Activated sludge and clarifiers: wastewater treatment plants in New Hampshire
19 plants · 40% of the state · 40 MGD reported by 18 plants
Klarifi identifies 19 publicly owned wastewater treatment plants with activated sludge and clarifiers in New Hampshire, 40% of the 47 plants in the state (40 MGD reported by 18 plants). The largest is Nashua WWTP in Nashua at 9.77 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 New Hampshire
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Nashua WWTP | Nashua | 9.77 | NH0100170 | May 2020 | 78 |
| 2 | Wrbp Franklin Wastewater Treatment Plant | Franklin | 5.19 | NH0100960 | Jun 2029 | 26 |
| 3 | Concord Wastewater Treatment Facility | Concord | 3.5 | NH0100901 | Aug 2027 | 8 |
| 4 | Pierce Island Wastewater Treatment Plant | Portsmouth | 3.28 | NH0100234 | Nov 2028 | 47 |
| 5 | Rochester Wastewater Treatment Facility | Rochester | 2.88 | NH0100668 | Jun 2028 | 3 |
| 6 | Leavitt E. Magrath Wastewater Treatment Facility | Hampton | 2.24 | NH0100625 | Feb 2026 | 29 |
| 7 | Huckleberry Hill Wastewater Treatment Facility | Dover | 2.18 | NHG58A003 | Jan 2026 | 30 |
| 8 | Keene Wastewater Treatment Facility | Keene | 1.87 | NH0100790 | Nov 2026 | 8 |
| 9 | Exeter Wastewater Treatment Facility | Exeter | 1.45 | NHG58A004 | Jan 2026 | 18 |
| 10 | Claremont Wastewater Treatment Facility | Claremont | 1.39 | NH0101257 | Sep 2021 | 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 New Hampshire
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in New Hampshire: 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 · NPDES permit · POTW · all terms