| This study investigates froth flotation of dispersed oil in the air sparged hydrocyclone (ASH). Several topics are considered: air bubble and oil droplet interactions in a centrifugal force field, adsorption of flotation reagents at interfaces, froth properties in the presence of dispersed oil, effect of ASH design and operating variables, plant evaluation of a modified ASH system, bubble accelerated flotation (BAF), in the treatment of fish processing wastewater.; Air bubble and oil droplet encounter occurs only due to interception; however, the efficiency of encounter is reduced by gravitational action. Collision contact times are less than 0.14 ms and cannot account for attachment that requires at least 2 ms. Sliding contact times vary from below 1 ms to almost 400 ms and can lead to film rupture/attachment.; Adsorption of dextrin may require very long times at the order of hours to achieve an equilibrium and conditioning time should be appropriately planned.; Dispersed oil significantly increased froth collapse rate; however, the dynamic stability was less affected, which is beneficial for ASH flotation. Silica particles wetted by oil increased froth collapse rate, but had negligible effect on dynamic froth stability.; Oil recovery in the 1-inch ASH was significantly lower than for the 2-inch ASH, 0.6% compared to 6.6% when unaided by flocculation. Higher centrifugal acceleration in the 1-inch ASH and the higher dissipation of energy were responsible for decrease in flotation efficiency. Polymeric flocculation yielded over 40% oil recovery in the 1-inch ASH.; The commercial BAF system (Empacadora Mar, Ensenada, Mexico) was very efficient in the removal of suspended solids and oil (96 to 99%); however, colloidal pollutants of size below 1 mum remained in the wastewater.; Flocculation with cationic polymers was required for satisfactory oil removal by ASH technology. Batch cell experiments needed a dosage of 1 ppm, while ASH tests required 10 ppm. Efficient oil removal (96-100%) by BAF could be attained using over 50 ppm of cationic flocculant.; Further improvement in oily wastewater treatment by ASH technology can be achieved by ASH design improvements and by the chemical control of flocs stability. |
