The FF (flocculation-flotation) process

A new on-line flocculation system (FF) has been developed which is coupled with a, rapid flotation to remove the aerated flocs (flocs with entrained and entrapped bubbles). These aerated flocs are formed only in the presence of high molecular weight polymers and bubbles and under high shearing (and head loss) in special flocculators. The air excess air abandons the flotation tank (a centrifuge or a column) by the top and the flocs float after very short residence times (within seconds). The aerated flocs are large units (some millimetres in diameter) having an extremely low-density. Process efficiency was found, in all cases, to be a function of the trilogy, head loss, type (and concentration) of flocculants and air flow rate. Mechanisms involved appear to include small bubble formation and their rapid occlusion (entrapment) within flocs, nucleation of bubbles at floc/water interfaces, polymer coiling as a result of salting out effects at the aqueous/air interface and plug flow type of mixing (flocculation) instead of perfect. Successful examples of emulsified oil and solids removal from water are shown and because in all cases were obtained high efficiencies (> 90% removal), at high hydraulic loadings (> 130 mh(-1)) it is believed that this kind of flocculation-flotation appears to have a great potential in solid/liquid or liquid/liquid separation. (c) 2004 Elsevier Ltd. All rights reserved.