Chlorine disinfection: US wastewater treatment plants
446 plants in 18 states · 1,208 MGD reported by 424 plants · 7 planning upgrades
Klarifi identifies 446 publicly owned wastewater treatment plants with chlorine disinfection in the United States (1,208 MGD reported by 424 plants). The largest is Deer Island Wastewater Treatment Facility in Winthrop, MA at 270.96 MGD. Each state below links to its own list with every plant.
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.
Chlorine disinfection by state
136 plants
98 plants
47 plants
37 plants
32 plants
23 plants
18 plants
14 plants
13 plants
10 plants
6 plants
4 plants
3 plants
1 plants
1 plants
1 plants
1 plants
1 plants
The largest plants with chlorine disinfection in the US
Other treatment technologies
Chlorine disinfection: 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 · Lift station · Inflow and infiltration · all terms