Microfiltration membrane technology

The original expanded film membranes were sold ia roUs as flat sheets. These membranes had relatively poor tear strength along the original direction of orientation and were not widely used as microfiltration membranes. They did, however, find use as porous inert separating barriers ia batteries and some medical devices. More recentiy, the technology has been developed to produce these membranes as hoUow fibers, which are used as membrane contactors (12,13). 

Membrane absorbers are continuous chromatographic supports, which circumvent some of the above-mentioned problems of particulate stationary phases. They were originally derived from membrane (filtration) technology. The immobilization of interactive (ionic, hydrophobic, or biospecific) groups on the surface of microfiltration membranes was found to increase the selectivity of certain separation procedure. Ideally such activated membranes, or membrane adsorbers, allow the selective adsorption of certain substances and substance classes, which may subsequently be eluted by means of a stepwise change of the mobile phase (elution buffer). More complete information on the various types of modern membrane technology can be found in some recent reviews [e.g., 31-33]. 

Filtration can remove fine suspended solids and microorganisms, and microfiltration membranes of cellulose acetate or polyamides are available that have pores 0.1-20 /xm in diameter. Clogging of such fine filters is an ever-present problem, and it is usual to pass the water through a coarser conventional filter first. Ultrafiltration with membranes having pores smaller than 0.1 fim requires application of pressures of a few bars to keep the membrane surface free of deposits, water flows parallel to the membrane surfaces, with only a small fraction passing through the membrane. The membranes typically consist of bundles of hollow cellulose acetate or polyamide fibers set in a plastic matrix. Ultrafiltration bears some resemblance to reverse osmosis technology, described in Section 14.4, with the major difference that reverse osmosis can remove dissolved matter, whereas ultrafiltration cannot. 

Membrane technologies can also be used in other parts of this total treatment system microfiltration could be substituted for the clarifier (see Figure 9), and reverse osmosis could purify the clarified effluent for re-use. 

M.C. Porter, Microfiltration, in Handbook of Industrial Membrane Technology, M.C. Porter (ed.), Noyes Publications, Park Ridge, NJ, pp. 61-135 (1990). 

In this chapter, the impact of other membrane technologies on the operation of RO systems is discussed. Technologies considered include microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) as pretreatment to RO, and continuous electrodeionization (CEDI) as post-treatment to RO. This chapter also describes the HERO (high efficiency RO—Debasish Mukhopadhyay patent holder, 1999) process used to generate high purity water from water that is difficult to treat, such as water containing high concentrations of silica. 

Membrane technology is a mature industry and has been successfully applied in various food industries for separation of undesirable fractions from the valuable components of the feed streams. The industrial membranes are classified into various categories such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and pervaporation. 

Vera L, Delgado S, and Elmaleh S, Gas sparged cross-flow microfiltration of biologically treated wastewater. Proceedings of the Membrane Technology in Environmental Management, Tokyo, 1999, pp. 131-137. 

Recent research efforts brought about new and exciting developments in membrane technology, some with direct implications for the membrane filtration of beer. For example, Stopka et al. [21] reported flux enhancement in the microfiltration of a beer yeast suspension when using a ceramic membrane with a helically stamped surface. A relatively simple modification of the ceramic membrane surface resulted in modified hydrodynamic conditions and disturbance of the fouling layer. As compared with a regular, smooth ceramic membrane of the same nominal pore size, the stamped membrane leads to higher flux and lower power consumption per unit volume of permeate at the same velocity of the feed. 

Jonsson, G. and Wetten, I.G., Control of concentration polarization, fouling and protein transmission of microfiltration processes within the agro-hased industry. Proceedings of the ASEAN-EU Workshop on Membrane Technology in Agro-Based Industry, Kuala Lumpur, Malaysia, 1994, p. 157. 

Membrane technologies have a great potential in the treatment of radioactive liquid wastes, as it has been proved throughout this chapter. In this sense, it is expected a growing use of the membrane processes in the radioactive field, with different possibilities alone, combined between them (microfiltration or ultrafiltration and reverse osmosis) or combined with other conventional processes like evaporation or ion exchange. Furthermore, some special membrane processes, like membrane distillation or liquid membranes, could be applied for the specific treatment of radioactive wastes. 

Microfiltration membranes can be used as pretreatment for other membrane technologies and to remove microbes and total suspended sohds (TSS) including fibers and particles. Retention of salts and dissolved organics is negligible, if they are not bound to the suspended sohds. MF can be used for the recovery of coating color pigments. MBRs generally use UF or MF membranes. The materials used in microfiltration are polyvinylidenefluoride (PVDF), polypropylene, polyethylene, polysulfone, polyether suUbne, Teflon, and ceramic materials. 

Membrane technology used in water reclamation includes five major membrane types reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and liquid membranes. These five types of membranes are discussed briefly, and examples of their applications in municipal and industrial wastewater reclamation is also described. 

Membrane separation is a relatively new and fast-growing field in supramolecular chemistry. It is not only an important process in biological systems, but becomes a large-scale industrial activity. For industrial applications, many synthetic membranes have been developed. Important conventional membrane technologies are microfiltration, ultrafiltration, electro- and hemodialysis, reverse osmosis, and gas separations. The main advantages are the high separation factors that can be achieved under mild conditions and the low energy requirements. 

Johnson, J. N., Cross-flow Microfiltration Using Polypropylene Hollow Fibers, Fifth Annual Membrane Technology Planning Conference, Cambridge (Oct. 1987)... 

In recent years, developing technology has led to the use of ultrafiltration and microfiltration membranes for juice clarification (1,4-13). The use of membranes has several advantages. Lower labor costs may be possible due to automation possibilities of membrane filtration (8). Filter aids such as diatomaceous earth (DE) aren t needed (9) so that product that would have been discarded with DE is saved, and DE acquisition and disposal costs are eliminated. Enzymes may be rejected by ultrafiltration membranes (4,12) causing the ultrafiltration equipment to act as an enzyme reactor (12), although some odor-active volatiles may be retained, resulting in some loss or change in flavor (8). 

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