Clarification by sedimentation

Optimal water management (water loop arrangement), water clarification by sedimentation, flotation or filtration techniques, and recycling of process water for different purposes. 

Several treatments are described elsewhere, in conjunction with the specific problems they treat or as applications of more general processes (physical treatments). This chapter presents clarification by sedimentation and racking, as well as protein fining and a few ofher freafmenfs not discussed in other sections. 

The usual objective of clarifying filtration is to separate solids at a very low concentration fi om a liquid stream. The liquid may be drinking (potable) water, wine, beer, oil, etc. and it is usually the liquid which is the valuable product. The techniques used in clarification processes include deep-bed, precoat, candle and cartridge filtration all of which involve capture of particles inside the porous mass of the filter. Such techniques produce clearer filtrates than those obtained in clarification by sedimentation. The filtration techniques listed are ofiioa complementary they are eirqrloyed for similar duties, but usually operate over different conditions of feed flow rate, feed concentration and process economics. These operating conditions are summarised in Table 6.1. 

By blocking fermentation for several hours, it permits a coarse clarification by sedimentation. 

Clarification A process in which suspended material is removed from a wastewater. This may be accomplished by sedimentation, with or without chemicals, or filtration. 

Clarification by either sedimentation or dissolved air flotation is the most common solid-water separation technique used for the removal of precipitates. In this process application, clarification... 

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... 

During the clarification or sedimentation step (Figure 7.1), the main objective is to allow gravity to settle the enlarged particles (Spellman, 2003, 476). Suspended particles may also be separated from the effluent by filtering (Spellman, 2003, 476). Once the effluent is essentially free of precipitates (that is, clear ), it may undergo additional treatment or be discharged. 

Clarification, by the sedimentation of suspended particles and precipitation of salts such a potassium bitartrate, is facilitated by storage in barrels. Their small volume reduces convective phenomena and allows the wine s temperature to cool markedly during the winter, encouraging both phenomena. The precipitation of unstable colloids, that can cause wine turbidity, also occurs during maturation. The precipitates are subsequently removed during racking. 

The clarification of juices, i.e. the mechanical removal of suspended solid particles from the juice, is generally carried out by sedimentation, filtration or centrifugation. These processes are very often combined in order to achieve a better result. 

Still existing turbidities will be eliminated by appropriate methods of clarification and stabilisation of the wine. Turbidity-causing matters are mostly proteins as well as oxidized and condensated polyphenols. Moreover, metal ions may lead to discolouring and sedimentation. Common methods of wine clarification are precipitation (fining), filtration or centrifugation. Clarification by means of filtration is achieved with cellulose or diatomaceous earth. 

From this it follows that one must first of aU look at sedimentation. In this respect it is important to note that even if sedimentation does not achieve exactly the separation required it may still be a valuable first step in a process and may be followed by filtration. A typical example of this is the well-known clarification of water in water works. Here sedimentation with or without flocculation is first carried out, and the still somewhat hazy overflow is then passed through polishing filters. To achieve the end result purely by sedimentation or purely by filtration would be prohibitively expensive. The combined procedure, however, is both practical and reliable. 

This external recirculation loop is operated with a solution that has been clarified, that is, from which crystals have been removed. This is performed in order to prevent secondary nucleation in the external recirculation loop, which now has the higher resistance level due to the heat exchanger used there. If no crystals are suspended in this external loop, it is not possible for the circulation pump used there to produce secondary nuclei. However, the statement that this solution is free of crystals is only partially correct In fact, in the clarification zone of a DTB crystallizer, the main mass of the crystals has indeed been separated out of the solution by sedimentation, but the finer crystals (fines) and the crystal nuclei with settling rates greater than upstream velocities are not separated out. The sum total of these... 

Titanium dioxide is manufactured by two processes, the sulfate process and the chloride process. In the sulfate process, ilmenite ore (FeTiOg) is dissolved in concentrated sulfuric acid and insoluble impurities are removed by clarification, flocculation, sedimentation and filtration. The resulting solution is further purified by crystallization to remove ferrous sulfate from titanyl sulfate solution. The titanyl sulfate solution is then hydrolyzed to give hydrated titanium dioxide, which is calcined at about 900 to 1100 °C to give the titanium dioxide pigment. Both anatase and rutile-type titanium dioxide pigments are produced using this method. 

Arachin, 93.7% iS2o 13.3 and 6.3% <820" 21.1, was examined in phosphate buffer, n = 0.5, pH 7.4, protein concentration 0.38 g./lOO ml., by means of light scattering apparatus. In a filtered solution arachin had an apparent molecular weight of 17,000,000 with ho/1120 of 1.8. On further clarification by ultrafiltration, the molecular weight was 333,000 with ho/1 no of 1.074. This value is in agreement with the accepted value for the molecular weight of arachin of 330,000 calculated from sedimentation and diffusion constants (89). 

The trend in the use of deep bed filters in water treatment is to eliminate conventional flocculators and sedimentation tanks, and to employ the filter as a flocculation reactor for direct filtration of low turbidity waters. The constraints of batch operation can be removed by using one of the available continuous filters which provide continuous backwashing of a portion of the medium. Such systems include moving bed filters, radial flow filters, or traveling backwash filters. Further development of continuous deep bed filters is likely. Besides clarification of Hquids, which is the most frequent use, deep bed filters can also be used to concentrate soflds into a much smaller volume of backwash, or even to wash the soflds by using a different Hquid for the backwash. Deep bed filtration has a much more limited use in the chemical industry than cake filtration (see Water, Industrial water treatment Water, Municipal WATERTREATiffiNT Water Water, pollution and Water, reuse). 

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