Hydrodynamic separations (HDS) for water treatments: from desalination to water recycle and reuse

Abstract

This paper describes a novel membrane-less separation technology which leverages the balance of hydrodynamic forces to enable selective removal of suspended contaminants from various water sources; we call it a hydrodynamic separator (HDS) technology. This novel technology uses centrifugal force to create transverse flow patterns in a curved channel that sweep suspensions to force equilibrium positions forming a concentrated particle band resulting in separation. This use of centrifugal force is different from that in traditional hydrocyclones and centrifuges where particles of different densities from the liquid are moved relative to the liquid using very high (100s 1000s) relative centrifugal force (RCF). The hydrodynamic separator uses hydrodynamic forces to move suspensions, requiring very low (<10) RCF. Furthermore, HDS has a unique advantage in that it does not require particulate density difference from medium. In this paper, we demonstrate successful separations in different scenarios where input waters fit into one of three categories: contain neutrally buoyant particles, contain high solids loading or contain high volumetric amounts of amorphous flocs formed by addition of flocculants. We also present two different versions of HDS separator designs: a particle separator with cutoff size of 8-12 um and a floc separator with cutoff size of 20-40 um. The former requires about 20 PSI of pressure while the latter less than 2 PSI. Properly tuned separator design allowed successful separation of samples in the 3 scenarios discussed in this paper. We envision the HDS technology to evolve as an important piece of the water treatment train for many fronts, from desalination to wastewater recycle and reuse.