Separation of activated sludge from purified waste water by Induced Air Flotation (IAF)

The Induced Air Flotation (IAF) applies a self aspirating and radially discharging funnel-shaped nozzle, which produces extremely fine gas bubbles by using only 10% of the purified waste water recycle as the propulsion jet. This nozzle is installed in a flotation cell, where intimate contact between flocs and gas bubbles takes place. The flotation cell is enclosed by a bigger vessel. In the resulting annular channel, the liquid throughput leaving the flotation cell exhibits laminar vertical motion from top to bottom which facilitates the separation of the residual flocs. This paper presents the process characteristics of an improved nozzle design which facilitates an optimization of its operating conditions. Using this technique for complete removal of biomass from purified waste water, the flotation kinetics have been measured and evaluated applying dimensional analysis. The results prove the suitability of this flotation technique and allow a reliable scale-up for an industrial flotation unit. In comparison to the Dissolved Air Flotation (DAF), the Induced Air Flotation needs only 10% of the total liquid throughput for gas bubble generation and a pressurized vessel and gas compressor are not required.