williamson County growth. Budget: ~$30 Million.
• Clarksville WWTP Biosolids Upgrade: Engineering design for improved solids handling and thermal drying. Estimated Budget: $20 Million.

C. Summary Statistics

5. Regulatory & Compliance Landscape

The Tennessee Department of Environment and Conservation (TDEC) Division of Water Resources enforces the state’s water quality standards. Tennessee operates under delegated NPDES authority from the EPA.

• Nutrient Reduction: TDEC has been tightening limits on Nitrogen and Phosphorus, particularly for plants discharging into the Tennessee River watershed, necessitating upgrades to Biological Nutrient Removal (BNR) processes.
• Consent Decrees: Nashville, Memphis, Chattanooga, and Knoxville have all operated under federal consent decrees, which mandate strict schedules for reducing Sanitary Sewer Overflows (SSOs). This is the primary legal driver for the billion-dollar investments seen in these metro areas.
• PFAS Monitoring: TDEC has initiated statewide sampling for PFAS in wastewater effluent. While strict limits are not yet in all permits, engineers should anticipate future PFAS treatment requirements in design phases.

Regional and Interstate Context

Tennessee borders eight states, and its two dominant river systems are shared across most of them. The Tennessee River enters north Alabama and returns through the state before joining the Ohio, while the Cumberland runs from and back into Kentucky, whose facilities operate under the same TVA-influenced framework and much of the same karst hydrology. For engineers working the Middle and East Tennessee markets, the Kentucky programs are the closest available comparison on both regulatory posture and geologic constraint.

In the west, Memphis discharges directly into the Mississippi River at the point where three states meet, and the metropolitan area extends across the line into DeSoto County. Water quality conditions on that reach are a joint product with Mississippi, and the high assimilative capacity that shapes Memphis permit conditions applies equally to facilities on the other side. In the southeast, Chattanooga sits within a few miles of the Georgia line on a stretch of the Tennessee River that has been the subject of a long-running interstate water allocation dispute, making the Georgia picture directly relevant to anyone planning around Tennessee River withdrawals or discharges.

6. Infrastructure Challenges & Opportunities

Inflow and Infiltration (I&I): The geology of Tennessee (karst terrain in the middle/east) combined with aging clay pipes results in massive I&I issues. During heavy rain events, plants like Nashville’s Central or Chattanooga’s Moccasin Bend see flow spikes of 300-400% above average. This creates a robust market for sewer rehabilitation, lining, and flow equalization basin construction.

Workforce Shortage: Tennessee faces a critical shortage of certified Grade 3 and 4 operators. Automation and SCADA upgrades are increasingly viewed not just as efficiency tools, but as necessary adaptations to a shrinking workforce.

Growth Concentration: The state’s capacity pressure is not evenly distributed. Rutherford, Williamson, and Wilson counties in the Nashville orbit have absorbed a disproportionate share of population growth, which is why Murfreesboro, Smyrna, Franklin, and Gallatin all appear in the capital project list despite being mid-size systems. For engineering firms, the growth corridor south and east of Nashville has produced more expansion work per capita than any other part of the state.

Wet Weather Storage as the Dominant Design Problem

The practical consequence of Tennessee’s karst geology is that peak-to-average flow ratios here are among the highest in the Southeast. Nashville’s Central plant is rated at 100 MGD but must accept 440 MGD during storm events, a 4.4 to 1 ratio that no biological process can absorb directly. The engineering response has consolidated around a consistent set of approaches: chemically enhanced primary treatment to strip solids from flows that bypass secondary, equalization basins sized to shave the peak rather than store the full volume, and real-time control in the collection system to use existing pipe capacity as distributed storage.

That last approach has gained ground because it is far cheaper per gallon of avoided overflow than building tankage. Utilities that instrument their interceptors and actively manage in-line storage frequently defer or shrink planned storage projects, which changes the vendor picture considerably: the work shifts from concrete and earthmoving toward level sensors, actuated gates, hydraulic modeling, and control system integration. For firms positioning in the Tennessee market, collection system intelligence is now competing directly with structural storage for the same capital dollars.

