Granular filtration clarification

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. 

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. 

Granular bed filters are used in ten coil coating plants to remove residual solids from the clarifier effluent, and are considered to be tertiary or advanced wastewater treatment. Chemicals may be added upstream to enhance the solids removal. Pressure filtration is also used in this industry to reduce the solids concentration in clarifier effluent and to remove excess water from the clarifier sludge. Figure 7.4 shows a granular bed filter and Table 7.13 presents the heavy metal removal data of a lime clarification and filtration system. 

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... 

If the liquor is not to be enzyme-converted, it is pumped to mud centrifuges and rotary drum filters which remove the suspended fats and insoluble impurities from the filtrate. Amino acids and peptides which may react with carbohydrates are also removed. Then the filtrate is passed through pulsed beds of activated carbon for clarification and bleaching. The temperature in the carbon column is maintained at 150-170°F (69-77°C) with a typical contact time of 90-120 minutes for optimum removal of impurities. Usually these columns contain packed granular carbon, although powdered carbon may also be used. 

The melted liquor is then purified by any of several combinations that include clarification and decolorization. In clarification, the liquor is treated chemically to remove suspended matter, colloids, and other impurities that contribute to turbidity. Clarified liquor is optically clear, but is still highly colored. Decolorization procedures include treating the clarified liquor with various filtration media, such as bone char, granular activated carbon, or ion exchange resin, either alone or in some combination. It is necessary to clarify the liquor before the filtration medium because the particulate impurities will quickly blind the filtration material and render it useless. 

Basic scheme of the white, refined sugar manufacturing process in a raw sugar refinery. Clarification can be phosphatation or carbonation, and decolorization can be with granular carbon, bone char, or ion-exchange resins. Filtration is not required if phosphatation clarification is utilized... 

A similar problem of clarification of cultural liquids also arises in the biotechnological production of nucleosides. In the Tripol e Biochemical Plant in (Ukraine), MN-200 exhibited, on the whole, better performance than commonly used activated carbons [48]. A comparative study of MN-200, Styrosorb IBP, Styrosorb 1 (MCDE, 100%), and granular activated carbon OU-A (Russia) was conducted by filtrating 200 mL cultural liquid of riboxin (inosine) production at 20°C or 250 mL aqueous saturated solution of technical crystalline riboxin at 60°C (to avoid nucleoside crystallization) through a 12 mL sorbent bed at a flow rate of 0.2-0.3mL/min. In both solutions pH was between 3.3 and 3.6. After rinsing the sorbents with water, they were regenerated with 100 mL 2 N NaOH. The results obtained are given in Table 11.3. 

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