Flotation is a separation process in which air or gas bubbles are directed at the solid par­ticles and then drive these particles to the liquid surface. Flotation is more beneficial and efficient for removing cells than sedimentation. Flotation can capture particles smaller than 500 pm in diameter (Chen et al., 2011).

According to the bubble size used in the process, the application can be divided into dissolved air flotation and dispersed flotation. In dissolved air flotation, the application of reduced pressure produces bubbles of 10-100 pm. This process is influenced by the tank pres­sure, rate of recycling, hydraulic retention time, and particle flotation rate (Uduman et al.,

2010) . In dispersed air flotation, bubbles of 700-1,500 pm are formed by the high-speed mechanical stirrer with an air injection system (Rubio et al., 2002).