Setting-up of modified fouling index (MFI) and crossflow sampler-modified fouling index (CFS-MFI) measurement devices for NF/RO fouling

Abstract

This paper deals with setting-up of modified fouling index (MFI) and crossflow sampler-modified fouling index (CFS-MFI) devices for prediction of fouling potential in a reverse osmosis (RO)/nanofiltration (NF) filtration system. The setting-up procedures of the laboratory-scale MFI and CFS-MFI devices operated in constant flux were described in detail. A practical approach to test the functionality of devices was also suggested. The devices are instrumented for monitoring transmembrane pressure, crossflow velocity, and flux at a desired time interval. A series of MFIconst.flux and CFS-MFIconst.flux tests were carried out using various types of membranes and foulants to determine the functionality and consistency of the newly developed system. The results showed that the differences between MFIconst.flux and CFS-MFIconst.flux values were more significant for high polydispersed foulants (e.g., 70–100nm colloidal silica and Aldrich humic acid) than monodispersed foulants (e.g., 22nm particle colloidal silica). When using the polydispersed foulants, the CFS-MFIconst.flux showed a better agreement with actual RO fouling trend than the MFIconst.flux. These observations proved that with the presence of CFS cell, the CFS-MFIconst.flux is capable of simulating a more realistic RO fouling behaviour than the MFIconst.flux value (without the consideration of crossflow effect). The successful setting-up of the fouling prediction devices in this study would provide a useful guide for future researchers on the fouling potential of membrane.