What is the largest wastewater treatment plant in Ohio?

Southerly Wastewater Treatment Plant in Lockbourne, treating an average of 82.1 MGD under NPDES permit OHL024741. Southerly Wastewater Treatment Center in Cleveland is second at 78.11 MGD.

How much wastewater do Ohio’s largest plants treat?

The 50 largest plants treat 651 MGD combined, 69% of the flow reported by all 837 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 · 651 MGD combined · 69% 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 82.1 million gallons per day. The 50 plants below treat 651 MGD between them, 69% of the flow reported by all 837 plants in the state, and serve about 4,733,840 people. Every plant links to its profile with permit, technology and compliance data.

All plants in Ohio →The 100 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, treatment technology and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Technology	Violations (3y)
1	Southerly Wastewater Treatment Plant	Lockbourne	82.1	706,507	OHL024741	Dec 2030	Clarifiers, Biogas silos	7
2	Southerly Wastewater Treatment Center	Cleveland	78.11	555,185	OHL024651	Dec 2030	Clarifiers, Biogas balloons	3
3	Akron WRF	Akron	44.82	321,892	OH0023833	Aug 2028	Clarifiers, Uncovered lagoons	0
4	City Of Toledo Division Of Water Reclaimation	Toledo	39.6	289,101	OH0027740	Jan 2029	Clarifiers, Uncovered lagoons, Biogas silos, Biogas balloons	3
5	City Of Dayton Water Reclamation Facility (0857100983)	Dayton	38.22	184,008	OH0024881	Apr 2027	Clarifiers, Biogas silos, Biogas balloons	17
6	Metropolitan Sewer Dis Little Miami WWTP	Cincinnati	21.87	136,312	OH0025453	Jun 2030	Clarifiers, Biogas balloons	8
7	Waste Water Treatment Plant	Youngstown	20.84	125,268	OH0028223	Oct 2028	Biogas silos, Biogas balloons	231
8	City Of Canton	Canton	20.5	110,970	OH0024350	May 2028	—	1
9	Neorsd Westerly Wwt Complex	Cleveland	18.52	91,067	OH0024660	Jun 2030	Biogas balloons	0
10	City Of Springfield Wastewater Treatment	Springfield	12.27	58,763	OH0027481	Feb 2030	Clarifiers, Biogas silos	39
11	Middletown Wastewater Treatment Plant	Middletown	11.69	51,033	OH0026522	Dec 2026	Clarifiers, Biogas silos, Biogas balloons	82
12	Maumee River Wastewater Treatment Plant	Waterville	11.65	84,393	OH0034223	Dec 2027	Clarifiers, Biogas balloons	15
13	Lakewood WWTP	Lakewood	11.52	50,848	OH0026018	Jul 2026	Clarifiers, Biogas silos, Biogas balloons	5
14	Lima WWTP	Lima	11.44	37,907	OH0026069	Jun 2028	Aerated lagoons, Uncovered lagoons, Cooling towers	35
15	City Of Euclid, Wastewater Treatment Plant	Euclid	10.45	90,347	OH0031062	Aug 2029	—	14
16	City Of Warren Water Pollution Control	Warren	10.13	42,553	OH0027987	Nov 2028	Clarifiers, Uncovered lagoons	68
17	Gary L Kron Water Reclamation Facility	Mentor	9.35	104,000	OH0043559	Mar 2027	Clarifiers, Biogas silos	29
18	Massillon WWTP	Massillon	8.87	62,192	OH0020516	May 2031	Clarifiers, Aerated lagoons, Biogas silos	0
19	Upper Mill Creek Water Reclamation Facil	West Chester	8.34	74,361	OH0072087	Dec 2023	Clarifiers, Aerated lagoons, Carrousels / oxidation ditches, Biogas balloons	33
20	Rocky River Wastewater Treatment Plant	Rocky River	8.3	84,130	OH0030503	Jan 2028	Biogas silos, Biogas balloons	15
