Dispersed air flotation

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

Several high-rate air flotation clarifiers (both DAF and dispersed air flotation) with less than 15 min of detention times have been developed for groundwater decontamination, industrial effluent treatment, resources recovery, and water reclamation. Both insoluble and soluble impurities such as... 

Wang, L.K., Adsorptive bubble separation and dispersed air flotation, in Advanced Physicochemical Treatment Processes, L.K. Wang, Y.T. Hung, and N.K. Shammas, Eds, Humana Press, Totowa, NJ,... 

Reay, D. "Removal of Fine Partides from Water by Dispersed Air Flotation. PhD dissertation, McCiU II., Montreal (1973). 

Hydrotalcite is often too fine grained to produce treatment columns with suitable permeability. As an alternative, the sorbent may be mixed with contaminated water in a tank (Lazaridis et al, 2002). The spent sorbent is then separated from the treated water by flocculation, flotation, or other separation methods (see Section 7.2.4). Lazaridis et al. (2002) investigated the use of surfactants with dispersed-air flotation to separate spent hydrotalcites from treated water. At ionic strengths of 0.1 M using KNO3, effective flotation and separation could be obtained by using a mixture of dodecylpyridinium chloride, sodium dodecylhydrogen sulfate, and a cetyltrimethyl ammonium bromide frother (Lazaridis et al., 2002,322,323). 

Foam Separation by Dispersed Air Flotation Cell Chemical Reagents for Adsorptive Bubble Separation Laboratory Foam Separation Tests Engineering Applications... 

Dispersed air flotation (or induced air flotation) Example Deinking flotation... 

All the aforementioned process terms can simply be called foam separation. It is important to note that although any type of technique can be used for bubble generation in a foam separation system, the most common bubble generation technique for a foam separation system is dispersed air flotation, which is also known as induced air flotation. 

To start the SBR foam separation (or dispersed air flotation, or induced air flotation) experiments, sufficient volume of raw water is adjusted to the desired pH with 1.0 A sodium hydroxide or 1.0 A sulfuric acid, an appropriate amount of surfactant is added to the raw water, and the ntixture is poured into the Foamer Tester (Fig. 7). Compressed air is then diffused through the liquid ntixture by means of a plastic cloth grid (Fig. 8). Foam is withdrawn from the top and collected in a container. The run is allowed to proceed until no additional foam is formed. A sample of the bulk liquid near the reactor bottom is analyzed for pH, color, turbidity, and other water quality parameters. The foam is collapsed in a beaker and its volume is measured. 

Fig. 8. Piping arrangement of a bench-scale batch dispersed air flotation system.

First-Stage Dispersed Air Flotation for Primary De-inking... 

On leaving the dispersed air flotation cell, the de-inked stock is further diluted before passing through another fine screening process to remove small solids. The materials are then pumped to a drum thickener prior to he dispersion stage. 

Although operation of the second dispersed air flotation cell is similar to that of the first, no further chemicals are added, as the inevitable carry-over from the first stage is sufficient. 

The dispersed air flotation (or induced air flotation) de-inking process allows the use of a wider range of printed waste paper. The amount of dirt in the finished paper is reduced, thereby improving quality and reducing the amount of reject paper. The brightness of the finished paper is improved without the use of chlorine bleaching. 

---