Operator Certification and the Regionalization Response

The workforce shortage and the regionalization program are the same problem viewed from two directions. A small utility district that cannot recruit a Grade 3 or Grade 4 operator cannot legally run a plant requiring one, and contract operations become the only alternative to consolidation. TDEC’s funding of regionalization feasibility studies is a direct response to this: connecting a struggling district to a larger municipal system solves the staffing problem, the compliance problem, and the capital problem simultaneously.

For operators, the shortage has improved leverage considerably, particularly for higher-grade licenses in the metro markets. For engineering firms, it has created a steady stream of work that has little to do with treatment process design: rate studies, interlocal agreements, asset condition assessments, and interconnection routing. The Fleming Training Center remains the state’s licensure pipeline, and its throughput is effectively the ceiling on how quickly the shortage can close.

7. Technology Trends in Tennessee

• Disinfection Evolution: A rapid move away from chlorine gas due to safety concerns. Large plants are moving to UV (Nashville, Memphis Stiles) or Peracetic Acid (Memphis Maxson pilots).
• Thermal Hydrolysis: Chattanooga’s adoption of CAMBI technology has set a regional standard for high-efficiency biosolids processing, generating class A biosolid fertilizer.
• Decentralized Treatment: In rapid-growth areas like Williamson County, decentralized STEP (Septic Tank Effluent Pumping) systems and small satellite plants are being used to bypass the lag time of massive central sewer expansion.
• Collection System Real-Time Control: Instrumented interceptors with actuated gates are being used to store wet weather flow in existing pipe volume, deferring or downsizing planned storage tanks in several consent decree programs.
• Chemically Enhanced Primary Treatment (CEPT): Increasingly specified at high peak-ratio plants as a way to treat bypass flows that cannot pass through secondary, rather than discharging them untreated.

The common thread across these trends is that Tennessee utilities are optimizing around wet weather rather than around average conditions. That is a meaningful distinction for vendors, because equipment selected on average-flow performance frequently underperforms when the governing design case is a four-hour storm peak several times larger.

8. Directory of Facilities

Browse our comprehensive directory of wastewater treatment plants in Tennessee:

• M.C. Stiles WWTP (Memphis)
• Metropolitan Nashville Central WWTP
• Chattanooga Moccasin Bend WWTP
• Memphis T.E. Maxson WWTP
• Kuwahee WWTP (Knoxville)
• Dry Creek WWTP (Nashville)
• Murfreesboro WRRF

West Tennessee: Memphis and the Mississippi Corridor

West Tennessee’s treatment picture is dominated by Memphis, which operates the two largest facilities in the region through the city’s Public Works department rather than a separate utility authority. Both Stiles and Maxson discharge to the Mississippi River, and the river’s assimilative capacity is the single most important fact about how they are permitted. Effluent limits that would be unachievable on a small Middle Tennessee creek are routine here, which historically allowed both plants to operate without tertiary treatment.

That permissiveness has narrowed. The consent decree work now underway is adding disinfection at both facilities, replacing chlorine gas with UV at Stiles and peracetic acid at Maxson, and rebuilding electrical and blower systems that had aged past reliable service. Outside Memphis, Jackson’s South Jackson facility is the only other West Tennessee plant of significant scale, and much of the region is served by small systems that are prime candidates for the regionalization studies TDEC is funding.

Middle Tennessee: Nashville and the Growth Corridor

Metro Water Services operates three plants across Davidson County, with Central handling downtown and the majority of the combined sewer area, Whites Creek serving the north, and Dry Creek the northeast. Central is the only one of the three with a genuine combined sewer legacy, which is why the Clean Water Nashville consent decree work has concentrated there, and why its wet weather peak of 440 MGD is more than four times its design capacity.

The surrounding counties tell a different story. Murfreesboro, Smyrna, Franklin, and Gallatin are all expanding rather than rehabilitating, driven by some of the fastest suburban growth rates in the country. Harpeth Valley Utility District occupies a middle position, serving western Davidson and Williamson County growth through a shared regional facility. For vendors, the Middle Tennessee market splits cleanly between consent-decree rehabilitation work in Nashville proper and greenfield capacity work in the collar counties.

East Tennessee: The Tennessee River Valley

East Tennessee’s facilities discharge into the Tennessee River system, where lower dilution and TVA reservoir management combine to produce tighter nutrient limits than the west sees. Knoxville Utilities Board operates three plants, with Kuwahee the largest, and has approached compliance through the Century II asset management program rather than a single large capital push. Chattanooga’s Moccasin Bend anchors the southern end of the valley and, through its thermal hydrolysis installation, has become the regional reference point for Class A biosolids production.

