Activated sludge and clarifiers: wastewater treatment plants in Oregon
39 plants · 31% of the state · 144 MGD reported by 37 plants
Klarifi identifies 39 publicly owned wastewater treatment plants with activated sludge and clarifiers in Oregon, 31% of the 127 plants in the state (144 MGD reported by 37 plants). The largest is Willow Lake WWTP in Salem at 42.45 MGD.
Activated sludge is the standard mechanical process for cities: aeration basins where bacteria consume organic matter, followed by clarifiers that settle the biomass out. These plants are identified by their circular or rectangular clarifiers and by the suspended-growth process code, and they are the main market for blowers, diffusers, clarifier mechanisms and instrumentation.
The largest activated sludge plants in Oregon
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Willow Lake WWTP | Salem | 42.45 | ORL026409 | Dec 2030 | 2 |
| 2 | Durham Waste Handling | Tigard | 24.25 | ORL028118 | Dec 2030 | 6 |
| 3 | Medford Rwrf | Central Point | 16.52 | OR0026263 | Jul 2026 | 1 |
| 4 | Gresham WWTP | Portland | 11.55 | OR0026131 | Aug 2026 | 0 |
| 5 | Albany-Millersburg WRF | Albany | 8.27 | OR0028801 | Jan 2031 | 2 |
| 6 | Tryon Creek WWTP | Lake Oswego | 5.22 | OR0026891 | Apr 2029 | 2 |
| 7 | Mcminnville WWTP | Mcminnville | 4.99 | OR0034002 | Dec 2008 | 2 |
| 8 | Grants Pass STP | Grants Pass | 4.92 | OR0028843 | Sep 2014 | 16 |
| 9 | Lebanon STP | Lebanon | 3.82 | OR0020818 | Oct 2030 | 39 |
| 10 | Oak Lodge Water Reclamation Facility | Milwaukie | 3.05 | OR0026140 | Mar 2027 | 3 |
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 Oregon
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in Oregon: 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: Activated sludge · Biological nutrient removal · Equalization tank · MGD · Lift station · all terms