Ohio Wastewater Treatment Plants

Introduction

Ohio stands as a critical junction in the United States water infrastructure landscape, managing two distinct and vital watersheds: the Lake Erie basin to the north and the Ohio River basin to the south. With a highly industrialized history and significant urban density, Ohio’s wastewater infrastructure is extensive, comprising over 2,000 publicly owned treatment works (POTWs). The state is currently in a phase of massive capital reinvestment, driven largely by aging infrastructure needs and federal consent decrees aiming to eliminate Combined Sewer Overflows (CSOs).

The regulatory environment is overseen by the Ohio Environmental Protection Agency (Ohio EPA), which enforces strict National Pollutant Discharge Elimination System (NPDES) permits, particularly regarding nutrient loads (phosphorus and nitrogen) to combat harmful algal blooms in Lake Erie. Currently, the state serves a population of nearly 11.8 million, with a total treatment capacity exceeding several billion gallons per day. For consulting engineers and equipment vendors, Ohio represents one of the most active markets in the Midwest, heavily supported by the H2Ohio initiative and robust State Revolving Fund (SRF) allocations.

Ohio’s facilities are profiled here as part of the site’s wider directory of US wastewater treatment plants, which allows engineers to compare capacity, treatment trains, and regulatory drivers across state lines. That national context matters in Ohio specifically, because the state’s northern watershed operates under Great Lakes nutrient frameworks shared with neighboring states while its southern watershed answers to Ohio River basin conditions.

Recent Developments & Projects

In the last 36 months, Ohio has seen a surge in large-scale infrastructure projects. The primary driver remains the mitigation of wet weather flows. Major metropolitan sewer districts—specifically the Northeast Ohio Regional Sewer District (NEORSD), the Metropolitan Sewer District of Greater Cincinnati (MSDGC), and the City of Columbus—are midway through multi-billion dollar Long Term Control Plans (LTCPs) mandated by federal consent decrees.

Notable recent developments include:

• Tunnel Systems: Completion of major segments of deep tunnel systems in Columbus (OARS), Cleveland (Project Clean Lake), and Akron (OCIT) to capture combined sewage for treatment rather than overflow.
• Nutrient Removal: Aggressive implementation of phosphorus removal technologies in the Maumee River watershed to protect Lake Erie, supported by H2Ohio grants.
• Energy Neutrality: A growing trend toward thermal hydrolysis and enhanced anaerobic digestion to maximize biogas production for Combined Heat and Power (CHP) systems, as seen in recent upgrades at the Southerly Wastewater Treatment Center in Columbus.
• Funding Influx: Ohio has been a significant beneficiary of the Infrastructure Investment and Jobs Act (IIJA), utilizing these funds to address emerging contaminants like PFAS and to subsidize projects in disadvantaged communities.

Top 20 Largest Treatment Plants in Ohio

The following list ranks Ohio’s wastewater treatment facilities by design average daily flow capacity (MGD). Note that peak wet weather capacities for these plants are often significantly higher due to CSO capture requirements.

*Note: Easterly’s capacity varies by operational mode; listed is typical design flow.

Detailed Profiles of Top 5 Largest Plants

Significant Regional Facilities (Rank 6-20)

• Easterly WWTP (Cleveland): Serves the eastern suburbs and drains to Lake Erie; specialized activated sludge process.
• Akron WRF: Features a BioACT system and recently integrated the massive OCIT tunnel storage system.
• Dayton WRF: Renowned for its rapid sand filtration and large-scale recharge basins.
• Euclid WWTP: Recently completed a $100M+ complete facility replacement/upgrade.

Ohio Facility Profiles by Operating Authority

Ohio’s treated flow is concentrated in a small number of authorities: the City of Columbus, the Northeast Ohio Regional Sewer District, the Metropolitan Sewer District of Greater Cincinnati, and the municipal utilities in Toledo, Akron, and Dayton. Each operates a distinct treatment portfolio with its own hydraulic constraints, biosolids strategy, and consent decree obligations, and vendors working the state need to understand those differences before positioning equipment. The profiles below summarize each facility and link to its full plant page.

