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Stormflow Events: Increasing Wastewater Treatment Capacity

​As extreme weather events, such as heavy rainfall or snow melt periods, become more frequent, municipalities struggle to effectively manage stormflow discharges, particularly if they still use combined sewer systems.

Unlike modern sewer systems that put sewage and stormwater flows in separate pipes, these older systems combine stormwater in the same sewer pipe as domestic, commercial and industrial wastewater. Combined sewer systems can easily overwhelm the capacity of wastewater treatment plants during periods of heavy rainfall or snowmelt. If the wastewater treatment plant is overwhelmed, excess wastewater may be discharged directly into local bodies of water before it has been treated. This discharge is a public health hazard due to the potential for triggering waterborne illnesses. In fact, more than half of all documented waterborne disease outbreaks since 1948 have followed extreme rainfalls.


To combat these challenges and increase wastewater treatment capacity during peak flows, Evoqua Water Technologies offers municipalities a variety of products that will fit every budget and type of facility.

Stormflow Products for Existing Infrastructure or New Facilities


BioMag® System Stormflow Capabilities
For facilities that need a solution for managing stormwater flows and want to keep their existing tankage, Evoqua offers the BioMag® system.  The system is a ballasted biological technology that improves the settling rate of floc. This results in rapid and reliable clarification. Additionally, the BioMag system enables secondary clarifiers to operate at higher hydraulic and solids loads than conventional alternatives. Since ballasted floc settles faster, the system provides safeguards during stormwater events to keep biological solids within the treatment system. Finally, the BioMag System can be easily implemented in retrofits with any type of activated sludge process.

CoMag® System Stormflow Capabilities
For facilities that prefer to handle stormwater events with a side-stream treatment, Evoqua offers the CoMag® System.  The system ballasts chemical flocculation, enabling high-rate clarification that handles a wide range of inlet fluctuations. When storms occur, the system goes online in less than 15 minutes to handle hydraulic surges. Once the rain event subsides, the CoMag System can go offline or serve as a tertiary treatment unit during dry weather.

Orbal® System Stormflow Capabilities
For facilities that want to replace aging infrastructure or need to construct a new wastewater treatment plant, Evoqua offers the Orbal® System, which delivers unmatched stormflow management capabilities. In fact, some facilities can handle up to 12 times peak flow with this technology—at least triple the capacity of any other oxidation ditch. By operating the tanks in a series, the Orbal System stores solids in the outer channels and diverts the stormflow downstream of the first reactor, preventing any loss of biological treatment during the storm event.