Sedimenting separators flotation

Flocculation. Flocculation (qv) uses chemical precipitation to effect separation (54). It is used to increase the rate of sedimentation and flotation. The resulting material known as floe can be removed by filtration, sedimentation, or flotation. 

Sedimentation and dissolved air flotation are the most common clarification processes for removal of precipitates. Either sedimentation or flotation is often preceded by chemical coagulation or precipitation, which converts dissolved pollutants to a suspended form, and by flocculation, which enhances clarification by flocculating suspended solids into larger, more easily separating particles. Simple sedimentation normally requires a long retention time to adequately reduce the solids content. The detention time of dissolved air flotation, however, is much shorter. When chemicals are used, retention times are reduced and clarification removal efficiency of either sedimentation or flotation is increased. A properly operated clarification system is capable of efficient removal of suspended solids, metal hydroxides, and other wastewater impurities.10-12... 

Separation or clarification techniques, grit separation, sedimentation, air flotation, filtration, microfiltration and ultrafiltration, and oil-water separation. 

Quantitative description of the hydraulic performance of the separation units (both sedimentation and flotation tanks) was one major aim of this investigation. The flow structure, such as conditions of turbulence (microscopic... 

Sedimentation and flotation tank performance is generally formulated on the basis of a surface-loading principle that stipulates plug flow conditions. Thus, the closer a reactor approaches plug flow conditions, the more likely a high solids-separation performance becomes. 

The separation units performance was analyzed by introducing a delta impulse. Over a period of less than 1 min the suspension from the aggregation chamber was directed into the sedimentation or flotation unit by means of a three-way switch. The flow pattern in the separation reactor was as little disturbed as possible. The resulting small number of aggregates was then fol-... 

The efficiency of the separation process, described as overall solids retention, was derived from particle-counting analyses through summation and integration. An attempt was also made to evaluate and interpret the observed removal behavior by analyzing data on specific microscopic suspension parameters such as floe shape. However, these latter data have not yet been incorporated into mathematical models. They have been used qualitatively to explain incongruencies observed in the performance of sedimentation and flotation tanks. 

Suspensions treated under conditions in which good floe formation exist are separated with higher efficiency in flotation units. For intermediary conditions of floe formation, sedimentation in well-designed tanks B and C and flotation tank D show comparable overall efficiency in liquid-solid separation. Flotation appears to be less favored than sedimentation if floe formation is accomplished by lower chemical dosages. 

For most particulates above 1 /xm in natural waters and wastewaters, the power-law coeflBcient appears to be greater than 3. Therefore, adequate removal of the particulate fraction by sedimentation or flotation requires a reduction in p by, for example, coagulation/flocculation, which shifts the major portion of particulate surface area and mass into size classes above about 30 /xm. If granular-media filtration is used as the particulate separation process, only particulate destabilization may be necessary to achieve desired removals. 

When a colloidal particle has a density different from that of the surrounding liquid, sedimentation (or buoyancy) will take place. The presence of the double layer gives rise additionally to the generation of an electric field that, summed over all the particles (if their average separation is larger than their size), generates the sedimentation (or flotation) potential. This is the Dom effect, a simplified theory of which will be described below [40-42]. 

Separation of these solids then occurs by sedimentation or flotation. The H2 gas generated on the cathode helps to float flocculated particles to the water surface (i.e., electroflotation). 

It is recommended to carry out miscibility tests to check that no separation (flotation, sedimentation, coagulation) will occur due to the preservation treatment. This is very important for coating slurries preservation where any rheological change in these complex formulations can destabilise the coating. These tests can include enduction ( draw down test ), brightness test, printability tests. 

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