What is the largest wastewater treatment plant in Maine?

Bangor Wastewater Treatment Facility in Bangor, treating an average of 4.38 MGD under NPDES permit ME0100781. Westbrook Waste Water Treatmemt Facility in Westbrook is second at 2.5 MGD.

How much wastewater do Maine’s largest plants treat?

The 50 largest plants treat 18 MGD combined, 99% of the flow reported by all 84 publicly owned plants in Maine.

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 Maine

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

Ranked by average flow · 18 MGD combined · 99% of the state's reported flow

Bangor Wastewater Treatment Facility in Bangor is the largest publicly owned wastewater treatment plant in Maine by reported average flow, treating about 4.38 million gallons per day. The 50 plants below treat 18 MGD between them, 99% of the flow reported by all 84 plants in the state, and serve about 198,316 people. Every plant links to its profile with permit, technology and compliance data.

All plants in Maine →The 100 largest US plants →Maine NPDES permits →

The 50 largest publicly owned wastewater treatment plants in Maine 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	Bangor Wastewater Treatment Facility	Bangor	4.38	38,856	ME0100781	Jul 2031	Clarifiers	14
2	Westbrook Waste Water Treatmemt Facility	Westbrook	2.5	23,987	ME0100846	Jul 2022	Biogas balloons	26
3	Old Orchard Beach Wastewater Treatment Facility	Old Orchard Beach	0.9	8,908	ME0101524	May 2020	Clarifiers, Biogas balloons	11
4	Bar Harbor WWTF Main Facility	Bar Harbor	0.82	3,700	ME0101214	Jan 2021	Biogas balloons	9
5	Falmouth Waste Water Treatment Facility	Falmouth	0.7	12,575	ME0100218	Dec 2023	—	3
6	York Wastewater Treatment Facility	York	0.67	9,400	ME0101222	Mar 2030	Biogas balloons	12
7	Old Town Wastewater Treatment Facility	Old Town	0.63	9,667	ME0100471	Sep 2029	Biogas balloons	2
8	Anson Madison Wastewater Treatment Facility	Madison	0.6	4,620	ME0101389	Apr 2031	Clarifiers, Aerated lagoons, Uncovered lagoons	2
9	Ogunquit Wastewater Treatment Facility	Ogunquit	0.54	1,000	ME0100986	Nov 2023	Clarifiers, Uncovered lagoons, Biogas balloons	8
10	Yarmouth Wastewater Treatiment Facility	Yarmouth	0.44	5,770	ME0100765	Aug 2022	Carrousels / oxidation ditches, Biogas balloons	3
11	Belfast Wastewater Treatment Facility	Belfast	0.42	6,668	ME0101532	Feb 2021	Biogas balloons	0
12	Lisbon Wastewater Treatment Facility	Lisbon	0.37	4,825	ME0100307	Oct 2029	Biogas silos	4
13	Calais Wastewater Treatment Facility	Calais	0.34	3,123	ME0100129	Nov 2021	Biogas balloons	11
14	Camden Wastewater Treatment Facility	Camden	0.32	3,731	ME0100137	Dec 2023	Clarifiers	6
15	Skowhegan Wastewater Treatment Facility	Skowhegan	0.31	4,536	ME0100625	Apr 2031	Clarifiers, Aerated lagoons, Biogas balloons	90
16	Livermore Falls WWTF	Livermore Falls	0.27	3,704	ME0100315	Oct 2029	—	14
17	Kennebunkport Wastewater Treatment Facility	Kennebunkport	0.26	3,700	ME0101184	Nov 2026	Biogas balloons	27
18	Madawaska WWTF	Madawaska	0.23	3,059	ME0101681	Dec 2024	—	6
19	Freeport Wastewater Treatment Facility	Freeport	0.23	2,452	ME0101036	Feb 2021	Biogas balloons	4
