Activated sludge and clarifiers: wastewater treatment plants in California
121 plants · 63% of the state · 614 MGD reported by 62 plants
Klarifi identifies 121 publicly owned wastewater treatment plants with activated sludge and clarifiers in California, 63% of the 193 plants in the state (614 MGD reported by 62 plants). The largest is Hyperion Treatment Plant in Playa Del Rey at 214 MGD.
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.
The largest activated sludge plants in California
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Hyperion Treatment Plant | Playa Del Rey | 214 | CA0109991 | Apr 2028 | 42 |
| 2 | Orange County Sanitation District Plant 1 | Fountain Valley | 77.37 | CA0110604 | Jul 2026 | 0 |
| 3 | Ccsf- Southeast Water Pollution Control Plant | San Francisco | 45.87 | CA0037664 | Sep 2018 | 13 |
| 4 | Stockton Rwcf | Stockton | 29.2 | CA0079138 | Jul 2030 | 57 |
| 5 | South Bay International WWTP | San Diego | 29 | CA0108928 | Jun 2026 | 3159 |
| 6 | Riverside City, Water Quality Control | Riverside | 27.72 | CA0105350 | Oct 2018 | 2 |
| 7 | Encina Water Pollution Control Facility | Carlsbad | 23.78 | CAL107395 | Dec 2030 | 11 |
| 8 | Oxnard Wastewater Treatment Plant (owtp) | Oxnard | 16.6 | CAL054097 | Dec 2030 | 137 |
| 9 | Oceanside Ocean Outfall | Oceanside | 10.7 | CA0107433 | Mar 2025 | 5 |
| 10 | Victor Valley Wastewater Reclamation Authority | Victorville | 9.48 | CA0102822 | May 2025 | 7 |
| 11 | City Of Tracy Waste Water Treatment Plant | Tracy | 8.9 | CAL079154 | Dec 2030 | 11 |
| 12 | Western Riverside Co Reg WWTP | Corona | 8.54 | CA8000316 | Jul 2020 | 47 |
| 13 | Hill Canyon WWTP | Camarillo | 8.09 | CA0056294 | Jul 2031 | 3 |
| 14 | Escondido City Of | Escondido | 7.8 | CA0107981 | May 2023 | 2 |
| 15 | Corona WWTP 1 | Corona | 7.64 | CA8000383 | Jun 2025 | 9 |
| 16 | Simi Vly Cnty Sanitation | Simi Valley | 6.5 | CA0055221 | Jul 2031 | 37 |
| 17 | Chino | Chino | 6.4 | CA8000409 | Jul 2027 | 519 |
| 18 | Clear Creek WWTP | Anderson | 5.67 | CA0079731 | Jul 2027 | 16 |
| 19 | Watsonville WWTF | Watsonville | 5.21 | CA0048216 | Jul 2019 | 8 |
| 20 | Manteca Wwqcf | Manteca | 5.18 | CA0081558 | Mar 2026 | 7 |
| 21 | Yuba City Wastewater Treatment Facility | Yuba City | 5.05 | CA0079260 | Mar 2024 | 21 |
| 22 | Water Reclamation Plant No. 4 | Thermal | 4.93 | CA0104973 | Apr 2028 | 11 |
| 23 | San Luis Obispo WWTP | San Luis Obispo | 4.23 | CAL049224 | Dec 2030 | 23 |
| 24 | El Centro WWTP | El Centro | 3.7 | CA0104426 | Mar 2024 | 17 |
| 25 | Camarillo Sanitary Dist Water Reclamation Plant | Camarillo | 3.57 | CA0053597 | Dec 2024 | 88 |
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 California
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in California: 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.