Figure 7.4 A—Time course of protein
in solution and permeate flow rate.
B—Correlation of protein adsorbed
and permeate flow rate.
value. In the presence of protein, there is a significant decrease of permeate flow rate,
especially during the first fifteen hours. The flow rate stabilises after 24 hours.
This behaviour correlates very well with the adsorption of protein, as the
representation of adsorbed protein (on the basis of protein remaining in solution), as a
function of permeate flow rate leads to a high correlation coefficient, (R^2 =0.977) (see
Figure 7.4). This confirms that the reduction in the permeate flow rate is due to the
presence of protein and not to an occlusion phenomenon caused by AOT film deposition
on the membrane surface or inside its pores.
Based on the experimental data, namely on the permeate flow rate in the presence and
in the absence of protein, the resistance due to the presence of protein can be estimated
(see example in Table 7.4). From Table 7.4 it can be verified that the global resistance of
the membrane increases 2.5 times after completion of the adsorption process and
opposing the permeate flow rate variation.
The capacity of membrane filtration is reduced by two phenomena, concentration
polarisation and membrane fouling, both leading to a decrease of flux across the
membrane. As a result of solutes deposition, a gel layer could be formed on the
membrane surface resulting in a higher feed side concentration as well as flux decline.
The polarisation effect can be observed in the transmission experiments (see Table
7.3). A solute concentration could be seen on the surface and inside the pores leading to a
concentration gradient that hinders the course of products and substrates through the
Multiphase bioreactor design 214