Activated sludge and clarifiers: wastewater treatment plants in Idaho
22 plants · 23% of the state · 82 MGD reported by 16 plants
Klarifi identifies 22 publicly owned wastewater treatment plants with activated sludge and clarifiers in Idaho, 23% of the 94 plants in the state (82 MGD reported by 16 plants). The largest is West Boise WWTP in Garden City at 62 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 Idaho
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | West Boise WWTP | Garden City | 62 | ID0023981 | Jun 2027 | 9 |
| 2 | Pocatello City WWTP | Pocatello | 6.79 | ID0021784 | Aug 2017 | 8 |
| 3 | Jerome WWTP | Jerome | 3.59 | ID0020168 | Jun 2015 | 4 |
| 4 | Lewiston WWTP | Lewiston | 3.31 | ID0022055 | Jan 2021 | 0 |
| 5 | Page WWTP | Smelterville | 1.36 | ID0021300 | Sep 2018 | 1 |
| 6 | Rigby WWTP | Rigby | 1.2 | ID0020010 | Dec 2021 | 9 |
| 7 | Payette WWTP | Payette | 1 | ID0020672 | Oct 2019 | 1 |
| 8 | Moscow STP | Moscow | 0.85 | ID0021491 | Jan 2031 | 0 |
| 9 | Heyburn WWTP | Heyburn | 0.71 | ID0020940 | Jan 2007 | 17 |
| 10 | Grangeville WWTP | Grangeville | 0.39 | ID0020036 | Apr 2025 | 3 |
| 11 | Buhl WWTP | Buhl | 0.29 | ID0020664 | Oct 2012 | 2 |
| 12 | Aberdeen WWTP | Aberdeen | 0.2 | ID0020176 | Feb 2021 | 18 |
| 13 | Grace WWTP | Grace | 0.08 | ID0023825 | Jun 2027 | 1 |
| 14 | Hansen STP | Hansen | 0.07 | ID0022446 | Oct 2012 | 7 |
| 15 | Riggins WWTP | Riggins | 0.07 | ID0020931 | Aug 2017 | 0 |
| 16 | Smelterville WWTP | Smelterville | 0.06 | ID0020117 | Sep 2018 | 21 |
| 17 | Fruitland Payette River WWTP | Payette | — | ID0021199 | Oct 2016 | 3 |
| 18 | Hayden Area Regional Sewer Board WWTP | Hayden | — | ID0026590 | May 2029 | 5 |
| 19 | Nampa WWTP | Nampa | — | ID0022063 | Oct 2021 | 27 |
| 20 | Priest River STP | Priest River | — | ID0020800 | Nov 2016 | 26 |
| 21 | Rexburg WWTP | Rexburg | — | ID0023817 | Mar 2028 | 41 |
| 22 | Weiser WWTP | Weiser | — | ID0020290 | Dec 2016 | 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 Idaho
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in Idaho: 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.