Variation and prediction of membrane fouling index under various feed water characteristics

Membrane fouling index such as silt density index (SDI) and modified fouling index (MFI) is an important parameter in design of the integrated RO (reverse osmosis) and NF (nanofiltration) membrane processes for drinking water treatment. In this study, the effect of various foulant characteristics on membrane fouling index was investigated systematically. As expected, the fouling index (both SDI and MFI) increased with increasing particle concentration. When organic matter was the primary cause of membrane fouling, the MFI based on cake filtration theory was not accurately measured due to internal fouling such as pore adsorption. The fouling index was determined mainly by particle characteristics when both particulate and organic foulants coexisted in the feed water. This observation was attributed to lessening of organic pore adsorption by particle cake layer formed on the membrane surface. Prediction of MFI by using Happel cell model for the hydraulic resistance of the particle cake layer was also performed. The effect of primary model parameters including particle size (a_p) and particle concentration (C₀), were accurately assessed without any fitting parameters, and the MFI values predicted by the model exhibited very good agreement with the experimental results.