Effect of Inorganic Colloids

In the previous chapters, the effects of colloidal fouling of MF and UF membranes was thoroughly studied. While the effect of these relatively large colloids on NF were not expected to be significant, a brief series of experiments were performed to check this. 

Ttiis is indeed the case. Flux decline is minimal, and for the larger particles the flux even increases slightly. Flux is generally expected to increase with parade size (see Chapter 3), but the colloids are also very large compared to the membrane pores . A red deposit is visible on the membranes after the experiments, indicating some membrane-coUoid interactions. 

Rejection (see Table 7.40) is highest at pH 8. This is probably attributable to the deposit morpholog) and charge, and requires further investigation before condusions can be drawn. 

As shown in Chapter 6 (UF), the aggregates (SPO) did not cause flux decline on the tight membranes. This was attributed to the fact that the aggregates are too large to deposit or cause flux decline. For this reason no experiments were carried out with the SPO aggregates/systems. 

Coagulation using ferric chloride was used in MF and UF to increase organic rejecdon. The interest in NF is to examine the effect of ferric chloride on the membrane flux and to assess if the presence of amorphous iron hj droxide parades causes severe flux decline. 

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