Disposable cartridge filters

Disposable cartridge filters are recommended over back-washable filters. Back-washable filters suffer from several limitations ... 

Disposable cartridge filters should be made of synthetic, non-degradable materials such as nylon or polypropylene. Their construction can be spun-bonded or melt-blown, string-wound, and pleated. These are described below. 

Microfilters use membranes with pores in the 0.1-1 pm range. They can filter out particles of dust, activated carbon, and ion exchange resin fines, and most microorganisms. Microfilters require low differential pressures (5-20 psi) and are available both as normal flow ( dead end ) and crossflow configurations. In pharmaceutical water purification systems, they are often used as disposable cartridge filters after activated carbon filters, softeners, and ion exchange beds. 

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. 

Many filters in chemical process units are either changed very rarely or are back-flushed automatically so there is hardly any exposure. Some filters, however, require frequent manual changing or cleaning and significant exposure may occur unless operators foUow the proper procedure. The filter container should be drained of any toxic material and then flushed and purged as needed so that when it is opened there is only minimal exposure. Zero exposure is difficult to achieve in situations where a disposable paper filter cartridge may retain and slowly release a material that cannot be removed by multiple flushes and purges. 

A consideration in the design of a Recoflo system is adequate pre-filtration of the feed solution. The fine resin beds employed in the system will plug-up with any suspended material that is not filtered out prior to treatment. This is not a major issue for chlor-alkali brines, however, which are relatively clean. Disposable polypropylene cartridge filters should suffice in most cases. 

Figure 7.10 Sterile filtration of a small-volume pharmaceutical solution with a 142 mm plate-and-frame filter used as a prefilter in front of a small disposable cartridge final filter. From Gelman Science...

Despite the limited volumes that can be treated before a filter must be replaced, microfiltration is economical because the cost of disposable cartridges is low. Currently, a lO-in.-long pleated cartridge costs between US 10 and US 20 and contains 0.3-0.5 m2 of active membrane area. The low cost reflects the large numbers that are produced. 

Membranes are available in sheet, roll, disk, capsule, cartridge, and hollow-fiber formats. For sample filtration, disk-format membranes are the most popular devices. Disks are sold in loose form or packed in disposable syringe filters or cartridges common diameters commercially available are 3, 7, 13, 25, 47, and 96 mm, or even larger. Samples are filtered by manually applying a positive pressure or in a vacuum manifold. 

In general, and in summary, cartridge filters have an integral cylindrical configuration made with disposable or cleanable filter media and utilize either plastic or metal structural hardware. Appropriate housings form the filter assembly and for large flows, multiple cartridges are installed in a pressure... 

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