Media types, cartridge filtration

There are two major types of filtration "cake" and "filter-medium" filtration. In the former, solid particulates generate a cake on the surface of the filter medium. In filter-medium filtration (also referred to as clarification), solid particulates become entrapped within the complex pore structure of the filter medium. The filter medium for the latter case consists of cartridges or granular media. Among the most common examples of granular materials are sand or anthracite coal. 

A common surface cartridge is the pleated paper constmction type, which allows larger filtration areas to be packed iato a small space. Oil filters ia the automobile iadustry are of this type. The paper is impregnated, for strength, with epoxy or polyurethane resia. Any other medium ia sheet form, similar to cellulose paper, such as wool, polypropylene, or glass may be used. 

The microbial challenge test can be performed on a particular filtration medium, whether disk or cartridge type, by following these general steps ... 

Human Burkitt Lymphoma ( Raji ) cells were obtained frozen from the American Type Culture Collection thawed, and cultured, in RPMI containing 10% Fetal Bovine Serum. The polymers for microencapsulation were dissolved in distilled water with pH adjustment to 7.4, and dialysed extensively against distilled water through a 104 Da cut off dialysis bag. The polymers were then pH adjusted to 7.4 and freeze dried to constant weight. Final preparation for the microencapsulation process was limited to dissolution in appropriate medium and filtration through a 0.4 pm cartridge. 

Filtration can be distinguished in two types (1) absolute and (2) depth. In absolute filtration a steel or plastic screen, cartridge, or paper filter removes particles from the oil. These filters have certain porosity and most of them retain particles down to 5 pm, when used for passive filtration [72]. If diato-maceous earth or other absorbents are used, they are mixed with the oil in the fryer at the end of the day and/or shift and the suspension is pumped through the filter and circulated through the filter and back into the fryer until a filter bed is established and the fryer is free of fines and particulates. Filter media suppliers recommend a dose between 0.1% and 2.0%, by weight on the frying medium [8]. 

The cartridges consisting of a single piece of filter medium are made from a perforated cylindrical core, of metal or stiff plastic, onto which the material of the filter medium is placed or formed. There are two basic types of integral media cartridges, depending upon which primary filtration mechanism is operating thin media, which work by surface filtration, followed if necessary by cake filtration on top of the surface layer and thick media, which work by depth filtration. 

Backwashable cartridge filters are available in a variety of designs using metal screens, permeable ceramic, or consolidated sand as a filter medium. Filters of this type are simple and lightweight hke the disposable cartridge filters, but they have the additional advantage of being backwashable. The media used in backwashable filters typically provide filtration of particles between 10 and 75 pm. 

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