20	Bucksport Wastewater Treatment Facility	Bucksport	0.23	3,168	ME0100111	Jan 2023	Biogas silos, Biogas balloons	9
21	South Berwick Sd WWTF	South Berwick	0.2	3,300	ME0100820	Jun 2030	—	2
22	Ft Fairfield Wastewater Treatment Facility	Fort Fairfield	0.16	1,663	ME0100226	May 2022	Uncovered lagoons	11
23	Fort Kent WWTF	Fort Kent	0.15	1,893	ME0102369	Dec 2021	Aerated lagoons, Uncovered lagoons	2
24	Newport Wastewater Treatement Facility	Newport	0.14	2,052	ME0100447	Mar 2028	Aerated lagoons, Carrousels / oxidation ditches	2
25	South Cape Elizabeth WWTF	Cape Elizabeth	0.14	4,162	ME0102121	Dec 2021	Carrousels / oxidation ditches	15
26	Wiscasset WWTF	Wiscasset	0.13	2,247	ME0100757	Aug 2025	—	10
27	Machias Wastewater Treatment Facility	Machias	0.13	1,335	ME0100323	Mar 2021	Biogas balloons	2
28	Bingham WWTF	Bingham	0.12	866	ME0100056	Feb 2029	Biogas silos	29
29	Northeast Harbor Wastewater Treatment Facility	Northeast Harbor	0.12	640	ME0101346	May 2025	—	8
30	Limerick WWTF	Limerick	0.11	640	ME0100871	Oct 2020	Aerated lagoons	64
31	Richmond Wastewater Treatment Facility	Richmond	0.09	1,419	ME0100587	May 2030	Carrousels / oxidation ditches, Biogas balloons	8
32	Milo Wastewater Treatment Facility	Milo	0.08	1,510	ME0100439	Mar 2028	Aerated lagoons, Uncovered lagoons	10
33	Hartland Wastewater Treatment Facility	Hartland	0.08	800	ME0101443	May 2023	Clarifiers, Uncovered lagoons, Biogas balloons	0
34	Bethel Wastewater Treatment Facility	Bethel	0.08	1,139	ME0101176	Dec 2027	Uncovered lagoons	42
35	Eastport WWTF	Eastport	0.08	1,183	ME0100200	Feb 2030	Biogas balloons	2
36	Veazie WWTF	Veazie	0.07	1,898	ME0100706	Sep 2030	Aerated lagoons, Covered lagoons	13
37	Warren Wastewater Treatment Facility	Warren	0.07	1,630	ME0102253	Mar 2030	Aerated lagoons, Uncovered lagoons	0
38	Sabattus Sanitary District	Sabattus	0.06	3,750	ME0101842	Nov 2021	Biogas balloons	1
39	Wastewater Treatment Facility Hulls Cove	Bar Harbor	0.05	156	ME0102466	Mar 2030	Carrousels / oxidation ditches, Biogas balloons	5
40	Peaks Island STP	Portland	0.05	500	ME0102237	Oct 2022	—	36
41	Washburn Wastewater Treatment Facility	Washburn	0.05	543	ME0101028	Sep 2029	Aerated lagoons, Uncovered lagoons	4
42	Searsport Wastewater Treatment Facility	Searsport	0.05	1,014	ME0101966	Aug 2025	—	0
43	Seal Harbor WWTF	Seal Harbor	0.05	1,010	ME0102555	Apr 2025	—	6
44	Passamaquoddy Wastewater Treatment Facility	Perry	0.05	—	ME0100773	Jul 2031	—	8
45	Ashland Wastwater Treatment Facility	Ashland	0.04	253	ME0101087	May 2027	Aerated lagoons	31
46	Blue Hill, Wastewater Treatment Facility	Blue Hill	0.04	582	ME0101231	Oct 2025	—	0
47	Frenchville Wastewater Treatment Facility	Frenchville	0.04	2,422	ME0101982	Sep 2029	Aerated lagoons	124
48	Penobscot Housing Indian Island	Old Town	0.04	—	ME0101311	May 2030	—	33
49	Castine Wastewater Treatment Facility	Castine	0.03	1,320	ME0101192	Aug 2026	—	6
50	Lubec Wastewater Treatment Facility	Lubec	0.03	940	ME0102016	Feb 2030	Clarifiers, Cooling towers	5

Largest plants in Maine: 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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