The MFI-UF as a water quality test and monitor

The MFI0.45 test to measure the particulate fouling potential of feedwater, was recently extended to incorporate smaller particles using a polyacrylonitrile 13 kDa (PAN 13 kDa) ultrafiltration membrane (MFI-UF). This study investigates various aspects of the new MFI-UF test to establish its general use for measuring the particulate fouling potential of feedwater; namely (i) proof of cake filtration via 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 feedwater viscosity. However, compression of the cake with increasing pressure was demonstrated for all feedwater. 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.