Activated sludge and clarifiers: wastewater treatment plants in Massachusetts
51 plants · 77% of the state · 390 MGD combined
Klarifi identifies 51 publicly owned wastewater treatment plants with activated sludge and clarifiers in Massachusetts, 77% of the 66 plants in the state (390 MGD combined). The largest is Deer Island Wastewater Treatment Facility in Winthrop at 233.7 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 Massachusetts
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Deer Island Wastewater Treatment Facility | Winthrop | 233.7 | MA0103284 | Jul 2005 | 3 |
| 2 | Upper Blackstone Wastewater Treatment Plant | Millbury | 24.1 | MAR053209 | Feb 2026 | 15 |
| 3 | Greater Lawrence Wastewater Treatment Facility | North Andover | 21.7 | MAL100447 | Dec 2030 | 10 |
| 4 | South Essex Wastewater Treatment Plant | Salem | 17.57 | MAL100501 | Dec 2030 | 33 |
| 5 | New Bedford Wastewater Treatment Facility | New Bedford | 16.7 | MA0100781 | Nov 2013 | 14 |
| 6 | Brockton Advanced Water Reclamation Fac | Brockton | 9.9 | MAL101010 | Dec 2030 | 10 |
| 7 | Pittsfield Wastewater Treatment Facility | Pittsfield | 7 | MA0101681 | Oct 2026 | 84 |
| 8 | Haverhill Wastewater Treatment Facility | Haverhill | 6.58 | MAL101621 | Dec 2030 | 4 |
| 9 | Taunton Wastewater Treatment Facility | Taunton | 5.36 | MA0100897 | Jul 2020 | 52 |
| 10 | Holyoke Water Pollution Control Facility | Holyoke | 5.02 | MAL101630 | Dec 2030 | 4 |
| 11 | Westborough Wastewater Treatment Plant | Westborough | 4.17 | MA0100412 | Apr 2027 | 2 |
| 12 | Northampton Wastewater Treatment Plant | Northampton | 3.84 | MA0101818 | Nov 2028 | 40 |
| 13 | Amherst Wastewater Treatment Plant | Hadley | 3.33 | MA0100218 | Jan 2029 | 42 |
| 14 | Billerica Wastewater Treatment Facility | Billerica | 2.88 | MA0101711 | Feb 2029 | 52 |
| 15 | Westfield Wastewater Treatment Plant | Westfield | 2.4 | MA0101800 | Nov 2028 | 0 |
| 16 | Gardner W W T F | East Templeton | 2.28 | MAG590013 | Oct 2027 | 75 |
| 17 | Hoosic Wastwater Treament Plant | Williamstown | 2.04 | MA0100510 | Dec 2028 | 2 |
| 18 | Marlborough DPW Water Division East Plt | Marlborough | 2.04 | MA0100498 | Mar 2027 | 13 |
| 19 | Rockland Wastewater Plant | Rockland | 2 | MAG590038 | Oct 2027 | 32 |
| 20 | Erving Wastewater Treatment Plant #2 | Erving | 1.72 | MA0101052 | Nov 2026 | 36 |
| 21 | Newburyport Wastewater Treatment Facility | Newburyport | 1.45 | MAG590035 | Oct 2027 | 0 |
| 22 | Greenfield Water Pollution Control Facility | Greenfield | 1.44 | MAG590014 | Oct 2027 | 31 |
| 23 | Palmer Water Pollution Control Facility | Palmer (three Rivers) | 1.2 | MA0101168 | Nov 2028 | 4 |
| 24 | Westerly Wastewater Treatment Facility | Marlborough | 1.16 | MA0100480 | Dec 2026 | 26 |
| 25 | Middleborough WPCF | Middleborough | 1.09 | MAG590042 | Oct 2027 | 11 |
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 Massachusetts
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in Massachusetts: 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.