Effect of Flux on Fouling

During these experiments the 100 kDa membrane consistently exhibited flux decline depending on the filtration conditions, whereas the 10 kDa membrane showed no such decline. Several factors could explain this. 

First of all, pore blocking could cause more severe flux decline of the 100 kDa membrane. This is addressed in the blocking law analysis in the following section. 

Secondly, the high flux of this membrane could cause severe concentration polarisation and membrane-solute interaction, or fouling (thus reach a critical flux where deposition starts to control flux). This effect can be controlled by variation of the transmembrane pressure and thus flux. 

Thirdly, the higher filtrate volumes used for this membrane could simply increase the cake mass and thus the resistance. The filtrate volume effect can also be examined very easily. 

Lower flux indeed decreased the amount of fouling by reducing possibly pore penetration and gel formation on the membrane. If the 100 kDa membrane is operated at a lower pressure and therefore lower flux, the decline is reduced and the final value is identical, at a much lower pressure. This clearly indicates the importance of cridcal flux and this requires further studies for surface water systems. Flux is obviously not proportional to pressure at these conditions (a pressure increase from 8 to 100 kPa should cause a 12.5 fold flux increase). 

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For the 10 kDa membrane no substantial flux decline is observed. These results are summarised in Figure 6.29. The 10 kDa membrane also has a much lower pure water flux and operational flux. The fluxes of the 10 kDa and 100 kDa membranes are verj similar at a calcium concentration of 4 mM 50 and 63 Lm h for the 100 kDa and 10 kDa membranes, respectively. It should be noted that the transmembrane pressures were 100 kPa (100 kDa) and 300 kPa (10 kDa). The effect of flux on fouling... 

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