Immersed membrane modules

In this case the fluid phase is aerated (in the case of aerobic bioreactor) that maintains the turbulent hydrodynamic conditions on the one hand, and prevents the forming of the cake layer on the immersed membrane module, on the other hand. The reactor description is also well known [67], and is not discussed here. 

The membrane module and design will obviously depend on the type of membrane used. The flat-sheet membranes are commonly constructed in a plate-and-frame configuration or as spiral-wound (SW) modules. F1F/CT/MTmembrane types are commonly manufactured into bundles that are installed in housing units or designed to be unconfined in the fluid, that is, immersed units. The membranes are... 

In Table 16.2 some of the typical characteristics of the various types of membranes and configurations are given. In MBR systems SW membrane modules are not used as the channels within the spiral are prone to clogging when the feed water has high suspended-solids concentrations. Tubular membrane systems are not common either as they tend to become very expensive due to the low area to volume ratio. Commercial MBR systems today are normally based on immersed FS configurations or H F/CT configurations. 

Hollow fiber membrane modules can be backwashed to remove foulants whereas tubular and most spiral configurations cannot be backwashed. Backwashing of traditional spiral-wound modules would break the glue lines holding the membrane leaves together or cause blistering and delamination of the membrane from the backing in both spiral and tubular modules (TriSep Corporation has recently developed a back-washable, spiral-wound module (SpiraSep—US patent 6,755,970), that is used in immersed systems see below). 

There are also techniques involving the use of nonporous, solid or liquid membranes that separate the donor phase from the receiving phase by an evident phase boundary. Most often used are three-phase systems (donor phase, membrane, and acceptor phase) or two-phase systems, in which one of the surrounding phases is the same as the membrane. Solid membranes are made of chemically resistant, hydrophobic polymers (PTFE, PVDF, PS, PP, silicates), metals (Pd alloys), or ceramic materials. Channels of membrane modules have a volume ranging from 10 to 1000 pL and, according to their geometry, can be classified as planar or fibrous. For setting up a membrane system, two modes can be used the membrane can be immersed in a sample (membrane in sample, MIS) or the sample can be introduced into a membrane (sample in membrane, SIM). In both systems, only a small amount of sample is in direct contact with membrane, because ratio of the membrane surface area to the sample volume is small. 

In submerged membrane filtration, UF/MF membrane modules are immersed in water in an open tank [94,95]. Water permeates the membranes under a small trans-membrane... 

Figure 5 Frequently applied dialysis setups. (A) Thin layer flow cell, (B) immersion membrane probe, (C) hollow-fiber membrane module, and (D) immersing hollow-fiber membrane probe.

In case of PMRs with photocatalytic membranes, the light source must be located in the vicinity of the membrane (compare Chapter Section 21.2). In some cases the light source can be positioned above both membrane module and feed tank (or inside them, when immersed UV lamps are used). 

The experimental plant consisted of an annular photoreactor with an immersed UV lamp connected with the permeation cell in which a pressurized flat sheet membrane or a submerged membrane module was located. 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

Today the majority of polymeric porous flat membranes used in microfiltration, ultrafiltration, and dialysis are prepared from a homogenous polymer solution by the wet-phase inversion method [59-66]. This method involves casting of a polymer solution onto an inert support followed by immersion of the support with the cast film into a bath filled with a non-solvent for the polymer. The contact between the solvent and the non-solvent causes the solution to be phase separated. This process involves the use of organic solvents that must be expensively removed from the membrane with posttreatments, since residual solvents can cause potential problems for use in biomedical apphcations (i.e., dialysis). Moreover, long formation times and a limited versatihty (reduced possibUity to modulate cell size and membrane stmcture) characterize this process. 

There is much more awareness of the possible effect of the electric fields normal to the plane of the membrane on the structure and on the function of membrane proteins. However, no such relation was experimentally documented. There is an appreciable amount of information on the potential dependence of channel conductance, which is assumed to be caused by shifts of charged groups within the channel (41). These shifts correspond to small changes in conformation that could not be detected by methods sensitive to the secondary structure of the proteins. In the present and in some previous reports (7, 8), we have shown that membrane potentials of comparable magnitude to the physiological membrane potentials are sufficient to modulate the secondary structure of membrane proteins. The effect may be direct or indirect. The indirect effect shifts part of the molecular fraction immersed... 

Audunsson [29] reported on a sandwich-type extraction module equipped with liquid membranes, prepared by immersing hydrophobic microporous membranes (e.g. PTFE membranes) in organic solvents for about 15 min. The inert men ranes then act as supports for the immobilized solvent. When an aqueous sample passes by the membrane, non-ionic components in the sample are extracted into the hydrophobic liquid film and transferred into an appropriate acceptor solution on the other side of the membrane. When the acceptor remains stagnant while the sample flows continuous ) for a defined period, a preconcentration is effected in the acceptor solution, which is subsequently transferred to the detector. The procedure is equivalent to extraction and back-extraction in a single step. More details on such a system used for sample cleanup in gas-liquid chromatography is presented in Sec. 3.7. 

A three-step catalytic reactors membrane separation (CRMS) configuration based on this concept is shown in Figure 13.13. A H2S reach stream would be compressed to 8 bar, preheated to 550 °C downstream of the third module, to be fed to the first reaction step consisting of fixed bed catalytic tubes. These catalytic tubes are immersed in the Claus reaction chamber, where Claus gases provide thermal duty required to carry out the H2S decomposition reaction. 

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