Activated sludge and clarifiers: wastewater treatment plants in Washington
73 plants · 58% of the state · 63 MGD reported by 22 plants
Klarifi identifies 73 publicly owned wastewater treatment plants with activated sludge and clarifiers in Washington, 58% of the 125 plants in the state (63 MGD reported by 22 plants). The largest is Riverside Park Water Reclamation Facility in Spokane at 31.72 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 | Riverside Park Water Reclamation Facility | Spokane | 31.72 | WA0024473 | Aug 2027 | 4 |
| 2 | Chambers Creek WWTP | University Place | 17.07 | WAR000727 | Dec 2029 | 0 |
| 3 | Richland City Wastewater Lab | Richland | 6.31 | WA0020419 | Sep 2021 | 0 |
| 4 | Camas STP | Camas | 2.62 | WA0020249 | Jul 2030 | 19 |
| 5 | Sunnyside STP | Sunnyside | 1.31 | WA0020991 | Jan 2020 | 1 |
| 6 | Clarkston WWTP | Clarkston | 0.71 | WA0021113 | Apr 2021 | 0 |
| 7 | Toppenish Wastewater Treatment Plant | Toppenish | 0.67 | WA0026123 | Dec 2030 | 29 |
| 8 | Omak Wastewater Treatment Plant | Omak | 0.53 | WA0020940 | Dec 2020 | 0 |
| 9 | Cashmere STP Facility | Cashmere | 0.39 | WA0023183 | May 2025 | 30 |
| 10 | Medical Lake WWTP | Medical Lake | 0.27 | WA0021148 | Jul 2019 | 13 |
| 11 | Montesano Sewage Treatment Plant | Montesano | 0.24 | WA0024660 | Nov 2029 | 0 |
| 12 | Dayton STP | Dayton | 0.19 | WA0020729 | Sep 2016 | 2 |
| 13 | Chewelah WWTP | Chewelah | 0.19 | WA0023604 | Nov 2016 | 1 |
| 14 | Brewster STP | Brewster | 0.18 | WA0021008 | Jan 2021 | 0 |
| 15 | Tulalip Wastewater Treatment Plant | Marysville | 0.17 | WA0024805 | Oct 2014 | 1 |
| 16 | Okanogan WWTP | Okanogan | 0.15 | WA0022365 | Sep 2030 | 1 |
| 17 | Winlock Wastewater Treatment Plant | Winlock | 0.15 | WA0021199 | Feb 2028 | 0 |
| 18 | Pomeroy Sewage Treatment Plant | Pomeroy | 0.09 | WA0021164 | Oct 2023 | 0 |
| 19 | Pacific Beach STP | Pacific Beach | 0.09 | WA0037095 | Aug 2030 | 37 |
| 20 | Asotin STP | Clarkston | 0.08 | WA0020818 | Aug 2023 | 1 |
| 21 | Toutle STP | Toutle | 0.06 | WA0037770 | Jun 2030 | 7 |
| 22 | Tekoa STP | Tekoa | 0.05 | WA0023141 | May 2019 | 35 |
| 23 | Bainbridge Island WWTP | Bainbridge Island | — | WAG994558 | Dec 2026 | 1 |
| 24 | Bingen POTW | Bingen | — | WA0022373 | Jun 2019 | 13 |
| 25 | Birch Bay Water And Sewer District WWTP | Blaine | — | WAG994542 | Dec 2026 | 0 |
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 September 11, 2026.