Further northeast, Kingsport and Johnson City serve the Tri-Cities region with facilities in the 26 to 29 MGD range, sizable systems that receive far less attention than the four major metros despite comparable per-capita infrastructure demands. Cleveland and Oak Ridge round out the region’s mid-size plants, with Oak Ridge carrying an unusual industrial legacy tied to the federal reservation.

9. Resources for Engineers & Operators

• Tennessee Department of Environment and Conservation (TDEC): Regulatory guidance and SRF funding information.
• Clean Water Professionals of Kentucky & Tennessee (CWP-KT): The primary Water Environment Federation (WEF) member association for the region.
• Tennessee Association of Utility Districts (TAUD): Provides training and certification for operators.
• Fleming Training Center: The state’s hub for operator licensure exams and classes.
• TDEC Data Viewer and Permit Search: Public access to NPDES permit conditions, monitoring data, and compliance history by facility. The starting point for verifying any capacity or discharge figure.
• EPA ECHO (Enforcement and Compliance History Online): Federal facility-level records, including discharge monitoring report data and consent decree status.
• TDEC Intended Use Plan and Priority Ranking List: The annual SRF funding priority list, published ahead of each cycle. The clearest forward indicator of where design and construction work will appear.

10. FAQ Section

How many wastewater treatment plants are in Tennessee?

Tennessee has approximately 260 public municipal wastewater treatment plants, in addition to numerous industrial and private decentralized systems.

What is the largest wastewater treatment plant in Tennessee?

Chattanooga’s Moccasin Bend and Memphis’s M.C. Stiles are effectively tied, at roughly 140 and 135 MGD design capacity respectively, and published figures for both vary with the basis used. Moccasin Bend leads on design flow and handles the higher wet-weather peak; Stiles serves the larger population at roughly 650,000. Cite whichever basis your application requires and trace the figure to the facility’s NPDES permit.

What funding is available for WWTP upgrades in Tennessee?

The primary funding vehicles are the State Revolving Fund (SRF) loans and the TDEC-administered American Rescue Plan (ARP) grants, which recently allocated $1.35 billion for water infrastructure.

Are Tennessee plants required to remove nutrients?

Yes, plants discharging into nutrient-impaired waters (common in East and Middle Tennessee) generally have strict Nitrogen and Phosphorus limits in their NPDES permits.

Who regulates wastewater treatment in Tennessee?

The Tennessee Department of Environment and Conservation (TDEC), specifically the Division of Water Resources.

Why do West and East Tennessee plants face such different permit conditions?

Dilution. West Tennessee facilities discharge into the Mississippi River, whose volume provides assimilative capacity that supports relatively permissive effluent limits. Middle and East Tennessee plants discharge into Cumberland and Tennessee River tributaries and TVA reservoirs, where lower flows and reservoir residence times concentrate nutrients and drive tighter nitrogen and phosphorus limits. Two plants of identical size can therefore face entirely different treatment requirements depending on which side of the state they sit.

How do I verify capacity and compliance data for a specific Tennessee plant?

Start with the facility’s NPDES permit through the TDEC permit search, which states permitted flow and effluent limits directly, then cross-check actual performance through discharge monitoring report data on EPA ECHO. Design capacity figures published in capital improvement plans and annual reports frequently differ from permitted flow, particularly at facilities in the middle of a consent decree upgrade, so any number headed into a specification or funding application should be traced back to the permit.

11. Conclusion

Tennessee’s wastewater sector is defined by a convergence that will not last indefinitely: federal consent decree deadlines, a one-time influx of ARP grant funding, and population growth concentrated in a handful of fast-expanding counties. The result has been an unusually dense pipeline of work across rehabilitation, disinfection conversion, biosolids upgrades, and greenfield capacity, all running at once.

For engineers, operators, and vendors, the practical starting point is identifying which of those drivers governs a given facility, since consent decree rehabilitation, nutrient compliance, and growth-driven expansion each bring different technologies, different funding paths, and different competitors. The facility directory above indexes the utilities where that work is concentrated.