Tangential-flow ultrafiltration system

Figure 15.6 Tangential-flow ultrafiltration system. (Courtesy PaU Corporation.)...

Humic substances account for 40-70% of the DOC in rivers and 5-25% of the DOC in the ocean (Table I). It is important to note that recoveries of adsorbed humic substances from XAD resins are not quantitative, so the chemical characteristics of the recovered humic substances are not necessarily representative of all the humic substances retained by the resin. Tangential-flow ultrafiltration retains 45-80% of the DOC in rivers and 25-40% of the DOC in the surface ocean (Table I). Essentially all of the DOC retained during ultrafiltration is recovered for chemical characterization. In general, ultrafiltration recovers a larger fraction of the DOM from these systems. These methods also isolate DOM based on different mechanisms. Adsorption onto XAD resins at low pH chemically fractionates the DOM and isolates the more hydrophobic components, whereas ultrafiltration principally separates components of DOM on the basis of size and shape. 

Hoffmann S. R., Shafer M. M., Babiarz C. L., and Armstrong D. E. (2000) A critical evaluation of tangential-flow ultrafiltration for trace metals studies in freshwater systems 1. Organic carbon. Environ. Sci. Technol. 34, 3420-3427. 

The difference between conventional dead-end filtration and cross-flow filtration is the configuration of the system. For large-scale operations, only cross-flow filtration will be used. The membranes for miocrofiltration as well as ultrafiltration are commonly utilized in a variety of filtration devices. There are three basic types of tangential flow filtration devices plate and frame, hollow fiber, and spiral wound membranes. 

This brief overview describes some experiences using tangential-flow and dead-end ultrafiltration techniques for concentration of eukaryotic cells, proteins and virus. The data and conclusions presented here have been drawn from process development work employing available apparatus and should be considered preliminary, rather than definitive or exhaustive. Previous ultrafiltration systems have been described (1-14) for both bench and pilot scale separations of proteins and virus. This paper primarily summarizes work on cartridge and sheet filter systems and their application to processes requiring sterilizable and contained systems. 

In its simplist form, the major hardware components of the ultrafiltration system are the storage tank, pump, and membrane package (Figure 2). Most of the output from the pump sweeps the membrane tangentially and returns to the process tank. The permeate flow is generally less than 10 of the total flow to the membrane. 

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