21	Muddy Creek WWTP	Cincinnati	7.73	80,528	OH0025470	Mar 2030	Clarifiers, Biogas balloons	18
22	Black River Wastewater Treatment Plant	Lorain	7.69	75,005	OH0026093	Nov 2027	Clarifiers, Biogas silos	6
23	Western Regional WRF	West Carrollton	7.67	88,254	OH0026638	Oct 2026	Clarifiers	2
24	Lesourdsville Water Reclamation Facility	Hamilton	7.64	65,027	OH0049417	Nov 2026	—	6
25	Sandusky WPC	Sandusky	7.47	36,245	OH0027332	Apr 2031	Clarifiers, Biogas silos, Biogas balloons	0
26	Beavercreek WRRF	Dayton	7.3	38,828	OH0025381	Nov 2030	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	47
27	Findlay WPCF	Findlay	7.22	41,213	OH0025135	Oct 2029	Clarifiers, Carrousels / oxidation ditches	1
28	North Regional Wastewater Treatment Plan (0857143037)	Dayton	7.07	69,382	OH0049646	Feb 2027	Clarifiers, Carrousels / oxidation ditches, Biogas silos	47
29	Mansfield Wastewater Treatment Plant	Mansfield	6.67	53,150	OH0026328	Mar 2030	Clarifiers, Biogas silos, Biogas balloons	428
30	Newark WWTP	Newark	6.66	50,383	OH0026671	Jun 2031	Clarifiers, Biogas silos, Biogas balloons	594
31	City Of Zanesville Wastewater Treatment Plant	Zanesville	5.91	49,058	OH0028240	Mar 2028	Clarifiers, Biogas silos	12
32	Medina County - Liverpool WWTP (sd #500)	Valley City	5.85	95,434	OH0043567	Nov 2030	Clarifiers, Biogas silos, Biogas balloons	6
33	Eastern Regional Water Reclamation Facility	Kettering	5.68	46,364	OH0026590	Feb 2031	Clarifiers	7
34	Mason WWTP No 2	Mason	5.56	22,496	OH0020494	May 2026	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	1
35	City Of Elyria Wastewater Pollution Control Plant	Elyria	5.49	52,738	OH0025003	May 2026	Clarifiers, Biogas silos	1
36	Lower East Fork Regional WWTP	Milford	5.43	55,640	OH0049379	Oct 2026	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	4
37	Lower Little Miami WWTP	Maineville	5.43	48,074	OH0071692	Feb 2026	Clarifiers	9
38	Hamilton Water Reclamation Facility	Hamilton	5.26	64,583	OH0025445	Oct 2026	Clarifiers, Biogas silos	7
39	Sycamore Creek WWTP	Cincinnati	5.2	24,200	OH0025488	Sep 2026	Clarifiers, Biogas balloons	18
40	Barberton WPCF	Barberton	5.02	28,805	OH0024007	Oct 2026	Clarifiers, Aerated lagoons, Biogas silos	9
41	French Creek WWTP	North Ridgeville	4.98	50,376	OH0044512	Oct 2027	Carrousels / oxidation ditches	5
42	Alum Creek WWTP	Delaware	4.87	65,613	OH0121380	Dec 2030	Uncovered lagoons	8
43	Sugarcreek WRF	Spring Valley	4.84	43,383	OH0040592	Apr 2031	Clarifiers	1
44	Lancaster Water Pollution Control	Lancaster	4.7	26,801	OH0026026	Nov 2028	Clarifiers, Uncovered lagoons, Biogas silos	19
45	Marion WPC	Marion	4.64	36,310	OH0026352	Apr 2030	Clarifiers, Uncovered lagoons	14
46	Willoughby-Eastlake Water Pollution Cont	Eastlake	4.47	42,529	OH0028126	Sep 2025	Clarifiers, Biogas balloons	82
47	Wooster Renewable Energy	Wooster	4.42	27,526	OH0028185	Nov 2029	Clarifiers, Uncovered lagoons, Biogas balloons	24
48	Fremont WPCF	Fremont	4.02	24,104	OH0025291	Sep 2029	Clarifiers, Biogas silos	7
49	Fairfield WWTP	Fairfield	3.88	44,396	OH0025071	Nov 2026	Clarifiers	3
50	Marysville WRF	Marysville	3.83	26,558	OH0136271	Jun 2028	Clarifiers, Aerated lagoons	7

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 September 11, 2026.

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