Flotation is a process in which suspensions, the partiecle phase of which has a specifec gravity less than that of the suspending mediu, are clarified by allowing the suspenede material to flat to the surface. Wher it is removed by skimming. In most applicationjs the effecive specific gravity of the suspended phase is artificaially lowered by the attachment of gas bubbles. This enables the process to be used for a wide variety of suspended solids. The specific gravities of which are slightly greater than those of their suspending media.
The gas bubbles required to effiect the flotation of solids may be generated in a number of ways, including by electrolytic means, by vacuum – activatied release of dissolved gases, by air injection throuth submerged diffusers and by dissolution or air at high pressure in part of the flow, with its subsequent release in fine bubble form on reuction of the pressure to atmospheric level. This latter method of bubble generation is the preferred method in water industry applications, hence the process is generally know an the dissolved arie flotation (DAF) process.
The process has long been applied in industry especially in mining and refineries, for two – phase sparation. It can be use to obvious avantage in water and wastewater treatment systems in place of sedimentaion in cases where particle settling velocities are low.
Specific uses of the process are:
To remove paper fibres from pulp and paper mill wastewaters
To remove oils, greases and similar substances from wastewaters. e.g. food processin, oil refinery and laundry wates:
To concenlrate metallic ores in the mining industry.
To clarify chemically conagulate waters in potable water production and
To thicken sewage sludge
Keywords:
polluted waters, treatment, flotation, dissolved air flotation , DAF
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Flotation for Treatment of Polluted Waters
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