Multiple MFI measurements for the evaluation of organic fouling in SWRO desalination

A series of MFI (modified fouling index) measurements were performed to evaluate and predict organic fouling potential and mechanism in seawater reverse osmosis (SWRO) desalination, by employing a multiple membrane array system (MMAS) in which microfiltration (MF), loose and tight ultrafiltration (UF) membranes were configured in a consecutive manner to determine the MFIs of particles, colloids, and organics. The results suggested that organic fractions manifested by colloid-MFI should be removed to control organic fouling effectively, as the organic fraction with MW ranging from 30 to 300kDa led to the most severe fouling in RO experiments. The variations in fouling potential according to solution conditions (i.e., pH and Ca²⁺) were also more accurately evaluated using multiple MFIs than with conventional SDI. This work demonstrated that the current fouling index, relying on a single membrane, could be improved by utilizing multiple membranes with different characteristics (e.g., pore size and hydrophobicity) to assess the fouling behavior of specific organic fractions.