Typical Industrial Filtration Conditions

Two significant operating parameters influence the process of filtration the pressure differential across the filtering plate, and the temperature of the suspension. Most cakes may be considered compressible and, in general, their rate of compressibility increases with decreasing particle size. The temperature of the suspension influences the liquid-phase viscosity, which subsequently affects the ability of the filtrate to flow throu the pores of the cake and the filter medium. 

Tlie discussions of the basic features of filtration given thus far illustrate that the unit operation involves some rather complicated hydrodynamics that depend strongly on the physical properties of both fluid and particles, as well as interaction with a complex porous medium. The process is essentially influenced by two different groups of factors, which can be broadly lumped into macro- and micro-properties. Macrofactors are related to variables such as the area of a filter medium, pressure differences, cake thickness and the viscosity of the liquid phase. Such parameters are readily measured. Micro-factors include the influences of the size and configuration of pores in the cake and filter medium, the thickness of the electrical double layer on the surface of solid particles, and other properties. 

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Consequently, membrane bioreactors are an example of the combination of two unit operations in one step for example, membrane filtration with the chemical reaction. In a typical membrane bioreactor, as weU as acting as a support for the biocatalyst, the membrane can be a very effective separation system for undesirable reactions or products. The removal of a reaction product from the reaction environment can be easily achieved thanks to the membrane selective permeability, and this is of great advantage in thermodynamically unfavourable conditions, such as reversible reactions or product-inhibited enzyme reactions. A very interesting example of a membrane bioreactor is the combination of a membrane process, such as microfiltration or ultrafiltration (UF), with a suspended growth bioreactor. Such a set up is now widely used for municipal and industrial wastewater treatment, with some plants capable of treating waste from populations of up to 80 000 people (Judd, 2006). 

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