City of Columbus Southerly Water Resource Recovery Facility

Southerly is the largest facility in the state by average design flow and the primary receiving point for the OARS deep tunnel. The City of Columbus Southerly Wastewater Treatment Plant combines conventional screening, grit removal, primary clarification, and activated sludge with Chemically Enhanced Primary Treatment for wet weather events, discharging to the Scioto River. Its biosolids train — gravity thickening, centrifuge dewatering, and incineration — makes it one of the most equipment-intensive solids operations in Ohio and a recurring source of dewatering, polymer, and thermal system procurement. Peak hydraulic capacity of roughly 330 MGD against a 114 MGD average design flow illustrates how heavily the facility is sized for combined sewer capture rather than base sanitary load. Engineers evaluating Columbus should treat Southerly and Jackson Pike as a linked system, since flow splits between them are managed at the collection system level.

City of Columbus Jackson Pike Water Resource Recovery Facility

Jackson Pike is the older of the two Columbus plants and carries roughly 68 MGD of average design flow serving about 350,000 residents. The City of Columbus Jackson Pike Wastewater Treatment Plant runs conventional activated sludge with anaerobic digestion, and the biogas produced is used for process heating and on-site energy generation rather than being flared. That digestion train distinguishes it from Southerly’s incineration-based approach and makes it the more likely candidate for future thermal hydrolysis or renewable natural gas investment. Master planning at the facility is currently focused on nutrient removal, which points toward aeration control, chemical feed, and secondary clarifier upgrades over the next capital cycle. For vendors, Jackson Pike is the Columbus site where digestion, gas handling, and process control packages are most relevant.

City of Columbus North Highlands Water Resource Facility

Beyond the two large regional plants, the Columbus system includes smaller satellite facilities that handle localized service areas and pressure relief. The City of Columbus North Highlands Water Resource Facility falls into this category, and it is worth reviewing for anyone building a complete picture of the city’s treatment portfolio rather than only its headline capacity. Satellite facilities of this type typically operate with tighter footprints, smaller operating staffs, and simplified process trains, which changes the equipment specification calculus considerably. Packaged systems, compact controls, and low-maintenance designs generally outcompete the heavy custom equipment specified at Southerly. Engineers preparing system-wide asset plans for Columbus should not overlook these smaller assets, since they often carry the oldest equipment in the utility.

NEORSD Southerly Wastewater Treatment Center

The district’s Southerly plant in Cuyahoga Heights shares a name with the Columbus facility but is an entirely separate operation, treating about 100 MGD average and over 400 MGD at peak. The Northeast Ohio Regional Sewer District Southerly Wastewater Treatment Plant uses a two-stage biological process — plastic media trickling filters followed by activated sludge — with dual media gravity filtration as tertiary treatment, discharging to the Cuyahoga River. Its Renewable Energy Facility uses fluidized bed incineration to process biosolids and generate electricity for plant use, making it one of the most energy-integrated facilities in the Midwest. The two-stage biological configuration is unusual enough that equipment sized for conventional single-stage plants often does not transfer directly. Southerly anchors the southern half of NEORSD’s Project Clean Lake obligations.

NEORSD Westerly Wastewater Treatment Center

Westerly is the smallest of the district’s three plants at roughly 33 MGD and the most heavily wet-weather driven, sitting in a densely combined-sewered part of Cleveland’s west side. The Northeast Ohio Regional Sewer District Westerly Wastewater Treatment Plant functions as much as a CSO treatment and storage asset as a conventional secondary plant, which shapes everything from screening selection to disinfection sizing. Facilities in this posture prioritize high-rate treatment, rapid startup, and equipment tolerant of long idle periods followed by sudden full-load operation. Storage tunnel construction in the surrounding service area has progressively changed the flow regime the plant sees. Engineers comparing the three NEORSD plants should expect Westerly to have the shortest average detention times and the most variable loading.

MSD Mill Creek Wastewater Treatment Plant, Cincinnati

Mill Creek is the largest facility in the Cincinnati system at roughly 100 MGD average and 240 MGD peak, discharging to the Ohio River and serving about 500,000 people. The Metropolitan Sewer District Mill Creek Wastewater Treatment Plant operates preliminary screening, primary clarification, activated sludge secondary treatment, and chlorination with dechlorination, and has recently completed extensive solids handling and odor control work. Because it sits at the center of MSDGC’s wet weather strategy, its headworks and primary capacity are the constraint that shapes decisions across the rest of the district. Odor control is an unusually prominent design driver here given the surrounding land uses. Vendors of screening, grit, solids handling, and odor control equipment should treat Mill Creek as the district’s reference site.

