Oxidation ditches: US wastewater treatment plants
1,496 plants in 48 states · 1,926 MGD reported by 1,333 plants
Klarifi identifies 1,496 publicly owned wastewater treatment plants with oxidation ditches in the United States (1,926 MGD reported by 1,333 plants). The largest is 91st Avenue WWTP in Tolleson, AZ at 78.71 MGD. Each state below links to its own list with every plant.
Oxidation ditches are ring-shaped activated sludge reactors with long retention times, common at plants between 0.5 and 10 MGD. They are recognisable from the air by their looped channels and rely on surface aerators or brush rotors, which are frequent replacement and energy-efficiency projects.
Oxidation ditches by state
261 plants
113 plants
94 plants
64 plants
62 plants
58 plants
57 plants
47 plants
45 plants
40 plants
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9 plants
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3 plants
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2 plants
2 plants
1 plants
1 plants
1 plants
The largest oxidation ditch plants in the US
Other treatment technologies
Oxidation ditches: 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.