FILTRATION PRACTICE

The function of the filter medium is generally to act as a support for the filter cake, and the initial layers of cake provide the true filter. The filter medium should be mechanically 

In the previous discussion it is assumed that there is a well-defined boundary between the filter cake and the filter cloth. The initial stages in the build-up of the filter cake are important, however, because these may have a large effect on the flow resistance and may seriously affect the useful life of the cloth. 

The blocking of the pores of the filter medium by particles is a complex phenomenon, partly because of the complicated nature of the surface structure of the usual types of filter media, and partly because the lines of movement of the particles are not well defined. At the start of filtration, the manner in which the cake forms will lie between two extremes — the penetration of the pores by particles and the shielding of the entry to the pores by the particles forming bridges. Heertjes(11) considered a number of idealised cases in which suspensions of specified pore size distributions were filtered on a cloth with a regular pore distribution. First, it was assumed that an individual particle was capable on its own of blocking a single pore, then, as filtration proceeded, successive pores would be blocked, so that the apparent value of the specific resistance of the filter cake would depend on the amount of solids deposited. 

The pore and particle size distributions might, however, be such that more than one particle could enter a particular pore. In this case, the resistance of the pore increases in stages as successive particles are trapped until the pore is completely blocked. In practice, however, it is much more likely that many of the pores will never become completely blocked and a cake of relatively low resistance will form over the entry to the partially blocked pore. 

There are two important effects due to particle sedimentation which may affect the rate of filtration. First, if the sediment particles are all settling at approximately the same rate, as is frequently the case in a concentrated suspension in which the particle size distribution is not very wide, a more rapid build-up of particles will occur on an 

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This chapter provides a summary of the governing expressions describing conventional pressure-induced filtration and a description of major equipment. Standard filtration practices refers to the most common or classical method of filtration, sometimes referred to as cake filtration. 

Ruth, B. F. and Kempe, L. Trans. Am. Inst. Chem. Eng. 33 (1937) 34. An extension of the testing methods and equations of batch filtration practice to the field of continuous filtration. 

Industry Survey on Current Sterile Filtration Practices 23 1996... 

Flood, J.E., H.F. Porter, and F.W. Rennie. 1977. Filtration practice today. Chemical Engineering 13 607-609. Grace, H.P. 1953. Resistance and compressibility of filter cakes, part I. Chemical Engineering Progress 49 6, 303. 

Good filtration practice requires careful regulation of the pressure at which the carbon-liquid mixture is delivered to the filter. At the start, the pressure should be low enough to permit a proper flow of clear liquid from the filter. Then as the filtration continues and the filter cake becomes thicker, the pressure from the pump should be increased to maintain the rate of flow but such an increase in pressure should be very gradual. 

The addition of proteolytic enzymes to the beer gives an unquestioned result from the point of view of stability, but (he mechanism of the action is yet to be elucidated. Beers, treated or not treated, have after filtration practically the same nitrogen content moreover, the deposits contain only an insignificant trace of nitrogen. We may then say that the albuminoid substance does not intervene directly in the formation of turbidity, as is often believed. It is probable that the peptonization produced by the enzyme added serves to kc ei) in equilibrium certain organic and inorganic substances, which under ordinary conditions are precipitated. 

In conventional filter-medium filtration practices, the filter medium may be described as the workhorse of the process. Proper selection is often the most important consideration for assuring efficient suspension separation. A good filter medium... 

The wastewaters generated in the dairy industry can be characterized generally as containing high concentrations of BOD, COD, and TDS. Settleable solids are not an important consideration in most dairy wastewaters, since all the organic material is in a colloidal or dissolved state. However, filtration practices are still important because sand or other gritty material may be present from tank truck washings. Cheese wastewaters, on the other hand, have hi er concentrations of settleable solids due to the presence of curd solids. 

Such fixed bed flocculation is normally accompanied by simultaneous filtration of the floes which are formed. This causes clogging and so the accumulated floes must be flushed away periodically (typically, every day) by backwash fluidization, as in normal deep bed filtration practice. 

This method is commonly used to determine pore sizes and the pore size distributions of a membrane because it is close to UP filtration practice dead-end pores are not evaluated. The membrane is characterized in wet conditions. In this technique, the pressure is kept as low as possible and thus no alteration of the membrane occurs. 

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