What is the largest wastewater treatment plant in Ohio?

Southerly Wastewater Treatment Plant in Lockbourne, treating an average of 112.28 MGD under NPDES permit OHL024741. Southerly Wastewater Treatment Center in Cleveland is second at 110.09 MGD.

How much wastewater do Ohio’s largest plants treat?

The 50 largest plants treat 881 MGD combined, 67% of the flow reported by all 843 publicly owned plants in Ohio.

How is plant size measured?

By reported average daily flow in million gallons per day (MGD) from EPA discharge monitoring reports, the standard measure of a plant’s size. Design capacity, the flow a plant is permitted to treat, is usually higher and is shown on each profile.

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The 50 largest wastewater treatment plants in Ohio

Name: Largest wastewater treatment plants in Ohio
Creator: Klarifi
License: https://klarifi.io/terms-of-service

Ranked by average flow · 881 MGD combined · 67% of the state's reported flow

Southerly Wastewater Treatment Plant in Lockbourne is the largest publicly owned wastewater treatment plant in Ohio by reported average flow, treating about 112.28 million gallons per day. The 50 plants below treat 881 MGD between them, 67% of the flow reported by all 843 plants in the state, and serve about 4,484,858 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.

All plants in Ohio →The 50 largest US plants →Ohio NPDES permits →

The 50 largest publicly owned wastewater treatment plants in Ohio by average flow (MGD), with population served, NPDES permit, expiry and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Violations (3y)
1	Southerly Wastewater Treatment Plant	Lockbourne	112.28	706,507	OHL024741	Dec 2030	9
2	Southerly Wastewater Treatment Center	Cleveland	110.09	555,185	OHL024651	Dec 2030	4
3	Akron WRF	Akron	59.62	321,892	OH0023833	Aug 2028	0
4	City Of Dayton Water Reclamation Facility (0857100983)	Dayton	51.69	184,008	OH0024881	Apr 2027	17
5	Metropolitan Sewer Dis Little Miami WWTP	Cincinnati	44.32	136,312	OH0025453	Jun 2030	8
6	Waste Water Treatment Plant	Youngstown	33.2	125,268	OH0028223	Oct 2028	231
7	Neorsd Westerly Wwt Complex	Cleveland	27.54	91,067	OH0024660	Jun 2030	0
8	City Of Canton	Canton	25.4	110,970	OH0024350	May 2028	1
9	Middletown Wastewater Treatment Plant	Middletown	21.19	51,033	OH0026522	Dec 2026	85
10	City Of Euclid, Wastewater Treatment Plant	Euclid	18.11	90,347	OH0031062	Aug 2029	12
11	City Of Springfield Wastewater Treatment	Springfield	17.12	58,763	OH0027481	Feb 2030	39
12	Maumee River Wastewater Treatment Plant	Waterville	15.06	84,393	OH0034223	Dec 2027	15
13	Gary L Kron Water Reclamation Facility	Mentor	14.71	104,000	OH0043559	Mar 2027	30
14	Lima WWTP	Lima	14.49	37,907	OH0026069	Jun 2028	35
15	Western Regional WRF	West Carrollton	14.48	88,254	OH0026638	Oct 2026	4
16	Rocky River Wastewater Treatment Plant	Rocky River	13.54	84,130	OH0030503	Jan 2028	15
17	City Of Warren Water Pollution Control	Warren	13.31	42,553	OH0027987	Nov 2028	68
18	Muddy Creek WWTP	Cincinnati	12.73	80,528	OH0025470	Mar 2030	20
19	Black River Wastewater Treatment Plant	Lorain	12.3	75,005	OH0026093	Nov 2027	6
20	Massillon WWTP	Massillon	11.5	62,192	OH0020516	May 2031	0
21	Sandusky WPC	Sandusky	11.27	36,245	OH0027332	Apr 2031	0
22	Lesourdsville Water Reclamation Facility	Hamilton	11.24	65,027	OH0049417	Nov 2026	6
23	North Regional Wastewater Treatment Plan (0857143037)	Dayton	11.24	69,382	OH0049646	Feb 2027	49
24	Mansfield Wastewater Treatment Plant	Mansfield	10.98	53,150	OH0026328	Mar 2030	426
25	Upper Mill Creek Water Reclamation Facil	West Chester	10.8	74,361	OH0072087	Dec 2023	37
26	Beavercreek WRRF	Dayton	9.73	38,828	OH0025381	Nov 2030	47
27	Findlay WPCF	Findlay	9.51	41,213	OH0025135	Oct 2029	1
28	Medina County - Liverpool WWTP (sd #500)	Valley City	9.15	95,434	OH0043567	Nov 2030	5
29	Hamilton Water Reclamation Facility	Hamilton	8.62	64,583	OH0025445	Oct 2026	7
30	Eastern Regional Water Reclamation Facility	Kettering	8.51	46,364	OH0026590	Feb 2031	7
31	City Of Zanesville Wastewater Treatment Plant	Zanesville	8.44	49,058	OH0028240	Mar 2028	12
32	Newark WWTP	Newark	8.3	50,383	OH0026671	Jun 2031	472
33	Sycamore Creek WWTP	Cincinnati	8.08	24,200	OH0025488	Sep 2026	15
34	City Of Elyria Wastewater Pollution Control Plant	Elyria	7.97	52,738	OH0025003	May 2026	1
35	Marion WPC	Marion	7.91	36,310	OH0026352	Apr 2030	14
36	Sugarcreek WRF	Spring Valley	7.88	43,383	OH0040592	Apr 2031	1
37	Lower East Fork Regional WWTP	Milford	7.83	55,640	OH0049379	Oct 2026	4
38	Mason WWTP No 2	Mason	7.31	22,496	OH0020494	May 2026	0
39	Fremont WPCF	Fremont	7.22	24,104	OH0025291	Sep 2029	7
40	Lower Little Miami WWTP	Maineville	6.9	48,074	OH0071692	Feb 2026	9
41	French Creek WWTP	North Ridgeville	6.82	50,376	OH0044512	Oct 2027	14
42	Lakewood WWTP	Lakewood	6.28	50,848	OH0026018	Jul 2026	5
43	North Olmsted WWTP	North Olmsted	6.03	38,661	OH0026778	Jul 2030	5
44	Wooster Renewable Energy	Wooster	6	27,526	OH0028185	Nov 2029	23
45	Willoughby-Eastlake Water Pollution Cont	Eastlake	5.93	42,529	OH0028126	Sep 2025	82
46	Oregon Wastewater Treatment Plant	Oregon	5.86	30,263	OH0052914	Nov 2028	1
47	Alum Creek WWTP	Delaware	5.81	65,613	OH0121380	Dec 2030	8
48	Fairfield WWTP	Fairfield	5.55	44,396	OH0025071	Nov 2026	3
49	Lancaster Water Pollution Control	Lancaster	5.38	26,801	OH0026026	Nov 2028	20
50	Marysville WRF	Marysville	5.36	26,558	OH0136271	Jun 2028	8

Treatment technology for each plant is shown with a free Klarifi account. Create one →

Largest plants in Ohio: questions

Sources and methodology

Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.

Data refreshed October 26, 2026.

Wastewater terms: WWTP · POTW · MGD · NPDES permit · Filter press · FOG · all terms

Cite this page

Journalists, researchers and educators are welcome to quote these figures. Please credit Klarifi as the source and link to this page.

Klarifi. “The 50 largest wastewater treatment plants in Ohio (2026).” Updated October 26, 2026. https://klarifi.io/facilities/ohio/largest

Need a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.

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