Activated sludge and clarifiers: US wastewater treatment plants
4,183 plants in 50 states · 15,110 MGD reported by 3,900 plants · 3 planning upgrades
Klarifi identifies 4,183 publicly owned wastewater treatment plants with activated sludge and clarifiers in the United States (15,110 MGD reported by 3,900 plants). The largest is GLWA Water Resource Recovery Facility in Detroit, MI at 416.18 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
691 plants
394 plants
300 plants
234 plants
208 plants
179 plants
164 plants
118 plants
117 plants
103 plants
102 plants
101 plants
85 plants
83 plants
82 plants
80 plants
79 plants
75 plants
74 plants
64 plants
59 plants
59 plants
59 plants
58 plants
50 plants
49 plants
46 plants
46 plants
45 plants
41 plants
39 plants
35 plants
33 plants
32 plants
30 plants
24 plants
22 plants
22 plants
19 plants
16 plants
13 plants
13 plants
10 plants
8 plants
5 plants
4 plants
4 plants
4 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 October 26, 2026.
Wastewater terms: Activated sludge · Biological nutrient removal · Equalization tank · Biosolids · Filter press · all terms