City of Toledo Water Reclamation Facility

Toledo’s Bay View facility carries about 60 MGD average design flow with wet weather capacity near 195 MGD, discharging to the Maumee River and, through it, to western Lake Erie. The City of Toledo Water Reclamation Facility pairs activated sludge with ballasted flocculation for high-rate wet weather clarification, and phosphorus removal is the dominant compliance driver rather than a secondary consideration. That places Toledo at the sharp end of the state’s harmful algal bloom response and makes chemical feed, filtration, and phosphorus monitoring equipment unusually important in its capital program. Roughly $90 million in Toledo Waterways Initiative upgrades has already delivered new aeration basins and high-rate disinfection. Of all Ohio facilities, Toledo is the one where nutrient limits most directly govern process selection.

City of Akron Water Reclamation Facility

Akron operates a roughly 90 MGD facility that was substantially reconfigured to receive flow from the Ohio Canal Interceptor Tunnel. The City of Akron Water Reclamation Facility uses a biological treatment configuration paired with tunnel storage, so its wet weather performance depends as much on conveyance and dewatering pump control as on the plant’s own unit processes. Headworks capacity has become the binding constraint since the tunnel came online, and a screening and grit replacement project is in design to address it. This is a common pattern statewide: tunnel projects solve overflow problems and then immediately create a new bottleneck at the receiving plant’s front end. Engineers should read Akron as a case study in sequencing collection system and plant upgrades together.

City of Dayton Water Reclamation Facility

Dayton treats roughly 72 MGD and discharges into the Great Miami River basin, a system with significant groundwater interaction and well field protection concerns. The City of Dayton Water Reclamation Facility is known for rapid sand filtration and large-scale recharge basins, an approach that reflects the region’s reliance on the buried valley aquifer for drinking water supply. Tertiary filtration at this scale is comparatively rare in Ohio and gives Dayton a filtration equipment profile closer to a water treatment plant than to a conventional POTW. Operators and specifying engineers should note the media, backwash, and underdrain requirements that come with it. Dayton is the clearest Ohio example of wastewater treatment decisions being driven by source water protection.

Collection Systems and CSO Programs by Metro

In Ohio, the treatment plant is rarely the whole story. Most of the state’s capital spending is directed at the collection systems feeding these facilities, and the plant pages linked above are best read alongside the collection system and consent decree history of each metro area. The summaries below cover those system-level records.

Columbus Collection System

Columbus operates a largely separated system with legacy combined areas in the urban core, and its Wet Weather Management Plan pairs the OARS tunnel with sewer separation and green infrastructure. The history and configuration of the Columbus Southerly Wastewater Treatment Plant and Sewers shows how flow from the tunnel system is routed and split before reaching treatment. The companion record for the Jackson Pike wastewater treatment plant and sewers covers the northern service area and the interceptors that determine how much flow each plant receives during storms. Because Columbus can shift load between two large plants, its wet weather strategy has more operational flexibility than single-plant cities. Engineers modeling the system should treat the two plants and their interceptors as one hydraulic problem.

Cleveland and the Northeast Ohio Regional Sewer District

NEORSD’s three plants are tied together by one of the largest tunnel programs in the country. The Northeast Ohio Regional Sewer District Easterly Wastewater Treatment Plant serves the eastern service area and discharges directly to Lake Erie, which subjects it to nearshore water quality scrutiny that the Cuyahoga River dischargers do not face in the same form. The district’s broader program record, including how it has approached green infrastructure, affordability, and adaptive management, is covered in a review of the Northeast Ohio Regional Sewer District’s success story. Project Clean Lake’s headline outcome — cutting annual overflow volume from roughly 4.5 billion gallons toward under 500 million — is the benchmark other Ohio utilities are measured against. The district is also unusual in operating regional stormwater management alongside wastewater conveyance.

Cincinnati and the Mill Creek Basin

Cincinnati’s overflow problem is concentrated in one watershed, and the Metropolitan Sewer District of Greater Cincinnati Mill Creek Drainage Basin record documents the geography that drives the district’s Lower Mill Creek Partial Remedy work. Rather than building a single large tunnel, MSDGC has pursued strategic separation, storage, and real-time control across the basin, an approach regulators have accepted under integrated planning. The plant-level record for the Mill Creek Wastewater Treatment Plant covers the receiving facility itself and its process configuration. The combination makes Cincinnati the state’s leading example of smart sewer instrumentation substituting for concrete. Vendors of level sensors, actuated gates, and control software have found more traction here than anywhere else in Ohio.

