Sedimentation Lamella

From the slow mix unit [T-100], the waste flows into the lamellar portion of the sedimentation clarifier [T-101].54 55 The lamella in the clarifier concentrates the metal hydroxide precipitates. Clarified effluent can be discharged to the sewer. 

Lamella settlers are gravity settlers that use a large number of inclined flat plates, closely packed, so that the distance between the plates is small. The gravitational action makes the cells move in the direction of the lower surface of the individual separating space between two plates. Once settled, the particles slide down in a layer towards the plate periphery and then into the sludge hopper. For the same required sedimentation area, lamella settlers are much more compact than vertical ones. Theoretically, their total sedimentation area is the sum of the horizontally projected areas of all plates. In practice, however, only 50% of this total area is effective [137]. The main problem with inclined settlers is that the cells tend to adhere to the plates. Special coating of the plate surface and vibration of the whole lamella pack may alleviate this problem. 

Thompson and Wilson [78] operated a 21-L air-lift perfusion reactor coupled to an external lamella settler. The sedimentation device bearing an angle of inclination of 30° to the vertical was maintained at 37°C. They found a reasonable agreement between the theoretical and experimental values of breakthrough for viable and nonviable cells in the harvest stream. As expected (see Eq. 8), the maximum perfusion rates increased with an increasing settling area. 

The system used by Stevens et al. [79] consisted of an air-lift reactor with an external lamella settler. They did not need to pump the cell suspension through the settler, since free flow convection was achieved by cooling the cell suspension (20 °C) before entering the sedimentation device. As also found by other authors, they could achieve selective retention of viable cells by varying the perfusion rate. 

Good descriptions of practical experimental techniques in conventional electrophoresis can be found in Refs. [81,253,259]. For the most part, these techniques are applied to suspensions and emulsions, rather than foams. Even for foams, an indirect way to obtain information about the potential at foam lamella interfaces is by bubble electrophoresis. In bubble microelectrophoresis the dispersed bubbles are viewed under a microscope and their electrophoretic velocity is measured taking the horizontal component of motion, since bubbles rapidly float upwards in the electrophoresis cells [260,261]. A variation on this technique is the spinning cylinder method, in which a bubble is held in a cylindrical cell that is spinning about its long axis (see [262] and p.163 in Ref. [44]). Other electrokinetic techniques, such as the measurement of sedimentation potential [263] have also been used. 

Lamella Settler Up to 3.0 Up to 7.5 Inclined tubes or parallel plates to increase sedimentation Various... 

It is of interest that in the continuous operation of inclined settlers, termed lamella settlers, where the sediment is withdrawn continuously from the bottom of the channel and clarified product continuously from the top of the channel, that two modes of operation have been shown to exist for the same rate of clarified flow (Probstein et al. 1981, Leung Probstein 1983). In one mode the feed suspension layer expands down the channel subcritical mode), as in Fig. 5.4.8, whereas in the other mode supercritical mode) the layer contracts. The appearance of one mode or the other depends on the geometry and the manner in which the suspension is fed into the settler and the clarified liquid withdrawn. We would suggest that under appropriate conditions there exist two types of steady solutions for all continuous sedimentation processes. 

Thirdly, a fourth section discusses chemical demul-sification processes. Floeeulation, ereaming/sedimentation, and coalescence and the lamella drainage model are covered. The fifth section discusses the expected performance demanded of demulsifiers for various systems and... 

The efficiency of the attachment process depends upon the size of the gas bubbles. Process equations are available for predicting the course of such separations these detign equations require the support of laboratory tests to provide relationsh s between flotation velodties, the volume of air per unit mass of soUds, etc. This chapter also deals with the design of inclined lamella separators vffiich tend to intensify the sedimentation eflfect, thus requiring smaller vessel volumes when conqiared with conventional equqtment. 

The particulate material obtained by sedimentation of broken chloroplasts consists of lamellae and lamellar fragments. Park (1963) has suspended this green precipitate in water and then precipitated it according to the critical point method of Williams (1953). When the precipitated material was dried down on a screen, shadowed with heavy metal for viewing in the electron microscope, and photographed, the material was found to be clearly lamellar in structure (Fig. 2). 

The size of the settlement basin is sometimes reduced by employing a series of internally mounted plates inclined at about 60° to the horizontal. In a similar manner to the lamella separator (see Section 1.1.2.3), the effective settling area is increased to allow sedimenting solids to slide down the plates and into the collecting well. Other variants include the vertical flow clarifier, the blanket clarifier and the circular clarifier the latter is similar in form to a conventional circular thickener but of a much lighter construction. 

An interesting combination of the Lamella sedimentation principle with an up-flow deep bed filter is known as the Rozka filter shown schematically in Figure 5.6. This is in fact a filter-assisted clarifier sometimes used in water... 

One last note about the lamella principle is to mention its enhancement with a high voltage electrostatic field. Generally, the enhancement of sedimentation velocities in non-aqueous suspensions by electrophoresis has been well exploited recently in solvent extraction. Jayaswal et a/." have combined the lamella principle with electrophoresis and applied the system successfully to colloidal suspensions modelling those in the production of synthetic fuels from coal, oil shale and tar sands. 

A fine fraction d<2 fjm) of kaolinite (Zettlitz, Germany) was used as a support for the preparation of nanoparticles. Disaggregation of the kaolinite lamellae in water was brought about by the intercalation of dimethyl sulfoxide (DMSO) (Reanal, puriss.) at 65 °C and 24 h in suspension (20 g kaolinite per 100 cm DMSO) under stirring. The redundant DMSO was removed by sedimentation with repeated washes with methanol (Reanal, a.r.) and decanting for 5 days. 

If the source water turbidity exceeds 100 NTU, than conventional sedimentation basins are often inadequate to produce turbidity of the desired target level of less than 2.0 NTU. Under these conditions, the sedimentation basin has to be designed for enhanced solids removal by installing inclined lamella-type plates or using sedimentation technologies that combine lamella and fine granular media (microsand or settled residuals) for enhanced solids removal. 

This is clearly a word to be used with care in any filtration and sedimentation context. It is used in this Handbook only in the general sense when unmodified, so that the term separator means any form of physical separation equipment. The term only has a specific meaning when preceded by a modifier magnetic separator , lamella separator , or, as is mainly the case in this section, gravity separator or sedimenting separator . 

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