Filtration clarifying filters

Screening Equipment Filtration Cake Filters Centrifugal Filters Principles of Cake Filtration Clarifying Filters Liquid Clarification Gas Cleaning Principles of Clarification Crossflow Filtration Types of Membranes Permeate Flux for Ultrafiltration Concentration Polarization Partial Rejection of Solutes Microfiltration... 

Before filtration Clarifying filter sheet no. 3 Clarifying filter sheet no. 5 Clarifying filter sheet no. 7 Clarifying filter sheet no. 10 Sterilizing filter sheet... 

In the precoat and body feed mode, filter aids allow appHcation of surface filtration to clarification of Hquids, ie, filtration of very dilute suspensions of less than 0.1% by volume, such as those normally treated by deep bed filters or centrifugal clarifiers. Filter aids are used in this mode with pressure filters. A precoat is first formed by passing a suspension of the filter aid through the filter. This is followed by filtration of the feed Hquid, which may have the filter aid mixed with it as body feed in order to improve the permeabiUty of the resulting cake. The proportion of the filter aid to be added as body feed is of the same order as the amount of contaminant soHds in the feed Hquid this limits the appHcation of such systems to low concentrations. Recovery and regeneration of filter aids from the cakes normally is not practiced except in a few very large installations where it might become economical. 

Granular bed filters are used in porcelain enameling wastewater treatment to remove residual solids from clarifier effluent (sedimentation effluent or flotation effluent). Filtration polishes the effluent and reduces suspended solids and insoluble precipitated metals to very low levels. Fine sand and coal are media commonly utilized in granular bed filtration. The filter is backwashed after becoming loaded with solids and the backwash is returned to the treatment plant influent for removal of solids in the clarification step.10-12... 

UV can also be used in water reclamation and reuse. An example is the reclamation of swimming pool water. Usually, the swimming pool water reuse process includes coagulation, filtration, clarifier, disinfection, and pH adjustment. The conventional swimming pool disinfection chemical is chlorine however, high concentrations of residual chlorine can be harmful to human health. The UV technology can be placed between the filters and chlorine disinfection unit as a pre-disinfection unit and remove pathogens. Hence, much less amount of chlorine (compared with the process without UV unit) is needed for residue disinfectant level. 

Filtration equipment will be briefly reviewed for the fiillowing categories hetch cake fillers, continuous cake fillers, and clarifying filters. 

Mechanisms of filtration (a) cake filter (i) clarifying filter (c) crossflow filter. 

In cake filtration the liquid passes through two resistances in series that of the cake and that of the filter medium. The filter-medium resistance, which is the only resistance in clarifying filters, is normally important only during the early stages of cake filtration. The cake resistance is zero at the start and increases with time as filtration proceeds. If the cake is washed after it is filtered, both resistances are constant during the washing period and that of the filter medium is usually negligible. 

Clarifying filters for liquids include the gravity-bed filters for water treatment mentioned earlier and a variety of small cartridge and edge filters of various designs. Some cake filters, especially tank filters and continuous precoat filters, are used extensively for clarification. In a batch unit, the filtration rate and solids removal efficiency are typically almost constant for a considerable period of operation, but eventually the solids content of the effluent rises to an unacceptable breakthrough value, and backwashing of the filter element becomes necessary. 

Y. Kwang-Sup, H. Joo-Heon, B. Dong-Ho, K. Seok-Joong, K. Soon-Dong, Effective clarifying process of reconstituted apple juice using membrane filtration with filter-aid pretreatment, Journal of Membrane Science 2004, 228, 179-186. 

The multi-pass test simulates well the behaviour of clarifying filters in hydraulic or lubricating fluid systems, because the recycle of the filtrate carries with it the undersized particles, so that the proportion of fine particles increases continuously during the test. It was the first filter test to become an ANSI standard, and is now incorporated into an international standard (see BS ISO 16889 1999). It should be noted that the beta ratio will be different from that determined by this test if it is used in a system that contains particle distributions that differ from the distribution used in the test. 

Vacuum leaf filters are less common, although cheaper than the pressurized version, because of the lack of a pressure vessel. They consist of an open tank full of the liquid to be filtered, into which the array of vertical leaves is submerged. Vacuum is applied through the filtrate manifold, and cake builds up on the leaves until cake removal becomes due. This kind of filter is mostly used with precoat as a clarifying filter, which is not only cheaper but also more easily inspected and maintained. 

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