Forward filtration

Protein transmission data (Fig. 8) indicate nearly 100% transmission of protein initially, but the fraction of protein transmitted decreased rapidly for forward filtration of a BSA-only solution and appeared to reach a steady value of only 35% transmission after 10,000 s. When a secondary membrane of yeast was deposited at the beginning of each cycle, and then filtration of a BSA solution was carried out, the protein transmission values remained at nearly 100% for about 4000 s and subsequently decreased gradually to about 60% after 18,000 s of filtration. With SMY, the amount of protein recovered in the permeate is more than two times that recovered after filtration of the BSA-only solution after 18,000 s. 

Backflushing can remove the fouling layer both at the membrane surface and within the membrane. The forward filtration time and the duration of the backpulse need to be optimized since permeate is lost to the feed side during the backpulse. A schematic is shown in Figure 9.19. See Ref. [17] for additional details. 

In contrast to the AN membranes, the CA membranes exhibit nonuniform particle deposition during forward filtration. As seen in Figure 2.9, the deposition occurs in localized patches, reflective of the uneven structure of the CA membrane surface. These DVO images were taken at lower magnification than those for the AN membrane, as otherwise the rough surface of the CA membrane would be out of focus. 

Figure 2.8 Videomicrographs of an AN membrane taken using DVO at various times (tj) of forward filtration of 0.05 g yeast at a transmembrane pressure of 2 psi (1 psi = 6.9 kPa) and a nominal wall shear rate of2500s Shown are the fractional coverage (jS ) and the measured permeate flux (Jf), where 1 LMH = 1 Lm h =2.8 X 10 m s From Mores and Davis [21]).

Figure 2.15 Photomicrographs of AN membranes after backpulses at AP(, = 2psi and various cumulative durations. Membranes were fouled by forward filtration with 0.05 g yeast at Afy=2psi for 5400s prior to backpulsing. is the fraction of...

Figure 2.17 Photomicrographs of AN membranes after (a) 300 s and (b) 1800 s of filtration with rapid backpulsing with tj=10s, APf = APf, = 2 psi and y = 2500s The top photos depict membrane surfaces at the end of a period of forward filtration, while those...

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