Interactions Between Flocs and Bubbles in the Separation Zone of Dissolved Air Flotation System.

The interaction between flocs and bubbles is crucial to achieve separation efficiency in the separation zone of the dissolved air flotation process. In this study, a micro-scale observation system was established to investigate the interaction between flocs and bubbles in the separation zone of the system. Four periodic interactions were observed-collision, adhesion, coalescence, and desorption (CACD). Small flocs achieved higher unit buoyancy (buoyancy per surface area) than that of large flocs. High collision probability can be obtained between bubbles and small flocs according to Stokes' law and Reynolds experiments. Simulation using Fluent indicated that low-pressure drag acting on small flocs resulted in a high probability of collision. Therefore, small flocs can capture bubbles and accumulate high enough buoyancy in a short time due to the high collision probability and low buoyancy required for small flocs to float. Moreover, the small flocs have a limited number of bubbles on the surface within such a short time, leading to a low probability of desorption and coalescence. The practical verification also show that small flocs are favorable for the high separation efficiency of the flotation process.