Spiral Membrane

Spiral membranes are the usual way to form flat sheet into modules. They have the characteristic that the feed and the permeate move at right angles. Since the membrane is always cast on a porous support, point-permeate values are influenced by the substrate. 

X. Shao, Y. Fend, S. Hu and R. Govind, Pectin Degradation in a Spiral Membrane Reactor, in Membrane Reactor Technology, R. Govind and N. Itoh (eds), AIChE Symposium Series Number 268, AIChE, New York, NY, Vol. 85, pp. 85-92 (1989). 

HERO—High-Efficiency RO Process Boosts Recovery Ratios, Cuts Cleaning Frequency," GE Water Process Technologies, www. gewater.com/products/equipment/spiral membrane/HERO.jsp... 

The combined solutions containing the enzyme from the cell separation step (approximately 160 liters) were then concentrated using a 40 square foot, 10,000 MWCO regenerated cellulose S40Y10 Diaflo spiral membrane (Amicon Division of W. R. Grace Co.- Conn., Danvers, MA). A roughly ten fold concentration of the enzyme was achieved in this step. Further concentration and diafiltration of the protein product solution were carried out at the lab scale. 

The BAHLM modules may be based on commercially available ion-exchange hollow-fiber or spiral membrane modules and equipment... 

Let s take a quick look at the spiral membrane element so that all of us have the opportunity to understand its makeup. 

Figure 5. A partially unrolled spiral membrane element known as a sepralator. The sepralator has a permeate ttd>e for collecting the permeate the membrane is laid onto a permeate carrier material and the edges of the membrane and the permeate carrier are glued together. The membrane is integrally cast onto a backing material as shown in the figure.

Figure 5. Flux versus membrane shear rate for an E. coli in a defined medium. Key — , device B (5 ft /0.45 m -cassette) — , device A (15 ft /1.4 spiral). Membrane used 100,000 MWCO. Note 10 gal/ft x day = 17 1/m x h.

Spiral elements are the most popular form of membrane filter today due to their relatively low cost. The membrane in a spiral element is wrapped with spacer sheets into a cylinder (Figure 22.49b). The suspension is flowing in parallel to the axis of the cylinder and the permeate flows spirally into the center collecting chamber. Although the design favors low solid concentrations, it is possible to run suspensions with high solid concentrations in a spiral membrane filter. 

Other bioreactor configurations have been developed specifically for immobilized enzymes and cells. Enzymes immobilized within polymeric membranes are used in hollow fiber (Fig. 16) and spiral membrane bioreactors (Fig. 17). In the hollow fiber device, many fibers are held in a shell-and-tube configuration (Fig. 16) and the reactant solution (or feed) flows inside the hollow fibers. The permeate that has passed through the porous walls of the fibers is collected on the shell side and contains the product of the enzymatic reaction. Also, instead of being immobilized in the fiber wall, enzymes bound to a soluble inert polymer may be held in solution that flows inside the hollow fiber. The soluble product of the reaction then passes through the fiber wall and is collected on the shell side the enzyme molecule, sometimes linked to a soluble polymer, is too large to pass through the fiber wall. 

Hollow fiber modules are sometimes used to culture animal cells that are confined to the shell side of the module the separately oxygenated nutrient solution flows inside the fibers and perfuses the cells on the shell side. In the spiral membrane reactor (Fig. 17), the membrane that contains the immobilized enzyme is rolled into a spiral and confined within a shell. The feed or reactant solution flows in at one end and the product is removed from the opposite end of the cylindrical shell. 

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