Fundamentals of Bubble Formation during Coagulation and Sedimentation Processes

Conventional coagulation and sedimentation processes can be significantly disrupted by gas bubbles, attaching to, and then floating coagulant floc. This study sought to understand the fundamental factors that lead to bubble formation and corresponding floating floc during coagulation and sedimentation. Gas bubbles (causing the floating floc) can form whenever the total dissolved gas pressure exceeds the local solution pressure, which can occur at localized minimum pressures during rapid mixing at high fluid velocities. Very high rate rapid mixers can cause bubble formation and floating floc even in waters undersaturated with dissolved gas. The formation and stability of floating floc are dependent on the local solution pressure, amount and type of dissolved gas supersaturation, temperature, length of rapid mixing, surface chemistry of the mixing paddle, floc, and attachment forces.