Oxidation ditches: wastewater treatment plants in Wisconsin
62 plants · 16% of the state · 53 MGD reported by 52 plants
Klarifi identifies 62 publicly owned wastewater treatment plants with oxidation ditches in Wisconsin, 16% of the 391 plants in the state (53 MGD reported by 52 plants). The largest is Green Bay Metropolitan Sewerage District in Green Bay at 27.53 MGD.
Oxidation ditches are ring-shaped activated sludge reactors with long retention times, common at plants between 0.5 and 10 MGD. They are recognisable from the air by their looped channels and rely on surface aerators or brush rotors, which are frequent replacement and energy-efficiency projects.
The largest oxidation ditch plants in Wisconsin
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Green Bay Metropolitan Sewerage District | Green Bay | 27.53 | WIL065251 | Dec 2030 | 7 |
| 2 | Sussex Wastewater Treatment Facility | Sussex | 2.57 | WI0020559 | Dec 2024 | 3 |
| 3 | Marshfield Wastewater Utility | Marshfield | 2.42 | WI0021024 | Sep 2023 | 4 |
| 4 | Ripon Wastewater Treatment Plt (duplicate) | Ripon | 1.59 | WI0021032 | Sep 2025 | 5 |
| 5 | Wi Dells Lake Delton Sew Comm | Lake Delton | 1.4 | WI0031402 | Mar 2022 | 0 |
| 6 | Baraboo Water Resource Recovery Facility | Baraboo | 1.29 | WI0020605 | Jun 2018 | 0 |
| 7 | Tomah Wastewater Treatment Facility | Tomah | 1.11 | WI0021318 | Mar 2024 | 54 |
| 8 | Western Racine County Sewerage District | Rochester | 1.08 | WI0028754 | Dec 2020 | 5 |
| 9 | Saukville Village Sewer Utility | Saukville | 0.98 | WI0021555 | Sep 2025 | 3 |
| 10 | Fontana-Walworth Water Pollution Control Commission | Fontana | 0.9 | WI0036021 | Dec 2023 | 21 |
| 11 | Slinger Wastewater Treatment Facility | Slinger | 0.77 | WI0020290 | Sep 2025 | 4 |
| 12 | Dodgeville Wastewater Treatment Facility | Dodgeville | 0.72 | WI0026913 | Dec 2025 | 0 |
| 13 | Chilton Wastewater Treatment F | Chilton | 0.71 | WI0022799 | Jun 2023 | 0 |
| 14 | Union Grove Village | Union Grove | 0.6 | WI0028291 | Jun 2025 | 3 |
| 15 | Stanley Wastewater Treatment Facility | Stanley | 0.53 | WI0021857 | Sep 2023 | 33 |
| 16 | Twin Lakes Wastewater Treatment Fac | Twin Lakes | 0.52 | WI0021695 | Sep 2023 | 11 |
| 17 | Turtle Lake Village Of | Turtle Lake | 0.51 | WI0025631 | Jun 2019 | 5 |
| 18 | Dousman Wastewater Treatment Facility | Dousman | 0.48 | WI0021351 | Dec 2021 | 9 |
| 19 | Clintonville Wastewater Treatment Plant | Clintonville | 0.45 | WI0021466 | Mar 2023 | 0 |
| 20 | Cross Plains Waterworks | Cross Plains | 0.4 | WI0020788 | Dec 2025 | 0 |
| 21 | Marshall Wastewater Treatment Facility | Marshall | 0.37 | WI0024627 | Mar 2024 | 0 |
| 22 | Silver Lake Sanitary District | Wautoma | 0.36 | WI0061301 | Mar 2023 | 0 |
| 23 | Dane Iowa Wastewater Commission WWTF | Mazomanie | 0.34 | WI0049816 | Sep 2022 | 0 |
| 24 | Ellsworth Wastewater Treatment | Ellsworth | 0.32 | WI0021253 | Dec 2021 | 93 |
| 25 | New Lisbon Wastewater Treatment Facility | New Lisbon | 0.31 | WI0020699 | Sep 2019 | 0 |
Contacts and project signals for every plant on this list
Klarifi adds verified decision-maker contacts, permit limits, discharge monitoring data and the capital projects planned in each city, filterable by technology, size and compliance record.
Other technologies in Wisconsin
Oxidation ditches in other states
Oxidation ditches in Wisconsin: 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.