Akron and Toledo Collection Systems

Akron’s consent decree work centers on the OCIT tunnel and a series of storage basins, and the system record for the Akron wastewater treatment plant and sewers traces how those assets connect to the water reclamation facility. Toledo’s program, delivered under the Toledo Waterways Initiative, is documented in the record for the Toledo Bay View Park wastewater treatment plant and sewers, which covers the storage basins and conveyance improvements feeding Bay View. Both cities illustrate the same sequencing lesson: storage capacity delivered ahead of headworks capacity produces a plant-side bottleneck within a few wet weather seasons. Utilities entering the design phase elsewhere in Ohio should build headworks capacity into the same funding package as the tunnel.

Facilities Sharing the Southerly Name

Two of Ohio’s largest plants are both called Southerly — one operated by the City of Columbus on the Scioto River, the other by NEORSD in Cuyahoga Heights on the Cuyahoga River. Confusing them is a common error in bid documents, permit research, and vendor territory planning, since they sit roughly 140 miles apart under entirely different operating authorities and consent decrees. The general record for the Southerly Wastewater Treatment Plant is a useful starting point for readers who encounter the name without a qualifying city. When specifying or referencing either facility, always pair the plant name with its operating authority.

Plants with Approved Budgets & Expansion Projects

Ohio’s wastewater sector is capitalizing on SRF loans and revenue bonds to fund massive wet weather compliance projects. Below are the most significant active capital improvement projects.

A. Major Projects Under Construction (2024-2026)

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

• MSDGC Lower Mill Creek Partial Remedy (Cincinnati):
  • Budget: ~$50-$100 Million (Phased)
  • Scope: “Smart sewer” technologies and strategic separation/storage to manage CSOs without massive new tunnels.
  • Status: Design and Adaptive Management phase.

• Akron WRF Headworks Upgrade:
  • Budget: $25 Million
  • Scope: Replacement of screening and grit removal systems to handle higher peak flows from the new tunnel.
  • Status: Design complete, bidding soon.

C. Recently Completed Major Projects (2022-2024)

• Euclid WWTP Replacement: A $110M comprehensive rebuild of the primary and secondary treatment trains, completed in 2023.
• NEORSD Doan Valley Storage Tunnel: $142M tunnel project completed in 2022 to control overflows in the University Circle area.

Regulatory & Compliance Landscape

Ohio operates under a delegated NPDES program managed by the Ohio EPA Division of Surface Water. The regulatory landscape is currently defined by two major pressures:

1. Lake Erie Nutrient Targets: Under the Great Lakes Water Quality Agreement and domestic action plans, plants in the northern watershed (Toledo, Cleveland, etc.) face stringent total phosphorus limits (often 1.0 mg/L or lower) to combat algal blooms.
2. CSO Long Term Control Plans: Virtually every major Ohio river city is under a consent decree. Regulators are increasingly open to “Integrated Planning” frameworks, allowing utilities to prioritize high-impact projects (like Green Infrastructure) over gray infrastructure if the environmental benefit is proven.

Technology Trends in Ohio

Engineering firms and vendors should note the following technology adoption trends across the state:

• Chemically Enhanced Primary Treatment (CEPT): Widely adopted in Columbus and Toledo to treat massive volumes of wet weather flow without biological upset.
• Thermal Hydrolysis (THP): Gaining traction for biosolids processing to reduce volume and increase Class A biosolid production.
• Real-Time Control (RTC): “Smart Sewer” sensors and actuated gates are being aggressively deployed in Cincinnati and South Bend (nearby) to maximize in-system storage, reducing the need for new concrete tanks.
• UV Disinfection: Rapidly replacing gaseous chlorine systems to improve safety and reduce residuals in aquatic habitats.

Complete Directory of Facilities

Browse our comprehensive directory of wastewater treatment plants in Ohio. (Select links below for full plant details).

Full plant pages for the facilities in this directory are linked from the facility profiles and collection system sections above, organized by operating authority and metro area.

