Filter media cartridges

Upon start-up of new cartridge filters, the initial effluent should be sent to drain. This is necessary to prevent fouling of the RO membranes with materials used in the manufacture of the cartridge filter media. For example, lubricants and emulsifiers are used in the manufacture of the strings used in string-wound cartridge filters. These materials can coat the RO membranes and foul them. In the case of polypropylene depth filters, phthalates are used in their manufacture. As little as 50 ppb of phthalate will irreversibly foul an RO membrane. ... 

When the pressure rises to the permissible maximum, the cartridge must be opened and the element replaced. Micronic elements of the fiber type cannot be cleaned and are so priced that they can be discarded or the filter medium replaced economically. Stone elements usually must be cleaned, a process best accomplished bv the manufacturer of the porous ceramic or in accordance with the manufacturer s directions. The user can clean stainless-steel elements by chemical treatment. 

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. 

These are housings of metal or plastic containing one or more replaceable and renewable cartridges which contain the active filter element, usually based on a polymeric filter medium or in some cases, sintered stainless steel. They are useful as polishing filters where the level of solids to be removed is relatively low, to prevent the filter from blocking up. 

In the filtration process, a liquid containing suspended solids is passed through a porous medium. The solids are trapped against the medium, and the separation of solids from liquids results. For large solid particles, a thick barrier such as sand may be used for smaller particles, a fine filter such as a filter cloth is preferable. Fluid passage may be induced by gravity, positive pressure, or a r acuum. A few of the more popular filter fypes are the plate and frame filter press, and shell and leaf and cartridge filters. 

It may be noticed that some of the filters discussed are operated continuously and some are not. For example, the rapid sand filter, the slow sand filter, the pressure filter, and the rotary vacuum filter are all operated continuously. The plate-and-frame press is operated as a batch. Thus, filters may also be classified as continuous and discontinuous. Only the plate-and-frame press is discussed in this chapter as a representation of the discontinuous type, but others are used, such as the shell-and-leaf filters and the cartridge filters. The first operates in a mode that a leaf assembly is inserted into a shell while operating and retracted out from the shell when it is time to remove the cake. The second looks like a cartridge in outward appearance with the filter medium inside it. The medium could be thin circular plates or disks stacked on top of each other. The clearance between disks serves to filter out the solids. 

In deep-bed filtration (Fig. ID), particles are caught inside the filter medium. Examples of deep-bed filters are granular beds and some cartridge filters. Deep-bed filtration is used for dilute suspensions (<100 ppm) containing fine particles that are not easy to be removed by sedimentation or cake filtration. 

The same cartridge filters with 2-4 sq. ft. surface area were employed in a pilot-scale production facility for semi-continuous growth of a murine lymphokine-producing cell line. This was done as dead-end filtrations, harvesting 80 to 85% of the 20-40 liter culture as cell-free filtrate and retaining 15 to 20% for inoculum to be regrown after volume restoration with fresh medium. No attempts were made to recirculate or back-flush the filter cartridges. 

These filters are used on slurries with small amounts of solids, usually less than 0.1%, and ganerally do not form any visible cake. Solids io be removed are usually very small panicles that may be trapped on the surface of the filter medium or within the medium. This typa of filter is usually used in a polishing application where excellent quality liquids are needed as in food or beverage, pharmaceutical, and electronic processing operations. The most common clarifying fillers are disk and plate presses, cartridge filters, precoal pressure filters, deep bed filters, and membrane filters. 

The mode of operation of an industrial dust collector may in very simplistic terms be compared with that of a traditional domestic vacuum cleaner i.e. dust-laden air is drawn by vacuum on to the surface of the dust bag , the filter medium retains the dust whilst the dust-free air is expelled into the atmosphere. In an industrial unit, the filter media comprise either woven or non-woven materials, and are normally sewn in the form of tubes (usually referred to as filter sleeves), flat enveloped shaped bags, or cartridges of various design e.g. flat panel or pleated. 

Once a cartridge is fully loaded with collected contaminant the ease of cleaning it for reuse, either manually or automatically, depends on the nature of the filter medium used and the construction of the cartridge. In this respect Purchas (1996) identified four categories of cartridge ... 

Figure 3.4 Typical grade efficiency curves for two types of cartridge filters (clean medium) ...

The driving force for filtration in pressure filters is usually the liquid pressure developed by pumping or by the force of gas pressure in the suspension feed vessel. Alternatively, or in addition, the liquid may be squeezed through and out of the cake by the mechanical action of an inflatable membrane, a piston or a porous medium pressed on top of the cake. Pressure filtration is, therefore, defined here as any means of surface filtration where the liquid is driven through the medium by either hydraulic or mechanical pressure, greater than atmospheric. The solids are deposited on top of the filter medium (as in all surface filters), with the possible exception of some cartridge filters which also use a certain amount of depth filtration. In this chapter, the suspension is assumed to approach the medium at 90° and this excludes the so-called dynamic fUter/thickeners or cross-flow filters (also driven by pressure) which are dealt with in a separate chapter (11). 

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