Bubbles hollow-fiber membrane

The core of double membrane stirrer perfusion bioreactors is a stirrer on which two microporous hollow fiber membranes are mounted, one of them being hydrophobic and used for bubble-free aeration, the second of them being hydrophilic and used for cell-free medium exchange [15]. This system has been reported to provide viable cell densities of 20 million cells per miUiliter for more than two months [106]. Although Lehmann et al. [15] have described the scale-up of this system to the 20-L and 150-L scale, it has been most commonly employed at the bench-scale. 

Nondispersive phase contacting, with reaction at the phase interface or in the bulk phases dehydrogenations Emulsion-free enzymatic splitting of fats Bubble-free oxygen/ozone supply in wastewater treatment via hollow-fiber membranes... 

An early example of a patent on membrane contactor for gas transfer is in Ref. [12]. Harvesting of oxygen dissolved in water and discharging of CO2 to the water is presented in Ref. [13]. A membrane device to separate gas bubbles from infusion fluids such as human-body fluids is claimed in Ref. [14]. A hollow fiber membrane device for removal of gas bubbles that dissolve gasses from fluids delivered into a patient during medical procedures is disclosed in Ref. [15]. Membrane contactors have also found application in dissolved gas control in bioreactors discussed in Refs. [16-17]. 

If the tube diameter is less than 10 mm, the liquid surface tension will affect the slug velocity and simulation predicts that for diameters less than about 5 mm with water the surface tension can stop the upward motion of the slug causing an air lock, implying careful assessment is required before applying bubbling to the lumen of hollow fiber membranes. 

Matsuoka H, Fukada S Toda K (1992) High oxygen transfer rate in bubble aeration using hollow fiber membrane a proposal of a new aeration system. Biotechnology and Bioengineering 40 346-352. 

A different application involves using the membrane for the delivery of one of the reactants (e.g., bubble-free aeration [4.14]). One recent example of such an application is that reported by Onken and Berger [4.15]. They used a microporous polypropylene hollow-fiber membrane for the controlled addition of oxygen in the biotransformation of cit-ronellol into 3,7-dimethyl-1,6,7-octanetriol by Cystoderma carcharias. 

FIGURE 10.41 Submerged hollow fiber membrane module, (a) flat sheet and (b) hollow fiber. (Reprinted from J. Membr. ScL, 221, Cui, Z.F., Chang, S., and Fane, A.G., The use of gas bubble to enhance membrane proeesses, 1-35, Copyright 2003, with permission from Elsevier.)... 

Figure 10 Stagnant and mobile bubbles in the lumen of a hollow-fiber membrane at a flux of 26 L/m h at (a) 5 min, (b) 6 min, (c) 7 min, and (d) 8 min from the start of filtration (Chang et al 2007).

The design of the first commercial modules has allowed the commercial application of membrane contactors for some specific operations. This is the case of the Membrana-Charlotte Company (USA) that developed the LiquiCel modules, equipped with polypropylene hollow fibers, for the water deoxygenation for the semiconductor industry. LiquiCel modules have been also applied to the bubble-free carbonation of Pepsi, in the bottling plant of West Virginia [18], and to the concentrations of fruit and vegetable juices in an osmotic distillation pilot plant at Melbourne [19]. Other commercial applications of LiquiCel are the dissolved-gases removal from water, the decarbonation and nitrogenation in breweries, and the ammonia removal from wastewater [20]. 

Until now, bioreactors of various types have been developed. These include loop-fluidized bed [14], spin filter, continuously stirred turbine, hollow fiber, stirred tank, airlift, rotating drum, and photo bioreactors [1]. Bioreactor modifications include the substitution of a marine impeller in place of a flat-bladed turbine, and the use of a single, large, flat paddle or blade, and a newly designed membrane stirrer for bubble-free aeration [13, 15-18]. Kim et al. [19] developed a hybrid reactor with a cell-lift impeller and a sintered stainless steel sparger for Thalictrum rugosum cell cultures, and cell densities of up to 31 g L1 were obtained by perfusion without any problems with mixing or loss of cell viability the specific berberine productivity was comparable to that in shake flasks. Su and Humphrey [20] conducted a perfusion cultivation in a stirred tank bio-... 

Air Sparging Gas sparging or injection of air bubbles has been effectively used to reduce concentration polarization and enhance mass transfer. " The secondary flows around bubbles promote mixing and reduce the thickness of the concentration polarization boundary layer. When the bubble diameter exceeds that of the membrane (tubular or hollow fiber), slugs are then formed further increase in bubble diameter has no effect on flux improvement. Large slugs can displace most of the boundary layer and cause the pressure to pulsate. This results in enhancing the flux. 

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