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, anddesorption (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 lowpressure 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 clue 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 arc favorable for the high separation efficiency of the flotation process. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study established a micro-scale observation system to investigate the interaction between flocs and bubbles in the separation zone of the dissolved air flotation process. It was found that small flocs have a higher unit buoyancy and collision probability with bubbles, enabling them to capture bubbles and accumulate enough buoyancy for efficient flotation separation in a short time. The simulation and practical verification both support the favorable role of small flocs in achieving high separation efficiency in the flotation process.