Comparative Assessment of Membrane Fouling Propensity Using Colloidal Silica as Foulant

Other than silt density index (SDI), modified fouling index (MFI) is claimed as one of most useful fouling predictive tools in the practice of reverse osmosis. In this study, the effect of colloidal silica particles on the MFI value with the presence of crossflow sampler (CFS) cell at the upstream of MFI setup was systematically investigated. Colloidal silica with the particle size ranging from 70-100 nm was used as the model foulant in this experiment. The feed silica suspension was 0, 50, and 200 mg/L. The effect of membrane pore size as the test membrane in the dead-end cell on the fouling indices was also studied. Polyvinylidene fluoride (PVDF) membranes with molecular weight cut-offs of 150 and 100 kDa were employed. As predicted, the experiment results demonstrated that the fouling indices increased significantly as the feed silica concentration increased. The CFS-MFI values were always lower than the MFI in all the fouling index tests due to the shear force effect generated under the crossflow filtration mode. The fouling index generated from PVDF100 was higher than that of PVDF150 due to the retention of smaller particles. For this reason, PVDF100 membrane was preferred to be used as the test membrane for fouling index tests using colloidal silica over the PVDF150.