Activated sludge and clarifiers: wastewater treatment plants in Maryland
41 plants · 35% of the state · 271 MGD reported by 39 plants
Klarifi identifies 41 publicly owned wastewater treatment plants with activated sludge and clarifiers in Maryland, 35% of the 117 plants in the state (271 MGD reported by 39 plants). The largest is Back River Wastewater Treatment Plant in Baltimore at 107.68 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 Maryland
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Back River Wastewater Treatment Plant | Baltimore | 107.68 | MDL021555 | Dec 2030 | 32 |
| 2 | Patapsco Wastewater Treatment Plant | Baltimore | 51.59 | MDL021601 | Dec 2030 | 22 |
| 3 | Piscataway Swge Plnt | Accokeek | 19.8 | MDL021539 | Dec 2030 | 25 |
| 4 | Little Patuxent Water Reclamation Plant | Savage | 16.76 | MD0055174 | May 2031 | 8 |
| 5 | Sod Run Wastewater Treatment Plant | Perryman | 9.48 | MDL056545 | Dec 2030 | 0 |
| 6 | Annapolis WRF | Annapolis | 7.94 | MD0021814 | Jan 2030 | 6 |
| 7 | Ballenger-Mckinney WWTP | Frederick | 7.11 | MD0021822 | Dec 2030 | 1 |
| 8 | Parkway Wastewater Treatment Plant | Laurel | 6.09 | MDL021725 | Dec 2030 | 2 |
| 9 | City Of Frederick Wastewater Treatment Plant-2012 | Frederick | 5.68 | MD0021610 | May 2031 | 23 |
| 10 | The City Of Bowie (ssos) | Bowie | 5.09 | MDL021628 | Dec 2030 | 7 |
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 Maryland
Activated sludge and clarifiers in other states
Activated sludge and clarifiers in Maryland: 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 · NPDES permit · POTW · all terms