Oxidation ditches: wastewater treatment plants in Wisconsin
63 plants · 16% of the state · 112 MGD reported by 56 plants
Klarifi identifies 63 publicly owned wastewater treatment plants with oxidation ditches in Wisconsin, 16% of the 394 plants in the state (112 MGD reported by 56 plants). The largest is EPA Superfund Site: Madison Metropolitan Sewerage District Lagoons in Madison at 39.37 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 | EPA Superfund Site: Madison Metropolitan Sewerage District Lagoons | Madison | 39.37 | WIG009756 | Sep 2026 | 2 |
| 2 | Green Bay Metropolitan Sewerage District | Green Bay | 36.81 | WIL065251 | Dec 2030 | 7 |
| 3 | Hartford Water Pollution Control Facility | Hartford | 5.48 | WI0020192 | Sep 2023 | 7 |
| 4 | Marshfield Wastewater Utility | Marshfield | 2.9 | WI0021024 | Sep 2023 | 4 |
| 5 | Sussex Wastewater Treatment Facility | Sussex | 2.75 | WI0020559 | Dec 2024 | 3 |
| 6 | Cedarburg Water Recycling Center | Cedarburg | 2.33 | WI0020222 | Mar 2022 | 1 |
| 7 | Ripon Wastewater Treatment Plt (duplicate) | Ripon | 1.48 | WI0021032 | Sep 2025 | 5 |
| 8 | Wi Dells Lake Delton Sew Comm | Lake Delton | 1.38 | WI0031402 | Mar 2022 | 0 |
| 9 | Baraboo Water Resource Recovery Facility | Baraboo | 1.31 | WI0020605 | Jun 2018 | 0 |
| 10 | Western Racine County Sewerage District | Rochester | 1.19 | WI0028754 | Dec 2020 | 5 |
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 October 26, 2026.
Wastewater terms: Oxidation ditch · Activated sludge · Biological nutrient removal · Anaerobic digester · NPDES permit · all terms