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Activated sludge and clarifiers: wastewater treatment plants in New Hampshire

19 plants · 41% of the state · 34 MGD reported by 18 plants

Klarifi identifies 19 publicly owned wastewater treatment plants with activated sludge and clarifiers in New Hampshire, 41% of the 46 plants in the state (34 MGD reported by 18 plants). The largest is Nashua WWTP in Nashua at 9.2 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.

Activated sludge and clarifiers plants nationwide →All plants in New Hampshire →Largest plants in New Hampshire →

The largest activated sludge plants in New Hampshire

The 19 largest plants with activated sludge and clarifiers in New Hampshire by average flow, with permit expiry and three-year violation count.
#FacilityCityAvg flow (MGD)NPDES permitExpiresViolations (3y)
1Nashua WWTPNashua9.2NH0100170May 202087
2Wrbp Franklin Wastewater Treatment PlantFranklin3.53NH0100960Jun 202922
3Concord Wastewater Treatment FacilityConcord3.2NH0100901Aug 20279
4Pierce Island Wastewater Treatment PlantPortsmouth2.38NH0100234Nov 202847
5Rochester Wastewater Treatment FacilityRochester2.35NH0100668Jun 20283
6Leavitt E. Magrath Wastewater Treatment FacilityHampton2.08NH0100625Feb 202627
7Huckleberry Hill Wastewater Treatment FacilityDover1.91NHG58A003Jan 202630
8Merrimack WWTFMerrimack1.37NHR053094Feb 20269
9Keene Wastewater Treatment FacilityKeene1.26NH0100790Nov 20268
10Claremont Wastewater Treatment FacilityClaremont1.2NH0101257Sep 20210
11Exeter Wastewater Treatment FacilityExeter1.1NHG58A004Jan 202618
12Hanover Wastewater Treatment FacilityHanover0.99NH0100099Jan 202145
13Lebanon Wastewater Treatment FacilityLebanon0.89NHR053176Feb 20262
14Milford Wastewater Treatment FacilityMilford0.78NH0100471Oct 2025191
15Hooksett Wastewater Treatment FacilityHooksett0.68NH0100129Sep 20181
16Suncook Wastewater Treatment FacilityAllenstown0.45NH0101390Jan 20279
17Newmarket, Town Of - WPCFNewmarket0.35NHG580013Nov 202617
18Woodstock WWTFWoodstock0.08NHG580020Nov 202629
19Pease Wastewater Treatment FacilityPortsmouth—NHG58A007Jan 202665

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.

Start a free trialKlarifi Plus: done-for-you outreach for this segment →

Other technologies in New Hampshire

Lagoon systems (15)Oxidation ditches (5)Anaerobic digesters and biogas (15)

Activated sludge and clarifiers in other states

Texas (684)Ohio (303)Pennsylvania (234)Indiana (209)New York (179)Illinois (160)California (121)Michigan (116)Kentucky (103)Georgia (97)Missouri (97)Tennessee (85)

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 September 11, 2026.

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