Resources for Engineers & Operators

• Ohio Water Environment Association (OWEA): www.ohiowea.org – The primary professional association for networking and training.
• Ohio EPA Division of Surface Water: Operator certification and permitting details.
• Ohio Water Development Authority (OWDA): The primary funding arm for water infrastructure loans in the state.
• Operator Training: The Operator Training Committee of Ohio (OTCO) offers CEUs and exam prep.

FAQ

How many wastewater treatment plants are in Ohio?

Ohio has over 2,000 permitted Publicly Owned Treatment Works (POTWs), ranging from massive regional facilities to small package plants.

What is the largest wastewater treatment plant in Ohio?

The Southerly Wastewater Treatment Center in Columbus is generally considered the largest by average flow, treating over 114 MGD on average.

Which Ohio cities are under Consent Decrees for sewage?

Most major Ohio cities including Columbus, Cincinnati (MSDGC), Cleveland (NEORSD), Akron, Toledo, and Lima are operating under consent decrees to reduce Combined Sewer Overflows (CSOs).

What funding is available for WWTP upgrades in Ohio?

Funding is primarily available through the Water Pollution Control Loan Fund (WPCLF) managed by the Ohio EPA and OWDA. Additionally, H2Ohio grants are available specifically for nutrient reduction projects.

What are the nutrient removal requirements in Ohio?

Plants discharging into the Lake Erie watershed face strict phosphorus limits, often capped at 1.0 mg/L, with many facilities optimizing to reach 0.5 mg/L to prevent algal blooms.

Why do two Ohio plants share the Southerly name?

The City of Columbus and the Northeast Ohio Regional Sewer District each operate a facility named Southerly, roughly 140 miles apart. The Columbus plant discharges to the Scioto River at about 114 MGD average design flow; the NEORSD plant sits in Cuyahoga Heights, discharges to the Cuyahoga River, and runs about 100 MGD. They fall under separate operating authorities, separate consent decrees, and separate permit numbers, so any bid document, permit search, or territory plan should always pair the plant name with its operating authority.

Which authority operates the Cleveland-area plants?

The Northeast Ohio Regional Sewer District operates all three major Cleveland-area facilities: Easterly, which discharges to Lake Erie; Southerly in Cuyahoga Heights, the district’s largest at roughly 100 MGD; and Westerly, the smallest at about 33 MGD and the most heavily wet-weather driven. The district also manages regional stormwater alongside wastewater conveyance, which is unusual among Ohio utilities and gives it a broader capital program than a plant-only operator.

Where is smart sewer technology being deployed in Ohio?

Cincinnati is the leading example. Under the Lower Mill Creek Partial Remedy, MSDGC has pursued real-time control — level sensors, actuated gates, and control software that maximize in-system storage — as an alternative to building additional large tunnels. Regulators accepted the approach under integrated planning. Columbus and Cleveland use real-time control as well, but as a supplement to major tunnel assets rather than as a substitute for them.

Related Topics

Ohio’s regulatory drivers do not stop at the state line, and engineers benchmarking capacity, nutrient limits, or consent decree structures usually look at neighboring states as well. Facilities in the Lake Erie basin share nutrient reduction frameworks with Michigan wastewater treatment plants, which face comparable phosphorus targets in the western basin. To the east, Pennsylvania wastewater treatment plants operate under some of the country’s longest-running CSO consent decrees, offering a useful comparison for utilities entering long-term control planning. Along the Ohio River, Indiana wastewater treatment plants share both the receiving water and much of the same combined sewer legacy.

Conclusion

Ohio offers one of the most active wastewater engineering markets in the Midwest, sustained by more than $3.2 billion in committed capital, a mature State Revolving Fund program, and the H2Ohio initiative layered on top of federal IIJA allocations. The work is unusually concentrated: a handful of large authorities set the technical direction, and their process choices — CEPT for wet weather, thermal hydrolysis for biosolids, real-time control for conveyance — tend to propagate to smaller utilities across the state within a few funding cycles.

For engineers, operators, and equipment suppliers, the practical approach is to work from the operating authority down rather than from the plant list up. Identify which consent decree or nutrient limit governs the facility, understand where it sits in its authority’s sequencing of tunnel, headworks, and process upgrades, then match the technology to that stage. The facility profiles and collection system records linked throughout this guide are the starting point for that analysis.