Wastewater Treatment Plants in Iowa
678 facilities · 2 MGD combined flow
Klarifi tracks 678 publicly owned wastewater treatment plants in Iowa with a combined average flow of 2 MGD, serving about 1,530,298 residents. 0 plants treat more than 1 MGD and 0 more than 10 MGD; 631 use lagoon systems and 69 have digesters or biogas infrastructure. The largest is Walnut City Of STP in Walnut at 0.99 MGD. 71 NPDES permits expire this year and 95 next year.
Every plant below links to a profile with average and design flow, treatment technology, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Showing facilities 1–200 of 678 by average flow — browse the rest with the page links below.
678 plant locations in Iowa; dot size follows average flow.
NPDES permits and renewals in Iowa
Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.
Largest wastewater treatment plants in Iowa
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Technology | Violations (3y) |
|---|---|---|---|---|---|---|---|
| Walnut City Of STP | Walnut | 0.99 | 0.39 | IA0042986 | Apr 2006 | Aerated lagoons, Uncovered lagoons | 40 |
| Clarion, City Of STP | Clarion | 0.82 | 1.5 | IA0030945 | Jan 2028 | Aerated lagoons | 13 |
| Fredricksburg WWTP | Fredericksburg | 0.17 | 1.2 | IA0028991 | Jan 2008 | Aerated lagoons | 0 |
| Shellsburg WWTP | Shellsburg | 0.13 | 1.15 | IA0033332 | May 2006 | Clarifiers | 0 |
| Ossian City Of STP | Ossian | 0.07 | 0.44 | IA0042781 | Sep 2006 | Aerated lagoons, Uncovered lagoons | 5 |
| What Cheer WWTP | What Cheer | 0.04 | 0.88 | IA0032468 | Apr 2006 | Aerated lagoons, Uncovered lagoons | 3 |
| Lester City Of STP | Lester | 0.04 | 0.05 | IA0026620 | Feb 2017 | Uncovered lagoons | 15 |
| Birmingham City Of STP | Birmingham | 0.04 | 0.38 | IA0023426 | Jul 2002 | Aerated lagoons, Uncovered lagoons | 16 |
| Mitchell County WW Pretreatment Plant | Osage | 0.03 | — | MO0030821 | Jun 2026 | Carrousels / oxidation ditches, Biogas silos | 111 |
| Atalissa City Of STP | Atalissa | 0.02 | 0.06 | IA0070998 | Apr 2006 | — | 4 |
| Maharishi Vedic City - South | Fairfield | 0.0079 | 0.05 | IA0078417 | Nov 2009 | — | 19 |
| Ackley WWTP | Ackley | — | 1.67 | IA0035297 | May 2030 | Aerated lagoons, Uncovered lagoons | 95 |
| Adair WWTP | Adair | — | 0.49 | IA0035416 | Jul 2029 | Clarifiers, Biogas balloons | 4 |
| Adel WWTP | Adel | — | 5.44 | IA0041921 | Nov 2027 | Uncovered lagoons | 2 |
| Afton City Of STP | Afton | — | 0.26 | IA0041831 | Jun 2027 | Uncovered lagoons | 0 |
| Agncy City Of STP | Agency | — | 0.62 | IA0057754 | Aug 2006 | Aerated lagoons, Uncovered lagoons | 15 |
| Ainsworth City Of STP | Ainsworth | — | 0.3 | IA0069183 | Apr 2027 | Uncovered lagoons | 13 |
| Akron City Of STP | Akron | — | 0.38 | IA0035211 | Aug 2028 | Uncovered lagoons | 4 |
| Albia City Of STP (north) | Albia | — | 1.27 | IA0036871 | Apr 2026 | Aerated lagoons, Uncovered lagoons | 62 |
| Albion City Of STP | Albion | — | 0.4 | IA0034321 | Apr 2030 | Uncovered lagoons | 29 |
| Alburnett WWTP | Alburnett | — | — | IA0024431 | Sep 2030 | Uncovered lagoons | 10 |
| Alden WWTP | Alden | — | 0.45 | IA0034339 | Aug 2030 | Uncovered lagoons | 4 |
| Algona City Of STP | Algona | — | 2.76 | IA0022055 | Feb 2028 | Clarifiers, Biogas silos, Biogas balloons | 13 |
| Allerton City Of STP North | Allerton | — | 0.05 | IA0054054 | Aug 2026 | Uncovered lagoons | 6 |
| Allerton City Of STP South | Allerton | — | 0.28 | IA0054046 | Aug 2026 | Aerated lagoons, Uncovered lagoons | 34 |
Iowa plants by treatment technology
All 678 plants in Iowa
Wastewater treatment in Iowa: 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.