Process scale microfiltration, membrane

Process scale microfiltration usually employs several membrane modules operating in parallel in order to achieve the desired permeate flow. Preliminary testing with a single module is undertaken easily and scale-up by means of proportioning the areas and flows may be sufhcient for process design. There are, however, important choices regarding the optimum method of operation ... 

The first commercial MBRs, in which an external microfiltration membrane module replaced sedimentation in the activated sludge (AS) process, were introduced in the 1960s by Dorr-Oliver Inc. [3]. Full-scale commercial MBRs entered service in North America in the 1970s, Japan in the 1980s, and Europe in the 1990s [4]. A reputation for excellent effluent quality... 

Porous membranes can be made of polymers (polysulfones, polyacrylonitrile, polypropylene, silicones, perfluoropolymers, polyimides, polyamides, etc.), ceramics (alumina, silica, titania, zirconia, zeolites, etc.) or microporous carbons. Dense organic membranes are commonly used for molecular-scale separations involving gas and vapor mixtures, whereas the mean pore sizes of porous membranes is chosen considering the size of the species to be separated. Current membrane processes include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), gas and vapor separation (GS), and pervaporation (PV). Figure 1 indicates the types and sizes of species typically separated by these different separation processes. 

This chapter is concerned primarily with process scale membrane fihratinn and phenomena or effects that are relevant to such filtration. Cartridge filtration has already been discussed in Chapter 6, hence most of the following work refers to membrane filtration under crossflow conditions. Hiis technique is applicable to both microfiltration... 

Reverse osmosis enables complete retention of aU dissolved compounds, even small monovalent ions. To avoid the membrane blocking and scaling before reverse osmosis, microfiltration, or ultrafiltration pretreatment can be applied. Apart from preliminary treatment, ultrafiltration can be used for separation of suspensions or colloids, which are often formed by actinides or ions such as " Mg, Fe, °Co, and Sb. Microfiltration found the application for waste dewatering after precipitation. Nanofiltration (NF) that uses lower pressures than reverse osmosis is applied for separation of bivalent from monovalent ions. The most common application of NF process in nuclear industry is boric acid separation from the reactor coolant. 

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. 

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