Activated sludge and clarifiers: US wastewater treatment plants
3,818 plants in 50 states · 11,371 MGD reported by 3,385 plants · 2 planning upgrades
Klarifi identifies 3,818 publicly owned wastewater treatment plants with activated sludge and clarifiers in the United States (11,371 MGD reported by 3,385 plants). The largest is GLWA Water Resource Recovery Facility in Detroit, MI at 349 MGD. Each state below links to its own list with every plant.
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 by state
684 plants
303 plants
234 plants
209 plants
179 plants
160 plants
121 plants
116 plants
103 plants
97 plants
97 plants
85 plants
83 plants
83 plants
81 plants
79 plants
73 plants
72 plants
63 plants
62 plants
59 plants
58 plants
58 plants
51 plants
50 plants
49 plants
47 plants
44 plants
42 plants
41 plants
38 plants
36 plants
34 plants
32 plants
29 plants
24 plants
22 plants
19 plants
19 plants
16 plants
13 plants
13 plants
11 plants
7 plants
6 plants
4 plants
4 plants
3 plants
3 plants
2 plants
The largest activated sludge plants in the US
Other treatment technologies
Activated sludge and clarifiers: 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.