The Aqua-Swirl™ Concentrator Conveyance Flow Diversion System provides full treatment for the most contaminated first flush,¯ while the cleaner peak storm flow is diverted and channeled through the main conveyance pipe. Many regulatory agencies are establishing water quality treatment flow rates for their areas based on the initial movement of pollutants into the storm drainage system.

The operation begins when stormwater enters the Aqua-Swirl™ through a tangential inlet pipe which produces a circular (or vortex) flow pattern that causes contaminates to settle. Because stormwater flow is intermittent by nature, the Aqua-Swirl Concentrator retains water between storm events providing both dynamic and quiescent¯ settling of inorganic solids. The dynamic settling occurs during each storm event, while the quiescent settling takes place between successive storms. A combination of gravitational and hydrodynamic drag forces encourages the solids to drop out of the flow and migrate to the center of the chamber where velocities are the lowest, as shown from extensive CFD modeling.

A large percentage of settleable solids in stormwater are reported to be small and have low settling velocities. Therefore, the volume of water retained in the Aqua-Swirl™ Concentrator provides the quiescent settling that increases performance. Furthermore, due to finer sediment adhering onto larger particles (less than 200 microns), these larger particles settle rather than stay suspended in the water.

The treated flow exits the Aqua-Swirl™ Concentrator behind the arched outer baffle. The top of the baffle is sealed across the treatment channel, thereby eliminating any possibility of floatable pollutants to escape the system. A vent pipe is extended up the riser to expose the backside of the baffle to atmospheric conditions, preventing a siphon from forming at the bottom of the baffle.

As recommended by the Center for Watershed Protection and some municipalities, the Aqua-Swirl™ can also operate in an offline configuration providing full treatment of the first flush; however this orientation will require the installation of additional manhole structures for diverging the flow to the Aqua-Swirl™ for treatment and converging back to the existing main conveyance storm drainage system.