Ultrafiltration costs

Tubular Modules. Tubular modules are generally limited to ultrafiltration appHcations, for which the benefit of resistance to membrane fouling because of good fluid hydrodynamics overcomes the problem of their high capital cost. Typically, the tubes consist of a porous paper or fiber glass support with the membrane formed on the inside of the tubes, as shown in Figure 24. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Whey has been used ia some substitute dairy products but aot as a source of proteia. Whey proteias have beea used ia dairy substitutes only siace the commercialisation of ultrafiltration (qv) technology. Membranes are used that retain proteia and permit water, lactose, and some minerals to pass through as permeate. Proteia coaceatrates are available from both acid and sweet whey and ia coaceatratioas of 35—80 wt % proteia. Whey proteia isolates are commercially available having proteia >90 wt%. The cost of these isolates is too high, however, to make them economical for substitute dairy foods. 

Large Plants The economics of microfiltration units costing about ilO " is treated under ultrafiltration. When ceramic membranes are used, the cost optimum may shift energy consumption upward to as much as 10 kWh/m. ... 

Ultrafiltration equipment are combined with other unit operations. The unique combination of unit operations depends on the wastewater characteristics and desired effluent quality, and cost considerations. 

Microfiltration and ultrafiltration have recently been introduced for the removal of particles down to any desired size. Their capital cost is relatively high. Experience with them is limited, and a short trial with a small-scale pilot element is advisable. Prediction of full-scale performance from such trials is normally quite reliable. 

Two other major factors determining module selection are concentration polarisation control and resistance to fouling. Concentration polarisation control is a particularly important issue in liquid separations such as reverse osmosis and ultrafiltration. Hollow-fine-fibre modules are notoriously prone to fouling and concentration polarisation and can be used in reverse osmosis applications only when extensive, costly feed solution pretreatment removes all particulates. These fibres cannot be used in ultrafiltration applications at all. 

Membrane Ultrafiltration Membrane ultrafiltration is often one of the favored unit operations used for the isolation and concentration of biomolecules because they can be easily scaled up to process large feed volumes at low costs. Toward the end of an ultrafiltration operation, additional water or buffer is added to facilitate the passage of... 

Theoretically, polymer-containing wastewater from desizing can be purified for water recycling by removal and reconcentration of the polymer by ultrafiltration or evaporation, but the high costs of investment and additional expenses for the disposal of the concentrate hinder the introduction of such techniques as a general treatment process. 

Therefore, an effective water system is required. Nowadays, several techniques can be used to obtain water of high pharmaceutical quality. These include ionexchange treatment, reverse osmosis, distillation, electrodialysis, and ultrafiltration. However, there is no single optimum system for producing high-purity water, and selection of the final system is dependent on factors such as the quality of raw water, intent of its use, flow rate, and costs. In the pharmaceutical industry, the different water classes normally encountered are well water, potable water, purified water, and specially purified grades of water, such as water for injection (e.g., MilliQ water). 

Biologically friendly ionic surfactants can be added to the wastewater at concentrations above the threshold value beyond which the surfactants self-assemble to form micelles. The resulting micelles can trap the hydrocarbon wastes since the hydrocarbon solutes prefer the hydrocarbon interior of the micelle over the aqueous environment outside. In addition, ionic wastes in the water adsorb to the polar heads of the surfactants (see Fig. 8.1). The resulting waste-laden micelles can then be removed more easily using ultrafiltration methods. Such a process, known as micellar-enhanced ultrafiltration (MEUF), can be made continuous, scalable, cost effective, and environmentally friendly (through the use of biodegradable surfactants). 

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