Activated sludge and clarifiers: wastewater treatment plants in Maryland
41 plants · 35% of the state · 274 MGD combined
Klarifi identifies 41 publicly owned wastewater treatment plants with activated sludge and clarifiers in Maryland, 35% of the 118 plants in the state (274 MGD combined). The largest is Back River Wastewater Treatment Plant in Baltimore at 114.1 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 | 114.1 | MDL021555 | Dec 2030 | 32 |
| 2 | Patapsco Wastewater Treatment Plant | Baltimore | 49.01 | MDL021601 | Dec 2030 | 22 |
| 3 | Piscataway Swge Plnt | Accokeek | 19.79 | MDL021539 | Dec 2030 | 25 |
| 4 | Little Patuxent Water Reclamation Plant | Savage | 16.68 | MD0055174 | May 2031 | 8 |
| 5 | Sod Run Wastewater Treatment Plant | Perryman | 10.81 | MDL056545 | Dec 2030 | 0 |
| 6 | Annapolis WRF | Annapolis | 8.48 | MD0021814 | Jan 2030 | 6 |
| 7 | Ballenger-Mckinney WWTP | Frederick | 6.92 | MD0021822 | Dec 2030 | 1 |
| 8 | Parkway Wastewater Treatment Plant | Laurel | 6.35 | MDL021725 | Dec 2030 | 2 |
| 9 | Ocean City Wastewater Treatment Plant | Ocean City | 5.88 | MDL020044 | Dec 2030 | 2 |
| 10 | City Of Frederick Wastewater Treatment Plant-2012 | Frederick | 5.4 | MD0021610 | May 2031 | 23 |
| 11 | City Of Salisbury Wastewater Treatment Plant | Salisbury | 5.05 | MDL021571 | Dec 2030 | 83 |
| 12 | Broadneck Water Reclamation Facility | Annapolis | 3.68 | MDL021644 | Dec 2030 | 106 |
| 13 | Westminster WWTP | Westminster | 3.41 | MD0021831 | Jul 2031 | 9 |
| 14 | Easton WWTP | Easton | 2.02 | MDL020273 | Dec 2030 | 2 |
| 15 | Freedom District WWTP | Sykesville | 1.97 | MD0021512 | Oct 2029 | 32 |
| 16 | Conococheague WWTP | Williamsport | 1.84 | MD0063509 | May 2031 | 0 |
| 17 | Maryland City Water Reclamation Facility | Laurel | 1.53 | MDL062596 | Dec 2030 | 27 |
| 18 | The City Of Bowie (ssos) | Bowie | 1.4 | MDL021628 | Dec 2030 | 8 |
| 19 | Northeast River Advanced WWTP | Charlestown | 1.25 | MDL052027 | Dec 2030 | 38 |
| 20 | Town Of La Plata | La Plata | 1.04 | MDL020524 | Dec 2030 | 111 |
| 21 | Celanese WWTP | Cumberland | 0.8 | MDL063878 | Dec 2030 | 0 |
| 22 | George'S Creek WWTP | Westernport | 0.77 | MD0060071 | May 2026 | 0 |
| 23 | Crisfield WWTP | Crisfield | 0.74 | MDL020001 | Dec 2030 | 45 |
| 24 | Wssc Damascus WRRF | Gaithersburg | 0.72 | MD0020982 | Dec 2028 | 3 |
| 25 | Mount Airy WWTP | Mount Airy | 0.69 | MD0022527 | Dec 2025 | 142 |
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 September 11, 2026.