Ultrafiltrate

Ultrafiltration. Ultrafiltration was described under pretreatment methods. It is used to remove finely divided suspended solids, and when used as a tertiary treatment, it can remove virtually all the BOD remaining after secondary treatment. 

The mechanism of ultrafiltration is not simply a sieve effect, but depends also upon the electrical conditions of both the membrane and the colloid. 

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

Finally, micellar systems are useful in separation methods. Micelles may bind heavy-metal ions, or, through solubilization, organic impurities. Ultrafiltration, chromatography, or solvent extraction may then be used to separate out such contaminants [220-222]. 

Partition coefficients are usually determined using ultrafiltration" or NMR" or UV-vis ... 

Table 1. Removal of Viral Particles from Fluids by Ultrafiltration...

Acrylonitrile fibers treated with hydroxides have been reported to be useful for adsorption of uranium from seawater (105). Tubular fibers for reverse osmosis gas separations, ion exchange, ultrafiltration, and dialysis are a significant new appHcation of acryUc fibers and other synthetics. Commercial acryUc fibers have already been developed by Nippon Zeon, Asahi, and Rhc ne-Poulenc. 

The axial filter (Oak Ridge National Laboratory) (30) is remarkably similar to the dynamic filter in that both the rotating filter element and the outer shell are also cylindrical. An ultrafiltration module based on the same principle has also been described (31). Unlike the disk-type European dynamic filters described above, the cylindrical element models are not so suitable for scale-up because they utilize the space inside the pressure vessel poorly. 

Cross-Flow Filtration in Porous Pipes. Another way of limiting cake growth is to pump the slurry through porous pipes at high velocities of the order of thousands of times the filtration velocity through the walls of the pipes. This is ia direct analogy with the now weU-estabHshed process of ultrafiltration which itself borders on reverse osmosis at the molecular level. The three processes are closely related yet different ia many respects. 

The idea of ultrafiltration has been extended ia recent years to the filtration of particles ia the micrometer and submicrometer range ia porous pipes, usiag the same cross-flow principle. In order to prevent blocking, thicker flow channels are necessary, almost exclusively ia the form of tubes. The process is often called cross-flow microfiltration but the term cross-flow filtration is used here. 

PVDF-based microporous filters are in use at wineries, dairies, and electrocoating plants, as well as in water purification, biochemistry, and medical devices. Recently developed nanoselective filtration using PVDF membranes is 10 times more effective than conventional ultrafiltration (UF) for removing vimses from protein products of human or animal cell fermentations (218). PVDF protein-sequencing membranes are suitable for electroblotting procedures in protein research, or for analyzing the phosphoamino content in proteins under acidic and basic conditions or in solvents (219). 

K. marxianus var. fragilis which utilizes lactose, produces a food-giade yeast product from cheese whey or cheese whey permeates collected from ultrafiltration processes at cheese plants. Again, the process is similar to that used with C. utilis (2,63). The Provesteen process can produce fragiUs yeast from cheese whey or cheese whey permeate at cell concentrations ia the range of 110—120 g/L, dry wt basis (70,73). 

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

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