Oxidation ditches: wastewater treatment plants in Illinois
58 plants · 9% of the state · 62 MGD reported by 57 plants
Klarifi identifies 58 publicly owned wastewater treatment plants with oxidation ditches in Illinois, 9% of the 664 plants in the state (62 MGD reported by 57 plants). The largest is Highland Water Reclamation in Highland at 5.55 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 | Highland Water Reclamation | Highland | 5.55 | IL0029173 | Mar 2031 | 28 |
| 2 | Frankfort, Village Of | Frankfort | 4.97 | ILL072192 | Dec 2030 | 7 |
| 3 | City Of Monmouth | Monmouth | 3.88 | ILL036218 | Dec 2030 | 19 |
| 4 | Village Of Bolingbrook STP #3 | Bolingbrook | 3.67 | ILL069744 | Dec 2030 | 17 |
| 5 | Kewanee STP | Kewanee | 3.5 | IL0029343 | Apr 2031 | 37 |
| 6 | Streator STP | Streator | 2.7 | ILL022004 | Dec 2030 | 51 |
| 7 | Lake In The Hills Sd | Lake In The Hills | 2.56 | ILL021733 | Dec 2030 | 2 |
| 8 | Effingham STP | Effingham | 2.21 | ILL028622 | Dec 2030 | 51 |
| 9 | Washington STP #2 | Washington | 1.88 | IL0042412 | Oct 2030 | 0 |
| 10 | Crest Hill East Stp, City Of | Crest Hill | 1.63 | ILL064998 | Dec 2030 | 136 |
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 October 26, 2026.
Wastewater terms: Oxidation ditch · Activated sludge · Biological nutrient removal · Sludge dewatering · Tertiary treatment · all terms