Solid/liquid separations are integral part of any wastewater treatment system. Particles heavier than water are commonly separated in sedimentation clarifiers. On the other hand, particles with densities lower than that of water are most often separated with flotation systems. This manuscript describes the development of hybrid centrifugal - dissolved air flotation system. The system was developed by combining high-energy centrifugal mixing of a liquid – liquid cyclone with pressurized dissolved air as a source of flotation bubbles. It is the only dissolved air flotation system in which 100% of the influent is aerated. Nucleation of bubbles occurs at the same time with nucleation of flocs inside the hydrocyclone columns. Solid/liquid separation occurs inside the columns under the influence of centrifugal forces. Tanks are only used for sludge skimming. Such design results in smaller footprint, sludge with higher solids content, lower coagulants and flocculants consumption and faster response times. These advantages are particularly important when using flotation as a pretreatment for membranes or bioreactors, since any overdose of chemicals can foul membranes or interfere with microorganisms metabolism. Classical hydrocyclone heads were also replaced with controlled mixing energy designed heads. Centrifugal forces with controlled mixing energy allow for application of high performance viscous flocculants and coagulants. Centrifugal vortex mixing is very efficient at activation of flocculant molecules and growth of large flocs without breaking either polymer chains or flocs.
Keywords: solid/liquid separations, hybrid liquid cyclone – dissolved air flotation, membrane pretreatment
The development and application of the hybrid centrifugal - dissolved air flotation system for wastewater treatment