Chlorine disinfection: wastewater treatment plants in Massachusetts
23 plants · 35% of the state · 388 MGD combined
Klarifi identifies 23 publicly owned wastewater treatment plants with chlorine disinfection in Massachusetts, 35% of the 65 plants in the state (388 MGD combined). The largest is Deer Island Wastewater Treatment Facility in Winthrop at 270.96 MGD.
Chlorine or chloramine disinfection, often followed by dechlorination before discharge, remains the most common effluent disinfection in the United States. Plants on gas chlorine are candidates for conversion to hypochlorite or UV, a recurring capital project driven by safety rules and permit limits on residual chlorine.
The largest plants with chlorine disinfection in Massachusetts
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Deer Island Wastewater Treatment Facility | Winthrop | 270.96 | MA0103284 | Jul 2005 | 3 |
| 2 | Upper Blackstone Wastewater Treatment Plant | Millbury | 30.02 | MAR053209 | Feb 2026 | 19 |
| 3 | New Bedford Wastewater Treatment Facility | New Bedford | 21.74 | MA0100781 | Nov 2013 | 14 |
| 4 | South Essex Wastewater Treatment Plant | Salem | 21.66 | MAL100501 | Dec 2030 | 33 |
| 5 | Pittsfield Wastewater Treatment Facility | Pittsfield | 9.85 | MA0101681 | Oct 2026 | 85 |
| 6 | Holyoke Water Pollution Control Facility | Holyoke | 6.07 | MAL101630 | Dec 2030 | 4 |
| 7 | Northampton Wastewater Treatment Plant | Northampton | 4.21 | MA0101818 | Nov 2028 | 41 |
| 8 | Amherst Wastewater Treatment Plant | Hadley | 3.36 | MA0100218 | Jan 2029 | 44 |
| 9 | Billerica Wastewater Treatment Facility | Billerica | 3.3 | MA0101711 | Feb 2029 | 51 |
| 10 | Hoosic Wastwater Treament Plant | Williamstown | 3.26 | MA0100510 | Dec 2028 | 2 |
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
Chlorine disinfection in other states
Chlorine disinfection 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 October 26, 2026.
Wastewater terms: Tertiary treatment · Ozonation · WWTP · FOG · Equalization tank · all terms