Trap, filtration

There are two different approaches available for taking samples of suspended matter from waterways. These are filtration or centrifugation of water samples and collecting settled particulate matter in a sediment trap. Filtration or centrifugation can be conducted on grab samples or on water which is pump-extracted from instream. It is necessary to measure volumes filtered or centrifuged to calculated concentrations or loads in water samples. 

The technique of the filtration of hot solutions has already been described in Section 11,28. The filtration of cold solutions will now be considered this operation is usually carried out when it is desired to separate a crystalline solid from the mother liquor in which it is suspended. When substantial quantities of a solid are to be handled, a Buchner funnel of convenient size is employed. The ordinary Buchner fimnel (Fig. 11,1, 7, a) consists of a cylindrical porcelain funnel carrying a fixed, flat, perforated porcelain plate. It is fitted by means of a rubber stopper or a good cork into the neck of a thick-walled filtering flask (also termed filter flask, Buchner flask or suction flask) (Fig. 11,1, 7, c), which is connected by means of thick-walled rubber tubing (rubber pressure tubing) to a similar flask or safety bottle, and the latter is attached by rubber pressure tubing to a filter pump the safety bottle or trap is essential since a sudden fall in water pressure may result in the water sucking back. The use of suction renders rapid filtration possihle... 

Direct interception refers to a sieve-type mechanism in which contaminants larger than the filter pore size are directly trapped by the filter. This sieve retention mechanism of particle arrest is the mechanism of choice and occurs owing to geometric or spatial restraint. This type of particle arrest is considered to be absolute, that is, it is independent of filtration conditions. 

Barrier Phenomenon. In red cell filtration, the blood first comes into contact with a screen filter. This screen filter, generally a 7—10-) m filter, does not allow micro aggregate debris through. As the blood product passes through the deeper layer of the filter, the barrier phenomenon continues as the fiber density increases. As the path becomes more and more tortuous the cells are more likely to be trapped in the filter. 

In the double-neutralization process, Na2SiFg is precipitated and removed by filtration at a pH of 3—4 (9). Upon raising the pH to 7—9, insoluble phosphates of Fe, Al, Ca, and Mg form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss at the second filter cake. Both the fluorosihcate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered recovery of soluble phosphates trapped within the cakes is difficult. 

By filtration mechanism. Although the mechanism for separation and accumulation of solids is not clearly understood, hvo models are generally considered and are the basis for the apphcation of theoiy to the filh ation process. When solids are stopped at the surface of a filter medium and pile upon one another to form a cake of increasing thickness, the separation is called cake filtration. When solids are trapped within tne pores or body of the medium, it is termed depth, filter-medium, or clarifying filtration. 

Use of filter aids is a technique frequently applied for filtrations in which problems of slow filtration rate, rapid medium blinding, or un-satisfactoiy filtrate clarity arise. Filter aids are granular or fibrous solids capable of forming a highly permeable filter cake in which veiy fine solids or slimy, deformable floes may be trapped. Application of filter aids may allow the use of a much more permeable filter medium than the clarification would require to produce filtrate of the same quahty by depth filtration. 

Body-aid (i.e., the filter-aid) and precoating are often mentioned in connection with pressure filtration and the difference in their application is (1) Body aid is used when the slurry is low in solids content with fine and slimy particles that are difficult to filter. To enhance filtration coarse solids with large surface area are added to the slurry and serve as a body-aid that captures and traps in its interstices... 

Diesel Trap Concepts [subscriber access]. .. in the surface-type filters. That layer is commonly referred to as "filtration cake" and the process is called "cake filtration", http // www.dieselnet.com/tech/dpf concept.html. 

---