The MFI-UF as a Water Quality Test and Monitor

152 153 In Chapter 5 the Modified Fouling Index using ultrafiltration membranes (MFI-UF) was developed to incorporate smaller particles into the MFI measurement. The polyacrylonitrile 13 kDa membrane (PAN 13 kDa) was proposed as the reference membrane for the MFI-UF test. This research investigates various aspects of the new MFI-UF test to establish its general use for characterising the fouling potential of feedwater; namely (i) proof of cake filtration via the stability of the MFI-UF over time and linearity of the index with particulate concentration, (ii) reproducibility of the MFI-UF with PAN 13 kDa membrane manufacture and membrane reuse (iii) the temperature and pressure dependency of the MFI-UF. The aforementioned aspects were examined using low ( e.g. tap water) and high fouling feedwater ( e.g. diluted canal water). Cake filtration was demonstrated for all feedwater tested. The MFI-UF was stable over time and proportional to particulate concentration. Reproducibility of the MFI-UF was found for 83% of the membranes tested and in five tests using one membrane, applying chemical cleaning in between. Correction to the reference temperature (20 °C) of the MFI-UF test required only correction of the feedwater viscosity. However, cake compression with pressure was demonstrated for all the feedwater tested. Therefore, compressibility coefficients were determined for a given feedwater and a global compressibility coefficient was calculated for correction to the reference pressure (2 bar) of the MFI-UF test. Application of the MFI-UF as a continuous monitor of feedwater quality was trialed and requires further investigation. 154