This paper describes the feasibility and application of a fluidic-based technology, called hydrodynamic separation (HDS), to separate suspended particles from liquid. It uses customized fluid flow patterns in a curved channel to create a pair of Dean vortexes that focus particles into a concentrated band near one channel wall. A splitter at the end of the channel divides the flow into a clean effluent stream and a concentrate stream. The focusing of particles is primarily due to a combination of hydrodynamic forces (drag, virtual mass, and shear), which causes a size rather than density dependent separation. This enables separation of particles with densities identical or close to that of their surrounding fluid, allowing this technology to be especially useful in situations where traditional methods are challenged, such as removal of buoyant particulates from primary clarifiers or separation of unsettleable activated sludge in secondary clarifiers. We tested HDS-based separators with samples that include neutrally buoyant polystyrene beads, activated sludge, primary clarifier effluent and powdered activated carbon to demonstrate its efficacy. In each case, high separation efficiency was achieved which reaffirmed our commitments to evolve HDS technology into an effective pretreatment solution.

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