Diatomaceous earth precoat filtration

Wang, L.K., Diatomaceous earth precoat filtration, in Advanced Physicochemical Treatment Processes, Wang, L.K., Hung, Y.T., and Shammas, N.K., Eds., Humana Press, Totowa, NJ, 2006. 

Untreated wine, before filtration Filtration through diatomaceous earth precoat Filtration throngh sterilizing filter sheets... 

Diatomaceous Earth precoat filtration for drinking water treatment... 

Filtration through a diatomaceous earth precoat (kieselguhr) formed by continuous accretion. 

Of course, filtering wine through a diatomaceous earth precoat follows this law. Although the principle is different, the same law also governs tangential filtration (Mietton-Peuchot, 1984), where the particles, concentrated along the membrane, behave like a cake. 

Immediately after the end of fermentation, there is a viable population on the order of lOVml of microorganisms. This value decreases rapidly to 10 or 10" /ml due to the effects of settling and racking. After filtration through a diatomaceous earth precoat, wines generally have viable populations on the order of 10 /ml. Populations may remain quite large in wines that receive no preliminary clarification treatment. 

The wine should be properly clarified prior to flat-sheet filtration at the time of bottling to ensure a satisfactory flow rate. This preliminary clarification may involve spontaneous settling, fining, centrifugation (Section 11.11) or filtration through a diatomaceous earth precoat (Section 11.6). 

Tangential microfiltration has been used in many wine treatment applications over the past 10 years. Suitable membranes are now available for clarifying must or untreated wines, as well as the final clarification of prefiltered wines. This technique may also provide an alternative to filtration through diatomaceous earth precoats, especially in cases where waste discharges could lead to excessive pollution. Tangential microfiltration is still. 

Filtration throngh a coarse diatomaceous earth precoat (2.3 and 1.5 Darcy) did not affect chemical composition. The same operation with fine earth (0.35 Darcy) reduced the polysaccharide and condensed tannin content by 10%. No organoleptic effects were identified when the samples were tasted one month after filtration. 

It is not advisable, nor is it useful, to filter wines on a fine diatomaceous earth precoat (0.35 Darcy) prior to flat-sheet filtration. 

Filtration. Any type of clarification is foUowed by filtration through leaf-type vertical or horizontal pressure filters. Carbonatated Hquors, containing calcium carbonate, may require addition of diatomaceous earth as a filter precoat. Phosphatated Hquors are generally filtered with the addition of diatomaceous earth as precoat and body feed. 

Precoat Procedure Precoat filtration tests are run in exactly the same manner as bottom-feed tests except that the leaf must first be precoated with a bed of diatomaceous earth, perhte, or other shave-able inert sohds. Some trial and error is involved in selecting a grade of precoat material which will retain the filtered solids to be removed on the surface of the bed without any significant penetration. During this selection process, relatively thin precoat beds of I to 2 cm are satisfactory. After a grade has been selected, bench-scale tests should be... 

Sometimes filtration can be improved by using filteraids. These filteraids, which are based on diatomaceous earth, improve the porosity of a resulting filter cake leading to a faster flow rate. Before filtration a thin layer is used as a precoat of tire filter (normally standard filters). After that a mix is made with the harvest broth and filtration is started. 

Another method, which is even more successful in preventing binding of the septum, is the use of a precoat.53 Before filtration is begun a coating of 2-6 in (5-15 cm) of diatomaceous earth or perlite filter aid is deposited on the surface of the septum. During filtration operations the scraper is set so that it slowly removes the precoat and, of course, with it the materials that would have plugged the filter. Since the precoat causes a considerable pressure drop, the rate of filtration is slowed down. Flow rates may vary from 2 to 50 gal/hr/ft2 (0.025-0.60 m/hr). The precoat material costs around 3 or 40/lb and is used at the rate of 10- 15 lb/1,000 gal of feed (1,200 to 1,800 kg/m3). 

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