Oxidation ditches: wastewater treatment plants in Illinois
58 plants · 9% of the state · 38 MGD combined
Klarifi identifies 58 publicly owned wastewater treatment plants with oxidation ditches in Illinois, 9% of the 641 plants in the state (38 MGD combined). The largest is Frankfort, Village Of in Frankfort at 3.32 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 Illinois
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Frankfort, Village Of | Frankfort | 3.32 | ILL072192 | Dec 2030 | 7 |
| 2 | City Of Monmouth | Monmouth | 2.64 | ILL036218 | Dec 2030 | 20 |
| 3 | Village Of Bolingbrook STP #3 | Bolingbrook | 2.52 | ILL069744 | Dec 2030 | 18 |
| 4 | Lake In The Hills Sd | Lake In The Hills | 2.19 | ILL021733 | Dec 2030 | 2 |
| 5 | Kewanee STP | Kewanee | 1.71 | IL0029343 | Apr 2031 | 37 |
| 6 | Cary Wwtp, Village Of | Cary | 1.38 | ILL020516 | Dec 2030 | 1 |
| 7 | Streator STP | Streator | 1.37 | ILL022004 | Dec 2030 | 31 |
| 8 | Effingham STP | Effingham | 1.34 | ILL028622 | Dec 2030 | 49 |
| 9 | Crest Hill East Stp, City Of | Crest Hill | 1.19 | ILL064998 | Dec 2030 | 135 |
| 10 | Washington STP #2 | Washington | 1.13 | IL0042412 | Oct 2030 | 0 |
| 11 | Woodstock South Stp, City Of | Woodstock | 1.07 | ILL034282 | Dec 2030 | 2 |
| 12 | Robinson Wwtp, City Of | Robinson | 0.97 | ILL030732 | Dec 2030 | 0 |
| 13 | Huntley East Wwtp, Village Of | Huntley | 0.82 | ILL029238 | Dec 2030 | 0 |
| 14 | Harvard Wwtp, City Of | Harvard | 0.81 | ILL020117 | Dec 2030 | 6 |
| 15 | East Dundee Wwtp, Village Of | East Dundee | 0.81 | ILL028541 | Dec 2030 | 24 |
| 16 | Manhattan Stw, Village Of | Manhattan | 0.81 | ILL020222 | Dec 2030 | 6 |
| 17 | Braidwood Stp, City Of | Braidwood | 0.77 | IL0054992 | May 2026 | 0 |
| 18 | Elburn Wwtp, Village Of | Elburn | 0.71 | ILL062260 | Dec 2030 | 13 |
| 19 | West Frankfort Stw, City Of | West Frankfort | 0.7 | ILL031704 | Dec 2030 | 0 |
| 20 | Huntley - West WWTP | Huntley | 0.69 | ILL070688 | Dec 2030 | 0 |
| 21 | Salem Stp, City Of | Salem | 0.69 | ILL023264 | Dec 2030 | 20 |
| 22 | Pingree Grove, Village Of | Pingree Grove | 0.66 | ILL077755 | Dec 2030 | 64 |
| 23 | Greenville Stp, City Of | Greenville | 0.66 | ILL026298 | Dec 2030 | 8 |
| 24 | Wilmington Stp, City Of | Wilmington | 0.63 | IL0026085 | May 2031 | 3 |
| 25 | Highland Water Reclamation | Highland | 0.62 | IL0029173 | Mar 2031 | 28 |
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 Illinois
Oxidation ditches in other states
Oxidation ditches in Illinois: 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.