Activated sludge and clarifiers: wastewater treatment plants in Washington
74 plants · 49% of the state · 297 MGD reported by 70 plants
Klarifi identifies 74 publicly owned wastewater treatment plants with activated sludge and clarifiers in Washington, 49% of the 150 plants in the state (297 MGD reported by 70 plants). The largest is Metro West Point in Seattle at 106.93 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 Washington
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Metro West Point | Seattle | 106.93 | WAL029181 | Dec 2030 | 275 |
| 2 | King County South WWTP | Renton | 74.4 | WAR002511 | Dec 2029 | 3 |
| 3 | Chambers Creek WWTP | University Place | 22.49 | WAR000727 | Dec 2029 | 0 |
| 4 | Three Rivers Regional WWTP | Longview | 17.43 | WA0037788 | Feb 2026 | 0 |
| 5 | Lott Wastewater Treatment Plant | Olympia | 12.08 | WAG994545 | Dec 2026 | 0 |
| 6 | Yakima Regional Wastewater Facility | Yakima | 8.67 | WA0024023 | Mar 2029 | 2 |
| 7 | Richland City Wastewater Lab | Richland | 5.91 | WA0020419 | Sep 2021 | 0 |
| 8 | Puyallup WWTP | Puyallup | 5.2 | WAR313277 | Dec 2030 | 0 |
| 9 | Ellensburg WWTP | Ellensburg | 3.59 | WA0024341 | Dec 2023 | 0 |
| 10 | Wenatchee Wastewater Treatment Plant | Wenatchee | 2.86 | WA0023949 | Aug 2015 | 10 |
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 Washington
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in Washington: 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 · Filter press · FOG · all terms